NACA Report No. 103

Summary

NACA Report No. 103 provides the result of a complete performance test of a 300 hp (224 kW) Hispano-Suiza 8F engine performed by the Bureau of Standards at the request of NACA. The testing was performed in the Bureau of Standards altitude chamber. The engine used in these tests was assembled by the Engineering Division at McCook Field and subjected to the standard dynamometer test for operation at ground level, then shipped to the Bureau of Standards and mounted in the altitude chamber without overhaul. After the altitude test it was returned to McCook Field for such flight tests as might be desired.

The folIowing tests were made:

1. a fuIl-power run at ground altitude at speeds from 1,400 to 2,200 rpm;
2. an altitude power run at full throttle and at speeds of 1,600 and 1,800 rpm from ground level to 25,000 feet in steps of 5,000 feet;
3. propeller load runs, in which the dynamometer load was adjusted to produce approximately the engine load that would be imposed by the propeller at speeds from 1,400 to 1,S00 rpm, at aItitudes of 5,000, 10,000, and 15,000 feet;
4. friction horsepower runs at the ground and at 15,000 feet.

Results:

1. maximum sea-level brake horsepower was 352 (262 kW) at 2,200 rpm;
2. maximum brake mean effective pressure of 128 lb/in³ at about 1,600 rpm;
3. the mechanicaI efbiency varies from 88 to 83% from speeds of 1,400 rpm to 2,200 rpm;
4. brake thermal efficiency, based on the lower calorific value of the, fuel maintains a constant value of 26% over the same range;
5. due to lack of an adequate aItitude control on the carburetor, the mixture became extremely rich at aItitudes of 20,000 feet and higher. BeIow this altitude, where the air/fuel ratio could be adjusted to give minimum fuel consumption consistent with maximum brake horsepower, the brake horsepower and brake mean effective pressure were found to bear a straight-line relation to carburetor air density;
6. at 1,800 rpm and at a density of 0.040 pounds/ft³, the brake horsepower is about 42% of that at the ground;
7. at 1,800 rpm and at a density of 0.040 pounds/ft³, the indicated horsepower is about 47% of that at the ground.

Conclusions

The test shows the inadequacy of the carburetor altitude control of air-fuel ratio for heights above 20,000 feet. It also shows how the relative importance of high mechanical increases with altitude.