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Old Jan 03, 2013, 12:03 AM
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"Auntie Samantha"
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USA, MO, Clever
Joined Dec 2009
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Build Log
FMS V7.5 P-51 BBD: Dyno Tuning the Prop!

I'm going to show how I Dyno Tuned the FMS 14" 4-blade prop!

I must admit, out of the box, this prop needed very little attention.

Dyno Tuning the FMS V7'5 4 blade prop (8 min 23 sec)

My vid is pretty much self-explanatory, but I will go into detail on a couple of things:

In the process of doing the 1mm prop shim mod to increase the blade pitch, I noticed the supplied 3mm x 17mm screws were not fully penetrating the embedded nylon material of the lock nut.

To better explain (and a lot less typing on my part) I found a really good explanation of how a nylon lock nut is supposed to work: "Nylon locking nuts, also known as ny-locks, have a small ring of nylon on one end that forms slightly smaller hole than the threaded hole going through the nut. When the nut is screwed onto a bolt, the bolt has to force its way through the smaller opening, causing the nylon to stretch. This stretching creates a huge amount of friction between the nut and the bolt, allowing the nut to stay tight for long periods of time without coming loose. Nylon lock nuts are especially useful for applications that involve a lot of vibration that would cause regular nuts to come loose."

That said, I decided I was going to use (8) 3mm x 20mm hex screws to secure the blades to the backing plate. As you can see in the thumbnails below, the 20mm screws penetrate the nylon with room to spare.

Note* When doing the 1mm shim mod it will throw the alignment of the screws off center slightly, but as you tighten the screws they will line back up. It also takes those four tiny index dimples out of the equation, so care must be taken to insure the forward edge of the blade feet are flush and parallel with the stops.

Once I'm happy with the balance of the prop/spinner combo, I mount it on the G&C 4250 540kv motor and do a run-up test. "FMS V7.5 P-51 BBD: The 540 Power Plant!" before installing it in the BBD.

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Last edited by Sandancer; Apr 25, 2013 at 07:50 PM.
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