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Bruce Tuncks

Reflexing flaps and ailerons

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It would be easy to just reflex the ailerons without making them adjustable during flight, but there would be little gain I think.

You could do a new flap position with reflex to match ( call it -1 flap ) and together with the reflexed ailerons, I would expect a few knots more cruise speed. But landing and take-off would be conducted with positive flap and negative ailerons.  Well it wouldn't spin easily, but the performance would be down. take-off distance would be increased.

It would be possible to make the ailerons adjustable in flight  by making the shaft that holds the stick lift and lower at the back.

Has any of this been done? 

 

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Your idea sounds interesting Bruce.  My Jabiru is the long winged SP (U/L).  The flaps on it are really long and ailerons pretty short.  I have the port flap slightly reflexed to compensate for the roll tendency caused by my weight in the pilot's seat - 90% of my flying is solo.  I don't think there would be much to gain from raising or lowering the ailerons for me.

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Flapperons have their downside.. You really need a different control style with them with more rudder lead. (and a more effective rudder than otherwise needed). Nev

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Had 'flapperons' on the Mk2 Kitfox. I found them to markedly reduce aileron effectiveness (especially at the reduced landing speed) and that flaps were, in any case, unnecessary to effect a well controlled landing. Side slipping was much better for controlling touch down.

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Posted (edited)
17 hours ago, facthunter said:

Flapperons have their downside.. You really need a different control style with them with more rudder lead. (and a more effective rudder than otherwise needed). Nev

Know of a cessna 180 that had a Robertson stol kit (aileron droop with flap extension) removed due undesirable side effects, owned by a very experienced Ag pilot.  

Edited by Thruster88

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7 minutes ago, Bruce Tuncks said:

I guess that the drooped ailerons made it more likely to tip stall, do you know more details thruster?

Yes that is what I heard. Drooping the aileron would "undo" the wing wash out to some extent.  

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11 minutes ago, Bruce Tuncks said:

I guess that the drooped ailerons made it more likely to tip stall, do you know more details thruster?

Exactly. From my observations there is no washout built into my Jabiru's wings. The washout is created by the rigging of the ailerons and increases with application of flaps.  That said, it's stall characteristics are very good, a tribute to the design.

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It's actually worse than that. Normal ailerons are set up to operate differentially with the UP flap being more Raised than the DOWN one is lowered. With flapperons extended you get the option of flap and MORE flap. Much more drag on the wing you are trying to lift and it will stall quicker also. If you get slow enough it won't react well so hence the RUDDER use comment. Nev

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23 hours ago, facthunter said:

Flapperons have their downside.. You really need a different control style with them with more rudder lead. (and a more effective rudder than otherwise needed). Nev

How do you mean "rudder lead"? Do you mean that to start a turn, you use rudder a moment before you start using aileron? 

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 There's a lot of what might be referred to as adverse aileron effect.. Better to anticipate it than try to correct later. Near stall it's just what you don't want.  Nev

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Why do most gliders have flaperons then, they are operating near the stall all the time and crancked over as well.  I say if gliders have them then they must be ok ?

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The A22 Foxbat, that's I used for training has Flaperons !, I found them good to use.

As it was my training aircraft I cannot compere it to others.

The Hummel has no flaps of any sort, so a little bit must be better than Nothing.

spacesailor

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44 minutes ago, FlyBoy1960 said:

Why do most gliders have flaperons then, they are operating near the stall all the time and crancked over as well.  I say if gliders have them then they must be ok ?

Nothing wrong with flaperons if they are designed into the aircraft from the get go and extensively tested by test pilots. 

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" if they are designed into the aircraft from the get go and extensively tested by test pilots. "

AND students.

spacesailor

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15 hours ago, facthunter said:

 There's a lot of what might be referred to as adverse aileron effect.. Better to anticipate it than try to correct later. Near stall it's just what you don't want.  Nev

Good point. The wing with the higher AoA slows down with adverse yaw. I fly a foxbat, which has both flaperons and adverse yaw. 

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 Edit. This was meant to be posted an hour or so ago but I didn't finish it due interruption.

    It's not a case of if a few have then and they fly, it's normal and there are no issues. They are for a purpose, mainly staying in the Air at low speeds and do offer challenges if you don't operate accordingly. People get into difficulties using "normal" differential flaps sometimes and the flapperons are more critical when you are actually trying to operate a flap as an aileron at the limits of extension. where it's a pretty" ordinary" flap and a very poor aileron, with NO UP movement at all available. Roll control at low speed is an issue with ALL planes from the design and operation point of view. A modern Jet has inboard and  outboard ailerons,  very complex Flaps and spoilers.   What I'm saying is flapperons are not the easy fix it appears to be, and have a downside and if you don't fly them properly they will bite you.  Nev

Edited by facthunter

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That low-speed control issue is why I'm designing an outer wing based on feather-like extensions that allow massively changes in surface area as speed changes. Birds have it, so why shouldn't we?

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 Maybe do what an AN 2 does?. The GAZELLE is OK at low speeds. and is pretty much without vices. Birds have it controlled very nicely but the design was developed over a long time.  Nev

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Old K, I wish you well but have to say that previous attempts at variable geometry have all disappointed their builders.

You would think that it would work with gliders, with their 2 distinct flight modes of thermalling slowly and cruising fast.

There was the Akaflieg telescopic wing glider and the pommy Sirius with its chord extension. They both got to fly and they didn't work well enough to justify the effort.

There was also a " bird tip " multi-surface winglet  tried with a glider and I think it worked ok, although this may only have been a wind-tunnel job.

But don't let us pessimists slow you down too much. Have fun.

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 With Gliding the radius of turn when thermalling is  important so the slower the better, to stay in the thermal, otherwise it's sink rate minimising or  if distance in time is the issue (best speed)  without getting low for your circumstances. (not able to get there at all and outlanding). . All these principles apply to long distance flying on least fuel. Selection of height re winds and  amount of fuel used per Km which is what really matters after all. Nev.

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7 hours ago, Bruce Tuncks said:

Old K, I wish you well but have to say that previous attempts at variable geometry have all disappointed their builders...

No worries, Bruce. I'm investing about as much money and time into this project as I can afford- which isn't very much! 

My ideal is to mount a set of man-made "feathers" on each outer wing. They would slightly pivot on a horizontal plane to control roll and rotate on a vertical axis to massively increase the area of the outer wing. 

 

The easy bit might be machining a strong, reliable "hub" to be mounted on the outer spar.

The challenging bit is developing viable feathers, which depends on super-light new materials.

Self-repairing would be an ultimate goal...

Further down the track could be software to control the whole lot, much as birds do.

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9 hours ago, facthunter said:

 Maybe do what an AN 2 does?...

It's well worth having a good look at an AN-2. I did at Wanaka when I visited a few years back.

My initial disappointment that all the fighters had been sold was replaced by fascination with the nearby museum, which had lots of cars and a few aircraft, including the Antonov biplane.

From memory, it had well-ducted ailerons and flaps on both upper and lower wings.

The manual prohibited flight below 24kts.

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10 hours ago, Old Koreelah said:

That low-speed control issue is why I'm designing an outer wing based on feather-like extensions that allow massively changes in surface area as speed changes. Birds have it, so why shouldn't we?

I'm pretty sure that the man made equivalent of feathers is a set of Fowler Flaps.

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