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edgraydallas
Joined: 13 Jun 2008
Posts: 74
Location: Dallas, Tx
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 Posted: Fri Sep 24, 2010 8:02 am Post subject: props and engines |
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Looking from comments from any of you Fox builders. I have replaced my 3 blade GSC original prop with a new 2 blade 68 inch Warp Drive with nickel leading edge. Doing this in preparation for adding floats in the near future. The Warp pulls great and ups the cruise speed about 8 mph (this is a 582 on a model 2 with lots of fairings and no wheel pants). But, there is a vibration in the engine that I never had with the three blade prop. The blades track perfect and pitch is equal. Blades brand new so I assume they are balanced. Is this typical for change from 3 blade to 2 blade?
Also, I am about convinced to order the Eggenfellner “Viking” for the Kitfox 4 1200 now building. I like the extra power for floats and the Honda reliability. Anyone know someone who has ordered one or has an opinion?
Ed Gray, Dallas, K2 582 and K4 building. Do not archive
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Tom Jones
Joined: 12 Mar 2006
Posts: 752
Location: Ellensburg, WA
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| Posted: Fri Sep 24, 2010 10:47 am Post subject: Re: props and engines |
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Ed, I switched from a three blade 68" GSC to a 72" two blade Warp square tip on a 503 Rotax with 3:1 gear box. The GSC three blade was smooth at all RPM. The two blade has a slight vibration at 3000 RPM only. At all other RPM it is smooth.
The two blade improved climb significantly.
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_________________
Tom Jones
Classic IV
503 Rotax, 72 inch Two blade Warp
Ellensburg, WA |
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propellerdesign(at)tele2.
Guest
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| Posted: Fri Sep 24, 2010 11:41 am Post subject: props and engines |
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Some years ago it was found out if the pitch was set equal at 75% radii on
both or all blades it run smoother, not all blades have the same twist from
there to the tip.
Also make sure every prop you mount on your plane is 100% balanced, get a
balancer!
Jan
www.jcpropellerdesign.com
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Sat Sep 25, 2010 6:24 am Post subject: Re: props and engines |
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Hi Ed,
Props, hubs, spacers and all the nuts and bolts forward of the prop flange are not in balance. They all play a part and every prop assembly before going on a plane should balanced. Everyone only thinks they should just check the prop, but there is more attached to that prop. You can get a nice prop and wheel balancer for about $125 and it is so easy to use a "Caveman could do it". I balance everything in front of the prop flange except the spinner. They are all off. You can use a standard washer on a bolt for the balance change. At the minimum a full prop assembly should be static balanced. I also have a Dynamic balancer that I use. I know most don't have a dynamic balancer, but you can seek out someone who has one.
The other thing that causes these types of vibrations is a poor carb balance or none at all. make sure the carbs are balanced. A lot of time on the gear box (over 800 hrs) will cause this because the bellville washers become weak and the friction torque on the gearbox gets low.
If you have questions you can call me.
Roger Lee
Tucson, AZ
520-574-1080
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_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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mikeperkins
Joined: 22 May 2007
Posts: 123
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| Posted: Sat Sep 25, 2010 6:40 am Post subject: Re: props and engines |
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As we've talked before, Ed, you might remember that I go back to the "Denny Days" of '86-'87. I recall quite well that the entire reason Denny specified a three-blade prop on the two-cylinder engines was to prevent harmonic vibration, regardless of the gear ratio. Where there is vibration, there is also fatigue.
Minimizing vibration:
Static balance, checked with bearings and shaft on a bench, 1 gram
Pitch, checked with a protractor, 1/4 degree
Dynamic balance, checked with a dynamic balance instrument, zeroed
Static tracking, checked with a stick in the ground, 1/8" max
Dynamic tracking at RPM, checked visually by ground-running the engine, 1/8" max.
Carb balance, checked with a flowmeter. (I have one if you want to borrow it).
Mike Perkins
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