Aces High Bulletin Board
General Forums => Wishlist => Topic started by: Dream Child on September 20, 2009, 06:46:15 PM
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Real WWII planes, in almost all circumstances, are nose heavy, so why does the tail always drop when losing the horizontal stabilizers? Though this does provide some good laughs if I lose the stabilizers on my FM-2 in the dueling arena, where I figured out I could make a continuous right hand turn without them if the flaps were down, and have all sorts of people yell about hacking the game... in real life, most of the time, the horizontal stabilizer and elevators are pushing down on the back of the airplane to make it fly, so if you lose them, the nose would drop, especially since you've lightened the tail even more by removing the extra weight.
While I don't want to get too realistic with the physics, I'd like to see this one fixed.
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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
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I have a few guesses on this, and I don't think it has a whole lot to do with weight, mind I'm not fully informed on airplane physics so I could be wrong.
Whenever I see a plane go nose up after I've just taken off the Hor. Stabs. they are generally mostly level, or, going up(ish). When this happens my guess is your planes wings are still creating lift, your Hor. Stabs. are no longer creating that nice stability like the name implies, and physics just put your nose up from the lift of your wings. Stall ensues and eventually like the old saying implies, what came up is now coming back down.
Again, just my guess, and by no means right.
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From my point of view, a plane without horizontal stabs becomes just like a leaf. It flutters up until the air over the wings is reversed, at which point they just slide downward as they're like a razor to the air.
But, that's just my theory.
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I have a few guesses on this, and I don't think it has a whole lot to do with weight, mind I'm not fully informed on airplane physics so I could be wrong.
Whenever I see a plane go nose up after I've just taken off the Hor. Stabs. they are generally mostly level, or, going up(ish). When this happens my guess is your planes wings are still creating lift, your Hor. Stabs. are no longer creating that nice stability like the name implies, and physics just put your nose up from the lift of your wings. Stall ensues and eventually like the old saying implies, what came up is now coming back down.
Again, just my guess, and by no means right.
Yes, you're still creating lift, but the center of gravity is forward of the center of lift, so nose goes down, not up. Remember, in real life, you're pushing down on the tail to make the plane fly. Stop pushing down on the tail and the nose drops, and in this case probably oscillate badly after that as there are no stabilizers to dampen things out.
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From my point of view, a plane without horizontal stabs becomes just like a leaf. It flutters up until the air over the wings is reversed, at which point they just slide downward as they're like a razor to the air.
But, that's just my theory.
Well, it would lose stability on one axis, and would probably oscillate badly, but would still end up nose down, as the center of gravity is in front of the center of lift.
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Looking at an aircraft simply from the aspect of CoG is like looking at how a computer works by examining a capacitor on the motherboard.
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It may not look right but I considered it for a while after the last collision I had with a tailess airplane (I would call it debris) and my conclusion was that the pitching moment takes precedence over the other forces at work once the tail parts company. Its lift on the tail that keeps the nose down and counters the pitching moment normally.
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Actually, an aircraft in flight losing the horizontal stablizers WOULD pitch nose up. It's not a factor of center of gravity, but how wings work to create lift. (for instance, an aircraft wing is not perfectly flat, not symmetrical in the vertical plane). There is a reason for that.
Probably best I just link to NASA =P
http://www.grc.nasa.gov/WWW/K-12/airplane/elv.html
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Actually, an aircraft in flight losing the horizontal stablizers WOULD pitch nose up. It's not a factor of center of gravity, but how wings work to create lift. (for instance, an aircraft wing is not perfectly flat, not symmetrical in the vertical plane). There is a reason for that.
Probably best I just link to NASA =P
http://www.grc.nasa.gov/WWW/K-12/airplane/elv.html
Interesting, from what I got out of that I was semi-right anyways.
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Actually, an aircraft in flight losing the horizontal stablizers WOULD pitch nose up. It's not a factor of center of gravity, but how wings work to create lift. (for instance, an aircraft wing is not perfectly flat, not symmetrical in the vertical plane). There is a reason for that.
