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Old May 09, 2015, 08:42 PM
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Thermal Camber Settings

Ok, I was having a chat today with a guy about camber settings on F3X TD/F3J type planes. I mentioned that I set my camber so that both the flaps and ailerons are dropped as desired and generally match how much they are dropped. Basically so I have a matched trailing edge.

The fellow I was talking with said he never drops ailerons in camber, just flaps. He feels that dropping the ailerons with the flaps in thermal camber reduces the roll authority too much for his liking.

So I got curious. What is the consensus of the Great and Mighty Internet??

Flaps and ailerons dropped to match?

OR

Flaps only?
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Old May 10, 2015, 01:15 AM
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Flaps and ailerons matched for me.

Mike Lee
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Old May 10, 2015, 02:42 AM
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It wouldn't be called "camber changing" if you were just dropping the flaps! If you don't droop the ailerons you are giving up a large portion of your wing and relying on a smaller portion to do the work. A well designed wing should not require any artificial washout to handle well.

I don't think that a few degrees of camber has that much impact on your roll authority. At least not if you have what I would consider typical amounts of aileron deflection. Slowing down will have a much larger effect by comparison.

If you were worried about it, I would (and do) just crank up the travel in those slow speed modes. I have the most aileron throw in "thermal" mode and the least in "speed" mode. This way I get a more consistent feel to the glider. But honestly, you don't really need that, you should be able to fly the plane without those nit-picky little tricks.
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Old May 10, 2015, 05:38 AM
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Flying more slowly reduces aileron authority.

In its self he is not correct as you can still have the same or more aileron travel. You can put the model in a vertical dive with a duration setting. You will have good aileron authority but you won't go as fast as you could.

I would see the inverse of that in that if you fly more slowly without proper camber (i.e at higher AoA) you will have more drag.
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Old May 10, 2015, 06:46 PM
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Over 200 views and only 3 answers. No need for an explanation.

Simple question, flaps only or flaps & ailerons in camber??
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Old May 10, 2015, 07:19 PM
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I like to make use of the whole wing for the best results for me.

Rates and mixes change when cambered to adjust for the slower flight. If you ask the airfoil and aircraft designers, they designed to use the full wing.

Airplanes do need to be set up to the capabilities of the pilot. So there are different cgs and different control rates to deal with the different reaction rates and pilot capabilities. Pilot errors can quickly negate and performance improvements.
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Old May 10, 2015, 08:30 PM
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My recommendation would be for most pilots to simplify and use essentially the same setup for all flight modes with the exception of camber. Pilots get all wrapped around the axle with programming complex setups and then don't have a clue if their plane is flying efficiently or not, and some are certain some things achieve a particular goal but are mistaken. Watch the planes fly; watch the hands on the sticks. Smooth pilots with skills can perhaps benefit from advanced setups. The rest would be better served with a bit more flying and a bit less tuning that is beyond their stick ability. 0.02c, and not what many will want to hear.

For the question of the thread, if the difference in camber is of the order of 2 degrees, then the resulting wing will fly approximately like it would if the full wing were of the intermediate camber. But as per any washout benefit that assumption is in error.

When our wings stall, due to the Reynolds numbers of the tips, the stall initiates as flow separation well in front of the hingeline. The setting of the trailing control surface will have very little effect on this. So the thought process which equates such unequal control surface settings with washout is incorrect.

If the wing designer did his/her job right, adding additional washout beyond the design parameters is unnecessary. The designer will have already taken into account turning conditions. Of course, perhaps not all designers have done so... But you'll already know if there is a problem. If one occasionally stalls the inner tip on a thermal turn, dropping that wing, where the thermal turn was not an unreasonable maneuver, then perhaps the wing does have a design issue. But setting flaps down a little only and not the ailerons will mostly just make the plane fly faster and come down faster. The flying faster part may give the illusion of having solved the issue...

Otherwise, uneven settings is not likely to improve the efficiency. It can affect the desired aileron differential setting for decoupling roll from pitch.

As for differential being used to reduce adverse yaw, for planes such as ours that is another misunderstanding. Adverse yaw is primarily caused by the relative tilting of the lift+drag vectors while a roll maneuver is in progress. Without roll rate, there isn't the classic adverse yaw (there are other sources of adverse yaw but beyond what I want to type out right now).

Our airfoil families have relatively low camber percentage. Most full size planes have relatively high camber percentage. This is a critical difference! The asymmetry of drag response with respect to aileron setting for + vs - travel is substantially an artifact of the camber of the airfoil. Less camber, less asymmetry.

For our wings, the asymmetry is small. Therefore adjusting differential to reduce overall drag or reduce adverse yaw is relatively ineffective.

It also has a glaring negative. That is, if differential is set so that the lift of the wing alters when small to moderate aileron deflection is initiated, then the plane produces a pitch response. If that pitch response is not compensated by an |aileron| -> elevator mix, which probably nobody does, then one gets misleading pitch behavior from the plane on roll input, which then requires greater skill of the pilot to read the air during maneuvers. In turbulent air, one may be nearly continuously maneuvering to slight degree for correction purposes, leading an insufficiently experienced pilot to be effectively unable to accurately read the air. Bad air reading leads to bad decisions which leads to poor flights.

I recommend adjusting differential in each flight mode such that small quick side-to-side wing rocking does not cause a net pitch change to the aircraft. This decouples at least those two axis. More advanced setup trying to tweak out that last 0.01% performance should be left to the true experts. But, such tuning is easier to determine through computer analysis than through flight as the air just isn't consistent enough for such fine tuning anyway. Nor is the difference ever likely to actually make a difference in flight.

Adjusting control throws though so that the wing most accurately mimics a propeller when ailerons are deflected does reduce overall drag. Aileron deflection should be in the rough order of magnitude of somewhat over double to triple the flaperon's aileron deflection for rolls. Actual optimal values will depend on a lot of things such as relative chord.

Just a side note - large control surface deflections add drag. Added drag needs to be compensated somewhere. It gets compensated by the loss of potential energy - ie, altitude, or by the loss of airspeed if one tries to maintain glidepath, or a bit of both.

Not written for planes other than DLGs, but if you haven't read it, some people at least might get some benefit from this: http://www.rcgroups.com/forums/showthread.php?t=1441098

Gerald
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Old May 11, 2015, 12:37 AM
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Quote:
Originally Posted by Silent-AV8R View Post
Over 200 views and only 3 answers. No need for an explanation.

Simple question, flaps only or flaps & ailerons in camber??
Flaps and ailerons included in camber changing modes here, and I would say 99.9% of the pilots I have flown with do so as well.

Bruce
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Old May 11, 2015, 02:16 AM
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I always move the ailerons and flaps
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Old May 11, 2015, 10:30 AM
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I make the entire trailing edge respond to camber.
On some of my slopers I've had good luck making the flaps match the ailerons
like one big control surface for hot dogging.
For thermaling and being efficient, I have less flap following the ailerons.
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Old May 11, 2015, 11:27 AM
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You got your answer in 3! WHY do you think more answers make it any more correct?
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Old May 11, 2015, 01:10 PM
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Quote:
Originally Posted by timmig View Post
You got your answer in 3! WHY do you think more answers make it any more correct?
I was sort of looking at it like a poll, but your point is taken. Thread closed
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