Originally Posted by Tommycat
does create the most drag with a damaged engine? (No power)
prop...or one that's stuck in one position
We did the math in University to figure this out, and then I tried it in flight after I got my license and verified it... On a Cessna 150 with a metal prop, and a homebuilt with a wooden prop.
A windmilling, fixed-pitch prop creates about the same drag as a flat disk the same diameter as the prop circle. A stopped prop creates the same drag as a 2x6 the length of your prop. The difference *is* significant, so if you can get it stopped, you'll be better off.
However: Unless you have a wood prop, or maybe composite, it'll be hard to get it to stop turning. A wood prop will stop with only a little loading via pitching up. The metal prop on the Cessna took a very high deck angle and low speed to get the blades to stop moving.
Once it's stopped, you have to rely on engine compression keeping it there. If you've blown a cylinder, or cracked a shaft, and have little or no compression available, you *can't* stop it. If you have a constant speed prop that's gone to coarse pitch, it'll be hard to keep it there as well. And if you get your RV up over 100mph or so in the descent, it's likely that airflow over the blades will start it spinning again.
So yes, there are benefits to stopping it, but there are a lot of practical limitations that might make it not worthwhile.