You'd better expand on moment arms and sources of thrust. I'm trying to figure out what a pusher is less stable than a tractor. In my 34 years of full-scale flying I have never heard of this.
Dan
I'm a complete newbie here, but I'm guessing he means that thrust from the rear of a plane will produce more movement from incorrect or unintended inputs than thrust generated at the front. I should also note, though, that the Commander and other Hobbyzone planes are 'mid-engine pushers'. That is to say thrust isn't generated at the rear, but near the CG. This is probably the case with most pushers (except maybe for some thrust vector planes like my Vulcan gliders), so the difference probably isn't that big...
Ever consider the possibility of it being the pilot ?
Ken
He is actually talking bollocks, because unlike e.g. someone pushing a wheel barrow, the thrust is always perfectly aligned along the aircraft axis, therefore the position of where the thrust is aligned cannot affect the lateral stability.
And how does that equate to a tractor being more stable than a pusher? Does the propeller have something to do with sliding around sideways when it slips?
Dan
I think when the mains are way forward, it is actually easier to take off.
When I get a squirreley plane, I just give it more throttle right from the start so the rudder takes over the directional control right away, rather than gradually building up ground speed.
Also a little toe-in helps.
On Thu, 27 Sep 2007 06:01:34 -0700, Dan_Thomas snipped-for-privacy@yahoo.com wrote in :
I don't have a pusher aircraft like the Commander--or a pusher of any kind.
I do wonder whether the gyroscopic precession forces might act differently with the propeller behind the CG instead of in front of it.
Most tractor taildraggers of my acquaintance lurch a bit to the left as power is brought up during the takeoff roll. It is practically second nature to me now to lean on the right rudder as I bring the throttle up. Cubs are particularly tricky with their narrow gear.
Something like that may be going on here, but in reverse.
Marty
Oops. I just took a look at the plane:
I would hand-launch it.
Dan,
What you say is completely true and I agree, but the argument may fail in the assumption on rigidity.
If the landing gear is not rigid, which I think is the case, any disturbance will make the pusher less stable than a tractor.
It is really difficult to figure out why it is not being able to taxi straight because many variables are involved, but intuitively speaking, if you are dragging something (even if it does not have wheels), it is more stable than if you are pushing it. If rigid and symmetric, it should not matter at all (we agree in that), but small deviations from perfect rigidity or symmetry could effectively produce a big difference in stability.
My last handwaving argument. If you are pushing and the airplane does not move straight, e.g., because the thrust is off axis or the landing gear is not symmetric, the thrust will produce a moment that will help the airplane turning further, making this inherently unstable. This is different from the tractor airplane.
Best regards,
Angel
If you bend the landing gear backwards, behind the CG, the nose willl fall...
"mjc13 @verizon.net>"
If the thrust is not straight (P-factor) or if the landing gear drags on one side, the tractor will deviate as much as a pusher. All jets are pushers, especially the MD series or most business jets, and they have no more trouble maintaining alignment than tractors. Anytime the thrust and drag aren't in line, there'll be deviation. Rudders were invented to control that. Propeller thrust isn't vectored, like the wheel thrust on a front-wheel-drive car. It's rigidly aligned with the fuselage, and it wouldn't matter if the prop was clear at the end of the tail (like the Taylor Aerocar, Spratt Controlwing, and several other) at the aft end of the cabin (like the Seabee or Lake Amphibian or a million ultralights), atop the cockpit (like the Teal amphib or Volmer Sportsman) in front (like most lightlanes) or WAY out front (like the turboprop singles like the Turbo Thrush or Turbo Air Tractor or Pilatus PC-6). Google any of these. None of these airplanes have zigzag habits. Point the airplane and the propeller drives it in that direction. Same as a ship, which is also a pusher.
Dan
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