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Trading diameter for pitch?

Old 06-05-2006, 01:09 AM
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Twmaster
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Default Trading diameter for pitch?

Hi all,

Got a bit of a quandary here. I've got a plane with an AXi 2208/34 under the cowl and I am limited to an 8 inch prop due to landing gear/wheels length. This is also flown on a 2S 1350 lipo. I'd like to get a bit more power out of the setup as while the plane flies, it flies anemically. So I am wondering if increasing the pitch would help since I cannot go with a larger diameter prop.

Thoughts?
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Old 06-05-2006, 01:18 AM
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bsoder
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greater pitch will give you more speed, at the expense of more watts. Won't really help your thrust (a little but not much.)

An example - these numbers are on a Hyperion 2213/24.
Code:
Prop    Volts    Amps    Watts    RPM     MPH     Thr(oz)
8x4e    11.02    6.58    72.54    8875    33.5    14.9
8x8e    11.02    11.73   129.28   7754    59.0    15.0
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Old 06-05-2006, 05:40 AM
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Sky Sharkster
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Default Pitch or Diameter?

Hi Mike, I tried an "E-calc" run for your motor but the highest # winds they carry is the 2208/26 (which I happen to own, it's in the "Astro hog" on my Avatar). Anyway, the possible solution I came up with is 3s LiPo instead of 2s. With the 8 x 4 (APC) it boosted the static thrust from (2s) 11.1 oz to 22.6 (3s). Prop speed went from 28.2 to 40.2. The downside? Duration (WOT) was 6.24 minutes (2s) to 3.32 min (3s). But with that much more thrust, I'd guess the throttle setting would be lower so it might work out. Worth a try if you've got a small 3s? Hobby-Lobby says the 2208/34's are OK with 3s or 10 cell conventional.
Ron
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Old 06-05-2006, 05:47 AM
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Twmaster
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Ron,

thanks for the numbers. Due to battery availability and that the ESC is buried in the fuse this is going to stay a 2 cell bird.

I have a Flying Styro 3 blade 9x7 I may try if no satisfactory results are obtained with other steeper 2 blade props.

The plane flies. It will even ROG from a smooth surface but really seems like it needs more 'bite'.
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Old 06-06-2006, 05:06 PM
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Matt Kirsch
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Watch your Amps, though. If you were at the battery's, ESC's, or motor's limit on the current prop, then going bigger will only cause more problems.

If your pitch is low enough now, increasing pitch will increase thrust quite signifigantly. It's when you get into really high pitches at really high RPMs that the law of diminishing returns starts to kick in.
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Old 06-07-2006, 05:22 AM
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Twmaster
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None of the gear is anywhere near it's limits. Yet.

I just need to find some spare time to try some other props out while connected to Ye Olde Whattmeter.



Thanks for the tips fellows.
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Old 06-07-2006, 07:06 AM
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timocharis
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tw,

You might consider upping the volts. You'd probably get a real thrill out of a 3s 730 (or equivalent) with an 8040 GWS prop. You'd be well within amp spec and have some fun. The GWS 8060 HD should also be okay, but it's hard to find numbers on that.

If you want to see some other comparisons, check out:
http://www.flyingmodels.org/motortest/index_e.htm

Just select your motor and see a bunch of APC test results.


Dave
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Old 06-07-2006, 07:22 AM
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Thanks Dave,

However as I said in my previous comments this is staying with two cells. If going to a three cell pack was 'just that simple' for me I wouldn't be asking these silly questions about bigger pitch.
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Old 06-07-2006, 10:50 PM
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timocharis
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This will pop your plane:

http://www.toddsmodels.com/Props/propsother.htm
Check out the four-blade. Probably a bit much (unless you're after some speed, too) but fun to consider.

Oops, noticed you'd already dropped the 3s idea.


Dave
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Old 06-08-2006, 02:36 AM
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Thanks Dave. I'm thinking that is going to be a bit much. Cool looking though.

One thought I did have while out on the road today. Perhaps drop an inch in size and increase the pitch?

I really need to get over to the LHS and pick up a few props to evaluate.
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Old 06-08-2006, 04:31 AM
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timocharis
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tw:

A completely reasonable approach would be to just cut down your 9x7 3-blade to 8 inches. Or just keep going until you hit the sweet spot.

If you haven't seen 'em yet, the GWS 8060 DD (or HD; same thing) is a pretty efficient high-pitch prop, and I'm sure you could drive it 2s. It does tend to be a little thrustier than most 6-pitch props.

I'm thinking a 7x6 would be too weak. The motor database says you'd be lucky to get 7oz thrust using 5 amps.


Dave
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