Probably best I just link to NASA =P
http://www.grc.nasa.gov/WWW/K-12/airplane/elv.html
Umm...no, not normally. It's a factor of center of gravity vs center of lift. If I have to push down on the tail to keep the nose of the plane up, and then I lose that push, the nose goes down. While the math is a bit messy, the concept is not.
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Looking at an aircraft simply from the aspect of CoG is like looking at how a computer works by examining a capacitor on the motherboard.
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). If I lose that downward push on the tail, the tail will rise, and subsequently, the nose will drop. Most, if not all, planes are cabable of operating with the CoG behind the CoF, but that is not normal operation, and the design is for normal operation with the CoG in front of the CoL.
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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
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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.
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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 on piece are maneuvering and 2. that this is innacurate.
I would agree except for those dreaded collisions being forced upon me by debris flopping up into my face.
I think what we see online is accurate as far as airspeed is represented but that after speed drops off the nose should then fall... but why not setup an experiment and see for yourself?
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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?
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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.
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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.
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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.
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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...
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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.
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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.
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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.
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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.
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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?
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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.
(http://i152.photobucket.com/albums/s199/guppy35/Havoc.jpg)
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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.
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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.
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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
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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
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I understood so, the plane without tail will violently pitch up, because the NP suddenly move front of the CG.
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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.
If you had lost just the stabilizers, this would be a valid argument. Losing body parts changes the center of lift more than what we're talking about here, and puts the stabilization point in front of the center of gravity.
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If you had lost just the stabilizers, this would be a valid argument. Losing body parts changes the center of lift more than what we're talking about here, and puts the stabilization point in front of the center of gravity.
You obviously didn't read the link I posted...
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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
This is really funny. Look at the equation and you see the lift produced by the tail is negative. In other words, it's pushing down on the tail of the airplane, kinda like what I said in the first place.
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You obviously didn't read the link I posted...
Obviously, I did...
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This is really funny. Look at the equation and you see the lift produced by the tail is negative. In other words, it's pushing down on the tail of the airplane, kinda like what I said in the first place.
[sigh]...
Which equation from that link are you referencing?
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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.
Okay, I'm interested. If the CG is forward AND the airfoil itself wants to rotate down, what is making the aircraft want to pitch up, besides the forces of the horizontal stab?
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Okay, I'm interested. If the CG is forward AND the airfoil itself wants to rotate down, what is making the aircraft want to pitch up, besides the forces of the horizontal stab?
Let's step back a moment (no pun intended)...
Think about a symetrical airfoil. A symetrical airfoil has no pitching moment through its entire range of useable AoA. Its design lift coefficient = 0, in that it produces zero lift at 0 degrees AoA. However, at any positive AoA up to but not including the stall AoA, a symetrical airfoil will produce lift, but will do so without producing any pitching moment. So, for example, at 4 degrees AoA on a plane with a symetrical airfoil, what other moments exist that make the plane want to pitch up? What other moments exist that make the plane want to pitch down?
Notice this graph that is in the link that dTango provided. What stands out when comparing the pitching moments of the different parts of the aircraft? (Cm = pitching moment).
(http://i125.photobucket.com/albums/p61/stonewall74/image6.gif)
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This is really funny. Look at the equation and you see the lift produced by the tail is negative. In other words, it's pushing down on the tail of the airplane, kinda like what I said in the first place.
With horizontal stabilizer = NP(lift) is behind of the CG = pitching down.
(http://fdm4bge.1g.fi/kuvat/VACGC/1_CG2NP.jpg/_small.jpg)
Without horizontal stabilizer = NP(lift) is front of the CG = pitching up.
(http://fdm4bge.1g.fi/kuvat/VACGC/1_NP2CG.jpg/_small.jpg)
If NP(lift) is front of the CG = pitching up
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I may be over simplifying this a bit but, if the aerodynamic center (for the wing), is forward of the the center of gravity the nose should pitch up.
