Area 51 experiments: The Furion rotorhead

[Laurens]

Lately I've been playing around with the Furion, and trying to tweak every bit of performance out of it that should improve it. One of those things is the rotorhead, which can be adjusted with loads of options. So far I've only flown it with the stock head, and experimented with the paddles and flybar weights. You can have a VERY well flying Furion with just the stock recommended settings.

Stock rotorhead:



However, with all these options its a shame to not try them. ErichF on this forum has made a very good writeup about all the things that can be adjusted in a rotorhead. Here's what he wrote:

Delta - the relationship of the blade grip pitch arm relative to the flybar feathering axis. If the pitch arm ball joint is directly above the flybar, or the centerline of the rotor head, this would be considered neutral Delta, or zero Delta. If, on a leading grip pitch arm, the ball is located on the grip side of the flybar, the Delta is positive, or "correcting" Delta. In this case, should a wind gust cause the blade to rise, the geometry of the correcting Delta would tend to take out blade pitch as the spindle, grip, and blade tilted upwards. The result is a positive, dynamic stability. The worse the blade excursion, the more the Delta influence, and therefore the harder the blade is brought back in track. The opposite, negative or uncorrecting Delta, works the other way. This setup is often considered for full-fuselage models, where the wind will work against the body more than the rotor disk. In that case, if the body is pushed to the side, inducing a roll into the wind, the result of the negative Delta is a countering force to raise that side of the disk, and bring the fuselage back to the original attitude and stop the model from drifting into the wind.

Bell Ratio - This is the ratio introduced by the Bell mixers located on the flybar carrier or blade grip pitch arms. This controls how much direct cyclic authority is sent to the blade grip, and is countered by the flybar (Hiller) input. Traditionally, higher Hiller ratios are used for more precise hovering and stability in fast forward flight. A higher Hiller ratio means that the flybar has more influence on direct blade pitch than the swashplate. A downside to using high Hiller ratio, is that it subtracts from your overall pitch range. Using too much can limit your pitch range so much that you don't have enough to get the -10 to +13 range typical of contest models. This is why some models have longer mainshafts, in order to get the required pitch range with a liberal amount of Hiller ratio.

Flybar Ratio - This ratio is the influence of the flybar on the Bell Mixers. Generally, the farther out the Bell mixers are on the flybar carrier, the higher the flybar ratio. You use this adjustment to balance the head response in the wing for hovering. Too high a flybar ratio, and the model will tend to drift into the wind. Not enough, and the model drifts downwind.

The first thing I'd like to try is getting a bit of positive delta, that should make the heli more stable and yet still capable of every manouvre thinkable. To allow this, there are three things you need to do:

- Flip the aluminium block in the bladegrip. The centerline from the bell mixer will be off center from the flybar.
- Change the ball in the bell mixer to the most outer position. Otherwise, the ball link from the swashplate won't fit anymore.
- Change the ball in the seesaw to the most outer position. Inputs given from the paddle will have more effect.

A closeup of the stock head, showing the seesaw and bell mixer:



The bell mixer:



And last but not least, the final result:



I still have to test fly it with this setup. Its going to be a suprise for me how its going to react. I hope that you guys will be experimenting too, and reporting back. At this moment, I don't use any flybar weight, and the stock paddles.

[dauste]

Hoi Laurens, you go first!

Seriously, I think we would all be very interested to see what kind of differences these geometry changes make.

I see from the pics you have got the BBT main blades installed. How are you finding those? I've got a new pair myself after losing my last set of SABs. I just need to paint up the tops in Orange though as I've got so used to flying like that, I'm afraid I'll lose orientation from a distance if I don't get them done.

[Laurens]

I've done a short hover here in front of the house, and that was very promising. Then I headed to the field, and in the beginning I was very impressed. Funnels, tictocs and hurricane's where really really locked in.

However, it did seem like I lost some of the pitch range. And with some stickbanging flips and rolls low, I felt like I was missing some cyclic too. I almost crashed it two times because of that, with one mistake leaving a long stain in the snow from the tailrotor. When I landed and disconnected the battery I found out why....

[dauste]

Ouch! Could have been nasty.. so if that ball hadn't come off, do you think you would have had the range and the locked in feel? I think you should get back out there now with your night gear on and let us know!!

[Laurens]

I still have to buy a simple jumper for that... I should do that soon.

The first part of the flight had a very locked in feel, and the whole heli was really controllable and stable. Hovering is way easier too. Tomorrow I'm going to fly some more.

[Thrasymedes]

Just a tip, you may want to recheck your maximum inputs when increasing the flybar ratio, into the third hole. Some helicopters do not allow for as much cyclic when using a higher flybar ratio and binds. With 7 degrees of cyclic and too high of a flybar ratio on my Razor it will bind in the head. To run 7 degrees cyclic and 11 collective I have to use the inner hole, the outer hole is probably good for 6 degrees cyclic and 10 collective.

With the inner flybar carrier hole you should be able to run ghastly amounts of cyclic and with the more active flybar it should be a wicked twisting beast. It will however, not likley feel locked in.

Good stuff.

[Laurens]

I recently switched back to the stock recommended setting. I like it that way better then with positive delta. Although it flies great with the most manouvres, flying 3D with piroettes gets really hard, especially with some wind.