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Old Oct 06, 2014, 02:15 PM
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United Kingdom, England, Worcester
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Question
What prop to use?

Hey,

So I've got my SkyFun - and all is good and well, until I asked my friend to launch it - naturally he launched it straight up even though I said forwards - anyway moral of the story is don't allow your friends to launch, they break propellers :P

Right so here's my setup:

NTM 28-36 2700kv Motor
Turnigy Plush 60A ESC
4s 2650mah Nano-Tech 35-70C (better C coming tomorrow).


Anyway - I ran a 5x5 TGS Sport prop and it ran perfect, though the motor + esc were completely cold, so that would suggest I may be able to go a tiny bit bigger?

I'm looking to replace the prop and came across the Graupner SPEED CAM ones, they seem to be highly recommended so I think I'll go for them, but struggling on size!

I wondered for a start what people think the max size prop I can run is? I aim for speed with this plane, so short bursts of fun is all good .

Looking at the props I can get made by Graupner there's 2 sizes - either a 4.7x4.7 or a 5.2x5.2 (or a 5.5x4.3) - just wondering if the 5.2 is ok, or if that extra 0.2 on both measurements will over amp the esc or not?

Any guidances as to how to actually work this stuff out would be much appreciated I'm not sure which of the 3 props would be best to go for!

Thanks,

Matt
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Last edited by Add1ct3dd; Oct 06, 2014 at 02:30 PM.
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Old Oct 06, 2014, 03:07 PM
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Letchworth, Great Britain (UK)
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Not all props, motors, and props are exactly the same, even if they're same make, model, and size. So, even if someone does advise that a certain brand prop of a certain size is good for them, you need to verify it with a wattmeter on your setup if you want to be sure you're not going to over-amp your motor or ESC.
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Old Oct 06, 2014, 03:32 PM
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OK that's a good point, I'll get all 3 and test them out - I presume start from lowest and work my way up?
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Old Oct 06, 2014, 03:42 PM
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If 5x5 was good, 5.2x5.2 might be the best starting point because, all else being equal, more pitch gives you more speed, which you say you want.

You don't have to start with the smallest, for you can gradually open your throttle while watching the meter, and shut it down if it begins to go too high.
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Old Oct 06, 2014, 05:56 PM
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Went for all 3 anyway - if the 5.5x4.3 is no use, that can go on my EFX Racer :]

Also ordered a wattmeter - it's been a long time coming, but just another tool in the ever increasing collection (8 years worth of RC stuff).

Cheers for the help, will go with it and see what's what .
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Old Oct 08, 2014, 12:41 PM
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Hey guys, following on from this got some results

4.7x4.7 = 54A on the bench
5.2x5.2 = 72A on the bench
5.5x4.3 = 72A on the bench.

Now, I know the Plush 60A will allow for 80A burst - so presume my 72A is fine, but for how long can I burst? Is it long enough to do a speed run, say 5-10 seconds? I also presume these numbers would be slightly lower in the air as you're moving, and have good cooling (won't lower numbers, but would help).

The motor and ESC are both situated on a SkyFun, and are in the path of air - so both have good cooling .

Also, which prop would give the greatest top speed, 2 of them are 72A, and I'm not sure how the numbers differentiate speed vs thrust.

I guess ideally a 5x5 would still be the best prop, its likely to sit around 60-62A judging at the figures, which was my original prop - but I wanted to test some quality props and sadly Graupner don't do a 5x5 SPEED CAM prop - any suggestions for good quality 5x5's?

Thanks
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Old Oct 08, 2014, 02:48 PM
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Don't just consider the ESC -- you need to remember that your motor is only rated for 50A continuous, or 595 watts, whichever is greater (that's about 40A if you're using a 4S pack)

Personally, I would stick with the 4.7x4.7, and just check that your motor is not too hot at the end of a flight.

All else being equal, larger diameter gives you more thrust, and more pitch gives you more speed.
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Old Oct 08, 2014, 02:49 PM
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That's true, cheers for the info

I'll run the 4.7x4.7 first, see how it goes - I remember being on the 5x5 the motor and esc were both stone cold (but then it was a cheaper prop so may not have been as efficient), so we'll go from there .
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