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  • Engine War II
    Posted by Bill Sweetman 1:30 PM on Jun 11, 2009

    One of the latest corporate entities to break out on Facebook is the F135 engine program. It's not quite as crazy as it sounded at first, because it allows Pratt & Whitney to update interested observers on the program - mainly, with changes to the associated blog - without clogging their e-mail boxes. It also permits unmoderated comments.

    Latest post on the F135 blog, from "Eagleblogger" (I have this image of Sam the Eagle in mind), concerns the Great Engine War. It's worth a read and is amusing if you were there at the time. 

    Take this quote: "The whole reason for the Great Engine War was a strained relationship between the Air Force & Pratt and Whitney at that time."

    You could call it that. You could call the Battle of the Somme a difficult period of inter-European cultural discourse.

    "As the F100 matured in the F-15, it experienced some performance challenges."

    Now, that's too harsh. There were only two main problems with the F100. The first was that it tended to stop running in flight and the second was that it wouldn't start again.

    The problem was called "stagnation stall".It was a nuisance on the F-15 and a positive embarrassment on the F-16, where AF ground crews enjoyed their frequent opportunities to purge and refill the hydrazine EPU. (In the event of hydrazine inhalation, administer Last Rites immediately.)

    It wasn't a matter of P&W's engineers being incompetent:  it was a product of the engine's very high pressure ratio and the way the engine got used in service, because with all the extra thrust at their disposal pilots tended to jockey the throttle more liberally. But between 1979 and 1982-83, every P&W briefing was a variation on "this time we've got it sorted, we promise." 

    And whether it was cause and effect or not, the customer could not fail to notice that the problem got resolved (digital engine control was a big part of it) after GE's F110 was brought in. 

    Seriously, the real question is this: Why was the JSF's alternate engine considered necessary in 1996, and again in 2001 - and without a plan to eliminate it if the F135 turned out fine - but is now a wasteful extravagance?

    The answer to the first part oif the question is not all about politics. A STOVL aircraft places unique demands on the engine. The operating cycle involves sustained maximum power at low-to-zero airspeeds where even a transient problem can be disastrous. At the same time, every ounce of thrust is needed, and that power has to be sustained through the life of the engine. 

    The answer to the second part is about politics and money:  overruns in other areas of the JSF program - most definitely including the F135 - have eaten the money for the second engine, but Congress has been unwilling to provide add-on funds for it and the program management has not wanted to ask.  Had the program as a whole stayed on budget this would not be an issue today. What will happen now - particularly since the F136 has been singled out as a worthy candidate for the chop by the White House - is anyone's guess.

    Tags: ar99, f135, f136, jsf

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