Author Topic: AH FM flaw or miss-conception? (Read 4968 times)

SFRT - Frenchy · « **on:** February 14, 2003, 08:28:19 PM »

I was teaching ground school to a bunch of private pilots yesterday. While explaining basic aerodynamics, it hit me on the head :

"In Aces High, when you shoot a guy and he looses his tail, the nose is going straight up"

Is it correct? In general aviation aircrafts (made a lil drawing), the CG is ahead of the Center of lift. So the plane has a tendancy to nose over. The vertical stab/ elevator is made to counter this moment by creating a down force.

If you shoot the tail off :

- You don't have this down force anymore, the nose wants to fall to the earth.

- The CG is even more foward, so the nose wants to nose over.

I know that Hitech is putting a lot of pride and work on his FM modelling ... Am I missing something or the FM in Aces High is not yet totaly based on "aerodynamics"? Maybe on Warbirds the CG is behind the Center of Lift, but I doubt it. I think maybe the moder jet fighters have them behind. As far as airliners, their CG is way ahead of their nose. (about 8ft on a 727).

capt. apathy · « **Reply #1 on:** February 14, 2003, 08:40:08 PM »

seems kinda inefficient.

I would think that if the cg was behind the wings and the tail lifting also you could have tail lift and all of your wing lift helping. so less drag for amount of lift = more lift and speed.

where with the cg forward and the tail pushing down you would you would have enough lift on the main wing to lift the weight of the plane plus whatever downward force is created by the tail. not only less lift but more drag for the amount of lift you do get.

why would they make them with the cg forward? visability (get the wing behind you) is the only thing that I can think of, is that it?

I have no idea as to where the cg is on warbirds, as I know little or nothing about aerodynamics other than the 'common sense' basics.

ra · « **Reply #2 on:** February 14, 2003, 08:59:54 PM »

Frenchy has it right. CG is forward so you can recover from stalls. Or else you would tail slide. Canard designs are nose heavy too, but the front wing is designed to stall before the rear wing, so nose pitches down in stall too.

ra

Ridge · « **Reply #3 on:** February 14, 2003, 09:09:29 PM »

Depends on aircraft, definately.

In my years of shooting down Japanese aircraft in CFS2, I have noticed that an A6M2 Zero will nosedive to a quick death in the shark infested water, while the D3A1 Val (which is modeled rather oddly, i think), when the tail is shot off, will aim skyward and fly in endless corkscrews for hours on end until you finally assign a wingman to blow his bellybutton outta the sky, as it "flies" soo erratically it is not in sights long enough to shoot at...

Regurge · « **Reply #4 on:** February 14, 2003, 09:29:41 PM »

Well according to this NASA Site what Frenchy said is desirable for stability. If this is the case with AH it doesnt make sense why most AC fall nose up, even bombers (which I assume you would want inerently stable).

The thing is we don't really know what happens to the tail when you loose it in AH. Visually it is gone but that is no garuantee that its mass and lift go to zero also.

Btw Frenchy you mean cg is 8ft ahead of center of lift on a 727?

GRUNHERZ · « **Reply #5 on:** February 15, 2003, 12:52:05 AM »

Normal airplanes with a aft CG will pitch up at slow speeds. When you loose tail in AH the plane pitches up volently and falls to earth nose high. This makes no sense because now the CG should be very very much forward as the loss of tail weight is more pronounced in CG calculation because of the long tail moments.

I think AH has this wrong.

Furious · « **Reply #6 on:** February 15, 2003, 04:02:33 AM »

trim an aircraft in level fight going about 200 mph. you need down trim to keep it level. once the tail is gone it will have to pitch up.

davidpt40 · « **Reply #7 on:** February 15, 2003, 05:08:30 AM »

Check this out. If you shoot the tail off an aircraft, that takes away the lift for the rear section of the fuselauge. Since that section of the aircraft is no longer producing lift, it is like adding extra weight and thus the nose pitches up.

Thats the only explanation I can think of. I think AH has it wrong.

Now check this out- A b17 was flying in formation and falling bombs tore off its horizontal stabilizers. The plane went into a unrecoverable dive and crashed. I have a sequence of pictures of it.

GRUNHERZ · « **Reply #8 on:** February 15, 2003, 06:46:55 AM »

Quote

Originally posted by Furious
trim an aircraft in level fight going about 200 mph. you need down trim to keep it level. once the tail is gone it will have to pitch up.

That doesnt explain why AH planes fall tail first. The engine is by far the heaviest and densest part of the plane - it would pull the nose down if the balancing tail weight was gone.

Seeker · « **Reply #9 on:** February 15, 2003, 07:41:53 AM »

Quote

Originally posted by GRUNHERZ
Normal airplanes with a aft CG will pitch up at slow speeds.

There are no normal aeroplanes with an aft G of G.

every non-canard aeroplane you'll ever see has a C of G forward of the MAC (Mean Aerodynamic Chord) line.

Check this thread

GRUNHERZ · « **Reply #10 on:** February 15, 2003, 07:53:50 AM »

Im saying if the CG is shifted too far aft for some reason.

Kweassa · « **Reply #11 on:** February 15, 2003, 10:37:17 AM »

This problem is often what I have thought, too.

In many other games, though not all of them can necessarily come within the levels of historic FM realism AH boasts, when the tail/aft section is fatally damaged, it depicts the aircraft going into a rapid, irrecoverable dive.

Come to think of it, in many WWII footages and gun cams I've seen, when a plane has been hit with a long burst, there's this typical smokey explosion with fumes and sometimes fire, and the plane noses down and plunges to the ground. I've never seen the instance like in AH before. (Though admittably I'm not really an adept when it comes to having seen many films or so..)

...

In my meeger opinion as a layman in aerophysics

, I think davidpt40 has got it right.

Due to the characteristic of how damage is delivered in AH, a damage to the aft section seems remove every influence the tail section control surfaces can inflict upon flight, instantly, abruptly, and cleanly. It's like a plane flies by, and then suddenly the aft stab section disappears into nowhere, and with it all the lift and influence it produced..

Frankly, I think it's a bit absurd seeing a plane instantly stop travelling forward(it almost does that..), nose up 90 degrees straight, and decend and crash on it's tail like a helicopter landing..

hitech · « **Reply #12 on:** February 15, 2003, 11:21:18 AM »

Misconception: You can move the cg behind the cp of the main wing and a plane will still be stable. You can not move it behind the total center of lift generated by both the tail and the wing.

Per your diagram both surfaces are producing up forces, but the tail is producing more torque than the main wing, hence it is still stable.

When the HStab is removed in AH all forces from it are removed from the flight model. Hence why they fly nose up do to physics.

HiTech

GRUNHERZ · « **Reply #13 on:** February 15, 2003, 11:49:59 AM »

Hitech but why does the AH plane keep falling nose high 90 degrees vertical? The engine is by far the greatest concentracion of weight in the plane - seems to me it should fall nose down after any wing/tail aerodynamic forces are negated by the 90 degree attitude of the falling tailess plane.

ra · « **Reply #14 on:** February 15, 2003, 01:00:00 PM »

Quote

Per your diagram both surfaces are producing up forces

I can't see how, it looks like the tail is counteracting the designed nose heaviness by creating negative lift. That is one of the attractions of a canard design, both wings produce lift, unlike a conventional design.

ra