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Bypass thrust
Posted: Sat Nov 05, 2016 6:49 am
by D-ECHO
Hi!
I know/have heard that modern engines have 12 times as much air passing by the actual engine as air passing through (bypass ratio 12:1, PW1000G), but does anyone of you know how much thrust is provided by the fan (bypass air) and how much by the gas engine?
Regards
Re: Bypass thrust
Posted: Mon Nov 07, 2016 1:27 am
by Octal450
I have not a clue sorry
I know the high bypass engines use more direct air turned by the fan, not the jet core, than low bypass.
Re: Bypass thrust
Posted: Mon Nov 07, 2016 1:18 pm
by jwocky
and it is not the same for all engines. You have to look up specific engine model specs.
Re: Bypass thrust
Posted: Mon Nov 07, 2016 1:58 pm
by KL-666
Is not the amount of thrust equal to the amount of air passing through? So if the amount of air passing through is in the proportion 12:1, the amount of thrust is also 12:1?
Kind regards, Vincent
Re: Bypass thrust
Posted: Mon Nov 07, 2016 2:26 pm
by D-ECHO
@KL I don't think so, as the air passing through the inner part should be much faster than the one coming from the big fan at the front.. @JWOCKY: e.g. for the PW1000G it's 12:1 but I can't anything regarding bypass thrust...
Re: Bypass thrust
Posted: Mon Nov 07, 2016 3:29 pm
by jwocky
Wewll, yeah, only thing, I can find is the general construction. Compressor: 1-stage geared fan, 2-3 stage LP, 8 stage HP, Turbine: 2-stage HP, 3-stage LP, but not much about the actual rpm and sizes. Technically, I would guess, the relation is aboutish
(total diameter - turbine diameter)*flow speed compressor : turbine diameter * (flow speed compressor+flow speed turbine)
but that is only a rough approximation because I have nothing about air resistance on the turbine stages which also changes with the rpm ... so, very very rough. But since you have the 12:1 already, you can rearrange that equation and since you have the outside diameter, you could calculate it backwards via the air amount?