Leadout position mystery

I have a few questions.

1. Why does a more aft leadout position usually result in less overhead tension? In other words, why does yaw, while creating potentially more line tension at 5' typically result in less tension overhead? Paul Walker spoke about the reason in his great Impact article some years ago but I never understood it. You would think that outward yaw would ALWAYS result in more line tension, this simply is not so.

2. Is there some way to watch the "wiggle" coming out of a hard corner to find the yaw "nuetral" point? (The wiggle is the little shimmies you see coming out of hard corners, especially on the bottom last corner of the triangle). In other words, lets say the airplane wiggles outboard first, then recoils to inboard. Which way do you move the leadouts and rudder? Would this indicate that a more or less yawed posion would be more nuetral?

3. How is the leadout position for initial trimming established? Brett and Ted say 3/4" to 1" behind the CG. Which is it? I have my CG measured very accurately and would like to set my leadouts per this rule.

4. What is the difference between moving the leadouts to induce yaw and moving the rudder to induce yaw?

Also, I watched Howard Rush's Impact very closely at the Nats this last year. Brett had described his corners as "non events" in terms of corner wiggles. Indeed, his Impact does fly particularly straight (as does Ted's TP, David's TP, and RO's SV). In an attempt to find this "non event" corner I have gone to progreesivly smaller diamter propellors (with great success I might add). So much so that I have disconnected the Rabe rudder on the Mr. Hyde (I modified the new Dr. J rudder for very little throw---maybe we shall see it again).

Long story short...how do I get the same corner? rush's Impact and my airplanes have the same wing and weigh within an oz or so of one another. The CG on the Mr. Hyde is 6 5/8" from the flap hingline. The Dr. J will be at 6".

I had the same question a while back. Check this thread for more info...

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=7865&forum=DCForumID1

>I have a few questions.
>
>1. Why does a more aft leadout position usually result in
>less overhead tension? In other words, why does yaw, while
>creating potentially more line tension at 5' typically
>result in less tension overhead? Paul Walker spoke about
>the reason in his great Impact article some years ago but I
>never understood it. You would think that outward yaw would
>ALWAYS result in more line tension, this simply is not so.

I thik ithas to do with the unecesary dragthat will be added to the ship. combat planes, being (compared to stunt ships) wont really care.

>2. Is there some way to watch the "wiggle" coming out of a
>hard corner to find the yaw "nuetral" point? (The wiggle is
>the little shimmies you see coming out of hard corners,
>especially on the bottom last corner of the triangle). In
>other words, lets say the airplane wiggles outboard first,
>then recoils to inboard. Which way do you move the leadouts
>and rudder? Would this indicate that a more or less yawed
>posion would be more nuetral?

Same answer as for question 3

>3. How is the leadout position for initial trimming
>established? Brett and Ted say 3/4" to 1" behind the CG.
>Which is it? I have my CG measured very accurately and
>would like to set my leadouts per this rule.

Those measurements are just guidelines, not fixed distances. Only inflight triming will tell you the positions tht will suit you best.

>4. What is the difference between moving the leadouts to
>induce yaw and moving the rudder to induce yaw?

The rudder induced yaw will vary acoording to airspeed.

>Also, I watched Howard Rush's Impact very closely at the
>Nats this last year. Brett had described his corners as
>"non events" in terms of corner wiggles. Indeed, his Impact
>does fly particularly straight (as does Ted's TP, David's
>TP, and RO's SV). In an attempt to find this "non event"
>corner I have gone to progreesivly smaller diamter
>propellors (with great success I might add). So much so
>that I have disconnected the Rabe rudder on the Mr. Hyde (I
>modified the new Dr. J rudder for very little throw---maybe
>we shall see it again).
>
>Long story short...how do I get the same corner? rush's
>Impact and my airplanes have the same wing and weigh within
>an oz or so of one another. The CG on the Mr. Hyde is 6
>5/8" from the flap hingline. The Dr. J will be at 6".
adjusting flap elevator

No two ships will corner the same, not even two Impacts built by Paul Walker himself

Brad asked:
>
>Long story short...how do I get the same corner? rush's
>Impact and my airplanes have the same wing and weigh within
>an oz or so of one another. The CG on the Mr. Hyde is 6
>5/8" from the flap hingline. The Dr. J will be at 6".

The big difference is TORQUE. Howards 40 has HP, but not nearly as much torque (the HP comes from the rpm). When I was flying the Impacts years ago, I could switch from the 40 VF to the 46 VF, and see a SIGNIFICANT difference in corner, flying at the same speed with the same prop, and same CG. The only difference was TORQUE. This is one of the reasons I was never "at one" with the PA 51's and 60's. They made my planes fly different. As an experiment, after using the PA for several years, I switched back to the 40VF for the '98 NATS. I don't feel I gave up anything doing that. Yes, I was down on brute horsepower, but I was able to make that up in finesse.

So, that was the plan for years with the Impact fleet. Keep the prop size to 11.3" diameter, and let the engine rev., and the plane would fly extreemly "clean" and the corners were a "non-event" as you described earlier. Now, I am approaching that with the 4-strokes now. The latest Mustang is much the same (in terms of "non-event" corners) as the earlier Impacts, but now with brute power and brute line tension. The difference is the power is from a 4-stroke, the prop is 13" diameter, and the flap/elevator ratio is 0.80.

So, to answer your question, I would speed up the elevator on your plane to "attempt" to make up for the extra torque your engine is generating.

Good luck.

p.s. As you visit the W.C. site, place your $50 in my hat as you pass through the turnstiles!

Brad,

I am in complete agreement with Paul. After watching two very well built and easily trimmed Staris's fly in Huntersville, doing dime corners and giving $10.00 change with no hint of doing anything else but incredible corners..it made me a believer. There is going to be a Staris and a PA .40 light in my future. I am saving pennies as I type this. Derek Barry's Staris gave Randy all he could handle in Huntersville and it only had about 20 flights on it according to Derek. of course Randy was helping Derek and Gene Martine get them finely trimmed.

Hi Jim,
I hope you get the cooling problem solved.
Aaron is well under way with a Satana (same basic plane as the Staris and Shrike) for a PA 40. Something to be said about the slightly smaller planes, especially at sites like Huntersville where it can be choppy and turbulent.
Both Gene's and Derek's Staris are a little on the heavy side, but it doesn't appear to affect them. And Derek's was a real rush job. And I really think this size plane fits Gene much better. He is flying better than I have seen him in a while.
For those that don't know, Derek lost to Randy by 1/2 point. I think the "boy" is well on the way back! Geezzzzz.... I can remember when Derek had to use both hands to fly!
Hope to see you Friday at Brodak's!
Bill <><
When the character of a man is not clear to you, look at his friends.
Japanese Proverb

"Rush job"? Are you beLittling this airplane?

>"Rush job"? Are you beLittling this airplane?

Yes, he was Howard.

Just be glad your name is not Howard Hand.

>So, that was the plan for years with the Impact fleet. Keep
>the prop size to 11.3" diameter, and let the engine rev.,
>and the plane would fly extreemly "clean" and the corners
>were a "non-event" as you described earlier. Now, I am
>approaching that with the 4-strokes now. The latest Mustang
>is much the same (in terms of "non-event" corners) as the
>earlier Impacts, but now with brute power and brute line
>tension. The difference is the power is from a 4-stroke,
>the prop is 13" diameter, and the flap/elevator ratio is
>0.80.
>
>So, to answer your question, I would speed up the elevator
>on your plane to "attempt" to make up for the extra torque
>your engine is generating.
>
>Good luck.

Actually, I am pretty happy with the sharpness of my corner at 1 to 1 flap/elevator ratio these days. Since switching to the 12" Eather the corner is much easier, more predictable, and certainly sharper. Funny thing is the run is steadier and the line tension has improved! Even overhead.

It seems the more I set my Mr. Hyde like a classic Impact, the better and easier it flies.

1. Removed the engine offset.
2. Removed the wiggle rudder.
3. Removed most of the rudder offset (will remove all of it next).
4. Reduced the diameter of the prop (I plan on trying even less).
5. Flap elevator ratio is 1 to 1 now.
6. Removed the counterbalanced elevators.
7. Sealed the hingelines front and rear (love that Scotch magic tape!)
8. Added slight downthrust to engine (jury is still out).
9. Low pitch high RPM engine run (low boost).
10. Ted Handle and cables (Doug really seems to like that the best).

I guess I was referring to Rush's "cleanliness" in the corner.

To tell the truth I suck at trimming...but I do not plan to continue on that path.

>p.s. As you visit the W.C. site, place your $50 in my hat
>as you pass through the turnstiles!
>

That would cost me a $100, as Christi will be with me! That is why I wanted to know if the fee "rumor" was true. Lucky it was not.

This should make for interesting reading. Lots of good questions here.

