Thoughts on "Best Glide"

455 Bravo Uniform

455 Bravo Uniform

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455 Bravo Uniform
Assuming I have an engine out, have been at best-glide, and I now I have an airport in sight.

If I'm coming in to land "power off" and I am still at best-glide speed, if I mis-judged my touchdown point, I am gonna land short. If I have no power, there is no way I'll be able to stay airborne any further.

Am I not better off coming in for the landing at something other than best-glide speed (faster, slower) and if I look like I'm gonna come up short, THEN go to best-glide? That would be the only way to have flying-distance "in reserve", with no power.

I was taught and hear that you never want to stretch your glide. That makes sense, because at best-glide, you can't stretch one iota more. So why not come in faster or slower, aiming for the touchdown point, and use best-glide to "stretch it" as it were.

:popcorn:
 
Coming in faster before the runway is made will just assure that you get to the crash site of short of the runway quicker.
 
...but yeah, once the runway is 100% assured adjust speed accordingly to get on a good power off glide path. Big difference between runway in sight and runway made.
 
Why would you want to hold anything in reserve in an emergency?

Just pick a feasible landing site to begin with. A field right at the edge of gliding range is not a good choice.
 
MAKG1 said:
Why would you want to hold anything in reserve in an emergency?

Just pick a feasible landing site to begin with. A field right at the edge of gliding range is not a good choice.
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You can't think of it as holding anything in reserve because you aren't. At a higher speed you are throwing away energy as you go, and you don't get it back...


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MAKG1 said:
Why would you want to hold anything in reserve in an emergency?

Just pick a feasible landing site to begin with. A field right at the edge of gliding range is not a good choice.
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Emphasize this; in the event of a forced landing emergency, your best options are often directly beneath you -- it's a trap to look at sites you probably can't reach. Fly safely.
 
You're better off to learn to judge your aim point sooner...you shouldn't be anywhere near the touchdown point when you first realize you're not going to get there.
 
Don't try for the approach end of the runway. Go for somewhere in the middle.

You are much better to slide off the far end at low speed than hit short at high speed.

Most runways will have plenty of length for landing, even touching down mid field.
 
Always go for best glide. It is easier to cut your glide down a bit if needed (slips, S-turns, flaps, combo) than it is to extend a glide (pretty much impossible). Why give yourself a handicap right off the bat?
 
FastEddieB said:
That makes absolutely no sense.

Does the popcorn emoticon indicate you're just trying to stir something up?
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I think what you guys are saying and what he was saying is two versions of the same thing, at least for the slip and or aim mid-field and 'come in high' answers. Once you have your target made and are doing something(other than best glide) to hit it you're doing what the OP was inquiring about. (unless you're circling at best glide as one reply suggested).
 
This topic is why purposely setting up a bad approach and using a forward slip to get down is a good idea every once in a while. So many never practice them.

Being able to do one effectively and properly is basically paramount in an engine out situation. You are very unlikely to have absolute perfect judgement of your touchdown point when you are holding best glide with all the other stress going on. Having to slip it down at the end is a very likely possibility.
 
I picked up a copy of "Stick and Rudder" recently, and have been reading this classic. The author discusses this exact question, and offers the OPs suggestion as one possible method of action under an engine failure. In fact, he cautions exactly against taking a best-glide to a field and not having 'anything in reserve' if an extra stretch is needed. But then concludes with experience dictating the method by the particular circumstances and that practice is the most important factor.

However, I personally feel that in most all situations a choice of landing spot should be made ASAP after failure, and that spot should be clearly close enough to make. In the unlikely event that the only options are at the edge of the available glide range, you are still best off going with best glide ASAP after failure to stretch as far as possible (and be as high as possible over any obstruction).
 
FastEddieB said:
That makes absolutely no sense.

Does the popcorn emoticon indicate you're just trying to stir something up?
Click to expand...

