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Help me understand props....

Old 05-03-2015, 02:53 PM
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Wagon1
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Default Help me understand props....

The manual for my Super Tiger 61 states that it can handle a prop from 10X8 to 12X7. What should I expect as I move from one to the other? I guess what I really need is a reference manual. Any suggestions? I am flying a SIG Astro Hog and really just want a spirited "advanced" trainer.

Thank you.

Mike
Old 05-03-2015, 03:06 PM
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FLAPHappy
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Originally Posted by Wagon1 View Post
The manual for my Super Tiger 61 states that it can handle a prop from 10X8 to 12X7. What should I expect as I move from one to the other? I guess what I really need is a reference manual. Any suggestions? I am flying a SIG Astro Hog and really just want a spirited "advanced" trainer.

Thank you.

Mike
Do a search on prop charts online, print it out and use it for a reference.
Old 05-03-2015, 04:27 PM
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guitarsbanjo
 
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genera rules but they do help. a larger diameter with less pitch is like running in a lower gear, more pull, less speed. And a smaller diameter and a higher pitch is faster. Going from a 10X8 though to a 12X7 is kind of like comparing apples and oranges. The 12X7 will load the engine more thus less rpms. the calculation I use (rule of thumb) is DXDXP= prop load so a 10X8 would would be 800 and a 12X7 would be 1008...so an 11X7 would be comparable to a 10X8, probably a little more pull with the 11x7 with a little less speed. FWIW I've run very few .61 size planes, but I usually settled on an 11X7 for my type of flying.

Austin
Old 05-04-2015, 11:00 AM
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Gray Beard
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Austin gave you the basic rule of thumb but I don't do any of the math. There are also several charts you can look at but the instructions give you a basic size idea of the props that the engine works well with. You pick out the basic starting prop then with a fist full of different sizes and pitches you go out and start testing props to see what one you the pilot likes best.
I like a slower plane with more pull, that equates to shorter take off runs and slower landings so I like a longer prop with less pitch.
If you do a search you can locate a photo John Buckner once posted of his prop wall, he has a better selection then most big hobby shops that he uses for testing.
In my case with your plane engine combo I would probably end up with a 12X 6 or 4 pitch. Maybe even a 13X 6 or 4?? I wouldn't know for sure until I spent the day testing props what I like best.
I have had enough .61s that I know I would be starting with a 12, probably an 8 pitch but that's just me and I know what I'm looking to achieve in the end.
Old 05-04-2015, 02:05 PM
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jester_s1
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I'd start with a 12x6 and an 11x7 on that plane. Those should let your engine unload in the air and make good power, and should make your vertical performance as good as you will ever need it for big loops and hammerheads. It will probably be readily apparent which one you like better after a couple of flights. I ran a 12x8 on my Super Tigre G90, and felt it took good advantage of all that torque. I think it would be a bit much on a .61 though.
Old 05-05-2015, 08:15 AM
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j.duncker
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APC 13 x 4 W for Wide works well on that size motor and a slow flying plane.

Slows down better for landing too.
Old 05-06-2015, 06:18 AM
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Hi!
12x6 is suitable for all .60-.61 two strokes but... for a larger ,slow flying model a 13x4,13x5, 13x6 or even 14x4 is more suitable.
On the other side if the spectrum; a smaller ,faster flying model a 11x8, 11x7,5 or even smaller diameter prop is more suitable.
Old 05-06-2015, 08:19 AM
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BarracudaHockey
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First, engines have RPM bands where they produce their most power.

Pitch (the second number) is the distance in inches an prop will advance through the air in one revolution. (its theoretical due to efficiency issues but it works for comparison)

The prop range is the range of props that will keep that motor in an RPM range thats safe for that engine and in its most efficient power band (again, give or take, there are exceptions to everything)

The higher the pitch the faster the straight line speed but the less pull on uplines.

Lower pitch, more "grunt' but less speed.

You generally adjust the diameter in that range to get the speed you want and the load that the engine operates best in.

As others have said, its a combination of the engine, the airframe, and pilot preference to which prop is "best".

Falcon Props brings a board full of props drilled for most popular engines in various sizes to big events, you can try different props. THAT my friends is the way to sell props IMO

Edit: Another generalization but an 8 pitch would probably be thought more as a 3D prop, a 10 pitch a sport or general prop, and a 12 pitch a speed (or warbird) prop. Some manufacturers like vess use letters, A, B, and C would be approximately 8, 10, and 12 respectively, though they have more pitch near the hub where the prop has the most torque with less at the tips where its less efficient.

Last edited by BarracudaHockey; 05-06-2015 at 08:23 AM.
Old 05-06-2015, 12:14 PM
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j.duncker
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8 pitch is a lot for 3D. The most I ever used on a 3D model was 6 inch with MDS 148 and 218.

Anything smaller was always 4 in pitch. I really liked the APC W range.

3 D hooligan[ retired.]
Old 05-06-2015, 03:13 PM
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daveopam
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11x7 is pretty good all around prop on a .61 12x6 would be my second choice for your plane. Think about pitch like this. Get in a manual transmission car. Take off in first and it will accelerate quick but top speed is not much. Take off in second and it will not accelerate as fast but top speed will be higher. 1st gear is the 4 pitch prop. 2nd gear is the 8 pitch prop. Ideally you want the load on the engine to be similar. So the 4 pitch prop can be 13" long (13x4) but the 8 pitch prop can only be 10" long (10x8).

David

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