(http://upload.wikimedia.org/wikipedia/commons/thumb/7/7d/AirStability.svg/760px-AirStability.svg.png)
I believe that for most of the aircraft in AH, we are not talking about symmetrical airfoils either, so the discussion of aerodynamic center can get rather more complicated.
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Baumer: Nice diagram. What the OP fails to realize is that with pictures describing Center of lift and CG. The Center of lift is normally shown as only the net lift of both tail and wing.
Flying with an down force on the tail simply creates more drag, and hence is not normally desired characteristic for fighters .
HiTech
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Baumer: Nice diagram. What the OP fails to realize is that with pictures describing Center of lift and CG. The Center of lift is normally shown as only the net lift of both tail and wing.
I'm assuming this is done with the elevators in a neutral position?
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Umm...no, not normally. It's a factor of center of gravity vs center of lift. If I have to push down on the tail to keep the nose of the plane up, and then I lose that push, the nose goes down. While the math is a bit messy, the concept is not.
Agreed, at least that's what we learned in Aero Eng.
What they're seeing is probably a dynamic effect. Modelled in level flight, I can't imagine a scenario where the airplane wouldn't pitch nose down after losing the horistab. THat's just because, in statically stable aircraft, anyway, the cg is forward of the Center of Pressure - the extent of which is labelled the static margin.
However, IRL, if you're already pitched nose down, you're doing so by creating lift on the elevator. Lose that and the nose will likely pop up.
Of course, even with the stab locked and power off, most a/c will exhibit classic phugoid (long period) motion, nosing up until lift abates from dropping KE, dropping the nose until lift recovers on both surfaces and causes pitch up. That's the nature of longitudinally stable a/c - self-recovering divergence. The short period motion has period proportional to the static margin to which you refer earlier (diff b/w NP and CG).
All I'm saying here, short form, is it depends on the force being created by the horistab at time of "separation event".
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Agreed, at least that's what we learned in Aero Eng.
What they're seeing is probably a dynamic effect. Modelled in level flight, I can't imagine a scenario where the airplane wouldn't pitch nose down after losing the horistab. THat's just because, in statically stable aircraft, anyway, the cg is forward of the Center of Pressure - the extent of which is labelled the static margin.
However, IRL, if you're already pitched nose down, you're doing so by creating lift on the elevator. Lose that and the nose will likely pop up.
Of course, even with the stab locked and power off, most a/c will exhibit classic phugoid (long period) motion, nosing up until lift abates from dropping KE, dropping the nose until lift recovers on both surfaces and causes pitch up. That's the nature of longitudinally stable a/c - self-recovering divergence. The short period motion has period proportional to the static margin to which you refer earlier (diff b/w NP and CG).
All I'm saying here, short form, is it depends on the force being created by the horistab at time of "separation event".
Ok, think about this. Most horizontal stab airfoils are symmetrical. They are also placed on the aircraft at a positive angle of incidence, relative the wing, typically at an angle that will minimize trim drag at the design lift coefficient for the wing. So even when the elevator is not deflected at all, the horizontal stabilizer is producing lift. Why, if the aircraft naturally has a nose down pitching tendency, do we decrease the amount of lift the H-stab produces in order to pitch the nose of the aircraft up? If the H-stab provides a "down" force, we would need to increase the amount of lift it produces in order to pitch the nose up. In actuality, we increase lift on the H-stab to pitch the nose down, and decrease the lift on the H-stab in order to pitch the nose up.
[EDIT] Center of pressure is not the same thing as Aerodynamic center. The static margin equation uses Aerodynamic Center, not Center of Pressure.
