Vario Bell 205 turbine with semi-scale head - problems - HeliFreak
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Old 08-04-2014, 03:03 PM   #1 (permalink)
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Join Date: Jun 2008
Location: Tønsberg, Norway
Default Vario Bell 205 turbine with semi-scale head - problems

I have a few questions regarding this head as I'm not able to get it into a condition where I consider it safe to even hover.

Model: Vario Bell 205 with JetCat pht-3-3 mechanics (20Kg takeoff weight, 2,36m rotor)
Rotorhead: Vario Semiscale Ord No. 1005/12 Rotorkopf für Bell 212. Viper X aluminium rotor blades.
Gyro: Bavarian Demon 3X (With the latest sensors (newer than desember 2013) that can be used on turbine without protective hood/covering)

I want to get in contact with fellow flyers who has a model that is flyable with this semi-scale rotor head, to learn from your experience.

Questions:
1. Is your model flyable with this semi scale head?
2. Do anybody use a FBL gyro?
3. Do anybody you use HeliCommand or Bavarian Demon FBL gyro?
4. How long are your servo arms on swash servos?
5. How much cyclic do you use on the blades (I get 5 degrees, should be 8 degrees)
6. Do you have any phasing issuses?
7. Does the 10Kg brushless Futaba BLS451 swash servos have enough power for this semi-scale head (its four of them)


My problem:
Shortly after the helicopter gets light on the skids, it starts to wobble in a fashion like an amplitude increase, until it is compldtely unflyable and unsafe wobbling faster and faster back and forth.

It looks like som phasing problem?
Could the approx 30 degree later mechanically phased dampening work against the gyro?
Could the extremely soft dampening on the Vario head be a problem for the gyro?
Any advise would be appreciated.

Attached is a video of a small liftoff, look from 30 seconds and onwards.
Scale Vario with 3X by bavarian demon. Unknown problem. (0 min 52 sec)


Damping and slack in feathering axis:
Vario Bell 205 scale head damping and slack (0 min 34 sec)


All help will be appreciated.
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Old 08-08-2014, 01:08 PM   #2 (permalink)
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I'm using the formerly known Helicommand HC3SX, now Bavarian Devil. I have it in my smaller Bell 412 with th PHT2 engine. Maybe I could help? I couldn't see your first video. In the second vid. I don't know if the head is supposed to be having that much of teetering movements like that? I also noticed that you have the 45 degrees swashplate setup. I have the same swashplate setup on my Bell 412. In the Bavarian HC3 software, I had to set the phasing to 45 degrees. At 30 degrees, you would have quite a bit of forward movement. Maybe this is why your HC3 is fighting to keep your helo stabilize and thus, created the bobbling fore and aft? Do you by chance have the FBL unit or your helo under "Self Level" active when you try to lift off the ground?
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Half landing skid. 2 servo horns. 3 ball links.

Last edited by yf222000; 08-08-2014 at 05:49 PM..
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Old 08-13-2014, 05:48 AM   #3 (permalink)
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Location: Tønsberg, Norway
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Thank you for help. I also added a thread for this subject here (which is a bit more active): http://www.scalerchelis.com/phpBB2/v...hp?f=7&t=16431

I don't have the self level gyro (I have 3X, its 3SX that has self leveling).

The mechanical servo to swash layout is H90+45 degrees (Bavarian Demon supports this directly in the SW, so no need for phasing there, just tell it this). In fact Vario recommended it to be setup like a normal swash. Then you invert the pitch, and you change every servo connector 90 degrees to the left (CCW) to handle the 90degree phasing needed with this semi-scale head (without more SW adjustments).

As to teetering - yes, I'm now 99% certain that the dampening of my head is too soft (very soft) and the reason for all problems. I added 2x0,9mm shims which tightened everything up a lot - to the point that the helicopter is flyable again. So I think the conclusion is that this semiscale head had the wrong o-ring dampeners. I have ordered a new set of soft and hard dampeners - and will give a new status when I have a test flight with them. Hopefully the Bell 205 will fly perfectly well then;-)
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