bypass ratio
hello all,
the bypass ratio, because it is a ratio or a fraction, by definition has no units.
eg. a bypass ratio(called the greek letter of lambda) of 8, means that for 1 unit of air going through the core engine for combustion, you have 8 units of free(no money required)air going through the fan. altitude & density affects both terms in the same way, so the bypass ratio remains the same. there is a simple formula(don't ask me to prove it) that says : delta thrust(F) = square root of(1 + bypass ratio). taking same example from above : delta F = sq.root of (1+8) = 3. so the high by pass engine produces 3 times more thrust than a straight(noisy) jet engine.
ram drag(= massflow x True aispeed)indeed as said in another post, reduces thrust output, but this is compensated a bit by the saturated thrust that comes into play only at higher altitudes for high bypass engines. so it is more or less a matter of give & take, resulting in thrust output remaining +/- constant with speed at high altitude. you will find definition of saturated thrust in the roll's book.
bm.