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Ok, think about this. Most horizontal stab airfoils are symmetrical. They are also placed on the aircraft at a positive angle of incidence, relative the wing, typically at an angle that will minimize trim drag at the design lift coefficient for the wing. So even when the elevator is not deflected at all, the horizontal stabilizer is producing lift. Why, if the aircraft naturally has a nose down pitching tendency, do we decrease the amount of lift the H-stab produces in order to pitch the nose of the aircraft up? If the H-stab provides a "down" force, we would need to increase the amount of lift it produces in order to pitch the nose up. In actuality, we increase lift on the H-stab to pitch the nose down, and decrease the lift on the H-stab in order to pitch the nose up.
[EDIT] Center of pressure is not the same thing as Aerodynamic center. The static margin equation uses Aerodynamic Center, not Center of Pressure.
Now I am a bit confused... This physics make my head hurt.
I though the planes, with traditional wing-tail configuration, have a horizontal stabilizer with negative angle of incidence to provide a negative lift for the Longitudinal stability.
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Now I am a bit confused... This physics make my head hurt.
I though the planes, with traditional wing-tail configuration, have a horizontal stabilizer with negative angle of incidence to provide a negative lift for the Longitudinal stability.
The H-stab creates positive lift. And, to paraphrase dTango, its not physics, its aerodynamics... :)
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Ok, think about this. Most horizontal stab airfoils are symmetrical. They are also placed on the aircraft at a positive angle of incidence, relative the wing, typically at an angle that will minimize trim drag at the design lift coefficient for the wing. So even when the elevator is not deflected at all, the horizontal stabilizer is producing lift. Why, if the aircraft naturally has a nose down pitching tendency, do we decrease the amount of lift the H-stab produces in order to pitch the nose of the aircraft up? If the H-stab provides a "down" force, we would need to increase the amount of lift it produces in order to pitch the nose up. In actuality, we increase lift on the H-stab to pitch the nose down, and decrease the lift on the H-stab in order to pitch the nose up.
[EDIT] Center of pressure is not the same thing as Aerodynamic center. The static margin equation uses Aerodynamic Center, not Center of Pressure.
Static Margin uses the NP (neutral point) - which is the resultant of ALL aero forces, including, e.g., the effect of the fuselage. Agreed on the point - and I think you can say Aero center too, as long as it is of the entire assembly. I think I misstated it up front but correctly defined it as based on NP later.
As for the question, perhaps you're getting tangled in convention. Clearly, just looking at a free body diagram, you'd need to decrease (or increase negative) the force on the h-stab to pitch nose up .
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The H-stab creates positive lift. And, to paraphrase dTango, its not physics, its aerodynamics... :)
With all respect, I still disagree
Please, see picture on below.
(http://fdm4bge.1g.fi/kuvat/pics/TH26G3.jpg/_small.jpg)
Picture is from
http://www.centennialofflight.gov/essay/Theories_of_Flight/Stability/TH26.htm
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As for the question, perhaps you're getting tangled in convention. Clearly, just looking at a free body diagram, you'd need to decrease (or increase negative) the force on the h-stab to pitch nose up .
Only if you consider the force acting on the H-stab is acting in a downward motion. Its not. Unless there's some down-wash or relative wind issue I'm not considering, the lift vector of the H-stab is up, in the same direction of the lift vector of the wing.
Again, answer why we de-camber the H-stab (by pulling back on the yoke/stick, which induces an upward deflection of the elevator and decambers the airfoil of the H-stab) and reduce lift to make the plane pitch up? Why do we increase the lift vector of the H-stab to make the plane pitch down?
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Only if you consider the force acting on the H-stab is acting in a downward motion. Its not. Unless there's some down-wash or relative wind issue I'm not considering, the lift vector of the H-stab is up, in the same direction of the lift vector of the wing.
Again, answer why we de-camber the H-stab (by pulling back on the yoke/stick, which induces an upward deflection of the elevator and decambers the airfoil of the H-stab) and reduce lift to make the plane pitch up? Why do we increase the lift vector of the H-stab to make the plane pitch down?
Actually it increase a negative lift ( relatively to wing) by changing a H-stab effective aoa and therefore causing the plane pitch up, which increase a wing aoa, which causing a extra lift for the climb / turn.
