Lift at high flight angles

I'm having difficulty in figuring out where lift comes from when in overhead manoeuvres.
Please correct my thinking.
In level flight essentially lift and weight and thrust and drag equalise and tension (ignoring any offset considerations) must largely equate to mV^2/r-(mSinè). OK?
When flying a wingover, for example, I believe the plane stays out on the lines (up!) due to the speed of the manoeuvre. The tension will decrease by the weight x Sin angle, but as long as the plane is flying quickly enough it will complete this manoeuvre. OK?
When flying circles overhead at say 70-80 degrees surely the lift must be considerably more than level flight to produce the same vertical vectored component. Yes?
Extra lift can (only?) be generated by extra speed or AoA?
Apart from any extra lift generated by the fuselage (surely small?), where does this extra lift come from?
Or, is it a fact that there is no extra lift generated and it is the centripetal force produced by the speed which keeps the tethered plane up?
Curious to understand….
Adrian

This reminds me of a time I was in a pub in England with some combat flyers. "You Americans have peculiar spelling," said one. I asked for an example. "Maneuver"

the overhead line tension is a result of at least two forces. Centripetal force which is reduced by gravity and lift from the wing and in a knife edge from the fuselage. Yes, fuselages can create lift, ask Bob Hoover and other stunt pilots.

Although Sparky makes fun of us, I agree with him, and not just about his not caring what others say. Wing lift, if you have the amount of tip weight that my friends have led me to accept, has little effect on line tension. It's just lift x the sine of bank angle, and if your airplane rolls from excessive tip weight, the line tension increment will be negative at the transition in the overhead eights. I think engine offset has a big effect, specifically the angle of the prop disk relative to the airstream. The sideforce due to the engine ain't merely thrust x sin beta. Air going through the prop at an angle gets bent, as it would going over a wing, and produces a lot of sideforce. I investigated this sideforce awhile back. The only paper I saw on it was written by Buzz Wilson's least-favorite professor. It underestimated the force I could clearly feel by moving the leadouts around on a combat plane, corroborating Buzz's opinion of the prof. If I were not so lazy, I'd mount an engine on a board stuck out a car window and and measure the force at different angles relative to the stream.

>>Actually the lift is Lift x cosine angle (from horizontal),
>
>Hi John
>Surely the TENSION formula is correct with Sine? 12 (lbs)-
>(4xSin90) = 8
>12 - (4xCos90) = 12
>
>My belief is that essentially centripetal force is keeping
>it up. Although engine offset must help I can't see there
>being enough thrust from a couple of degrees of engine to
>support the plane (sorry Sparky - I do love your planes
>though!). Fuselage lift must assist - but it would be
>interesting to test a CL plane with a boom fuselage!!!!
>My Spelling Checker keeps trying to spell it 'maneuver' -
>had to teach it a lesson and make English UK the default -
>sorry chaps!
>Adrian

Don't take my word for it. ASK Billy about engine off set.

>>I'm having difficulty in figuring out where lift comes from
>>when in overhead manoeuvres.
>
>
>Your question is a good one.
>
>They don't always stay up there.

You want it to stay out there? OUT THRUST!

I might add Speed guys angle their engines in 1 degree.

>Sparky
>What about planes that have NO out-thrust (engine or rudder)
>that stay up there without problems. I ask the question
>again.....

They don't have the line tension like they would have if they did!

Igor had an explanation just a couple of weeks ago, but I don't agree with all of it. Some of the very specific language and definitions gets me as frustrated as Robert, and I am an Engineer.

Igor actually argues the fuselage causes negative lift - simply because of the mathematical calculation that the inside surface of the fuselage is at a shorter distance from the center of the circle. Therefore, air is traveling faster on the outside of the fuselage, so the lift from the fuselage is directed into the circle.

Poppycock.

As Tom McClain states, knife-edge flight is common in full size stunt. Not only that, but every RC Pattern plane worth its stuff can sustain knife-edge flight as long as the fuel holds out. These things cannot be explained by centripetal force, or even engine side thrust (no offense, Robert).

Angle of attack, speed, and surface area causes the lift. Even slight deviations from the horizontal create enough angle of attack to sustain lift in knife edge flight. Those designs that create enough lift with minimal rudder deflection perform best. Too much weight, too little speed, or not enough side area, and the rudder deflection becomes great enough to create drag, not lift.

It might seem hard to believe this, because we strive for maximum lift from the wing - with efficient airfoils and lots of wing area. However, we have to remember that the wing is essentially neutral in level flight, with angles of attack altering so minimally to sustain altitude, that the hopeful result is a model tracking on "rails." The wing, its airfoil, and all of that area are there for maneuvers.

In the case of the fuselage, it only needs to be large enough to sustain enough lift for neutral bouyancy at the top of the circle. (Never mind that many RC jobs now perform manuevers with active lift from the fuselage in knife-edge flight.) In my opinion, even slight differences in angle of attack are enough to overcome supposed lift directed inward.

This fuselage angle of attack can be achieved with line rake, engine offset, or rudder deflection. It may even exist in sufficient force with no offsets at all. In the case of combat planes, centripetal force and speed is probably everything in control line flight. Otherwise, we'd see more RC combat planes without rudders, but they all seem to use them, or at least side fins. I suspect that they will eventually fall out of sky in knife edge otherwise.

Just my opinion.

Engineer's exercises:
1. Determine the length resulting from an altered angle of attack and see if that speed difference overcomes the dimensional difference between inner and outer fuselage sides in circular flight. e.g., Does the air travel faster on the inside surface of the fuselage?
2. Draw a control volume slightly larger than the wing fuselage joint, or larger than the small area defined by the force structure existing at the CG/leadouts/bellcrank. Determine whether circular flight, and the resulting airstream direction, results in increased angle of attack at the forward fuselage without any increase in yaw.

>Just my opinion.
>
>Engineer's exercises:
>1. Determine the length resulting from an altered angle of
>attack and see if that speed difference overcomes the
>dimensional difference between inner and outer fuselage
>sides in circular flight. e.g., Does the air travel faster
>on the inside surface of the fuselage?
>2. Draw a control volume slightly larger than the wing
>fuselage joint, or larger than the small area defined by the
>force structure existing at the CG/lead outs/bell-crank.
>Determine whether circular flight, and the resulting
>air stream direction, results in increased angle of attack at
>the forward fuselage without any increase in yaw.

While I admit I understand none of the mathematics of the things you speak of I do understand that a Toilet seat will fly given enough thrust. And It will stay on the end of the lines. As I have built one to prove a point years ago. All this being said I guess thats one reason why people are proponents of heavy aircraft and no engine offset.

But in my case I will stick with the things I know work. Like asymmetrical wings , engine offset , rudder offset and line rake.

>
>While I admit I understand none of the mathematics of the
>things you speak of I do understand that a Toilet seat will
>fly given enough thrust. And It will stay on the end of the
>lines. As I have built one to prove a point years ago. All
>this being said I guess thats one reason why people are
>proponents of heavy aircraft and no engine offset.
>
>But in my case I will stick with the things I know work.
>Like asymmetrical wings , engine offset , rudder offset and
>line rake.

Robert,

We are saying the same thing, and I agree with you. The toilet seat is a perfect example. Angle of attack, combined with enough power and speed will let a flat-wing 049 fly. Fuselages do the same thing - but they even have taper, to boot. Moreover, our circular flight causes it all the time. My point about the control volume is that this is easy to see if you look at anything more than just the wing-fuselage joint. The fuselage is always crabbing, resulting in an angle of attack to produce lift to the outside of the circle.

Tom-

>Igor actually argues the fuselage causes negative lift - simply because of the mathematical
>calculation that the inside surface of the fuselage is at a shorter distance from the center
>of the circle.

I just got back in town and found this interesting thread. I remember Igor's post. Although he said that a fuselage tangent to the circle makes inward "lift", he did not make this explanation (which would actually explain an outward force). He said that the lift was inboard because the fuselage behaved as though it had an inward camber (convex inward). He equated the relatively circular airflow (from the fuselage traveling in a circle) acting on a straight fuselage to a straight airflow acting on a circular (cambered) fuselage.

Naturally the relative airflow is outward on the nose and inward on the tail; so it is easy to get an outward yaw to compensate (same direction as the cambered airfoil's pitching moment wound be). However, this effect is quite small compared to inertial (not centripetal, not centrifugal) forces generated in circular flight (which is CAUSED by centripetal force).

I should have said earlier I have removed all rudder and engine offset on my ships and believe they are better for the reduced yaw and perform well up above with plenty of tension.
Adrian

>I should have said earlier I have removed all rudder and
>engine offset on my ships and believe they are better for
>the reduced yaw and perform well up above with plenty of
>tension.
>Adrian

Please don't take this the wrong way.

I wish you the best of luck and tight lines.

There IS a lift - positive or negative, and also there is something what you might change with your rudder removal - yaw stability, but in any case, the centrifugal force is major force keeping the model overhead.

>but in any case, the centrifugal force is major force keeping the model overhead.

Maybe for a combat job, but not everything else.

>>but in any case, the centrifugal force is major force keeping the model overhead.
>
>Maybe for a combat job, but not everything else.

copyed from post above

While I admit I understand none of the mathematics of the things you speak of I do understand that a Toilet seat will fly given enough thrust. And It will stay on the end of the lines. As I have built one to prove a point years ago. All this being said I guess thats one reason why people are proponents of heavy aircraft and no engine offset.

But in my case I will stick with the things I know work. Like asymmetrical wings , engine offset , rudder offset and line rake.

>There IS a lift - positive or negative, and also there is
>something what you might change with your rudder removal -
>yaw stability, but in any case, the centrifugal force is
>major force keeping the model overhead.

We need to set a New Year's Resolution condemning Engineering semantics from further posts, but I'll make one last stab:

Speed and lift keeps the model overhead. Centripetal force merely keeps the lines tight, and produces the pull.

OK, I agree ... like last time:

>>>Speed and lift keeps the model overhead.<<<

Yes, true, but it will be exactly the same WITH speed and WITHOUT lift too

OK, to take it seriously I did the calculation.

