Get rid of tail heavy physics

[Nemisis]

I always thought that plane with no elevators would dive faster than a pony running away from a c47.  which brings another related item, why how can a plane with 1/2 a wing still be able to fly at full speed.

semp

Well I don't think loosing a wing would affect top speed all that much. If anything it seems like it should increase it provided the plane still has enough lift with half a wing to stay airborne. Think about it, a wing creates lift, but is only able to create enough lift to stay airborne when flying fast enought. A wing has nothing to do with how fast something can go other than drag and simmilar items caused by the wing. The only thing that would detract from the top speed would be increased drag by creating jaged edges where there was a streamlined wing.

I'm by no means an expert. So will someone please correct me if I'm wrong?

[Dream Child]

Rather academic whats happens to your airplane after the stabs are shot loose, unless you are also saying this "tail-heavy" modeling 1. has an effect when planes still in one piece are maneuvering and 2. that this is innacurate.

While it's hard to prove #1 from where I sit, it is inaccurate. I believe this is why the stall modeling isn't right, but again, it would be hard to prove from where I sit.

[Dream Child]

I think this fellow discusses aftward CGs (nose heaviness) and pitching moments rather well but consider well what he is saying (the opposite of what I suggested):

http://ciurpita.tripod.com/rc/rcsd/lowSpeedStability/lowSpeedStability.html

What he's saying is that one needs to have downward force on the elevator during flight to have pitch stability. This is also why most planes are designed nose heavy. When they're tail heavy they're unstable. An example of this is a P-51 with aft tank above 1/4 (or 1/3? don't remember) full, and is why the AAF prohibited heavy maneuvering until the aft tank was below that point. Many modern fighters are designed unstable, but they use computers to control and deal with the problems.

[Dream Child]

Well I don't think loosing a wing would affect top speed all that much. If anything it seems like it should increase it provided the plane still has enough lift with half a wing to stay airborne. Think about it, a wing creates lift, but is only able to create enough lift to stay airborne when flying fast enought. A wing has nothing to do with how fast something can go other than drag and simmilar items caused by the wing. The only thing that would detract from the top speed would be increased drag by creating jaged edges where there was a streamlined wing.

I'm by no means an expert. So will someone please correct me if I'm wrong?

Well, you would also get some sideways push (yaw) that would have to be corrected with the rudder, due to the change in drag of the damaged wing. You would lose lift on that side due to reduced wing area at same angle of attack, so would need to correct with remaining aileron. All this would add drag back into the equation. How much extra drag is the question, so would depend on how much wing you lost, how jaged the edge is, and perhaps how much control is available for correction depending on how bad and what side the damage is, and engine torque (direction) will affect what side is easier to deal with too.

[Stoney]

Umm...no, not even close. I'll say this as simply as I know how. Under normal flying conditions, one has to push the tail down to make the plane fly level. This is because the CoG is in front of the Center of Lift (CoL).

Somebody quick, go tell Burt Rutan that the Long-EZ is defying the laws of physics...

The horizontal stabilizer is a lift-producing device.  Think about what happens when a lift vector at the tail suddenly goes away...  Now, that being said, I will say that I believe there is something fishy about the pitching moment on some of the aircraft.  For example, both the P-47 and P-38 POH's both state that the aircraft will be nose-heavy after lowering flaps.  I have yet been able to find the patience to do the math that would either a) explain why it works opposite in-game or b) prove that the in-game aerodynamics are wrong.  I still suspect...

[Dream Child]

Somebody quick, go tell Burt Rutan that the Long-EZ is defying the laws of physics...

The horizontal stabilizer is a lift-producing device.  Think about what happens when a lift vector at the tail suddenly goes away...  Now, that being said, I will say that I believe there is something fishy about the pitching moment on some of the aircraft.  For example, both the P-47 and P-38 POH's both state that the aircraft will be nose-heavy after lowering flaps.  I have yet been able to find the patience to do the math that would either a) explain why it works opposite in-game or b) prove that the in-game aerodynamics are wrong.  I still suspect...

The Long-EZ is a canard wing aircraft. In it's case, the horizontal stabilizer produces lift because it's in front of the wings, hardly comparable to what we're talking about. It's backwards compared to the aircraft we fly here. None of the aircraft in this game have the horizontal stabilizers in front of the wings.

If the horizontal stabilizer is in the back of a plane like a traditional aircraft, and like all aircraft in Aces High II, to be stable, the horizontal stabilizer has to push down to make the plane fly. I really shouldn't have had to state that I wasn't speaking of canard type aircraft in this discussion.

[Stoney]

The Long-EZ is a canard wing aircraft. In it's case, the horizontal stabilizer produces lift because it's in front of the wings, hardly comparable to what we're talking about. It's backwards compared to the aircraft we fly here. None of the aircraft in this game have the horizontal stabilizers in front of the wings.

If the horizontal stabilizer is in the back of a plane like a traditional aircraft, and like all aircraft in Aces High II, to be stable, the horizontal stabilizer has to push down to make the plane fly. I really shouldn't have had to state that I wasn't speaking of canard type aircraft in this discussion.

