The complete r/c model airplane FAQ.
Model airplane engine propeller FAQ (NEW!!!)
Performance notes and comparisons on different prop brands:
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What do the numbers mean?
The first number is the prop diameter. The second number is the prop pitch. This is the theoretical distance that the prop would move forward if rotated one revolution. If you were to mount your prop on a shaft and submerse it in jello, you could see this in action... A 10x6 prop is 10" in diameter, and in theory, the prop will move forward 6" in one revolution. The pitch can be thought of similar to the transmission in your car. A low pitch (like on a 10x4) is like low gear on your car--lower speed, but more power. A high pitch is more like a high gear--higher speed, but it takes longer to get to top speed, and you may lose power on the verticals.
Propeller Rules of Thumb
First, for two blade props, the "load" the prop will give the engine is approximately the diameter times pitch. For example, a 9x7 (load factor of 63) prop will approximately load the engine the same as a 10x6 (load factor of 60).
Second, to move to three blade props and maintain the same load, drop one inch in diameter.
Third, a larger prop with lower pitch will provide more thrust but lower top end speed. A smaller prop with high pitch will speed the plane up on the horizontal, but the thrust will be reduced. Think of a helicopter prop--they have a huge diameter, but a low pitch for maximum thrust, but they travel at low speeds.
Fourth, the fewer the blades, the more efficient the prop is. Sure, four bladed props look cool on your scale plane, but they are inefficient, especially in the RPM ranges that our models run. It is very popular in the racing circles to run single bladed props. YES! Single blades--they actually balance them with a lead weight.
Note that all of the different brands of propellers have different efficiencies and characteristics. For smaller planes (17" and under), APC seems to be the best by quite a bit. They have a good stiff blade that is very efficient. With the larger planes & props, downline braking is a factor to consider. Because of this, the wider blades are popular.
Pilots Notes On Propellers:
This will give you an idea of how the prop brand can effect your flight performance. I own about 5 engines that run 16x8 propellers. The MA (Master Airscrew) 16x8 consistently runs almost 1,000 rpm slower than the APC prop. The MA has the advantage of better down-line breaking (it is much wider, especially at the tips), and that's about it. (Well, ok, it's cheaper too.) They limited the vertical of my Laser, though--with the APC, the plane was limited only by my abilities, whereas the MA would fall off well before I lost sight of it. So, with the APC, not only was the top speed improved, but the thrust was noticeably improved as well.
I was flying my MidWest Extra 300s powered by a BME 44. My standard prop for this setup is a Menz 20x8. This is a wide blade prop that provides good thrust and downline braking. With an Extra, I obviously don't want top end speed. When I switched to a Top Flite 20x8, the vertical performance seemed to increase, but the acceleration was not quite the same. When you compare the blades, this makes sense, as the TF is wider at the tips. With the Master Airscrew Scimitar, the acceleration was quicker, but the vertical performance seemed like it may have weakened a bit. This makes sense here, because the MA Scimitar is a thin bladed prop.
On Forte props: I have seen the thrust measured on a 26x10 Forte alongside a Menz 26x10s, the load is a little more, the thrust a little less than the Menz. Jim--IMAC list
Yesterday I tried out my new MSC 32-10 prop on my
Edge. Very nicely made. Really quite a different sound- much quieter than
comparable size props that I've heard. You don't get the ripping noise
that bothers everybody. The most outstanding attribute of this prop is its
pulling power, especially at the lower end of the RPM scale. It
accelerates like a hotrod with a 4.56 rear end (ok I'm a car guy too.)
During hovering, I noticed that the throttle was considerably lower on the stick than with my 3blade, to maintain a constant hover. It required a little change on the throttle curve setting to make it feel the same. If you want to make it quieter, for a lot less $ than a CF 3Blade, try one of these. And practice throttle management!!
Here's Mike's website address: http://www.mscprops.com Don McLellan, GSAL list
Just flew the MSC 32 x 10. Quite impressed! What would one cost me shipped to Atlanta?The odd thing was that I suddenly heard ALOT of wind noise from the plane cutting through the air....I suppose because there was less prop noise. I've run some very quiet 3 blades and haven't heard that wind noise. Strange! Ron SA list
The MCS is
one large chunk of wood. At 1st I wasn't going to put it on...then I said
if I have to cut my spinner forget about it....then I'm at the field and threw
it on, had to cut my spinner there (carbon fiber). This thing has massive
blades. I was running a 27x10 Mejzlik and had to enlarge the cut-out for
the MCS 25x10. It is a true 25" so its only a 1/2 inch or so shorter
than a Menz but the hub and blades killed some serious trees.
Cool things are zero spool up time for messing around and getting out of 3D trouble, slower tip speed so its quieter, and seemingly less p-factor on long verticals. It does unload in the air though. Pulls great.
Still waiting for some 27x10 woods and still think that will be my preferred prop. The Mezjlik is too heavy......the MCS 25x10 turns the same as the Mezjlik 27x10 in the 6200 to 6300 range... while the Menz S 26x10 turns 6500-6600. Perry, SA list
Prince Aircraft Company (specializes in props for ultralites, Goodyear Blimp, etc......sold by TNT
Prince prop ....32 x 10
Has the new "P" tips (CF tips) on a maple prop.
Cost approx. $180.00
Can be re-tipped for $60.00
DA 150 about 12hrs run time, Amsoil 100:1
temperature at time of testing = 89 degrees, Atlanta area = 1000 ft above sea level, Stock DA canister mufflers, rpm = 5900.
Remarks: hard pulling prop, pulls like a tractor, not fast....very constant speed, exceptional braking on downline. Ron, Atlanta Area
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Revised: April 18, 2006 .