AIRPLANE PERFORMANCES — HAMLIN AND SPENCELEY 431 



Performance characteristics represent those already attainable at the 

 present state of development. 



3. Ram-jet engine. — Of the four power plants considered, the ram- 

 jet represents the only hypothetical design under consideration, it being 

 the only type of propulsion not actually known to exist as a flight 

 article. As a basis for the theoretical engine performance, the analysis 

 presented in reference 1 is used herein. This type of power plant will 

 not operate at zero air speed, and consequently cannot take off. Aux- 

 iliary take-off means are assumed to launch the airplane and accelerate 

 to a flight speed of 350 miles per hour, at which time the ram-jet is 

 started. Since no logical engine output rating exists in this case, a unit 

 of a size suitable for 10,000-pound fighter is assiuned. 



Combustion temperatures of the order of 3,000° F. are assumed to be 

 structurally possible since moving parts do not exist to complicate the 

 problem. Successful operation in this regime has been demonstrated. 

 Already turbine buckets are operatmg in a 1,500° F. gas temperature. 

 Kerosene fuel to the engine is provided by a turbine- driven fuel pump. 



4. Rochet motor. — The rocket motor, being small and light, has been 

 chosen as a 9,000-pound thrust unit, which takes advantage of a high 

 thrust output without presenting impractical arrangement or installa- 

 tion problems. An example of actual application is the well-known 

 German Aie 163. For practical reasons an existing type of rocket 

 motor using a bipropellant fuel system has been chosen, leaving room 

 for considerable improvement with further research in the relatively 

 near future. 



The problem of supplying the fuel and oxidizer to the motor at high 

 pressure is solved by turbine-operated pumps using the same propel- 

 lants for power. 



5. Maximum thrust available (figs. 1-3). — Immediately apparent 

 is the fact that the conventionally powered airplane will have the low- 

 est maximum speed at all altitudes and, also, that it is essentially a low- 

 altitude power plant. Obviously, the ceiling of this airplane will be 

 inferior. Furthermore, the maximum speed limitation is absolute as 

 indicated by the fact that above GOO miles per hour the propulsive effi- 

 ciency limitation due to compressibility effects causes the thrust avail- 

 able practically to vanish. The slope of the curve indicates good accel- 

 eration characteristics in level flight below maximum speed and also 

 that climb characteristics will be relatively good. 



Considering the rocket airplane, maximum performance is obviously 

 superior under all conditions. Inasmuch as atmospheric pressure 

 variation is but a small percentage of the motor chamber pressure, the 

 small variation in thrust with altitude has been neglected. Air speed 

 has no effect upon thrust output. At low altitudes only does the 

 ram- jet offer competition in available thrust, but this is offset by the 

 fact that airplane drag at high air densities is also extremely high. 



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