Why do Russian Fighter Jets have higher Bypass than the Western ones??

[wile coyote]

If you compare AL31,41 (used in Flankers) vs F119, PW100-229 (used in F22,F14B, F15E, F16C) and the RD33 (used in Mig 29) versus the Eurojet and the F404(used in Hornets) it always seems like the Russians always go for Higher Bypass Turbofans.

Why is that?

Lower Bypass( for the same fan diameter) should give better performance at the cost of range and endurance. Do the Russians Prioritize Range over performance? The Flanker already has a massive fuel tank and the Fulcrum is a point design interceptor anyways. So what other reason ?

 

[overscan (PaulMM)]

Incorrect assumption.

Previously USSR fighters used turbojets. AL-31F and RD-33 had lower bypass ratio than F100 of the era when they were being designed.

Subsequently US engines went to lower bypass ratios for several reasons.

 

[1635yankee]

If you compare AL31,41 (used in Flankers) vs F119, PW100-229 (used in F22,F14B, F15E, F16C) and the RD33 (used in Mig 29) versus the Eurojet and the F404(used in Hornets) it always seems like the Russians always go for Higher Bypass Turbofans.

Why is that?

Lower Bypass( for the same fan diameter) should give better performance at the cost of range and endurance. Do the Russians Prioritize Range over performance? The Flanker already has a massive fuel tank and the Fulcrum is a point design interceptor anyways. So what other reason ?

While bypass ratio can be important, it's also important to remember that the fan pressure ratio is also quite important for performance, especially as Mach number increases. Western engines tend to operate at higher turbine inlet temperatures and higher cycle pressure ratios than Russian engines (although this has decreased due to technology transfer to Russia since the end of the Cold War* and as Western engines creep closer to the limits of material performance). I suspect that even with the lower bypass ratio, western engines have better cruise performance.

 

[wile coyote]

Incorrect assumption.

Previously USSR fighters used turbojets. AL-31F and RD-33 had lower bypass ratio than F100 of the era when they were being designed.

Subsequently US engines went to lower bypass ratios for several reasons.

Ok I should've clarified I was thinking about the 4gen fighters and onwards. What I meant is that the Al41,31 etc. consistently have a higher bypass ratio than any Western Jet

 

[wile coyote]

While bypass ratio can be important, it's also important to remember that the fan pressure ratio is also quite important for performance, especially as Mach number increases. Western engines tend to operate at higher turbine inlet temperatures and higher cycle pressure ratios than Russian engines (although this has decreased due to technology transfer to Russia since the end of the Cold War* and as Western engines creep closer to the limits of material performance). I suspect that even with the lower bypass ratio, western engines have better cruise performance.

Interesting.But, From what I've seen the Russian Engines actually have better TSFC numbers. Western Engines also seem to be more Supercruise capable as well, Example FA18C, F22, Eurofighter etc.

 

[Nicknick]

Are the Russians still using the intercoolers/heat exchangers to the bypass air? This could be a good explaination for the higher bypass ratios.