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Power off landings - glide slowly, or glide fast?

We all know that once you are at Vbg then there is no way to stretch the glide range (other that 2nd order factors like gliding mostly downwind).

Langewiesche makes the point that one should glide slower than Vbg, because one can then easily stretch the glide when the need to do so becomes apparent, which will usually happen close to the ground, simply by pushing on the yoke.

However, the same can be achieved by gliding faster than Vbg…

I guess the former method gives you more time to consider your fate

One ex RAF fast jet pilot told me how they practiced a fairly extreme case of the latter method, in turboprops, and gliding really fast, for maximum options when popping up from under a low cloud layer. Needs serious balls, but you will be dead at 90kt same as at 160kt if you don’t get visual.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Needs serious balls, but you will be dead at 90kt same as at 160kt if you don’t get visual.

But it is better to be dead instantly from a crash at 160kt than surviving a 90kt crash badly hurt for another 15 minutes while you wait – in vain – for rescuers to arrive…

EDDS - Stuttgart

IF you choose to glide more slowly than the recommended glide speed, you have committed yourself to a crash, unless you can return to an on speed or faster glide in the final few hundred feet. I have always trained to find the more near place, and make a good landing there, than stretching to crash somewhere that might appear to be better – even if this means ditching instead of making shore. Arriving to the beginning of the flare with less than “best” glide speed results in a crash.



Home runway, in central Ontario, Canada

Peter wrote:

One ex RAF fast jet pilot told me how they practiced a fairly extreme case of the latter method, in turboprops, and gliding really fast, for maximum options when popping up from under a low cloud layer.

There is a procedure called a Radar PFL which was designed for Hawk and Tucanos. The predecessor, the one-in-one was a Hunter speciality. In both cases, the aircraft were set up to be at range=height; in other words, 10000ft at 10nm, 9000 at 9 etc. In the Hawk (the Hunter was a little before my time) this would result in the aircraft hitting overhead at about 350KIAS. This gave more than enough energy for a quickie high key, low key circuit to land.

No one ever described to ATC what the pilot would do if he didn’t break cloud overhead the airfield! :0

Oh, there was also something called the Canberra Icing Letdown, but I’ll keep that story for another day.

Fly safely
Various UK. Operate throughout Europe and Middle East, United Kingdom

Peter wrote:

Langewiesche makes the point that one should glide slower than Vbg, because one can then easily stretch the glide when the need to do so becomes apparent, which will usually happen close to the ground, simply by pushing on the yoke.

That doesn’t sound like “stretching the glide”, i.e. gliding further, it sounds like compressing the glide.

In fact I would say that flying slower reduces your options.

Darley Moor, Gamston (UK)

Peter wrote:

Langewiesche makes the point that one should glide slower than Vbg, because one can then easily stretch the glide when the need to do so becomes apparent, which will usually happen close to the ground, simply by pushing on the yoke.

Who is this Langewiesche? But he has a very valid point IMO. Gliders soar at minimum sink ratio, and travel at best glide ratio to get from one thermal to the next (basically).

The natural thing to do is to glide at minimum sink ratio, and use best glide ratio when you need it. This will give you more freedom and more control. Minimum sink ratio is slower than best glide ratio. There is no need to travel faster down than you really have to.

ENVA ENOP ENMO, Norway

LeSving wrote:

Who is this Langewiesche?

I had to google him myself when I first encountered his name on an aviation forum some years ago. He has written aviation textbooks which seem to be popular in the States, maybe also in the UK. I have never heard of him or read anything by him in all my years in that business. But that must of course not mean that what he writes is not correct. However his books were written more than half a century ago and I am pretty much certain that all good things contained in them have already found their way into training syllabi around the world.

One more thing: In all these gedankenexperiments about best glide speeds, two vital things are often forgotten:

1) Wind. Wind changes everything, especially when it is strong compared to a (slowish) best glide or minimum sink speed.
2) Unless one is very far from safe shores, optimum gliding distance is not usually required. We have had this topic before and I stand my case that much more damage caused during forced landings comes from overshooting the landing site, not undershooting.

Last Edited by what_next at 20 Feb 12:56
EDDS - Stuttgart

what_next wrote:

However his books were written more than half a century ago and I am pretty much certain that all good things contained in them have already found their way into training syllabi around the world.

Sure, but the popularity of his books, especially “Stick and Rudder” are not so much what he talks about, but how he presents the information. He is good in dissecting the topics and present them to pilots who don’t fancy the calculator part of flight dynamics by reasoning the working principles. That is, what makes his books quite valuable, even today.

mh
Inside the sky.
EDXE, EDXF, Germany

Google found me this link here (http://www.ulmrecord.com/reports/knowledgebase.php?article=31) from where the book can be downloaded as pdf (legally or not, who knows? Around here copyrights expire after 70 years and the book is 73 years old – but the 70 years refer to the death of the author). I have it now on my iPad for possible reading in the future. Or not.

Last Edited by what_next at 20 Feb 15:03
EDDS - Stuttgart

In the book it says copyright renewed by the author in 1972. According to wiki he died in 2002.

Administrator
Shoreham EGKA, United Kingdom
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