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Old Mar 06, 2013, 12:51 PM
jrb
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Edina, MN, USA
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Interesting not the outer 1/3!

Because it's an APCE (16x10)?

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Old Mar 06, 2013, 01:08 PM
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I'm confused What's going on? Seems like an interesting experiment but I'm not sure what I'm looking at
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Old Mar 06, 2013, 01:21 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
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Three guesses on what prop I use on my Spit ?

Correct, an APCe 16" x 10", and I love how it FLIES. Flies being the important word.

Now when you get your test bench flying, you may realise that there is a difference between static tests and flying.

Spitfire 5 (5 min 11 sec)
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Old Mar 06, 2013, 01:36 PM
jrb
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Edina, MN, USA
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I like how my Mustang files with 4; Toledo w/2 is OK too:


Jim's electric RC P51 @ 95mph (2 min 18 sec)



H9 Toledo Special Full Throttle Pass (0 min 11 sec)



Jim's RC Electric Toledo near 100MPH (2 min 6 sec)



!
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Old Mar 06, 2013, 02:22 PM
We want... Information!
Bruce Abbott's Avatar
Hastings, New Zealand
Joined Jan 2001
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Quote:
Originally Posted by Nereth View Post
I'm confused What's going on? Seems like an interesting experiment but I'm not sure what I'm looking at
The outer 1/3rd of his prop produced no airspeed?

Failed experiment?
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Old Mar 06, 2013, 04:59 PM
jrb
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Don't think so Bruce -- repeatable:
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Old Mar 06, 2013, 05:06 PM
Hey Ya'll!! Watch THIS!!
Michael Paxton's Avatar
Nashville TN.
Joined Mar 2006
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If I reading this right. The outer third has no air movement to it...or little.
It would make sense that it is this way to hold the rest of the blade in position by just adding a flat plane that resists twisting.
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Old Mar 06, 2013, 05:23 PM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
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The outer 1/3rd of the blade is normally responsible for producing most of the thrust.

It appears you've bolted a motor to a stand and have used a pitot tube to measure the propwash velocity. I don't truthfully know the relationship, if any, between propwash and net thrust, but I suspect this test's results aren't incredibly useful.

I think that measuring the thrust produced by any given section of the blade with some accuracy would require physically removing the portions you don't want to measure and taking thrust readings with something like Phil's test stand, using the same RPMs across all tests.
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Old Mar 06, 2013, 05:56 PM
Hey Ya'll!! Watch THIS!!
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Oh well. Sounded good to me.
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Old Mar 06, 2013, 06:20 PM
jrb
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Edina, MN, USA
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Apce?
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Old Mar 06, 2013, 06:41 PM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
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Yes, the prop appears to be of the APC E variety. Is that all you're trying to determine? No need for the fancy graphs and tests... The prop's type is written right there on the blade

Instead of posting these cryptic graphs with a couple words and zero background information, why not give us at least a few sentences describing a bit about what it is you're doing, how you're doing it, what you're using, and what you intend to show or prove. The test results aren't exactly self-explanatory.
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Old Mar 06, 2013, 07:01 PM
Space Coast USA
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Space Coast
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Quote:
Originally Posted by Michael Paxton View Post
If I reading this right. The outer third has no air movement to it...or little.
It would make sense that it is this way to hold the rest of the blade in position by just adding a flat plane that resists twisting.
Interesting theory - I've noticed on many of my props the outer~1/3 has very little if any pitch.
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Old Mar 06, 2013, 10:18 PM
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Interesting theory - I've noticed on many of my props the outer~1/3 has very little if any pitch.
If it's well designed though, it should still be ejecting air at the same speed - but way more of it since it is covering a larger area.

It's probably just that the pitot is having trouble picking up whatever the airflow is like. Pitots generally like to be in undisturbed air as far as I know (not that I even have one).

As C4H10 said, the best method might be to take a prop, measure thrust, then incrementally cut off an inch or so of it and remeasure each time at the same RPM (don't let it spin up more!) to get the result.
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Old Mar 07, 2013, 03:01 AM
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Norway
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Originally Posted by jrb View Post
Don't think so Bruce -- repeatable:
Measure the thrust with a digital scale (the true force) holding back
Your test gear.

Then cut of 1/3 of Your prop and do the experiment again.

I'm prettur sure You will get a difference ...
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Old Mar 07, 2013, 03:33 AM
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United States, NC, Smithfield
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Doesn't thrust come from the prop pulling air through it rather than pushing it out?
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