Does the elevator/stabilator generate upward force?

In article om,
" wrote:

Plus I'm pretty sure my statement was pretty odvious in it's direction
to the original author

fwiw - no, your intended direction was not all obvious.

--
Bob Noel
Looking for a sig the
lawyers will hate

"Dan" wrote in message
ups.com...
Ok, this is a followup to the previous discussion about forward control
pressure during the landing rollout. Can someone tell me if the
elevator/stabilator can actually generate an _upward_ force, or does it
simply generate a downward force for climbing and less downward force
for a decent?

Does the nose fall due to the CG being forward of the center of lift,
or does the elevator actually push the tail up?

We are talking about tricycle gear planes, not taildraggers... The PA28
series specifically.

--Dan

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

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)

Yes, the elevetor generates lift, negative lift, 99.9% of the time, in
stable flight. If you look at most diagrams of aircraft forces, you
will see the CG with a force vector down, then behind that the center
of lift with a force vector upwards. Finally, the elevator is usually
drawn with a force vector downwards as well.

I would say there is a distinction between tailwheels and tricycle gear
aircraft. On a tailwheel, the CG is behind the main gear, on a
tricycle gear plane the CG is in front of the main gear.

Thanks for the example of the outside loop, I understand now. While
observing the range of stabilator deflection on a PA28, it seems to be
able to generate a _heck_ of a lot more downward force than upward
force, but apparently upward force is possible as well.


--Dan




wrote:
I'm kind of alarmed to hear that an instructor didn't explain to you
that the elevator generates lift.

"Dan" wrote in message
ups.com...
Ok, this is a followup to the previous discussion about forward control
pressure during the landing rollout. Can someone tell me if the
elevator/stabilator can actually generate an _upward_ force, or does it
simply generate a downward force for climbing and less downward force
for a decent?

Does the nose fall due to the CG being forward of the center of lift,
or does the elevator actually push the tail up?

We are talking about tricycle gear planes, not taildraggers... The PA28
series specifically.

--Dan


Take the seat belt off the yoke of your PA28 and measure the angle between :
horizontal and the airfoil chord ( a line from the leading edge of the
stabalizer and the trailing edge of the elevator). You can use a yardstick
and protractor to get close enough. This will approximate the angle of
attack of the tail feathers with the aircraft in a level flight when full
forward stick is applied - right?. I suspect that it will be, what, 10 - 15
degrees? So, if the tail foil has a significant positive angle of attack,
how could it not be generating postitive lift?

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

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

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

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

wrote in message
ps.com...
Plus I'm pretty sure my statement was pretty odvious in it's direction
to the original author... just like you said... your post had nothing
to do with it. Sorry if I've caused irrperable offense.

It should be apparent by my reply that it was *not* obvious. You replied to
my post, rather than the one to which you were commenting, which made it
look very much like you were addressing my post (even though you weren't).

As far as your apology goes...there's no irreparable offense to apologize
for, but you could instead simply apologize for not quoting, and posting in
reply to the wrong post, causing confusion.

Thanks,
Pete

"Dan" wrote in message
ups.com...
Yes, the elevetor generates lift, negative lift, 99.9% of the time, in
stable flight. If you look at most diagrams of aircraft forces, you
will see the CG with a force vector down, then behind that the center
of lift with a force vector upwards. Finally, the elevator is usually
drawn with a force vector downwards as well.

In straight and level flight on most airplane designs, the elevator *does*
provide a downward-directed force. So that's what is put in diagrams of
aircraft forces by default. That doesn't mean that's what the elevator
always does.

I would say there is a distinction between tailwheels and tricycle gear
aircraft. On a tailwheel, the CG is behind the main gear, on a
tricycle gear plane the CG is in front of the main gear.

In the air, the location of the CG relative to the main gear is entirely
irrelevant. Even on the ground, the location of the CG relative to the main
gear has nothing to do with what aerodynamic forces the elevator can
generate.

Thanks for the example of the outside loop, I understand now. While
observing the range of stabilator deflection on a PA28, it seems to be
able to generate a _heck_ of a lot more downward force than upward
force, but apparently upward force is possible as well.

I haven't looked closely, but I'm pretty sure that a typical design for a
horizontal stabilizer is to give it an angle of incidence that provides for
some preferred amount of downward force in straight and level cruise flight.
Assuming symmetrical deflection of the elevator up or down, this would limit
the upward force to something less than the downward force. Of course, this
design restriction could be avoided by providing greater downward deflection
by the elevator than upward.

Pete