Picture on below is made originally for the flaps, but it works basically same way, if you turn it up-side down for the H-stab.
(http://blenderartists.org/forum/attachment.php?attachmentid=66332&d=1237144852)
Ok, this is just how I understand it.
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Well the guys as NASA explain it this way,
"The elevators work by changing the effective shape of the airfoil of the horizontal stabilizer. As described on the shape effects slide, changing the angle of deflection at the rear of an airfoil changes the amount of lift generated by the foil. With greater downward deflection of the trailing edge, lift increases. With greater upward deflection of the trailing edge, lift decreases and can even become negative as shown on this slide. The lift force (F) is applied at center of pressure of the horizontal stabilzer which is some distance (L) from the aircraft center of gravity. This creates a torque
T = F * L
on the aircraft and the aircraft rotates about its center of gravity. The pilot can use this ability to make the airplane loop. Or, since many aircraft loop naturally, the deflection can be used to trim or balance the aircraft, thus preventing a loop. If the pilot reverses the elevator deflection to down, the aircraft pitches in the opposite direction."
http://www.grc.nasa.gov/WWW/K-12/airplane/elv.html (http://www.grc.nasa.gov/WWW/K-12/airplane/elv.html)
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Baumer: Nice diagram. What the OP fails to realize is that with pictures describing Center of lift and CG. The Center of lift is normally shown as only the net lift of both tail and wing.
Flying with an down force on the tail simply creates more drag, and hence is not normally desired characteristic for fighters .
HiTech
Airfoils have the least wind resistance when they are producing no lift, so any force up or down on the tail produces extra drag, the problem is that pushing up on the tail (providing lift) also produces instability, an undesirable trait in airplanes. While many modern fighters are unstable in design, they also have computers to deal with such a thing. Making a plane too stable also hampers it from maneuvering, so no, you don't want a bunch of down force on the tail to make it fly. Aircraft are also dynamic with respect to the center of gravity, something you already said you don't model, or do you only not model it with respect to losing parts?
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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
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the flaps, but it works basically same way
Absolutely the same way, just not the way you're understanding it. When we drop flaps, we increase the Cl at the same AoA--i.e. we increase lift. Obviously there are other results, but for illustrating what's happening at the elevator, will keep it simple. Dropping flaps changes the camber of the airfoil on the wing, and therefore, a downward deflection of the elevator increases lift, since the elevator increases the camber of the h-stab.
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I can understand why this effect could bother someone, but seriously, if your
tail is gone, the fight's pretty much over. :)
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I can understand why this effect could bother someone, but seriously, if your
tail is gone, the fight's pretty much over. :)
Actually, I'm really thinking big picture here. If the physics are done correctly, then the airplane characteristics will correctly fall in place, no tweaking necessary to get correct effects. The simple one to see is when someone loses both wings. They should spin like a drill bit due to the engine torque, but instead they "fly" in a nice arc until contacting the ground. Having said that, I'm not sure I want totally realistic physics in a simulator like this, as it will likely make the planes too hard to fly for many people here.
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In level flight, the net force of tail and wing should be at the same point as CG. Otherwise, there will be a pitching motion, right?
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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.
Yes, but I'm saying loosing part of a wing won't affect speed in and of itself with the exception of drag created by the jaged edges. The rest of that stuff will cause a reduce in airspeed, and is required due to the loss of part of a wing, but loosing part of a wing in and of itself won't have a negative effect on airspeed.
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...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
You do that and I will be much happier!
Add the A-36 Apache and Uptown will send you a bottle of Whiskey.
Top that off with your wish "I wish AH had support for dual sound drivers so ear phones and mics could be split off from speakers" and I will send you two bottles of Whiskey myself!
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In level flight, the net force of tail and wing should be at the same point as CG. Otherwise, there will be a pitching motion, right?
