timz
Posts: 6081
Joined: Fri Sep 17, 1999 7:43 am

Turbojets On "White Knight"

Tue Nov 09, 2004 9:23 am

http://www.scaled.com/projects/tierone/data_sheets/html/white_knight.htm

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?
 
widebodyphotog
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.

-widebodyphotog
If you know what's really going on then you'll know what to do
 
gigneil
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.

N