Originally posted by Pyro
Kweassa, are you sure that's 45 degrees? Because that would put the Spit's peak roll rate at 23 degrees per second which is obviously not correct. It would take a Spit pilot 8 seconds to enter an immelman at 200 mph. I would be interested in seeing the whole report that that comes from, because something is being omitted or misrepresented.
No, it`s perfectly believable. The 45 degrees seems to be some kind of standard with British measurements, ie. what are the deflection, stick forces etc. required to obtain the same rolling velocity - it`s good for comparing aileron effectiveness.
The above graph is from a test with Spit I. tested against a 109E. I find it perfectly believable that with fabric ailerons it had such a poor roll rate. The stick force mentioned here ~56lbs, is about the maximum for a pilot, perhaps even a bit more, so it shows the absolute limits.
It`s also in line with the later Spit roll rate tests, ie. :
NACA 868 roll doc, unknown Spit type (British calculations?), 50 lbs : about 40 deg/sec at 400mph
NACA`smeasurement of Spit VA (metal ailerons) and others, 30 lbs stickforce:
It would show about 30 deg/sec at 400mph. Note however that only 30 lbs is used, somewhat lower than maximum.
Also there`s AVIA 6/10126, comparison of Mustang and Spit ailerons, mid-1942, so probably a Mk V or IX.
In order to obtain steady 45 degree/sec roll rate at 300 and 400mph with the Spit, the following deflection and stickforce required :
at 300mph, 8.45 degree aileron deflection required, and 24 lbs stickforce
at 400mph, 10.3 degree aileron deflection, requires no less than 71 lbs stickforce.
For comparison the Mustang required only 23 lbs stickforce for the same roll rate, at 400mph..
I guess the 400mph stickforce figure was extrapolated from the force curves at lower speeds. 71 lbs is way more than the typical 50 lbs used (not impossible, but you want to compare like with the like, not extra-strong pilots vs. avarage pilots), in fact the NACA`s report on flying characteristics of the Spitfire specifies that the pilot was unable to excert more than 40 lbs on the stick.
8.45 deg/sec translates to about 1/3 deflected ailerons (matches nicely with the Spit I graph).
It also mentions : "Most of the difference is due to the large loss of effectiveness of the Spitfire ailerons due to wing twist".
Similiarly, NACA 868 on pg 7 mentions in regard of effects of wing twist :
"A somewhat similiar analyis made by Morris and Morgan of Great Britiain shows that at an IAS of 400mph the aileron effectiveness of the British Spitfire aeroplane is reduced by about 65%, principally due to wing twist."
For comparison, similiar data for P-47C-1-RE was 31%.
So I guess, for early Spits about 20 deg/sec roll rate , and about 30-40 deg/sec roll rate for the later (metal aileron ones) at 400mph is approximiately correct.
The cause for that are :
a, High stick forces on the Spitfire at high speeds
b, Too flexible wings, wing twist reducing roll rate and leads to aileron reversal at relatively low airspeeds.
