Apr 03, 2012, 08:24 AM
Australia, VIC, Melbourne
Joined Nov 2006
More nose-gear work.....
1) Steering servo area cut out
2) Ply mount for the servo
3) Ply mount glued in
4) Servo and retract in to check alignments etc
5) Retract control horn and home-made 'pushrod block'
Approx 7mm square piece of 3mm alloy, with two 2mm holes for the control arm
and the pushrod clevis
6,7,8) Control arm close ups
9) Retract screwed in and motions checked.
The home-made alloy block is actually better than the usual steering arms sets that give a plastic piece for that, so I am happy that I will do that on all of them from now on. The block needs to be able to rotate on the control arm shaft during steering, whilst allowing the clevis to pivot also - just during retraction.
The steering arm is a standard 3mm collared arm, cut down and drilled for the long 2mm 'control arm' bolt. The block gets aligned along that bolt during steering servo and retraction testing, then the nuts used above and below it are locktited once that is all aligned. (eg in 7th pic)
The hole for the clevis has to be dead in-line with the trunion pivot (brass bush) at 90deg (to the side of it) so that the pushrod does not cause the landing gear leg to rotate at all during retract operation. It will stay dead straight at all times. I use a separate channel for the steering servo and mix the steeering to the gear switch, thus the instant you flip the gear switch the steering cannot turn anymore. Thus it stays dead straight into the retraction process, plus can never be turned whilst stowed away.
The retract box had to have some of the side cut away, to allow the clevis a wide enough arc of movement. You would normally make a larger box really - it would need about 3mm more width per side to fit it and be symmetrical still. But seeing I used the F-100 retract opening width as it came, the box itself had to have that bit cut-away. If I did it again I would do the wider box!! More out to those moulding lines you can see in the plane there. (eg seen in Pic 9)
There will be a cover that runs from ahead of the steering servo, back to the cheater hole - just allowing the leg and steering arm to have opening clearance.
With a fair bit more effort, you could add gear doors and run them off a sequencer - with the mains having doors then also. Maybe one day I will....
The HK-314 retract has a 3mm hole, which fits the stock supplied stub fine. At the top end of it I grind a "colllar" into it (a 2mm wide, 0.5mm deep, ring). This is so you can use two grub screws in the trunion bushes to 'mildly clamp' the peg and thus it can rotate freely for the steering, whilst unable to move up or down in the trunion. You locktite the grub screws in so they stay positioned correctly for that.
I usually drill out the trunions to 4mm and use 4mm piano wire stubs, but for this case I decided to leave it at 3mm and then I can upgrade it later, after the 3mm eventually wear a bit of slop into the trunion.
Last edited by PeterVRC; Apr 03, 2012 at 08:30 AM.