How much down Elev are you putting in your "Flap System" at full flaps and crow??? I am just finishing up a Flash build.

Thx,
Rex

It has been some time since I have looked at it...I will check tonight if you like. I do have down for sure. What i do is set up flight modes so I can trim on that first flight and then I just transfer to the flap system and zero out the trims...nonetheless, I will check for you later....

That would be great if you could, thanks! Or, I can see if Chad can do it...appreciate it!
Rex

No, it increases the stall speed. Up aileron reduces or even reverses the camber, thereby reducing or even reversing the lift force and turning it downwards. The remaining part of the wing now has to produce more lift at the same speed and it can only do it by raising its AoA, so it reaches its stalling angle at a higher speed. Crow adds drag but does so by demanding more lift hence more induced drag from the remaining portion of the wing. If you want drag that's fine but your stall speed has gone up. Gliders that tend to have very low stall speeds anyway don't generally care about that.
H

1320FB, David Gladwin, Gordon W, and Harry C, good job!!

Reflexing ailerons won't ALWAYS improve wing aerodynamics, without or with flaps (crow). Each aircraft is unique, YMMV, and so on...

Don't tell the folks at Robertson (STOL mfgr) that drooped ailerons don't work. They didn't get the memo, have been carrying on for decades. [X(]

Crow works great on my Stick 40, but with a fair amount of power and MINIMAL aileron use. Lands in 10 feet.

Give it a try, works in some cases (but I gotta believe a small amount of flaperon would benefit most cases).

Interesting question. This is what I can say. When ailerons are in up position the lift coeffient (Cl) of wings decreases therefore stall speed is higher. Drag benefits on ailerons can only be achieved when alpha is low. The only advantage you'll get is higher stall angle. If you want to slow down on landing don't use this on final or instead use it moderately on opposite (downside like flaps). Advantage: higher Cl, higher drag at high alpha. Disadvantage: lower stall angle and rearward center of pressure (pitch moment down). You may use this braking method (crow) with flaps on low alpha descend with caution.

Good explanation!
The reason you might feel for a lower stall speed is because of the center of pressure shifted forward where you got higher lift at positve angle. Sometimes we feel losing lift when deploying down flaps due to moment effect but the reality we gain lift, opposite to the crow.

Dang!!!!!! always thought "crow" was bragging about the super smooth, greased on landing you just done! Learn something every day!!

Bruce

As you say, it can be a false perception due to the pitching effect of crow or flap. The primary effect of lowering flap is to make the wing pitch nose down and thus make the model dive, giving the impression that putting the flaps down reduces the lift. Putting ailerons up for crow will make the wing pitch nose up so the plane rotates up and climbs, giving the impression that up aileron increases lift.
Those effects are complicated by other factors though, such as the location of the tailplane in the downwash and the effects of sweep putting the changing lift and pitching forces ahead of or behind the CG. Those effects due to the layout of the plane can make the movement of aileron or flaps have the opposite effect to their pure moment of pitching around the Aerodynamic Centre. Raising ailerons on a swept wing model not only causes nose up pitching around the AC but a downward force behind the CG, so you get a double whammy effect trying to raise the nose and thus compensating for the natural stability that is trying to lower the nose at low speeds. Lowering the flap on the swept wing creates a nose down pitching around the AC but the increased lift well ahead of the CG produces a nose up force and the outcome of that may be a small nose up or down or no net force. So the effects of moving control surfaces around can be quite different simply due to wing sweep, but in general crow will result in less nose down or even a nose up pitching, meaning the pilot is pulling back less on the stick at low speeds, and thus may give some people a false impression that the wing is working better.
H

Good points Harry , Might I also add that the effect, drag wise, on raising trailing edges varies dependent on aerofoil section, symmetrical, semi-symm or a type such as a glider section with under camber at the aft part. Think proof of this can be easily seen by the fact that many high performance sailplanes can use a litte negative flap to achieve greater range at higher speed suggesting that l/d ratio which defines distance from height is improved and as lift is constant the drag must have been reduced.

Angle of upset may also be significant with perhaps some reduction in drag at small angles but followed by a rapid increase as angle increases. Every wing section will vary.

As an aside it was interesting to note that the Mig 27s at the JWM BOTH employed aileron DROOP (or at least the ouboard wing section as it probably uses tailerons for roll control) wiith the TE and LE flaps extended and the wings swept forward. No signs of tip stall there.

And if anyone STILL thinks that aileron upset lowers stalling speed take a look at all the airliners landing with upset ailerons at an airport near you . My guess is ZERO ! (but the flaps will all be DOWN )

Great to see a healthy and productive debate on RCU.

Regards,

David.

