WALTER KERR wrote:

Hi Dale,

 

Did the 123's windmilling engine have the blades at flat pitch?

Yes, about as flat as you can get.  When the jug blew, it came off with such force that it went through the cowling, and severed all the oil pressure feathering lines to the prop.  Large fire blazing away with all that oil everywhere  Large quantity of 115 / 145 octane in nacelle tanks behind the engine.  Lots of pucker factor.  When the engine seized, the blades were still very flat to the wind and still a lot of drag ... but a lot less than having to wind crank 18 dead cylinders.  We were almost able to maintain altitude with the other engine running at max continuous power.

 I did engine off testing in my RV6A 160 lyc with 80 inch pitch metal sensenich prop. The glide slope was not measured to be any difference whether I windmilled the prop at best L/D speed or whether I pulled up slowed enough to stop the prop turning and then returned to same speed.

There is a massive difference in drag between a shut off engine with an uncontrollable prop that cannot be feathered forcing you to continue turning the cylinders over by the "windmilling effect" alone ... and just powering back a perfectly good motor.  Imagine the drag you would have if you threw a rod, shut off the fuel, but still had to continue turning the engine over at the same speed.  FORCED windmilling of a dead engine ... no fun at all.

In all fairness, the sprague clutch mentioned would be closer to the situation you relate ... it would disengage, and thus NOT be required to turn the engine over.

Dale Smith