Problem of the Month: May 2009

Just after the J-58 was redesigned to incorporate my recover bleed air concept, I was transferred to the new RL-10 rocket engine project in 1959. The RL-10 was derived from the "Suntan" project, a hydrogen fueled turbojet, intended to power a high Mach number reconnaissance plane, the CL-400 designed by Kelly Johnson at the Lockheed Skunkworks. Twenty years later I found out that the two projects, Suntan and J58, were actually competing with each other. Kelly canceled the project when he realized it would require hydrogen storage facilities around the world for refueling the CL-400. Dick Mulready, the Suntan Project Manager, was encouraged by the Air Force to convert the jet engine into a rocket engine, the RL10. The history is well documented in a book I helped Dick write. I recommend reading, "Advanced Engine Development at Pratt & Whitney," by Dick Mulready, SAE, 2001.

The CL-400

The Rl-10 rocket engine was unique in several ways:

1. it was the first liquid hydrogen - liquid oxygen fueled rocket engine,
2. it was the first rocket engine built by Pratt & Whitney
3. and it was and still is the only rocket engine without a gas generator. Liquid hydrogen is passed through the tubes that make up the RL10 rocket engine skirt. It comes out as a high pressure cold gas that is expanded through a turbine to drive the hydrogen and oxygen turbopumps. The engine has the highest specific impulse in the world because of the fuel and the lack of a gas generator.

The engine performance specification required that be within ± 2% of the target thrust and mixture ratio, hydrogen to oxygen. I was given the problem of designing a trim procedure for the mixture ratio and thrust controls. The objective was to:

1. ensure the engine was within target ranges,
2. that it would repeat are subsequent firings within the ranges and
3. that the trim procedure could be accomplished with a minimum propellant consumption.

Among the RL10 engineers there were many suggested trim procedures. Which one was best?

Problem of the Month: Apr 2009

In my patent on the "Recover Bleed Air Engine," I included a variable inlet guide vane. This would provide increased airflow and thrust at high Mach number. The Engineering Manager Bill Brown said, "Variable guide vanes are a General Electric fix. We will never put in a GE fix." A few months later Bill Brown added a variable inlet guide vane to the J-58 engine.

Bob Boyd was one of the first performance engineers on the J-58 and recently sent me an E-mail concerning the early applications of the engine plus a link to a French website that documents the J58 development program:

"The first Mach 3 engine design studies were for the JT-9 or J-91 which was aimed at the XB-70. But in the mid-50's, that project was still somewhat hazy and in 1956, the Navy showed some interest in a Mach 3 engine and the company initiated some design studies for what became the JT11/J58 which was smaller than the JT9. The Navy was interested in a strike aircraft which could cruise at Mach 2.5 with the ability to have short burst to Mach 3+. They initially wanted to fit it to the North American Rockwell A3J-1, which became the RA5-C Vigilante. I remember having some conversations with Frank Little at NAR Columbus on this application. Frank eventually came to work for us in Florida after Columbus failed to win in the VFAX (F-14) competition.

There were also two projects by Vought designated the V-418 and V-419 that grew out of this effort. These became the F-8U-3 Crusader III with the first to be fitted with a J75 and the second with a J58. But skyrocketing costs caused the Navy to scale back its efforts and only the J75 powered F-8U-3 came out of this project."

There is a French web site that appears to have a pretty good synopsis of the engine development (in English).

Problem of the Month: Mar 2009

In late 1957 I was asked to transfer to a black secret project, the J58 engine, which would be tested at a new facility in the Florida Everglades near Lake Okeechobee. As my wife was pregnant I could not leave until the next spring so I was asked to create a computer program, a thermodynamic simulation. I believe this was the very first engine computer simulation. I was assigned a computer analyst to do the programming. My job was to formulate the model such that it was mirror the performance of each of the engine components. To do this I had to study and understand how component would work at the target speed of Mach 3.0. I concluded that the engine would never make it as the compressor would be deep in surge and the afterburner would melt for lack of cooling. My solution is described in my patent on the "Recover Bleed Air" engine, dated October 1958. It was called the "RBA" engine until Bill Brown, the Engineering Manager, discovered that those are my initials. The rest of the story I relate in my presentation to the University of Tennessee which you may view through this link.

Problem of the Month: Feb 2009

In May of 1955 I was released from active duty on destroyers and reported to work at Pratt & Whitney Aircraft in East Hartford, Connecticut. I was assigned to the J-75 Engine Performance Group. At that time the J-75 was the most advanced and most powerful engine in the world. The head of the group, Norm Cotter, held weekly group meetings. At my first meeting Norm explained that the J-75 engine performance, fuel consumption, had degraded from the levels attained during the last winter. Exactly one year later Norm gave the same speech. Perhaps I was the only one that noted that as it was my anniversary.

I had just completed my first course in statistics so I decided to correlate everything that might effect fuel consumption including ambient temperature, and pressure, and humidity. Gas Turbine fuel consumption is corrected for variations in ambient temperature by a "theta" correction. Theta is the ratio of absolute temperature to standard absolute temperature, (the equivalent of 59 degrees Fahrenheit). Fuel consumption is corrected dividing it by the square root of theta. This means that if you plot fuel consumption against thrust, the data from cold days should plot on top of data from hot days. Therefore I was surprised to find a correlation between corrected fuel consumption and ambient temperature. On log-log paper the plot formed a straight line with a slope of 0.18. This meant the theta correction was wrong. The question was why? After digging through the theory of Buckingham Pi corrections, the source for the theta correction, I found out the square of theta eliminated Mach number effects on fuel consumption. Further research led me to the Gas Tables published by MIT. I found if I plotted the specific heat of air against temperature on log-log paper it had a slope of 0.18. The true correction should be theta raised to the 0.68 power, not 0.5 power.

Pratt & Whitney immediately adopted the new correction and later all the jet engine companies in the world followed suit.