Single blade prop

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Kez

Well-Known Member
Joined
Feb 27, 2003
Messages
1,230
Many early control line rat racers used a single blade prop. I still do not understand the advantage of a single blade prop vs a two bladed prop of the same pitch. If there is a clear advantage, why hasn't it been tried in RC boats? I can imagine it would require a pretty bulky counter weight for balance.
 
Gary Pruesse tried it, he raced the Mini Gold Cup with one back in the early 70’s. In order to balance he still had to add a lump of solder/lead to the hub where the missing blade was. Thanks John
 
Hi John,
What is the advantage of running a single blade prop?
Other than a bulky weight to balance the missing blade, causing drag and affecting hydro dynamics. In my opinion, a single bladed boat prop cannot really be dynamically balanced on a static prop balancer.

kez
 
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The difference is the airplane prop is in the air at all time. The boat prop would work if it was under water at all times also. But to counter balance any one blade prop would be a nightmare. Most of our boats run surface drive these days thus having one blade on the water at the same time which is close to the same as a single blade. The only difference that it is running at two times the speed if it is a two blade prop.
 
I agree totally with what Mark said. When Gary tried the single blade many were still running subsurface drives. I see no reason to revisit it today. There are far more things to do to a boat to increase performance.
Thanks John
 
I guess my point is that there is no advantage to running a single blade prop whether it is air prop or marine. If it works, DC3 would have been running these.

Thanks, kez
 
Actually, when used on an aircraft, a counterbalanced single blade is more efficient as there is not the turbulence from one blade affecting the airflow over the other. What you have to remember is that the blades used on aircraft are considerably longer and narrower than on a boat prop so the counterweight's turbulence doesn't affect the air going over the single blade
 
the first boat prop made was single blade. looked like a screw more than a prop. Have had this in my head for some time will have to give it a try some day.
 
I can't imagine a single blade propeller working on a model boat for most of the reasons listed above. but they do work on model airplanes. Single blade propellers are used exclusively on F2A controline speed airplanes with .15 engines turning in the 40K RPM range and speeds well over 200 MPH. You can see some of these on Youtube. The single blade is less drag and more efficient than the usual two blade prop. I made some spinner hubs for some of these engines some 25 years ago for a friend who was building some airplanes for this class. The counter weight was built into the spinner backplate and there was a special way that the spinner, backplate, prop assembly, etc. had to be balanced. It would not work if you static balanced it like a regular propeller. I have the formula for the way we balanced these somewhere around here in one of my books. It was a pain in the a$$ to make this stuff and balance them but when they were right it really helped the performance.
 
Plus single bladed racing air props could be adjusted (pitch wise) with a thin shim between the spinner backplate and prop hub. Its racing -------- no amount of pita is too much to get an advantage. Mono lines, line groupers come to mind.
 
I use to race F5D pylon planes in the early 2000s. There was a guy in Australia that made 1 blade props and I tried a few. The first thing you will notice on a 1 blade is they are a lot louder. I found them to be as fast as 2 blades but not really faster. Because you only have 1 blade in the air, you could get away with using more pitch. That's how they can be faster. But they were incredibly hard to balance so they could spin up to full potential. Also, a 1 blade prop was a lot of money, $75. versus $4.00 for a 2 blade APC. In F5D you really needed to be able to adjust the pitch according to weather conditions. APC props could be adjusted in pitch by using a heat gun, so the fastest guys used those and not too many 1 blades flew in competition, even though we all had some in our box. The 1 blades had a counter balance of lead on one side which was hiding under the spinner. I don't see how you could make a good prop for a boat but I'm sure it could be done. But with props half out of the water, I see a 1 blade not working as well for heat racing versus a 2. They could possibly work in a saw boat because a 1 blade loads the motor less, but there very difficult to balance properly and hard to make. It would take some dedication to get one to work.
 
Came across this on youtube.

If you watch some of the YouTube videos with engines like these when they fly them in the F2A speed airplanes you will notice that when the engine is started it starts out with a low RPM. The person holding the airplane will point the nose of the airplane downward which will lean the fuel mixture ( it uses a suction fuel tank ) and the engine will come up a step on the pipe ( increase the RPM's ). The mechanic will then launch the airplane ( which is in a dolly with wheels which will drop away when the airplane gets airborne ) and the pilot will then grab a pole next to him ( we call it a pylon ) and whip the hell out of the airplane until it jumps up again on the pipe in the 40K RPM range. The pilot then then puts his hand in a "u" shaped swivel on top of the pylon and he is timed by officials on the outside of the circle for 7 or 10 laps ( I forget which ) for his official speed. The pilot needs to be rather athletic to keep up with the airplane. Check it out.

Dick Tyndall
 
Hi,
the reason for a single blade propeller is that the singelblade has only one fortex on the blade tip rotating. This fortex is loss but as Dr.Martin Hepperle say, the number of blade dosnˋt influence efficancy very much and moore blade have higher efficancy as the blade load is lower.
http://www.mh-aerotools.de/airfoils/jp_propeller_design.htm , An singel prop makes only sence when running full submerged under a hull. I know only one Austrian F1kg modelboater running such small carbon fiber made propeller. We beat him by other boat setup.
I you give it a closer look a two blade surface running propeller is like a singleblade propeller as allways only one blade is in the water , having only one fortex. With three blade it is close to and four blade worke like a two blade full submerged in water. A othe sideeffect is the at very high rpm the turbolence of the blade destroy the airflow of the other blade . Single blade run in cleaner condition. In F5D electric pylon racing they do test witch good result as the last worldchampion fly with a singleblade prop. And other have nice design like this in the pic , a outrunnermotor with singleblade. Run fast doing 71 sec for the 10 lap race and is very noiceless as the outrunner has higher torque and lower rpm . This was the first race for this boy and he is doing very well. http://www.rc-network.de/forum/content.php/447-F5D-Pylonracing-in-Herzebrock
With a friend we designed some test adjustable pitch propellers . With a single blade it can be a self , trust related operation design. The pin show how to place the hinge.Thisnanglemcan be different for higher or lower effect. If trust at low speed is high the blade will force forward it lower the angle of attack and at higher speed the rpm rise and the trust is lower the blade swing a little back and rise the angle of attack allowing higher speed. Need a lot of propellers to get the right one , but has worked nice.

Happy Amps Christian
 

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Super cool props was the guy that made the one blade when I flew F5D. Of course we were running 7 or 9 Ni cad cells at the time. I wondered Christian if you guys were playing with single blade props.
 
I've made a few and tested them. Obviously balance is the hardest part. I got them balanced enough to test, but that last "perfect" balance zone is elusive.
I agree with the two blade theory's above. they are basically one blade at a time with sub-surface drives.
A fun project for sure.
 

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