If I do not count with that circular flow making inward lift, if I do not count with negative lift on deflected rudder to keep outyawed nose, then the best effective AoA is 1 deg. That is because of too small aspect ratio, which makes effective AoA much smaller. So the best lift coefficient at that angle can be ~0.1

If I take usual area and speed of stunt model I will get number approx 5Newtons. If I take smallest centrifugal acceleration 2G and weight 1500g that makes force 30N. Excuse that SI units, but it does not matter. The important is correlation - centrifugal force overhead is 6x stronger force than available lift. And at the same time the weight of the model 15N is 3x more then available lift 5N - so it is far too little to keep it overhead.

>OK, to take it seriously I did the calculation.
>
>If I do not count with that circular flow making inward
>lift, if I do not count with negative lift on deflected
>rudder to keep outyawed nose, then the best effective AoA is
>1 deg. That is because of too small aspect ratio, which
>makes effective AoA much smaller. So the best lift
>coefficient at that angle can be ~0.1
>
>If I take usual area and speed of stunt model I will get
>number approx 5Newtons. If I take smallest centrifugal
>acceleration 2G and weight 1500g that makes force 30N.
>Excuse that SI units, but it does not matter. The important
>is correlation - centrifugal force overhead is 6x stronger
>force than available lift. And at the same time the weight
>of the model 15N is 3x more then available lift 5N - so it
>is far too little to keep it overhead.

There's a lot left unsaid or assumed between "best effective AoA" and "best lift coefficient ... can {only} be ~0.1".

Everyone totally neglects the existence of RC model aircraft, but I guess that's to be expected on a CL forum. Please explain why RC aircraft, at similar speeds and weights (or less)), sustain knife-edge flight without centripetal force.

Higher speed, straight trajectory, ability to fly sideways.

>
>Quoted from a few post up
>
>I'll bet they have some effective outthrust due to airplane
>yaw. There's still good ol' mv^2/r.
>
>What ever that means?

Looks like Igor is looking at this thread, too, so I'm probably really going to catch it.

mv^2/r is the equation for centripetal force: mass times velocity squared, divided by radius. It does nothing whatsoever to explain knife-edge flight (as mentioned by Tom Mc.)

Might be time for some more Howard special effects, too.

Thrust,with enough you can maitain speed, speed
gives you available G, G gives you AOA
with enough thrust you can climb in a 89 degree
AOB pulling 10 G, would love to put a G meter in a
stunt or combat ship. Rudder and offset help,my
humble thought.. Happy holiday

Guys,

Maybe I missed it in this long thread but I think it is important to note the significant difference between CL flight and "free flight". That difference, of course, is the fact that we "fly" in a tethered environment. Everything we do in our hemisphere is affected by that tether. Surprisingly, much of what we do when we "fly" within that environment has little and sometimes nothing to do with "lift".

Knife edge flight, as discussed earlier, is simply not aa significant issue with us as a result. In the free flight world (RC, modeling style "free flight", full scale, whatever) straight line flight with the wing perpendicular to the force of gravity requires significant yaw/thrust effects to maintain a constant altitude (or in the presence of truly significant thrust) actually gain altitude. In order to maintain altitude in that attitude some combination of lift (generated from inefficient sources such as the fuse) and thrust must be available and employed consciously be the operator (pilot).

The wing may, by the way, in fact still be producing lift if it is at a positive angle of attack to the relative airflow. Any lift it does produce will, however, have no affect on the aircraft's "altitude" but will instead alter its "track" across the ground since that lift "vector" will be pretty much at right angles to the gravity vector. Thus free flight knife edge flight with a lifting "cambered" airfoil will generally require some "down" elevator to counteract the lift vector's attempt to drive the aircraft in a positive or "up" direction.

In a tethered environment, however, the need for lift to stay airborne can be totally eliminated. As long as the center of gravity of a "vehicle" (doesn't even have to have wings) is ahead of its center of pressure (like an arrow with fleches or feathers on the end), if some force exists to drive it to a high enough speed it will maintain its path around the point of tether. The equivilant of "level flight" with our c/l ships.

A control line speed ship, for instance, once up to speed could pretty much dump its wings altogether and still "fly" just fine.

Uncle Jimby may want to jump in with a description of the world famous "Aroone Cup" racers flown every September not far from the scene of the Reno Air Races.

Thus, even when your stunter is momentarily in "knife edge attitude" as it crosses over the top of the wingover, it isn't lift that is keeping it there, it is the multiple force of gravity created by its own mass, it's velocity and the fact that the "tether" is forcing it to fly the "radius" discussed in the mass X velocity squared divided by the tether radius formula.

No question, at the time we are "passing through" the tethered equivilant of the knife edge attitude, there is a small amount of lift produced by the fuselage and the thrust vector. Both will be more or less depending on the attitude of the airplane on the end of the lines. Both, however, wil be very modest in comparison to the tension provided by the tether, the mass and the velocity thereof.

We often do produce "lift" at the top of the circle and, like the knife edge flight example above, the lift we thus produce acts at "up to 90 degrees" to the force of gravity and causes the track of the airplane to perform things like overhead eights, the top of hourglasses and vertical eights.

Now, we can by going to extremes as I've discussed in other threads, achieve a situation where you might well require thrust offset and fuselage lift to enable controlled flight at that segment of the hemisphere.

That point will be achieved when we either slow the airplane or increase the radius of tether to the point that line tension is at or less than one G. As you approach this condition your wingovers will gradually morph into true knife edge flight and the appropriate maneuver by the pilot during the wingover will be to "duck" as the ship passes by.

Ted Fancher

Edited to change numb n*^&s reference to "area" when Ishould have said "radius".

>>That point will be achieved when we either slow the airplane
>or increase the radius of tether to the point that line
>tension is at or less than one G. As you approach this
>condition your wingovers will gradually morph into true
>knife edge flight and the appropriate maneuver by the pilot
>during the wingover will be to "duck" as the ship passes by.
>
>Ted Fancher

Very good Ted.

I once heard a story of Al Rabe not being so lucky as to duck.

>
>In a tethered environment, however, the need for lift to
>stay airborne can be totally eliminated. As long as the
>center of gravity of a "vehicle" (doesn't even have to have
>wings) is ahead of its center of pressure (like an arrow
>with fleches or feathers on the end), if some force exists
>to drive it to a high enough speed it will maintain its path
>around the point of tether. The equivilant of "level
>flight" with our c/l ships.
>
>A control line speed ship, for instance, once up to speed
>could pretty much dump its wings altogether and still "fly"
>just fine.

Sparky
Don't take this the wrong way either, but now is the time to remove your offsets!!!
Still love yr planes
Adrian

>
>>
>>In a tethered environment, however, the need for lift to
>>stay airborne can be totally eliminated. As long as the
>>center of gravity of a "vehicle" (doesn't even have to have
>>wings) is ahead of its center of pressure (like an arrow
>>with fleches or feathers on the end), if some force exists
>>to drive it to a high enough speed it will maintain its path
>>around the point of tether. The equivalent of "level
>>flight" with our c/l ships.
>>
>>A control line speed ship, for instance, once up to speed
>>could pretty much dump its wings altogether and still "fly"
>>just fine.
>
>Sparky
>Don't take this the wrong way either, but now is the time to
>remove your offsets!!!
>Still love yr planes
>Adrian

Thanks for the compliment but I'll keep them in.

I respectfully disagree, Ted. Granted, knife-edge effects may not be as much as is needed to maintain line tension at the zenith.

However, the climb in the wingover is not due to centrifugal/centripetal force, neither is the dive to level flight altitude. CF is there to maintain control, which requires pull, or the lines go slack and control is lost. Then the plane is subject to any whimsy. (Although there are many first hand accounts that the plane may fly very well without any tension or tether. Thong, anyone?)

In control line flight, the plane is still flying: producing lift in response to maneuvers, and moving forward in response to engine thrust. The tether just restricts the flight to a circular rotation. Of course, that means CF is a result - but it is not the cause.

Neither would a control line plane - once up to speed - fly just fine without wings. Any deviation will result in a loss of speed, and the plane will not fly just as fine. Otherwise, we're wasting a whole bunch of time and effort discussing and building with aerodynamics in mind.

I keep missing the memo where we're all supposed to be swinging around dead weights on a string.

>I respectfully disagree, Ted. Granted, knife-edge effects
>may not be as much as is needed to maintain line tension at
>the zenith.
>
>However, the climb in the wingover is not due to
>centrifugal/centripetal force, neither is the dive to level
>flight altitude. CF is there to maintain control, which
>requires pull, or the lines go slack and control is lost.
>Then the plane is subject to any whimsy. (Although there
>are many first hand accounts that the plane may fly very
>well without any tension or tether. Thong, anyone?)
>
>In control line flight, the plane is still flying: producing
>lift in response to maneuvers, and moving forward in
>response to engine thrust. The tether just restricts the
>flight to a circular rotation. Of course, that means CF is
>a result - but it is not the cause.
>

Hi TomB

I probably didn't make the distinction quite clear enough when I referred to a c/l plane "flying" just fine with no wings. I was trying to make the distinction between "flying" to stay in the air and the fact that a mass either swung or driven about a tether will elevate itself as outward "G" forces predominate over the pull of gravity.

it is absolutely true that either a rock swung by a swinger or a "vehicle with the proper relationship of thrust, center of gravity and center of pressure" will, in fact elevate above the inclination demanded by gravity when the object...rock or vehicle...is not in motion. when it goes fast enough it will almost literally be spinning around the tether in a pretty good approximation of what we call "level flight" in the c/l world.

It is my opinion that it makes little practical difference whether the energy to provide the circulation about the tether comes from the guy swinging the bucket around him or from thrust aboard the vehicle at the end of the tether. Once the mass is in motion and restrained from its natural straight line tendency by the tether the resulting acceleration will elevate the object. Up to but not quite ever to exactly perpendicular to the pull of gravity as long as the axis of rotation is vertical (in line with gravity).

Neither the rock or the vehicle needs lift in the conventional aerodynamic sense for this to occur.

It is absolutely true, of course, that the energy imparted to achieve the elevated relationship to the point of tether could be assisted by some lift from aerodynamic forces. This is, in my admittedly poorly informed opinion, one of the reasons that FAI speed ships--even when constrained by the requirement for two lines and alky/oil fuel--would outperform the classic AMA styled speed ship which was little more than an engine with enough "wing" to prevent the ship from rolling up the lines from torque during a hand launch.