>I have a few questions.
>
>1. Why does a more aft leadout position usually result in
>less overhead tension? In other words, why does yaw, while
>creating potentially more line tension at 5' typically
>result in less tension overhead? Paul Walker spoke about
>the reason in his great Impact article some years ago but I
>never understood it. You would think that outward yaw would
>ALWAYS result in more line tension, this simply is not so.

Outward yaw will actually waste energy. If we could fly with our lines totaly straight out to the plane a perfect 90 degree angle from the spinner tip to the LO would make the most line tension. If the plane flys around canted outward it wastes energy and the tension suffers. Now that is in a perfect world which we all know doesnt exist. Of course our lines are bowed a bit so we use the slider to get it as close to 90 as possible. The overhead being the place where the plane's wing is doing the least amount of lifting and you are relying totaly on the motor this is where this shows up the most. That is why I think larger props pull more upstairs. You are already flying in a very small area and your wing is not near as effective up there. Yaw your plane out and you loose energy. The motor is fighting the lines in an outward yaw as well as propeling the plane forward. Plus when the plane is yawed outward too far you start getting all these roll tendencies which also TAKE AWAY tesion in a BIG way. That probably has more to do with the loss of tension than anything...at least I think so.

>
>2. Is there some way to watch the "wiggle" coming out of a
>hard corner to find the yaw "nuetral" point? (The wiggle is
>the little shimmies you see coming out of hard corners,
>especially on the bottom last corner of the triangle). In
>other words, lets say the airplane wiggles outboard first,
>then recoils to inboard.

How can you really know. It flys through a 15' corner at 60 mph. Can you really see which way it is "wiggling" first?

Which way do you move the leadouts
>and rudder?

If it wiggles out first you move the LO forward. Pretty simple and or loose TW. Leave the rudder straight. Delicate game here. Been there done that many times. Always it has worked best for me to move the LOs and leave TW alone.

Would this indicate that a more or less yawed
>posion would be more nuetral?

Huh???

>
>3. How is the leadout position for initial trimming
>established? Brett and Ted say 3/4" to 1" behind the CG.
>Which is it? I have my CG measured very accurately and
>would like to set my leadouts per this rule.

Set it at 1" and start from there. Like ION said it really is a per plane deal. You know how I do it. Hang the plane. If you have your CG fairly far aft it will go to a pretty good locale to start with. You can also stand off it a ways and really see what kind yaw your initial LO position is going to induce. We tried it on SP and the CG was far forward and the LOs slid all the way to the back. Of course we didnt start there but it told us what you were in for right away. I hung my new Forerunner up this way, just enough yaw to see it from about 15' away and it flys great. Yes it is barbaric but it does work. A trick I got from Tom Farmer about 10 years ago and I still start with it today and it still gives me a very good ballpark position. On the Saturn I didnt do it this way and I went with a measurment and it flew like crap for about a week and I was working on it and someone watched it fly and had me do about 15 laps at about 20' and when I landed he walked over and moved the LOs forward about 1/4" and pow the plane came on. He could see the yaw in the level laps. So to each plane it's own. Just hang it and set the angle by eye and it will work pretty close as a starting point.

>
>4. What is the difference between moving the leadouts to
>induce yaw and moving the rudder to induce yaw?

The rudder is more effective as the speed goes up. That is why Berringer uses motor offset instead. The motor offset will always be there no matter the speed. He still trims the model to fly straight ahead, no more outward yaw than is needed.

>
>Also, I watched Howard Rush's Impact very closely at the
>Nats this last year. Brett had described his corners as
>"non events" in terms of corner wiggles. Indeed, his Impact
>does fly particularly straight (as does Ted's TP, David's
>TP, and RO's SV). In an attempt to find this "non event"
>corner I have gone to progreesivly smaller diamter
>propellors (with great success I might add). So much so
>that I have disconnected the Rabe rudder on the Mr. Hyde (I
>modified the new Dr. J rudder for very little throw---maybe
>we shall see it again).
>
>Long story short...how do I get the same corner? rush's
>Impact and my airplanes have the same wing and weigh within
>an oz or so of one another. The CG on the Mr. Hyde is 6
>5/8" from the flap hingline. The Dr. J will be at 6".

Dropping the Rabe rudder made a HUGE difference in what I felt. Last year the plane was wondering around in corners and major loss of tension in hard triangle corners. Even with the rudder set to as little as it would move. I think the shape of your rudder plays a huge role in it also. The moveable part extends way back so even a little movement makes a huge impact.

There is so much difference than what you and Howard are doing it is endless.

It isnt just about getting the CG n the right spot. We learned that with Furias. I think MOI has alot to do with it. I know you probably arent buying it but it really does. Howard has alot less in the first three inches of the nose of his airplane than you do. So you get the CGs set the same. Well his Elev only has to move a 40 spinning an 11.5" 2 blade. Yours has to move an 82 spinning a 12" 3 blade. And as Paul said there is a major torque difference there and that also plays a huge role! Your motor just trys to fly in a straight line so much more than Howards you have to have alot more movement in your elevator which means it is a bigger event for you to trun the same corner as him. He just slips by with the slightest flip of the elevator where as you are having to get some real movement to do the same thing. This gives you a higher AoA which will in turn put more work on the wing and demand more lift from the flaps. Bob's new plane. Long TM very little movement in the surfaces creates an effortless looking corner, at least it looks clean to me. You are going the right way with smaller diameter props. I flew your plane and there was a world of difference in that one and the SP. Sp had a 12" on it the last time I flew it and it was no where near what the Hyde is. It was nice and clean until about half way through when the fuse did it's thing. By the way Steve said you did an excellent job on your repair. Going up in ele ratio is an option as Paul says it gives the tail more power and keeps a lower AoA on the wing. There is plenty of area so less flap wont hurt.

I think you should get out your new plane and go from there. Hyde is good. NOW GET THE NEW ONE OUT! It has a shorter nose. This reduces MOI even more. It will also be easier for the plane to get a handle on that big torque factor. I think this is the better answer. Leave the Hyde where it is. It is a great flyer. Now pull out the new one and go to the next level!

>This should make for interesting reading. Lots of good
>questions here.

Yes, and interesting comments from Doug.

>I have a few questions.

Me, too.

>>1. Why does a more aft leadout position usually result in
>>less overhead tension? (snip)

>Outward yaw will actually waste energy. If we could fly
>with our lines totaly straight out to the plane a perfect 90
>degree angle from the spinner tip to the LO would make the
>most line tension. If the plane flys around canted outward
>it wastes energy and the tension suffers. (snip)

I agree with the outward yaw wastes energy bit, but I have a question on this theoretical 90 degree angle to the spinner tip thiung? Shouldn't we be thinking of a perfect 90 degrees from the CG? If we tried this motorless plane attached to a line on a fishing pole thing (a technique that teaches a lot about trimming, by the way) and attached our line to the nose of the plane, we would be whirrling it around with the lane facing us and the tail all the way out. Centrifrugal force. If we attached our line to the cg or a perfectly trimmed airplane, then the plane would fly normal. In practice we attach the lines in relation to the cg location on the inboard wingtip to add stability. And, since the lines are affected by drag, and drag is increased by speed, the lines will, in practice, bow back slightly. The leadout location at the wing tip will thus need to be angled back slightly to match the amount of bow on the lines (an angle which can only be approximated at this time since it is affected by line size, line length, aircraft speed, the "pull" on the lines generated by the plane, etc.)

>Now that is in a perfect world which we all know doesnt exist.
>Of course our lines are bowed a bit so we use the slider to
>get it as close to 90 as possible. The overhead being the
>place where the plane's wing is doing the least amount of
>lifting and you are relying totaly on the motor this is where
>this shows up the most. That is why I think larger props pull
>more upstairs. (snip)

I agree with what you said about the prop. With the lines being bowed, we aren't actually going with 90 degrees, however, but with whatever angle matches the bow of the lines at the wing tip, and the angle of the bow from the wing tip to the cg. That is why they are always set at some distance aft of the cg at the wing tip. That is also why it is now common to use an adjustable leadout guide since this angle can be affected by so many things. (See above)

One other factor that hasn't been mentioned is the affect of gravity on the lines (and the plane). When the plane is straight overhead and in perfect trim, gravity is going to help straighten out the bow on the lines. We would, thus, need a more forward setting than straight and level flying. Moving the leadouts forward slightly can thus help maintain proper trim up above and increase tension there while bleeding off a little tension down below where we can afford to give it up. Essentially we seek to achieve an approximate balance in line tension between level flight and about 45 degrees, realizing that the effects of gravity in the real world will still cause us to lose some tension straight overhead. As an example, you may trim for 3 gs (three times the weight of the plane) in level flight and 2 gs straight overhead.

