Get rid of tail heavy physics

[Stoney]

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?

[Ex-jazz]

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  

Hitech, you joking dolt!  

[PJ_Godzilla]

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  

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).

[Stoney]

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...

[hitech]

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

[Kazaa]

Even I knew that one HiTech.

[Stoney]

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.

[RTHolmes]

Question

Is the Scale 1 showing the CG weight figure OR less/more?

(Image removed from quote.)

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.

[PJ_Godzilla]

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.

[hitech]

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

[Ex-jazz]

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.

Picture is originally from
http://www.free-online-private-pilot-ground-school.com/Aeronautics.html

[Ex-jazz]

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?

 

[Wedge1126]

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.

[RTHolmes]

(Image removed from quote.)

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

[Stoney]

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?