Which brings up something I've always wondered. Why doesn't the
compressor and turbines of a jet engine have that effect but on a much
larger scale? I imagine the gyroscopic effects of the rotor in an
F110 on an F-16 would be nothing to sneeze at.

It can be a problem at very slow speeds, which is why the Pegasus engine in
the Harrier has its two spools (low and high pressure) counter-rotate.
Offhand, I can't remember if the F100 or F110 do as well, but then a/c like
the F-15 and F-16 are unlikely to spend much time slow enough for it to
matter (thrust-vectoring nozzles can help there). OTOH, the engines for the
F-35 probably have to counter-rotate.

Guy


In general, engined have counterrotating spools for efficiency not gyroscopic
effect. Most Brit engines use thhis approach but it is hell on bearings because
of the higher rotaional speeds. The three spool RB211 is kind of the ultimate
in that regard.

I'd guess that gyro effect isn't really an issue with the airframe guys since
with most engines since the mass is concentrated more in the center of the
rotors instead of in the periphery whless gyroscopic and centrifugal forces are
generated.

From what I recall from my involvement in the F100-220 and F110-100 engines,
the engine bearing and structural guys are the most concerned because of loads
and load paths during throttle transients. Didn't come up during the
airframe-engine integration meetings. Don't recall it as an issue in my J79
flying days either.

My memory is hazy on this but I think the F119 in both the F-22 and F-35
versions does not employ counter-rotating spools either. Now what forces the
lift fan generates to the airframe is a different story I an sure.

Steve