>>2. Is there some way to watch the "wiggle" coming out of a
>>hard corner to find the yaw "nuetral" point? (The wiggle is
>>the little shimmies you see coming out of hard corners,
>>especially on the bottom last corner of the triangle). In
>>other words, lets say the airplane wiggles outboard first,
>>then recoils to inboard.
>
>How can you really know. It flys through a 15' corner at 60
>mph. Can you really see which way it is "wiggling" first?
>
>Which way do you move the leadouts
>>and rudder?
>
>If it wiggles out first you move the LO forward. Pretty
>simple and or loose TW. Leave the rudder straight.
>Delicate game here. Been there done that many times.
>Always it has worked best for me to move the LOs and leave
>TW alone.

Question: I agree that if it "wiggles" out first you need to move the LO forward, but why would one even think of tip weigbt at this point? I agree that adding tip weight (rock on a string) would help hold the plane out on the lines, but this should be adjusted for level flying and to make sure there is no tip dropping in the hard corners. I don't understand why it would even be considered as a stabilizing effect for yaw (agreeing with Doug).

>Would this indicate that a more or less yawed
>>posion would be more nuetral?
>
>Huh???

I think I read Doug as saying any yewed condition is not neutral.

>>3. How is the leadout position for initial trimming
>>established? Brett and Ted say 3/4" to 1" behind the CG.
>>Which is it? I have my CG measured very accurately and
>>would like to set my leadouts per this rule.
>
>Set it at 1" and start from there. Like ION said it really
>is a per plane deal. You know how I do it. Hang the plane.
> If you have your CG fairly far aft it will go to a pretty
>good locale to start with. You can also stand off it a ways
>and really see what kind yaw your initial LO position is
>going to induce. (snip) Just hang it and set the angle by
>eye and it will work pretty close as a starting point.
>

Doug's answer is fine. I just want to repeat what I said above that the leadout location is dependent on line rake in flight which is affected by line size (known) line length (maybe yet to be determined) flying speed (can be adjusted) weight of the plane (known) and other factors (such as adjustable rudder, engine offset--even nose moment) all of which work together.

>>4. What is the difference between moving the leadouts to
>>induce yaw and moving the rudder to induce yaw?
>
>The rudder is more effective as the speed goes up. That is
>why Berringer uses motor offset instead. The motor offset
>will always be there no matter the speed. He still trims
>the model to fly straight ahead, no more outward yaw than is
>needed.

I don't think we should use the leadouts to induce yaw. We should move leadouts to follow whatever yaw is being produced elsewhere.

Another thought on rudder induced yaw: Our goal is constant flying speed even in maneuvers and in overheads. And since that goal is never totally achieved, our leadout position is always set at a compromise. Now, as I stated above, the faster the plane flies, the more the lines will bow and the farther aft the ideal leadout position would be. And the farther out the plane yaws, the farther aft the leadout position should be. However, if we are using rudder offset to achieve this yaw and there is ANY change in aircraft speed (which there is) as the plane slows, the leadouts will want to be moved forward. But as the plane slows, rudder induced yaw also decreases meaning the lines should be moved forward even more. As the plane speeds up again the lines will want to be moved back. And the greater effect of rudder induced yaw will cause the lines to want to move back even further. So, if there is any change in speed of the airplane (which there will) the rudder offset just increases the difficulty in achieving a good compromise location for the leadouts.

>>This should make for interesting reading. Lots of good
>>questions here.
>
>Yes, and interesting comments from Doug.

Be nice...

>I agree with the outward yaw wastes energy bit, but I have a
>question on this theoretical 90 degree angle to the spinner
>tip thiung? Shouldn't we be thinking of a perfect 90
>degrees from the CG? If we tried this motorless plane
>attached to a line on a fishing pole thing (a technique that
>teaches a lot about trimming, by the way) and attached our
>line to the nose of the plane, we would be whirrling it
>around with the lane facing us and the tail all the way out.
> Centrifrugal force. If we attached our line to the cg or a
>perfectly trimmed airplane, then the plane would fly normal.
> In practice we attach the lines in relation to the cg
>location on the inboard wingtip to add stability. And,
>since the lines are affected by drag, and drag is increased
>by speed, the lines will, in practice, bow back slightly.
>The leadout location at the wing tip will thus need to be
>angled back slightly to match the amount of bow on the lines
>(an angle which can only be approximated at this time since
>it is affected by line size, line length, aircraft speed,
>the "pull" on the lines generated by the plane, etc.)

OK. I think we can all agree on that. Everyone should read that paragraph and understand it. Heck, even I understand that much.

>One other factor that hasn't been mentioned is the affect of
>gravity on the lines (and the plane). When the plane is
>straight overhead and in perfect trim, gravity is going to
>help straighten out the bow on the lines. We would, thus,
>need a more forward setting than straight and level flying.

Now see, that is an answer to the question!!! Bravo! In fact, Leonard is the first person to actually offer SOME KIND OF EXPLANATION. I am not sure it is correct, but it seem to make some sense. Is Leonard correct here fellas? Anyone?

>Moving the leadouts forward slightly can thus help maintain
>proper trim up above and increase tension there while
>bleeding off a little tension down below where we can afford
>to give it up. Essentially we seek to achieve an
>approximate balance in line tension between level flight and
>about 45 degrees, realizing that the effects of gravity in
>the real world will still cause us to lose some tension
>straight overhead. As an example, you may trim for 3 gs
>(three times the weight of the plane) in level flight and 2
>gs straight overhead.

OK. Excellent.

Is he right?

>>>2. Is there some way to watch the "wiggle" coming out of a
>>>hard corner to find the yaw "nuetral" point? (The wiggle is
>>>the little shimmies you see coming out of hard corners,
>>>especially on the bottom last corner of the triangle). In
>>>other words, lets say the airplane wiggles outboard first,
>>>then recoils to inboard.

>>Which way do you move the leadouts
>>>and rudder?

>Question: I agree that if it "wiggles" out first you need
>to move the LO forward

<snip>
Why? Why? Why?

To answer my own question (using the responses so far). THE AIRPLANE is causing the yawing! This may seem obvious to the rocket scientists, but it is not to me, and I have been doing this a while (still a short timer compared to most).

So.... the airplane is yawing...huh... the line leadout position has nothing to do with the yaw... huh... so using that logic the rudder is aligned too far out. Here is my logic. The last corner of any inside square manuever is always a little faster than the others. That is drop corner and the airplane is accelerating due to gravity. So if the speed is increasing, the rudder is becoming more effective at that instant, causing the yaw (wiggle) which always kicks outboard first.

Moving the leadouts would not "fix" the wiggle. The wiggle must be fixed, and then the leadouts optimized for that position. True?

>but why would one even think of tip
>weigbt at this point?

Roll is coupled to yaw. One does effect the other some.

>>>4. What is the difference between moving the leadouts to
>>>induce yaw and moving the rudder to induce yaw?
>>
>>The rudder is more effective as the speed goes up. That is
>>why Berringer uses motor offset instead. The motor offset
>>will always be there no matter the speed. He still trims
>>the model to fly straight ahead, no more outward yaw than is
>>needed.
>
>I don't think we should use the leadouts to induce yaw. We
>should move leadouts to follow whatever yaw is being
>produced elsewhere.

OK. I understand. I agree.

>
>Another thought on rudder induced yaw: Our goal is constant
>flying speed even in maneuvers and in overheads. And since
>that goal is never totally achieved, our leadout position is
>always set at a compromise. Now, as I stated above, the
>faster the plane flies, the more the lines will bow and the
>farther aft the ideal leadout position would be.

I don't know about that...

Slow flight creates much more "bow" than fast flight, especially with a heavy plane. The faster one flies the more centrifugal force, the more force available to straighten the bow in the lines casued by drag. Same with airplane weight (somewhat---never proved that one to myself in practical terms).

And the
>farther out the plane yaws, the farther aft the leadout
>position should be. However, if we are using rudder offset
>to achieve this yaw and there is ANY change in aircraft
>speed (which there is) as the plane slows, the leadouts will
>want to be moved forward. But as the plane slows, rudder
>induced yaw also decreases meaning the lines should be moved
>forward even more. As the plane speeds up again the lines
>will want to be moved back. And the greater effect of
>rudder induced yaw will cause the lines to want to move back
>even further. So, if there is any change in speed of the
>airplane (which there will) the rudder offset just increases
>the difficulty in achieving a good compromise location for
>the leadouts.

Not sure I agree with the specifics of the effects of the speed on the yaw as you desribed, but I certainly agree with the diagnosis. Yaw will change with speed if the airplane is preset to yaw on purpose. So setting the rudder in a yaw position is bad. Right?

>Not sure I agree with the specifics of the effects of the
>speed on the yaw as you desribed, but I certainly agree with
>the diagnosis. Yaw will change with speed if the airplane
>is preset to yaw on purpose. So setting the rudder in a yaw
>position is bad. Right?

Al's idea of using a moving rudder to counteract precession is good. It actually counteracts yawing tendencies. Using the rudder simply to produce yaw is bad.

You are correct in that increased centrifrugal force can cause the bow in the lines to straighten out, but we are then also assuming that there is ample tension on the lines to counteract yaw. The biggest problems always occur where the amount of tension is the least, and that is when the bow in the lines will again become most noticeable.

