Does Aileron setting increase drag ???

[Raf-CSB3]

Hello,
Talking about aileron increase the drag when they are 1 inch up. Because the angle of attack change thu the elevator produce more drag to keep up the altitude.
I don't think so, remembering when I've flown glider, we use the flaps as little as 3 degree up to increase speed. That doesn't affect the drag. But with an aircraft is different because you need to keep an altitude.
So this is my point of view for an aircraft set with a normal CG position (in the middle of the graph):
If the ailerons are 1 inch up (reference of the trailing edge of the wing), your speed is increased to keep the same amound of lift, because the camber of the wing is less (in the area of the aileron only). The angle of attack of the elevator change a little to keep the altitude but its arm is so far I think the drag of the elevator is negligeable.
The aircraft is a convair 580. flying at 278 TAS @ FL200, with passagers.
Thank you for your help,
Raf

[Genghis the Engineer]

I *think* so; I can certainly think of a microlight (the Flightdesign CT) where the ailerons and flaps are reflexed (set trailing edge up) in the cruise to allow the aircraft to fly faster with the same power.

I'm not entirely sure of the theory behind it, but would hazard a guess that by reducing the effective AoA of the outboard section of the wing, you are moving the spanwise lift distribution inboard. This should reduce the induced-drag-inducing formation of wingtip vortices.

I'd hate to try and quantify it without experimental data however.

G

[Mad (Flt) Scientist]

As always, the answer is "it depends" :)

And what it depends on is how good a job the original wing designers did in optimising the design, and whether the conditions you are specifically considering were one of the design conditions they worked with.

If you consider the wing to be rigid, then what you're really doing is redefining the section of the outboard wing (where the ailerons are). Add in aeroelasticity, and you're also effectively changing the designed washout. If both of those were well chosen, then any change will take you off the design point, and will increase drag (as Ghengis mentions, you're changing the spanwise lift distribution; that may or may not be a positive or negative effect). You will get a bit more drag from the discontinuity at the edge of the aileron, but it may be a secondary effect. You'll also get some changes in pitching moment, especially if the wing is highly swept (which is also likely to exacerbate any twist effects). The actual lift distribution change will NOT affect the trim drag (same amount of wing lift at 1'g' flight) but a pitching moment change may affect trim drag; again I'd expect this to be secondary at best.

If I had to guess, I'd say "more drag" based on the assumption Convair knew what they were doing. But it's just a guess.

[barit1]

Not necessarily. Although Convair certainly knew what they were doing, minimum cruise drag may not have been #1 priority. Given that it was a short-haul machine in a time of low fuel prices, handling qualities probably had more weight in the marketplace.

That said, wouldn't a spanwise lift shift to the inboard improve low-speed airleron response?

[Mad (Flt) Scientist]

Maybe. But reflexing both ailerons puts them both in the relatively inefficient TE up condition; usually we see a less effective roll control in the up direction (until the wing stalls due to flap effects, but that's usually outside normal aileron parameters). I'd say you probably get better aileron effectiveness by slightly drooping the ailerons, putting both on the 'good' side of neutral.

But I'd say it would be quite a minor effect in most cases, unless you had control system tension issues and needed to preload the cables....maybe.

[Raf-CSB3]

Thank you all,

It's very interesting to see all that you know. Concerning the Convair, this question was asked only because my captain has seen the ailerons a little bit up (maybe 1 inch above the trailing edge see from the cockpit). It's not a setting from the maintenace dept or convair manual.

As I ever seen in flight test manuals and reference guides, the answer is depending of what we're talking about.

Thank you for your help.

Raf

Mad are you from Qc?

[cavortingcheetah]

:hmm:

Wouldn't this be a design consideration for the Convair, which is a relatively heavy and slow aircraft, to help obviate aileron drag or adverse yaw in turns and thus give the machine better roll control? Any slight increase in drag in level flight due to 'offset' ailerons would be more than compensated for by added roll stability and efficiency?
Presumably the ailerons are differentials as opposed to Frise ailerons?
Is that of any relevance?:)

[stevef]

Just for interest's sake, DC3 ailerons (differential/Frise) are rigged to give a 7/8" trailing edge droop with the control wheels centred. They ride up to the true neutral position in flight.

[dixi188]

The BAC1-11 had (has) an aileron Anti Up Float cable circuit linking both ailerons to prevent the ailerons rising in flight.
I know of an occation in the early 1980's at Gatwick where this cable had not been tensioned correctly (about 70lbs instead of 125lbs if my memory is correct) and on a C of A renewal test flight the crew had a nasty shock when doing the stall/stick pusher tests, one wing suddenly dropped sharply. Presumably this was the outboard wing stalling because the aileron was high.
Are you sure your Convair ailerons are correctly rigged and tensioned?
Stay safe, Dixi.

[Mad (Flt) Scientist]

Presumably this was the outboard wing stalling because the aileron was high.

Sounds odd; if the ailerons were deployed upwards that would tend to UNLOAD the outboard wing, which would tend to reduce the likelihood of an outboard stall. Unless the wing was very flexible and the ailerons were twisting the outboard panel so as to reduce the effective washout, but I don't recall the 1-11 wing as looking like one that should be susceptible to that (high AR, thin)

[dixi188]

Thanks Mad.

Doesn't sound right now you mention it. Maybe it was just a loss of roll control with floppy ailerons. They are driven by servo tabs.

I was maintenance at the time (Not my error!) and did the cable adjustment and rigging ckecks. Next test flight was OK.

[On Glide]

Reflexing ailerons like on gliders and the Flight Design CT reduces drag because the aerofoil is designed to run laminar flow far back on the lower surface with the flap in the reflexed position. When the flap is down the pressure gradient ahead of the flap causes transition of the laminar b.l. earlier. On modern gliders with cruise (reflexed) flaps, the curvature is continuous over the flap hinge, the hinge line itself if faired over with flexible mylar and the laminar b.l. runs all the way onto the flapperon with forced transition via blowholes (pneumatic turbulators) at 95% chord. With careful design elements like this it is possible to acheive a max L/D of 52 on an 18m glider!

OG

[Dan Winterland]

I've flown many glider types where the ailerons were moved up with the flaps to reduce drag. The VC10 which I lalso flew has aileron upset. This was a manully activated system which at certain weights and heights moved the ailerons up by about 10 degrees (depending of mark). This was for wing bending relief and increased the fuel consumption.