Yes, sort of. I was bitten by a troll last night. I thought about posting anon, but figured screw it. I'll ask the silly question that's been burning in my mind, even though I may get flack for it. I'm bored. Need to fly.
 
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jbrinker said:
I picked up a copy of "Stick and Rudder" recently, and have been reading this classic. The author discusses this exact question, and offers the OPs suggestion as one possible method of action under an engine failure. In fact, he cautions exactly against taking a best-glide to a field and not having 'anything in reserve' if an extra stretch is needed. But then concludes with experience dictating the method by the particular circumstances and that practice is the most important factor.
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That's EXACTLY what prompted my question for discussion here. I had not thought about this before reading this book a few months ago. It was the winter boredom and 2 weeks of vacation that nudged me to post my question.
 
If you need to get to the field, there's nothing better than best glide. The best bet is to have a field CLOSER than your max range. My one (off-airport) engine failure I circled down and used a normal base-to-final turn (there were no better fields further away).
 
I had the same thoughts during my PPL training. On a calm day, I took my Archer up to 6,000 AGL, 6 miles away from the practice strip, lined up on a straight in approach, and cut power. I did this all day long, from various distances, altitudes, and angles from the runway, including directly overhead. Furthermore, I practice this at least once per month. (Although not necessarily to that extreme.) Because of it, I'm quite adept at picking a good place to land and making it there. I've also gotten pretty darned good at slipping it in.

From this experience I can tell you that those who say pick a spot nearer you that you're sure you can make, are absolutely right. It's pretty easy to lose excess energy just before touchdown, but impossible to get it back.
 
Know your best glide airspeeds. In my plane, at solo weight it's 76 KIAS, and at max gross it's 82 KIAS.
 
You can scrub off excess speed by coming down faster or slower than best glide. Oh yes you can.
 
And that's why you should just find a field that leaves lots of room for error.

Almost no one in a high stress situation is going to perfectly hold an exact best glide speed, especially in bumpy conditions while running restart flows, while coming up with an exact correction for wind and weight in the moment.

If the field you picked requires the entirety of what best glide will give, your field is too far.
 
In a Cherokee that I fly, best glide is 73, where as landing speed is about 65, so pretty easy to come in best glide then pull up a little and you're at landing speed.
 
Go and get a few flights ( or better yet a rating) in a glider. You will truly understand the huge importance of best L/D and what it will do for you.


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George Mohr said:
Also, from my CFI: better to roll into the trees at the departure end of the runway at 20mph than crash into the tops at the approach end at 100mph.
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Did he teach you steep approaches and heavy use of slips?


You be amazed how quickly you can loose altitude and/or speed with a well done slip.

I've said it before, slips are one of the maneuvers that WILL save your bacon given enough hours flown.
 
orange said:
In a Cherokee that I fly, best glide is 73, where as landing speed is about 65, so pretty easy to come in best glide then pull up a little and you're at landing speed.
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I think that's true of most small singles. And very much on purpose. Best glide is basically max L/D (actually, that's best endurance, but it's numerically close), which is also where the peak in the power curve is. Slower than that, and you're "behind the curve." You can land that way, but not without power.

Don't confuse approach and landing speeds, though. Landing at 65 will be very bad news for your nosegear and prop. It's a LITTLE fast for approach, but will do fine on a runway that isn't really short.
 
James331 said:
Did he teach you steep approaches and heavy use of slips?


You be amazed how quickly you can loose altitude and/or speed with a well done slip.

I've said it before, slips are one of the maneuvers that WILL save your bacon given enough hours flown.
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Yes indeed. Get setup for something like 1/3 of the way down the open field. Slow to approach speed, full flaps, and adjust with a slip as needed. Error on the side of being long.
 
orange said:
In a Cherokee that I fly, best glide is 73, where as landing speed is about 65, so pretty easy to come in best glide then pull up a little and you're at landing speed.
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Which isn't going to give you any distance. It might transiently get you over an obstacle, but you're going to contact the ground sooner than if you'd maintained best glide.
 