>Al's idea of using a moving rudder to counteract precession
>is good. It actually counteracts yawing tendencies. Using
>the rudder simply to produce yaw is bad.

Agreed. However the procession is not always enough to need a moveable rudder. Get to 14" and a slightly moveable rudder will help it. Much less than that and it really is not needed, in my limited test world anyway. The planes are large enough to overcome the procession caused by the smaller diameter props. Especially when you start flying 63" spans on 12" props. There just isnt enough prop to need the moving rudder. At this point it causes more problems than it fixes. History helps to prove this out as well. Now build a small 35 size plane and run a 13 or a 12 and you could need a moving rudder. It really isnt a universally needed part of the model. Not a bad thing to have it be an option. But not like a LO slider or TW box which are must haves.

I think I saw Matts and it was moving out both ways. I would think this would really foul it all up. I know Windy's rudder moves out both ways. This should really screw up the insides right? WRONG! I flew it and it simply glided through every corner. I was an absolute dream and the corners were the NON EVENT type that Brad describes. His rudder moves the wrong way on the inside portion of the pattern. Yet it flys straight and clean. Explain that one...??

>
>You are correct in that increased centrifrugal force can
>cause the bow in the lines to straighten out, but we are
>then also assuming that there is ample tension on the lines
>to counteract yaw. The biggest problems always occur where
>the amount of tension is the least, and that is when the bow
>in the lines will again become most noticeable.

Yes and the tension on the lines goes DOWN as the speed decreases. Fly a 4.9 lap and a 5.9 lap and you will see. Fly three loops to 30 degrees and kill off speed and tension goes down. Fly loops to 75 degrees and the model keeps the tension all the way around.

>(snip) procession is not always enough to need
>a moveable rudder. Get to 14" and a slightly moveable
>rudder will help it. Much less than that and it really is
>not needed, in my limited test world anyway. The planes are
>large enough to overcome the procession caused by the
>smaller diameter props. Especially when you start flying
>63" spans on 12" props. There just isn't enough prop to need
>the moving rudder. At this point it causes more problems
>than it fixes. History helps to prove this out as well.

Hey, Doug, we are pretty much agreeing on things here. I like that. You mention that it is "not needed", and that is true. I can be helpful, however, even with smaller props (although the amount of help diminishes as the size/weight/rpm of the prop diminishes in relation to the plane. There are no absolutes, however, and smaller props whirling faster will cause as much precession as somewhat larger props turning slower. Add weight to the prop (or spinner) and you, again, add more precession.

You mentioned Matt's plane. His is (I think) 690 square inches that was originally turning a 13 inch three blade prop. He trimmed it first with a fixed rudder (moveable feature disabled). Rudder set at approximately zero. Got it pretty well in trim, but it was "softer" in the upper corners of the hourglass and upper left corner of the square eight. Still quite flyable, however, and better than a lot of planes. (Matt flew a couple of fellow modelers' planes that actually scared him at those junctions for their lack of tension--still using a PA-61 on a pipe, however, and with much less prop). Matt then hooked up the Rabe rudder to the already trimmned plane and there was an immediate and noticeable difference. And this without any trimming to the rudder throw at all. Since then he has gone to a 13.5 inch prop and finds it a quite useful feature, even though his engine rpm is slower than a lot of pipe setups. (Remember, higher rpm can cause even smaller props to exhibit the same characteristics.)

So, the real question is "need" verses "useful" or "helpful". One may not need it with a smaller prop, but one may still find it helpful. The big thing is adjustability. Matt attaches his to the elevator with an adjustable slider. He noticed later that Paul Walker had used a very similar method of attaching to the elevator as did Matt. This allows not only the ability to adjust the amount of throw (at the rudder horn) but the amount of assymetry in the throw. I think Al had mentioned somewhere that he had about a 4:1 ratio of throw for "down" verses "up".

You need not only the ability to adjust, but then you need to make the effort to do the adjustment. In Brad's situation, for instance, the problem may be in how it is set up, not that it IS set up. If you have adjustable leadouts, move them forward slightly, backward slightly, until you find the optimum point of adjustment. If you make other adjustments, go back and start over. Same with the Rabe rudder. We found it much easier to adjust everything else first and then the rudder, but found an immediate benefit in using it. (I like tension. So does Matt.)

>Now build a small 35 size plane and run a 13 or a 12 and you
>could need a moving rudder. It really isn't a universally
>needed part of the model. Not a bad thing to have it be an
>option. But not like a LO slider or TW box which are must
>haves.

Again, "helpful" and "need" are probably the two key words. Matt's 94-97 Stukas were "small 35 size" planes (570 square inches, FP 35 powered) that ended up with a 12.5 x 5.5 Bolly prop up front. Still, it didn't have the Rabe rudder. We had done limited experimenting with that up to that point. In fact, the 96 plane ended up with a 53 in the nose turning a 13 inch three blade. Still flew quite well without any offset or adjustability to the rudder. Would the Rabe rudder have helped? Probably. But it didn't "need" it. (Although anything that helps can, in the end, garner more points.)

>I think I saw Matts and it was moving out both ways. I
>would think this would really foul it all up. I know
>Windy's rudder moves out both ways. This should really
>screw up the insides right? WRONG! I flew it and it simply
>glided through every corner. I was an absolute dream and
>the corners were the NON EVENT type that Brad describes.
>His rudder moves the wrong way on the inside portion of the
>pattern. Yet it flys straight and clean. Explain that
>one...??

Hey, I don't always explain every thing. I only know what (sometimes) works. Although, like you, I do try to understand why when I discover that it does. I guess I would have to look at his rudder to see just exactly what it is doing, but originally when we set it up it was turning out with "down" elevator and (slightly) in with "up" elevator. It may be that at full deflection the rudder pulls back out again, I don't know. Wherever it is at is where it seemed to work the best.

Each plane is going to be different. Each situation is going to be different. That's why we need adjustments. And that is why we need to be willing to use them. Make one adjustment at a time, one flight at a time. If it helps, that is your new "square one". If it hurts put it back and make a different adjustment. Make small steps (it doesn't do any good to move from too far back on your leadouts to too far forward) at a time, and keep notes. It took Matt over 200 flights on his first pipe ship before he was confident enugh with it to take it to the Nats. It took another 50 flights up there to actually get it in "final" trim. The second one followed the first and was much easier to trim. His new one has a couple of changes and has one "little" problem yet that may, because of time, relegate it to back up status. It actually looks quite good to me from the judges position (nice tight corners) but he can "feel" it so we need to work that out.

>>
>>You are correct in that increased centrifrugal force can
>>cause the bow in the lines to straighten out, but we are
>>then also assuming that there is ample tension on the lines
>>to counteract yaw. The biggest problems always occur where
>>the amount of tension is the least, and that is when the bow
>>in the lines will again become most noticeable.
>
>Yes and the tension on the lines goes DOWN as the speed
>decreases. Fly a 4.9 lap and a 5.9 lap and you will see.
>Fly three loops to 30 degrees and kill off speed and tension
>goes down. Fly loops to 75 degrees and the model keeps the
>tension all the way around.

Again, we totally agree. Increasing lap speed should increase tension, and if the tension increases it can counteract drag on the lines. Someone elsewhere here mentioned the computer program that one can use to approximate leadout location and it uses the assumption that increased speed (increasing tension) will offset increased drag so that the bow in the lines remains constant. However, we aren't totally a "rock on a string". We are flying an airplane around a circle. We could, for instance, take a full-house radio control airplane, put a set of lines on it, have the radio operator fly it around our circle and feel absolutely no tension on the lines. There would be a lot of bow then. We could also have him yaw the airplane away against the lines and have a lot of tension on the lines. In either case it would be flying at the same speed. This is an extreme example, but the flight trim does affect tension, and such tension can be "dialed" in or out at any speed. Still, if you do not change the trim but simply increase the speed, the line tension should (will) go up.

At Muncie's contest this past week-end (as most every else in the country, it seems) the winds were blowing up a storm. It was windy from the get-go and didn't let up. Several flyers wisely left their planes in the car (I say "wisely" because if you are not comfortable in those winds, don't fly. It isn't worth losing a plane). Only one, as I recall, elected to fly a second flight (and he didn't improve anything). In those conditions Matt's plane was running lap times about one tenth of a second faster than "normal" and it powered right through. I didn't ask him about tension, but it does help--epsecially in the overheads or when you go up wind.

Semper fly (with my apologies to the Marines).

>You need not only the ability to adjust, but then you need
>to make the effort to do the adjustment. In Brad's
>situation, for instance, the problem may be in how it is set
>up, not that it IS set up. If you have adjustable leadouts,
>move them forward slightly, backward slightly, until you
>find the optimum point of adjustment. If you make other
>adjustments, go back and start over. Same with the Rabe
>rudder. We found it much easier to adjust everything else
>first and then the rudder, but found an immediate benefit in
>using it. (I like tension. So does Matt.)

