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Old 07-12-2019, 04:09 AM   #12 (permalink)
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Join Date: Feb 2014
Location: Vancouver, BC

Two key items for multiblades

(forgive me for covering things you may already know)


Simply stated, you want your blades to reach max deflection 90deg before the requested resultant force.

On a two blade set up the control links are rigged mechanically at 90deg to the blades. For example, if the swash is tipped straight forward, when the link rods get to the 12 o'clock and 6 o'clock positions the blades will be at the 3 and 9 positions which facilitates the phenomenon of phase lag where the force applied comes out 90 degrees later (which is why for forward flight the blades are at max pitch at the 3 o'clock position on a ClockWise rotating rotor disc)

For a multiblade head you have two choices:

1) Keep the link rods oriented straight up down between the swash and the grip links and use FBL phasing adjustment to achieve the correct phasing (there is typically an option in their programming to do this). Example, for forward flight you may need to tell the FBL to tilt the swash 28deg off center, i.e. it may be tipped toward the approximate 1o'clock position in order to get the blades to the 90 deg phasing


2) turn the upper swash (which angles the links) until the blades achieve the 90 deg difference relative to the lower swash angle. ie with the swash tipped straight forward, turn the upper swash until the blade at the 3 o'clock position (like in the example above) reaches max pitch.

In some case, often with the 5 blades, there simply isn't room to angle the links without running into issues with the links binding at certain swash angles and collective inputs.

Option No.1 would be preferred for more direct link rod force to the grip and avoiding the aforementioned binding of the linkages that may come from using No.2

There are some heads that have link rods called "J arms" that have this adjustment built in so you don't need to do either. The swash operates as if it was a two blade system. I have one on my MD500 from and it works great.

The other key item is BALANCE.

As long as you have a good quality head and blades you should have close CG's on your blades and then only need to balance them to each other. I use a digital scale that gets them within .01 grams and have had excellent results.

Hope that all made sense.

It sounds more complex than it is
1:5 BK-117 - 1:4 MD500E - 700 MD500E - 700 B222

Last edited by Trooper7; 07-12-2019 at 04:29 AM..
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