Hello everyone! This is my first post so here goes. How do you determine the proper spinner size for an engine? Is there an advantage/disadvantage to a small or big spinner? I'm getting a OS 91 Surpass engine and would like to know what size spinner I would need. If there is other factors like size of prop and type plastic/aluminum spinner that influences my decision let me know. thx

Welcome to RCU MUTTLEE!

Spinner size is dictated more by the airplane that the engine. Most ARF's provide a spinner and most kits tell you what size you will need to get.

MOST of the time, you will have to enlarge the holes for the prop. A Dremel tool makes quick work of this.

On more powerful engines, like four-strokes, you might be wise to choose a aluminum spinner over a plastic one. Those 4-strokes make a lot of torque and the backplates on plastic spinners sometimes can't handle the extra stress. Aluminum spinners generally spin truer than plastic ones, too.

Jesse

The spinner size is selected by the size of the cowl and the profile of the plane.

Sometimes... the prop hub limits you from going down to the spinner size you desire for appearance. In those cases, you can find that the shaped prop nuts by DuBro and others will work (great for apprxoimating the rounded hub on a Corsair....)

Or maybe the shaped nut is too small and the smallest spinner that is safe to use on the prop is too large for the desired appearance. We usually fudge with an oversize one when that happens. Some people will build up the prop hub and CARVE a custom spinner in this case...

The guy at the hobby store told me when I bought mine that the outer diamater at the back of the spinner is not to extend above the lower edge of the carbs intake throught. He said larger than that would interfear with the carbs airflow and anything smaller is fine. Sounded good to me so I used a 2 1/4 on my .40 ASP.

Hate to say it... the guy at the hobby shop is clueless...

You can put a 6 inch spinner on a .40 engine if it suits the model. it won't interfere with the carb getting enough air. (you may need to do some air directing to cool the engine though)

So it's really more of an "appearance" decision than anything? Maybe someone could relate...I'm building a Carl Goldberg Matrix 40 3D ARF so as long as the backplate doesn't go above the engine cowl it should look alright? Thanx for all the info

FHHubber is right on, it's totally an appearance thing, the guy at the shop is clueless.

Next time you talk to him, ask how 4-strokes and other engines with rear-mounted carbs work .

(for intersting carb setups, those of you who heard about the Trans-Atlantic model thing might find it amusing to know that the engine used (an OS .61 FS, modified quite a bit), had the carb mounted on the end of a rather long bit of plastic tubing, and the carb was actually back inside the fuse, behind the firewall. It was also a carb from a .10 size engine, itty bitty.)

I've used spinners bigger than the carb many times, no big deal.

One thing a bigger spinner can do, is make your plane go faster. If you have a stick-type or other model with an exposed flat firewal, mounting a spinner that is about the size of the fuse, or a little bigger, will help reduce the drag of the front of the plane, and make you go a little faster.

Oh, and if you are worried about covering too much of the prop, don't be. The vast majority of the thrust is generated by the outter portion of the prop. You can cover quite a bit with out much of an effect.

You hobby shop guy is wrong. What do you do with a 4 stroke that has the carb in the back????