Full span flaps and separate full Span ailerons?

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addaon

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For the design I’ve been working on, I have approximately full-span elevons that optimized at a taper from 25% chord at the root to 21% at the tips — analysis suggests it helps with accelerated stall behavior, but going beyond that cost roll authority.
 

addaon

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Unstable aircraft, so elevons down at increased AoA. Shorter chord toward the tip has the effect of a bit of washout; the locally-smaller flap increases CLmax less, but also decreases AoA at stall less. This applies for all slow flight in theory, but the elevon is split into three sections spanwise that are scheduled together in normal flight, but additional washout is added by scheduling the inboard surface down more at low speed; this is a much larger effect than the elevon taper, but it only applies to “DC” slow flight; when load rapidly increases towards an accelerated stall the scheduling does not immediately apply and so the taper helps.
 
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lil_cub

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View attachment IMG_5500.MOV

Something to think about (please don't shoot the messenger). The hinge point is near the front so flap area isn't lost and when the gap seal is installed it turns the (smooth) air straight down. We tried droops and a few things but it comes back to what works well, is simple and still allows good control.. flap in the prop-wash (9-10') and aileron beyond. If using slats its been our finding that the wing can be pretty flat and still remain stable in slow flight. This layout provides reflex as well. While full length flaps work we found control more desirable. ;-) It needs to be noted that the wing should be well tuned before installing slats to prevent causing more issues.
If full length flaps are required you might consider replacing the ailerons with spoilers.
 

Tiger Tim

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Boeing airliners usually have almost full span flaps with roll spoilers. The ailerons are short span.
The Cessna Caravan has small-ish ailerons that help make it feel like an airplane and roll spoilers ahead of the outboard end of the flaps to help with roll rate.

If you don’t want your design to be in the company of a boring Caravan you can tell people the setup was inspired by the P-61 Black Widow.
 

Vigilant1

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I think I am missing something basic. Why not slats across the whole front of the wing to extend the chord, instead of trying to increase the increase energy in the boundary layer?

Tim
Why not make the wing bigger? Why not blown flaps? Why not a "simple" boundary layer suction system?
There's no point in suggesting options or even pros/cons unless we know the objective and the constraints.
 

tspear

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@Vigilant1

Hmm, I could have been more specific. When people want to increase the chord of the wing to increase the lift without affecting cruise; the standard answer is flaps on the back of the wing. And slats to increase the boundary layer allowing for higher angles of attack to again increase lift.
My question is why only focus increasing the chord from the back of the wing? Why can you not increase the chord from the front of the wing?
I would guess I am missing something simple; but who knows?

Tim
 

BBerson

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Flaps don’t usually increase chord. Fowler flaps do increase chord when deployed.
I don’t know of any experimenters that modified and increased a wing chord. Usually they would build new wings so the cg stays the same, I suppose. But again, I don’t know of any. Many have increased span.
 

wsimpso1

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Has anyone done this ? Even thought about it ?
Lots of folks have. Every time someone works the trade for where to transition from aileron to flaps. More aileron raises max roll rate, more flaps lowers landing speed. Try to run them together and we get flaperons.

Works great in high perf sailplanes where they need to shift the lift curve to minimize drag for the speed that they are flying by trimming flaps up or down, while keeping roll control. They do not usually need landing speed reduction - they have quite low wing loading and landing speeds - so they can optimize for lift curve shifting.

Try it in a back country airplane, and the game is different. They need lots of aileron performance AND lots of landing speed reduction. Try to make flaperons work there and it gets more difficult. We must have enough aileron down movement left for landing maneuvers which limits flaps, so not much flaps here or not much roll authority. Then there is the issue of it tends to produced stall along the wing - spin entries, wing drop, etc. All bad.

Some folks have rigged separate flaps and ailerons with ailerons that droop when flaps are applied. This way, the flaps lower the landing speed a lot while also getting a little more stall speed reduction from ailerons. Sometimes it is an advantage, sometimes not so much.

Best compromise usually ends up being flaps inboard and ailerons outboard. Nice stall behavior starting at the root, nice slow landings, good roll control.

