The gallery above reproduces “Flash Performance of the P-51D Airplane Equipped with Acid Aniline Rocket Motor,” a test report of The Air Proving Ground Command at Eglin Field, Florida dated October 3, 1946. The object of the tests was to determine the operational suitability of the P-51D airplane equipped with an acid-aniline rocket motor. Two P-51D-25 airplanes, serial nos. 44-73099 and 44-74050, were used for this test. Both were standard production airplanes except for the rocket motor installation.
The rocket motor was located at the aft end of the coolant radiator exit duct. The rocket fuel was a mixture of 65% aniline and 35% furfuryl alcohol, by weight; the oxidizing agent was red fuming nitric acid containing 6½% excess nitrogen dioxide and 5% potassium nitrate by weight. These propellants, as well as compressed nitrogen to force the propellant through the system, were carried in specially designed, non-jettisonable external tanks suspended from the bomb racks. The left tank carried 330 lbs of acid; the right tank contained 125 lbs of the aniline-alcohol mixture, and 27 lbs of nitrogen at a pressure of 2000 psi. The total weight of the rocket system, including the propellants, was approximately 1,090 lbs.
The rocket motor could be used continuously or intermittently, but the combustion rate, and hence the thrust, could not be varied. The unit installed In airplane No. 44-73099 had a rated thrust of 1300 lbs, and the propellants carried were sufficient for approximately 1 minute of continuous operation; the unit installed in airplane no. 44-74050 was rated at 690 pounds thrust with a duration of approximately 2 minutes.
Development of the rocket-boosted Mustang was prompted by the appearance of significant numbers of German turbojet and rocket propelled fighters in late 1944, which caused considerable consternation among allied forces, which had no operational fighter of comparable performance. To meet the immediate and urgent needs of the European theatre, every effort was made to develop various devices, adaptable to fighter airplanes then in service, to provide “flash performance”—momentary performance greatly superior to that afforded by existing war emergency power ratings. Among the proposals that received active consideration were the application of nitrous oxide injection to internal combustion engines; the use of impulse jets, such as the Ford JB-2 engine; solid fuel rocket motors, of the type commonly used for JATO work; and liquid fuel rocket motors such as those described in the report above.
The acid-aniline rocket motor installation in the P-51D was developed in the spring of 1945 by North American Aviation, Inc., with the cooperation of the Aerojet Company, which manufactured the rocket motors. The first installation (airplane no. 44-73099) was ground-fired at Inglewood about a month before the end of the war with Germany; the second (airplane no. 44-74050) about two months later. Although the original need ceased to exist when Germany collapsed, this work was continued with a view of using jet-assisted fighters against the Japanese kamikaze, and in particular, against the rocket-propelled Baka.
The Pacific War came to an end, however, before rocket-on flights were made with these airplanes at The Air Proving Ground. The major portion of this project was thus conducted with the realization that the specific installation, as carried out in the prototype airplanes, would never be militarily employed; interest was focused on certain very general characteristics, knowledge of which would be useful in assessing the merits of future proposals for rocket assist in fighter airplanes.
Testing yielded the following conclusions:
- The jet-assisted P-51D airplanes equipped with acid-aniline rocket motors were not operationally suitable and were not useful for any military purpose.
- The dangers and difficulties inherent in the handling and use of nitric acid were excessive. It was extremely unlikely that it would ever be desirable to use rockets based on the acid-aniline combination in any aircraft applications.
- The drag caused by the external fuel and oxidizer tanks was not large enough to have important effects on the top speed of the airplane.
- The rearward CG shift caused by the rocket motor installation had a very serious and undesirable effect on the stability and handling characteristics of the airplane.
Staff at The Air Proving Ground recommended that no further attempts be made to develop acid-aniline rocket systems as auxiliary power for fighter airplanes.
To read the report in depth, please click through the gallery above; photo quality is not ideal but the best available at the time of writing.
All images from NARA Archives II, College Park, MD, RG 18