Does the elevator/stabilator generate upward force?

Allen wrote:
wrote in message
oups.com...

Allen wrote:
wrote in message
ups.com...

Allen wrote:

I once saw a pair of mechanics doing a full power run-up in a Maule.
They
were holding brakes on and forward elevator, the tail was about six
feet
in
the air standing still. So yes. Why do you separate the nosewheel
from
the tailwheel? They both fly with the same principles.

Allen

Aha, but you have to allow for the thrust line being so far
above the drag line, which in this case is the ground where the wheels
are locked. That thrust produces a pitching couple that raises the
tail
much more effectively than the down-elevator. If the pilot holds full
forward elevator at the start of the takeoff roll, the tails of most
taildraggers won't come up until some considerable forward speed is
attained, and then the tail is rising mostly because the centre of
pressure of the wing, being behind the mains, is lifting it. Using
forward elevator will lift the tail sooner but it sure is not entirely
responsible for the rise.
Wheelbarrowing is also mostly caused by too-fast landing
speeds, not just forward elevator. It's worse with flaps down because
the wing's CP is ahead of the mains and is raising the tail.
Down-elevator isn't even necessary at high-enough speeds. The
nosewheels of most trikes is closer to the ground than the mains in
level flight attitude, and will contact first with the high airspeed
reducing AOA.

Dan (Instructor in taildraggers and trikes and a mechanic too)

I have seen a Super Cub land with a 40 knot (or so) headwind and come to
a
complete stop, then raise the tail off the ground with the engine at
idle.
I see you point about the thrust affecting pitch though, used that all
the
time landing the Lear, as you bring the power levers to idle the nose
pitches up and automatically puts you into the flare.
Allen

But that 40-knot headwind is still lifting the wing, even with
the airplane motionless, making it very easy for the elevator to LIFT THE
TAIL. The airplane is almost flying.

Dan

Ah ha, the answer to the OP's question.

Allen

Sort of. But when flying a taildragger, you soon learn that
the elevator's tail-raising ability isn't very strong at all. When we
teach normal takeoffs in the Citabria, we accelerate with the elevator
neutral (wherever it wants to be) until the tail rises about four
inches off the pavement, then begin applying back pressure to keep it
from coming up any more. By the time it flies off, you have
considerable up-elevator in just to keep the tail down in climb
attitude, and that force will be required, with reduction as speed
increases, until climb speed is reached and stabilized. At that time
the stabilizer's downforce will be strong enough to keep the airplane
in climb attitude.
If we applied no backpressure during takeoff, the tail would
rise alarmingly to level flight attitude all on its own. If solo, the
nose could get pretty low. The wing is lifting, and since the airplane
is designed to go nose-down when speed is low, it will do just that as
the wings take the weight off the wheels. When we do tail-high
takeoffs, we apply full forward stick to get the tail up much sooner,
but as speed builds backpressure will be needed at some point to
control the attitude.
Can't blame all the attitude changes on the elevator. The
wing's lift as opposed to the wheels placement also has a huge effect.
We have balanced airplane models we use to demonstrate these things to
the students. They can see the tail come up when we lift the wing at CP
with our fingers and wheels leave the table.


Dan