Rob's Hangar

Before I start: This mod really does make a huge difference. It will make the 4#3B helicopter responsive like never before, self stabilizing and not rolling in any other direction than your stick input. See my videos here.

But only if the flybar angle is set exactly to 45°. If its not, you will end up with the same performance as in the known Bell/Hiller Mod or the other available b/h mods with the original 90° flybar. However with this mod the flybar angle can be set. I’m working on an improvement in how to set the angle exactly AND have it stay that way (thinking liquid metal, loctite, epoxy, bigger screw…) Maybe someone will come up with the perfect solution.

Bell Head on the Walkera 4#3B

So the two major weaknesses of this Mod in advance:

• the M1 head-screw might be to weak and get bent or break
• the balancer bar part of the head might rotate out of the 45° angle

Both problems can be solved, I’m sure – but a head made from one piece of metal will always be more durable.

Here are the parts i used

• Walkera 4G3 mixer arms (xtreme might also work): HM-4G3-Z-38
• dogbone/ball links made from 4#3(A) linkage set HM-4#3-Z-08 (or xtreme b/h mod parts)
• Walkera 5G6-1 aluminum upper rotorhead: HM-5G61-Z-26
• Walkera 5G6 or Lama2 balancer bar: HM-5G6-Z-02
• Walkera 4#3B brass flybar connector (paddle holder) M-4#3-Z-04
• M1 screw about 4mm long
• a second 4#3(B) rotor head ring: HM-4#3-Z-07

Tools

• drill bits: 1mm, 1.5mm, 2.5mm
• file, metal saw and the other usual stuff
• triangle or something to measure the balancer bar angle exactly

Take the shaft out of the 5G6 upper rotorhead. Take cap of. Drill the whole for the shaft all the way trough. Cut the head off with a metal saw (see pic).

drill through the head so the M1 screw can go through

Cut the head off with a metal saw (see pic).

some parts

Now the hole in the lower side of the head will be drilled to 2.5mm (maybe start with 1.5mm to be more exact), but only about 1mm deep. This is where the 5G6 head will sit on the 4#3B head (silver cap taken off). You might have to file the 5G6 head where it was cut to make it exactly even. Now you can screw the 5G6 head onto the 4#3B head with the M1 screw. The M1 will fit into the 4#3B. Make sure the screw wont touch the feathering shaft going through the head into the bladegrips.

Now the M1 screw is something of a weak point in the mod. I need a thread cutting drill bit to make a M1.3 thread in the 4#3B head – an M1.3 screw would strengthen the connection significantly. Also this is critical because the connection should not rotate in flight, as the angle will be off (not 45° anymore).

Now to the balancer bar. Take off the weights and cut the bar to 95mm (other length will also work, matter of taste, this will change responsiveness and self-stabilisation). Both sides need to be exactly equal length. Cut the second 4#3B rotor head ring/ flybar holder into two pices (see pic). put them on the balancer bar.

The 4#3B flybar connectors / paddle holders will be put on the ends (not to hold paddles, just to hold the weights).  Put the 5g6 balance bar weights on. Heatshrink them to the flybar connectors.

Connectors as in pics. Length of dogbones swash to mixer about 17mm.

M1 screw through the 5G6 head into the 4#3B head

head with balancer bar, links are off, silver cap is off

Side without balancer bar, balancer bar with weights, heatshrinked

The original rotor head ring will stay on to get the rotation from the head to the swash without putting load on the dogbones that go to the mixerarms. Put a short piece of 1mm carbon or steel where the 4#3B flybar usually goes and fix it with the screws like the original flybar.

Tighten the main head screw in the blue 5G6 head, set the angle to 45° exactly (use a triangle, measure exactly, VERY EXACTLY). the 5G6 flybar has play of about 10°.this is a bit of a problem. More on that later.

It is critical to set the flybar to 45° – if its off just 3-5° TBE (toilet bowl effect) will be there. In flight you will know when you have set it right.

Which dogbone holes on the plastic swash to use is up to you. Use the longer arms for the mixerarm connectors if you want even more cyclic response. The shorter ones are fine for very precise hovering.

linkages - note the rotor head ring still in

Which parameters can be changed / adjusted?

• length of balancer bar
• weight of balancer bar weights or paddles
• link from swash to mixers either from long swash-arms or short swash-arms

The balancer bar angle can be changed of course, but once you have found the perfect 45° you never want to change that.

head closeup

short version: