Flapless Stunters

Alan,

I sorta liked the flexi-flaps. But I agree, it's just about flapsless. Seems to track better than the GeeBee did, too. Did you get to try it with a Saito 72?

For those who weren't there, Alan uttered the oft-repeated refrain of "Watch this!" and held the elevator at full deflection while easily and casually flipping the flaps up and down through what appeared to be the full range of travel. It's really goofy looking.

Not so goofy looking is the performance of the model in the air. Although Alan's fine hand at the controls can't hurt, it's a real good package.

certainly don't NEED flaps for competitive performance. Mostly they let you get a decent turn carrying 10 extra ounces of paint. No flaps makes the plane a lot simpler to trim out.

I flew my Fancher "Doctor" the other day. This is a high A/R stunter without flaps. Maybe there's something magic about this plane, but I think the configuration is about perfect without flaps.

>I flew my Fancher "Doctor" the other day. This is a high
>A/R stunter without flaps. Maybe there's something magic
>about this plane, but I think the configuration is about
>perfect without flaps.
>
>Floyd
Of course it's magic, Flyod. That was the whole idea!

Ted. I really don't believe in magic, but my grandkids do after reading all the Harry Potter books!

My DOCTOR weighs 39.8 oz dry, with OS 40FP. I think that would be in the "light" category. I have fought a wing warp, but it seems to be straight now, and flies great. I think (Wild Bill, forgive my sin of waxing scientific) that the combination of a long tail moment and ample stab area gives plenty of authority on turns. And less mass can't hurt either!

Ted,

>>Sheesh, Ferocious said in two sentences what it took me four or five pages to say in the Doctor article. Seems I need a good editor.<<

Well, maybe, but your so colorful!

Guys. My recent article in Model Aviation magazine on my 1950 WILDMAN 60 was published exactly as I wrote it, without a single word changed.

So who needs an editor?

Howard,

If I understand the situation correctly, you have new flaps to build and a broken fuselage to repair. You have time for SSW playfulness when, exactly?

And you have to write and practice your speech, presented on behalf of District 11. Maybe you can do that on your way to Riverside.

Don't the flaps help you stop turning as well as starting a turn, smoothing the maneuver out. The Giles, at least at Brodak, turned sharp, but had trouble stopping its turn, causing it to look jumpy. The controls were probably too responsive. But could the lack of flaps contributed to the problem, since flapless planes generate no negative lift (or opposite lift) caused by the flaps stopping and slowing the momentum of a turn.

It seems to me that a lot about stunters (the proportions, typical weight, construction methods) are more art than science. Shapes and dimensions (and the use of flaps) evolving over time, using what works, using what makes smooth maneuvers that present well. I heard Windy among many others say that he doesn't weigh the parts of his plane. He wants planes that perform. Meaning, I guess, that light weight per se doesn't a good stunter make. I've heard others say that Noblers that weigh bellow 40 ounces or so are dogs. George Aldrich himself is reputed to have said this.

Flaps add lift and reverse lift and perhaps other magic/art. Could be that the equations demonstrating this would take moocho number crunching to demonstrate. Newly designed planes are still test flown. After ninety years of designing full size planes and despite a concentration of the most advance technology, there's still a mystery and art to aircraft flight, even in CL Stunt.

Dennis,

Yea, it's all Voodoo. The best flying plane I ever owned is a test plane for an idea I had. It's a profile that was in clear dope for 2 years (and not likely ever to see paint). No flaps and some rather strange aerodynamics are involved. But I like the way it flies.

I don't really know if flaps help you stop turning, but I do know that a really long tail moment and a very big stab and elevator do.

But I like the way it flies.
>
>I don't really know if flaps help you stop turning, but I do
>know that a really long tail moment and a very big stab and
>elevator do.
>
>

Randy Powell

There are two components in a turn:
1) The ability of the plane to turn on its axis (center of lift) and to stop turning.
2) The ability of a plane to overcome the tendency to slide in the previous direction due to momentum and begin to move in the new (desired) direction.

For a good example of point number 2, stand down wind and watch an airplane go into a wingover. The plane will rotate (rather) quickly, but slide beyond the point of rotation. In order to hit the same point on the way back, you will need to begin your turn well before the desired point. This is one of the reasons that 5 foot corners are near impossible. The plane will rotate quickly enough. It just will not stop skidding.

Tail size, leverage, CG location, and speed will all help point number 1. A flapless plane needs more speed to rotate quickly. But speed is also the ally of point number 2.

Greater wing area (bigger fly swatter), slower speeds, lighter weight, greater thrust, and more lift (flaps) will all aid in decreasing the effects of point number 2.

Thus a large wing area, light weight, flapless airplane can be made to turn tight. It will be able to rotate more quickly when flying faster, however. Weight is the enemy (point number 2) and seed increases the negative effect of weight in the turn. Flaps help to overcome this, and enable you to fly slower to achieve the same degree of rotation which also makes for an easier flying pattern.

So, flapless airplanes can be done. Is it the way to go? Well, the Berenger plane has small flaps, but is it the way to go? What are your design goals? Combat ships don't need them. Virtually every serious competition stunt design has them. Are they needed? You tell me. Just remember point number 2.

Len,

I think there are other things to consider as well. Certainly more wing area (flapless) helps. Aspect ratio has an impact also. A higher aspect ratio coupled with a thick, relatively blunt airfoil can reduce the speed requirements for a given weight. Vertical and horizontal wing taper also has substantial effect.

The Berringer design has a number of interesting features. The flaps appear to be more cosmetic (does anyone really take a flapless competition stunter seriously?), but certainly have some effect. The very long tail moment coupled with the elevator counterbalances and a very far forward balance point also contribute to the plane's stability and ability to turn tightly without too much "slide" and with acceptable stick pressure. The wing is highly tapered both vertically and horizontally and has a relatively thick and very blunt airfoil. Almost a combat type airfoil.

It's an interesting approach to solving some of the points you bring up but I suspect it wouldn't fly much differently if the flaps were fixed. Be interesting to find out.

>There are two components in a turn:
>1) The ability of the plane to turn on its axis (center of lift) and to stop turning.
>2) The ability of a plane to overcome the tendency to slide in the previous direction due to
>momentum and begin to move in the new (desired) direction...

>Tail size, leverage, CG location, and speed will all help point number 1. A flapless plane needs
>more speed to rotate quickly. But speed is also the ally of point number 2.

All points well taken. However, the negative pitching moment of flapped (highly cambered) airfoils is also relevant here. They work against point #1 with regard to initiating a turn. They require more tail moment (from arm length and horizontal surface area) to pitch quickly and hold a given pitch angle, while the added lift then helps provide the needed centripetal acceleration to maintain the turn. Inertia and "circular airflow" effects (Zaic) ultimately limit useful tail lengths for any given turn radius.

The combination of flaps with these other related variables apparently combine to produce a harmonious and effective aerobatic machine in most respects. The flaps not only increase lift, but smooth out the transitions. The necessary longer tail moment arm stabilizes level flight. A little flap droop has been used as a level-flight stabilizing tool via elevator "slop" or blanketing. Ted, Brett, and you, I think, have pointed out that this negative pitching moment due to flaps also allows a significantly further back c.g. with reasonable pitch stability - which in turn helps the turn.

Still, overall, this must compromise turn radii. I was watching a local combat flyer looping successively 5-10 times at high speed (100 mph laps) in what appeared to be diameters of 10-12 ft. I don't know how much speed was lost to induced drag, but simple computations of g's experienced by that plane (v^2/rg) lead to figures I'd be embarassed to quote here, unless speed was markedly reduced. I'm sure that the speed aided lift coefficient a bit through increased Reynolds number for this flapless model, but if you set lift equal to centripetal force in turns and solve for "r", V drops out leaving r proportional to M/(A*CL). Or, as you otherwise pointed out, a light model with larger area and high lift coefficient will turn tightest. While flaps add lift, it appears that the flapless type can be made to turn well due to inherently lighter weight (less structure/mechanism and shorter tails), lower inertia, and probably higher angles of attack. Except for planes that slide even more around turns, while hanging on their props, it appears that the tightest turning planes (Netzeband-type stunters as well as combat types) have been flapless. That leaves smoothness, precision, and presentation in manuevers apparently in the flapped stunters' favor.

Little of this really SEEMS to explain the Berringer plane's apparent abilities though. I can't search out its A/R without losing this post*; so here it is.

