all flying tailplane
all flying tailplane
Why do it if it's not fun?
Joined: Jul 2001
Posts: 4,782
Likes: 12
From: Bournemouth
Very simple really. A conventional tail-plane has a fixed surface, with elevators at the trailing edge which move up and down in response to pilot commands, thus changine the angle of attack of the surface as a whole. In an all-flying plane, there is no fixed part - the pilot alters the angle of attack by moving the whole surface. The PA28 is a very common example, so you can probably go down to your local airfield to see it in action - just move the tail-plane up/down, and notice that the whole thing moves, instead of just the back part.
The advantage of this setup is that it gives a very powerful control surface. Usually, it turns out to be too powerful, and the control forces required to move it in flight are too light, so they are often fitted with an anti-balance tab to increase the amount of force required to move it.
Hope that helps.
FFF
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The advantage of this setup is that it gives a very powerful control surface. Usually, it turns out to be too powerful, and the control forces required to move it in flight are too light, so they are often fitted with an anti-balance tab to increase the amount of force required to move it.
Hope that helps.
FFF
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Joined: Dec 1998
Posts: 4,282
Likes: 6
From: Escapee from Ultima Thule
Not so much too powerful since the surface is sized to provide the appropriate amount of force.
One of the arguments for an all moving surface is that the surface can be smaller, thereby reducing drag.
The problem is that the movement of the Center of Pressure vs. the pivot point changes as AoA is changed.
Increased AoA causes the CoP to move forward and can cause a reduction in the control column force with increased movement. It's even possible for a design to have the CoP move far enough forward that the surface has an uncommanded movement and 'locks' into a fully deflected position.
The generally desirable feedback is an increase in control column force with increased surface deflection. Uncommanded movement isn't exactly welcome either...
A tab is used in these cases to cause a restoring force, increasing the control column force needed to move the surface with increasing deflection.
One of the arguments for an all moving surface is that the surface can be smaller, thereby reducing drag.
The problem is that the movement of the Center of Pressure vs. the pivot point changes as AoA is changed.
Increased AoA causes the CoP to move forward and can cause a reduction in the control column force with increased movement. It's even possible for a design to have the CoP move far enough forward that the surface has an uncommanded movement and 'locks' into a fully deflected position.
The generally desirable feedback is an increase in control column force with increased surface deflection. Uncommanded movement isn't exactly welcome either...
A tab is used in these cases to cause a restoring force, increasing the control column force needed to move the surface with increasing deflection.
Do a Hover - it avoids G
Joined: Oct 1999
Posts: 2,201
Likes: 0
From: Chichester West Sussex UK
Another way to restore some force is to include a ‘positive bob weight’ in the circuit. This is just a weight on the end of a lever attached to the flying tailplane (or elevator) control run in such a way that it tends to apply forward stick. Then as you pull g it tries to move the stick/wheel forward even harder so giving you the desired ‘stick force per g’ You can tell whether an aircraft has one of these devices because the stick will always fall forward when you let it go on the ground.
Joined: Dec 1998
Posts: 4,282
Likes: 6
From: Escapee from Ultima Thule
I think the C177 cardinal tailplane slot was a design mod. added at some point after certification when problems were identified with the implementation.
I recall reading - somewhere, damned if I know where - that there were incidences of tailplane stall during landing.
The hold off with increasing AoA of the tailplane eventually exceeded its ability, resulting in a stall ==> loss of downforce ==> slam the nosewheel into the runway.
The whole thing seems to have been an attempt to cater to fashion ie "Our competitor is selling a whole series with it & beating us over the head with its theoretical advantages....so we'll have one too."
I recall reading - somewhere, damned if I know where - that there were incidences of tailplane stall during landing.
The hold off with increasing AoA of the tailplane eventually exceeded its ability, resulting in a stall ==> loss of downforce ==> slam the nosewheel into the runway.
The whole thing seems to have been an attempt to cater to fashion ie "Our competitor is selling a whole series with it & beating us over the head with its theoretical advantages....so we'll have one too."
ex-Tanker
Joined: Apr 2000
Posts: 907
Likes: 0
From: Luton Beds UK
5 pennyworth...
The Handley Page Victor Mk1 had an all flying tailplane too. It was pretty "touchy"and the feel came from "feel cans" filled with dynamic pressure air.
When you trimmed, you actually trimmed the feel can mechanism until you felt no pressure, leaving the control run - and with it the tailplane, at whatever angle it was.
As the aircraft got older, these feel cans became leaky, resulting in an extremely light elevator control - which made it, however too easy to overstress the ship. (AUW <80 tons, flying in formation in certain versions).
When you trimmed, you actually trimmed the feel can mechanism until you felt no pressure, leaving the control run - and with it the tailplane, at whatever angle it was.
As the aircraft got older, these feel cans became leaky, resulting in an extremely light elevator control - which made it, however too easy to overstress the ship. (AUW <80 tons, flying in formation in certain versions).
