The fresh air door actuating mechanism is controlled by a small 6″ linear servo and a lever linkage that gives maximum force at door closure. The air box was just clecoed and clamped in place because it will have to come off when the top fuselage half is joined (soon!!).
Custom fiberglass parts were fabricated to interface the fresh air hoses to the conduits. There will also be penetrations through the canard bulkhead for fresh air for pilot and copilot. The electrical cables on the copilot side are the crosstie and aft ground wires.
It turns out that the version of hydraulic pump supplied to Velocity is configured with the UP side as the high pressure side and the DN side as the low pressure side. The pump itself is symmetrical, producing full pressure independent of rotation direction. Changing the DN side to be the high pressure side requires swapping the internal pressure relief valves at the base of the pump, and recalibrating them for the desired pressure.
As an aside, simply switching the hydraulic lines between the UP and DN side will not work, because the internal valve configuration of the pump requires that hydraulic cylinder retraction (which is our gear up) occurs on the DN side of the pump. The difference lies in the excess hydraulic fluid volume that must be supplied to the cylinders when the UP side of the pump runs (our gear down). Confusing? You betcha.
Scott S. offered to do this PRV swap and calibration at the factory, but I had the required equipment to do it and adjust the PRV settings.
The nose and main landing gear hydraulic systems were connected to the hydraulic pump and power was supplied to the hydraulic pump bus. The emergency gear operation switch (in the pilot’s emergency panel) was wired up to allow testing of the gear retraction and extension.
As the video shows, the hydraulic pump pressure relief valve opens before the high pressure set point on the solenoid switch is reached. The result is that the hydraulic pump continues to run after the gear is up, and the “screeching” noise is the pump’s DN-side PRV opening.
Further investigation is required.
A few modifications were made to the nose landing gear doors and their open/close linkage.
During landing gear extend/retract testing it was difficult to find a nose gear door adjustment that satisfactorily held the doors shut, but opened promptly enough to prevent the doors from rubbing the tire on extension. I decided to remove the raised foam area on the doors to help prevent interference with the nose tire. The foam was sculpted and formed with EZ-poxy with flow, and then covered with carbon fiber for extra strength.
The rod ends on the nose gear door closing linkage were replaced with more sturdy and larger -3 versions that will not pop apart. I used left-threaded rod ends on the doors, and tapped an aluminum rod to act as a pushrod whose length can be adjusted by twisting it like a turnbuckle.
Because space in the keel is at a premium, I designed a smaller gizmo that attaches the MLG cables to the hydraulic cylinder. Fabrication of these parts are beyond the scope of the tools I have in my shop, so I set this out for fabrication – ouch$.
The new device has several features. It has an aluminum cylinder that fits over the actuator shaft, but it is threaded on a 1/4″-28 rod and so the MLG retraction limit can be adjusted by simply screwing the cylinder to the desired location and then locking it in place with a jam nut. In addition, the MLG cable rod ends fit into the device and tension/travel can be independently adjusted with nuts. Once adjusted, the nuts are secured with safety wire.
Instead of a nose-mounted oil cooler, I am using that location for a fresh-air inlet with a variable-opening door. I fabricated a door for the inlet using a foam-core sandwich panel, fit it to the opening in the fuselage, and attached it with a hinge just forward of the opening.
A fresh air distribution box was fabricated with flanges to attach to the fuselage and holes for standard SCAT ducts to route the fresh air.
When trying to swing the gear with compressed nitrogen, it was apparent that the main landing gear hydraulic cylinder was leaking. After pressurization and retraction, if the cylinder was valved off, the gear legs would slowly fall down. The leak seemed to be around the actuator shaft and not internal leakage around the piston.
Since I had to do the same teardown and seal replacement on the nose gear actuator, I decided to pull the MLG cylinder out and replace all of its seals too.
The fuel selector valve will select which fuel tank (or aux tank) delivers fuel to the sump tank. I decided to add a 1/2″ inlet to the sump tank, level with the fuel selector valve, which will now be the fuel inlet. This required cutting a hole in the back of the sump tank and adding a new hard point. The rear cutout was glued back in place with floxxy-poxy and leak-checked.
I will use one of the existing fittings in the upper corners of the sump tank for fuel return from the engine fuel servo, and simply cap the other one. I added an emergency shutoff ball valve on the fuel feed line to the engine.
Based on the results of the previous fuel selector valve tests, I made the decision to put the fuel selector valve between the whale tail and the landing gear bulkhead, just above the MLG pulleys and between the right and left brake hydraulic lines.
The Andair valve I purchased (Right, Left, Off, and Aux) has four 1/2″ ports, and orientation is important for the fuel lines and for the shaft linkage. I fabricated an aluminum sheet metal mount that will mount to the landing gear bulkhead. The valve position is slightly right of center because the shaft runs in the right side of the keel.
I calculated that even a steel 1/4″ diameter shaft of the required length would have too much torsional deflection, so I opted to make the shaft from 3/8″ aluminum. The estimated torsional deflection is about 3 degrees. The tank selector is mounted just below the instrument panel, accessible by both pilot and copilot. From there, a shaft runs down to a 90 degree gearbox, and then the shaft runs aft all the way the the whale tail, supported by oillite bushings. A u-joint directs the shaft up to the selector valve.
It is pretty busy in this area with the battery and solenoids, hydraulic pump, brake lines, MLG retraction cables, and fuel selector valve. I still have to route the landing gear hydraulic lines and a cable conduit in the keel, so it will get even tighter.
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