SK

PS. *Edit: OK. Reasonable to light wing loading, slightly higher than average aspect ratio, higer than usual taper ratio, forward c.g., high forward lateral area, long tail moment arm, and some disagreement on airfoil thickness and leading edge curvature. Hmmm. I'll think further on it.

We're all in the anecdotal boat here, aren't we. No way to scientifically test (how do you cut down the variables of construction, pilot, weather conditions)? Elevator slop is an interesting and for many an apparently effective way to assist smoothness, tracking and transition. Perhaps this allows the milder flap effect to slow the turn before the elevator input hits. I guess model airplanes like motorcycles (I rode them a lot years ago) are never actually in balance but are in a dynamic state of imbalance and adjustment. It only looks (or feels) right.

At Brodak Windy talked about elevator slop in the MS Ashley reducing wander in level flight and helping with the accuracy of transitions. (I think that's what he meant.) The 1/4 inch of self leveling elevator is a bit amazing considering the rigidity of the MS Ashley's carbon fiber structure. Make it all stiff than season with marvel mystery bugah woohguh.

>Make it all stiff than season with marvel mystery
>bugah woohguh.

I guess the more I talk about model airplane "theories" the more I prefer to just go back to the good ol' days of bugah wooguh. The best science is still pretty unfounded at best. At least the bugah wooguh was more easily ignored. No one really wants to read a theorum anyway, right?

Just thinking out loud here..

I THINK there is a myth to the self-leveling elevator. Once the ship gets in the air there is pressure on all of the surfaces. The elevator is not just flopping around back there. It gives you the ability to roll in some deflected flap and keep the elevator close to level or a small amount of up or whatever is needed to fly the plane level. The deflected flap helps to create lift by changing the AoA without titling the nose up, and a cambered airfoil also creating lift. If you set it up to a dead flat level flap level elevator you can see a little hunting. No positive AoA and you get no lift. Some guys just build in some up incidence in the stabilizer to get the very same effect as a loose elevator or added in down elevator at a level flap. All of my really good flying planes will have a down elevator when the flap is level. I always have an adjustment on the pushrod so I can set the length after the initial flights are done and I always end up with a little bit of down elevator with the flap level.

Of course this makes you think there will be more corner one way than the other but the amounts of down elevator is pretty minimal so it doesn’t really come into play.

JMHO…

Doug,

I agree with you here. It's been my experience that the need to put slop into an elevator horn is due to either improperly adjusted pushrod length or incorrect stabilizer incidence. It seems a solution to a mechanical trim problem that was either built in or improperly adjusted in.

But, that's just me. Picky, picky, picky.

I am a great admirer of the Phil Cartier approach. Going up against the top five all winter projects of classic art with a three hour in the shop ready to paint foam/Home Depot piece of disposable fun. The contrast is worth plenty of laughs. Hey, Phil is in expert flying the Giles. No doubt he will place above many good ones who take a conventional approach. For those of us sporting and learning and bumping the grass, what model could be more appropriate. But do flaps nonetheless add some smoothness and tune ability etc.

D.

Dennis,

did you know that Bob Hunt is a bike man also?

He even gives courses in safety...

God bless you!

In Christ,

>A flapless plane needs more speed to rotate
>quickly. But speed is also the ally of point number 2.

I dont know about this one. It is gets tricky because it all has to do with the planes relative weight and power. If the plane is light enough it(flapless) can trun just as hard as its slow flying flapped(heavier) brother. Steve has his Berringer (54oz) at a 5.6 lap on full length lines and it turns hard. Plenty hard. I would think it would need to go faster also, due to the baby sized flaps. However it has a Strong motor and it is light weight. The speed isnt needed. The wing makes the lift even at the slower speed.
>
>Greater wing area (bigger fly swatter), slower speeds,
>lighter weight, greater thrust, and more lift (flaps) will
>all aid in decreasing the effects of point number 2.

Yep.

>
>Thus a large wing area, light weight, flapless airplane can
>be made to turn tight. It will be able to rotate more
>quickly when flying faster, however. Weight is the enemy
>(point number 2) and seed increases the negative effect of
>weight in the turn. Flaps help to overcome this, and enable
>you to fly slower to achieve the same degree of rotation
>which also makes for an easier flying pattern.

