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Buzzsaw-
09-01-2005, 07:06 PM
Salute

I am sure everyone has noticed the changes in 4.01 as far as their individual favorite aircraft is concerned.

However, not all aircraft have been affected the same by the changes.

One of the areas where we see very different effects is in Pitch Stability. People have posted here, regarding the Spitfire and P-51.

Anyone can do this test.

Pick an aircraft, in Quick Mission Builder on the Crimea map at 1000 meters.

Trim the aircraft so it flys hands off level.

Wait for it to hit 450 kph.

Start a Ntrk recording, then apply a full 100% pitch movement (up) on your joystick. IMMEDIATELY center the stick after the movement, and takes your hands off it. Do not apply reverse elevator to correct the movement. People with force feedback joysticks may find it hard to do this test.

Allow the pitch ocillations which result to continue till they dampen out and the aircraft is stable again.

Stop the video recording, and play the track. Use your zoom key to give you a gunsight view so you can see the degree of the ocillations more clearly.

If you do this with a series of aircraft, you will see that different types have greater or less pitch ocillation effect, some with greater amplitude or duration.

Most of the time I counted 8 ocillations.

The aircraft which had the greatest amplitude of pitch ocillation and which took the longest time to dampen, were the heavier aircraft: For the Allies, the P-47, and for the Germans, the 190. The P-47 bounces back and forth more like a giant inflatable balloon rather than a 7 ton aircraft.

The aircraft which had the smallest ocillations were the slat equipped 109's, La5's/La7's and LaGG-3's. The amplitude of the ocillations were small, and they dampened out very quickly.

Now, correct me if I'm wrong, but basic physics tells me that a heavier aircraft, with a larger wingspan, is going to be inherently more stable than a lighter, smaller aircraft. It has more inertia, and requires more force to move. Plus the weight and larger wingspan will dampen any motions more quickly.

Yet in the game, the opposite applies to most smaller aircraft, in particular, slat equipped aircraft.

This is not always the case with smaller, non slat equipped aircraft. Planes such as the MiG-3 are very unstable, as are the Spitfires.

I have not yet done tests at lower speeds.

Comments?

Buzzsaw-
09-01-2005, 07:06 PM
Salute

I am sure everyone has noticed the changes in 4.01 as far as their individual favorite aircraft is concerned.

However, not all aircraft have been affected the same by the changes.

One of the areas where we see very different effects is in Pitch Stability. People have posted here, regarding the Spitfire and P-51.

Anyone can do this test.

Pick an aircraft, in Quick Mission Builder on the Crimea map at 1000 meters.

Trim the aircraft so it flys hands off level.

Wait for it to hit 450 kph.

Start a Ntrk recording, then apply a full 100% pitch movement (up) on your joystick. IMMEDIATELY center the stick after the movement, and takes your hands off it. Do not apply reverse elevator to correct the movement. People with force feedback joysticks may find it hard to do this test.

Allow the pitch ocillations which result to continue till they dampen out and the aircraft is stable again.

Stop the video recording, and play the track. Use your zoom key to give you a gunsight view so you can see the degree of the ocillations more clearly.

If you do this with a series of aircraft, you will see that different types have greater or less pitch ocillation effect, some with greater amplitude or duration.

Most of the time I counted 8 ocillations.

The aircraft which had the greatest amplitude of pitch ocillation and which took the longest time to dampen, were the heavier aircraft: For the Allies, the P-47, and for the Germans, the 190. The P-47 bounces back and forth more like a giant inflatable balloon rather than a 7 ton aircraft.

The aircraft which had the smallest ocillations were the slat equipped 109's, La5's/La7's and LaGG-3's. The amplitude of the ocillations were small, and they dampened out very quickly.

Now, correct me if I'm wrong, but basic physics tells me that a heavier aircraft, with a larger wingspan, is going to be inherently more stable than a lighter, smaller aircraft. It has more inertia, and requires more force to move. Plus the weight and larger wingspan will dampen any motions more quickly.

Yet in the game, the opposite applies to most smaller aircraft, in particular, slat equipped aircraft.

This is not always the case with smaller, non slat equipped aircraft. Planes such as the MiG-3 are very unstable, as are the Spitfires.

I have not yet done tests at lower speeds.

Comments?

FritzGryphon
09-01-2005, 07:23 PM
I'd imagine pitch oscillations are a matter of angular momentum versus the stabilizing force. During each oscillation, the stabilizers would negate some of the inertia, converting it to drag (like an oleo converts motion to heat). Weight, especially weight far from the CoG, would make this tendancy worse. Stabilization, in the form of wings, stabilizers, and other surfaces would reduce it.

