Not really sure where to post this but since I want to use them on primarily .020-.061 size engines I figured better post here.


I don't know much about these but have read in several places that they are more efficient than multi blade props and used to see them on pictures of the speed planes in magazines.

The biggest thing I need to learn is how to make a counterweight. Seems one could make a counterweight that could be used over and over, so long as you can easily change the weight for balancing purposes. Keep in mind that having this feature is not a high priority but if I could do this, it would be convenient.

I show a picture of a Air-O single blade prop I saw for sale once. This hub/counter balance looks as though a blade could be replaced and even the pitch might be adjustable. Adjustable pitch is another feature that would be nice but would probably be less safe.

For now my idea is to make a sheet metal 'basket' that would fit over an existing prop hub. I wonder what I could get away with and still be relatively safe regarding type of metal and thickness. I believe I could use metal from the side or bottom of a food can. Solder or lead could then be put inside for balancing. The actual balancing part is a mystery as well. Taking weight away not so hard as it can be drilled or ground off. Adding weight should I take off too much could be more difficult. With care this won't be a problem as small amounts could be taken from the blade so adding weight to the counterbalance won't be necessary.

Any advice or experience would be nice. I should add that I know of no manufacturer of single blade props.

Also I should add that I made a single blade prop once in my early days of modeling for a rubber powered helicopter from a plan in American Aircraft Modeler. The prop or in this case rotor blade was designed to be single and lead solder was wrapped around a wire for balance.
It worked very well and everyone who saw it said it wouldn't fly because it looked wrong with only one rotor blade. It in fact flew quite well and I guess this has been something that I want to experiment further with.

Any help or advice would be appreciated.

Robert 

There are several advantages to be had with the single blade prop.  First is that it is always running in "clean" air.  Second is that the swept area is larger because you use a larger diameter than you would otherwise.  Finally the tip speed is higher due to the larger diameter, thus a higher Reynold's number and better aerodynamics.  I have often thought that this would be ideal for stunt, but it hasn't gotten high enough on my "to do" list.  The best single bladers put the weight behind the center line of the blade.  The off angle torque of the weight counters the lift of the blade to reduce the load on the crankshaft.  (How much to do this is anyone's guess, and probably only accurate at a single rpm)

" Of course, due to the short moment arm of the CW, the prop will be A LOT heavier than a 2-blader."

Paul, this is very true but I would pay that price just to see the faces of folks at the field when I go to start it.
OK. You have a point about the all up weight being higher but when it comes to most any aspect of performance one must make a sacrifice somewhere. If you want more power, there will be a sacrifice in fuel economy so in order to make  runs as long as before you will need a bigger tank which will probably weigh more and carry more fuel which will definitely weigh more canceling out at least partially some of the power gain from what ever that mod must have been.

Larry, Those points you make are correct as far as I remember, each and every one.

I need to point out that I do not want to (at this time)  use one of these props for RPMs higher than what the MFG would claim for their engine. I plan on using strictly stock engines. I am not interested in competition, Mostly I like to do things a little differently than than the majority of modelers which may be one of the reasons I like Half A engines and control line flying. I plan on using them for everyday type flying. One reason is that it is very difficult to find certain size and brand props these days. Just sort of preparing for the day... Besides When carving the prop I won't have to make sure the blades look identical!

Robert

Hi Robert,
I may be the self-professed expert in single blade model airplane props .
When I was a kid in the 50s, I often used single blade props on my OK Cub powered hollow logs and other 1/2A planes.
It wasn't for any scientific or technological reason but one of economics. At best, I had to scrimp and save my money and use all the ingenuity I could muster just to do 1/2A control line flying.
My paltry twenty-five cent weekly allowance would only buy one wooden Top Flite 6x3 prop and it only took several flights with their controlled crash landings to break a blade. We kids would then wrap and glue copper wire, scavenged from electrical wire, around the broken blade stub until the prop balanced and then we would go out and fly until we broke the other blade. Statistically, the single blade'r would last twice as long. I'm not sure we noticed any difference in the already lousy performance! Often, the blade would snap so close to the hub that we could not wrap it with wire.
  This resulted in an invention. I came up with a strap about 1/2" wide by 1-1/2" long made up of three or four folded layers of tin can stock. I drilled a hole at each end, one for the prop bolt and the other for a bolt holding a number of washers which could be added to balance the broken prop. This strap replaced the front prop washer. This worked really neat and repairs could quickly and easily be implemented in the field.
This was all rendered obsolete when nylon props became available. We thought we had died and gone to heaven!
Thanks for evoking these memories, I had forgotten how resourceful we kids could be in pursuit of our passion!

Orv.

Robert
There is nothing in the current CL Speed rules about a single bladed prop but I have attached a copy of the 1986-1987 PRINTED rule book that covers making a Single Bladed Prop.  Sorry for the poor copy.  If you need a better copy I will have to set up my digital camera and photograph the page.

Clancy

The chart is hard to read in the copy:
Minimum thickness for metal used for construction of weight retainer for single-bladed propellers.

Engine displacement
.000 cu. in. to .0504 cu. in. = .015 in.
.0505 cu. in. to .1525 cu.in. = .040 in.
.1526 cu. in. to .4028 cu. in. = .080 in.
.4029 cu. in. to .6500 cu. in. = .120 in.

I could make it out Larry, it says steel or brass.
Thanks Clancy, I can make out what's what from what you posted but others could benefit from a larger view.

The "basket" as they call it is pretty much as I had imagined. They do show a detail I had not thought of and that would be flat sheets of lead in the bottom for the balance. My initial thoughts were lead shot for balance but I also know you don't want anything loose to worry about when it comes to rotating mass! The best Idea I had thought of up till now was an adjustable bolt and nuts. My problem with the bolt and nuts is that if something came loose... Loctite would be useful here.

Robert

I have never used a single blade prop, but it would probably impose a LOT of side thrust causing excessive wear on the crankshaft if you intend to use it a lot.

Good luck with it.

George