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All Forums >> RC Airplanes >> Pylon Universe - RC Pylon Racing >> QM-40 Racing >> RE: wood props
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RE: wood props - 3/16/2007 4:19:20 AM   
iamtom


 

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From: Cincinnati, OH, USA
Status: offline 		Lee only 2 tries? The first one could be a 58 prop.
Tom

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RE: wood props - 3/16/2007 5:43:08 AM   
daven



Posts: 6764
Joined: 12/7/2001
From: Andover, MN, USA
Status: offline 		I've sanded down a couple myself the last few days. I messed the pitch up on the first one, kept doing it backwards?

The second one turned out pretty good. I'm going to take it down to Florida next month and see what the experts thing (Tom, Grunk, and DK).. I'd hate to spend a bunch of time sanding these things if I was doing it wrong. I don't want to dunk it in CA till I know its decent. Its tought knowing how thin to go on the blades.

I made a nice little mitre saw jig that cuts these props right at 7 3/8". I'd take a picture, but I don't have a camera set up on this computer.

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RE: wood props - 3/16/2007 2:07:08 PM   
diggs_74



Posts: 1268
Joined: 1/20/2004
From: Emerald, WI, USA
Status: offline 		Don't worry Tom, what I lack in skill and pactience, I make up for in "pig headedness" I will keep trying.. I've got about 5 blanks left so I'll try at least that many more times..


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Lee LaValley
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RE: wood props - 3/16/2007 4:45:02 PM   
HighPlains


 

Posts: 2640
Joined: 3/2/2003
From: Over da rainbow, KS, USA
Status: online 		What are you using for blanks?

Are you changing the pitch? Checking for pitch variations side to side? You do know that on some where the pitch doesn't match up, you change the back side of the hub to even out the pitch?

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RE: wood props - 3/16/2007 4:50:58 PM   
Ed Smith


 

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Joined: 12/29/2001
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quote:

I've sanded down a couple myself the last few days. I messed the pitch up on the first one, kept doing it backwards?


Dave,

Do not feel bad.

At the CAPS Dayton race acouple of years ago Mike Deneve spent all Saturday evening carving a Q40 prop. At the end of the evening he held up his pride and joy "Killer" prop.

Now Mike is left handed, when he held it up to show us..................................

Ed S

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RE: wood props - 3/16/2007 5:10:19 PM   
diggs_74



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From: Emerald, WI, USA
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quote:

ORIGINAL: HighPlains

What are you using for blanks?

Are you changing the pitch? Checking for pitch variations side to side? You do know that on some where the pitch doesn't match up, you change the back side of the hub to even out the pitch?


I think the blanks were some I had got from Darrol.. I have the pitch gauge and used it accordingly.. However, I'm not clear on what you're talking about in regards to the hub.. Do you have some more info you would like to share??




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Lee LaValley
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RE: wood props - 3/16/2007 5:26:19 PM   
daven



Posts: 6764
Joined: 12/7/2001
From: Andover, MN, USA
Status: offline 		I'm using Zinger 8x7's now, and maybe some Zinger 9x8's that I bought by mistake.

I'm trying NOT to change the pitch, just using props that have the pitch at roughly 8 - 8 1/4 at station 7. Most of the props I bought were good, and at $2.50 a piece thats not too bad.

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RE: wood props - 3/16/2007 5:37:06 PM   
HighPlains


 

Posts: 2640
Joined: 3/2/2003
From: Over da rainbow, KS, USA
Status: online 		It depends on how they were carved by machine initially. For instance, Rev-up props had the pitch side cut referenced to the front side of the hub. A slight variation of hub thickness (one or two thousands of an inch, making the hub slightly tapered) resulted in the blades having different pitches relative to the backside of the hub. So you would hear stories of how out of a dozen props, only one or two would have equal pitch between the blades. The solution was to square the hub of the prop on the backside.

I would imagine that most prop carving equipment has similar problems.

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RE: wood props - 3/16/2007 6:06:33 PM   
DHG


 

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From: Denver, CO, USA
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quote:

ORIGINAL: diggs_74

quote:

ORIGINAL: HighPlains

What are you using for blanks?

Are you changing the pitch? Checking for pitch variations side to side? You do know that on some where the pitch doesn't match up, you change the back side of the hub to even out the pitch?


I think the blanks were some I had got from Darrol.. I have the pitch gauge and used it accordingly.. However, I'm not clear on what you're talking about in regards to the hub.. Do you have some more info you would like to share??


