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Old Mar 28, 2012, 08:50 PM
Time for me to Fly...
Mr. Wiz's Avatar
United States, MI, Fenton
Joined Jan 2000
8,663 Posts
Question
What do you do when you're between props?

So here is my dilemma. I have a power system that isn't giving me the watts at the prop I want with an APC 14x7E. The 14x8E gives me the watts I want but the pitch speed is too high IMHO for a Telemaster. Nobody makes a 15x7. What do I do? APC makes a 15x6 glow prop. Should I try that?
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Old Mar 29, 2012, 12:02 AM
Registered User
Alameda, CA
Joined Dec 2006
2,924 Posts
Sorry, but APC makes a 15x7E .

What C batteries are you using, and what is their condition?

Getting new batteries of a higher C might just do it.

Also, you might try cutting down a 15" prop. It gets a little tricky with bigger props, but it can be done.

Hope this helps.

Steve
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Old Mar 29, 2012, 01:32 AM
Don't worry be happy :)
Stark's Avatar
Joined Sep 2001
642 Posts
Also try the XOAR wood props for electric. They have more "bite", better acceleration, in my experience.
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Old Mar 29, 2012, 03:41 AM
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Australia, ACT, Kambah
Joined Feb 2001
3,269 Posts
In my experience with trainer style models apparently excessive pitch speed doesn't seem to hurt, and in fact for a well overpowered model, seems to result in better part throttle, ie reduced rpm, performance. I'm talking 75-83 (12x10, 13x10) mph pitch speed for an LT-25 - seems nicer overall than the 50-60mph mark (12x6, 12x8). Even with the prop supposedly stalled for a while takeoff is never an issue - I only use 1/2 to 2/3 throttle anyway.

If it flies OK with the 14x8, ignore the pitch speed
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Old Mar 29, 2012, 04:13 AM
Registered User
Staffs, UK
Joined Nov 2003
10,765 Posts
A 15x7 is probably not a practical option anyway. It will take quite a lot MORE power than a 14x8. 15x6 is roughly equivalent on power but then you'll have even less pitch speed.

It sounds like you're doing all this theoretically on the ground. I'd suggest flying the two props you have a few times and seeing if you really have a problem.

Steve
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Old Mar 29, 2012, 04:49 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
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Sorry Mr Wiz, but why are you measuring watts to determine how a plane will fly ?

"I have a power system that isn't giving me the watts at the prop I want..."

I always thought that was the wrong way to go. Having the right prop give the right sort of flight style for the model, I have always thought was the better way to go. The wattmeter is just a safety device to check you wont let any magic smoke esc.
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Old Mar 29, 2012, 07:29 AM
Time for me to Fly...
Mr. Wiz's Avatar
United States, MI, Fenton
Joined Jan 2000
8,663 Posts
Quote:
Originally Posted by sgomes View Post
Sorry, but APC makes a 15x7E .

What C batteries are you using, and what is their condition?

Getting new batteries of a higher C might just do it.

Also, you might try cutting down a 15" prop. It gets a little tricky with bigger props, but it can be done.

Hope this helps.

Steve
Ok I see it on the APC prop list but it seems nobody stocks it. I'll give APC a call.
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Old Mar 29, 2012, 07:32 AM
Time for me to Fly...
Mr. Wiz's Avatar
United States, MI, Fenton
Joined Jan 2000
8,663 Posts
Quote:
Originally Posted by eflightray View Post
Sorry Mr Wiz, but why are you measuring watts to determine how a plane will fly ?

"I have a power system that isn't giving me the watts at the prop I want..."

I always thought that was the wrong way to go. Having the right prop give the right sort of flight style for the model, I have always thought was the better way to go. The wattmeter is just a safety device to check you wont let any magic smoke esc.
You're right, Ray. I haven't flown it yet and I intend to fly them both to see which I like better. I may well have to live with one of those although I now see a 15x7 on the APC web site. We'll see
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Old Mar 30, 2012, 01:09 AM
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Sammamish, WA, USA
Joined Jan 2010
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Quote:
Originally Posted by eflightray View Post
Sorry Mr Wiz, but why are you measuring watts to determine how a plane will fly ?

"I have a power system that isn't giving me the watts at the prop I want..."

I always thought that was the wrong way to go. Having the right prop give the right sort of flight style for the model, I have always thought was the better way to go. The wattmeter is just a safety device to check you wont let any magic smoke esc.
+ This
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