Perfectly well said...

Indeed, the airplane would be best suited to be pre-trimmed without the wiggle rudder, and then the wiggle added. In fact, my biggest mistakes in the past have been relying on the rudder too much to mask the real trim issues with the plane.

A teeny tiny bit of rudder on the outsides would still be nice, even with the small prop...

Actually, Len I think I picked up 9 points toward pushing Allen Goff out of second which was the goal. Alas,I was a few points short of this and also the only nonpiped Expert on the field with my Stalker powered plane from 97. I had some pucker pull-outs last weekend but honestly had only two full pattern flights so far this season before showing up in Muncie. My first official being my third flight of this season. Its an ok fair weather plane but a real hand full in the wind.

Matt flew extremely well and his plane handled the breeze very well without loss of shape nor any significantly noticeable wind up in the stiff breeze. A testimony to the piped application. When Matt was testing several years back I believe my piped Chevelle was one of the planes he flew and got nervous about overhead tension. Conversely I could barely keep my hand from shaking after flying his stump puller! A simple difference of preferred feel and flying style. My last couple of seasons have been less than practiced and little new testing or trimming to say the least. Had I been working with a new motor set up again, I would probably have wanted to get that settled in before making any fine trim adjustments provided the plane would track, not roll in nor fall out of overhead maneuvers

Speaking of engines and type of power delivery, I certainly feel that this plays a significant part when trimming. If you are trying out new motors and props it probably would pay dividends to reach a comfort zone and a standard in the set-up prior to making lots of trim changes to the surface deflections etc. . As noted, prop diameter plays a big part in the rest of your trimming as does two-four versus piped versus 4 stroke. While certain standards go across the board, all setups here are a bit different when it comes to fine tuning.

>Matt flew extremely well and his plane handled the breeze
>very well without loss of shape nor any significantly
>noticeable wind up in the stiff breeze. A testimony to the
>piped application. When Matt was testing several years back
>I believe my piped Chevelle was one of the planes he flew
>and got nervous about overhead tension. Conversely I could
>barely keep my hand from shaking after flying his stump
>puller! A simple difference of preferred feel and flying style.

John, Matt and I would be the first to acknowledge that this is preferred feel and flying style. But it is something that can be dialed in simply by the engine application as well as the rest of the tim of the airplane. And he and I both just happen to like the feel of knowing that the airplane is at the end of the lines--even when flying upwind.

Oh, and if you thought that plane was a stump puller, he saw your response here and made the comment that the plane you flew then was nothing compared to what he is flying now. It does take a little weight training at the beginning of the season, however. As an aside he also discovered he might need to warn the pit lady who holds his airplane for launch beforehand. That tail wheel will never be the same. (Apparently the ground thrust caught her off guard. No harm done.)

>I agree with the outward yaw wastes energy bit, but I have a
>question on this theoretical 90 degree angle to the spinner
>tip thiung? Shouldn't we be thinking of a perfect 90
>degrees from the CG?

Yeah that is what I really meant. It was late.

>
>One other factor that hasn't been mentioned is the affect of
>gravity on the lines (and the plane). When the plane is
>straight overhead and in perfect trim, gravity is going to
>help straighten out the bow on the lines. We would, thus,
>need a more forward setting than straight and level flying.
>Moving the leadouts forward slightly can thus help maintain
>proper trim up above and increase tension there while
>bleeding off a little tension down below where we can afford
>to give it up. Essentially we seek to achieve an
>approximate balance in line tension between level flight and
>about 45 degrees, realizing that the effects of gravity in
>the real world will still cause us to lose some tension
>straight overhead. As an example, you may trim for 3 gs
>(three times the weight of the plane) in level flight and 2
>gs straight overhead.

I am with you pn all of your answers. However I would like some explaination on how gravity straightens the lines when overhead. It would seem the other way around. I hold my handle in one spot and as the plane goes up the gravity pulls more bow in the lines. Oh and how do you trim for a specific G? I mean how do you measure that?

>
>Another thought on rudder induced yaw: Our goal is constant
>flying speed even in maneuvers and in overheads. And since
>that goal is never totally achieved, our leadout position is
>always set at a compromise. Now, as I stated above, the
>faster the plane flies, the more the lines will bow and the
>farther aft the ideal leadout position would be. And the
>farther out the plane yaws, the farther aft the leadout
>position should be. However, if we are using rudder offset
>to achieve this yaw and there is ANY change in aircraft
>speed (which there is) as the plane slows, the leadouts will
>want to be moved forward. But as the plane slows, rudder
>induced yaw also decreases meaning the lines should be moved
>forward even more. As the plane speeds up again the lines
>will want to be moved back. And the greater effect of
>rudder induced yaw will cause the lines to want to move back
>even further. So, if there is any change in speed of the
>airplane (which there will) the rudder offset just increases
>the difficulty in achieving a good compromise location for
>the leadouts.

I think you ahve this backwards. Or at least on all the planes I have ever trimmed it worked opposite of what you are saying. I just experienced it tonite. I had a flight or two at 5.8 and there is a noticable bow. Then one at 5.0 and the lines are pretty much striaght out. If it worked the way you are saying then everyone would go slower and not faster. The drag on the lines has more effect on it slower speeds due to less centrifical force. At least that is how it plays out around here.

Doug, if you will:

>>>fly with our lines totaly straight out to the plane a perfect 90 degree angle from the spinner tip to the LO would make the most line tension<<<

then it certainly does not make most line tension. In that case your fuselage produce lot of inward lift. You need ~1 deg outward yaw to be neutral.

BTW if your rudder is large enought, the nose will poit out that angle itself.

Your questions touch on a number of things I agonized over many years ago. There are fairly simple answers to most of them, but they involve some math.

Line "bow" and the "rake" angle where lines reach the wingtip CAN be estimated -- Pete Soule' did a short article for the ?70-71? Aeromodeller Annual that works quite well. "Bow" and the resulting "rake" angle DON'T change with model speed! Centrifugal force (line tension) and "bow" (line drag) BOTH change with velocity. ...in the same 'sense', so: faster means both more CF and more line drag, and both change the same with the speed change.

Gyroscopic precession is a significant factor, with our heavy props, high RPMs, and spinners. In 'normal' --counter-clockwise upright-- flight, pitching the model up causes precession pushing the nose away from the center, and vice versa. J van Hattum, from Holland, had an article on a way to estimate precession couples, in another Aeromodeller Annual. It also works quite well. Precession is a good reason to use a 'reversed' bellcrank (flap pushrod inboard of pivot). When we pitch UP, we transfer part of line pull to the UP line. The center of line pull slides ahead of the pivot, or CG, whichever reference we want, and tends to pull the nose IN -- countering the precession pushing it out. This also works, in reverse, on DOWN control moves.

And, my favorite -- panel sizes... I had to do this one on my own. Say the CG of the model moves 1º around the flight circle as we study it. a spanwise line through the CG sweeps an area that is narrower at the inboard tip than at the outboard tip -- clear on that?
We can figure the difference. The point where the AREA swept is split exactly in half is where the fuselage centerline should go. Lift and drag inboard and outboard are equal in flight! No roll or yaw... at any maneuvering loads, at least from lift & drag. Precession causes some yaw, which make one wing move faster than the other, and that introduces some roll.

A lot more... All of it an approximation that works reliably enough without going off the deep end in technical perfections. Lemme stop here, just teasing y'all on the goodies...

Hi

If we look at the physics formluae for drag and centrafugal force, we
can draw some conclusions.

Fc = M * V^2 / R

Where:

Fc : Force centrafugal
M : Mass of aircraft
V : Velocity of aircraft
R : Radius of turn

D = 1/2 * p * V^2 * S * Cl

where :

D : Drag
p : Density of air (1.225 kg/m^3)
V : Velocity
S : Surface area
Cd : Coefficient of drag

As the bow in the lines is a product of the Fc and D vectors, and both forces are proportional to V^2, you might expect that the bow should remain the same at all speeds. It doesn't. The reason for this is that air will more easily flow smoothly over a surface or around an objest at high speed than at low speeds. That means, Cd is not constant but increases as the velocity is reduced. There is a relationship between velocity, length of a body (line diameter), air density and viscosity. That is known as Reynolds number (Re). Theory is that at the same RE coefficients are the same. That is, if you halve the size of an object, you have to double it's velocity to get the same flow characteristics and therefore coefficients of lift, drag and moment. In SI units, RE is approximatly = 68459 * V * L where L is the length of the body in metres. This concept of RE is practical on full size aircraft but on very small objects it tends to break down some due to scale effects in the boundry layer. The upshot of this is that as the plane slows down, line drag is proportionally larger with respect to centrifugal force so the bow in the lines increases. I expect our models yaw in slightly as a result though a sufficiently large fin and properly aligned should resist this to some extent.

