Brake Lines and Brake Calipers

The routing of the brake lines needs to be such that there is adequate length to accommodate the retraction of the gear, and that the excess stays out of the way of the gear leg during the MLG movement into the down position.  The flexible brake hose was routed close to the gear leg pivot axle, and from there, terminates at an AN bulkhead elbow fitting through the landing gear bulkhead.  Hard aluminum tubing will run to the front of the aircraft from these fittings.

A significant portion of the landing gear door holder plate had to be removed to prevent interference with the brake caliper.  I want to be able to remove the brake caliper without having to remove the gear axle, so this was a necessity.  I will find alternate ways to hold the gear doors when that time comes.  Finally, a 3/8″ thick brass bushing was used during assembly of the MLG over-center mechanism to hold the mechanism forward and prevent interference with the header tank fittings.

Fill and Finish MLG Legs

The next step on the MLG legs is to fill the surface, smooth, and get a coat of primer onto the surface.  I have deviated from the plans and I am using steel-braid brake line and AN hydraulic fittings for the brakes instead of the Nylaflow tubing.  I added four studs to the lower surface of the gear leg to attach Adel clamps to hold the brake line in place.  The studs consist of a MS24694 #8 x 1/2″ screw that is placed through the center of a thin 1″ square wafer of phenolic (or fiberglass). The wafer and screw are adhered to the surface with a dollop of thick cabo, and the squeeze-out is used to make a smooth fillet around the wafer. This is then covered with 2x bid. When cured, the edges are sanded smooth.

The coarse weave of the carbon fiber and fiberglass socks on the gear legs were filled with Velocipoxy+micro, and contoured with a spatula.  After this cured, the legs were sanded smooth and excess micro was removed. Then, cabo was added to Velocipoxy until a syrupy consistency was obtained.  This mixture was spread on the surface of the sanded micro  with a squeegee to fill pinholes.

The pinhole fill layer was then sanded again to eliminate any ridges left by the squeegeeing.  After masking the booties and the upper portions of the gear leg (where they fit in the socket), two coats of UV Smooth Prime were brushed onto the gear legs. These coats were sanded smooth with 320 grit paper – this is easy since the UV Smooth Prime is so soft.

Once the UV Smooth Prime coats (which fill all remaining pinholes) are sanded baby-skin smooth, the gear legs were sprayed with 3 cross-coats of Stewart Systems Eko-Prime, which is a water-borne gray primer.  Eko-Prime is harder than the underlying UV Smooth Prime, and should be hard enough to fly with.

Fitting Booties on MLG Legs

I purchased the aluminum “booties” from the factory, as this is an opportune time to install them.  The booties are supposed to help with dissipation and spreading of the thermal load due to braking during the landing rollout.  Some folks have experienced sag of their landing gear legs due to the temperature rise in the brakes during extended taxi and hard braking.

My first job was to remove the existing axle from the gear leg.  This was impossible to accomplish without a hydraulic press.  Once the axles were removed, the cut line on the bottom of the gear leg was marked to fit the inside shape and angle of the bootie, while replicating the position of the axle flange.  The gear legs were (gulp) cut with a jigsaw – no turning back now…  Then the edges and corners of the gear leg were sculpted to fit the interior shape of the bootie socket.

After reinstalling the gear legs into the fuselage and verifying that the height and angles of the axles were correct, the gear legs were glued into the booties with Velocipoxy + cabo, with a smooth fillet around the edges of the joint.  After curing, the holes were drilled for the bootie through-bolts.

Powder Coating NLG Parts

In an effort to make a few things look spiffy, I sent a bunch of metal parts to a local shop to be powder-coated.  Most of these parts were for the NLG actuating mechanism, the NLG fork, and the NLG shimmy dampener.  I also got the aileron bell crank brackets and the MLG leg booties powder coated.  My aircraft is going to have black legs – sexy.

Miscellaneous MLG Stuff

Taking care of some miscellaneous items associated with the main landing gear.  First things first, re-glue and clamp my favorite rocking chair using resorcinol-phenol glue – amazing stuff.  Ripple the hangar cat approves.  I plan to mount the MLG dump valve inside the keel, accessible by a fold-up door at the pilot’s right armrest, instead of in the inset cutout in the side of the keel.  So I made some sheet metal bracketry to attach the dump valve to the inside of the keel wall.  Also, the MLG retraction pulley mount was beefed up with a fillet of cabo+flox, followed by a layer of triax. I also ground off the shoulders of the MLG hydraulic cylinder mounting bracket because this was in the way of the hydraulic fittings.  Now the hydraulic lines can be installed fore/aft without making sharp bends inside the keel.

Main Landing Gear Retraction Test

I finally received the main landing gear hydraulic cylinder from the factory, over a year late.  It was installed in the keel tunnel and the retraction cables were attached to the MLG over-center mechanism.  Instead of hooking up the hydraulic pump, I decided to use nitrogen to test the retraction.  There is a stored energy problem with using gas, so I was very careful to manually help the retraction through the portions that required the most pressure.  I found that the over-center lock bar disengaged at about 380 psi, but it only required about 100 psi to hold the MLG in the retracted (up) position.

Shimmy Dampener

Received the new shimmy dampener from the Velocity factory.  Scott S. asked that I send the big aluminum NLG fork to the factory so he could drill the mounting holes.  Scott turned it around in a little bit over a week, and then my job was to drill the flange at the end of the gear leg to accept the bolts for the pivot pin holder.  Getting up close to the gear leg with a drill is difficult, so I opted for an extra-long bit so I could keep the alignment of the drill bit to the normal surface of the flange.  Also, some of the flange weld had to be ground away so the pivot pin holder would lie flat on the flange.  Test fit and assembled – seems to work great.

Main Landing Gear Thrust Bearings

I decided to install thrust bearings on both sides of the MLG pivot bushing to prevent the metal-metal (bushing to bolt-holder) contact and potential wear and slop in the MLG system.  This mod was first described by Dale Alexander in the Builder’s Forum section of Velocity Views 1Q 2004.  To accommodate the width of the thrust bearing, I had to grind down the existing steel pivots that have already been glued into the gear legs.  Care was taken to grind only enough to fit the bearing in place, and to maintain the position of the gear leg on the pivot bolt (because the retraction mechanism has already been fit). The grinding was followed by fine filing to make sure that the remaining bushing edge was flat and perpendicular to the pivot axis.

After the thrust bearings were installed, the MLG legs moved very smoothly. The side of the fuselage and portions of the gear pockets were trimmed to allow the gear legs to retract fully without interference.  Adequate clearance between the gear user legs and the sump tank fittings was verified.

Nose Gear Guides

After the guide parts were edge-filled with micro, cured, and sanded, they were tacked into place with hot glue.  Care was taken to make the guides vertical, flush with the door opening, and spaced appropriately from the nose gear axle.  Once tacked into place and clamped, the supports were tacked in place, and then the joints were filleted with cabo and covered with 2x BID.

Nose Landing Gear Guides

Guides were constructed to keep the nose wheel straight as it retracts through the nose gear doors.  This is to ensure that the nose wheel does not catch and hang on the doors or the edges of the nose gear door opening during extension.  That would result in a “bad day” and substantial repairs.  Plans call for making the guides out of a few layers of BID, but I chose instead to make them a little bit beefier, making a composite sandwich with some 3/8″ divinylcell foam.

A big sheet of sandwich was made, then the nose gear guides and supports were cut out with a jigsaw.  Foam was removed from the edges in preparation for some micro.