Billski
 

wsimpso1

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@Vigilant1

Hmm, I could have been more specific. When people want to increase the chord of the wing to increase the lift without affecting cruise;

Take an existing design, add chord and several things happen, all bad:
  • More wing area is more drag, so it can not fly as fast on same power;
  • More wing area and more chord is more pitching moment at any given speed, demanding more tail volume. Tail volume adds either fuselage wetted area or tail are or both, which also is more drag, so it can not fly as fast on same power;
  • More wing area and tail volume is more weight, and WEIGHT IS THE ENEMY of all performance measures in airplanes.

the standard answer is flaps on the back of the wing. And slats to increase the boundary layer allowing for higher angles of attack to again increase lift.
My question is why only focus increasing the chord from the back of the wing? Why can you not increase the chord from the front of the wing?
I would guess I am missing something simple; but who knows?

Tim
Flaps and slats extend Vsf to lower speeds, and are used to advantage in jetliners. They have to be done absolutely right to get much real advantage from them. They also add weight and complexity and development time. Ask yourself what your mission and cost constraints are and then work to your mission and cost. Most of us will never justify the big multi-slotted flaps and leading edge devices on jetliners...
 

Riggerrob

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I think I am missing something basic. Why not slats across the whole front of the wing to extend the chord, instead of trying to increase the increase energy in the boundary layer?

Tim
Slats also increase drag, so are really only a solution to reducing stall speed and accepting the decrease in cruise speed.

The only time I have seen that work well is when a Sportsman STOL kit is installed on Cessna 182 and 206 jump planes. The Sportsman STOL kit increases wing area along the leading edge. The Sportsman STOL kit starts by installing leading edge cuffs to increase the wings' leading edge radius, which makes stalls slower and more docile. Since Sportsman leading edge cuffs extend another 8 inches (?) forward, they also increase wing area. This increase in wing area, combined with flap gap seals substantially increases lift and climb rates. One owner of a Cessna 206 jump-plane bragged that the kit paid for itself in only one year.
At the same time, jump-plane owners often also install wing tip extension kits (e.g. Wing X) to further increase wing area and lift. The Wing X kit also allows an increase in gross weight, which allows early, straight-tail Cessna 182s to legally carry 4 skydivers.
 

Bille Floyd

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Lots of folks have. Every time someone works the trade for where to transition from aileron to flaps. More aileron raises max roll rate, more flaps lowers landing speed. Try to run them together and we get flaperons.
...
Some folks have rigged separate flaps and ailerons with ailerons that droop when flaps are applied. This way, the flaps lower the landing speed a lot while also getting a little more stall speed reduction from ailerons. Sometimes it is an advantage, sometimes not so much.

...

Billski

I use split flaperon a lot on RC ; with the computer mixing ability , a bunch
of different combinations can be tried in the same flight. One that works
well is split flaperon where the root flap goes do twice as much as the
tip , so twist is added when more flap is applied , and ya still get
adequate roll control. Gonna need a Lot of rudder ; if split flaperons
are used , (a Lot of rudder)!

Bille
 

tspear

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Ask yourself what your mission and cost constraints are and then work to your mission and cost. Most of us will never justify the big multi-slotted flaps and leading edge devices on jetliners...
Oh, I am not planning to ever do it unless it is offered by the "factory".
I did not consider the complexity aspect of the multi slats or flaps to get the most benefit. I was thinking a simple single slat to extend forward to increase wing area, and potentially wing chord.

Tim
 

Bille Floyd

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... But any attempt to extend forward defeats the purpose. It should be a large radius that droops. The Sportsman cuff is a poor design. Installation Pictoral

The Rutan VariEze , used a leading edge cuff ; it was mostly for stability
i believe ?
My friend Dave took me up in his VariEze and showed me how easy
it was to enter a spin , (inside wing stalled easy) and "could" be held in that stall.
Fast forward :
Dave asked me to paint his outside leading edges ; after cutting off the
cuff's , and installing the , (vortilons) . We went up together to see if those
vortilons actually worked . Dave tried to enter a spin, and I could hear
the wing buffet and start to shake a bit, and the inside wing acted like it
wanted to stall ; but OH Dang -- it came right out immediately !! Then Dave
tried it again and held Full up elevator with full ruder ; the inside wing
would start to stall, and come right out ,(over and over again) it simply
would Not stay stalled !!!

Back to back flights ; The vortilons worked for stability , "WAY" better
than the cuff's ; AND the plane picked up a few extra knots of speed
after the cuff's went ByBy .

There is my take, on the subject.

Bille
vortln09.jpg
 
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