747400sp
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Why Did RB-57F Need The Extra J 60 Turbojets?

Sun Sep 24, 2006 6:20 am

The RB-57F was powered by two TF 33 turbo fans and two J 60 turbo jets. The RB-57F was not big plane, so I would think the two TF 33 had enough power to get the thing off the ground, so why they need those two J 60?
 
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ptrjong
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RE: Why Did RB-57F Need The Extra J 60 Turbojets?

Sun Sep 24, 2006 7:27 am

According to my 1974 The Observer's Basic Military Aircraft Directory, the auxiliary J60s were not always carried. Their mountings could also be used for tanks or other equipment. So, the TF33s could indeed get the thing off the ground even with extra weight. I guess the auxiliary engines, like the huge wingspan, were needed to get the thing to 75,000 ft and keep it there.

Peter Smile
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prebennorholm
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RE: Why Did RB-57F Need The Extra J 60 Turbojets?

Fri Oct 06, 2006 8:30 am

At 70,000 feet max engine power will have dropped to something like 5% of sea level power.

So Ptrjong is right. They were there to get it up there before it ran out of fuel. And to keep it flying up there.

Also those J60s were not chosen by accident, but because turbojets lose slightly less power at high altitude than turbofan engines.
Always keep your number of landings equal to your number of take-offs

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