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Why Is The TF-34 Such A Low Powered Engine?

Sat Apr 15, 2006 12:16 pm

I was reading a book on military aircraft, and I found out the TF-34 and TF-39 was built on the same design but the TF-34 down size to around a TF-30, F-100 and F-110 size. So why is a high by-pass that use the design of the powerful TF-39 and is around the size of a powerful engines like the TF-30, F-100 and F-110 so weak. Do not tell me it is because the TF-30, F-100 and F110 have after burner because even at dry thrust the TF-30, F-100 and F110 is more powerful.
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RE: Why Is The TF-34 Such A Low Powered Engine?

Sat Apr 15, 2006 2:01 pm

Engines are designed to meet thrust, installed weight, demonstrated reliability, optimal altitude range, specific fuel consumption, fleet commonality, production cost criteria...There are many others parameters, but some of these directly oppose each other. For ex, reliability often runs counter to efficiency (EFC) b/c a "looser" engine may last longer, but burns more fuel as a result of cycle losses...

The engine that meets the most important tradeoffs, as specified by the design, wins out.
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RE: Why Is The TF-34 Such A Low Powered Engine?

Sun Apr 16, 2006 2:48 am

I'll build on the foundation laid by EssentialPowr.

The Navy solicited proposals for an ASW aircraft. Vought designed the S-3 Viking, which ultimately became the first application of the TF34. The S-3 had specific thrust requirements at takeoff, climb, loiter, approach, etc. The TF34 had to meet these requirements, along with fuel consumption to meet aircraft range requirements. GE determined what bypass ratio best met these requirements. This dictated the size of the fan and core.

The core of the TF34 is smaller than that of the low bypass turbofans you mentioned. The TF30, F100, and F110 all have multi-stage fans delivering higher fan exit pressure, and variable nozzles, allowing them to optimally expand that greater pressure. You simply can't expect low and high bypass ratio machines of similar fan diameter to deliver same thrust.

As they say, you're comparing apples to oranges.
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