As Fc is proportional to V^2, we get a lot more force for a small increase in velocity. This is felt as line tension. So while engine offset and yaw out mean the thrust is pulling out more, that may not be enough to counter the loss from slightly reduced velocity.

If line tension is low, say 2G level, the effect of gravity is you get 1G overhead. That's just 50% the line tension. But if line tension is high say 4G level, you get 3G overhead, a loss of only 25%. Compared to the 50% loss before, this is not nearly so noticable. I think how we percieve things comes into play. Many of our sences work on a logrithmic, not linear scale. This means we are far more sensative in the low range of the scale than the heigh end. If it were not so, we would hardly be able to feel the weight of a 1 oz stone nore be able to judge the heavier of 2 pebbles nore hear musical scales etc. So I believe that the overall increase in line tension is not perceived nearly so well down low where it was already reasonable as it is perseived overhead where it was perviously inadequate.

All that assumes the same velocity level as overhead but if the plane is slower overhead, any increased thrust from squaring up the plane will have far less effect in level flight where speed was already heigh because drag is proportional to V^2, at a lower initial speed, you get more velocity increase out or the same amount of extra power and this results in far more line tension by the same V^2 rule.

Now about manouvering. Changing course applies more lifty from the wings we can see from :

Cdi = (Cl^2 / pi AR ) * k

where :
Cdi : coefficient of induced drag
Cl : Coefficient of lift
pi : 3.142
AR : Aspect ratio
k : Plan form correction factor

that induced drag will rise sharply with moterate increases in lift coefficient. That will slow our plan coming up into a wingover, the turn puts on the breaks and then the engine has to haul the plane up against gravity. A well set up engine is needed to put on the power at the right times. Also the very tight turns in squares really kill speed and sevearly effect line tension. While higher AR wings help maintain speed in the turn, it is Cl that is the bigest factor here.
Cl can be reduced by opening up the turns, reducing weight or increasing wing area.

There is much much more that could be said, so little time.

Lou, Ken you are ignoring one very important moment. It is outward yaw moment of fuselage and engine thrust. If you implement it to the equation, it will show you significant changes regarding speed even if you ignore RE number.

Igor,
I just gave a short, minimally tech comment. You know I place the fuselage at the dynamic center of the span, so I can center the thrust, drag, torque, precession and yaw vectors as well as possible to reduce their effects. But, right, I did not emphasize that...

Ken,
Do you have an estimate of the speed variance at the wingtip end of the lines from the sharpest or slowest corner to slick level flight? 10%? 15%? From 80 fps (I still think SAE rather than SI) 15% is down to 68 fps (47 MPH)? -- briefly -- followed by strong acceleration back to 'flank' speed around 55 MPH?

I'm a bit concerned that looking at RE for small cylindrical objects like the FRONT line (aft line is in the chop behind it) may rely too much on large scale tech. Over past decades, my relatively brute force approach has had reliable results, even when drastic layout appearance changes were involved. I've tried various refinements, and found insignificant influences from several that some people agonize endlessly about. I don't knock the extra effort, just I prefer other aspects of our hobby.

The flier is so much more important than the model, that I am content to rough out numbers I know will fly predictably -- and well. That puts it up to ME to learn to fly it to its full potential.

Ken,

Thank you and forgive me for not spotting it sooner. You describe one of the largest varying factors in our maneuvering stunters -- change in Induced Drag. Igor, Bill Netzeband, very few others recognize how powerful this can be...

Reducing the discussion to an 'it must be' level - sort of like disregarding extraneous terms to see the effects of key terms...

If the model (per Bill Netzeband) can pull 35g in a turn, pitching up into a wingover climb 'must' at some instant need 35 times as much lift as level flight, right?

We can solve for an effective level flight C(L) at 1g lift. From that we can put a rough number on level flight C(D(i)).

C(L) somewhere in the turn can be 35 times as great. C(D(i)) varies as the square of C(L), so the induced drag coefficient, thus induced drag, can rise to about 1225 (35^2)times its level flight value, at least at that instant. Even if a force is small, 1,225 times as much gets to be important.

Note: Other terms in the basic equations that don't change -- AR, area, air density. Velocity does change, but as a response to drag changes.

And everyone's assuming that the effect on the amount of bow in the middle of a catenary, of tension on the ends and the drag along the length (which is the shape the lines assume due to drag), are the same magnitude...

I wonder if they are. I remember the professor talking about catenary curves at the end of freshman calculus, but I don't really care to revisit the details...

>And everyone's assuming that the effect on the amount of bow
>in the middle of a catenary, of tension on the ends and the
>drag along the length (which is the shape the lines assume
>due to drag), are the same magnitude...
>

Not me. The drag can be calculated on the basis of line size, line length, and speed (0r lap time). But smooth lines will be different from cables, 7 strand cables and 19 strand cables will be different, and clean lines and dirty lines will be different. (Even wet and dry will be different.)

And, as to the bow, we have the above drag to calculate, and then we have the tension to calculate. This is not a simple centrifrugal force calculation, as the trim on the airplane can greatly affect the "pull" as can the power train driving it. We can run the same airplane, trimmed the same way, switch props, fly the same lap times, and the pull will be different. We can take the same airplane and switch from a PA 61 to a PA 65, and using the same prop and lap speeds notice an increase in line tension. (Been there, done that.) Now, tell me, how do you put that into a spread sheet and calculate precisely where the leadouts should be located? You can get an approximation, but from there it is "try and fly." That is why we have adjustable sliders, else you could set them at a certain location as shown on the plans, set the "perfect" tip weight, adjust the engine for lap speeds, and you would be done.

1. Why does a more aft leadout position usually result in less overhead tension? In other words, why does yaw, while creating potentially more line tension at 5' typically result in less tension overhead? Paul Walker spoke about the reason in his great Impact article some years ago but I never understood it. You would think that outward yaw would ALWAYS result in more line tension, this simply is not so.
Simple. It is question of interaction between rudder, leadout drag and line pull. If you have lines too front, the torque to the vertical axle of model from line drag will be much higher that toque from line pull (as leadouts should be aft of CG where is that pull concentrated – at least that majority from centrifugal force). So as leadouts go toward nose, the line pull balances the line drag less and less. It means there is excessive inward moment, which must be balanced by rudder instead of line pull (the sum must be always zero). Now if model goes to higher line elevation, the pull is lowered (including its effect to the equation) and model tends to yaw out thanx too much rudder effect. That will bring little fuselage lift and especially some fraction of prop thrust is converted to line pull. It means “front position” has some self-regulating effect, which is not present, or missing or even opposite if lines are too back.
I cannot agree too much with that drag theory. If we speak about some constant yaw added by lines too aft, it would be present also in level, and that could be solved by higher TO rpm and that will solve the same problem the same way also overhead. However I agree that it IS happening, I just say it is not primary reason.
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2. Is there some way to watch the "wiggle" coming out of a hard corner to find the yaw "nuetral" point? (The wiggle is the little shimmies you see coming out of hard corners, especially on the bottom last corner of the triangle). In other words, lets say the airplane wiggles outboard first, then recoils to inboard. Which way do you move the leadouts and rudder? Would this indicate that a more or less yawed position would be more neutral?
First out – lines front. The reason is also simple. The input to lines means has a feedback. That feedback means higher tension in lines. What we want is uniform angle to lines. So if that higher tension means input “nose out” then it is probably too back.
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3. How is the leadout position for initial trimming established? Brett and Ted say 3/4" to 1" behind the CG. Which is it? I have my CG measured very accurately and would like to set my leadouts per this rule.
Depends on many many things like weight, speed, line length, span, line diameter, rudder offset …… forget it. Do it as Brett says and trim it afterwards. And yes, it was already written in other messages, it is different in level and overhead, so you must find your optimum anyway.
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4. What is the difference between moving the leadouts to induce yaw and moving the rudder to induce yaw?
I think my answer from first point tells all, they just must match each other. And not only that. Brett wrote some years ago how he trim for proper flying in round figures and in corners. It was about matching AC of wing with AC of tail. And there is also proper position of fuselage to lines making proper response of line tension in maneuvering (what can change shapes of figures – it was in some another thread also). So I think if you will trim that AC-to-AC problem another way (for example outboard flap size or movable stab) then you will probably end up at little inward rudder offset with little more aft line position. That flies very well in calm, unfortunately makes problems in wind and especially turbulence. So I would say forget theory, make the rudder straight and put leadouts accordingly. That is good start point for trimming.

>Ken,
>Do you have an estimate of the speed variance at the wingtip end of >the lines from the sharpest or slowest corner to slick level flight? >10%? 15%? From 80 fps (I still think SAE rather than SI) 15% is down >to 68 fps (47 MPH)? -- briefly -- followed by strong acceleration >back to 'flank' speed around 55 MPH?

