In a light twin with fixed pitch props, there's a really good chance that the dead engine won't windmill anyway at the best speed for staying aloft/climbing.On our small, maybe automotive powered two-seaters I wonder if a prop with skinny blades like a Warp Drive could be streamlined enough when stopped. It would need a prop brake or maybe just a PSRU ratio that doesn’t allow windmilling.
Well, at least if the dead engine is still making compression.
If it's a problem, the brake set from a mountain bike could be used to stop the spinning and not do further damage to the engine. Spring loaded, just release the cable. If it deployed by mistake somehow, just keep applying the throttle until we burn through the brake pads.