View Full Version : Multi-blade balance

08-18-2007, 02:46 AM
Had a bad imbalance even after spinning up the blades and having
them centered on the head relative to each other.
Being a three blade head there was no way to use any of the
balancers that are commonly used for two blade heads where the
blades "teeter" on a hinge point, won`t work for three blades unless you balance two blades and then the third blade against the other blade and keep going until you got them all the same, very time consuming.
This method does all the blades at once on the head with all the rotating
components. Very simple to disconnect the collective and elevator ball links and lift the whole head/swash right off the mainshaft in one piece. Hirobo MRB-III head, see Hirobo conversion by P901 for full description of the machine.
(Saves all the pitch adjustments, etc).
You can see from the photos that the pointer is right on center.
When I started the pointer was 3/4" off center!
(The blades all weighed 98 grams on my digital scale).
(Might have done better initially if I had a scale that went to the tenths of a gram but anyway this method does a static balance of the whole assembly.
The pointer is suspended first without the head and the dot is made on the paper, this is the starting reference point. Spool up to center the blades in the grips and let the blades coast to a stop without touching the head, lock the blade grip screws to hold the blades in the grips without any lead/lag movement. Then the head is installed on the pointer shaft and the relative imbalance can be seen.
The suspension string is tied down low next to the head at the plane of rotation.
Cutting the balancing tape on the blade tips by 1/4" increments can dial the balance "spot" on.
Took about a half hour to make the pointer shaft out of 8mm (scrap? titanium) suspended from a hook in the ceiling with some 100# salt water fishing line.
The pointer does not touch the paper so that the head can balance free.
Probably balanced to better than a tenth of a gram. Sweet.

Comments, suggestions please.

08-18-2007, 06:44 AM
that is a sweet head, and a great tip. I'll have to remember that if I ever get into multi's.