I was (re-)reading a post on the Malibu forum, where a new owner checked the actual glide range of his aircraft by shutting the engine down. (He did restart without problem ,and my post here is not about whether this was a good idea or not). What strikes me is the following:
- he saw almost no difference between corse and fine pitch, maybe because lack of oil pressure
- he couldn’t stop the prop, even stalling
As a result, his glide was significantly worse than book (1.5nm / 1000 feet instead of 2.2nm) which leads me to revisit my engine out scenari. I’ve never trained by shutting down the engine so have always approximated the book values with a combination of power and landing gear, so I have actually no experience of how easy it is to stop the prop (other than having the engine blow out entirely of course). Have people done it, and how?
In reality there are many more important tasks than trying to stop the prop. Some airplane you almost have to stall before the prop will stop – and that doesn’t really improve the glide – and it’s not without risk, especially in a Malibu and at low altitude.
Hi,
tried this in C172 many years ago actually with an instructor. It required quite a long time at least 1 min at below 50kts knots to get the prop to stop. A heavier CS prop in fine pitch (parking position due to lack of oil pressure) probably takes even longer. The thing was to reduce speed so the prop visibly was slowing down and then wait..
Alexis wrote:
especially in a Malibu and at low altitude.
Well indeed. But not so at typical cruising altitudes, where you actually have a lot of time. At 20k feet, if you gain 7nm of glide by managing to stop the prop, that’s worth investigating.
mcrdriver wrote:
It required quite a long time at least 1 min at below 50kts
That’s a very good point – the prop needs to loose inertia.
mcrdriver wrote:
tried this in C172 many years ago actually with an instructor
Until today I have not dared turning off the engine ignition and/or pulling the mixture. Feels like asking for trouble although I know it should be harmless.
denopa wrote:
That’s a very good point – the prop needs to loose inertia.
Also has to do with compression. On an engine with good compression and a lot of cylinders, it should stop more easily. Same for light MT prop versus heavy McCauley.
I have done it in my Warrior with the ignition key, at 5000 ft above EDMS, The Warrior is such a great glider. Put the ignition on “both” and it starts immediately. Have not stopped the engine with the mixer at altitude though, and wouldn’t … and I’d not try it in the Cirrus with a 1:8 glide.
Alexis wrote:
I have done it in my Warrior with the ignition key, at 5000 ft above EDMS, The Warrior is such a great glider. Put the ignition on “both” and it starts immediately. Have not stopped the engine with the mixer at altitude though, and wouldn’t
That’s a recipe for disaster. If you turn off the ignition but leave the mixer in, a lot of unburned fuel will collect inside the engine and in the exhaust. The moment you turn back on the ignition, all that fuel can ignite, you get a big blast and cause severe damage to your airplane.
Sorry, no I did not do that – i remembered it wrong. I pulled the mixer, turned of the ignition and then I put it on both and advanced the mixer..
I am well aware that you could blow off the whole exhaust otherwise :-)
It’s ten years ago …
Edit: checked an old video where made these experiments … we just pulled the mixer and advamced it back.
Please share?
It’s a V-8 tape, can’t digitize it at the moment, but will! No iPhone back then … ;-)
