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Making your own racing propellers

The process of making a Quarter 40 prop is simple. The diameter of the finished prop should be 7- 3/8" before you run and trim it. We make the blanks the same pitch on both blades by shifting the hub and just checking the pitch at station 5. If it is the same there, it is good at all stations. The next step is to change the pitch of both blades from station 5 to 7 only. At station 7, the pitch should be 3/4 of an inch more than you measure at station 5. The increase in pitch is a gradual change from station 5 to station 7 and continue at the same rate to the tip. The reason that I am suggesting the " more rather than give you specific numbers, is that there are many old pitch gauges out there and they are not all the same. If you use our blanks and do this, the numbers will work. It will not on all other blanks.

Prop Blanks
QM40-01

Prop blanks and template
Prather Prop
Pitch Guage
QM40-10

Prop Cutting
Template
QM40-05

When you finish the backside of the prop, move to the front. You want to strive for about .100 to .110 thickness at station 5.  Move the high point to the rear as you shape to the tip. The tip will be close to 40% of the cord for the high point. Make the blade taper to nothing when you look at it from the front. You are looking for a smooth look, with no fast tapers at the tip.

 Finish the bare props with thin Ca. One coat at first, then after I run them on an engine, on a test stand, I trim them to the RPM I am looking for. Then put on another several coats of Ca, sand and polish.

I look for different RPM ranges so that no matter where we travel, I have props that will turn in the 23.5 range. On the test stand, I have finished racing propellers that vary 1000 RPM's in 100 increments.

See, there is no magic. Making good props just takes time. I spend 2 to 2 1/2 hours on each racing prop. Most of them work very well. 

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