Get rid of tail heavy physics

[Ex-jazz]

in the diag CL is behind the CG, therefore the aircraft is pitching down. we are discussing what happens when an aircraft in level flight loses its tailplane. I guess you get what you pay for

Yes, indeed.

And when you lose the h-stab. / tail, the plane CL/NP is shifting instantly next to the wing AC, means, a front of the CG >>> pitch up violently.

[hitech]

Ex-jazz, read the whole thing carfully, it said "normally" behind the CG. With a Cessna it is.

The Wing CL force can just as well be ahead of of the CG as long as the force from the Horizontal Stab is greater (more precisely the resultant torques) when an AOA is generated. The key is just like the picture of the ball showing a static stable system, the same thing will happen with a plane even with the wing CL is ahead of CG.

HiTech

[Ex-jazz]

Ex-jazz, read the whole thing carfully, it said "normally" behind the CG. With a Cessna it is.

The Wing CL force can just as well be ahead of of the CG as long as the force from the Horizontal Stab is greater (more precisely the resultant torques) when an AOA is generated. The key is just like the picture of the ball showing a static stable system, the same thing will happen with a plane even with the wing CL is ahead of CG.

HiTech

Thank you for your feedback, Hitech.

I will study more about this issue 

[Wedge1126]

Are there any planes in AH that have their CG ahead of their wing CL?

[Ex-jazz]

Hey?! Hold your horses!

In my linked Cessna picture is actually a same situation, as in my linked Ball with shaft picture.

The 'NP' and 'CL' are pointing the center of the lift of whole plane(wing-tail), not just a wing AC.

I still believe, I'm right.

But

If I'm wrong, then I will learn something new


 This was the last one. I promise

[Dream Child]

So when the h-stab is shot off, the plane should flip over nose down instead of the way Dan's picture shows the A-20 flipping nose up?

Perhaps you didn't look at the picture. It wasn't just the stabilizers that were gone.

[Dream Child]

I've seen a footage of an air-race midair collision in which a rear approaching plane collided with another plane flying in front of it. I took particular interest in the result, since it almost exactly replicated what happened in AH.

The plane behind smashed into the tail of the plane in front, and removed the whole rear fuselage - the horizontal, vertical stabs were gone in an instant. Obviously, the pilot of the plane behind tried to avoid the collision, and most of the damage was done by the props which just simply chopped off the rear end of the plane flying in front of it.

It was exactly the same thing as seen in AH when a plane fires at the target and blows off either the whole aft fuselage, or the two horizontal stabs.

... and what ultimately followed, was again, the same thing as seen in AH.

The plane which suddenly lost its tail, flipped upwards nose-high. The only difference was that in AH, the planes flips nose-high and then falls downwards in that state, whereas in real life, the plane flips upwards nose-high, and then the momentum of the flipping goes on and ultimately tumbles the wreckage, and it falls down to the ground tumbling and spinning in all directions.

At that moment, I was impressed by how AH got it right.

Obviously, in real life, things happen in the way how AH describes it, Dream Child, not in the way you think it might.

Perhaps you missed the original post. I'm talking about when you only lose the horizontal stabilizers.

[Stoney]

Well, if Ex-Jazz and PJ's assessments are correct, it doesn't matter that its just the H-stab or the entire empenage, the result would still be a violent pitch up.

Does anyone have an in-game aircraft CG data?  I can find everything else to do the stability equations except for the CG data.  It could be an interesting excercise...

[Dream Child]

Actually, you can do this with a flying wing. There is such a thing as a statically stable flying wing but, as you've surmised, you need it creating some downforce aft to counteract the pitch moment caused by the lifting surface. You can think of it, if you like, like a compound wing that serves the same purpose as the wing plus h-stab on a conventional tailed aircraft.

You've also surmised, but for the wrong reason, that using an h-stab, or compounded wing, to create an aft downforce is somehat inefficient. This is generally true - creating downforce at some distance from the cg increases induced drag - both from the surface creating the negative lift (the h-stab) and from the wing itself - which has to create lift to counter the grav force PLUS that negative lift from the h-stab aforementioned.

This is a good time to introduce THE CANARD, whose forward h-stab lifts UP to counter the pitch caused by the wing which lifts aft of the CG.

