Newbee Propeller question?
 

I have read and basically understand the trade offs in speedvs power that comes with changing prop size and/or pitch. AndI understand the risk of overheating and hurting parts of the plane. However, I am curious about using after market props of the same size as originalon my planes.

I picked up a Master Airscrew 9X6 prop for electric planes for my HZ Super Cub and PZWildcat. These planes both came with 9X6 props. But the new prop looks much thinner than the stock 9X6, so before i tried it on either plane I was wondering if there is enough of a difference to worry about or can I use any 9X6 prop that will fit the shaft on the plane?

Thanks
Jim

RE: Newbee Propeller question?
 

Jim,

There is no difference between 9x6 props. There is a difference between a slow flyer prop and a regular prop. The slow flyer props are weaker and meant for less rpm motors. If your plane came with a slow fly prop and you put a regular.prop on your just waisting a few pennies. A 9x6 prop no matter what kind is still a 9x6 prop. It's still 9 inches in diameter and moves forward 6 inches for every revolution it turns.

Hood luck and happy flying.

RE: Newbee Propeller question?
 

I don't completely agree with Chocks on this one. For the same reason that changing the number of blades affects the power dissipation of a 9x6 prop, the stiffness and overall blade shape will affect the performance of your motor.

For example, at my club we fly combat foam wings (Assassins and Swift II's), and a common tweak is to use a 1600kv Turnigy motor on 3S with a HobbyKing 7x6 "APC-like" prop which stresses the motor pretty hard but gives good performance, and over 200 watts. Switching to a TGS 7x6 prop is too much for the same motor, and causes them to overheat pretty quickly - the TGS prop is much sturdier, has thicker blades and scimitar tips.

However, in your case I agree with Chocks - I'm sure the manufacturer built-in a good margin of error in the selection of the power system, so you will be fine with any 9x6 prop. If your plane did not originally use a Slow Flyer prop, DON'T put one on, as they are a lot less resilient, and you don't want prop blades coming off at 10,000 rpm, do you?

Hope this helps...Chris

RE: Newbee Propeller question?
 

<span lang="EN">

Thanks Chocks and Chris, that does help. I am pretty sure the Master Airscrew is likely a step up in quality over the plastic prop that came on the planes. They do look a little more to scale and improve the appearance of the planes. Even if they just fly as well as with the original prop, I'm still ahead.

Thanks
Jim</p></span>

RE: Newbee Propeller question?
 

To amplify on what Chris has said, props of the same size are not necessarily equivalent. Among props of the same size, some designs are more or less efficient than others. The differences in efficiency can be important, especially in electric flight.

Replacing a prop with one of lower efficiency will likely cause the motor to draw more current. If it draws too much current, you might possibly exceed the rating of the motor, the ESC, or the battery. If you plan to do a lot of experimenting with different props, it is worth getting a wattmeter so you can measure the current being drawn.

You may even find instances where a smaller prop draws more current than a larger one, due to a big difference in efficiency.

- Jeff

RE: Newbee Propeller question?
 

To amplify on what jdetray has said, the best prop efficiency is also dependant on the right combination of motor efficiency with battery efficiency relative to the planes aerodynamics and flying weight. Efficiency to one pilot(competitive pylon racers) may be inefficient to another pilot(seeking thermals to ride as long as possible with competitive sailplanes)

During take-off and a thrust burst there's initially considerable slippage. When cruising with a good tailwind each prop revolution of overall efficiency should advance the plane more than 6 inches. Flying against/into a headwind even with the most efficient prop, engine, airframe, etc its impossible for each revolution of a 9x6 prop to advance the plane 6 inches. Ideally, the most efficient prop is the one best matched to the plane's flying weight, aerodynamics, and most efficient power plant. In the real world of flying nitro ain't cheap.

You could spin your brain attempting to determine which prop is most efficient when considering both thrust and speed requirements when converting from a brushed setup to a brushless setup. Much of it depends on your flying preference. Do you want to go 80 miles an hour using a speed prop or just cruise using a slow-fly prop or get the best efficiency from an electric sailplane. Even then 'efficiency' is a balancing act between the prop, motor, battery, flying weight and a pilot's flying temperament.