Do you know what a pitching moment is?  And, a horizontal stabilizer is a LIFT surface, regardless of whether it is in front (as a canard) or in back.

[BnZs]

Do you know what a pitching moment is?  And, a horizontal stabilizer is a LIFT surface, regardless of whether it is in front (as a canard) or in back.

The fact that it is lifting surface does not mean that lift must be directed *up*.

1. Most normally-configured aircraft have center of gravity ahead of their center of lift. This is considered vital for positive stability, and having a center of gravity aft of the center of lift is considered positively dangerous.

2. Most "normal" airfoils have a negative coefficient of moment. In plain English, their tendency is to actually want to pitch downwards. In this case, it follows then that the horizontal stab of an aircraft which is normally configured must actually generating *down* force to hold the nose *up*.

3. Thus the OP's surprise at aircraft pitching nose-up when they suddenly loose the horizontal stab is understandable...IF we assume the planes modeled in AHII have a CoG ahead of the center of lift AND we assume that the airfoils have  negative coefficient of moment.

EDIT: Stoney, whether flaps increase nose-up or nose down pitching tendency has alot to do with the airfoil. Airfoils with a high and negative coefficient of moment tend to pitch down with flaps, while airfoils with a low coefficient of moment may tend to pitch up. Laminar flow airfoils tend to have a high and negative coefficient of moment.

[Chalenge]

Just to make a point here: the change in moment coefficient with respect to flap deflection depends only on the ratio of flap chord to total chord.

ALSO: I believe that symmetric airfoils do not produce a moment about the aerodynamic center. I will probably have to stick to that belief no matter how airplane wreckage acts in AH.

MOST (and I capitalized that because of BnZs overuse in generalizing) aircraft designers in WWII avoided the 'negative lift' scenario on the tail because it reduces aerodynamic efficiency. It is not a requirement though and MOST planes of the era have both positive and negative lift on the tail over some portion of its allowable configurations (nothing being constant for trim power or weight through a flight). Probably the best designs (your laminar flow for example) will exhibit NO lift on the tail during trimmed flight with no elevator deflection at the design cruise airspeed and altitude. Outside of that condition all bets are off.

Generally speaking what happens when the tail is knocked off of these planes is the wing will seek an angle of attack that makes the pitching moment about the CG equal to zero. You must bear in mind that the CG has just changed drastically.

[RTHolmes]

wings and tailplane both generate lift. remove the tailplane and the CoL moves forward, presumably in front of the CoG, the nose pitches up. hows that?

[Guppy35]

If a picture is worth a thousand words, here are two thousand words.  First images I thought of when i read the initial post.

Flak hit from below, forcibly removes the A20's tail.  You can see the pieces flying back.  Based on getting hit from below and the arguments above, the nose should have pitched down.  Sure looks like he pitched up.  Not making light of what may  be photos of two aircrew getting killed, but there is no doubt the nose pitched up as the initial photo and the following were taken from the same plane and the first shows the trailing A20 from slightly above.

[moot]

This exact topic was debated before on this forum.  Hitech and other aero heads took part, with diagrams and everything.   Find that old thread and you can get a headstart on debating it further.

[Stoney]

Thus the OP's surprise at aircraft pitching nose-up when they suddenly loose the horizontal stab is understandable...IF we assume the planes modeled in AHII have a CoG ahead of the center of lift AND we assume that the airfoils have  negative coefficient of moment.

In order to illustrate what the horizontal stabilizer actually does for the plane, I'll explain how the elevator works, from an aerodynamic perspective.  During flight, the horizontal stabilizer, as BnZ points out, provides pitch stability.  It creates the necessary lift to maintain the pilot's desired AoA on the wing.  When the elevator (attached to the horiz stab) is deflected up (pilot pulls back on the stick), it decambers the horizontal stabilizer, decreasing the lift created, reducing the moment applied at the tail, and allowing the nose to pitch up.  When the elevator is deflected down, it adds camber to the horizontal stabilizer, increasing the lift created, and forcing the nose to pitch down.

BnZ, there is a difference between net pitching moment for the entire aircraft, and the airfoil pitching moment.

[Stoney]

Moot jogged my memory.  dTango posted this link from an earlier thread.  This explains the math behind the issue:

http://adg.stanford.edu/aa241/stability/staticstability.html

[hitech]

I agree 100% with how challenger described things, but to be clear, AH does not model any weight reduction nor what would be the accompanying CG shift when loosing AC parts.

Also there is a great film of an aircraft attacking a ship where you see the pitch up when the tail is shot off.

If you wish detailed diagrams do some searches.

Also the confusion for most people comes from the very simple explanation of stability shown in most pilot training manuals.

The OP has most correct in his thoughts of how pitch ups work. We do have one short coming in the model at the moment that pyro and I have been speaking about adding.

Right now CP , lift, drag are all modified with flaps usage, but we do need to add a CM curve also to modify the basic wing CM. This will allow us to fix a few planes that pitch incorrectly with flaps.

HiTech