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Shutting engine down for training purpose

I’m puzzling. Of course one does the typical “engine out” training, but the engine is not out during that exercise, we all know that. It is idling. Prop and mixture full forward.

This situation can be trained to quite some standard, but I’m not convinced that this gives a real training for real engine out situation. The glide ratio stays quite constant. It is just a short pattern. Of course it opens the eyes to see how fast the ship will sink towards ground. But to estimate a glide from that training? Say when the engine quits in cruise at 10.000 feet. From that exercise you don’t even have time to get a feeling for the behaviour during glide, because everything goes so quick.

But how differently behaves a typical SEP when the engine really stops? The prop will most probably be windmilling if the engine’s not blocked. The prop lever will do exactly nothing. I don’t buy that there’s any difference in lever position, because in typical SEP installations the governor is designed to let the prop rotate at at least 1400 RPM. But on idle or cutoff the prop will not be turning much faster than that if you stay at best glide speed or below. So the springs keep pushing the prop to fine pitch.

I would also be interested to see whether I could make my prop stop from windmilling and at which speed.

And then there is the shock cooling argument if you shut the engine down in flight.

What do you guys think: Is there something to obtain from such a training? Or is it just too bad for the engine and the risk involved in that sort of training not justifying it?


UdoR wrote:

But how differently behaves a typical SEP when the engine really stops?

I have had one real one. Towing gliders with a Piper Pawnee. The typical descent is rather fast when the glider (finally in this case ) let go. It must have stopped sometime during that descent, but I didn’t notice anything before I wanted power again, and no power came. The glide ratio of the Pawnee isn’t exactly stellar, but I can’t say I noticed any difference with the windmilling prop compared with idle. Physically there must be some difference, but at least in the Pawnee it’s just too small to notice. Wind, turbulence, thermals etc tends to enter into the equation also. Way up there, you don’t visually see anything difference, except if looking at the VSI. Is it a thermal, is it a downdraft, or is it more drag from the prop? How to tell?

There are procedures made by clever people ages ago that will let you touch down at the right spot regardless of actual L/D. Just too bad they are not normally taught today.

I don’t know if shock cooling really is any issue at all. It’s more the shock heating that occurs once the power is applied again IMO (no time is given to let the engine gradually heat up as in a normal start and take off).

The elephant is the circulation

I also thought the same when doing practice forced landings – just how representative would they be with an engine at idle rather than an engine which had given up the ghost – until I was given training after buying my current aircraft – the instructor said: Let’s do some engine failure practices" and suddenly pulled the breaker for the electric fuel pump – my Rotax has two electric fuel pumps, meaning, with the auxiliary fuel pump switched off, the engine quit and the propeller stopped – this surprised me as I expected the electric constant speed propeller to windmill.

It’s not the only time we did that routine, the instructor made me perform 4 landings with a stationary propeller from different locations around the airport such that I could gain a feeling for the glide performance of the plane, for which I’m grateful – one was carried out at pattern height, half way down the downwind. This in itself was for me an eye opener as the plane was able to glide all the way around to land (17:1 glide ratio).

EDL*, Germany

In the case of single engined airplanes, some engine “off” gliding practice is beneficial. It is wise to know for your type what it actually does in this situation. Some constant speed props can be selected (and will move to) coarse, others will move to that pitch setting on their own. If a constant speed prop is going to move to, and remain in fine pitch, that’s something you should know. If you’re flying a single which will feather, lucky you! There are a few. If you’re flying a PT-6 powered airplane, you can actually feather it at idle power, and leave it running. I have done this many times in the Caravan. Be very, very gentle bringing it out of feather though!

Depending upon what propeller you have, the drag from windmilling may be significantly greater than while completely stopped. This is worth undestanding. In my recent testing of one constant speed propeller airplane, I have found that the rate of descent windmilling is 1700 FPM, while prop stopped is 1100 FPM. That’s a different that one should really know about! My (MT 3 blade) flying boat has a 1600 FPM idle power, fine pitch rate of descent. When I select coarse pitch, it’s 1100 FPM. I have not tried engine off gliding in it yet, I want a longer runway than my home runway before I fool around with that, lest it does not restart! Whenever I do shutdown testing, I do it on high final approach to a suitable runway. I have confused a few air traffic controllers with this request!

