on small motors <.15, are spinners needed?

do they serve any pupose other than making the plane a little more visually appealing?

Yes and no. Spinners aren't really required on any size engine. They do make it easier to start with an electric starter and as you noted, more visually appealing.

They have no aerodynamic properties???? They sure look like the'd help airflow around the nose.

Technically they do streamline your model a little more. But unless you're in a racing event or going for a world speed record they are stricly decorative. After all we really aren't that concerned with that last couple of % of fuel economy or that last couple of % of speed.

The plastic ones can save a crankshaft in a hard crash..... Yes I have expreimental data t osuppor this......

hahah - that made me laugh!

It still looks like it is the easiest way to improve aerodynamics on a plane - especially no cowel planes like sticks. It all seems like it gets harder after that. I'd guess retracts are the next thing to do but that is a lot harder than adding a spinner.....

I think I have had a plastic spinner cushon impacts too!

OK, so they DO have a function I guess..... And yes I've had both the rubber ones and the plastic ones absorb their share of kinetic forces. The plastic ones actuall absorb quite a bit of energy when they shatter.

I read an article in a older(80's or 90's) model mag about spinners. IF I remember right their tests should an increase of a few hundred rpm using a spinner. Granted it was on a larger engine like a .40 or something but I would think some of it would carry down to our smaller engines.

LAter,
Tim

My buddies Scale Race II ( a plain Bearing or Fox 15BB varient of Scale Race) is 2 tenths a second faster around the circle with a spinner than without. 140 laps per race, he uses the spinner. Course if you ding the prop on landing you loose everything pulling the prop, but a clean race saves you 28 seconds and THAT is a lot in any race. Multiple tests with different props, this was the average.

If you're not racing though, it's merely an opinion of looks and ease of operation.

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

I don't know what it means, but if you don't have any donuts to offer I wish you wouldn't mention them. Dang, there goes the stomach again.

You sir, are evil.

Well, as a matter of fact I DO have donuts here.. but face it, by the time I lose a bet to you, get them packaged up, and they arrive by mail - they just aren't going to have the same appeal as the fresh article. Actually, our grocery store has the best donuts of any outfit around here, they make nice yeast donuts daily and the chocolate glazed are a fine piece of work. Remember, jeans come in any waist size you need. Myself, I always buy the "stretch" variety, they just seem to feel better for some reason now that I am well on the other side of 40..

And I still hate small plastic spinners.. [8D]

I haven't weighed a spinner and compared it to the weight of a 1/2A prop, but I'm guessing it would add 40 to 60% to the rotating mass. While this might help smooth out the engine at idle, it will retard acceleration and require power to keep the spinner rotating. If mass were good, we wouldn't be using small aluminum prop washers, we would be hanging fat fender washers on there anticipating that additional rpm gain.

Don't you big engine car guys dump those steel flywheels and replace them with the lightest aluminum flywheels that will work? With the size engines we run, any power robbing addition has an impact -- I'm not sure that drag reduction will be enough to compensate.

Just my call, others feel free to prove me otherwise. BTW, I don't have any donuts.

If your speaking of Cox engines...I have had better balance without the factory spinner. Using one extends the bolt length required, and if the face of the prop isnt square (most cases) it will push the spinner off to the side, or simply not locate right. Usually the bolt threads are smaller than the internal threads in the crank, and have slop to allow that to happen. The longest screw the better.

If your going to use one, it sometimes takes a few attempts at tightening to true one up. A slight tap with a long dowel past the prop as its running (if you want to risk the chance of hurting yourself) will sometimes get it to run perfectly true and balanced.

You can call me crazy for suggesting that now, but I haven't found a better way to do it with a solid spinner. Machinist indicators can help if you want to mess with the setup.

Seen that too. I much prefer a good fitting washer and shorter machine screw.

Andrew - yup, IMHO the more rotating mass the more the precession forces during any kind of directional change, the more sideload in the crankshaft and thus the more mechanical friction. In equilibrium flight (for those brief moments where that actually occurs), there is still the extra mass cantilevered in front of the bushing/bearings, and thus the more sideload as well. How much effect I cannot quantify, but I bet the last of those day-olds in the fridge it is a factor to some degree. This is one reason I DETEST the concept of heavy spinner nuts for aircraft balance. I cannot think of a more cruel place to put a big chunk of metal. I would always choose slightly more weight, located aft of the prop and NOT on the crankshaft, on the motor mount or wherever is convenient as an alternative. Brass spinner nuts get another barfing smiley from me: [:'(]

MJD

The GZ .061 spinner is a masterpiece of machine work, and I would think is adaptable to other 1/2A engines. I've never had any luck with plastic spinners on 1/2A engines. Anything but running perfection will rob gobs of power.

Andrew, depends on the application. Sprint cars dont use a flywheel. Some drag mobiles used to run a heavy wheel to keep the "Rs" up right after dumping the clutch. This thinking might be considered "old hat", but those pictures that you used to see of a '68 Camaro resting on its' back bumper probably had something to do with a 40 pound flywheel spinning at 7500 meeting the back half of the [soon to be woke up] drive train.

CP,

I have aCS(GZ) 3 piece spinner I have ran on a Norvel .061 from a few years back. Like you said very nice indeed. Just had to make an adaptor for it.

LAter,
Tim

CP --

I'll certainly take my lessons from the more experienced -- I expect there are a bunch of high end car guys on this forum. Unfortunately, I've never owned a vehicle that would spin much of anything at a high speed, although I have spent quite a bit of time running 4 wheels in the mud.

it never hurts to have a nice leading edge to the prop. Even though it is not necessary, I like to have them just to use my electric starter