Flaps help you to fly, a larger heavier model, slower. If the model is overly light weight and you had big flap movements it will actually hurt you. GMA said to light Noblers didnt fly so well. What if they were that light and the flap movement was way reduced? They would fly good. Look at a Gieseke Nobler. He reduced the flap sizes to improve the performance of the lighter model he was building.

>
>So, flapless airplanes can be done. Is it the way to go?
>Well, the Berenger plane has small flaps, but is it the way
>to go? What are your design goals? Combat ships don't need
>them. Virtually every serious competition stunt design has
>them. Are they needed? You tell me. Just remember point
>number 2.

Falps are so weird. I think they really help with the precision part of the game. They help keep the handle loaded up, found this out on my own littel experience. They help the feel of the model, even the tiny ones on the Berringer model. All of the flapless models I fly, not very many and they are small 35 or smaller, all have line oscillation. My flapped planes dont seem to have this near as bad and can be trimmed out. However this comes back to the power issue. the big models have all this power that the smaller non flappers dont.

Flaps may bring in alot of trim questions but they allow you to fly much larger heavier models with hard tight corners that "appear" to rotate around an axis. They aslo "appear" to have none of the sliding tendencies you talked about in Point 2. Point 2 is very real! I have had many sliders in my day. Masking it is the key. The easiest way is to get a powerful motor with good strong props.

However I have yet to see anyone in the last ten years make a real attempt at a full sized(60) Flapless stunter, running the newer piped motors or the new 4s motors. That doesnt mean guys arent doing it I just havent heard of it. But the Berringer planes are darn close and as the 4s motors get better quality and power all of sudden that design is flying really well. Hmmmmmmmm.......could power really have that much to do with it???.....YES.........

>Flaps may bring in alot of trim questions but they allow you
>to fly much larger heavier models with hard tight corners
>that "appear" to rotate around an axis. They aslo "appear"
>to have none of the sliding tendencies you talked about in
>Point 2.

I posted this last winter.

"Secondly, the 4 stroke is simply more inherently stable than the equivalent 2 stroke, even with the same prop. With props that make the most of a 4 cycle, the stability is even more apparent. Couple that with a more forward CG and the package is super stable (and I don’t mean HEAVY, I mean stable). That is why it simply requires more elevator force to overcome that stability. Also, because of this, the counterbalanced elevator can be utilized (inherently less stable) because a loss in stability is not realized and elevator moments can be lessened. The counterbalances would be especially important when loads are elevated in the wind. Certainly the “wall” is pushed back with the counterbalances. Fitz tested the counterbalanced tail, maybe he should have more the CG forward. My 2004 planes will be counterbalanced. It is too late for 2003 (wrong).

Thirdly, the 4 stroke planes make more lift in the same airframes. I have seen this first hand. Airplanes that stalled with 2 cycles, never even considered stalling with the big 4 cycle. Less flap is required for a given weight, that is all there is too it. On a light wing loading airplane even less is required. I plan on leaving the flap size alone and dial out flap and add elevator. Berringer chose instead to nearly eliminate the flap and keep the wing loading low. "

GMA said to light
>Noblers didnt fly so well. What if they were that light and
>the flap movement was way reduced? They would fly good.
>Look at a Gieseke Nobler. He reduced the flap sizes to
>improve the performance of the lighter model he was
>building.

A simple solution that everyone seems to always forget about. Bob specifically changed the Nobler to fly more aggressively at a lighter weight. No magic.

>Don't the flaps help you stop turning as well as starting a
>turn, smoothing the maneuver out. The Giles, at least at
>Brodak, turned sharp, but had trouble stopping its turn,
>causing it to look jumpy. The controls were probably too
>responsive. But could the lack of flaps contributed to the
>problem, since flapless planes generate no negative lift (or
>opposite lift) caused by the flaps stopping and slowing the
>momentum of a turn.

I guess that means we can ignore all the flapped ships that overshot corners hmmm?

Normally overshoot in a sharp corner is due to improper trim of the balance point and the control system and lack of practice with the plane(my excuse). Flaps don't start or stop the turn any faster or better or contribute negative lift or other aerodynamic oddities.

The Berringer designs have all the right things for a tight turns and precise flying- heavy, powerful engine(for balance and pulling through maneuvers), large tail for stability and control authority, noseheavy for stability, counterbalanced stab to adjust the control loads.

