Posts: 6149
Joined: Fri Sep 17, 1999 7:43 am

Turbojets On "White Knight"

Tue Nov 09, 2004 9:23 am


It says the Spaceship One carrier uses J85s to climb to 53,000 ft. Did they choose turbojets (instead of fans) because of better high-altitude performance? If so, is it just the afterburner that makes it perform better, or does the J85 itself outperform a comparable fan?
Posts: 885
Joined: Wed Jun 30, 1999 9:23 am

RE: Turbojets On "White Knight"

Tue Nov 09, 2004 9:51 am

I believe the J85-GE-5's were chosen because they were available and they could get them at a very low price. A comparable turbofan would be something like A TF-731 or a PWC PW-300, both vastly more expensive engines even on the used market, and much heavier as well. I do remember watching the documentary and seeing an F-5 or T-38 trainer in the background sans engines, so I it's possible they were removed to that aircraft and transplanted to White Knight. The all up weight for White Knight and Spaceship One was about 17,000lbs giving a thrust to weight ratio of 2.2:1, and without Spaceship One close to unity. The J85's thrust would be behind those turbofans I mentioned at altitudes below 10,000 feet or so but after that the J85 would leave them far behind as far as thrust is concerned.

If you know what's really going on then you'll know what to do
Posts: 14133
Joined: Fri Nov 08, 2002 10:25 am

RE: Turbojets On "White Knight"

Tue Nov 09, 2004 10:14 am

Turbojets do performa a lot better at altitude, yes.