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Old Oct 23, 2006, 10:44 AM
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albireo's Avatar
Sacramento, Ca.
Joined Jul 2003
1,518 Posts
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How to cut prop down in size?

I've read for YEARS that people take larger props and cut them down to use with different motors. I see this and wonder how it's to be done... I have a box full of 10x4.7 props and could use some 8x4 sizes. Do I just cut an inch off each end? What about the shape at the end? I see the shape is a specific curve...
Any suggestions would help!
Thanks,
Joe
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Old Oct 23, 2006, 12:01 PM
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foxabilo's Avatar
United Kingdom, England, Redditch
Joined Jul 2006
199 Posts
Ok first things first, I dont advise anyone to cut props down as they are made and modeled/shaped etc to be a set size and the flow over the surface is calculated to be most efficent over the area of the actual prop and not some reduced version of itself.

The dangers include the prop flying into many shards of pin sharp plasic/glass/other bits, unbalenced vibration destroying motors and mounts and inifficent thrust.

OK.. that said IF you still want to cut them down then you use a litttle physics to get this as good as they can be, One method is to mount the prop to a motor and that to a lowerable platform and place abrasive material under it so you can slowly lower the blades onto the surface as they spin this will ensure that an even amount is removed from each end, usualy this method is used at the end of a prop cut down to smooth the ends off, you should make detailed notes/take pictures of the prop ends before the cut and try to tool the ends to be the same.

Also for the major cut down you can take a peice of marking wax chalk/marker pen to spin the prop slowly, again fixed into position and mark the blades as they spin with a thin white line to make your initial cuts.

Ensure the blades are then smoothed and balenced and stand well clear when you open the tap to WOT.

I still advise against it though
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Old Oct 23, 2006, 12:11 PM
From Earth to the Moon!
albireo's Avatar
Sacramento, Ca.
Joined Jul 2003
1,518 Posts
Well, I didn't realize it could be as hazardous, I'm glad you warned me. Don't need to save few bucks and ruin my eyes/models/garage...
Thanks!

Joe
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Old Oct 23, 2006, 12:16 PM
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maverick06's Avatar
USA, PA, Media
Joined Apr 2005
906 Posts
I've done it once, it works fine... just make sure the balance is perfect...

On a few 8x4 props I have been known to glue a broken blade back on... yeah its stupid... but when you dont have any other props at the field, it seems like a good solution... not had any problems yet!

My suggestion is not to do that either... haha

Rick
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Old Oct 23, 2006, 05:27 PM
Sussex, UK
RobinBennett's Avatar
Crawley, West Sussex, UK
Joined Jun 2004
7,374 Posts
It can work for low powered planes, but the prop won't be as efficient as a proper 8x4.

The tip shape isn't that important, but if the balance is wrong you'll get a lot of vibration.
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Old Oct 25, 2006, 09:56 PM
Fly lower!
aerolite's Avatar
West Texas
Joined Jan 2005
2,391 Posts
Prop cutting article with photos

This is an article I did for our club newsletter a few months back. I've done lots of props, and they work great!
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Last edited by mini ifo; Oct 25, 2006 at 10:25 PM.
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Old Oct 26, 2006, 10:31 AM
From Earth to the Moon!
albireo's Avatar
Sacramento, Ca.
Joined Jul 2003
1,518 Posts
Thanks! Great article! Especially timely since I was needing it for my JAR, and you've helped me there too!
Joe
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Old Oct 26, 2006, 11:10 AM
Fly lower!
aerolite's Avatar
West Texas
Joined Jan 2005
2,391 Posts
Albireo, glad I could help. It's always nice to know someone actually reads these articles.

Keep us informed on the JAR progress. I should have a new one with photos in the near future.

Dennis
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