The FAI ship had a stipulated wing area (I forget the exact area requirement...but very big, as much as two or three times, that of vintage AMA ships of the era). That larger area provided the lift to actually "fly" the airlane and thus all the energy put into circulation about the tether (thrust) could be utilized for forward (OK, circular) motion. They were therefore just as fast or faster than the nitro buffed much higher power engines of the era in the tiny AMA ships.

Finally, I would point out that the tethered vehicle, given adequate energy, can circulate about the point of tether in any plane...including vertically with the axis of rotation at right angles to gravity.

In fact, I belive if you could somehow tether four or more such vehicles in such a fashion that they are all equidistant radially from each other on the tether you would have the control line equivilant of a gyroscope with all the attendant properties thereof.

Ted

>Neither would a control line plane - once up to speed - fly
>just fine without wings. Any deviation will result in a
>loss of speed, and the plane will not fly just as fine.
>Otherwise, we're wasting a whole bunch of time and effort
>discussing and building with aerodynamics in mind.
>
>I keep missing the memo where we're all supposed to be
>swinging around dead weights on a string.

The most unique example of tethered flight is that of spacecraft in orbit around the earth. The earth (gravity) is the tether (centrifugal force) that prevents the spacecraft from proceeding on a straight line (centripetal force) into the solar system. The spacecraft remains in orbit or tethered flight due to its velocity just as one of our stunt ships can remain directly overhead because its velocity maintains the aircraft at the end of the lines. Lift is not needed. Lift from the fuselage can help, but it is not needed.

>The FAI ship had a stipulated wing area (I forget the exact
>area requirement...but very big, as much as two or three
>times, that of vintage AMA ships of the era). That larger
>area provided the lift to actually "fly" the airlane and
>thus all the energy put into circulation about the tether
>(thrust) could be utilized for forward (OK, circular)
>motion. They were therefore just as fast or faster than the
>nitro buffed much higher power engines of the era in the
>tiny AMA ships.

I think there are two or three factors at work here. The first is, as you say, wing area. But it's not that the AMA A Speed plane was making less lift than the F2A plane. To fly in a horizontal plane at the same speed, both will need to produce the same amount of lift. Take the lift away, and what keeps the plane off the ground would the the vertical component of line tension - LineTension*cos(theta) where (theta) is a very small angle between the lines and the horizontal. In other words, the plane will never ever reach the horizontal plane, it will have to hang below it, because in the horizontal plane, (theta) = 0 and cos (theta) = 0.

What is really hurting the smaller AMA A Speed plane is that it has to fly at a higher angle of attack and has to produce more induced drag to produce the necessary lift. Also consider that the F2A airplanes have that very long inboard wing - not only is it high aspect ratio, I've also heard it said that they're actually a fairing for the last few feet of line (the portion which travels the fastest)!

The other thing to consider is engine development. Current F2A engines are, I think, despite the lack of nitro, more powerful than the A Speed engines of even the early 90s. F2A also allows full tuned pipes, I don't remember if A Speed does or not. It is interesting to note that Formula 1 Pylon racers did 170-175 mph on 70% nitro fuel, while the current F3D Pylon racers are way over 200 mph, on zero nitro.

>In fact, I belive if you could somehow tether four or more
>such vehicles in such a fashion that they are all
>equidistant radially from each other on the tether you
>would have the control line equivilant of a gyroscope with
>all the attendant properties thereof.

Interesting idea. It'd probably precess, too..

>However, the climb in the wingover is not due to
>centrifugal/centripetal force, neither is the dive to level
>flight altitude. CF is there to maintain control, which
>requires pull, or the lines go slack and control is lost.
>Then the plane is subject to any whimsy. (Although there
>are many first hand accounts that the plane may fly very
>well without any tension or tether. Thong, anyone?)

I think pretty much everyone agrees that a fuselage can produce lift if it's yawed out, even slightly. And you do have to agree that you can tie a rock to a string and swing it around in a vertical plane. Whether or not the lines serve to control the plane, they can also perform the same function as that string. You'll have to admit that. It CAN keep the plane travelling in a circle above your head in a wingover when the plane actually wants to fly off at a tangent.

The thing is, these forces can be calculated. We know the speed a control line stunt plane flies at. We know it's weight. We know the line length. It's a simple matter to calculate, then, the pull generated by the simple fact that the plane is flying a certain speed on lines of a certain length. Anyone who has had Physics 101 knows the equation to use.

We can also calculate the lift that can be produced by the fuselage flying at a certain speed at a certain angle of attack. This is harder to do, but we have people here who can do it.

Igor's done both the above. He tells us that the speed alone is enough to account for all the line tension you're likely to encounter in a wingover. Why not try it? It's easily verifiable. The second calculation is more difficult, but given the results from the first calculation, why would we need another source of tension?

>In control line flight, the plane is still flying: producing
>lift in response to maneuvers, and moving forward in
>response to engine thrust. The tether just restricts the
>flight to a circular rotation. Of course, that means CF is
>a result - but it is not the cause.

Sure, something has to keep the plane moving forward with the right velocity. If the engine quits in the entrance to your wingover, you know what's going to happen.

>Neither would a control line plane - once up to speed - fly
>just fine without wings. Any deviation will result in a
>loss of speed, and the plane will not fly just as fine.
>Otherwise, we're wasting a whole bunch of time and effort
>discussing and building with aerodynamics in mind.

Sure, for horizontal flight, and for doing loops and such, you need wings. But imagine for instance a skeletal fuselage (i.e. no side area, but with the same weight as a normal fuselage) with engine running (and contrarotating props, so it doesn't roll itself up on the lines.. ), attached to lines and handle. Supposing you use some sort of spring launcher to launch this thing vertically at what would be normal flying speed. The engine will keep it going up at the same speed. What happens? It'll fly a nice "wing"over and bury itself in the ground on the other side of the circle, of course. And our calculations (good old F=mV^2/R - mg) will enable us to predict with a high degree of certainty the line tension there was overhead. What happens if the lines break half way up? The fuselage will leave the hemisphere at a tangent and bury itself some distance away from the circle. What produced the line tension (i.e. in the case where the lines didn't break)? The weight-on-the-string effect.

>I keep missing the memo where we're all supposed to be
>swinging around dead weights on a string.

Again, you must admit a lead weight swung on a string CAN be swung in a "wing over", with some "line tension". What said lead weight cannot do is a loop.

>I did, but I see little more letters there:
>
>>>>Yes Tom, the fuselage does lift. But opposite - toward the circle. At least if it is tangent. Therefore I think it is better to have little yaw out - small, but positive - at least to keep it at zero lift.<<<
>
>You see that part >>>if it is tangent<<< ?

So, does that mean you didn't state that lift was into the circle?

I would submit that even perfect tangency would result in enough angle of attack on the fuselage to produce lift out. The fuselage has a non-zero length, and so the nose is effectively pitching up relative to the airstream, as it continues to accelerate around the circle. You would actually have to point the plane into the circle slightly to produce lift into the circle. Even then, enough speed might produce sufficient centripetal force to keep the lines tight. As some have noted, that was a common trick in speed circles to make the most of the available energy.

Perhaps it's the semantics again, and whether a perfect tangency is ever really possible.

>>>So, does that mean you didn't state that lift was into the circle?
<<<

I wrote what I wrote, and that is:

IF tangent -> inward lift.

Sorry if it makes semantics problems.

If you have really troubles to understnad, try following imagination: Imagine round airstream straight and imagine straight fuselage round appropriately. You will have slightly chambered airfoil at zero AoA in straight stream. That MAKES lift - nonzero lift. Oriended opposite to the chamber. In case of fuselage it means lift toward the center of circle. ... better?

>
>If you have really troubles to understnad, try following
>imagination: Imagine round airstream straight and imagine
>straight fuselage round appropriately. You will have
>slightly chambered airfoil at zero AoA in straight stream.
>That MAKES lift - nonzero lift. Oriended opposite to the
>chamber. In case of fuselage it means lift toward the center
>of circle. ... better?

No, Igor, it's not better. The curvature and camber is not creating the lift, anymore than "camber" in a symmetrical airfoil (and our fuselages are generally symmetrical - rudder's excepted). The AoA is creating the lift. You said earlier that the rudder deflection actually forms the back end of a camber, with lift in the opposite direction, but that's a trivial component compared to the AoA at the nose. At the point of sustained knife-edge flight, the rudder becomes little more than a surface anomaly with some drag. The drag is enough, though, to drop the tail and raise the nose - creating the needed AoA for lift.

Many believe that downward flap deflection causes a pitch-down, why is it hard to believe that with the rudder on the fuselage? In the case of the fuselage, there is no additional tail to add another moment arm to correct for that pitch reaction. So, the higher AoA produces the needed lift, and knife-edge flight is sustained. (A tail-less combat plane also comes to mind - a surface deflected upward at the trailing edge does not produce lift down.)

It may be that that enough yaw in engine thrust can offset gravity in certain cases, but this does not explain many observed effects, either.

We can agree to disagree. I just have an aversion to comparing CL flight to swinging around a dead weight on a string. That explains the pull force to a large extent, but there's a lot more to it.

>>>The curvature and camber is not creating the lift<<<
Wrong. Chamber on and airfoil MAKES lift even at 0 AoA.
>>>The AoA is creating the lift.<<<
Thust this is also wrong. AoA itself does not necessarily make a lift. You need CIRCULAR FLOW around airfoil otherwise you do not have any lift. If your wing with so little aspect ratio cannot make circular flow, it will NOT make lift. Does not matter on AoA – it will even not STALL as would wing with ususal aspect ratio with the same airfoil.

The wing will make lift also without airfoil shape (e.g. circular crossection) and without AoA if you CAN make circular flow another way, for example to force air to rotate by boundary layer (rotating surface).

You say you are engineer, but what I see is just ignoring facts. Try to seriously enumerate lift of the fuselage at different angles and it ill open your eyes.

>If you have really troubles to understnad, try following
>imagination: Imagine round airstream straight and imagine
>straight fuselage round appropriately. You will have
>slightly chambered airfoil at zero AoA in straight stream.
>That MAKES lift - nonzero lift. Oriended opposite to the
>chamber. In case of fuselage it means lift toward the center
>of circle. ... better?

