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Author Topic: How do you know which prop is right?  (Read 2701 times)

Offline Matt Colan

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How do you know which prop is right?
« on: September 15, 2009, 04:00:53 PM »
Grandpa has been experimenting with props on his P-47.  So far he's had a 12-5 Zinger cut down to 11.5-5, a full 12-5, and now he's tested a 3 blade bolly 12-4.25 cut down to approxamitely 11.5.  All he needed to do with the bolly is bring it up in pitch a little bit and it should fly good with it.  The motor he is running is an LA 46, completely stock.  How would we know which prop is just right for the motor as all 3 of the ones I just mentioned work well?

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Matt Colan

Offline Gene O'Keefe

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Re: How do you know which prop is right?
« Reply #1 on: September 15, 2009, 04:22:51 PM »
My LA 46 likes the APC 12.25x3.75 cut down to 11.75
 
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Offline Jim Thomerson

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Re: How do you know which prop is right?
« Reply #2 on: September 15, 2009, 04:50:27 PM »
Fly and try.  You may find that different props fly the airplane differently at various points in the pattern. 
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Offline Steve Helmick

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Re: How do you know which prop is right?
« Reply #3 on: September 15, 2009, 07:45:52 PM »
The two most often recommended props for the .46LA are the 11.5 x 4 and 12.25 x 3.75 APC's. Try both, and try the 12.25 trimmed down to 12" and 11.75". Whichever one you like the best is your "baseline" prop. Test all other props and follow up with a re-test with the APC...that's what Pete Peterson calls a "reality check". It just makes good sense. Keep trying different props as they become available. Avoid preconceived notions about prop design, because they will surprise you to no end!  :o Steve
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"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

steven yampolsky

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Re: How do you know which prop is right?
« Reply #4 on: September 19, 2009, 03:18:33 PM »
Quote from: Matt Colan on September 15, 2009, 04:00:53 PM
How would we know which prop is just right for the motor as all 3 of the ones I just mentioned work well?

If the motor runs hot, you may have too much prop.
If the motor RPM's drop in the maneuvers instead, you may have too much prop

ok, this starts to sound like "you might be a redneck". let's continue  ~>

if the motor is very sensitive to temperature and humidity changes, you may have too much prop.
if you the tips of the prop are green from the grass, you may have too much prop.
if the motor cannot maintain the RPM it could with smaller props, you may have too much prop.
if the model moves at 4.2 sec laps while turnin 7500 RPM's, you may have too much prop.
if the model feels like someone stuck a pound of lead on the nose, you may have too much prop.

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Offline Matt Colan

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Re: How do you know which prop is right?
« Reply #5 on: September 19, 2009, 04:53:30 PM »
Well Steve, the bolly was eliminated due to breaking the blade on an inverted flameout landing.  He is now fixing it with a bunch of carbon fiber and epoxy, and he's going to bench run it in a few days when he balances it and makes it look nice.  I tell him to tell me when he's going to run the prop, that way I know when to not go over there ~>

The 12-5 Zinger is now the prop we use, and that's running consistently at 8500 at around 5.2 to 5.3 lap times, and the motor doesn't overheat.

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Matt Colan

Alan Hahn

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Re: How do you know which prop is right?
« Reply #6 on: September 22, 2009, 09:41:29 AM »
It's always the prop the other guy is using! LL~
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Offline Matt Colan

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Re: How do you know which prop is right?
« Reply #7 on: September 22, 2009, 05:23:13 PM »
The 12-5 Zinger turned out to be not so great.  He put on a 12-5 Power prop and the motor liked it more, with more revs, looked like the plane liked it to.