In short, no. To demonstrate this, pick up a broom by the end of the handle and hold it parallel to the ground. The center of gravity is somewhere in the middle of the broom. All the lift is at one end. You could do the same thing with the wings, though it would be a very innefficient system to be that far from the center of gravity.
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Yes, but I'm saying loosing part of a wing won't affect speed in and of itself with the exception of drag created by the jaged edges. The rest of that stuff will cause a reduce in airspeed, and is required due to the loss of part of a wing, but loosing part of a wing in and of itself won't have a negative effect on airspeed.
The F8F Bearcat was designed (attempted anyway) so that catastrophic loss of both wing outer sections would increase speed and decrease turn radius. In AH if you lose a wing tip your plane will speed up (or at least has in the past).
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I can understand why this effect could bother someone, but seriously, if your
tail is gone, the fight's pretty much over. :)
I did mention that an FM-2 can go around in circles with the stabilizers gone, right?
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Well that doesn't seem very well modeled :D
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Well that doesn't seem very well modeled :D
I found this out in the DA. Needless to say, there were several protests on open channel after that one...
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Well that doesn't seem very well modeled :D
Question. What is a stabalizer, and how does it function?
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In short, no. To demonstrate this, pick up a broom by the end of the handle and hold it parallel to the ground. The center of gravity is somewhere in the middle of the broom. All the lift is at one end. You could do the same thing with the wings, though it would be a very innefficient system to be that far from the center of gravity.
In your broom example, I would also be applying torque.
In my example, the tail and wings would generate a net force equal to and opposed to gravity. Where is the torque coming from?
Edit: I think from your argument, the torque would be from the downforce generated by the tail. I'm looking for the explanation from the opposing argument where both the wing and tail generate positive lift.
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In short, no. To demonstrate this, pick up a broom by the end of the handle and hold it parallel to the ground. The center of gravity is somewhere in the middle of the broom. All the lift is at one end. You could do the same thing with the wings, though it would be a very innefficient system to be that far from the center of gravity.
Dream Child, I believe there is an error in your analogy that might help explain the various forces that have been discussed in this thread so we can all understand it better.
First let me restate Wedges question with a slight rewording;
In level flight (with no other acceleration forces, i.e. stable in all 3 axis), the net force of tail and wing should be at the same point as CG. Otherwise, there will be a pitching motion, right?
From my education the answer is yes, the vector for lift and weight are exactly equal and in the opposite direction from one another, as are the vectors for thrust and drag.
Or another why to look at your analogy is this. Your hand is the wing (for the broom) the CG is aft of your hand, and the bristle end is where the horizontal stabilizer should be. But since it's been shot-off I ask you this. Which direction is the part in your hand trying to move up or down?
I'm not trying to stir the pot but I think there are some fundamental terms that we (or at least me) should all be clear on to properly discuss this topic. As Wedges question stated he was asking about net lift not just the wing lift component.
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Question. What is a stabalizer, and how does it function?
For the purposes of this discussion, a stabilizer is the non-moving part of the tail that holds the elevator. The elevator controls pitch (up/down).
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In your broom example, I would also be applying torque.
In my example, the tail and wings would generate a net force equal to and opposed to gravity. Where is the torque coming from?
Edit: I think from your argument, the torque would be from the downforce generated by the tail. I'm looking for the explanation from the opposing argument where both the wing and tail generate positive lift.
Looking at the question again, yes, the net force at the CG has to be zero to keep from changing pitch. Didn't do a good job reading the question first time.
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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.
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Only if you consider the force acting on the H-stab is acting in a downward motion. Its not. Unless there's some down-wash or relative wind issue I'm not considering, the lift vector of the H-stab is up, in the same direction of the lift vector of the wing.
Again, answer why we de-camber the H-stab (by pulling back on the yoke/stick, which induces an upward deflection of the elevator and decambers the airfoil of the H-stab) and reduce lift to make the plane pitch up? Why do we increase the lift vector of the H-stab to make the plane pitch down?
NO, no, and no...