>I'm a bit concerned that looking at RE for small cylindrical objects >like the FRONT line (aft line is in the chop behind it) may rely too >much on large scale tech. Over past decades, my relatively brute >force approach has had reliable results, even when drastic layout >appearance changes were involved. I've tried various refinements, >and found insignificant influences from several that some people >agonize endlessly about. I don't knock the extra effort, just I >prefer other aspects of our hobby.

>The flier is so much more important than the model, that I am >content to rough out numbers I know will fly predictably -- and >well. That puts it up to ME to learn to fly it to its full potential.

>\BEST\LOU

Hi Lue

You Americans are a bit slow, about time you caught up with the rest of the world and adopted System Inernational (SI).
HE HE!

I did a rough calc once on mean speed in manouvers but did not have good data on engine thrust varience with airspeed. Also I was not accounting for momentum coming into the turn. These are very major factors and require flight sim type programing to handle it well. Probably get better results from strobe protography of a real plane.
If you loosing 15% in speed, that equates to a 28% loss from maximum line tension. Scary if it's overhead ???

Re. Igor pointing out our ignoring engine offset. This has only a linear influence on line tension while speed has an exponential influence. That is why I targeted speed as the major factor. If you can improve speed in the turns by maximising power at this airspeed and reducing induced drag, then line tension will be disproportionatly improved.

Eg A 15% loss in speed gives a 28% loss of line tension while a 10% loss in speed gives a 19% loss of line tension. That is a 9% improvement in line tension for just 5% more speed.

I am mainly into design, haven't built to someone elses plans for decades now. I just like the research and development thing. I use maths to set out new designs but trial and error to trim and refine so I only account for the major factors in the math to establish starting parameters for a new degign. Math is usefull for this and as an aid to determine the relative importance of things, helps keep perspective but I would not advocate total reliance on the results.

I did a calc for line sweep angle from CG, simply based on centrafugal force and drag. I had concerns that the Re of line diameter would be in a whole different airflow relm and the cd value would be way too small but it seems to have worked out OK for a starting position anyway. I think I just used the standard 0.6 round body value, mabybe beefed it up some (0.9), can't remember but calced the same drag for both lines. The problem with taking advice like 1 inch behind CG is you don't always know what size plane that referes to and it may not translate to your size plane. I fly 15s for fun now so numbers appropriate to comp stunt modles are way too large for me.

One major problem in all of your calculations, and I mean MAJOR is we are not flying a rock on a string. We are flying and trimming an airplane. Yes, centrifrugal force enters in, but I can take my 50 ounce airplane flying on 66 foot lines with 5.3 second lap times and someone else's airplane of the same weight on the same lines with the same lap times and there will be a noticeable difference in pull. Just changing props and keeping the lap times the same can make a big difference. All of these calculation programs and mathamatics can be thrown out the window as far as I am concerned. There is a relationship to speed and all that, and higher lap times with the same plane/trim will produce more pull, but the engine setup and trim have a lot more to do with it than pure centrifrugal force.

>One major problem in all of your calculations, and I mean
>MAJOR is we are not flying a rock on a string. We are
>flying and trimming an airplane. Yes, centrifrugal force
>enters in, but I can take my 50 ounce airplane flying on 66
>foot lines with 5.3 second lap times and someone else's
>airplane of the same weight on the same lines with the same
>lap times and there will be a noticeable difference in pull.
> Just changing props and keeping the lap times the same can
>make a big difference. All of these calculation programs
>and mathamatics can be thrown out the window as far as I am
>concerned. There is a relationship to speed and all that,
>and higher lap times with the same plane/trim will produce
>more pull, but the engine setup and trim have a lot more to
>do with it than pure centrifrugal force.

Yes Leonard I do agree trim factors also have a major influence, I am only pointing out that of all the major factors, speed has an exponential effect on line tension. Therefore we stand to gain most by minimising the loss of speed in turns. It is not about maximum speed (lap times) at all. What I am advocating is improving the minimum speed as much as possable, not the maximum speed. You would think that a light model would mean not much pull but the centrifugal pull of your 50 oz model works out to the equivilant of 141oz centrafugal force but loose 50% of your speed and that drops to just 35 oz force. It's a bigger factor than most people realise but certainly not the only one.

The reason I got onto speed in the 1st place is that in regard to LO position, getting the right spot makes more power available and this will improve minimum speed by a greater margin than it will maximum speed. It's not just about thrust line, another reason is that at max speed piston motors are reaching the limit of their RPM and produce relatiely little thrust. At lower air speeds engines produces more thrust. Commonly max thrust is produced at zero airspeed. Therefore reducing drag in general will have more effect on min speed than on max speed helping to maintain a more even speed. Isn't this also one of the effects of a tuned piped and 2-4 break, to maintain a more even speed?

However there are other factors lke the ones you mention. There is only so much time to type posts so I neglect some of the factors and leave them to others. Surely a complete disitation from any one person is not expected here.

I use 1.0 for a Cd. The static part is easy. Dynamics are difficult.

If you know natural frequency of lines, then from centrifugal force to lines from radius and speed you can _relatively_ easy calculate impulse to the tip in corner. But much better fun is, if you hit natural frequency by time of corner. It can resonate and it can be reason that you cannot make squares of some size at given speed and line tension.

If I estimate natural frequency of “some” model with line tension 20{N} on one line, line diameter 0.4{mm} and 20{m} long, then the natural frequency is ~3.5Hz what makes lamda 1/4 =0.07 s. That is time when lines are back in proper position after the impulse. But after 0.14s or 0.28s what could be time of corner, the next amplitude can interact with fly off from corner, and if you eventually hit one of following cycles in next corner, it can completely kill whole figure.

BTW the natural frequency is = sqrt( line tension / weight of one {m} ) / ( 2 * line length )

… and sorry for metric units

Ron B.
F4Fguy

There is no mystery.All of this was covered in the series of articles "Wild Bill Netzband did in A.M. in the July/Aug.,and Sept./Oct '66 and Dec.'67 issues.It was expanded over some time during Bill's stint as "Round and Round "columnist for M.A.N.. It's also been addressed by Charles Buffalano in articles in S.N..It' a simple force relationship and Bill even took the math out of it by supplying nomographs.All you need do is supply the numbers for your situation and plug'em in.I've been using these for years and have yet to need more than very minor adjustment for particular conditions.

Incidentally,the first time I saw a true engineering approach to this was in Raoul Hoffmann's "Model Aerodynamics Made Painless",published in 1954.The solution was essentially the same as Bill's without the nomographs.

The precession can be accurately determined if you get accurate polars for each prop you propose using,which can be done with a simple bifilar pendulum setup.

Ron,

I just love it when you talk dirty to me this way.

>Ron,
>
>I just love it when you talk dirty to me this way.
>
>Dan

Ron B.
F4Fguy

Dan:

Anything for you baby!

Im not sure if this is co-incidence or what.

But i campained a particual model for 3 years, flew VERY well, but always gave a small roll in the outside square corner where the wing would rise when viewd from the pilot's angle.
I tried many different trim changes, non of which altered it, Im not talking about every manouver just sometimes in some outside courners.

I had a conventional leadout position, re: next to eachother.

My new model i decided to try them so each one was on its own "rail" much like the early thunderbirds. This was done so I could fiddle with the leadout positon fore/aft on both up and down lines.

I found the problem dissapeared almost immediatly No roll on either corner anytime day or night.

I intend to stick to this setup, as both aircraft were virtually identical. As i said, im not sure if this is co-incidence or what, but i cant think of anything else that would have caused this effect.
hence, i cannot think up any other reasons why it worked.

Perhaps someone who has done similar, has had similar experiences??

Incase your not sure what I mean here is a quick diagram.

------o------o------- Conventional leadout guides.

---------o-----------
---------o----------- New leadout guides.

There is nothing new about over/under leadouts. In my opinion they are poor choice for trimming a stunt ship. First, and most important, when loaded, they impart a slight rolling moment to the aircraft. That moment is always in the same direction which would have a line tension increasing on inside maneuvers and a line tension losing on outside maneuvers or vice versa depending on which leadout was the "up" leadout.

Next, they would be a bitch to build if made adjustable, and all leadouts should be adjustable.

Last, In 1966, I turned the bellcrank over to make the up leadout the front one. This has a small beneficial effect on yaw. You heard it here first, actually, it was in the Bearcat article in AAM March 1970 issue. I'm sure it had been done before for conveneince, but this was the first time it was done deliberately to achieve a specific aerodynamic effect and had the idea explained in print.

OK, I get the part about the rolling moment (because one leadout will be above, the other below the ideal vertical position, though if they're close enough, then it shouldn't matter much), but if you make the bottom leadout the "up" leadout, and it is loaded when you pull "up", then it'll cause outward roll and you gain line tension in the turn. Then, if you pull "down", the top leadout is loaded, and that causes an inward roll, but since you're pulling negative Gs and turning outside, the effect should still be an increase in line tension through the turn, since you're really rolling outwards if you count the inside of the turn as "up".

Or am I missing something?

If you put the leadout guides on one block that moves in a slot, it should be fairly easy to build, wouldn't it?

