Tricycle Angle of Attack On The Ground

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GESchwarz

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What angle of attack should a tricycle gear plane have while on the ground. I'm thinking it should be just a little negative to keep it on the ground until pilot gives input, but not any more than necessary, as that I suppose could contribute to pilot induced oscillation. A little negative would help keep it on the ground post touchdown too. I just haven't read anything on this topic.
 

Dan Thomas

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What angle of attack should a tricycle gear plane have while on the ground. I'm thinking it should be just a little negative to keep it on the ground until pilot gives input, but not any more than necessary, as that I suppose could contribute to pilot induced oscillation. A little negative would help keep it on the ground post touchdown too. I just haven't read anything on this topic.
Negative can cause problems. The airflow will force it down in the takeoff roll, and since the lift is ahead of the mains, it forces the nose down and makes more work for the elevator to lift the nose, so there's a sudden pitch-up when the nose finally rises and the negative lift disappears and abruptly reduces the load on the tail. That can cause overpitching and maybe result in an accident.

JMO.

Dan
 

Dan Thomas

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Best angle is about 12 degrees. You get that with the best configuration: a taildragger.

:)

Dan

Shoot. Used an emoticon. There goes my Man Card for another three weeks. I will be stuck flying trikes until I get it back....
 

fly2kads

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I went back and looked in Pazmany's book, and was reminded that he doesn't address this question directly. The mains are positioned first, based on tip-back angle while landing at aft c.g., without flaps. The nose wheel is placed such that it carries the desired portion of the aircraft's weight. Tip-over angles and clearances are checked. Nothing that I can see about static angle of attack. I presume it's not mentioned because you're using the elevator to rotate into takeoff attitude, anyway.
 

Aircar

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Tricycle that squat tail down are notorious for extending the take off run -you create induced drag and form drag rather than accelerate--the Victa Airtouer was bad in this respect and worse after the spring gear sagged a bit over time or with a bit of overload ...
 

DaveD

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I'm with James. Zero lift or just slightly above should be the target to minimise drag and maximise acceleration. However with flaps down that may not be achieveable/practical.

Even with flaps up the wing is likely to be at a couple of degrees incidence to the fuselage/datum, couple that with a cambered airfoil which doesn't produce zero lift until a small negative aoa and you're not going to get zero lift until the fuselage is around -5 deg (i.e. nose down). I'd aim for fuselage level or very slightly nose low, you don't need negative lift... at zero lift you've got gravity to keep you on the ground!
 

rtfm

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Good question, and thanks for asking it. I'm thinking about the same thing.

Duncan
PS Any news on the fabled "Schwartz-pipe"?
 

pwood66889

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"What angle of attack should a tricycle gear plane have while on the ground?"
Not much works for me. My ride has troubles when the angle goes positive = "squirrely" on roll out.
Percy in SE Bama, USA
 

GESchwarz

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I especially like the comments about minimizing drag on the takeoff roll by having the AOA at neutral to a couple degrees negative. On the other hand, with 10 to 20 degrees flap for takeoff, is it going to matter what the static AOA is?
 

TFF

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What happens if too much negative incidence in the ground is it will pin it's self to the ground. The elevator has less leverage at the gear than CG. The airplane would probably need too much control to rotate and then it will leap up in an overcontrol state. Probably a lot of PIO during talkeoff.
 

GESchwarz

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What happens if too much negative incidence in the ground is it will pin it's self to the ground. The elevator has less leverage at the gear than CG. The airplane would probably need too much control to rotate and then it will leap up in an overcontrol state. Probably a lot of PIO during talkeoff.
That is the most important consideration.
 

Pops

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Back in the 50's flying rudder only RC models on escapement, with tri-gear. Would set the wing neg and when the ground speed got to the speed that enough down force was on the stab, the model would rotate like using elevator and would have the stab trimed for a steep ROC at close to stall. Would have to keep the model in a turn most of the time to stop a stall. So with that trim, a couple 360 spirals, there would enough excess speed for a loop when you level the wings, etc. Loops, stalls, and spins on rudder only. Dan
 

TFF

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I love single channel RC. Maximum use of the minimum.

When flying a plane, the minute you start the engine, you are flying the airplane. In heavy winds you "fly" the plane on the taxiway using the controls. You want a plane to act like all other airplanes. The Ercoupe has the wonderful statistic of having the top spot in landing accidents. It is not because it is hard, but because of the coupled rudder, landing takes a different tact from normal. If you land one like a normal plane in a crosswind, tou have a good chance of ground looping it. You want instincts to be transferable. During landing if you really have to plant it like on a short runway, once the wheels are down you can lift the flaps; kills the lift at the speed. On Takeoff anything 20 kts faster than liftoff speed should be in the air. The brakes and wheels are only good for emergencies at those speeds.
 

Pops

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I love single channel RC. Maximum use of the minimum.

When flying a plane, the minute you start the engine, you are flying the airplane. In heavy winds you "fly" the plane on the taxiway using the controls. You want a plane to act like all other airplanes. The Ercoupe has the wonderful statistic of having the top spot in landing accidents. It is not because it is hard, but because of the coupled rudder, landing takes a different tact from normal. If you land one like a normal plane in a crosswind, tou have a good chance of ground looping it. You want instincts to be transferable. During landing if you really have to plant it like on a short runway, once the wheels are down you can lift the flaps; kills the lift at the speed. On Takeoff anything 20 kts faster than liftoff speed should be in the air. The brakes and wheels are only good for emergencies at those speeds.
I have owned 3 Ercoupes. A lot of the landing accidents on Ercoupes are overruns at the end of the runway. The reason-- When landing in a crab with coupled aileron and nose wheel steering. Upon touchdown of the mains wheels the aircraft will turn to the direction of travel. That makes the upwind increase in airspeed and the down wind wing decrease in airspeed and causes the upwind wing to lift letting the cross wind to get under the wind and lifting it even more until the airplane is "Wheelbarrowing" on the down wind wheel and nose wheel and the nose turning downwind. You can't lower a wing with ailerons because that would turn the nose wheel making it worse. The only thing you can do to help is add power to help the wing come down, and hope you can get stopped before you get to the end of the runway or lift off again and hope you clear the trees. Hence the runway overruns. The Ercoupe has a higher crosswind component than most aircraft at 25 mph. The old Goodyear brakes were like dragging your feet, thank God for the Cleveland brakes. Dan
 
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