Heavy planes with high wing loading and small stabilizers would be the most bouncy. Light aircraft with low wingloading and large stabilizers would be most stiff. Long nosed/tailed planes have weight further from the CoG, and therefore higher moment of inertia. High aspect ratio wings also would make it worse, low aspect ratio would be better.

If I had to guess, I'd say Ta-152 is the most porpoisy, because it's heavy, small stabilizers, long nose, long tail and high aspect ratio wing. P-47, Bf-110, FW190D, etc bad too.

Least porpoisy would probably be the Zero, I-16, P.11c, Gladiator, etc. Anything light, short, with big wings and tail surfaces.

Adding weight to a plane, in form of gunpods, bombs, droptanks, rockets would also increase porpoising. Especially if the weight is far below the CoG. For example, put gunpods on a 109K4, and the oscillating gets much worse.

ECV56_Rolf
09-01-2005, 09:10 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by FritzGryphon:

If I had to guess, I'd say Ta-152 is the most porpoisy, because it's heavy, small stabilizers, long nose, long tail and high aspect ratio wing.

</div></BLOCKQUOTE>

Excelente guessing! It´s unstable to the point of being useless.

On P47 is strong but not as negative as in the Ta. If all this fisics are rightly applied, this plane was useless.

p1ngu666
09-01-2005, 09:11 PM
the sideways movement would be better on the plane with more side area, probably would reduce the amount of yaw u could put on tho. the sideways moments would be like a car hitting the snowbank, it will pull u straight http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif
if done correctly, and u dont mind loosing hte rear bumper on your rally car http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

slats would help u avoid a stall, but the moving in and out quickly would perhaps upset the stability, as the lift generated would change quickly

LEBillfish
09-02-2005, 12:34 AM
No expert yet a few things strike me in considering this.....(edit..in re-reading I guess just agreeing with FritzGryphon)

First off, the plane though the elevator is doing the work would essentially pivot about the wing...Yet the wing would not likely aid in recovery

Second, the larger the wing the more effect it would have on working as a good pivot (ex. P47) yet in contrast a more narrow wing would make a poor pivot (slipping through the air some rather then being the solid point)

Third, the larger the horizontal stabilizer it should dampen the effect easier...

Fourth, weight obviously would have an effect...and it's distribution

Fifth, the ability of the engine to recoup torque would have an effect (how quick it recovers back to full steady power)

Sixth, distance from pivot to tail and nose

However, it would be the combination that determines the end effect...

So the worst case would be a plane with a large wing, small horizontal stabilizer, a heavy plane, weight in nose (so hence tail) vs. equally distributed, and a high H.P. engine.

Best case would be narrow wing that dampens (slats), large H. Stabilizer, light plane, weight more over wings or equally distributed, and a low H.P. engine.

In other words, you perform the maneuver and the plane pivots about the wing (considering slip (think high speed stall)) then snaps back, drag of the horizontal stabilizer "helping" to dampen it, affected by the ratio of weight in the tail and engine vs. over the wing, as the H.P. of the engine determines how violent the snap back is....

So a P47 with a great pivot (large wing little slip), average H. stabilizer (modest dampening), high weight and heavy nose so heavy tail, and high H.P. with great recovery would be a clear worst case.......While a A6M2 w/ great pivot, yet large H. Stabilizer, light weight and light tail and nose, low H.P. so slow recovery would be much better....

An ideal perhaps being the P38 with an average pivot, huge h. stabilizer, light tail and nose (engines at wing) and though high H.P. it close to the pivot....

Like I said, no aeronautical engineer yet just seems like common sense....

Sideways oscillation more H.P. to weight, vertical stabilizer and pivoting about the engine.

Ugly_Kid
09-02-2005, 02:27 AM
It's not primarily a factor of inertia, other factors play significantly more role. Centre of gravity position vs. neutral point, horizontal stab area vs. wing area. One important additional factor in a prop fighter with pulling prop is the propeller itself. In this type of configuration the prop tends to increase the instability, a pusher one stabilizes. So you can also guess size of prop and HP doing more or less. One could also add aeroelasticity as a factor, even stiffness of controls cables vs rods - name it. There is, however clear rule of thumb with which you could assess the stability by just glancing the aircraft.

Ugly_Kid
09-02-2005, 03:21 AM
Incidentally, as the aircraft in the game feature different force response to the stick and since the aircraft themselves have different elevator authority - yank the stick fully back and let it swing isn't telling a thing, since the starting point (for example, resulting angle of attack) differs...