The origin of crow braking is in the world of F3B competion gliders. These evolved at a time when all moulded machines where becoming the norm, and these were the low drag airframes. Part of the task for these competions is a spot landing, timed to the second. The best way to acheive a succesful spot landing is to do a steep approach, but for this a large increase in drag is necessary. Large flaps that depress up to 90 degrees evolved, but these can cause large pitch changes, especially as the airspeed increases. The use of raised ailerons then evolved in order to reduce the pitch change, as well as add a little more drag. A secondary effect is to sometimes give the ailerons a little more bite. Whilst the rule for flaps is "as much as possible", the angle the ailerons go up needs careful fine tuning to achieve the desired results.
As has been said here the actual effects vary dramatically between airframes and in partucular with wing sections. Despite what has been said here, raising the ailerons is very effective in some aircraft at reducing tip stalling and at least one full size glider reflexs the ailerons up for evey landing specifically to reduce its rather nasty tip stalling tendency.
Pitching the ailreons up alone is not crow strictly speaking, and the angle necessary to get a useful result, may in some aircraft be so much theat it reduces aileron effectiveness.
My new Eurousport is significantly lighter than my old old Mk1 version. Nor does this one have an airbrake and it does float on.rather. I intend to experiment with crow to see if I can fix this. Clearly on thsi model equal amounts of down on the inner surface and up on the outer surface will be the starting point.

This has been my experience with jets as well "My understanding is it serves two functions.
It allows a lower approach speed (lower stall speed) and allows for a higher AOA."
However, you have to be careful with how much you raise the ailerons especially on planes with higher wing loadings
since this has the effect of reducing lift somewhat and you might sink faster
than you want... SO my recommendation would be to start with small aileron deflections (up)
and then work higher in small increments until you are satisfied with the sink rate and landing speed.....

As several of us have pointed out, several times, that is wrong. It increases stall speed and demands a higher approach speed.
H

Not on my planes, i get much slower landings, rock stable in landing turns at slow speed.
Crow works.
I will stay with it thanks.

Paul G

The increase in stall speed with reduced camber is an aerodynamic fact. Your perception might be different though.

I hate to add my aerodynamic explanations here as there are others who are far more knowledgeable than me. However, using crow effectively reduces the camber of that area of the wing where the ailerons are. As seen from the graph below, reduced camber will cause a reduction in the maximum available CL before stall. This means that the aircraft will stall at a higher speed. However, the angle of attack at which this will occur will be higher.

Therefore, I guess it is possible that you may have the illusion that the model is flying slower due to the higher pitch attitude but in reality it isn't. The theory is probably irrelevant anyway as the numbers will be tiny for the situation we are discussing. This is made somewhat more irrelevant when combined with the knowledge that most people make their approaches miles above the stall speed anyway.

For the persistent but aerodynamically challenged:

Flexing an aileron upwards makes "lift in a downward direction" along that portion of the wing, and that's half of what banks your airplane (The other aileron moving downward and increasing lift on that side is the other half). With us so far? Good.

Flexing BOTH ailerons up makes "lift in a downward direction" along the portion where the ailerons are located on both wings simultaneously. Still with us? You sure? Great, you're almost there, so hang on.

With both ailerons flexed up part of each wing dedicated toward making "downward lift", and there is less wing on each side still making "upward lift".

There is no way, none, that an aircraft in this configuration has a lower stall speed. That. Is. Physically. Impossible. It may indeed be flying more slowly than without the reflexed ailerons simply because of the extra drag, but the stall speed is higher. Not lower. Period.

Sorry, I'm not picking on anyone. I promise. The physics just is what they is.

If I learned anything from the now infamous "Downwind Turn Myth" thread though, it's that some will deny the truth at all costs rather than even contemplate the possibility that they have been operating under false impressions or assumptions. Them folks just is what they is too, so God bless 'em!

You would have to ask Jerry. He knows.

Better inform BAe systems, Boeing, Airbus etc then Paul, they are all making their flaps go in the wrong direction! If only they moved them upwards not downwards, they would land so much slower

Very well explained by HarryC…

Luckily i was not talking about the flaps

Using crow on landing has negligible effect for light aircraft due to load distribution and pitch up effect. However using crow on landing for high wing loading jets can endanger due to decaying airspeed. After all it turns to be unforgiving aircraft once it reaches to the critical flight envelope.

Hopefully I can also enlighten this for benefit of our jets. The high speed airflow on the top of the wings that produce suction or lift is being interrupted by this crow. It produce high pressure lower speed airflow between the ailerons and the wings. It produces downward push and pitch up moment to the wings. On the otheside since it has the (negative) camber, it accelerates the lower speed high pressure air under the wings. Instead of lift it produces negative lift. However the crow reduces the air separation over the wings at high AoA which is a good advantage. The wings had still the total lift coming from the original fixed camber and AoA. During this process that reduces the resultant lift force, it also shifted the center of pressure forward (closer to CG) that reduces the stability of the plane.

That doesn't matter Paul. Aircraft don't differentiate between flaps and ailerons, to a wing it is the same thing - a portion of the back of the wing moving up or down. If moving ailerons up increased lift, so would moving the flaps up. If your Hawk creates more lift when the aileron moves upwards, you must have a very unique roll response!

Your understanding of aerodynamics/physics seems partial, it has everything to do with the location of different config, spanwise.

Why is washout so important on modern airplane (with reflexed airfoil, ((only towards the outboard span of the wing with a negative incident)) ? A: to improve low speed handing

Perhaps you could use a electic foamy and increase lift (incident) on the outboard only, to find out it will do nothing but to snap into uncontrollable spins like crazy at low airspeed

of course it matters

Also have a look at a beechjet. They have no ailerons. Only spoilers on top of the wings near where the aileron should be. If you guys thinking crow adds lift then all the beechjets have thier spoilers hooked up backwards .