AH... I see what you're getting at! The airflow around the fuselage is curved, so the fuselage behaves like a cambered wing with the camber pointing inwards if you consider the motion of the air relative to the different parts of the fuselage. That's neat - I'd never have thought of that.

Not precise, but works well to understand it.

Now try to think further - such airfoil has pitching moment in wide range of AoA that is also answer why it tries to yaw out.

Yup..

And air pushes on the inside of the nose and the outside of the tail, producing this moment.

If the plane is yawed out, wouldn't the pitching moment be the same as for a normal wing? That would be nose down, or in this case nose in?
I think that a fuselage, in spite of the large "tip losses" still acts like a wing, just one of very low aspect ratio.
Along some central line flow is over the nose and straight back to the tail so circulation must still be produced. The low aspect ratio allows this lift to be produced at very high angles of attack without stalling.
One trick with the indoor R/C planes is a flat turn. You can actually turn a smaller radius using the rudder and there is no chance of stalling.
I am not sure it is important for overhead line tension however. Unless the yaw angle is pretty large the vectored thrust of the motor is probably a bigger value.
Pat MacKenzie

>>>If the plane is yawed out, wouldn't the pitching moment be the same as for a normal wing?<<<
The pitching moment comes from shape, and it depends on AoA only little. It changes at extremes where some separation appears. So if our fuselage is in extremes +/-5deg AoA, ten pitching moment is more or less constant. It is visible on second picture showing moment polar.
Regarding tip loses. The fuselage has aspect ratio ~0.1 and the lift/drag polar shows that the lift coefficient only hardly exceeds 0.1 – and the polar on picture is for AS=1!!! At 0.1 it will be far worse. The airfoil can stall only if makes lift so such low AS wing will really not stall at all, but it does not mean that it makes lift. It will only hardly get to effective AoA more than 1deg.

>>>Unless the yaw angle is pretty large the vectored thrust of the motor is probably a bigger value. <<<
That is. The prop is typically half of the span and most useful props are at pitch 4” (like that range GWS 10x4.7). They like to hower on prop, so it really does not need too much lift at all .

>If the plane is yawed out, wouldn't the pitching moment be the same as for a normal wing?
>That would be nose down, or in this case nose in?

With Igor's explanation of Curved (circular) airflow relative to the fuselage being equivalent to curved fuselage relative to straight airflow, the camber is convex inward to the circle. Cambered airfoils have negative pitching moments, which relative to the circle, would be nose outward.

Hi Serge
Thank you for yr clear explanation on post 65. I go along with that absolutely.
Re:

FWIW, I am also told though on this and another forum by
>more expert aerodynamicists (one is head of aeronautical
>research at a NASA lab) that the molecules actually don't
>reach the trailing edge simultaneously.

This I also believe is true and also explained in John Denker's excellent publication on flight. I extract the following drawing and comment. Quote:The most remarkable thing about this figure is that the blue smoke that passed slightly above the wing got to the trailing edge 10 or 15 milliseconds earlier than the corresponding smoke that passed slightly below the wing.
This is not a mistake. Indeed, we shall see that if this were not true, it would be impossible for the wing to produce lift.
This may come as a shock to many readers, because all sorts of standard references claim that the air is somehow required to pass above and below the wing in the same amount of time. I have seen this erroneous statement in elementary-school textbooks, advanced physics textbooks, encyclopedias, and well-regarded pilot training handbooks.

Many thanks

>Hi Serge
>Thank you for yr clear explanation on post 65. I go along
>with that absolutely.
>Re:
>
>FWIW, I am also told though on this and another forum by
>>more expert aerodynamicists (one is head of aeronautical
>>research at a NASA lab) that the molecules actually don't
>>reach the trailing edge simultaneously.
>
>This I also believe is true and also explained in John
>Denker's excellent publication on flight. I extract the
>following drawing and comment. Quote:The most remarkable
>thing about this figure is that the blue smoke that passed
>slightly above the wing got to the trailing edge 10 or 15
>milliseconds earlier than the corresponding smoke that
>passed slightly below the wing.
>This is not a mistake. Indeed, we shall see that if this
>were not true, it would be impossible for the wing to
>produce lift.
>This may come as a shock to many readers, because all sorts
>of standard references claim that the air is somehow
>required to pass above and below the wing in the same amount
>of time. I have seen this erroneous statement in
>elementary-school textbooks, advanced physics textbooks,
>encyclopedias, and well-regarded pilot training handbooks.
>
>Many thanks
>
>Adrian

Yes. I agree with this and post #65.

>
>FWIW, I am also told though on this and another forum by
>more expert aerodynamicists (one is head of aeronautical
>research at a NASA lab) that the molecules actually don't
>reach the trailing edge simultaneously. However, the final
>result is that the Bernoulli's equation does end up being
>satisfied, partially because the l.e. stagnation point
>moves downward as the airfoil is pitched up. I like to think
>of the inertial forces of the molecules as they are being
>displaced adding to the pressure forces on the "bottom" and
>subtracting from the air pressure on the "top" of a lifting
>airfoil.
>
>SK

Well, yes - I mentioned that on a thread a while back, too. The molecules do not meet at the trailing edge, which is what conventional wisdom always told us. Perhaps my own conventional wisdom was in error by assuming that Igor was stating that fuselage lift is into the circle because of relative speed differences between the inside and outside fuselage surface. That was the only way I could deduce that

It turns out that we really don't know the mechanics at the molecular level, which kind of puts all of this into the realm of empirical knowledge. Personally, I think an airfoil causes a shear stress gradient within a flow field, causing the molecules underneath to push up in response to the shear. Same thing - different interpretation.

As far as the circles, I see what you are explaining on the inside, but my sketches seem to conclude an even bigger arc on the outside. It still looks like an edge-on airfoil in a flow field,where the angle of attack is to the outside of circle. The constantly deflecting nose (relative to the airstream) presents a much longer obstruction for the air to flow around and over (to the outside).

Perhaps I'm just not seeing it again.

Adrian,

Thanks for the kind words. For another way to view likely factors keeping it 'out there' consider:

CF (ahem..) calculates from terms including V-squared; I think we all agree on that.

If the model is moving forward at 55 MPH,(88kph) in unloaded level flight, does anyone maintain that it loses half its airspeed in maneuvering high on the hemisphere? I hear more talk of 'constant speed'; 'no slowing' with our newer, more powerful engines and pipes, etc.

Most of us seem satisfied that our stunt models 'pull' about 3g. IF the model loses half its 'cruise' velocity, "CF" falls to 1/4 as much as in low, cruising flight. Simple enough? If that occurs overhead, "CF" is less than static model weight, agreed?

However, if the common claim of constant (I'd rather hear 'more nearly' constant...) velocity is accurate, then we still have as much 'pull' AT THE MODEL POSITION as in low level cruise. We don't FEEL that much 'pull' because of the trig involving the weight- and CF-vector directions. E.g., directly overhead, a very brief condition, 100% of model weight opposes the 'pull.'

I cannot believe that forward speed stays constant. The rise in induced drag to turn a tight corner is huge, and MUST retard forward speed. - Some - If we lose 1/3rd of 'cruise' speed, CF falls to about 45% of that at cruise. If we lose only 1/4 of basic airspeed, we still have 56% of cruise CF.

As we accept cruise CF to be about 3+ g, the 1/3 speed loss case cuts gross CF to a bit over 1.4 times model weight. The 1/4 speed loss case brings gross CF down to about 1.7 times static weight. (Again, remember, this refers to the tether force felt by the model simply calculated as CF. The effects of the other vectors would still need to be addressed.)

On a 2 kg model, after losing a third of forward speed, the CF still exceeds model weight by 0.8 kg; after losing 1/4 of its speed, CF is still 2.4 kg greater than model weight. (Remember the caveat about the other factors...)

Quite a change from a 6 kg cruising 'pull' but still on the favorable side. The other aerodynamic and direct force factors add/subtract to this.

I also consider propellor thrust an 'elastic' factor: engine RPM while unloaded is established by mixture, prop, and a few other trimming factors. The models accelerate until they 'catch up' with most of the advance rate at the in-flight RPM. They 'slip' from ideal advance rate (found from RPM and pitch) only enough to counter the low drag of an unloaded stunter. ...not much. Apply a rapid, large load (i.e., turn a corner) and the slippage increases as the model slows. This should be easily seen as an increase in thrust applied to the model... Any trig effects of the deliberate structural engine offset and the "natural' offset from straight fuselage flying a curved path) reflect the force involved. In unloaded flight the force - prop applied thrust - is small. In high-g maneuvering, the drag to overcome is much larger; thrust applied to the model rises, and the trig value of that force outboard rises with it.

Said otherwise: engine offset does little under unloaded conditions, but gains effect as the prop becomes more heavily loaded.

Good post Lou
Looking at the formula I see on 60ft lines T=M @ about 44ft sec. Then it comes down, offsets or not!
Adrian

>Yes Serge, they do not reach TE simultaneously, the biggest
>problem is, that airfoil makes changes of speed over and
>under the airfoil. So we cannot expect that speed on left
>side is lower than on right side. If you do those concentric
>lines, you see that air hits nose and tail at some angle and
>that forces fraction of air to flow on left side and the
>presumption is not valid anymore.

OK, this is quick and dirty, but it does show the air following a cambered trajectory. I don't know that this proves the outside fuselage doesn't experience something similar, especially with the nose always assuming a greater-than-zero AoA in the vertical dimension:

>>>especially with the nose always assuming a greater-than-zero AoA<<<

and that makes lift toward the center of circle even bigger ... it is about air steam, not about particles ... -> more air on left side -> higher speed -> lower pressure ... simple

Look those two pictures. It shows an airfoil at some angle. It clearly makes some lift. The amout and conditions are on picture also.

Now turn the LE down. You say that the LE (nose of the fuselage) has some negative AoA so it will make negative lift and thus lift of whole airfoil will be smaller ... as you see just opposite is true, that turned LE makes even bigger lift. ... BTW that is what are slots on LE for.