The Giles takes a different tack- easy and fast to build(3 hrs of shop time to take the wing from parts to ready to paint) cheap with an LA 40, a big wing and relatively low weight to get adequate turns, and no flaps to screw up the trim or flight characteristics. Everytime I fly it I'm amazed at how predictable it is.

Another advantage to no flaps is reduced maneuvering drag. My second flight at Brodak had severe lean run problems, but that didn't stop me from literally coasting through the parts of the eights. A flapped plane probably would have fallen out of the sky.

I've heard others
>say that Noblers that weigh bellow 40 ounces or so are dogs.

Ron B.
F4Fguy

They've never flown a 37 oz. one.Or,maybe a straight one.

Am I wrong or do the Beringer planes look like enlerged slow combat ships,both in moments and airfoil?Gary T.

> You are right about the effect, but this is not a
>4-stroke vs. 2-stroke phenomena - it's a speed stability
>issue that doesn't have a lot to do with the number of
>strokes the engine has.

Higher revs and
>associated less pitch tend to help more than diameter at
>high pitch because of the HP difference.
>
> Brett

I would buy that this is not unique to the 4 cycle. Of course, one of the planes I am referring too had a PA 61 on it, but I really like the term "speed stability".

I would, however, argue the RPM/pitch part. I think the RPM and pitch, whether high or low, is not casuing the speed stability. It is the PULL. I used the word "thrust" or the term "static thrust" once before. You explained that was the wrong term. I would however, like to know the correct term for the PULL. Once the airplane is set up to achieve nice lap times and manuever times, let's say Doug and I are both flying in the manuever the same speed. The Saito will still pull harder on the ground even though I am only spinning the prop 8700 RPM and he is 10,600 RPM. Both pull like heck, don't get me wrong, but nothing resists sitting still like the 4 cycle.

It's the torque right? Torque + prop = PULL.

I think the RC aerobatics guys would say that high RPM is not as speed stable either, I think.

Bob Baron’s flapless Humbug took a 4th at the 1971 nats. It had a small elevator like a Flight Streak
Willis

I agree with Willis that the elevator is small in proportion to the stab on the 1971 Humbug.
John Tate
Norfolk Aeromodelers

This is going to be a just for fun NATS. I'll be over at the combat circles helping judge the team Trials over the weekend and dabbling in Speed lImit and Fast.

Some stunt planes along too, just for sport flying. Come on over and try one.

I have heard that the only person who could fly a Humbug at a Nationals level of performance was Bob Baron. It was reputed to be a very squirrely machine in anyone else's hands.

Anyone else hear that or otherwise?

Let me tell you a story. About 17 years ago when I flew in Clearwater Fl a guy that I flew with came to the field with a Thunderbird,the inverted motor version and the flaps were loose. They just hung down, they were not conected in any way. When he flew it the flaps moved in the direction that you would expect them to.I pinned the flaps level and he flew it again and it would not turn as clean as before.IT became much easer to mush or stall around corners not at all clean as when the flaps were allowed to be free.I do not know the reason for this but it may be the same thing you are getting with the flexy flaps.
Ed Ruane

Does the real Sukoi have flaps like a model?
I also noticed in all the various answers that some have mentioned props. A prop in rotation is a gyroscope. Limit a gyroscopes rpms or lessen its diameter and the force required to change its direction go down. Also a prop with too much pitch will cavitate and lose its push. No such thing as pull or lift. You push a wagon, not pull it. Props are pushed from the rear just like a wing is pushed up by pressure differential. Also nearly every real airplane has incidence built into it to increase "lift" at level flight. If you place your hand on the handle of a wagon, you will note that the force applied is to the back of the handle, therefore you are pushing the wagon.
Mass, inertia, speed are the only things we are trying to control in moving an airplane through the fluid air. Dontcha just love it??

If you look at the pressure diagrams on a working airfoil, you will immediately see that props ARE pulled more than pushed. The pressure drop on the upper surface is greater than the pressure rise on the bottom, and as such they are both pushed and pulled, with the pull dominant.

The resultant force, is of course tension on the crankshaft in addition to torque resistance.

Larry, The suction on upper side of airfoil can be also significantly dominant. If you look at leading edge on airfoil, you can see that pressure drop is FAR higher than pressure on lower high-pressure side.

