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Originally Posted by fish314 Yeah, you're probably right. My experiences with constant speed props is pretty limited. Flew em about 8 years ago, but only for about 15-20 hours. Most of my experience is with jets. For this question, though, it should be immaterial, however, because if constant speed props don't lose the ability to produce thrust as velocity increases, they would still suffer a reduction in Vy with altitude due to the shift in the power required curve. In other words, the "JET" explanation above would be the same phenomenon in a constant speed prop, but a fixed prop would have 2 factors affecting it.
Oh, well. That'll teach me. Think before you speak (or type!)  |
I have been looking at my explanation for Vx in an earlier post and I realized I should take my own advice and look at the graphs. It's tough to justify why Vy would decrease by looking at the excess power graphs because they move up and to the right like the excess thrust graphs do. I think it's kinda important to note that in terms of true airspeed, both Vx and Vy increase with altitude. However, Vx increases at a greater rate than Vy. Vy increases about 1% per 1000ft, but when you convert TAS to IAS (2% per 1000ft), it shows a 1% decrease. Oh well, so much for simplicity.