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Matt Colan

Alan Hahn

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Re: How do you know which prop is right?
« Reply #8 on: September 22, 2009, 08:26:02 PM »
Quote from: Matt Colan on September 19, 2009, 04:53:30 PM
Well Steve, the bolly was eliminated due to breaking the blade on an inverted flameout landing.  He is now fixing it with a bunch of carbon fiber and epoxy, and he's going to bench run it in a few days when he balances it and makes it look nice.  I tell him to tell me when he's going to run the prop, that way I know when to not go over there ~>

.......<snip>



Tell Grandpa not to do that!! n1 :X

That's the problem with high $ items. We all have a tendency to do dumb things (I know I do too!).
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Offline Matt Colan

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Re: How do you know which prop is right?
« Reply #9 on: September 23, 2009, 01:45:12 PM »
Quote from: Alan Hahn on September 22, 2009, 08:26:02 PM
Tell Grandpa not to do that!! n1 :X

That's the problem with high $ items. We all have a tendency to do dumb things (I know I do too!).

I told him, and I thought we were initially going to give it to Windy, and see if he could fix it, but then he decided to do it himself.  He did talk to Mike Chiodo and he gave him the same warning I did, but probably different wording, so he called Windy, but haven't heard what he's said yet.  He's flexed it and it doesn't flex, so he says, but I got a feeling, that prop isn't going to last turning a high RPM.

He did fix a 13-6 Bolly that I chipped (i know, my fault) at the end, and we've been running that prop for a long time on an ST 60 which vibrates.  That was at the end of the blade, not right in the middle like this one.  I'll have to ask him what Windy says.

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Matt Colan

Offline Matt Colan

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Re: How do you know which prop is right?
« Reply #10 on: September 23, 2009, 02:35:27 PM »
Windy told him not to use it, so grandpa, since he did such a nice job fixing it, is going to use it as a static prop, so if we go to the Nats (yeah right, or when we go to Brodak), we'll put that prop on it for appearance judging  ;D .

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Offline Steve Helmick

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Re: How do you know which prop is right?
« Reply #11 on: September 24, 2009, 08:26:25 PM »
Matt...According to the rules, you're supposed to fly the model just as it's presented for Appearance Judging. No prop switching unless you can convince them that you broke it. Showing them the nose end of the model broken off at the LE will probably work. Do yourself a big favor and 86 that prop! It's not worth ruining a model to save a few bucks. Fixing a slightly splintered tip is a whole different deal...the fibers aren't broken, just separated. CA will fix that alright. See below for the quote from the rulze.  H^^ Steve

"10. Appearance. Models shall be judged for appearance complete and ready to fly. After model has been judged, nothing will be removed from or added to the model which, in the judges’ opinion, changes in any manner the appearance of the model from the way it was when presented for appearance judging. However, during an attempt for official flight after the contestant has begun to crank the engine, if it becomes necessary to remove the propeller spinner for change of propeller, etc., then it is permissible to leave off the spinner for that particular flight. Any damage to the model after judging, or changes that may be made as a result of such damage, will not be cause for loss of appearance points."
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"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline Matt Colan

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Re: How do you know which prop is right?
« Reply #12 on: September 25, 2009, 11:13:01 AM »
Actually CA doesn't work with the carbon and epoxy for those props according to Windy's prop video, so we use epoxy, not CA.

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Matt Colan

Offline FLOYD CARTER

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Re: How do you know which prop is right?
« Reply #13 on: October 14, 2009, 02:58:51 PM »
Wow!  I don't know just how many times I've busted a prop taking off during an official contest flight.  More than once.  So far, it has resulted only in an attempt, and with a new prop, an official flight.  So, I was guilty of changing the model configuration between flights, which seems to be against the rules!

What would be the difference if I just changed props between flights to accomodate weather conditions?  Is that a rules violation?

Floyd
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Offline Steve Helmick

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Re: How do you know which prop is right?
« Reply #14 on: October 14, 2009, 05:27:38 PM »
Changing one prop for a similar or identical off the shelf unit is different than having a finely finished "show only" prop, don't you think?  I doubt if anybody would care if you changed your APC for a Master AirScrew to fly with. We might actually encourage it!   H^^ Steve
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"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

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