The H-stab is most definitely producing downforce when you're flying level at constant speed. What you call decambering is actually a camber increase (viewed upside down) and increases that negative lift. That's the force that causes the pitch moment and it very definitely points down.
Believe me on this. I got my MSE Aero from Stanford and worked in windtunnels at NASA ARC for years.
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In short, no. To demonstrate this, pick up a broom by the end of the handle and hold it parallel to the ground. The center of gravity is somewhere in the middle of the broom. All the lift is at one end. You could do the same thing with the wings, though it would be a very innefficient system to be that far from the center of gravity.
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.
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Question
Is the Scale 1 showing the CG weight figure OR less/more?
(http://fdm4bge.1g.fi/Files/10001/VACGC/pics/CGNPTAC.jpg)
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Question
Is the Scale 1 showing the CG weight figure OR less/more?
(http://fdm4bge.1g.fi/Files/10001/VACGC/pics/CGNPTAC.jpg)
Ooow Ooow Ooww mista cata mista cata. :)
HiTech
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LOL hitech back in the day!
(http://blogs.poz.com/shawn/horshack.jpg)
My answer would be, it depends on if the aircraft is a taildragger or not! :)
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NO, no, and no...
The H-stab is most definitely producing downforce when you're flying level at constant speed. What you call decambering is actually a camber increase (viewed upside down) and increases that negative lift. That's the force that causes the pitch moment and it very definitely points down.
Believe me on this. I got my MSE Aero from Stanford and worked in windtunnels at NASA ARC for years.
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?
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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?
It's because the airplane wing-tail configuration is dramatically changed, which moves the NP (or center of lift) front of the CG... I think :noid
Hitech, you joking dolt! :)
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It's because the airplane wing-tail configuration is dramatically changed, which moves the NP (or center of lift) front of the CG... I think :noid
Hitech, you joking dolt! :)
I'd buy that. After all, you've just removed a major/highly authoritative (for fighters) lifting surface and the NP is usually well aft of the CG (in a statically stable a/c).
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I'd buy that. After all, you've just removed a major/highly authoritative (for fighters) lifting surface and the NP is usually well aft of the CG (in a statically stable a/c).
So, if I understand you correctly, the net pitching moment of the whole aircraft is negative, but when the horizontal tail is shot off, the net pitching moment immediately becomes positive? You understand why I'm a little dubious of that? The weight loss of the empenage should shift the CG forward dramatically, given the large arm of the empenage moment. I'm a little curious as to whether or not we could simulate the movement of the NP and the CG with the loss of an A-20 empenage. Obviously, we'd need to estimate the weight of the assembly which might be the long-pole in the tent that prevents it.
Also, this would mean that non-symmetrical h-stab airfoils would be inverted? And that negative angles of incidence would be used?
[edit] I keep thinking that there's some downwash effects that we're not considering here...
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Stoney: As I have stated in AH we do not change the CG based on removing a tail only the forces of air.
But in the real life example of the A-20 since the plane pitches up, the net center of lifting force has to be ahead of the new CG. Obviously the CG moves forward when removing the tail, so it tells you that the normal nose & wing parts of the air plane put the lift point ahead of the cg.
HiTech
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Even I knew that one HiTech. :aok
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Stoney: As I have stated in AH we do not change the CG based on removing a tail only the forces of air.
But in the real life example of the A-20 since the plane pitches up, the net center of lifting force has to be ahead of the new CG. Obviously the CG moves forward when removing the tail, so it tells you that the normal nose & wing parts of the air plane put the lift point ahead of the cg.
HiTech
Understood regarding the lack of CG change in-game--I was referring to the real-life example framed by Dan's photos.
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Question
Is the Scale 1 showing the CG weight figure OR less/more?
(http://fdm4bge.1g.fi/Files/10001/VACGC/pics/CGNPTAC.jpg)
not relevant or helpful, as it doesnt represent a conventional aircraft design. see Baumer's diagram on p3, which neatly illustrates my one-sentence answer on p2.
