Pratt & Whitney J-91 vs General Electric J-93 GE-1, GE-3, and GE-5 Questions

[KJ_Lesnick]

Normally, I would just look through my books but I don't have very much information about the J-91 other than it had a 9-stage compressor, a twin-stage turbine, a 7:1 pressure-ratio, a trans-sonic compressor, a 55-inch diameter, and that the J-58 was an 80% scaled down version with a higher pressure-ratio and a variable IGV to lower it's (the J-58's) pressure-ratio at high supersonic speeds, and that it had an afterburner that could burn either JP-4 or HEF-3 -- Plus I've heard conflicting data regarding the thrust output of the J-93's from 27,000 lbf to 31,500 lbf


I'm wondering the following questions...

1.) How the thrust levels of the J-91 using conventional fuel (JP-4 in combustor and afterburner) compared to the J-93 GE-1 using conventional fuel (JP-4 in combustor and afterburner)?

2.) How the thrust levels of the J-91 using conventional fuel (JP-4 in combustor and afterburner) compared to the J-93 GE-3 using conventional fuel (JP-4 in combustor and afterburner)?

3.) How the thrust levels of the J-91 using conventional fuel (JP-4 in combustor and afterburner) compared to the J-93 GE-3 using JP-6 (in both combustor and afterburner)?

4.) How the thrust levels of the J-91 using high-energy fuel in afterburner compared to the J-93 GE-1 using high energy fuel in the afterburner?

5.) How the thrust levels of the J-91 using high-energy fuel in afterburner compared to the J-93 GE-5 (GE-3 used only JP-4 or JP-6) using high-energy fuel in the afterburner?


KJ Lesnick

 

[F119Doctor]

I see that this thread never had a response, maybe there are some experts out there that can fill some of the blanks for you:

1. From what I have read, the J91 was designed for an airflow of 400 pound per second. The J58 was scaled down to approximately 300 pps, so with all else equal the J91 ratings would be ~30% higher than the J58

2. These are sea level ratings. At M3, inlet heating has raised the inlet temperature to 600F+. Limit for the J58 was 800F (427C). As the inlet temperature goes up, the effective rotor speed slows down. At M3.2 cruise, even though the J58 mechanical rotor speed was being held at 100%, the corrected rotor speed was 65%, just above idle airflow. At low corrected airflow and pressure ratio, the compressor is pushed toward stall, with the back end of the compressor being too small for those conditions. The inlet guide vanes going cambered and the mid compressor bleed provided the stall margin necessary. The genius of Ralph Abernathy was to capture the bleed flow and reintroduce the air into the engine flow in the afterburner. The bleed bypass and the IGV cambering occurred at approximately M2.2 where it had little effect on engine airflow to prevent causing the SR-71 inlet to unstart.

3. I don’t think the high energy fuels made much difference to these engine thrust levels, since you are limited by the amount of oxygen to burn. But you could go further since you didn’t need as much of the fuel to produce the same heat release. But there were a lot of impacts to the use of the boron ZIP fuels, and they were never pursued beyond experimental testing.

 

[sferrin]

I see that this thread never had a response, maybe there are some experts out there that can fill some of the blanks for you:

1. From what I have read, the J91 was designed for an airflow of 400 pound per second. The J58 was scaled down to approximately 300 pps, so with all else equal the J91 ratings would be ~30% higher than the J58

2. These are sea level ratings. At M3, inlet heating has raised the inlet temperature to 600F+. Limit for the J58 was 800F (427C). As the inlet temperature goes up, the effective rotor speed slows down. At M3.2 cruise, even though the J58 mechanical rotor speed was being held at 100%, the corrected rotor speed was 65%, just above idle airflow. At low corrected airflow and pressure ratio, the compressor is pushed toward stall, with the back end of the compressor being too small for those conditions. The inlet guide vanes going cambered and the mid compressor bleed provided the stall margin necessary. The genius of Ralph Abernathy was to capture the bleed flow and reintroduce the air into the engine flow in the afterburner. The bleed bypass and the can cambering occurred at approximately M2.2 where it had little effect on engine airflow to prevent causing the SR-71 inlet to unstart.

3. I don’t think the high energy fuels made much difference to these engine thrust levels, since you are limited by the amount of oxygen to burn. But you could go further since you didn’t need as much of the fuel to produce the same heat release. But there were a lot of impacts to the use of the boron ZIP fuels, and they were never pursued beyond experimental testing.

This book has a several pages on the J91. Doesn't say anything about the -7 anywhere else. Maybe it was the variant they wanted to use for the nuclear propulsion effort? The J89 appears to be the Allison rough equivalent to the J91.

 

[F119Doctor]

The Jack Connery’ book is a good read!