FastEddieB said:
Reminder: Best glide also varies with wind.

Slightly faster into a headwind, slightly slower with a tailwind.
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Airspeed, or groundspeed? If you mean groundspeed, I see that. But isn't this whole discussion about best glide airspeed? Can you elaborate on why the best glide airspeed would be different based on wind?
 
Its an old glider trick that the top of the performance curve is pretty flat, meaning that a few knots faster costs you very little in glide ratio. But those few knots equal pure wind penetration when flying into a headwind, so its worth the trade.
 
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Van Johnston said:
Airspeed, or groundspeed? If you mean groundspeed, I see that. But isn't this whole discussion about best glide airspeed? Can you elaborate on why the best glide airspeed would be different based on wind?
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Best glide is about maximum distance covered, so ground speed is part of the equation.

For best endurance, it's all airspeed.
 
455 Bravo Uniform said:
Assuming I have an engine out, have been at best-glide, and I now I have an airport in sight.

If I'm coming in to land "power off" and I am still at best-glide speed, if I mis-judged my touchdown point, I am gonna land short. If I have no power, there is no way I'll be able to stay airborne any further.

:popcorn:
Click to expand...

Yes, you want options either way if you mis-judge your glide, and you should be making constant, small corrections. Just talking airplane configurations, if your default glide is with the prop at fine pitch at best glide speed, if you want to "stretch" the glide you can do that by pulling your prop back and losing some of the drag.

If you are gliding too long, you can shorten your glide by any number of ways, going well above best glide, getting below best glide speed, slipping, flaps etc...

This is why its best to fly a pattern, you can also stretch or shorten your glide by increasing/decreasing the amount of distance you need to cover before you get to the runway. Looking a little short on base? increase the rate of turn so you are pointing at the runway faster. Looking long? Make a lazy turn with a bit of an S in the end of it.
 
Those of us who fly motorless deal with these issues every time we fly. First and foremost, if possible choose a site you can easily make with some reserve altitude. You can shed the extra altitude without too much difficulty, but there is no way to get any more. Second, the atmosphere is a dynamic place. Between where you start your glide, you may encounter lift, sink, headwinds, tailwinds, and low level rotor. You may encounter all of them, so don't assume you have the field made until you're over it, and be prepared to make adjustments. Third, when you're close to the ground, some more speed is in order, to have a little reserve of kinetic energy if you need it. Lastly, we like to aim for the middle of the runway/landing zone. In an emergency you may not have that option, but as George Mohr said, if you have to err, go long.

Hopefully one of the sailplane pilots will chime in here.
 
FastEddieB said:
Reminder: Best glide also varies with wind.

Slightly faster into a headwind, slightly slower with a tailwind.
Click to expand...

A lot of folks forget that. A 60-kt glide into a 60-kt headwind means no groundspeed. An 80-kt glide would get you some distance. With a good tailwind, it might be better to fly at minimum-sink airspeed, often not far above the stall.
 
Good stuff. Besides being fun and interesting, some glider training is going to get on my bucket list.
 
Van Johnston said:
Airspeed, or groundspeed? If you mean groundspeed, I see that. But isn't this whole discussion about best glide airspeed? Can you elaborate on why the best glide airspeed would be different based on wind?
Click to expand...

Dan and MAKG1 summed it up nicely.

If the goal is to reach a goal on the ground, then you need to go a bit faster into a headwind and slower with a tailwind to get as far as possible. Dan's "reducto ad absurdum" is one I use as well.

Think of it as, if you have a headwind, you want to minimize your time in that headwind - go faster. If you have a tailwind, you want to maximize your time in that tailwind - go slower*.

If the goal is minimum sink, then wind does not matter.


*Same logic applies when choosing an airspeed/power setting at cruise with a headwind or tailwind.
 
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