>Look those two pictures. It shows an airfoil at some angle.
>It clearly makes some lift. The amout and conditions are on
>picture also.
>
>Now turn the LE down. You say that the LE (nose of the
>fuselage) has some negative AoA so it will make negative
>lift and thus lift of whole airfoil will be smaller ... as
>you see just opposite is true, that turned LE makes even
>bigger lift. ... BTW that is what are slots on LE for.

Igor,

Once again, you assume the worst in my thinking. Why would I be saying the nose is presenting a negative AoA relative to the center of the circle, and then argue that lift is not into the circle?

Your example shows the opposite, and that is what I have been trying to say - the air is constantly coming from the inside surface of the nose. So, the nose is constantly presenting a positive AoA with respect to the inside of the circle.

more head banging ...

>Tom-
>
>>As far as the circles, I see what you are explaining on the inside, but my sketches seem
>>to conclude an even bigger arc on the outside.
>
>I think that outside, the molecule follows a similar path
>(roughly parallel, depending on fuselage's planview shape),
>separated from the path of the inner molecules by the width
>of the fuselage. This makes the fuselage in transposition
>look like cambered airfoil whose inner surface is convex
>toward the center and whose outer surface is concave toward
>the outside. If the fuselage is convex in planview, the
>displacement of the outer molecule might be actually smaller
>(shorter path for moving molecules/still plane model).
>
>
>SK

Check my post #87 - not time enough to draw it really pretty. Perhaps the scale of the circle radii are misleading, but I think that would affect the inside results, too.

Anyway, it definitely shows an air molecule would follow a cambered trajectory on the inside. I think my point is that the AoA (in the vertical) represented by the nose, creates a more lengthy path for the molecule. I'm not even sure how to show it geometrically, except as I've mentioned before - looking down on the fuselage is analgous to the flat plate or airfoil cross-section undergoing a postive AoA with respect to the airflow.

Another question - would the insignificant radii differences at 60 ft (+or-) really cause enough of a cambered effect to offset the nose AoA?

>Anyway, it definitely shows an air molecule would follow a
>cambered trajectory on the inside. I think my point is that
>the AoA (in the vertical) represented by the nose, creates a
>more lengthy path for the molecule. I'm not even sure how
>to show it geometrically, except as I've mentioned before -
>looking down on the fuselage is analgous to the flat plate
>or airfoil cross-section undergoing a postive AoA with
>respect to the airflow.

Actually, if the fuselage acts as a wing, the air will be made to flow along its surface - i.e. in a straight line. The air WANTS to flow in a curved line (it's not really the air flowing, but the fuselage moving, but let's ignore that for a moment) but the fuselage makes it flow in a straight line. The consequence of this is that the fuselage disturbs the air in the same way that a cambered airfoil (camber down) would in air that moves in a straight line - the air in front hits the front surface, while the air at the back hits on the other side.

>Another question - would the insignificant radii differences
>at 60 ft (+or-) really cause enough of a cambered effect to
>offset the nose AoA?

Remember there's nose aoa, but there's the opposite aoa on the tail.

In any case, I think Igor's shown, pretty much, that these effects are small compared to mv^2/r effects.

> Now, does the person exert the outward force,or the inner force? That's where I get confused.

The person exerts the inward (centripetal) force and feels the outward reaction (centrifugal) force exerted by the plane as it resists changes in its motion. I'm pretty sure that the force you feel is the outward force acting on your fingers through the handle being pulled by the plane through the lines. You feel this reaction force because you are pulling inward on the handle. It's difficult to imagine through all the intermediary things like synapses and muscles, etc. down to molecular forces and lower, but I think that the overriding principle is that we feel what acts on us. In this case its the necessary equal and opposite reaction to the force we exert.

>Regardless, you also mention that low aspect ratio wings perform much better in practice
>than in theory,...

I should note though that while the reattachment of vortices makes things better for ultra-low aspect ratios than elliptical lift distributions predict, they still suffer from higher induced drag, requiring much greater a.o.a.'s than typical wings of equal area to achieve any given lift. So too much outward yaw could conceivably affect speed to the point of significantly affecting line tension, since tension depends on the square of the speed.

The advantages of low-A/R (.75 - 2.5 typically) aircraft are that they generate greater lift without flaps at extremely high angles of attack, while flying quite slowly (if they have a lot of thrust) for STOL performance - OR they can land at normal speeds with short thin wings that allow high speed flight at low-drag a.o.a.'s. That's the argument for more side area, if you didn't already have good tension from "CF".

This is a Newtonian physics problem, and they are always solved by drawing a "free body diagram" which accounts for all of the forces acting on a body. So here goes my attempt.
Just to warm up here is the standard free flying co-ordinated banked turn. The analysis leads to the standard result that 2Gs occur at 60 degrees of bank. Easy stuff.

Now for the tethered case. Unlike in level flight the center of the rotation is not the pilot, but instead is at a point straight overhead at the altitude of the model. The result is interesting. The line tension is the same as you would get doing a wingover, mv^2/r - mg sin(theta). The lift is very different from the free flying solution.
Essentially the lift being generated has no effect on the line tension because the vectors are at right angles ( Assuming the plane is trimmed to neither bank in or out!).
Pat MacKenzie

Just finished reading all the posts on lift at high flight angles. If I understand the question, the plane is making tight circles at the top of the circle, not doing a wingover. I will relate my experiance with a Brodak 38 Special. Pulled it off the hook three weeks ago and cleaned the dirt and dust off of it. Put on OS 35FP with 4 ounce tank. Also stock muffler. The plane yawed out considerably with leadouts set according to plans. Talk about line tension. This is with about 2 degrees offset on engine. Moved leadouts forward about a 1/4 inch. It helped but plane was mushing thru corners. Did I mention I had stock bellcrank with tall control horn. Changed to Fox 3 inch bellcrank and pushrod half the distance from pivot point. Took stock muffler off and put on tongue muffler. Flew the plane today. Oh, the rudder is offset 3/8 of an inch. Did not move leadouts from last flight. The plane now shows promise as my helper said it was one of the best flights I have made in the last month. Still had good tension and no overcontrolling. But, check your plane next time while flying and see how the plane is flying on the end of the lines. If you will think about it, the airplane will try to fly straight. The lines keep it in the circle. But as I learned the hard way with the SweetPea, the lines were too far forward. I could not run fast enough to save the plane when it turned it at me. I do have a plane that has no offset in either the engine or the rudder, but, with the leadouts back a little it stays on the end of the lines. --DOC

Pat,

Excellent and clear! Thanks!!

The only other thing I might try to add is that at all times while the model moves in flight, its forward speed (velocity, I was taught, should be considered straight-line) is instantaneously at the length of the lines, and can relate to circular motion at that radius. When flying level at a given altitude, as your diagram makes so clear, we have a condition a very little like free-flying in a bank, *BUT*, PLUS the tether influence.

In a curving flight path, moving in the direction of excess wing lift, pull has no direct effect on the aerodynamics. The instantaneous path still needs centripetal 'correction,' so we still have some pull to work with. As Adrian (I think it was) figured 44 fps as where CF and Mass are about equal, and 44 fps is about 30 MPH (~50 kph) that is SLOW!

Lift, again, operates at right angles to the tether force, unless the model rolls significantly in flight. The trig of lift required to maintain level flight above lines-level altitude, is a real problem. The WING is foreshortened as seen along the weight(gravity) direction!

Flying a great circle segment, like a wingover or an hourglass climb/dive, that instantaneous forward speed still uses the same radius (plus or minus a few inches, perhaps) for finding the V term to square in the CF equation. ...we still get 'pull.'

Ted is correct that a rock on lines can be swung fast enough to rise above the angle it would hang at if it weren't moving. But consider the trig involved in finding the speed it would need to fly level at the same height as the point of tether! Mathematically impossible for steady, sustained flight at that height, unless we've changed the definition of X/0. Now, "zooming" dynamic flight, from tilting the (geometric) plane the (model) plane flies, WILL allow flight above the point of tether -- on one side of the lap, anyway.

If a plane is in a turn (i.e. a loop), the velocity vector at any given instant is still at a tangent to the circle, so the F=mV^2/R equation still holds. Of course, planes making tight loops will tend to fly slower than planes flying in a straight line, simply due to induced drag caused by the lift (perpendicular to the lines and to the flight path) produced by the wings, so line tension will usually be less than in straight flight.

>>>Higher speed, straight trajectory, ability to fly sideways.
>>
>>Add also side area. Some RC planes have huge side areas, and
>>are designed to do things like knife edge loops. E.g. the
>>Hots.
>
>Well, I just had to think it was joke when "ability to fly
>sideways" was included in the comment.

I think he actually meant "knife edge", not flying sideways. You have to make allowances for those of us who don't speak English as our first language.

>It's kind of like
>saying a CL Stunt plane can fly loops because it has the
>"ability to fly loops." Side areas are no more extreme than
>those in CL Stunt. Fuselage width is a lot different, but
>I'm not sure that's an advantage. A 40-sized HOTS (kind of
>obsolete these days) has no more side area than many
>40-sized stunt ships - maybe less.

You're saying this doesn't have more side area than most CLPA designs?

[photo not recovered: 41d391ba1764a0b5.jpg]

>About your earlier comment - there is not as much yaw these
>days with RC knife-edge as you might think. I've also seen
>rolling circles with no deviation from level flight.
>Certainly, the mention of knife edge loops implies quite a
>reserve of lifting capability in a sideways direction. If
>the yaw from rudder deflection is really creating the knife
>edge, one would think that there would be very little left
>to do an entire loop.

Some are better at it than others, but they all yaw significantly if you watch them closely. The faster they fly, and the more side area they have, the less yaw is needed. Some need a little rudder, some need more. You might even design the plane to be neutrally stable in knife edge, in which case it might not need rudder at all - just move the side area forwards to the point where it pitches up on its own. (In which case, you'd probably be using the rudder a lot to keep the thing flying straight since it won't want to do it on its own..) But it would still need to be yawed to some degree to knife edge.

In any case, you need more rudder to knife edge loop than to fly level in knife edge - some planes can do it, some can't. Again, it depends on speed, power and side area. Are you seriously suggesting NO angle of attack is needed for knife edge flight?

