1. Introduction:

...........Since the full throttle level speed tests were made on this aircraft with an Allison V.1710-F21R engine fitted, a replacement F21R has been fitted. Level speed and boost measurements were required at full throttle from ground level upwards with a modified induction manifold fitted. This manifold differs from the standard type normally fitted in that it has been redesigned with the flame trap deleted.

...........To obtain the difference in level speed performance and in the maximum boost obtainable at full throttle due to "cleaning-up" the induction manifold, repeat tests were made with a standard manifold fitted. Comparison with the previous results could not be made because of the change of engine.

2. Condition of aircraft relevant to tests.

....2.1 General. The general features of the aircraft as tested have been fully described in the 24th Part of this Report. For the first part of these tests a modified induction manifold was fitted, which had been redesigned with the flame trap removed. The standard manifold with flame traps was fitted during the latter half of the tests.

....2.2 Engine details and limitations. An Allison V.1710-F21R engine Nos. 6342/206646 was fitted for these tests, replacing the previous engine which failed during the course of the tests reported on in the above mentioned report. As mentioned in the latter report, the F21R is similar to the F3R except for the supercharger gear ratio which is lowered form 8.8:1 to 7.48:1 in the F21R, giving increased power at low altitude.

...........The operational limitations at the time of the tests for the F21R are given below:-

...........* For test purposes at this Establishment full throttle from ground level upwards was allowed for 5 minute periods.

....2.3 Loading. The tests were made at a take-off weight of 8,955 lb. representing the typical Service loads for the type.

3. Tests made.

...........Level speed measurments were made between 500 ft. and 15,000 ft. with the radiator exit duct closed (the intake scoop being sealed shut), using full throttle at all heights. The tests were first made with the modified induction manifold fitted and repeated with a standard manifold fitted.

4. Results of tests:

....The performance measurements have been corrected to standard atmospheric conditions and to 95% of the take-off weight viz. 8510 lb., by the methods given in Report No. A.& A.E.E./Res/170. A "strut correction" has been applied for the Kollsman type underwing strut mounted pressure head, the source of this correction being ARC report 6420.

....The full results of the level speed performance are given in Tables I and II and Fig. I. Briefly the results were:-

5. Discussion of results:

...........It will be seen from the results that fitting the modified induction manifold increases the maximum true airspeed by about 4 mph. and the maximum full throttle boost at ground level by about 0.8" of Hg.

...........When comparing these results with the standard manifold fitted and those given in the 24th part of this Report under similar conditions, it will be seen that the two sets of results agree reasonably well; and small changes could easily be ascribed to possible variations in power of the individual engines fitted.