But I think he means that even pressure drop, it is still in positive absolute pressure, and that there is nothing like negative pressure. It is true (almost) of course if we speak about air or liquid. However there are certainly also interactions making REAL PULL. We have magnets, we have interactions between atomic particles, we have gravity, so why we cannot pull??? Does it mean we do not have glue?

Magnetic lines of flux do not pull, they get behind the object and push. They are circular. There is no such animal as Suction, just push caused by pressure differential. There is no such animal as lift, just pressure differential, or push towards the low pressure side. It is called suction or lift or pull because no one really could explain it until later, by then those words, right or wrong are in the lexicon. Check it out with any physics teacher. I got into a heated argument over this and lost.

> some have
>mentioned props. A prop in rotation is a gyroscope. Limit
>a gyroscopes rpms or lessen its diameter and the force
>required to change its direction go down.

Ron B.
F4Fguy

Or,reduce it's moment of inertia by other means,such as reducing it's mass,i.e. a thinned wood prop of the same diameter,or a blade shape which moves the center of mass nearer the hub.
I've measured the moment of inertia of a number of props.You'd be surprised at the spread between props of the same size and pitch.Also,how much you can move it around.

The full size Sukhoi does not have flaps at all. As far as I know there are only two types of full size planes that have "Stunt" type controls. The Hirth Acrostar from Germany which there are only 5 left, has flaps and drooping ailerons linked to the elevator, and the Ultimate Biplane series from Canada's Gordon Price, which has the ailerons linked to the elevator by a very simple mixer you can see if you just look at the base of the stick

>The full size Sukhoi does not have flaps at all. As far as I
>know there are only two types of full size planes that have
>"Stunt" type controls. The Hirth Acrostar from Germany which
>there are only 5 left, has flaps and drooping ailerons
>linked to the elevator, and the Ultimate Biplane series from
>Canada's Gordon Price, which has the ailerons linked to the
>elevator by a very simple mixer you can see if you just look
>at the base of the stick

The problem with full-size planes is the pilot. With our CL stunt planes we are trying to approach the impossible 5 foot corner and at least make it look acceptable in the eyes of the judge. What we are doing is pushing the envelope for the ability of the airplane to turn and turn properly as tightly as possible.

In the real world the airplane can turn much tighter than the pilot. Once you have reached the limitations of the pilot, there is not only no need to turn any tighter, but it would be suicide to do so. (OK, the airplane can turn tighter, but the pilot blacks out. The next maneuver in the program will be the uncontrolled power on crash!)

Anyway, that's the main reason why you don't see coupled flaps or designs with large tails, etc. in the real world, as are common on our little ships.

Larry, it depends on angle of attack. If you have low positive angle of attack, the drag does not grow so dramatically till 50 deg or even more. But if you are at negative AoA (it happens on tail) then the drag really grows quickly AND as the lift is limited thanx than negative AoA than the lift/drag ratio is even worse.

I think Alan is correct, the Beringer plane is essentially a flapless design. The function of the vestigial flaps is not to provide lift, but to create adverse pitch. They make the plane easier to drive along a precise path by creating a counteracting "control tension" with the very powerful elevator.
Derek Moran

>I think Alan is correct, the Beringer plane is essentially a
>flapless design. The function of the vestigial flaps is not
>to provide lift, but to create adverse pitch. They make the
>plane easier to drive along a precise path by creating a
>counteracting "control tension" with the very powerful
>elevator.
>Derek Moran

Call them whatever you want to call them, but they are flaps and they function like flaps. Some designs (more than we have previously admitted) benefit from having either shorter flaps or longer throw to the elevators. The tail seems to swing more and gives the impression of turning a more precise (sharper) corner. It all depends on wing loading, CG location, moments, and so forth. Bob Hunts latest offering at the Nats also had shorter flaps than usual. And even though the Beringer design carries this to the extreme, make no doubt about it, they still are flaps, they function like flaps, and the plane would not turn the same without them.

Len,

I guess you'd have to see Alan's plane. They may tecnically be flaps, but with that horn (as Alan notes). they ain't much. And after seeing it fly, I mostly agree with Derek. The purpose has more to do with "steerability" that lift.

But hey, whatever. The plane flies very well. Or at least it did.

Ted,

Billy buids pretty darn light, and he still uses flaps...

God bless you!

In Christ,