Active stability is another story altogether - but is primarily done for maneuverability and efficiency and does away with pesky control surfaces making (usually) unnecessary forces.

Actually, I was trying to point out that you could have both the wing and elevator very far on one end, far away from the center of gravity. This would mean a very large wing and large elevator/stabilizer surfaces, but would be very inefficient as the downforce that the elevator would have to produce would be great, and the wing would have to be much larger to deal with the large down force the elevator had to produce. I'm not going to claim I did a good job of explaining what I meant, however.

Stoney already brought the canard subject in, and tried to say that because it produced lift, then the rear stabilizer would also produce lift. I told him no. That was on back on page 2.

[Dream Child]

Dream Child, producing an up force does not produce an unstable aircraft. As long as the net force of tail and wing is behind the CG the aircraft will be stable.

The drag difference is if you create a down force then the wing will have to produce the weight of the plane + the down force in lift, I.E. the extra drag comes from the wing do to needing more lift.

When the Horizontal stab is producing lift in the up direction, the wing will have to produce less lift.

HiTech

If the CG is behind the wing/body center of lift, then any additional G force put on the body will push the tail down, and enough G will eventually produce a reversal of control effect. Reversal of control effect is one of the reasons why the P-51 was dangerous to fly with fuel in the aft tank.

[hitech]

Ex-jazz: In you weight picture  the scale would show more than the weight of the ball. I Did not see an answer maybe I missed it.

Ex-jazz: I am more than happy to help you understand, if you are asking if with the setup of your Cessna picture , would the nose pitch up or down, the answer is the nose would pitch down if losings the tail.

But how most planes in AH are set up, the Center of wing lift is forward of the CG not behind the exact point and distances changes with different load outs. And hence the nose pitches up.

If you have question about how this setup can be stable feel free to ask any more questions you have.

HiTech

[Stoney]

Nevermind...

[Swatch]

Well, I just graduated an AerospaceEngineer and I wanted to prove I still understood/remembered this stuff after a summer... so here for your viewing (and learning) pleasure...



An aircraft is only dynamically stable in the air (trimmed) when all its moments add to zero.  Presented above are the primary contributors to your pitching moment and how they balance.  I tried to give emphasis to larger forces/distances which produce larger moments.  The two most important forces on an aircraft is its main wing lift and the weight of the aircraft.  In a STATIC sense, these two forces must be nearly equal, therefore if your CG moves behind your neutral point you have two VERY large, nearly equal, forces trying to pitch your aircraft's nose into the air. Contrary to popular belief, the horizontal tail is actually not providing a downward force at all times.  In fact (as stated earlier) in fighters, you want your horizontal tail to be as unloaded (producing little force) as possible.  This is done by balancing the moments from your wing lift and CG.  A loaded horizontal tail creates drag, and this is wasted energy.

One also has to realize that a neutral point is not really tied to the physical world like the CG or an aerodynamic center.  A neutral point is just the point where if you move your CG beyond that point, your aircraft becomes dynamically unstable.  Its kinda a question of which comes first... the neutral point or the tail design.

[PJ_Godzilla]

Congrats, Swatch, and welcome to the dubious fraternity. I'm a lifetime Sigma Gamma Tau and did undergrad and grad at UM ('86) and Stanford ('87) in Aero/Astro and walked away from all that with a trip to the darkside.

That's right: management. I work on the corp turnaround team here at Ford doing PD Process reengineering. There's nothing "aero" in sight.

Don't do it. If they offer to pay for an MBA, just say no. THe first time someone shows you a process map, feign incomprehension. Drool and stare if they start talking valuation.

Why? Because that road ends with you sitting in a meeting, dreaming of doing something else.

Let me know if you want a friends and family discount on any of our vehicles. It's the least I can do.

Also, nice beating the dead horse properly...

[Ex-jazz]

Swatch, thanks a lot. Very informative.

"In fact (as stated earlier) in fighters, you want your horizontal tail to be as unloaded (producing little force) as possible.  This is done by balancing the moments from your wing lift and CG."

If I understood this correctly, minimum horizontal tail load is achived only in specific velocity, which is up to the altitude and load(fuel, ammo & ords). Best cruising speed with minimum trim drag.

Yep, the horse is well-done.