Talk:General Electric TF39

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ILA ?[edit]

What is, or was, 'ILA'? It crops up, but with no explanation on first mention.

RASAM (talk) 20:34, 4 March 2012 (UTC)[reply]


Internationale LuftfahrtAusstellung (Berlin) 46.115.68.157 (talk) 20:14, 29 November 2012 (UTC)[reply]

Precision in the Specifications section[edit]

In the Specifications section, the fuel consumption is given as ~3.7646 lb/s (1.7075 kg/s). The implied precision in 3.7646 seems strange, given that the difference between 3.7646 lb and 3.7647 lb is less than a hundredth of an ounce. If the actual measurement is well defined to such a high degree of precision, then so be it; but also strange is the "approximately" or "around" symbol ~ that precedes the given value. (So, the rate is *around* 3.7646 lb/s? Like, it's in the *ballpark* of 3 pounds and 12.23 ounces?) A third issue is that the kilogram equivalent of 3.7646 lb, when rounded to four decimal places, is 1.7076 kg, not the stated value 1.7075 kg. (Note 1 lb = 0.45359237 kg exactly.)

I suggest rounding both values to a smaller number of decimal places. 14:20, 7 July 2017 (UTC)Jzimba (talk)

What does the source say? Andy Dingley (talk) 14:44, 7 July 2017 (UTC)[reply]
Good question - I don't know / couldn't find it online.Jzimba (talk) 15:49, 7 July 2017 (UTC)[reply]
Probably because this is a nonsense figure at all. The thrust-specific fuel consumption is important (although figures I've seen quoted vary in that final figure), but claiming "fuel consumption" for a jet engine makes no sense, unless it's qualified as to what thrust and other conditions it's operating at. Trim it to two place max, and even then it needs to be annotated as to what it represents. If you have the optimal cruise thrust for which the TSFC was measured, then you could multiply it out from that reasonably. Otherwise the Pilot's Notes for an aircraft using it will have it (obviously this figure needs to be known for fuel planning).
Fairly obviously the figure here has been calculated (inaccurately) by taking the TSFC figure and the max thrust. The trouble with that is that aircraft don't operate continuously at max thrust (depending on what this "max thrust" means - takeoff ratings are regularly used, but might not be sustainable for long periods). Also the TSFC figure will be wrong, because that's usually quoted as the "best" figure achievable, for the optimum efficient cruise, which is better than some smoke-trailing max thrust figure. See how the CF6 TSFC is cited as a range 0.307 - 0.344 between two very precise numbers [1]. Those are numbers measured under equally precise conditions. Andy Dingley (talk) 09:39, 8 July 2017 (UTC)[reply]

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