Roll rates

[bigjava]

i try tipying in google some keywords looking for p-38 roll rate original documents and details and Reading the result i say to myself:
"heheh  Find it!!"

try to imagine my face opening that links.....


link p-38 Chart

DAMNED NET!!!:rolleyes:

[Bullethead]

Fariz said:

The p38 was a large heavy fighter not suited  for quick snap or slam-bang maneuvers, and had a particularly slow initila responce  in roll due to a high laterl inertial characteristic

This of course makes perfect sense due to the heavy engines out some distance from the axis of rotation.  But I'm curious to know if there are any reports of this problem also coming into effect when trying to STOP a roll.  Inertia isn't something you get rid of, you can only overcome it.  So once you got the P38 rolling, you'd think it would also have taken a while to get it to stop, forcing the pilots to "pull some lead" on their desired stopping roll angle.

I know a guy who was shot down in a P38 over North Africa.  I'll see if I can get anything from him on this subject.

[F4UDOA]

Here is the P-38L with boost.



And here is the original with others

[MrCoffee]

>The p38 was a large heavy fighter not suited for quick snap or
>slam-bang maneuvers, and had a particularly slow initila
>responce in roll due to a high laterl inertial characteristic

You mean "polar of moment". Much of the weight displaced on a P-38 is not close to its center of gravity but located outwards such as with the dual engines and the twin tail booms and the heavy nose mounted guns and ammo. In normal single engine fighters, you have the center fusalage then the engine up front with maybe fuel tanks at the wing roots. Still weight is displaced down the centerline of the fusalage. Nevertheless in the P-38, the tail booms weight is marginal compared to the weight of the two Allison Engines though the Turbos and exhaust ducting and radiators are located there (oil cooler upfront below prop). Then the landing gear as well, front-aft.

[F4UDOA]

Here is some F4U roll data.



The 400MPH figure for the F4U is a limit of 1/4 stick throw at 400MPH because of an aileron overbalance/Vibration.

Annecdotally from AHT "you couldn't really feel it unless you push hard against the stops". What the actual roll rate is with a full throw I have no idea.

[Fariz]

Originally posted by ramzey
data is better word?

No, chart is ok. Just not everything can be shown by chart. The second one by F4UDOA is from the same source, America 100 thousand. Just what I described above is not reflected by charts, they gave some "average" rollrate speed (degrees per second/alt). To reflect inertia you need (degrees/seconds) for each measured alt. Have not seen such charts.

[straffo]

you can ask here Pyro : http://pub131.ezboard.com/ballboutwarfare

[F4UDOA]

What do you mean Fariz?

How else can you measure roll? Unless your saying that there is a deley from the time you move the control to the time the A/C starts rolling and then you start timing the roll?

I think that is roll inertia and is included in the 360 degree roll time already especially in the P-38. Otherwise you would have a deley that I don't think is realistic. Somewhat like WB3 ala MushBirds.

[gripen]

It appears that there is a problem with older NACA roll rate charts. It seems that they measured peak roll rate at one speed and then calculated chart using this rate and controll force limits. That P-40 roll rate graph in the AHT is a good example; wing twist and spongines of the controll system does not show up in the chart. Reports showing this can be found from here (P-36, P-40, Spit and Hurri report vs P-40F report, also P-63 report shows this).

RAE and NACA measured peak roll rate using special equipment like gyro etc. This means that differences in the acceleration or deacceleration of the roll does not show up in the charts.

gripen

[Fariz]

Originally posted by F4UDOA
What do you mean Fariz?

How else can you measure roll? Unless your saying that there is a deley from the time you move the control to the time the A/C starts rolling and then you start timing the roll?

I think that is roll inertia and is included in the 360 degree roll time already especially in the P-38. Otherwise you would have a deley that I don't think is realistic. Somewhat like WB3 ala MushBirds.

That is what I mean, it is some "relactunce" in plane responce. At most planes it will be neglectable, but for some shall play role.

Normally roll numbers measure time for a full roll then devide it to 360, and give degrees per second. But this way initial responce time can't be reflected. To reflect it you need to show how many time it took plane to take 45 degreed, then how many to get 90 degrees etc. I have not seen such data.

I am not advocating any way of modeling planes, because my knowledge in this field is very limitted. It was asked if there is something which may help them to model roll, I posted some info.

[OIO]

heh, fly with force feedback stick. That imo simulates the inertia to counter the current roll rate of the plane.

As always, the trick is in the wrist.



*hides under a rock*

[Batz]

It appears that there is a problem with older NACA roll rate charts. It seems that they measured peak roll rate at one speed and then calculated chart using this rate and controll force limits. That P-40 roll rate graph in the AHT is a good example; wing twist and spongines of the controll system does not show up in the chart. Reports showing this can be found from here (P-36, P-40, Spit and Hurri report vs P-40F report, also P-63 report shows this).

RAE and NACA measured peak roll rate using special equipment like gyro etc. This means that differences in the acceleration or deacceleration of the roll does not show up in the charts.

gripen

What he said. Unless you belive that p40 rolled at 160dps at 360mph.

The 109e should get re-examined. If theres any plane that rolls worse in ah I have found it.

[F4UDOA]

Batz,

I have read annecdotal reports of the 109 out rolling the P-51 at approximately 200MPH. Your chart would seem to support that showing a 4 sec 90 DPS roll at 200MPH then dropping to 8 econds at 300mph. However the 300MPH roll is worse than the current AH model and the Spitfire is even worse than the 109.

Do you have the rest of that report? I think it is on the Spit test web site.

[Batz]

yep its on the spit web site but from tests done with the ah 109e-4 it appeared to roll to slow above 300mph. Test of the mk 1 appeared that the spit rolled a bit to good.

I use word like appeared because I found it difficult to test roll accurately. I think wilbuz and urchin tested it as well and came to a similiar conclusion. It may very well be correct in ah.

I am only talking about the 109 emil.

[Zigrat]

Hey pyro,
How do you model flight? How do you represent aerodynamic forces and moments.... and how did you get the moments of inertia necessary for the dynamical equations, I have found information on more modern airplanes (see NASA CR-2144: Aircraft Handling Qualities Data
Linearized aero data for the NT-33A, F-104A, F-4C, X-15, HL-10, Jetstar, CV-880M, B-747, C-5A, and XB-70.) but I have no idea how you would get this type of info for these old airplanes. My guess is you probably have to use the DATCOM (The USAF Stability and Control Digital Datcom. AFFDL-TR-79-3032 ) but still I don't think you can calculate moment of inertia stuff from that. I guess it wouldnt be that hard if you knew individual airplane component weights (ie how much does the wing weigh, the vstab and h stab, fuselage, engine,  etcera) but again I have never seen this data listed for ww2 airplanes. I am sure you have good sources though

Well I guess we need to know what input information you need. Like has been said, simply maximum roll rate information isn't gonna help that much since air combat is dynamic, not steady state