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  #1  
Old 11-08-2006, 05:23 PM
Glos Glos is offline
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Default Refinishing the prop.

Ok Winter is coming so now is the time to do those home projects.
I plan to refinish the prop but can't decide what to do after the old finish is off.

Epoxy
Urethane
Varnish
Wax
Paint with a clear coat.

Would appreciate any and all suggestions/experiences.

I prefer to keep the wood finish but am open to options. I had it redone in 95 and epoxy coated but the epoxy is now dinged up & pealing off in spots. The wood is OK
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Old 11-08-2006, 10:43 PM
ZG4Me ZG4Me is offline
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Hmmm.

I hear the tip speed is around 1/2 Mach (~380 MPH), am sure someone will correct this non flyer

A bumblebee at 60 MPH will broaden your vocabulary on a motorcycle, can only imagine the dent it'd make at "tip speeds".

I'd go with an epoxy (Imron?) formulation. You should be able to find clear. Gawd sakes, if you spray this yourself, wear a good respirator, and lots of air changes. Once catalyzed, the fumes are deadly to your lungs.

Wax would be nice, but it doesn't protect from the elements very well. Apply constantly. I like "Tre-wax" for furniture stuff, very hard.

[Poly]Urethane works well on your dining room table.

Clear urethane (automotive two part urethane) should work too, add a flex additive. Flex additive will flatten the sheen (none to a lot), depending on quantity added. But see tip speeds above.

I are not a flyer, YMMV, don't forget to floss, ...

Rick
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  #3  
Old 11-08-2006, 11:49 PM
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JonC JonC is offline
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Quote:
Originally Posted by ZG4Me View Post
I hear the tip speed is around 1/2 Mach (~380 MPH), am sure someone will correct this non flyer
72" diameter prop @ 2900rpm has a prop tip speed of 959ft/sec (653mph).
66" diameter @ 2900 is 569mph
66" @ 2000rpm is 392mph.
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Last edited by JonC : 11-09-2006 at 12:12 AM.
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  #4  
Old 11-09-2006, 10:59 AM
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Epoxy finish = 11 years, can you ask any more of a finish?
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Old 11-09-2006, 02:28 PM
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Epoxy finish = 11 years, can you ask any more of a finish?
Sure.... I want it to shed blood and guts easily so I don't have to scrub it...
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Old 11-09-2006, 07:28 PM
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How low do you fly?
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Old 11-10-2006, 11:10 AM
Don P-Factor Don P-Factor is offline
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Propeller tip speed formulas should also be calculated with your forward velocity component included with the rotational speed. Also dont forget density/temp changes affect the Mach number. Unfortunately I cannot find the formula right now. Anyone? Tip speeds may exceed Mach number but efficiency suffers past. 92mach. Noise also increases. Sorry off topic. I vote for Epoxy skim coat! Don.
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Old 11-12-2006, 03:38 AM
Carolynne Carolynne is offline
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Hi,

I made a prop for my Long Ez couple of years ago. It has two plies of UND crossing at 60 degrees wrapped around the leading edge and overlapping at the TE with a glass to glass close out.

It was EZ to do and also because of all of the squeegeeing, teh glass layer was of very consistent thickness, which made balancing afterwards a snack too. It was painted with a single pack polyurethane that i used on the rest of the aircraft.

After about 100 hours in service, it has a few chips in the paint, from stones kicked up but not a mark on the glass substructure.


Carolyn
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Old 11-12-2006, 03:20 PM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by Carolynne View Post
After about 100 hours in service, it has a few chips in the paint, from stones kicked up but not a mark on the glass substructure.
Don't fly in rain much, eh? :-). Do that a few times at RPM's over 2200 or so, and you'll watch your leading edge deteriorate, glass or no glass :-).
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Old 11-12-2006, 04:48 PM
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Quote:
Originally Posted by Marc Zeitlin View Post
Don't fly in rain much, eh? :-). Do that a few times at RPM's over 2200 or so, and you'll watch your leading edge deteriorate, glass or no glass :-).
Good point, Marc. So, which finish do you recommend?
- Epoxy
- Urethane
- Varnish
- Wax
- Paint with a clear coat
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  #11  
Old 11-13-2006, 02:05 AM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by Falcon View Post
Good point, Marc. So, which finish do you recommend?
- Epoxy
- Urethane
- Varnish
- Wax
- Paint with a clear coat
Any of those will work fine at protecting a wood prop if maintained properly. My point was addressed to the physical makeup of the propeller, not the finish. NO finish will protect in rain. AFAIK, a good nickel or urethane leading edge will do the best in rain, but even those will erode if exposed enough. As far as a propeller is concerned, flying in rain is like flying through a bazillion freaking BB's.

I've got a Catto prop - it's a wood core with a glass wrap (MANY layers of glass). I've had to fill and resand my L.E. twice due to rain erosion, and will eventually have to send the prop in for refinishing. Talk to A&P's - they see the same thing on aluminum props on spam-cans.
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Old 11-13-2006, 03:55 AM
Carolynne Carolynne is offline
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Hi Marc,

I dont actually avoid rain, but then again, I fly for fun, so if the weather is too cruddy ( technical term ) i may choose to stay on the ground. If i do encounter rain in the air, I have no problem with throttling back to less than 2200 rpm and watching the free wind tunnel happening outside the canopy. (I still worry about the stagnant air on the upper trailing edge of the Roncz canard, but clearly the canard isnt worried........)

I originally had a B&T prop with a urethane leading edge and this too eroded in the rain and required refinishing from time to time. so fiddling around trying to put a urethane leading edge on the new prop semed a little futile.

So while i make no claims for my finishing method being bullet proof, so far with appropriate throttle control it seems to be holding up.

Carolyn
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  #13  
Old 11-13-2006, 04:47 AM
chasingmars chasingmars is offline
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Quote:
Originally Posted by Don P-Factor View Post
Propeller tip speed formulas should also be calculated with your forward velocity component included with the rotational speed [...] Unfortunately I cannot find the formula right now. Anyone?
No need to remember this one, it's a straightforward application of geometry:

Tip speed = square root ( (forward speed)^2 + (angular velocity x radius)^2)

Angular velocity here is radians/sec. To go from RPM to rads/s multiply by Pi/30. The above is insensitive to unit of length, but be consistant, if you use inches, remember the result is in inches/sec.

If you want the tip speed at any particular point on the blade, just use the radius at that point, rather than the tip radius.

Quote:
Originally Posted by Don P-Factor View Post
Tip speeds may exceed Mach number but efficiency suffers past. 92mach. Noise also increases. Sorry off topic. I vote for Epoxy skim coat! Don.
The mach number that efficiency sees a serious drop in efficiency is dependant on the critical mach number of the airfoil, that varies by airfoil section. 0.92 sounds a bit high, and you probably want a bit of margin away from that anyhow.
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