Prop question???

[Alan Resinger]

With so much interest in electric and coming up with the "perfect" set up power train wise, I've decided that even with the availability of great props, we need to do some experimenting.  Igor used a CF three blade to win the Worlds last year and Paul was using one the last couple of times I flew with him last year.  Unfortunately there are very few 3B on the market yet, probably due to the fact the most electric flyers use pusher props, Igor and Paul excluded.
Some years ago before all the 3B CF  props became available, I made a number of wood 3B props. Most were made for the ST60 but I also made a few in smaller sizes for some other flyers.  Now that I've gone to electric I want to try some experimentation with props.  I got out all by cutting jigs and slotting saws and cut up a few Xoar 12 X 5 props so I could assemble one.  After finding my old assembly jig I grabbed a few different CF props that I had used over the years and upon checking them found that most of them had blade misalignment.  These props were Bolly, Eather and Mezlik props so all were guilty of having some bad molds.  Some had one blade off by about 1/8" at the tip of a 12.5" prop.  The best of the 6 or 7 that I measured was an Eather 10.5 X 5.75, which was near perfect. 
My question is what do you think the difference makes if the prop blades are not exactly spaced at 120 degrees? 

[Bart Klapinski]

   



       Most carbon props I can think of are not light weights. The biggest probably I can think of is vibration. One may be able to get a good static balance on the prop ,but I'm not sure if it would maintain the balance when running on an engine. This wouldn't do the engine shaft/bearing any good.

                  Tempest

[RandySmith]

With so much interest in electric and coming up with the "perfect" set up power train wise, I've decided that even with the availability of great props, we need to do some experimenting.  Igor used a CF three blade to win the Worlds last year and Paul was using one the last couple of times I flew with him last year.  Unfortunately there are very few 3B on the market yet, probably due to the fact the most electric flyers use pusher props, Igor and Paul excluded.
Some years ago before all the 3B CF  props became available, I made a number of wood 3B props. Most were made for the ST60 but I also made a few in smaller sizes for some other flyers.  Now that I've gone to electric I want to try some experimentation with props.  I got out all by cutting jigs and slotting saws and cut up a few Xoar 12 X 5 props so I could assemble one.  After finding my old assembly jig I grabbed a few different CF props that I had used over the years and upon checking them found that most of them had blade misalignment.  These props were Bolly, Eather and Mezlik props so all were guilty of having some bad molds.  Some had one blade off by about 1/8" at the tip of a 12.5" prop.  The best of the 6 or 7 that I measured was an Eather 10.5 X 5.75, which was near perfect. 
My question is what do you think the difference makes if the prop blades are not exactly spaced at 120 degrees? 

Maybe you should check the pitch on wood props made thru the ages, and ones now !, also many plastic glass, Nylon props, while your at it check the holes to see if they are off center?

Regards
Randy

[Mark Scarborough]

I think you might see a dynamic issue, as was stated,,

however,, Alan, you are aware that XOAR makes wood electric three blade props right?

as an aside, I was in communication with XOAR a few years ago, and they offered that they would be willing to do some reverse pitch props,, I cannot recall but it was either lots of 10 or lots of 100 ) yeah I know but it was a while ago

[Randy Powell]

http://www.xoarintl.com/rc-propellers/electric-props/PJI-E-Electric-Beechwood-Tri-Blade-Propeller/#spec

[Alan Resinger]

 Randy and Mark,
I have a couple of Xoar three blades.  Limited sizes plus the fact that the 12" dia. is really wide in the hub area and won't fit inside my little 1.75" spinner.  I'm really just curious about the fact that the props I really looked at had blades that were misaligned. 
Randy S. 
I don't think I've used many props without checking the pitch and balance.  Can't even come close to counting the number of props I've had that had the hubs be seriously out of balance.  When I've made some full sized props for homebuilts and air boats I almost always had to add weights to the hubs to make them balance. That would be difficult and dangerous to do on a model prop due to the small dimensions.  You are right about the number of props that have off center shaft holes.