Position error and performance trials have been completed on this aircraft at a take-off weight of 9200 lb. without external bombs or fuel fitted.

      The principal results are as follows :-

1.   Climb

1.  Introduction.

      Performance trials were required on this aircraft which is fitted with a Packard Merlin V.1650-3. This Report gives the results of the determination of the Position Error Correction, all-out level and cruising level speed performance, and combat and normal rating climb performance with no external bombs, fuel tanks, etc. Provisional information on these results was forwarded to MAP by letter dated 29th March 1944. Tests made since the despatch of that letter have resulted in a slight modification of the climb performance results.

      Check performance trials will be made on this aircraft when carrying 2 - 75 gallon drop tanks and also when carrying 2 - 500 lb. bombs.

2.  Condition of aircraft relevant to tests.

      2.1  General. Reference may be made to photographs appended.

      Chief external features:-

      Four .5" machine guns, ports sealed; ejection chutes sealed.
      Multi ejector exhaust manifolds, the shroud-plates of which were removed for the tests to prevent damgage to the ignition harness in the event of a stub burning out.
      Air intake under nose just aft of spinner; an ice guard was fitted half way along the air scoop.
      Radiator under fuselage in usual position for Mustang aircraft. In accordance with recommendations from the USA a stop was fitted which prevented the radiator flap from closing fully (clearance of flap when close: 7¼ ins).
      Aerial mast, no external aerials.
      IFF aerial, 14" long, under starboard wind.

      2.2  Pitot-static head details. Details of the normal, underwing pitot-static head, are given in Fig.1.

      2.3  Loading. The tests were made at TSL conditions, i.e. at a take-off weight of 9200 lb. with the C.G. at 99.8" aft of the axis of reference, undercarriage down.

      2.4  Engine details and limitations. The engine is a Packard Merlin V.1650-3, Maker's No.V.300740, and is fitted with a Bendix pressure carburettor. Reduction gear ratio 0.479.

          The following are the relevant limitations:

      3.1  The position error in level flight, flaps and undercarriage up, over a speed range 120 - 360 mph ASI, was determined by the aneroid method.

      3.2  Performance on the climb was measured:

      (a)  at normal rating to 4000 ft. changing supercharger gear at a manifold pressure of 39 ins. of Mercury in MS gear (about 22000 ft.)

      (b)  at combat rating to 42000 ft. changing supercharger hear at a manifold pressure of 53 ins. of mercury in MS gear (about 17500 ft.)

             The best gear change altitude was dertermined in each case by separate MS and FS gear climbs and the best climbing speeds used were determined from partial climbs.

      3.3  All-out level speeds were measured from 2000 to 20000 ft. in MS gear and from 20000 to 38000 ft. in MS gear.

             Maximum cruising level speeds were measured from 4000 to 26000 ft. in MS and from 24000 to 37000 ft. in FS gear.

4.  Results.

      4.1  All performance results have been corrected to standard ICAN atmospheric conditions and the level speeds to 95% of the take-off weight, by the methods of Report No. A. &A.E.E./Res/170. The compressibility correction applied has been calculated using the methods of Report No. A. &A.E.E./Res/147 and Addenda. A "strut" correction based on ARC Report No.6420 had been applied. A supercharger constant of 0.002 has been used.

      4.2  The results are given in Tables I to IV and Figs. 2 to 5. Maximum cruising level speeds above 33,000 ft. are not given owing to inconsistencies thought to be caused by variations of propeller efficiencies due to high propeller-tip Mach Nos. This is being investigated and will be reported later.

5.  Discussion of Results.

      5.1  The PEC on this aircraft is less negative than the mean value of PEC's on five other aircraft. This might be due to a slight difference in the pitot head incidence relative to the mainplane.

      5.2  The following table gives comparison of the performance results with those obtained on a Mustang III by North American Inc. (Report No.NA.5798). The combat climbs and all-out level speeds were made by the firm with the boost control adjusted to give a maximum of 61" of mercury. For comparison, the corresponding results determined at this Establishment are quoted for this value of the manifold pressure.

             The actual take-off weights on test were 9200 lb. (A. & A.E.E.) and 8460 lb. (NA) but the N.A. results below have been corrected to 9200 lb.

             There is fairly good agreement between level speed results, the N.A. Report being 2 to 4% optimistic compared with the present results. On the climb the maximum difference is 8% although on the whole the agreement is quite reasonable.

6.  Conclusions.

      6.1  The maximum rates of climb if this aircraft are as follows :-

      6.2  The maximum all-out level speeds are:

             424 mph at 15,500 ft., in MS gear and
             450 mph at 28,000 ft., in FS gear

             The maximum cruising speed in MS gear is 406 mph at 20600 ft.

7.  Further developments.

             Cooling and fuel consumption trials are in progress. Repeat performance trials will be made with two 75 gallon drop tanks fitted, and also with two 500 lb. bombs. The effect of engine RPM on level speed will be investigated.