Increasing Cyclic Rate on Hawk/Falcon - Phil Noel (copyright)

A big advantage to the Century Hawk, Raven & Predator main rotor heads, is their dynamic stability. It is almost impossible to get them to flutter. In its most severe form, this is called the dreaded "woof and poof" syndrome. Even when using very dynamically unstable mainblades and combining these with worn servos and control links that will introduce play into the control system, one would be hard pressed get this head to "lose its' composure".
Another big advantage, is how easy it is to tune these rotor heads for a desired cyclic response rate, without sacrificing much hover stability, predictability and/or control precision. In its' stock form it is relatively docile. This is because the manufacturer does not know the flying ability of the purchaser. Consequently by having the stock configuration set to be relatively docile, any flyer is guaranteed success.

You may have noticed that many of the new designs hitting the market now are also using this head design. They will have the blade grip pitch controls coming from the front of the blade grips instead of from the trailing edge, and will have the bell/hiller mixers on the blade grip control arms instead of on teh flybar seesaw.

But now if one wants to really burn up the field. How can he increase the maneuverability rateon the stock Hawk Pro rotor head.?

Here are a few ways. First we must insure that the radio set up is optimized. ( I am assuming you have both the main needle and the hover needle set so there will be no leaning at full throttle and at half throttle.)

1 - Make sure you are using a good set of symmetrical rotor blades of the appropriate length.

2 - Set your throttle/pitch curves for a rotor speed of at LEAST 1800 RPM (with the 6mm/thrust bearing upgrade on the Hawk, 1900+ is even better). Be sure they are set so that any collective loads do not cause the rotor speed to decay.

3 - Set the total cyclic throw for at least 6 degrees

NOTE: #4, #5 & #6 apply if you are not using a governor.

4 - Now set a fore/aft elevator to throttle mix, so that the rotor/engine speed will stay as consistent as possible when applying fore/aft cyclic through maneuvers requiring it. Depending on the power system used, this may vary from 30% to 80%.

5 - Set a similar roll cyclic to throttle mix so there will be a consistent rotor/engine speed through maneuvers requiring roll cyclic inputs.

CAUTION: Be sure that these mixes do not overdrive your throttle servo under any of these conditions. Many radios have programs in their software that can be used to control this. If you have a more basic radio, I would suggest that you set your throttle ATV to its' max limits. Then attach the ball on your throttle arm at a distance from center that will not cause any binding when the stick is at full down and the throttle barrel at cut off and with the stick full up at 100% throttle barrel opening.

6 - If your radio has adequate mixes, I would also suggest that you set up a rudder to throttle mix so that the rotor/engine speed stays the same even when there is increased load from the tail rotor movements.

NOTE: Now you may better understand the advantages of the more advanced radios over the basic entry level units. It is virtually impossible to insure a reasonable set-up as described above with the basic 6 channel helicopter radios that only have 3 pont curves and limited throttle mixing. One could only do so with these type of radios when used in conjunction with a throttle governor such as the GV-1.

Without proper throttle to load mixing, as soon as one gets into even the most basic 3D maneuvers, he will find that the cyclic rate may be slower then desired because the throttle is not opening enough to deal with the increased cyclic loads. They may not realize that the engine is not being allowed to develop the necessary power (throttle barrel is not being opened enough) to accommodate the acceleration desired through the cyclic movement. The resultant engine rpm deceleration (bogging) will also make the unaware believe he needs more power.

Also, if one is "over pitching" the system through the maneuver, even increasing engine size will not solve the problem. If an engine can pull 10 degrees of pitch at an 1800 rotor speed in a straight climb, how can we expect it to deliver enough power to accommodate any additional loads when we are at full throttle/full collective? So if you have your throttle/collective stick at max, and you now throw in an additional 6 degrees of cyclic (a total load now of 16 degrees!) one must expect any motor to bog (even a 50 engine on 30 size 550mm blades will bog under these circumstances).

Now that we are sure we have the heli/radio set properly, we can move on to fine tuning the rotor system. Here are some hints that will increase cyclic response rates (in the order of simplicity and resulting return):

1 - Remove the flybar weights.

2 - Replace the stock paddles with some that have a good airfoil, larger area and that are the same weight or lighter, like those from the Swift 16. (On the Raven with the 4mm flybar, I have found the 50NX paddle to be very good here.) I believe you can now get them also for 3mm flybars. This would then be a good possible alternative for the Hawk. (NOTE: 3D paddles like the K&S 328 series will increase the cyclic rates, but because of their thin airfoil and the sharp leading edges, they can become TOO pitchy in forward and backward flight and remove too much stability in the hover.) Converting the 3mm flybar system on the Hawk to the stiffer 4mm unit of the Raven will also help here.

3 - Replace the two short balls (CNLR1010) on the inner star of the swashplate (Step #8) with two of the medium balls (CNLR1011).

4 - Replace the two H13167E special balls on the seesaw assembly (Step #2) with the longer CNLR1017 units.

5 - Flip the Bell Mixer Arm (H13189A) so that the area facing the blade pitch arm (has the molded stand off) is to the outside.(Step 3). Be sue to have an M3x5x0.5 spacer between the inner ball bearing of the bell mixer and the blade grip control arm.

6 - Replace the long CNLR1012 with the shorter CNLR1011 on the bell mixer arm (Step #3).

7 - To insure no binding at extreme contol throws and flybar angles I also move the seesaw plates inboard by trimming off 1mm from each end of the HI3167C tie bars. This moves the plates further inboard leaving more clearance for the contol arms from the swashplate to the bell mixers.

8 - You can also experiment with different lengths of flybars. There are a number of different lengths available from K&S of Japan. (see items in the "Products" section of our web site). Generally the longer the flybar the faster the acceleration rate will be into and out of a cyclic command.

You can use these in any combination to tune to a cyclic "feel" that you like.

NOTE: After any change, check all control travels and combinations for binding as you rotate the head through 360 degrees with the cyclic stick at each of the four corners. If you find any limit travels to insure there is none.