My personal opinion is that the tiny amount of streamlining they offer is more than offset by the fact that small high rpm engines are really sensitive to imbalances that can be caused by less than a good quality small aluminum spinner. I have run into balance problems a few times on small engines with plastic spinners and refuse to use them anymore, ever. As far as I am concerned for example, with all due respect to them for other products, I think the Ace 1/2A spinners are a piece of crap and I would never bolt one to any 1/2A engine I care about. I also avoid spinners on sport aircraft as much as possible unless I already own a decent aluminum spinner of the appropriate size. On a scale or sport scale model, where the model would look dorky without it, then a spinner is "worth it" in my mind IF it runs true.

On scratch built small models I avoid conjuring up designs that "need" spinners. As to an increase in rpm, yeah that might be true with a good, small aluminum spinner on a 1/2A, but I bet you dollars to donuts (whatever that means but people say it) that with a plastic spinner you'll see zero gain to a loss on one. Just my call, others feel free to prove me otherwise.

Yes I am curmudgeonly about plastic spinners on small engines.. this smiley perfectly expresses my attitude: [:'(]

MJD