Mar 302012
 

Avid students of the history of jet propulsion may be aware of “Jake’s Jeep,” a ducted-fan engine similar to the Campini design that was developed at NACA Langley by Eastman Jacobs and Albert E. Sherman from 1941 to 1943 before being abandoned in favor of superior turbojet technology imported from England. Even a dedicated research airplane was proposed in July 1942 to test the engine and research the frontiers of transonic flight; a detailed history of this ill-fated program is available on the NASA History Program Office site.

Less well known is another series of proposals made by a young assistant aeronautical engineer named Richard C. Scherrer at the NACA Ames Aeronautical Laboratory from 1942 to 1943 to develop both a jet engine and a research aircraft to test it. Likely unaware of the work being done at Langley, let alone of the top secret acquisition of the Whittle engine by Air Corps Chief Hap Arnold in the spring of 1941, Dick Scherrer never managed to acquire the necessary support to continue his jet propulsion research. Nonetheless, his efforts are an interesting side note in the history of jet engine development in the United States and reflect the intelligence and initiative of an engineer who would go on to have a long and productive career in aerospace.

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First page of Richard C. Scherrer's initial proposal memo
A supportive letter from Lewis A. Rodert
Cover memo to Scherrer's 4/14/43 jet propulsion system proposal
First page of Scherrer's critique of British turbojet engines
Rodert's 8/19/43 letter to Jack Parsons
Cover memo dated 9/13/43 to Scherrer's jet airplane proposal

Scherrer’s first known memorandum, dated October 31, 1942, called for the design and test of a jet propelled airplane based on a constant-pressure combustion cycle. The main objects were the complete aerodynamic and thermodynamic investigation of the airplane; construction and test of the components of the system; and the installation and test of the system in a wing-nacelle mock-up.

The jet propulsion system proposed by Scherrer appears to have been a variation of the Campini concept, in which propelling air was taken at the stagnation point on the wing leading edge and compressed by dual centrifugal pumps. After the air was compressed, it was expanded to a large static pressure in the combustion chamber and fuel was injected and ignited. Internal cooling air was taken through the nose of the test nacelle, passed over the cylinders of the starting/driving engine and then aft around the compressors and combustion chamber. The internal air was drawn into the exhaust stream by the ejector action of the jet. Compressors were to be driven either by a conventional aircraft engine or a gas turbine located between the combustion chamber and the nozzle. A diagram of the system (“Fig. 2”) is shown at the end of the memo in the gallery above.

On April 14, 1943, Scherrer wrote up a “Description of a Proposed Jet Propulsion System” for which he sought a patent. (None has been found in the Google Patent database, though a fascinating one from much later in his career is available). This was a further refinement of his previous proposal, a combination of a gas turbine-compressor unit, operating on a continuous combustion cycle, with a Meredith cycle. The purpose of the combination was to make possible the use of high temperature combustion and still use a gas turbine drive for the compressor. The essential parts of the system were a compressor (centrifugal or axial); combustion chamber; heat exchanger; turbine wheel; and nozzles. Scherrer sent the memo to Donald H. Wood, Chief of Aerodynamics at NACA Ames; it was accompanied by a supportive letter from Lewis A. Rodert, presumably Scherrer’s immediate supervisor.

This was followed on August 15, 1943 by a memo from Scherrer to Jack Parsons, Chief of the Flight Research Division at Ames, commenting on the Halford and Whittle jet propulsion units observed in England by NACA personnel in October of 1942 and July of 1943. In the memo, Scherrer emphasized that the basic designs of the British units were similar to what he had proposed in February 1943 (presumably the same engine described in the April 14 memo summarized above). He also highlighted several weaknesses of the British designs, such as the burner combustion-chamber combination and turbine wheel employed. Scherrer appears to have believed that he could produce a superior engine if given the necessary resources. Rodert provided another letter of endorsement with the memo, but no funding was forthcoming.

The final and most interesting Scherrer memo dates from September 13, 1943; it proposed the design, construction and test of a jet-propulsion airplane able to operate at high mach numbers in order to compare  the calculated and actual performance of both the jet unit and the airplane under these flight conditions. The purposes of the project were as follows:

  1. Compare the calculated and actual performance of a jet-propelled airplane and its components.
  2. Apply and check the results of contemporary aerodynamic research at high Mach numbers.
  3. Make stability and control studies in flight at high Mach numbers.
  4. Provide a basis for future research by determining what problems were actually critical in the design of a jet-propelled airplanes and their components.
  5. Obtain data on which future designs could be based.

Diagram of Richard C. Scherrer’s proposed jet engine dating from September 13, 1943.

Scherrer then provided a detailed description of the test procedure and equipment for the project. The aircraft was a simple tailless design with a thick, unswept, low aspect ratio wing. The unusual planform was dictated by structural as well as aerodynamic considerations. Scherrer planned to use boundary layer control at two locations on the wing—at the leading edge upper surface and in the 50-60% chord region to prevent separation at the landing condition. The fuselage was of circular cross section with a nose intake. The simple basic form of the airplane was considered desirable in order to eliminate all possible sources of shock waves. It had a span of 20 ft, a length of 26 ft, a wing area of 270 ft², a gross weight of 5,000 lbs, and an estimated maximum speed of 500 mph at 30,000 ft.

Three-view of the Scherrer Jet Propulsion Airplane designed to reach 500 mph at 30,000 ft.

In his concluding remarks, Scherrer noted that the amount of flight research that had been conducted at high mach numbers was negligible and that which had been done was confined to the curing of compressibility troubles on conventional aircraft. He argued that the proposed project was important as a check on laboratory tests and would prove to be a vital link in the existing accelerated development of high performance, high speed aircraft.

Postscript

It is interesting to note that Dick Scherrer graduated from the University of Washington with a BSC in Aeronautical Engineering in 1942 and joined the Ames Aeronautical Laboratory that same year; by the fall, he had submitted his first proposal to build a jet aircraft. From early on, it is obvious that Scherrer was an innovative and ambitious engineer looking to break new ground in his chosen field. While Scherrer failed to get his jet engine and research aircraft off the drawing board, he would go on to have a long and productive career in the aerospace industry, as his Wikipedia entry attests. Scherrer stayed at Ames until 1959 when he joined Lockheed-California, where he played a key role in the development of both the P-3 Orion and S-3 Viking aircraft. He also oversaw wide range of military aircraft systems and study proposals, including transonic VTOL attack and covert turbofan prototypes, rotary wing aircraft studies, advanced fighters, attack aircraft, surveillance and ASW patrol aircraft systems. He even designed a number of rides for the Disneyland theme park as an independent engineering design consultant between 1955 and 1965. However, Scherrer is most well known for his pioneering work on revolutionary stealth aircraft designs with extremely low radar cross sections that led to the Lockheed F-117 Nighthawk and Northrop Grumman B-2 Spirit. By any measure, Dick Scherrer has left a remarkable legacy in the history of aerospace.

All images from NARA Pacific Region, San Bruno, CA, RG 255

High Resolution Drawings

For only 99¢, readers may purchase a high resolution DRM-free PDF download of the jet engine diagram (3000 x 1865 pixels) and three-view drawing (3000 x 2346 pixels) shown immediately above through our shop on Gumroad.com.

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