Is "Best Glide" misleading?

[MauleSkinner]

Check out “Glider Polars” starting on page 5-8 of the FAA Glider Flying Handbook for an explanation of how headwind or tailwind affects glide, including the “1/2 the headwind” rule of thumb.
https://www.faa.gov/regulations_pol...s/aircraft/glider_handbook/media/gfh_ch05.pdf

 

[flyingcheesehead]

Minimum sink speed (which I think is typically close to Vx) has no place in your engine out planning. Once you have the field made, slowing to minimum speed is good for survivability and such but it will never get you to the right field.

Unless there's a reasonably strong tailwind (ie, one that is most of the difference between best glide and minimum sink), in which case minimum sink may get you farther over the ground.

Yeah, but it’s going to give you the lowest decent rate, which imo, is more important. Lower decent rate = more time to try and sort things out. There’s no way to stretch your glide unfortunately.

Best glide does NOT give you the lowest descent rate. Minimum sink does.

 

[MauleSkinner]

Unless there's a reasonably strong tailwind (ie, one that is most of the difference between best glide and minimum sink), in which case minimum sink may get you farther over the ground.

if you have a polar to work with, you’ll find that an infinitely high tailwind will never quite make min sink speed optimum. Increasing 1/2 the headwind is a reasonable rule of thumb, but the decreases are going to be a much smaller percentage of tailwind.

 

[RyanB]

Best glide does NOT give you the lowest descent rate. Minimum sink does.

Keep in mind though minimum sink is quite slower than best glide is, so it can definitely impact your glide range. Just because you stay in the air longer doesn't mean you're going further, and I think that’s the biggest takeaway between the two.

 

[flyingcheesehead]

Keep in mind though minimum sink is quite slower than best glide is, so it can definitely impact your glide range. Just because you stay in the air longer doesn't mean you're going further, and I think that’s the biggest takeaway between the two.

True... And I think there's value in understanding both, and what they give you. I was just pointing out that the words you typed weren't correct.

I really wish they would publish minimum sink speeds for airplanes...

 

[RyanB]

True... And I think there's value in understanding both, and what they give you. I was just pointing out that the words you typed weren't correct.

I really wish they would publish minimum sink speeds for airplanes...

Fair point and I agree, I wish they would too!

 

[Bill Watson]

I’d suggest that if the task is to find a safe spot to crash/land on, a top priority is knowing the wind - approximate direction and speed. In any situation with a 10 knot or better wind, the ‘circle’ around things you can reach is more of an oval and you are on the upwind end of oval.

Getting the glide speed right within 5 to 10 knots is good enough, as long as you are on the high side.

Having spent a lot of time gliding around below 2,000 feet urgently picking fields, the effect of the wind dominates in terms of selecting and reaching possible landing spots (except in calm conditions).

I think a lot about the wind and power-off glides when flying down the Atlantic coast between say STARY and OMN on V437. The wind is usually off shore. Thinking about the nearest airport in case of a failing or failed engine at 6-9k is all about the wind. If one can get a quartering tailwind by turning one way or another when trying to head back to shore, it will make all the difference in the world.


Sent from my iPad using Tapatalk Pro

 

[Jeff767]

Using max up trim in a Cherokee 180 does indeed give you best glide, as demonstrated this morning by my Flight Review applicant, at least for our weight, CG and whatever atmospheric factors affect that.

It can do that at only one specific CG value.