So you say it is only question of tip weight, yes?

>OK, I get the part about the rolling moment (because one
>leadout will be above, the other below the ideal vertical
>position, though if they're close enough, then it shouldn't
>matter much), but if you make the bottom leadout the "up"
>leadout, and it is loaded when you pull "up", then it'll
>cause outward roll and you gain line tension in the turn.
>Then, if you pull "down", the top leadout is loaded, and
>that causes an inward roll, but since you're pulling
>negative Gs and turning outside, the effect should still be
>an increase in line tension through the turn, since you're
>really rolling outwards if you count the inside of the turn
>as "up".
>
>Or am I missing something?
>
>If you put the leadout guides on one block that moves in a
>slot, it should be fairly easy to build, wouldn't it?

That outward roll causes problems, like the tip dropping in the bottom of a corner. And it can drive you nuts at an intersection. In the "good old days" this was purposely done with exaggerated assymetry and differential flaps. Now we go the opposite way--more flap outboard just to prevent it from happening.

Isky,

Nope. You gor it right. I obviously didn't think it through. sorry, I try to do better than that.

Hi Al

No problem.. It's interesting to think about these things.

Another thing I've always wondered about. Are the leadout guides really "loaded" unequally when the controls are applied? This is what all the arguments about the relative position of the guides are based on.

Unless the bellcrank is moved all the way against one of the stops, both leadouts should have the same tension on them, no matter what the control position is at the time, right? In any case, the tension isn't on the leadout guides, it's on the bellcrank. The leadout guides do function as the "hanging pivot point" for the model, nonetheless, but the force exerted by the leadouts on the guides are at 90 degrees to the leadouts, I think.

Or are the aerodynamic forces on the tail and flaps large enough to cause a significant difference in tension on the two leadouts? Is the restoring force on the handle significant in relation to overall line tension?

Al..

I was no harder to install it under/over that it would have been to make them along the same line.

All I did was use 2 Windy adjustable leadout guides, and removed the 2nd leadout guide on both of them, installed the track, as per normal, just did it twice.

I realised they are nothing new, i was jsut wondering if anyone had had any experince with them, AS it was the 1st time in years ive ever done this setup.

Reversign the bellcrank, Do u continue this practice on ur current ships??

>In the war betweem "ground vs Aircraft" one is YET to lose

Oh, PJ, have you never seen a divot?

Yes, since the 1970 Bearcat article, I've used the reversed bellcrank on all of my airplanes. It was theoretically advantageous then, so it remains.

>>>It was theoretically advantageous<<<

There is also theoretical disadvantage - positive feedback to control system from gyro precession ... everything good costs something

Don't see it, so no reason to change. Particularly since I effectively minimize the gyroscopic processional effects with an actively compensating movable rudder.

I've been using the over/under configuration on my combat shps for some time now, with great success. Sure seems to even out the turning, no matter which direction. Of course, a combat ship is an entirely different animal, with different desired goals, than a stunt ship. I still use fore-&-aft leadouts (with the front being up, by the way, Al) on everything else.
--Ray

>I've been using the over/under configuration on my combat
>shps for some time now, with great success. Sure seems to
>even out the turning, no matter which direction. Of course,
>a combat ship is an entirely different animal, with
>different desired goals, than a stunt ship. I still use
>fore-&-aft leadouts (with the front being up, by the way,
>Al) on everything else.
>--Ray

On a lot of Combat planes, we actually use one common leadout guide. This only works if you don't use leadouts, though, or snag-proof connectors.

It is very simple. If you have any yawing imput (does not matter if by handle, hinging lines or just turbulence) then it has input to control system, becase of line separation at leadouts. And now for yaw out:

1/ up line front - makes "up" input that makes by precession even more yaw out and even more "up" parazitic input. That is amplifying positive feedback

1/ down line front - makes "down" input that acts by precession against yaw out. That is dapfing negative feedback.

So aft leadout up can effectively dampf "hunting" or waving in turbulent air, but also can make clean fly off from corner.

I always try both configurations. My leadouts are constructed, that they allow crossing lines in wing. I try both and choose that better. It depends on bellcrank size, line tension necessary for corner and yaw stability. For example my last model has controlled rudder with up line aft. My model built for turbulent air in Sebnitz two years ago had also that configuration with fixed rudder and with logarithmic unit reducing hinge moment was very good configuration for that terrible turbulent field. But I have also very light model for strong clean wind here in our area and that has up line front.

Igor,

I think you may have it backward, or, maybe we are saying the same things using different language.

With fore and aft leadouts there will be a slight yaw input from loading (pulling on) one or the other leadout. the loaded leadout will tend to swing into alignment with the CG and loaded flying wire.

If the front (up) leadout is loaded (pulled on) there will be a moment which will tend to align that leadout with the CG and loaded flying wire. The wing tip will have a tendency to swing slightly rearward to align the loaded leadout with the CG and loaded flying wire. In short, there will be a tendency for the airplane to yaw slightly inward. Since gyroscopic precession on inside maneuvers (loaded up leadout), is nose out, this should provide a slight correcting moment to gyro induced outward yaw.

If the rear leadout becomes the loaded leadout (pull on down line) that leadout will tend to swing the wingtip slightly forward to align the CG and the loaded down flying wire. This slight outward yawing moment is opposite (anti) the gyroscopic precessional tendency to yaw inward, and would be somewhat correcting.

Granted the forces are minimal, but they are acting in a beneficial direction and must be better than a leadout configuration which acts in a detrimental manner, even if only slightly so. I only suggested that one should be better than the other without implying that large forces were involved. I simply said that if one were slightly good and the other slightly bad, then why not turn the bellcrank over to take advantage of any possible anti-gyroscopic, slightly good, moment. This was good advice in 1970 and represented a new thought about stunt aerodynamics. I only claim to have published an original thought and explanation about the orientation of our common bellcranks.

I still think I'm right. Try this experiment. Pick up a stunt ship and hold it suspended by its leadouts. If you hold it suspended by its front leadout only, it will hang slightly yawed in (wing tip back) as the leadout aligns with the CG. If you hold it by the rear leadout only, it will hang slightly yawed out or nose down (wingtip forward) as the leadout aligns with the CG. These are beneficial yawing moments because they are opposite the yaws induced by gyroscopic precession.

These slight yaw inputs are anti-gyroscopic and will provide a slight correcting moment.

>>>If the front (up) leadout is loaded (pulled on) there will be a moment which will tend to align that leadout with the CG and loaded flying wire.<<<
…
>>>I still think I'm right.<<<
Yes, I definitely agree in terms of yaw damping.

But I wrote about another effect. I mean what happens at any external or internal input to lines and its feedback. For example I will show it on your description:

>>>If the front (up) leadout is loaded (pulled on) there will be a moment which will tend to align that leadout with the CG and loaded flying wire.<<<
Exactly, it means if you make some input to lines by handle, the prop will try yaw out, but your front line does not allow it – by some additional tension in that front line – exactly as you described it. And that extra load is extra input to that original input from handle. Pilot can easily learn it in maneuvering, so it does not make too much problems.

But the same can happen also at any EXTERAL input to model. For example if turbulent whirl kicks the tail. Any yawing or pitching kick converts to yaw (yawing directly and pitching because of precession) and that AMPLIFIES that external input if front line is up and damps if front line is down. This has nothing to do (or only little) with yaw damping as you described it. It is another effect. Just there are two different effects, one is well solved if front line is up, and another is solved if front line is down.

The demand imputs are so much stronger than external incidental yaws that I'm surprised you bothered to analyze the possibilities. It's front up line for me and I believe I did a service to stunt flyers by pointing out the possible benefits of the inverted bellcrank in 1970.

Treid both bellcrank positions many times. Never noticed any difference once it was all trimmed out.

Does that mean that, in your opinion, no such effect exists? Did I suggest the effect would be strong enough to separate from other trim effects. I only suggested that front up leadouts would be advantageous if a detectable effect existed. Put the bellcrank in any way you like but,why deride a theoretical argument unless you have valid, carefully reasoned, contrary theoretical argument. The fact that you can't tell the difference when you fly your airplanes hardly qualifies.

Leonard,

Yes Ive seen a divot..And the 100 bits you need to pick up to make one!

Never left a divot on a concrete circle tho

>Leonard,
>
>Yes Ive seen a divot..And the 100 bits you need to pick up
>to make one!
>
>Never left a divot on a concrete circle tho

You just haven't been around long enough. I'll grant, the airplane didn't fare too well. Engine didn't fare too well. But it made a dent.

Doug, the reasou could be too small distance between lines. If you want completaly ballance precession on modern model with rather bigger or hi rew prop with slow controls, you will need 2" and more to ballace the yaw. So typical separation 1/4" is really not enough visible.

But are you speaking about the same model? If you have trimmed model, try to exchange leadouts - do some starts and put it back, I think you WILL see differences even with small line separation.