I agree re min sink when over water and out of glide range.
The rest of the situations will depend on the circumstances. I think in most cases a pilot will correctly focus on restarting the engine – unless it stopped dead with a bang. And best glide range should give more options because if you see a suitable site down below, well before running out of range, you can always just orbit while descending.
I also think that in some cases one needs to be continuously planning where to go if the engine stops e.g. when overflying the Alps. It gets even more interesting if you are in IMC above them 
In that case one needs to be running a proper topo map and have a plan in hand, continuously.
Thanks for re-posting
Peter wrote:
I also think that in some cases one needs to be continuously planning where to go if the engine stops
Yes, you still need to have “survivable landing spots” in the plan before flying performance and field landing techniques, but I think the most important is to keep “generating lift generated” irrespective of the spot, some managed to survive some nasty accidents into forests/mountains while some end-up upside down on the flat…
On terrain, I found the last 100kms of the FAI sailplane championship in Chile in the middle of the Andes always interesting to watch
OK, folks. Thanks for all the various angles presented to this subject.
I am going to wrap it up a bit, at least from my point of view, referring back to my opening post.
1) this thread DID confirm that most pilots DO instruct / have been instructed or simply intend to glide at Vbest glide in case of an engine out scenario
2) most of them recommend/use Vbest glide for various reasons, but NOT really for its glide distance maximizing characteristics. That’s an interesting point to take away.
3) the primary reason stated was stall margin (some might call it “instructor angst”)
4) Indeed, the most tangible and simple reason is that Vbest glide is published in any POH, whereas Vmin sink very often is not. That is a very simple explanation. It’s difficult for instructors to recommend a speed which is not published in the POH. Point well taken,
5) most probably, in an engine failure emergency one will not have the mental resources to maintain precision on the airspeed. So again, just keep the speed at a safe and somewhat efficient number and that’s it.
6) I totally don’t understand, once again (we had this topic once before and even back then I was utterly confused) Pilot_DAR. In typical (=not heavily modified) PPL training and basic VFR touring aircraft, Vbest glide does give tons of energy margin from Vso speed. Way sufficient for a flare above the landing site. In German PPL training, we do tons of power-off glide landings exercises onto a runway (“Ziellandeübung”). These are routinely done at Vbest glide or somewhat below on short final and never is this an issue in terms of energy left for the flare.
In fact, in case of an off-field emergency landing, I WANT the flare to be quite short, since that minimizes the time and distance I spend flying at one metre of height over some unknown pasture, A longer flare would increase the risk of flying into some poorly visible pasture fence or similar. So, head for (the middle of) the selected landing field, make a short flare and settle down at minimum possible speed; all within a few seconds. No need to make it a greaser on that particular occasion.
7) gliding at anything above Vbest glide will decrease both the time AND the distance the aircraft will glide. So, strictly from the performance point of view, it never makes sense to do that (leaving wind out of the equation for a second). Flying a bit slower than Vbest glide will slightly decrease the distance, but slightly increase the amount of time you will glide. So, not necessarily is this a bad idea. Add to this the fact that Vbest glide (and of course also Vs) are normally published for max gross weight, and in most instances, one WILL be below max gross weight, so this is another reason why it might make sense to tend a little bit below published Vbest glide speed. But then again, these are all details; see 5)
8) see 4 again
boscomantico wrote:
7) gliding at anything above Vbest glide will decrease both the time AND the distance the aircraft will glide. So, strictly from the performance point of view, it never makes sense to do that (leaving wind out of the equation for a second).Well, yes. But if you don’t fly Vbg with precision (and chances are you’re not as you’ll be handling the emergency) then it’s better to be slightly fast than slightly slow.
I said the contrary (from a performance point of view).
I have always doubted the “best glide” concept, because the equation fundamentally is meant to fail.
It gives a false sense of security, because it takes Vbg as an exact number (taken from the POH, and maybe adjusted for weight), and puts it into an equation where all the other factors are unknowns, variables and guesstimates.
Which leads us to thinking when up there in an emergency we can somehow predict the distance similarly precisely. We know Vbg, we know how far we can glide, correct ? Wrong. We don’t know all those other factors precise enough to compute a distance. Where ‘farther down there’ is the I-can-make-it border ? How strong is the wind, from where does it exactly come ? We make mistakes, we cannot think clearly, we look out, we estimate, we hope, we guess, we maybe try to do the right things, but we don’t know. Our head explodes. What’s worse, if we are being given a ‘nearest airfield’ by ATC or GPS device or skydemon or garmin pilot, we might be tempted to reach that, only to find out later in the approach that it doesn’t work and we are out of other options.
A very interesting video I once saw (I’ll try to find it) said, forget all that, forget about best glide because it distracts you from what is really necessary. Forget to think about the distance you can possibly or maybe or hopefully glide. Instead, look down, in a funnel directly below you, at an angle of say 45° max, make a turn, choose a spot right down there, and land. Which may involve a steep dive if you find you’re not high enouog for a 360… So, minimum sink speed makes a lot more sense than best glide, at least initially.
boscomantico wrote:
In fact, in case of an off-field emergency landing, I WANT the flare to be quite short, since that minimizes the time and distance I spend flying at one metre of height over some unknown pasture, A longer flare would increase the risk of flying into some poorly visible pasture fence or similar.
On 6), I think the opposite, why not just land as you have done it 100 times before? once on final approach: stable Va speed, no last minute left/right turn, landing fully held off, stick full back on touchdown at slowest airspeed and hope for the best?
Best glide/min sink concepts only apply above 500ft AGL, landing is better done as usual (into wind, flat/uphill, Va, aiming point…), besides, on changing settings, it seems to me that a PPL student is well trained to land on various surfaces/power/runway/wind configs shortly before his skill-test, so probably much proficient in these than an experienced PPL who rarely pull power off or land flapless…
At what height will you be able to see obstacles? A Group member had a reduced power situation, over Fort William going to Mull. He turned back to a known airstrip. It was set out for horse jumping.
He headed for a group of very large fields. When committed, he saw power lines. Then a fence. He went under the power line, over the fence, but hit another fence before being able to stop. No injuries, but aircraft damaged.
(I think landing on the strip and hitting the pony jumps might have caused less damage. There were no people or ponies there at the time.)
Maoraigh wrote:
At what height will you be able to see obstacles?
For fences, they are completely invisible above 1000ft AGL, you may see stark colour change, stock gathering in one side, or drinking troughs…
For power lines, you will never see the wires (apart from 3 seconds before they touch the fuselage) but you will probably see power/telephone pylons, if you approach perpendicular to a road between sparse countryside houses, always assume there are on your final and plan enough energy to fly above them, flying bellow them is not an option
The rule of thumb is to avoid landing in a place that is already occupied (human or cattle) but I guess all of the rational decisions goes to the bin once the vario hits -1000ft/min
There seems to be plenty of theory in this thread, but not much experience.
It’s not often that I agree with @Pilot_DAR, but he knows this business and I tip my hat to anyone who can do four engine-out landings without airframe damage. The only experience I might add is how to set down in a mature (closed canopy) spruce plantation and trot away without a scratch: full flap, level and unload the wing, get the stall warner tweeting, minimum forward speed. The airplane will decelerate and then nose over as it drops through the canopy, but that’s the only slightly exciting bit. Obviously, the airframe may need a bit of TLC thereafter, so this is a technique that one doesn’t want to practice more often than necessary.
