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My fix for the famous Raptor "flutter" or "woof"
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I had this "jig" built to test and correct crooked headblocks.
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I have been tinkering with Raptors since they came out, and every one I have owned has fluttered, so I was on a mission to find out why. I have spent allot of time trying to figure it out with the help of a friend who is a machinist.
Aside from the usual items which can cause flutter on any helicopter which include, 1) bad thrust bearings, 2) bad radial bearings, 3) AFT chord c.g. blades, bent mainshaft, bent spindle, etc, the other item which is causing flutter on most raptors which have the above listed parts in good working order is:
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4) CROOKED HEAD BLOCKS!
I have done all the other mods, trying to alleviate the problem, but was only successful in delaying the onset of flutter. Mods include, 0 delta, negative delta, metal blade grips, tightening all bushings, bearings, so there was no play, aluminum pitch rocker, lube this, grease that, etc, etc. Some blades will also flutter sooner than other brands. I have tried lots of different brands, composite and wood.
If you look at your static tracking, (height of each blade tip), while the heli is on the bench, you will know if your head block is crooked or not. Just measure the height of each blade tip using your transmitter’s antenna. (assuming your blades are not warped)
Due to variations in molding, some headblocks are more "crooked" than others. We have found the headblocks "crooked" in more than one axis as well. How crooked your head block is will probably determine whether your blades will flutter or not.
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Our test was to line bore, ream and steel sleeve the stock head blocks. A "jig" was made to hold the plastic headblock perfectly in a milling machine. The test was successful. After the "fix", both blades had perfect static tracking, and with identical pushrod lengths, the blades had perfect dynamic tracking in flight, no adjust necessary.
Have you ever wondered why your (dynamic) tracking in flight was way off, when you just checked the pitch and length of the pushrods while at the bench. If you have a "crooked" head block, you will have to make the pushrods unequal in length to compensate, and while it will track at some rpm’s, at higher rpm’s, or some pitch settings, it may not and that's when the blades "flutter". It is very hard on your control system and servos!
For those of you with other brands that are experiencing flutter, check the static tracking and see for yourselves. For those of you who think static tracking is not important, IT IS!
I know most people are not going to have the tools or a machine shop to fix a $9 headblock so the only option is to buy a metal head block. I have bought several and they worked very well (no flutter). Static tracking was off about 1/16 ", not enough to cause flutter (you have to take into account a little slop from the grips and bearings).
At the moment, I think Quick UK (not Quick World Wide), has the best metal headblock on the market. I bought a couple from Heli-hut and they were also good, but I would recommend the Quick UK block. I have not had very good luck with Quick World Wide products at all!
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