BALANCING 3 BLADED PROPS

Hello everyone,

Can anybody indicate me how to propperly balance a 3B CF prop?
(I have a Top Flite magnetic balancer)

Many thanks,
Claudio.

Claudio,

I use 2 balancers when I do 3 blades. I use a Robart wheel balancer first to get it close. Mark the blades with a felt pen or something (1,2,3). Put it on the balancer with No. 1 blade up. Work on the lower 2 blades until it balances. Turn the prop to put N.2 blade up and work on the two lower blades until it balances. Put No. 3 blade up and it should balance. If not, keep working in rotation until it balance with Nos. 1, 2 or 3 up.

I then take the prop and put it on a horizontal balancer. The one I have has a small aluminum hub that goes into the prop hole. It has a small hole milled into the end. This is placed on the base that has a sort of needle sticking up. The prop should just lay there horizontally. If it drops to one blade, work on that blade (or piece of hub) until the prop can lay on the pin without dropping.

Randy....
good advice. They take about ten times the patience of two blades. I have taken to dragging mine over to Windy and asking him to check them....he generally grabs them from me and fixes them real quick...

I would add that I first check eack blade for equal length, and usually itch them first, too.

See Ya

>and usually itch them first, too.

I generally scratch if they itch.

Bill <><

>
>See Ya
>
>Peabody

Bill:
The CF ones I pitch while I itch.

See Ya

Peabody,

Yea, I left that out. Check the blade length.

Claudio,

I might add that the Top Flite magnetic balancers are looked at very skeptically by some of us. Maybe it is no longer an issue, but just prior to buying one I found out that two friends had found the centering cones are their units were slightly out of true.

It's worth checking your prior to putting absolute faith in it.

LAST EDITED ON Oct-14-04 AT 04:22 PM (CDT)
 
You could remachine the cones, but if there is any variation on the edge break around the hole in the prop, it will have a similar effect.

I like the Top Flite magnetic balancer, but suspect it is better than needed. You might be satisfied to just get it as close as you can without going crazy, mark the heavy blade, and put it opposite the piston at TDC. Steve

I like the Robart wheel job I have. Seem sto work. The horizontal balancer is (I think) a Prather. I've had it a very long time, but still seems to work OK.

Thank you Steve.
Locating the slightly heavy blade opposite to the piston's TDC is a nice trick I've never thought about.

Hi Dan.
I'll check for this right now.

Thanks,
Claudio.

Thanks a lot Randy.
I'll add the horizontal balancing procedure.

On the other hand.. If one buys a 2-blade CF prop, such as Bolly, how can one change the pitch. I know people do it. I can't do it.

So, once one has $30 invested in a CF prop and it isn't the right pitch, how does one change the pitch?

Perhaps there is someone who can do this?

Hi Floyd,
Well.....I believe you need a pitch gauge of some type. I use a Prather model.
Whether it measures the true pitch as compared to others, I don't know but I use it more to ensure that both blades are the same, and to increase or decrease the relative pitch.
I use a hair dryer or heat gun (some use very hot water) to heat the blade and I slide my thumb and fingers down the blade with a twisting motion. I then submerge the blade in water. Randy Smith, IIRC, recommends to lay it flat and let it cool. It takes practice and usually a couple tries. It's very easy to go too far at first.
HTH
Bill <><

>On the other hand.. If one buys a 2-blade CF prop, such as
>Bolly, how can one change the pitch. I know people do it.
>I can't do it.
>
>So, once one has $30 invested in a CF prop and it isn't the
>right pitch, how does one change the pitch?
>
>Perhaps there is someone who can do this?
>
>Floyd

Hello Floyd,
It's relatively easy to repitch a CF prop. You'll need a good pitch gauge (Prather has a very nice one) a pot of hot water (deeper than the lenght of the blade) and some patience (maybe a lot of it..)
Submerge the first blade in the pot of hot water for a couple of minutes at 1 1/2 inches from the hub and then twist the blade in the direction you want to go and hold it for 5 seconds or so (use some cloth gloves to avoid burning youself...ask me how I know this) Then
locate the prop on the pitch gauge starting at 2 inches from the hub (you have to go from the hub to the tips) and check for the desired pitch. Do the same with the other blade (of course they must be equal)
Go to the other station and repeat the process 'till you're done.
The force applied to twist the blades will be less as you approach the tips. Re-check each blade in each station to be shure one blade is identical to the other (this may take several twisting actions)

Hope that my english is good enough to explain this...
Good luck,
Claudio.

If you can't find a pitch guage, try the Tulsa Gluedobbers web site. They have the original magazine article for the Hooptee guage. You can make it yourself. If made properly, it actually works well. I use it myself. Just cheap, I guess.

>Hello everyone,
>
>Can anybody indicate me how to propperly balance a 3B CF
>prop?
>(I have a Top Flite magnetic balancer)
>
>Many thanks,
>Claudio.

Here's what I use.

by any act, error, or omission, I have, intentionally or
unintentionally, displayed any breedist, disciplinist, sexist, racist,
culturalist, nationalist, regionalist, localist, ageist, lookist, ableist,
sizeist, speciesist, intellectualist, socioeconomicist, ethnocentrist,
phallocentrist, heteropatriarchalist, or other violation of the rules of
political correctness, known or unknown, I am not sorry and I encourage you
to get over it.

When I was doing a grumman XF5F a few years ago RC with 2 Tartan 1.3's with homemade 15/10 props I used a high point balancer and actually found that it was easier to balance the light blades to the heavy one. Usually requires a little extra varnish on the light blades.
And yes if your reading this I actually did use stock Zinger 15/10 props to make my 3 bladed props. They were very safe at the top rpm of 11k that the motors were expected to hit.
This is not a project for the enexperienced although the process is fairly simple but requires upmost precision in the manufacture of them.
My flying friend Carl Dannenhauer made the first DC3 from Nick Zeroli's plans and we made custom props 16/10 3 blade for his 2 Quadra 35's the plane was features in a Hot Stuff add in the early 80's. This plane was 54 lbs and would take off and fly at 3/4 throtte and fly very realistically at 1/2 throttle.
Dennis

Robert,

I'm with you. I use a heat gun (paint remover type), a rag and a pitch gauge.

Like the Junar plans. After flying the USA-1, I'm thinking about it.