Spinner size
 

Can you guys advise me on what spinner size for a .61 Four Stroke. Its going on a Hangar 9 40 Ultra Stick. Normally I kind of match the plane to the spinner needed. But in this case, what would you do ? Thanks.

RE: Spinner size
 

Really it doesn't matter what size spinner you use. It's not going to affect the performance of the engine. Just be sure that whatever size prop you use that the spinner will fit over it. And also you want one that will look good for the plane and engine size of course. But if you just want an idea, I use a 2 1/4 inch aluminum spinner on a .91 Saito engine.

RE: Spinner size
 

Its really a matter of what looks best TO YOU on the model. I'd use a 2.5 inch on the .40 size Ultra Stick.... or a DuBro shaped aluminum nut.

RE: Spinner size
 

I read in a 1940's model book that the spinner should cover the center 1/5 of the prop for greatest prop efficiency. That would be a 2 in spinner for a 10 in prop. Sounds about like what most use.

Jim

RE: Spinner size
 

I would bet that the book actually said... no more than 1/5 the dia... The center 1/5 of the prop is the least efficient area of the prop. This portion, of wood props, typically has a very fat (draggy) airfoil because of the need to maintain strength to keep the blades from flying off.

They were dealing with gasoline engines running an average of 4000 rpm also... Though the engines COULD run higher rpm.. that is where they tended to develop maximum thrust. (one 1939 advertsement notes that an engine was brought up to 9,000 rpm in testing... then the manufacturer's recommended prop for the engine is the size that matches the engine's rated horsepower at 4000 rpm acording to the prop design articles of 1938.)

We aren't as worried about efficeincy either... Our typical .40 size trainer's power to weight ratios are higher than most late 1930's to early 1940's FF models.

Some of the old information is still very good. Some of it is just "interesting." (truth is stranger than fction stuff... like the model with a wing resembling a paddlewheel off a sternwheel riverboat.)

RE: Spinner size
 

I am not sure the nut is large enough to fit the starter cone.

RE: Spinner size
 

The shaped nuts do fine n the cones... pull the cone and put it in backwards. the small hole is meant to center on a prop retaining nut with no spinner... it works GREAT on the DuBro shaped spinner-nuts.