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Stoney: As I have stated in AH we do not change the CG based on removing a tail only the forces of air.
But in the real life example of the A-20 since the plane pitches up, the net center of lifting force has to be ahead of the new CG. Obviously the CG moves forward when removing the tail, so it tells you that the normal nose & wing parts of the air plane put the lift point ahead of the cg.
HiTech
There you go, Stoney. I'd reiterate that the net pitching moment of the whole aircraft, if it isn't pitching, is ZERO. As for this pitch about the horistab, the airfoil section of the stab varies plane to plane but I think they usually use a symmetrical one. There'll be some angle of incidence relative to the wing and some range of positive/negative elevator deflection.
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PJ_Godzilla: all though your basic premis is correct about cg and Center Lift being same point after the sum of forces is almost correct there are other forces I.E. things like CM that produce a torque but not a force on the airframe. So the resultent Center of Lift would have to compensate for this by being a little off of the CG.
But this is only a minor point in this discussion.
But what we normally refer to as the Center Lift being behind the CG is that with out any pilot input, if the air flow direction is changed by way of the plane changing directions or the air changing directions, will the resultant force be ahead or behind the CG. This is what is normally refereed to as stable if the force is behind the cg or unstable if it is ahead of the cg.
HiTech
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not relevant or helpful, as it doesnt represent a conventional aircraft design. see Baumer's diagram on p3, which neatly illustrates my one-sentence answer on p2.
(http://fdm4bge.1g.fi/kuvat/pics/Figure%203-12%20Longitudinal%20stability.jpg/full)
Picture is originally from
http://www.free-online-private-pilot-ground-school.com/Aeronautics.html
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PJ_Godzilla: all though your basic premis is correct about cg and Center Lift being same point after the sum of forces is almost correct there are other forces I.E. things like CM that produce a torque but not a force on the airframe. So the resultent Center of Lift would have to compensate for this by being a little off of the CG.
But this is only a minor point in this discussion.
But what we normally refer to as the Center Lift being behind the CG is that with out any pilot input, if the air flow direction is changed by way of the plane changing directions or the air changing directions, will the resultant force be ahead or behind the CG. This is what is normally refereed to as stable if the force is behind the cg or unstable if it is ahead of the cg.
HiTech
How that wing airfoil cause downward moment should calculated in?
If it is effecting from wing AC, how it should add to the NP net moment?
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I'm starting to get confused. Is CG normally in front of or behind the wing? When I say the "wing" I mean the wing's center of lift.
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(http://fdm4bge.1g.fi/kuvat/pics/Figure%203-12%20Longitudinal%20stability.jpg/full)
Picture is originally from
http://www.free-online-private-pilot-ground-school.com/Aeronautics.html
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 :)
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There you go, Stoney. I'd reiterate that the net pitching moment of the whole aircraft, if it isn't pitching, is ZERO.
Point taken. I intended to say that without the h-stab's vector, the plane would naturally have a negative pitching moment? More specifically, in straight and level flight, without the h-stab's vector, the plane would have a negative pitching moment?
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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.
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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
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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 :)
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Are there any planes in AH that have their CG ahead of their wing CL?
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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 :)
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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.
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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.
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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...
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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.
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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.
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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
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Nevermind...
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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...
(http://swatch.homeip.net/ACStabilityTailRemoval.PNG)
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.
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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...
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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.
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Well it only took five additional pages after the matter was put to rest. :D
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Kind of was wondering what everybody was spewing after The Man spoke................... :lol
Well it only took five additional pages after the matter was put to rest. :D
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Sometimes a picture is worth a thousand words...
... or in my case $1,000. (best guess for how much that picture cost me to learn how to do... :rolleyes:)
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Sometimes a picture is worth a thousand words...
... or in my case $1,000. (best guess for how much that picture cost me to learn how to do... :rolleyes:)
LOL :)
I can only think it, your drawing ability is way better than mine.
HiTech
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.