If it’s a fixed pitch prop, sure, shut down, and understand what the engine does, and how it glides. I used to do that in the 150, and it was delightful to glide prop stopped. Again, make sure it’s going to start again! If the plane has no starter, I’d do it at a very high altitude over a suitable runway, so you have room to dive for a windmill start, or, make the runway power off!

If it’s a multi engined airplane, engine shutdowns should be at altitude only. Practice engine off approaches are just not worth the risk. I’ve done them in a number of twins, and understanding feathering/unfeathering is good. ON the other hand, most twins I have flown will give you a zero thrust power setting to simulate flying with a feathered engine. Be very aware that in some twins, if you shut down, and do not get it feathered about a certain engine RPM, the pitch locks will engage, and feathering will be impossible. In a real engine failure situation, this is rather dangerous, and should have you in mind of a committed landing, using only a little power from the other side. If during practice, make sure you can get the engine running again, so you don’t end up doing a committed unfeathered landing from a practice event!

In any case, if a piston engine, consider the possible effects of shock cooling before you shut down, and consider the effects of very cold air over time on the ability to restart. I had a 310 engine on a winter day be very difficult to restart.

Home runway, in central Ontario, Canada, Canada

Pilot_DAR wrote:

the pitch locks will engage

Interesting. This shouldn’t exist in a Single. Obviously I was talking about a single, because in a Twin you train the OEI stuff to death. But not so in a single, other than the landing out of a dedicated height above field.

I’m not quite unfamiliar with gliding, and have many hours soaring in different TMGs, some with retractable prop, some with electrical constant speed prop that do feather. It’s out of this experience that I am curious to find out the best settings with a healthy engine and not when there’s stress in the cockpit. The difference on my Comanche with respect to glide ratio is already impressive with gear retracted / extended, but would be interesting to see how the engine behaves.

It is a big difference if you can get it gliding according to book values (I read about something like 1:13 optimal glide for a Comanche 260, which means that for each 3000 feet of height above terrain you get 7 miles of range, that could be around 20 miles for typical cruise altitudes) or whether one has to calculate conversatively like 1:6 or less, because you just don’t know how it will perform.

Thank you for the very interesting input on this, Pilot_DAR.

Last Edited by UdoR at 27 May 07:04

Pilot_DAR wrote:

has a 1600 FPM idle power, fine pitch rate of descent. When I select coarse pitch, it’s 1100 FPM

With a constant speed prop, you literally have an adjustable airbrake. Not so much with a fixed pitch prop.

The elephant is the circulation

LeSving wrote:

With a constant speed prop, you literally have an adjustable airbrake

But only in the case that the prop is windmilling at too high RPM. I’m not convinced that the autorotation of the prop at best glide speed is in fact high enough to get the prop to coarse setting. But I don’t know that, how should I? On my aircraft with a hydraulically operated prop the governor sets pitch according to RPM, by means of flyweights. If RPM is say below 1200 it won’t alter the pitch when pulling back the blue lever, it will stay in fine pitch, or “as fine as possible” to maintain the RPM. You can try this on ground, with slightly above idle RPM and pull back the blue lever. Could well be that nothing happens below a certain RPM. Or in other words: you won’t shut down the engine by the blue lever. And it seems to depend to a high degree on the setup installed on the very aircraft, according to my understanding of what Pilot_DAR added. That’s also a valuable input.

Last Edited by UdoR at 27 May 07:13

UdoR wrote:

Is there something to obtain from such a training?

well, becoming proficient in precise engine off landing might one day pay of
my experiance is that on RV14 flight characteristics change significantly with the engine off, I mean off, not idle

full disclosure, I learned flying on gliders and till today, more air time on gliders than airplanes


If RPM is say below 1200 it won’t alter the pitch when pulling back the blue lever, it will stay in fine pitch, or “as fine as possible” to maintain the RPM.

Years, that’s true. There are many variations. On aerobatic planes, it will usually default to course, but I think only if the oil pressure is lost. Full airbrake it is then

The elephant is the circulation

This is a good thread too.

Shoreham EGKA, United Kingdom
49 Posts
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