Speed graphs for Spitfire and Hurricane

[IvanK]

In the various Spit Speed tests in the Nat archives I actually came across one report that actually achieved better speed at 2800RPM than 3000RPM. It was so unusual that it was cause for comment in the report. I will try and hunt it down.

Edit Found a ref to this phenomenon in Hurricane I ROTOL trials. In the Hurricane test they specifically tested for for this phenomenon as it had occurred on Spit I ROTOL trials on aircraft N3171 in AAE/692. This reference in the Hurricane report AVIA 16/681 Hurricane I ROTOL Trials.

Here is the relevant page in the Hurricane tests that references it:



EDIT 2
Here is the text from the N3171 report:

4.2 Controlling R.P.M. Speed tests were made at three heights below full throttle height with the boost pressure maintained constant at 6¼ lb. per sq.inch whilst the R.P.M. was varied over a range from 2600 to 3000.

The results show that the maximum level speed is reached with the airscrew controlling at 2800 engine r.p.m. On increasing the r.p.m. to 3000 the speed was reduced, on the average by 4 m.p.h.

For the particular engine fitted there is a reduction of 17 b.h.p. at constant boost (+6¼ lb) when the r.p.m. are increased from 2800 to 3000. The loss of speed is therefore probably due to the loss of power accompanied by a slight decrease in airscrew efficiency. The matter is being further investigated by Messrs.Rolls-Royce and Messrs.Rotols. It will be noted that reducing the R.P.M. from 3000 to 2800 lowers the full throttle height by 2000 feet.

Conclusions.

1.This aeroplane has a much better take-off and climbs faster than other Spitfires fitted with wooden fixed pitch or metal two pitch airscrews.

2.There is a drop of 13 m.p.h in maximum level speed compared with the 2-pitch airscrew aeroplane but of this, 8 m.p.h. can be attributed to sources other than the airscrew.

3. Below full throttle height an increase in speed of about 4 m.p.h. can be attained by controlling the engine R.P.M. at 2800 instead of 3000.

4.The limiting diving speed can be reached much more rapidly with this aeroplane than with Spitfires fitted with fixed pitch wooden and 2-pitch metal airscrews.

This text cut and paste coming from here:

http://www.spitfireperformance.com/n3171.html