Although not a gear backup system, I have seen one of BV's ARF Bobcats that he had rigged up with a single system for brakes and retracts, not just using a common air tank......as I recall, it was set up so that if you lose air with the gear up, you lost brakes, but then don't need brakes if you are landing gear up.......if you lost air with the gear down, you still had brakes as he tapped off the down line.....if you lost air before the split into up/down lines, you of course were screwed, i.e....the airline came off the tank....he used a modified eccentric circular output wheel on the servo that controlled a button valve and slow servo speeds to control the whole thing....this was on the P-60/BC that he was trying to keep as light and as uncluttered as possible.....this system dispensed with a separate brake valve, it's servo, and a second air tank....

I have used his old Bandit system of controlling the full nosegear door on my Kingcat, tapping off the retract lines to the nosegear and using a button switch that is activated by the N/G strut when it comes up (BV used to use an overcenter rotation of the output arm of the gear servo for control of the button switch)....either way, foolproof with only one retract servo, HiFlow retract valve, and button valve for the whole system.....

I think Paul Hopkins went with the servo so that he had control of the air flow from brakes to retracts.....it only took a brief moment to blow down the gear.....you could then switch back to standard lines and get your proportional brakes back.....important as buzzing thru an overrun without brakes often can do more damage than a gear up.....

Point of gear not locking down with the overcenter without air on it is a good one.....I know that Robart 630 will not lock down and stay locked down without at least 30 lbs air if there is any bumping around during the landing roll.....I found this out as I fly off grass most of the time......other gear like AirMagic, Tom Cook, Century Jet and BVM stay locked quite tight once locked down...

Interested to hear how Bob's trials went.......


Tom