The only plane I've ever seen that did axial rolling circles with no elevator input was a sheet foamy electric someone brought to the field that was made out of EPP. Darndest thing you ever saw - the fuselage twisted so much that in a roll, the tail lagged behind the wing by about 45 degrees! He was rolling pretty fast, too - if he tried slower rolls they wouldn't have been axial without the rudder.

>In any event, a knife-edge loop disproves the entire notion
>of a deflected rudder creating camber over the entire length
>of the fuselage - which would result in lift in the opposite
>direction.

I don't follow. When did anyone say that a deflected rudder causes camber over the entire length of the fuselage? Igor's analogy was based on the fact that the airflow around the fuselage is curved, not straight. The rudder gives the pitching moment, not the lift. The lift comes from the angle of the fuselage to the airflow (i.e. sideways angle of attack).

>>>>Higher speed, straight trajectory, ability to fly sideways.
>>>
>>>Add also side area. Some RC planes have huge side areas, and
>>>are designed to do things like knife edge loops. E.g. the
>>>Hots.
>>
>>Well, I just had to think it was joke when "ability to fly
>>sideways" was included in the comment.
>
>I think he actually meant "knife edge", not flying sideways.
>You have to make allowances for those of us who don't speak
>English as our first language.

Right - but I'm called out for using non-specific engineering terms. Anyway, you're arguing the same thing. The statement would've been worse if "knife-edge" was used. It would be different if I was trying to make a comparison with a helicopter, and then ask why can't a stunt plane hover? Before you react to that - NO, I'm not talking about 3D designs - and the HOTS was not a 3D design.

>
>>It's kind of like
>>saying a CL Stunt plane can fly loops because it has the
>>"ability to fly loops." Side areas are no more extreme than
>>those in CL Stunt. Fuselage width is a lot different, but
>>I'm not sure that's an advantage. A 40-sized HOTS (kind of
>>obsolete these days) has no more side area than many
>>40-sized stunt ships - maybe less.
>
>You're saying this doesn't have more side area than most
>CLPA designs?
>
>[photo not recovered: 41d391ba1764a0b5.jpg]

Link doesn't work, but if it's the HOTS, that's not a rebuttal. The side area may be distributed differently, but a 40 sized HOTS style plane has no more side area that would be significant. Besides, there are other designs that will fly as well without as much.

>
>>About your earlier comment - there is not as much yaw these
>>days with RC knife-edge as you might think. I've also seen
>>rolling circles with no deviation from level flight.
>>Certainly, the mention of knife edge loops implies quite a
>>reserve of lifting capability in a sideways direction. If
>>the yaw from rudder deflection is really creating the knife
>>edge, one would think that there would be very little left
>>to do an entire loop.
>
>Some are better at it than others, but they all yaw
>significantly if you watch them closely. The faster they
>fly, and the more side area they have, the less yaw is
>needed. Some need a little rudder, some need more. You might
>even design the plane to be neutrally stable in knife edge,
>in which case it might not need rudder at all - just move
>the side area forwards to the point where it pitches up on
>its own. (In which case, you'd probably be using the rudder
>a lot to keep the thing flying straight since it won't want
>to do it on its own..) But it would still need to be yawed
>to some degree to knife edge.

It depends on for how long, and to what extent. Certainly the plane may drop without significant rudder deflection. However, as has been noted in some of the other posts, that point of truly sustained knife-edge at the zenith of CL hemisphere may be very small. The sustained speed may be enough until gravity takes over to maintain CF and line tension.

Unlike some of the other arguments, I do not think it is CF that made the plane arrive at that point, nor is it CF that makes the plane fly beyond it. It is speed, combined with thrust and lift. The RC plane does it the same way, but more rudder is fed in until the yaw becomes intolerable, or a different design is employed.

Thanks for at least discussing the RC case.

>
>In any case, you need more rudder to knife edge loop than to
>fly level in knife edge - some planes can do it, some can't.
>Again, it depends on speed, power and side area. Are you
>seriously suggesting NO angle of attack is needed for knife
>edge flight?
>
>The only plane I've ever seen that did axial rolling circles
>with no elevator input was a sheet foamy electric someone
>brought to the field that was made out of EPP. Darndest
>thing you ever saw - the fuselage twisted so much that in a
>roll, the tail lagged behind the wing by about 45 degrees!
>He was rolling pretty fast, too - if he tried slower rolls
>they wouldn't have been axial without the rudder.

I didn't say it wasn't without control input. That's what makes a rolling circle so difficult - perhaps impossible without programmed controls. The point is that the plane has enough lift in the sideways attitude to do it. You could not accomplish it without some lift or huge amounts of thrust - otherwise the control deflections would just cause it to drop even further.

>
>>In any event, a knife-edge loop disproves the entire notion
>>of a deflected rudder creating camber over the entire length
>>of the fuselage - which would result in lift in the opposite
>>direction.
>
>I don't follow. When did anyone say that a deflected rudder
>causes camber over the entire length of the fuselage? Igor's
>analogy was based on the fact that the airflow around the
>fuselage is curved, not straight. The rudder gives the
>pitching moment, not the lift. The lift comes from the angle
>of the fuselage to the airflow (i.e. sideways angle of
>attack).

I completely agree that the lift comes from the angle of the fuselage. Thank you! Perhaps I mistakenly came to that conclusion because Igor described the rudder deflection as causing negative lift on the fuselage. Maybe he was describing a localized effect that explains the pitch down of the tail - more language differences maybe.

>
>… I am lazy to make such nice pictures …
Go on Igor - don't be lazy!!!!!!! I'd like to see "the other way"
Adrian

Picture is not so problem, just imagine cetripetal force spanwise (to the pilot). The line tension then will be combintion of that force and (minus as we are over the ground) gravity at some angle.

Edit:

So if you read his last line on second picture it is exactly what I mean

Lift is perpendicular to lines so the do not mix together and gravity mg with lift works the same way.

The main idea was that ift and line tension are not mixing, o if you do some math around you can always separately work wit lift and with lie tension. Only the gravity spreads its efect to both of them.

> Thanks,
>I just hope I got my "sums" right. From total lack of use my
>math is pretty rusty.
>Pat MacKenzie

Pat - what programme did you use to draw yr diagrams?

Autocad. Much easier to do a scribble on a piece of paper, but only I would have understood what I had done!
Pat MacKenzie

> Autocad. Much easier to do a scribble

Quit giving away the trade secrets. Pretty soon, everybody will be doing it.

Pat-

I did the math last night when I saw your post. I got the same results. 'multiplied one equation by sin and the other by cos of angle - in both orders - and combined by addition or subtraction, as appropriate, in each case. Neat.

>Pat-
>
>I did the math last night when I saw your post. I got the
>same results. 'multiplied one equation by sin and the other
>by cos of angle - in both orders - and combined by addition
>or subtraction, as appropriate, in each case. Neat.
>
>SK

Serge,

Well, yes - and Pat constructed some very nice looking diagrams. I will try to quit after this, but the whole idea of a free body diagram is kind of the point.

When you draw the lift vector as completely perpendicular and centered on the wing, it automatically precludes any other possibility.

That is not intended to be critical of Pat's effort. It may very well be that any other effects are safely assumed to be trivial, but that was kind of the point of the discussion in the first place.

Thanks.

* EDITED for simplicity *

Rolling circles are usually programmed. Very skilled pilots can do them manually, but they're not pretty.

Consecutive rolls on a straight line is trivial with almost any pattern plane. Properly trimmed, aileron input is all that is used. Less forgiving planes or trainers generally get some up and down elevator as the wing turns back parallel to the ground.

Now if you were to fly one until the speed dropped, that probably wouldn't be the case - but it would be so far away, you couldn't see it anymore, either.

Accomplished pattern pilots can do very pretty rolling circles without having to use a program. I'm not sure what you'd program in any case, the rudder deflection depends on which side of the fuselage is pointing up at the time so it's the same principle used in a slow roll, except it becomes vastly more difficult because you have to work the elevator as well. (Yeah, in a slow roll you do have to push on the elevator to some degree during the time the airplane is belly up.) People have been doing rolling circles since before computer radios, and full size pilots do them, too.

Less accomplished pilots make much sloppier rolling circles, of course - the recent craze has been those sheet foam 3D planes and you see people trying to do rolling circles all weekend. Problem is you need something like 45 degrees nose anytime the airplane is knife-edged.

I see what Serge means - yup, an up defelection of control surfaces on the trailing edge of a wing will mean a decrease in lift produced at a given angle of attack. However, if it causes the wing to pitch up, that will mean an increased angle of attack and consequently more lift. But you still remain with the reduced capacity to produce lift at a given angle of attack, and added drag. It would be the equivalent of reducing your wing area. Which is why short coupled elevator-on-trailing-edge combat planes have not been in style since the early 1960s, and also why delta winged jet fighters without canard surfaces went out of style about the same time.

Isky,

I don't disagree with any of what you've said. I do think programming allows an easier rolling circle, because I think you can track the elevator (probably don't need the rudder in a lot of designs) without worrying about controlling the roll. Although, I'm certainly no expert, neither can I do it - I've only seen it.

> Check out Lou and Brett's post in this thread:
>http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=6659&forum=DCForumID1
> They state in their opinion it is load on the engine in
>conjunction perhaps with where it is on the power curve, not
>fuel head changes, that account for "boost".
> You and I ( and Len as well I think) have come to the
>conclusion it is the change in fuel head.
>
>Pat MacKenzie

Pat (preaching to the choir),

Fudge! Why am I not surprised? I guess one could really stretch a point and feel that way with a very over-powered engine running in a wet 2-cycle. Add muffler pressure, or even a pipe, and it probably seems that way even more - especially when the prop loads and unloads. Of course, it's gravity that causes that, so why doesn't gravity cause variations in the fuel pressure?

Because it's only a weight on a string and CF is everything!!! (sarcasm - just in case someone doesn't understand that)

BTW:
1. Combat bladder tanks contradict the whole thought. They work so well exactly because they make the engine run impervious to any G-forces - including centrifugal force.
2. A good 4-2 engine (Fox 35) will do it reliably on the ground simply by lifting the plane's nose up and down.
3. In that non-existant hobby with the letters "RC," everyone knows you set the engine for a slightly wet 2 cycle, so that it won't sag in maneuvers - and you check it by raising the nose up and down to test before you taxi out!

