Properller Selection
08-13-2003 | 01:47 AM
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From: singapore
Properller Selection
Hi
I've a 30-size fun fly plane installed with an 40-size glow engine of about 1.5kg overall weight.
Currently, I use 10x6 propeller. I find it difficult to hover as if the power is lacking. Vertical climb is only possible if I were to speed a long straight line before the climb.
Does the propeller selection affect this aerobatic capabilities? What type of propeller is suitable?
Thanks for any help or tips.
I've a 30-size fun fly plane installed with an 40-size glow engine of about 1.5kg overall weight.
Currently, I use 10x6 propeller. I find it difficult to hover as if the power is lacking. Vertical climb is only possible if I were to speed a long straight line before the climb.
Does the propeller selection affect this aerobatic capabilities? What type of propeller is suitable?
Thanks for any help or tips.
08-13-2003 | 03:39 AM
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Properller Selection
Yes! It definitely makes a difference.
Think of the props as the gears in your car...A short high pitched prop would be a high gear and a long flatter prop would be the lower gear.
With the lower gear you get quicker acceleration, lower top end speed, more braking at slow speeds, and more thrust.
With the higher gear acceleration goes down, top end speed goes up, braking at slow speeds goes down, and you lose thrust.
The 10x6 is about 5th gear in a 6 speed tranny...
Try an 11.5x4 which is just about 1st gear in 5 speed. A 12.25x3.75 would be 1st in a 6 speed...
My favorite is the APC 11.5x4! Perfect on my Thunder Tiger Pro .46 on my Profile Sledge. It's the one in my avator...
Think of the props as the gears in your car...A short high pitched prop would be a high gear and a long flatter prop would be the lower gear.
With the lower gear you get quicker acceleration, lower top end speed, more braking at slow speeds, and more thrust.
With the higher gear acceleration goes down, top end speed goes up, braking at slow speeds goes down, and you lose thrust.
The 10x6 is about 5th gear in a 6 speed tranny...
Try an 11.5x4 which is just about 1st gear in 5 speed. A 12.25x3.75 would be 1st in a 6 speed...
My favorite is the APC 11.5x4! Perfect on my Thunder Tiger Pro .46 on my Profile Sledge. It's the one in my avator...
08-13-2003 | 04:43 AM
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From: Lincoln,
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Properller Selection
A 10x4 would only have a drastic effect if you can spin it a lot faster. From a 10x6 to a 10x4, all you are changing is pitch.
I too use the gear analogy (offered by Bottlerocketwar) when explaining props to new pilots, however you might care to note that it is just an analogy. Static thrust for the most part is directly related to prop diameter and RPM. Pitch has basically nothing to do with static thrust. Then why pitch down when moving to larger props? It is to keep the engine running at the proper RPM. If you increase the diameter without decreasing pitch, the load on the engine will increase, possibly to a point where the engine doesn't work well or at all.
So, by moving to a 10x4 from a 10x6, you must rely upon RPM increases from the lower prop load to increase thrust. Engines have a preferred RPM they like to run at when wide open. If the engine is already running at its preferred RPM with the 10X6, you may not see much RPM gain by moving to the 10x4 and you could end up breaking the engine if it over revs.
Pitch loads are pretty much linear, i.e. twice the pitch increases prop load by two. Diameter on the other hand is an exponential function. Twice the diameter is close to 16 times the load. So, in the 10 inch diameter range, a good rule of thumb is you must increase/decrease pitch by 2 for every inch of change in diameter. As you can see, either of the two props Bottlerocketwar listed basically adhere to this rule of thumb. The 11x4 you mentioned would also be a good prop to try.
Also keep in mind that the type of prop can also drastically effect thrust. In that size range (10"), the best props for thrust that are easy to obtain will be APC.
I too use the gear analogy (offered by Bottlerocketwar) when explaining props to new pilots, however you might care to note that it is just an analogy. Static thrust for the most part is directly related to prop diameter and RPM. Pitch has basically nothing to do with static thrust. Then why pitch down when moving to larger props? It is to keep the engine running at the proper RPM. If you increase the diameter without decreasing pitch, the load on the engine will increase, possibly to a point where the engine doesn't work well or at all.
So, by moving to a 10x4 from a 10x6, you must rely upon RPM increases from the lower prop load to increase thrust. Engines have a preferred RPM they like to run at when wide open. If the engine is already running at its preferred RPM with the 10X6, you may not see much RPM gain by moving to the 10x4 and you could end up breaking the engine if it over revs.
Pitch loads are pretty much linear, i.e. twice the pitch increases prop load by two. Diameter on the other hand is an exponential function. Twice the diameter is close to 16 times the load. So, in the 10 inch diameter range, a good rule of thumb is you must increase/decrease pitch by 2 for every inch of change in diameter. As you can see, either of the two props Bottlerocketwar listed basically adhere to this rule of thumb. The 11x4 you mentioned would also be a good prop to try.
Also keep in mind that the type of prop can also drastically effect thrust. In that size range (10"), the best props for thrust that are easy to obtain will be APC.