Lee,

Hold the prop at the hub, between your finger and thumb, and look down one blade from the tip to the hub. Notice how it looks like a wing. Note the angle of attack.

Now rotate it slightly with your finger and thumb to increase the angle of attack of this "wing". Notice what happens to the other "wing" when you do that.

Just a little sanding on the back of the hub can make the angle exactly equal on both sides.

I wish I had all the props that people have thrown away because of this.

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RE: wood props - 3/16/2007 6:24:35 PM   
HighPlains


 

Posts: 2640
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From: Over da rainbow, KS, USA
Status: online 		I find that sanding is too hard to control. I scrape the wood with a razor blade.

Of course, just because the two blades have equal pitch along the stations, doesn't mean that the pitch curve is correct for racing.

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RE: wood props - 3/16/2007 7:02:24 PM   
proptop



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Joined: 10/18/2002
From: Rome, NY, USA
Status: online 		I'm having difficulty locating a pitch guage...is Edmunds still in business? I have e-mailed Darrol Cady but he hasn't replied? (maybe a phone call?)

In the meantime, I have tried my hand at one...
I bought a package of 6 Zinger 8X7's and sanded one for practice, and it "looks good" FWIW...but guess I will find out when I run/fly it. I'm going to stand behind the engine when it gets running for sure, but I think I left it too thick anyway, so I have my doubts if it's gonna be worth trying. (just used the "worst" prop in the bag for starters)

Dave...the Zinger 8X7's you have all seem to check out to around 8" pitch?

I could make an angle guage or templates so I could get the same angle(s) on each blade at the various stations, but I wouldn't know exactly what the pitch (in inches) would be. Is there a calculation that translates the angle in degrees into pitch in inches? (gotta be something like that, right? But I ain't none too good at that there arithmatic )

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RE: wood props - 3/16/2007 7:20:03 PM   
diggs_74



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Joined: 1/20/2004
From: Emerald, WI, USA
Status: offline 		Ok, I see what you're saying on the hub.. That makes perfect sense.. Thanks..

By the way, does anyone have a good measurment for the thickness the blades should be at each station?? I wasn't real sure on how thin to go.. I thought at one time some either posted some thickness data or I read it in an article some where..


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Lee LaValley
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RE: wood props - 3/16/2007 7:28:04 PM   
daven



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Joined: 12/7/2001
From: Andover, MN, USA
Status: offline 		Proptop, I didn't measure all of mine, just two. The first one pitched about 7 1/2 at station 7 (pretty similar on both sides) and after just a little sanding (I will use the razor blade method next time) I was over 9 pitch. It came up quick, probably the new sand paper. I tried to take it back the other way, and soon had what I would consider a nice paint stirrer.

The 2nd prop was about 8 1/8" perfect on both sides, so I barely scuffed the bottom flat with my block to take off the gloss, varnish, or whatever is on the prop and just worked on the top half.

Calipered measurements at each station would be usefull, as well as rough percentage of where to move the highpoint. I think my current biggest issue is how much to thin the TE of the blade, and how sharp to do the LE? It looks good, but I won't know a thing till I run it.

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RE: wood props - 3/16/2007 8:15:38 PM   
HighPlains


 

Posts: 2640
Joined: 3/2/2003
From: Over da rainbow, KS, USA
Status: online 		The Prather gage was laid out in "Stations", starting with Station 1 and continuing to Station 13. Station 1 was closest to the hub. What makes it all fun, is that it is a metric design, and Station 1 is two cm from the blade that reads the angle. Each Station after number one comes in 1 cm increments. I believe all the other prop gauges are laid out the same as the Prather. Not a problem, as 2.54 cm equals an inch (2,54 for those of you still lost in the old world). Or 0.3937 inches is about 1 cm.

I don't really want to get into the merit or lack there of between the measurement systems. Though did it really make sense to go to a standard based on the distance between the equator and the north pole divided by 10 million?

To determine the degrees of a certain pitch at a certain station, you first need to calculate the circumference of that station. To maintain station that nearly everyone uses, you will have to also covert between metric and inch measurement, since everyone uses inches. So Station 7 is really 8 cm from the hub, and that means it is 3.15 inches.

Calculate the circumference = 6.28 x radius gives a distance of 19.79 inches.

Divide the pitch in inches by the circumference in inches and take the arctangent of this number to determine the angle in degrees at that station.

Couldn't be easier!

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