Shutting engine down for training purpose

Generally, a fully idle engine drags more than a non-moving prop. Engine friction at best glide speed is generally enough to stop the prop completely. Windmilling takes a lot more airspeed. So in a real engine out situation you end up with less drag and a better glide ratio.

1. Most engine out exercises teach you to continuously adjust your path based on trajectory, and there should always be some room for adjustment, as long as possible
2. There may also be engine settings that more or less accurately reproduce the same drag / glide ratio as a stopped engine (like 15% power)

In any case, stopping the engine during an exercise is a really bad idea. Especially if doing low altitude real glide estimations, you have tens of seconds max to do a hot start. And if your starter happens to fail (or you get vapor lock, or get some starting setting wrong, or even it takes too much time), you crash basically for free.

It reminds me of a fiercely lead discussion on sailing forums: is it better to stop/block a prop for a sailing race or let it windmill (actually, watermill) ?
If it takes more energy to drag a windmilling prop through the water than a fixed one, why does the prop start moving anyway when you pick up speed after setting the sails ? Does it really start moving against a higher force relative to the stae it is in ?
Should the total system not stay at the lower possible energy level (read: with the prop staying still) ?
I may very well be missing/forgetting something from the old discussion, but that was the essence…

I know it’s not perfect, but this is something a simulator based on Xplane (which actually models the aerodynamics of the different components, including the prop if I’m not mistaken) can yield some good take aways. Another thing you can do to practice, if you have a retractable, is to put the gear down with an engine setting which gives you “book” descent rate.

By the way during my turbine training, I was absolutely shocked by the glide performance of the PA46 with the engine at iddle, it’s excellent, and when the instructor put it at what he estimated to be zero trust (120lbs of torque), it felt the thing would NOT come down ! That gave me quite a bit of confidence in the published numbers for the piston version, which are in excess of 2nm per 1000 feet of altitude, assuming you can put the prop in coarse.

maxbc wrote:

Engine friction at best glide speed is generally enough to stop the prop completely.

not my experience

maxbc wrote:

In any case, stopping the engine during an exercise is a really bad idea. Especially if doing low altitude real glide estimations, you have tens of seconds max to do a hot start. And if your starter happens to fail (or you get vapor lock, or get some starting setting wrong, or even it takes too much time), you crash basically for free.

there are countless examples of airplanes big and small flying and safety landing engine out: space shuttle, B767, A320 on Hudson River etc

Engine friction at best glide speed is generally enough to stop the prop completely.

On most SEPs with Lyco/Conti engines, no.

I’ve seen it done, by (IMHO) a cowboy FI, in a C152, and it took around Vs and with the nose about 30 degrees up.

Let’s say engines don’t stop spinning and create more drag than when idling (it’s still unclear if this is actually the case – most probably yes since the idle engine is counteracting part of its internal resistance at least, while RPM would be very similar). So in theory you would get a better glide ratio estimation by cuting off the engine during exercises.

Basically engine out is an emergency situation (no matter the cause). Don’t put yourself voluntarily in an emergency situation just to evaluate glide distance. If you then land in a field and damage the prop or landing gear you’ll pay for everything from your own pocket, as insurance can’t pay for damage induced as a result of voluntary causes.

You may also get your license removed for not ensuring the satefy of the flight.

Think of how many power-off glides you’ll have to do in order to get a good grasp on your real glide distance. Especially if you want it to be useful at the time you need it (maybe a year or more after practicing), you would need to do this more than once. You need to do it in different wind conditions.
Aircrafts falling short of a runway (like the other thread) are most likely based on bad decision making (i.e. choosing to attempt the runway instead of choosing a closer, safer field), or lack of other options, and are most probably not a result of bad gliding estimation specifically because during training the engine was idling instead of windmilling.

On reddit a CFI says he cuts off the mixture above a runway (“with the right student and right conditions”), which is far off from doing that over a longer distance to estimate gliding ratio.

Instead, learning to adjust your profile in order to make the field (i.e. don’t do a straight in one shot but use the different circling exercises which allow for continuous adjustments almost until the very end; aim a little high and make use of flaps or slip to dissipate extra energy) is a much safer and more versatile training method than doing the required dozens of engine cutoffs just to slightly better estimate the gliding ratio.

A lot of self-induced risk for a questionable result.

My guess, when you want to practice engine out landings you don´t mess with the mixer, just leave it where it was for cruise and pull back the power . So then you get normal idle speed as set on the ground and no reason why the engine should stop just by windmilling. Most forumites here will not believe it but while training for PPL all pilots in the school REGULARLY made ALL landings with engine at idle. This was easy once you knew where to set idle from pattern altitude to exactly hit the runway in gliding configuration. You set flaps AS REQUIRED , so this helped when you found out late you were too high for the runway. Sort of brakes then. We did lots of Ziellandungen , meaning you arrived at say 2000 ft above the airfield and set idle speed exactly over the runway for gliding down . So you had 2000 ft to share for a square , no curved approaches, but a square with 500 ft each side for loosing height. Simple to do, turn right 90 degrees and watch altimeter for 500 ft loss , then turn right 90 degrees for next 500 ft loss, another 90 degrees and 500 ft, so with last side of square you will be in perfect position to hit the runway. All sides of square made with idle engine certainly, no problems from that. Reason: In an engine out emergency you will do same actions in gliding configurations so better do trainings to get used to this, best in PPL training as well. With our radial and huge wooden prop we keep some minimum power for landings as the glide at idle would be a dramatic angle. Vic