Air System Installation
I had no choice but to use hydraulics on the landing gear because the design doesn't have mechanical up/down locks but relies on hydraulic lock (trapping the fluid in the cylinder) to lock the gear in position. However, the gear doors, speed brakes, and wheel brakes be operated via hydraulics or pneumatics. The gear doors and speed brakes use conventional BVM and Ultra Precision air cylinders. The wheel brakes are an Airworld design, but it is the same brake unit as is used on the MiG-21 and L-39 and I have personnally witnessed their successful operation using air.
I considered the pro's and con's of going with an air system as follows
Disadvantages of Using Air
1) limited supply of compressed air as opposed to hydraulic pump which will continue to provide fluid
2) additional components (fill valve, tanks) means more weight
3) I only had one extra hydraulic control valve - this would be handy to keep as a spare. I'd have to order at least three more from Austria.
4) High technical risk - the retract system needed to be replumbed due to the long retraction/extension times. Who knows what issues I might find with hydraulic doors and especially hydraulic brakes.
Advantages of Using Air
1) Low technical risk. We all have lots of experience with air systems and thus the probability of success (on the first try) is quite high.
2) Clean installation. The air lines are smaller and easier to route.
3) Ease of maintenance. It's air, not oil. I'd already taken one oil shower when I forgot to unplug the battery before disconnecting the pressure line.
Needless to say, after making this comparison, it was an easy decision to go with an air system. Although there would be the weight of the tanks and fill valve, these components probably weigh less than 4mm or 6mm oil-filled tubing.
Other builders have put their receiver/power distribution systems in the nose and have installed the gear door, speed brake, and brake valves/servos in the mid-fuselage. I decided to swap those locations and install the air valves & servos in the nose and the Jeti CB200 and Bavarian Demon Cortex Gyro in the mid-fuselage. Access to the nose is much better (especially after I did the removeable nose cone bracket - see post #1032) so the installation & maintenance of the air components would be easier, and having the CB-200 in the mid-fuselage would shorten the servo wires to the flight controls (rather than having to run them all the way up into the nose).
The air component board is installed about 3/4" forward of the nose gear forward former. This gives room for the cockpit floor which overhangs the former. The rear brackets are mounted just outboard of the cockpit sides. In order to improve maintainability, the board is screwed to the rear brackets, but the board is captured at the front by slots in the front brackets. Therefore only two screws need to be removed to remove the board.
To facilitate the routing of the air tubing, i ground a slot theough the forward gear former on the right side; the hydraulic lines and fuel fill are routed along the left side.
Jim