SonexBuilders.net

As I slowly (hindered by MGL MX1 antics) get used to my RevMaster powered sonex-a I got to wondering a few things about glide ratio and air restarting.

It's not something we practice often as powered-pilots, shutting down the engine in flight, but it seems it could be valuable in getting to better know your plane. Engines can and do stop, occasionally, seems it would be helpful if a power loss was practiced while under ideal circumstances. How many here have done this on their VW based power-plants?

Q. What airspeed have you found required to keep the propeller (I have a prince p-tip) turning?

I know pulling the mixture is such a benign event with the right airspeed and altitude. However the thought of doing so gives me butterflies. There is always the thought....What if it doesn't restart. Share your expirences.

OK, next time I'll use the search then ask my questions. Instead of the other way around...
viewtopic.php?f=4&t=6371&hilit=air+restart

Though, perhaps someone has further comments to the discussion.

Hi Brock,

A little more info on air restarts: http://sonexbuilders.net/viewtopic.php?f=7&t=4652&p=35614&hilit=air+restart#p35614

Don't know the answer to the windmilling question.

Wes

While doing glide tests (not with the Sonex) I was routinely starting and stopping a prop. The determination being (as expected) that you glide further with a stopped prop compared to windmilling. I was high over a deserted airfield while testing. Getting the prop to actually stop windmilling required pitching high and well below Vg - almost to a stall - to get the prop to actually stop. That was a heavy metal prop with a lot of inertia. "Dive to restart" tests - to get the prop to spin again - showed that the prop could start the engine more easily at higher altitude than at lower altitude. Put that down to the "lower" (thicker air) density altitude at low altitudes making for a denser mixture in the cylinders and so harder to compress.

Where I used the starters - restarts were simple "hot" starts per the book from a mixture standpoint.

I have never considered repeating the tests with the Sonex. The light Prince prop has no inertia and I GUESS it will probably stop very easily.

The restart will PROBABLY require the starter and for the AeroVee/AeroInjector I would use the hot start procedure.

Graeme, all of your information is correct, except your explanation of the air density and starting ability seems a little suspicious…

Never really understood the physics behind a stopped prop being less drag but it is in fact hugely less drag than a windmilling prop. In a real engine failure, our light props will stop quickly. If someone has already tested actual glide (knots, fpm, altitude, weight) that would be interesting to review. It would also be interesting to compare that to idle glide to know what the difference is. I suppose idle, as everything else, is all relative to what the builder has built.

Cheers, Gordon

Stopped Prop less Drag. The elastic powered model plane guys have the data on it. In their endurance contests they arrange that the prop stops when it is out of elastic and they glide farther. Something about a toothpick (stopped prop) drag compared to a spinning flat disk offering drag and using energy. Sailing ships are the same. You lock the prop - you don't let it trail - unless using as a generator).

The other aviation standpoint would be a twin with an engine failure. You secure and feather the failed engine to minimize drag and keep the plane controllable.

--

To my DA / compression start theory. I got very repeatable results and was trying to figure what it was. It was my long time mechanic who had been an AP in the Air Force who immediately suggested it on the basis of something he learned there. It might be something else.