Originally Posted by
Cubdriver
No! The best glide angle for range purposes is based on L/D max, period. It does not vary with anything else. It is a known value for a particular airplane design, and it does not have anything to do with weight, density, or wind conditions at the time.
He said, "distance over the ground" while you are discussing movement through the airmass. He has it right. Though I would swap some of his words for clarification: best glide angle -> furthest distance achieved & best L/D -> L/D max.
Ok, except pull the " & angle" out of this sentence lest it be incorrect. The angle is exclusive to any factor except L/D and in the case of maximum range, L/D max. Best glide speed Vg varies (only), and here's the equation:
Again, angle relative to the ground, he is right. Relative to the air, I would swap terms as mentioned above just for clarification.
Yes it is. Perhaps you mean the "published" Vg is not always correct, and the true Vg may differ due to circumstances- and I agree with that. The airplane will not go as far through the air without being at L/D max. Ground location is another issue altogether.
Again, in terms of ground location as his post suggested before, he is right.
I got my glider handbook out. It says the term for this kind of glide speed is "the speed to fly" (as Oldveedubs pointed out also), and it is not technically a best glide speed.
Unless you have a variometer equipped, speed to fly is irrelevant. A glider pilots speed to fly accounts for lift, sink, headwind, and tailwind. Interestingly enough, lift/tailwind result in flying closer to, or at, min sink, a slower speed. Conversely, a sink/headwind results in increasing your speed to fly above Vbg. The reason was already given by ryan; reducing or increasing the effects of the moving airmass, both up/down and forward/backward.
Ryan: I wouldn't have any issues with the engine one as engines build, to my very limited knowledge, is fairly linear. Increase piston size x% increases fuel flow y% and power z%. Drag curves are not linear, leading me to believe, as UAC seemed to confirm, there is a limit to the rule of thumbs usefulness.
I do introduce it, though I only gloss over it. I much rather focus on judgement required to pick a landing site and skills to safely fly at or near best glide until the flare. If pilots did that, I suspect 90 percent of the engine failures encountered would result in a safe landing.
In response to your real world experience, you had a particularly unusual situation. For the most part, we are talking about what speed to fly when total power is lost. Your situation would have been best if flown at min sink with the engine as lean as possible, I assume you did this.