I give up - again.

Pat and TomB,

HNYear, anyway...<g>

We just look at different things, differently. Of course, I'm mostly thinking Stunt models. Wild Bill's max estimate IS for corners, and I worked out that proper size rounds add about 10g in the lift direction, plus/minus the trig of the gravity direction.

At 10g, or ranging from 9g to 11g if the loop were done in a vertical (geometric)plane, the Induced Drag rise is still ~100 times what it was in low, level...

The matter of the nose-up leaning happens in STATIC conditions - no dynamic factors: the model isn't moving. No wing lift; no induced drag; no CF and no funny angles regards the earth. Yes, it is a good check that you won't starve it off in flight, but beyond that it has little relation to the dynamics.

It took me some effort to get a convincing grasp of the dynamic vectors. So, we see that diffrently - or don't our models fly? Flight is a dynamic condition: static condition is not flight.

Another heresy? When a 4/2 type engine breaks up to 2-cycle mode, it first LOSES RPM. It sounds like more RPM, because we hear the pulse each revolution, not every other. It MIGHT wind up higher than its 4-cycling, unloaded RPM, after a brief time elapses, or it might not. Hasn't anyone else ever had a break from 4- to 2- on a turn downwards? If static head were all, that couldn't happen.

Lightly built and very highly powered combat models probably also vary RPM according to loads, but the engines are much nearer ultimate peak. With a light model, straight-flight Induced Drag is very small. Even a 10 to 20g series of moves is well within the engine's "envelope." It's 2-cycle all the way, and hard to hear a few hundred RPM shift unless it starts pinging or 4-cycling. Some speed fliers use audio (tape) recording from pilot position to check in-flight RPM. ...be interesting if we did something like that with the various combat classes...

Anyway, we each use what we believe works for us. Confidence is more important than absolute, laboratory certainty. Some of us try to be a bit more analytical, some don't. We all enjoy a good flight. That's where it counts.

There is a neat data logger on the market that could provide some useful data for this discussion:
http://www.eagletreesystems.com/Plane/plane.html
RPM, airspeed and 2 axis G load at 40 samples /second. (It also samples a bunch of stuff of no interest to C/L).
I have been leaning towards getting one for my bigger electric R/C stuff.


Pat MacKenzie

I had a Rabe-type rudder on a Twister. I never got it adjusted right and eventually abandoned it. At one point I was getting out rudder pretty much the same with either up or down control. At that point the airplane had much more than usual tension in the overhead 8's. So I am thinking that the fuselage was being yawed out and giving more lift than usual. I never decided if the square corners with that setting were just amusing or really frightening.

Fascinating gizmo, Pat,

...but as you say, it does a bunch of stuff we don't need.

I also bet the recorder looks like late at night at an octopus toga party when all the cables are plugged in!

>This is somewhat true for level flight, but the discussion
>was about overhead. CF overhead is (mv^2/r)-mg, so
>the greater mass has much less effect overhead.

True. Igor posted somewhere else that based on lap times, in level flight the stunt plane pulls 3mg, so overhead, if you don't have fuselage lift, it'll be 2g. For a 64 oz. (4 pound weight) stunter that's still a good 8 pounds of pull! The Combat plane will be pulling 9mg in normal flight, 8mg above, but since its mass is 20 oz. (1.25 pound weight) in level flight it is pulling 11.25 pounds while overhead it is pulling 10 pounds.

>Regardless,
>either plane with more line rake will pull harder in level
>flight. It is less clear whether it does so in the
>overhead. Obviously, there is some balance to shoot for in
>obtaining the trim you want, but that admits that there
>is an effect to balance between pull from velocity
>and pull from yaw (horizontal lift or thrust).

I must admit, a lightbulb really went on over my head when I read Igor's idea of using a forward leadout position coupled with more rudder. I would never have thought of doing that in a thousand years. It's a self-regulating mechanism - more pull, the nose comes in, resulting in less fuselage lift and less vectored thrust. Fly overhead, you get less line tension, so the nose swings out more, and the line tension gets restored somewhat.

>Thanks for the response. I would have never guessed the
>speed difference between higher versions of the Fox's. I
>only had the MK 3's. The cranks broke at the counter weight
>web mostly from hydrogen embrittlement - even did a lab
>report on it once:
>
>http://home.comcast.net/~thomas.blanchard/cl/FoxCombatSpecialMK3.pdf

That's a very interesting report. He didn't actually carry out any tests - he simply stated that Howard Rush's home oven heat treatment was consistent with the annealing treatment, which reduced hydrogen embrittlement, and the steel used for the crankshafts was one that was subject to the same. It wasn't actually the counter weight web that broke, the cranks broke in a plane just ahead of the crankpin/web region.

There's no mention at all made about the crank inside diameter. My knowledge of the matter is admittedly second hand, via Bob Bearden. When I drove up for the 1983 (?) MACA Nats in Chicago and stayed at his place, he showed us a Mark IV that he had had the crank opened up using EDM.

If I recall correctly, the only difference between a Mark III and Mark IV was the Mark IV's extended intake, which was designed to take a Slow Combat venturi insert. I never did have a Mark III. Common advice back then was, if you wanted to fly the Mark IV in Fast Combat, you had to change the bearings to one of those Fafnir ones with the riveted cage. For Slow Combat, the stock bearings were fine.

Fairly recently, Will Rogers from New England showed up at the Nats with some Bear Sidewinders and Mark IIIs. He ended up in the Slow Combat finals with Andy Mears. Andy was flying a Nelson. You could really hear the difference - the Nelson was turning quite a bit faster than the Fox, airspeed was also quite a bit less. Still, Andy just barely won the match.

>>
>>http://home.comcast.net/~thomas.blanchard/cl/FoxCombatSpecialMK3.pdf
>
>That's a very interesting report. He didn't actually carry
>out any tests - he simply stated that Howard Rush's home
>oven heat treatment was consistent with the annealing
>treatment, which reduced hydrogen embrittlement, and the
>steel used for the crankshafts was one that was subject to
>the same. It wasn't actually the counter weight web that
>broke, the cranks broke in a plane just ahead of the
>crankpin/web region.

Umm - the "He" was me. It certainly wasn't a scientific test, but there were at least 6-8 engines amongst us that blew cranks at the same position, in just a couple of flights with brand-new engines. This was at NAS Memphis, and I think the hobby shop there was pretty convenient (just down the Interstate a ways) on the Fox distribution list, so we got engines pretty quick from the factory.

After the relieving in the oven (I think I pointed out in the report that household ovens don't have temps high enough to anneal steel), the cranks would last forever - in fact they never broke again. The conversations with Duke confirmed the steel type used, and he admitted that he was changing the formulation with later versions.

Remember this was Materials Science, too, so we were looking at these things under the microscope - the breaks had all the signs of brittle fracture, not a yield or shear to failure.

As far as your crank-web comment, I think the diagrams were pretty specific, despite my apparently less than perfect description in the previous post, I guess.

>
>There's no mention at all made about the crank inside
>diameter. My knowledge of the matter is admittedly second
>hand, via Bob Bearden. When I drove up for the 1983 (?) MACA
>Nats in Chicago and stayed at his place, he showed us a Mark
>IV that he had had the crank opened up using EDM.
>
>If I recall correctly, the only difference between a Mark
>III and Mark IV was the Mark IV's extended intake, which was
>designed to take a Slow Combat venturi insert. I never did
>have a Mark III. Common advice back then was, if you wanted
>to fly the Mark IV in Fast Combat, you had to change the
>bearings to one of those Fafnir ones with the riveted cage.
>For Slow Combat, the stock bearings were fine.

Everyone changed to the Fafnir bearings. SOP for Fox's, New Departure Hyatts for ST's. I remember often getting into arguments with the Dixie Bearing counter salesman. He would try to argue with me that every bearing was constructed to Government specs, and there was no difference with the Fafnir. Funny how some people get.

>
>Fairly recently, Will Rogers from New England showed up at
>the Nats with some Bear Sidewinders and Mark IIIs. He ended
>up in the Slow Combat finals with Andy Mears. Andy was
>flying a Nelson. You could really hear the difference - the
>Nelson was turning quite a bit faster than the Fox, airspeed
>was also quite a bit less. Still, Andy just barely won the
>match.

That's nice to know. You will hear no argument from me about whether the Nelson is faster - it better be for that price. It just chafes me for anything that size to be that expensive. PA's and Aero Tiger's included. I know there are always customers that will pay that much, but geez - I can get an Echo Chain Saw for that, or a decent chunk of a Honda lawnmower. I can practically get a Husqvarna lawnmower with the Honda engine. Fox should've never had to compete on that level.

Oh well - thanks for posting again! I hope you're doing well.

>Umm - the "He" was me.

Oops.. Sorry, didn't notice. (That's supposed to be a sheepish grin.. I wish there were a smiley with little sweat drops on it..)

>Everyone changed to the Fafnir bearings. SOP for Fox's, New
>Departure Hyatts for ST's. I remember often getting into
>arguments with the Dixie Bearing counter salesman. He would
>try to argue with me that every bearing was constructed to
>Government specs, and there was no difference with the
>Fafnir. Funny how some people get.

Heh heh heh..

Did you get the C3 clearance ones? Those are pretty hard to find, don't know if they're really necessary on the Mark III/IVs. The bearing I got for my Wylie from George Aldrich was C3. Henry says he had to get some bearing manufacturer to make them specially for him in the sizes he needed.

>>Fairly recently, Will Rogers from New England showed up at
>>the Nats with some Bear Sidewinders and Mark IIIs. He ended
>>up in the Slow Combat finals with Andy Mears. Andy was
>>flying a Nelson. You could really hear the difference - the
>>Nelson was turning quite a bit faster than the Fox, airspeed
>>was also quite a bit less. Still, Andy just barely won the
>>match.
>
>That's nice to know. You will hear no argument from me
>about whether the Nelson is faster - it better be for that
>price. It just chafes me for anything that size to be that
>expensive. PA's and Aero Tiger's included.

