NACA Roll Rate Chart: Is it accurate?

[wells]

From the looks of it, things like adverse yaw were not accounted for?  The dihedral would play a large part in that.  For example, a 10 degree yaw with 5 degrees of dihedral could take 1 whole degree off the helix angle in the roll (0.017 rad).  Based on that, the results could be anywhere from 25-35% off the mark.  Also, look at the slope of the lines, from the minimum speed to that where maximum roll rate occurs.  Ideally, it should be linear with speed.  The fw-190 is very close.  The Typhoon isn't, recording a roll rate that is 86% of that expected at 250 mph.  I suppose that stretching of control cable could explain that, but it still starts off with a low helix angle.  Why would that be?  It could be due to the wing being 50% thicker than most wings, meaning that the upper and lower surfaces of the wing converge at the trailing edge at a steeper angle.  The steeper that angle is, the closer the airflow is to separating from that part of the wing.  This means the ailerons can't deflect as much without stalling.  On the plus side, the thick wing should give lots of stall warning as the separation point gradually creeps forward on the wing as the angle of attack is increased.

[juzz]

wells, this page is the start of the description of the flight test procedure: http://naca.larc.nasa.gov/reports/1947/naca-report-868/index.cgi?page11.gif

This chart shows the comparison of helix angles(the next page is the angular velocity comparison): http://naca.larc.nasa.gov/reports/1947/naca-report-868/index.cgi?page41.gif

Pages 39 and 40 describe the purpose of including the charts. And on page 76 there is a chart showing details of the aileron setups for the tested a/c.

[wells]

From pg 40 of the report...pretty much sums it up!

 

The wide variations in the performance of airplanes having Frise ailerons may be an indication of the well-known fact that Frise ailerons are extremely sensitive to each of a large number of design parameters.

[funkedup]

 

the chart is right on. I am sad to admit, but Spitfire rolls to fast in AcesHigh, while 190 rolls to slow

This was not written by me.

To the amazinhunk who wrote it:
I hope HTC logged your IP and that they ban your ass.
At least learn to spell in English before trying to impersonate me.
And I have been saying the Spit rolls too fast since long before many of the current crop of Luftwhiners even knew about this sim, so it's not like you've accomplished anything.

[Jekyll]

I don't think its absolute rollrate performance that is troubling the 190 drivers.  Does it really matter if the 190 is 8% too slow in roll at such and such speed?  Probably not.

It's the relative roll performance which appears to be the problem.  I've heard it suggested that the 190 rollrate has been turned down to avoid warp-rolling issues - it just rolls too durn fast in real life for our imperfect internet to keep up with.

So just to show the postion, here is extracted data from the same rollrate chart, expressed in a different way.

I took the NACA and AH data for planeset comparison, basically 190 -v- the world.  Worked out the rollrate differences based on NACA data, the rollrate differences based on AH data and subtracted one from the other to find the difference in performance.

   

So, for example, look at the Spitfire at 225 IAS.  The difference is roughly -23 degrees.  That means that at that speed the Fw190 rolls 23 degrees/sec too slowly AS COMPARED TO THE SPITFIRE.

Not absolute roll performance.. relative roll performance.

Now, I don't know whether the original NACA report is accurate: for all I know the NACA team might have been sitting on a shady veranda, sipping Margueritas when they should have been out testing aircraft.  So the value of the comparison is going to be affected by the reliability of the NACA source material.

As you can see, I haven't bothered to compare all the AH planes.  Frankly, it bores me to even attempt it.  I'd have to re-test the P51B, perhaps the P47D-11 etc and I just dont have the time to do so.

I've already posted the link to the excel spreadsheet containing all the test results.  If anyone else wants to do the tests, be my guest.

But I'll say one thing before I go:  If this roll performance issue had been one which disadvantaged the P51, the Spitfire, the P47 or (God forbid) the F4U, it would have been fixed months ago.  



[This message has been edited by Jekyll (edited 06-05-2001).]

[MANDOBLE]

Again, an excelent graph Jekyll <S>!

[funkedup]

 

If this roll performance issue had been one which disadvantaged the P51, the Spitfire, the P47 or (God forbid) the F4U, it would have been fixed months ago.

You really believe that BS?