Max glide vs. min sink speed

Adding to Pilot_DAR:

As usual, there is no substitute for knowing what is right for your particular aircraft.

Keeping a high enough speed is especially important for draggy aircraft (including retractables with the gear down, and if flaps are out in the final stages of the approach) and for those with high wing loading. You will need the energy for the flare, which for some types is really a quick sharp pull a few feet above ground even if at best glide speed (just try it in a T-Tail Arrow…).

On the other hand, if you fly in a motor glider, you can – and perhaps, should – fly slower.

It is worth noting that gliders have different minimum approach speeds depending on how much of the airbrake they have out – the more drag, the higher the minimum approach speed.

boscomantico wrote:

Why do we instruct best glide speed in case of an engine failure?

Because it makes the handling and performance of the aircraft safe, recognisable and predictable, which is what is needed to maximise chances of a succesful outcome in a very critical situation with a pilot that very often has limited experience.

Of course, every pilot should aim to expand his repertoire, and he could take advantage of a slightly slower speed for increasing time available for troubleshooting and preparing for the landing, and for extending the glide in a downwind. Conversely, a higher speed could make the difference in a headwind that would otherwise prohibit reaching the desired landing spot.

For the final approach I would always aim for exactly the book speeds, not more, not less. With a little extra for turbulent/ wind shear conditions, just like normal. But any other speed than normal gliding approach speed would make it less likely to hit the desired touch-down spot.

Unfortunately, when giving training flights, biennials, proficiency check, some (mostly young) instructors think that there is only one right way to do things, and they may not themselves understand the advantages of selecting different glide speeds, so they may not be able to judge if an experienced pilot (e.g. one with sailplane experience) is flying safe and well during a simulated engine failure.

huv wrote:

But any other speed than normal gliding approach speed would make it less likely to hit the desired touch-down spot.

I don’t agree. If the spot is very close underneath you, you can, and may have to, slip at a faster speed to get in. Hitting the desired touchdown spot is more dependent upon pilot skill, and speed management than achieving a stated “best glide speed”. I would much rather, and train others to, look for the closer spot, not depend upon, nor attempt to achieve “best glide speed”. Do what is needed to get the plane to a position on approach to the spot you like, with height and speed you’ve practiced landing from.

I agree that pilots with sailplane experience will be much more aware of techniques to optimize a glide. Such experience seems more common in the UK and Europe than in North America. Here it seems that most pilots are only planning to fly A to B with an engine they think will run for the whole flight. Usually they are right, when they’re not, they’re less prepared.

Flight manual speeds are the second best way to know the best way to fly the aircraft, practice is the first. Yes, the flight manual speeds for an aircraft in original condition will be good, and should be the first reference. But when the aircraft has been changed (remove wheel fairings/install STOL kit/flap seals/speed mods/skis/floats) the optimum speeds may change, and in the absence of a (or some) flight manual supplements with changed speeds, you’re on your own to figure it out. So, you should figure it out – there’s no excuse to not practice!

Pilot_DAR wrote:

If the spot is very close underneath you, you can, and may have to, slip at a faster speed to get in.

Ok let’s look at that. I’ve seen it done many times, increasing speed to loose height because the spot is very close. What invariably happens is that you spend less time flying in the headwind, that the headwind usually decreases as you descend quickly to a lower altitude, and you get down to ground effect with excess speed having to bleed of more speed before touch down. All three factors makes things worse, i.e. extend the glide, the opposite of what was attempted. For this reason I often make a point of demonstrating (to experienced pilots), that if it seems you might have trouble reaching the spot, immediately increase speed as that will stretch the glide.

If you are high, then depending on wind strength and aircraft type, an efficient way to loose height is reducing speed, which can steepen the glide significantly. I do not recommend this on final approach generally because it takes away some of the margin to stall especially in case of wind shear, but it does demonstrate a principle and I do attest that it works in reality.

You are of course right that many aerodynamic modifications change the reference speeds and I recognize you are an expert on this. However, I am not sure the average pilot is able to determine how much the speeds should be changed just by practising. When a pilot recognises that Vy and best glide speeds decreases a little with wheel fairings off then I am impressed – most pilots do not have a clue, and for them it may be safer to fly the original book speeds than to find new speeds for themselves, although I agree that is far from optimal.

“it is very important, that pilots practice full landings from at least 500 feet up, with no power.”
Agree with P.DAR. There are runway marks which you can use for an imaginary fence, before trying grass strips.
When I restarted flying, with my regained PPL, I hit the imaginary fence many times with the C152, but never reported it. “Nor was the pilot required to report it.”

Maoraigh wrote:

In an SEP, fly fast enough to keep the prop turning. I’ve never done a forced landing, but have lost and regained power several times. With a windmilling prop, there’s an instant response as you fault trace.

On the other hand, if the prop stops, drag will reduce and glide ratio will increase noticeably, so I’d say a stopped prop is a good thing. On the third hand on most types you’d have to fly very slowly to actually stop the prop so it’s likely not worth it.

Know your aircraft

Practice – to validate how the a/c performs at the POH best glide speed. When the engine stops is not the best time to start experimenting with best glide Vs lowest sink rate!

Know what your a/c gliding descent rate is with wings level and at different bank angles. My a/c descends at between 1500-1800FPM depending on a/c weight, but this can hit 2200 FPM down in a 45 degree banked turn.

Above all : “Aviate – Navigate – Communicate”

Aviate – make sure the a/c remains flying. Nothing else matters if the a/c stops flying.
Navigate – Fly to a safe landing. Forget the a/c, it belongs to the insurance co. Focus on minimising injury to those on board. As said above, going through the far hedge at 10-20kts is infinitely better than stalling and spiralling in from 50 or 100 ft.
Communicate – tell someone where you are landing, so that they will get the emergency services enroute to you.

Very few PPL’s are able to execute a good PFL. They simply don’t do it often eneough.
Most don’t trim for best glide. They initially fly too fast, then too slow as they try to stretch the glide.
Many can’t pick a good field.
Most overestimate how far they can glide – and consequently choose fields that are too far away.
Most don’t know thier stall margin, particularly in a turn

Overland, in case of engine failure, max glide speed.

Overwater, far from the coast, minimum sink speed: reason, you spend more time in the air, more time for trasponder, ELT and radio calls for position identification.

boscomantico wrote:

I also found the Debonair is a quite poor glider. Get the gear and flaps down and it gets even worse.

Pull the prop fully back and the sink rate improves by about 300-400 fpm. No Beech or Debonair will sink at much less then 1000 ft / min though.

There’s a very good book by an american ex-fighter pilot, Nate S. Jaros, “Engine Out Survival Tactics”… he flies a V-tail himself and the book runs a Bonanza or Debonair as examples, incl. the numbers. Good literature for everyone, but especially helpful for Bonanza / Debonair / V-Tail pilots.