When people bring up this subject on the Combat forums, someone usually points out that back in the old days, people used to pay that much or even more for all the engine rework. As a consequence, the really hot engines weren't available to everyone. You also had to run lots of nitro and the engines didn't last long. They point out the Nelson seems to last forever (until someone midairs your engine.. I remember one Duke Fox Memorial where the last 2 matches resulted in four destroyed Nelsons..), don't burn plugs and run very fast on 10-15% nitro, and there are enough made that anyone who wants one can buy one.

I agree about the price, though I don't have any philosophical objection to anyone charging what they want for something. I've never owned one, I've never been able to afford one. But I wish I'd picked up one of the two or three used ones that have crossed my path over the years.

>I know there
>are always customers that will pay that much, but geez - I
>can get an Echo Chain Saw for that, or a decent chunk of a
>Honda lawnmower. I can practically get a Husqvarna
>lawnmower with the Honda engine. Fox should've never had to
>compete on that level.

They came pretty close with the Mark VII. It was about half the price, also had a 17mm crank and was just a teeny bit slower. Problem was, I don't know if they actually made much money off them - someone remarked to me that the cranks were probably hand made on a lathe. I have one that I bought of Howard, it's in pieces. I never did reassemble it after I took it apart after it ate a circlip.

Isky,

I've mentioned that mode shift from 'braking' a benched, 4-cycling engine, too, in threads where Ted hadn't spoken yet. Mention of that phenomenon goes back several years; WHO said it first is lost in the mists...<g>

Oddly, with some engines, I've detected a full or partial firing mode shift from *slipstream obstruction* by the needling hand... To check that what I thought I'd heard WAS actually there, I tached engines before and during the time I had my hand flat, open, parallel to and behind the prop disk (maximum 'blank wall' obstruction to the slipstream flow.)

RPM drop was slight, if at all measurable, but clearly sounded 'faster' even when a clean break to 2- didn't occur. Benched diesels, where fat-4-cycle is a no-no, shift sound to a harder-working tone, with similar RPM effects. Although I like to keep dynamic and static conditions clearly separate, I see a useful "simulation," here, of the type of increased load on the prop disk that occurs when drag sharply slows a model in flight.

I've also recommended trying ***VERY CAREFULLY*** applying a carefully held soft rag to the spinner -- (make SURE hands and rag are firmly controlled, and will NOT get snagged into that meat slicer!)

Sure enough a minor RPM drop, from the added LOAD, accompanies a mode break, or harsher, higher sound in the same mode (i.e., 'wet two' type of run.) On the bench, I have NOT seen the mode shift, or 'load-sound-shift within a mode', increase RPM above that before the load was applied! As load is reduced, RPM rises ===of course=== and the initial mode or sound resumes as intial RPM is reached.

Caveat: This applies for stunt engines -- most likely not stressed as hard as racing or combat engines. More highly stressed operating conditions may heat an engine more, more quickly, which can affect run mode. (Wild Bill, testing McCoy Srs21 engines with Testors, noted this: Overheated incoming charge in the bypasses - when the engine is running too hot - related consistently to the 'runaway' problem. That is (was?) when the engine switched to 2-cycle, and never broke back to 4-, making that part of a stunt flight VERY interesting... The overheated engine metal, apparently, pre-heats the charge, which then burns more easily, or something very similar to that. 4-cycling depends, in part, on a cooler, wetter mix going to the combustion chamber.)

Maybe someone should name a stunter, "Occam's Razor?" ASIR, that is a logical process where everything unnecessary is pared away by test until what is left, however absurd it may seem, MUST be the correct answer... (How often did Holmes tell Watson something like that??)

Hi,

could someone please explain what the 4/2 cycle modes mean? I am reading these messages and I have no idea what you are talking about. I thought that the simple glow/diesel model engine is just 2 cycle type engine (you now there are some important parts missing when compared to typical 4cycle engine - valves, etc).
Maybe it is my poor knowledge of english language or I missied something important.

Thanks
Dalibor Toman

4 cycling because of ignition every other revolution - strong explossion does not allow good scavenging next revolution

>>>We call it the 'crow' ... the sound what cocks do<<<

I did not hear it yet , it must be some combat slang, stunt guys used tou call it "tarok" (like that card game) didn't you hear it?

BTW where are you from? Do you fly only F2D or also something else?

>4 cycling because of ignition every other revolution -
>strong explossion does not allow good scavenging next
>revolution
>
>>>>We call it the 'crow' ... the sound what cocks do<<<
>
>I did not hear it yet , it must be some combat slang,
>stunt guys used tou call it "tarok" (like that card game)
>didn't you hear it?

As Isky already wrote - what I was observing was not the 4cycle sound probably (the motor did large difference in RPM and power periodically).

>
>BTW where are you from?

I live near Svitavy city (the last place where F2D competitions are prepared here in the Czech Republic every year)

>Do you fly only F2D or also
>something else?

Long ago (20 years) I was flying CL as a school boy. Then I have no time/interest to continue it. I was always interested in F2D (althought I never saw it). Then in 2004 I have found that it is possible to see an F2D competition just near my home. I went to Svitavy and spent 2 days watching flyers doing the crazy loops and eights (and crashing planes of course). It was something I had to try - so I bought some planes and motors immediately to see if I am able to fly the hypersensitive wing (sometimes I am ). And since I have the luck to have 2 other F2D lovers near to me I can fly with them often (to verify that they are both still much much better than me .

I don't fly anything else. Currently I am fascinated too much by F2D. Other C/L (and RC o course) don't offer so much fun as the C/L combat flying, sorry .

Regards
Dalibor Toman

In a Combat engine, especially .15s, that's actually a sign of being too lean. The engine quits firing momentarily because it is starved of fuel, until some fuel builds up in the intake system and crankcase, at which point it starts firing again.

If you want to hear what four stroking sounds like (yes, even on an F2D engine), just open the needle valve a little until the engine sounds slightly "rough", then open it a little more. The sound frequency will drop several notes and there will be lots of oil spitting out the back.. Strange as it sounds, some Stunt engines are run this way during the flight!

>In a Combat engine, especially .15s, that's actually a sign
>of being too lean. The engine quits firing momentarily
>because it is starved of fuel, until some fuel builds up in
>the intake system and crankcase, at which point it starts
>firing again.

but in my case the problem disappeared by tightening the needle (or I am starting to be completely confused ). On the land I can simulate the same motor behavior by opening the needle too much (Fora, Kozol)

>If you want to hear what four stroking sounds like (yes,
>even on an F2D engine), just open the needle valve a little
>until the engine sounds slightly "rough", then open it a
>little more. The sound frequency will drop several notes and
>there will be lots of oil spitting out the back..

I will try it next time I have a chance to go to the field (there should be deep winter here now but in the fact we have no snow no real low temperatures but just windy and very wet weather) )

Regards
Dalibor Toman

>but in my case the problem disappeared by tightening the
>needle (or I am starting to be completely confused ). On
>the land I can simulate the same motor behavior by opening
>the needle too much (Fora, Kozol)

Ah.. in that case, it might just be very, very rich..

>>If you want to hear what four stroking sounds like (yes,
>>even on an F2D engine), just open the needle valve a little
>>until the engine sounds slightly "rough", then open it a
>>little more. The sound frequency will drop several notes and
>>there will be lots of oil spitting out the back..
>
>I will try it next time I have a chance to go to the field
>(there should be deep winter here now but in the fact we
>have no snow no real low temperatures but just windy and
>very wet weather) )

Get a pair of those Combat Kites from Bobby Mears! Fantastic for windy days when you don't want to fly airplanes. The windier the better, because they fly faster. I got a pair of them, but unfortunately, there's very little wind most of the time.. The couple of times it was windy, I got all my RC friends to try them out. Next, I'll let them fly some CL planes. "Yeah, it's just like flying a kite.. heh heh heh.. "

>
>Get a pair of those Combat Kites from Bobby Mears! Fantastic
>for windy days when you don't want to fly airplanes. The
>windier the better, because they fly faster. I got a pair of
>them, but unfortunately, there's very little wind most of
>the time.. The couple of times it was windy, I got all
>my RC friends to try them out. Next, I'll let them fly some
>CL planes. "Yeah, it's just like flying a kite.. heh heh
>heh.. "

There are some light graphite stunt kites that will perform in a 3 mph wind. Larger, two-line and quad-line stunt kites with a good breeze can pull skiers or boards. Stunt kiting has some very real comparisons with CL. It also has a sub-culture all its own. Stand still in the circle with a stunt plane and do continuous maneuvering with loops, eights, etc., and you pretty much get the feeling.

Fighter kites are something different - small, single line tissue covered kites that are more "juggled" than controlled, by balancing periods inbetween slack lines and tight pull.

Of course, I'm not telling you anything you don't know - some of that stuff originated in your part of the world.

You've probably already checked for this and it is probably not the problem, but if the needle is loose, air will leak in around it, leaning the mixture. Then, by turning the needle in, the mixture can often be richened, because it tends to slow or cut off the leak. Opening it up to "richen" the mixture under these circumstances does just the opposite. This naturally opens up the possibility that the correct setting cannot be achieved without stopping the leak, perhaps by inserting some fuel tubing around the needle and squeezing it down as you turn the needle in. FWIW.

dada,

Glad to help!

As Isky says, hard surging can -- usually does -- mean too 'lean' (not enough fuel to run smooth) on high speed engines. 4/2 stunt run changes sound more than power, so no hard surging when mode changes. Too 'lean' on high speed engines means about most possible power until something changes. Then engines can surge, sometimes.

We call mode change with rich stunt 4/2 run a 'break.' Our male chickens (roosters, cocks) crow too. Female chickens (hens) "cackle." Both sound different from 4/2 stunt 'break'.

Isky likes high performance engines; likes teasing stunt fliers, too. Highly regarded guy, though.

>>>Second, engine response *reacts* to loads.<<<

That is the point. Engine does not "see" the direction or gravity. It is not mounted to the "globe", it is free so gravity is not "visible", it must first slow down and only then all other effects like AoA on prop blade or shaft load or fuel leaning can start its work. Then it comes question how strong the feedback is. It can be too small (slowing more and more), or it can keep the speed well, or it can be too strong and accelerate too much - just because some of those effects are with positive (unstable) feedback.

BTW, it is not only uphill and downhill, it is also in corners, so can easily happen that model will accelerate from corners like F1 even downhill.