Landing Gear Progress

11/5/2009

Slowly but surely, I am getting there. the RV landing gear mod is well underway and I am now beginning to see the light at the end of the tunnel.

I initially (wrongly) assumed the landing gear sockets were a single thick tube, reamed up to marry with the legs, not so. After some digging and poking around in actual RV7 leg sockets, I realized there was a sleeve in each end of the socket. This gave the false impression from the outside that the sockets were around 1/8 wall thickness, when in fact the main tube socket was about half that with the thickness being made up by the sleeves that go in either end. I never did find out why they are sleeved, it is either due to weight saving, or the fact that the gear leg inside the tube flexes somewhat under loads so some space is required in there, or maybe a combination of both.

For more cross referencing, I took a long look at acropilotbret's (member on biplaneforum.com) Pitts RV gear mod, specifically the engine mount area. I couldn't copy verbatim, since the Pitts gear does not sweep back like on the Skybolt, so forces will be from a different direction. But his blog and a drawing he has on the blog came in handy, not to mention the build pics he has up there. Thanks Bret.

A machinist friend made me the sleeves. These were rosette welded in place by a TIG buddy. He had to first make a temporary insert to fit into the sleeve while the sleeve was being welded to the outer tube. The I.D. of the sleeves were purposely left slightly under size (0.010) so I could eventually sneak up on the final fit with a reamer.

The sockets were now ready to be part of a truss. I laid out the truss design on MDF, taking measurements and angles from the dry mock-up I had created on the fuselage. The tube notching turned out to be very accurate and neat, thanks to a tube notching online application. I just punched the variables (angle, tube O.D.'s etc) into an online form, and the form outputs a printable drawing which one cuts out and glues to the tube, then simply cut around the printed guidelines. It worked great. Tube notching software.

Once tacked, I took the truss to my TIG buddy, Seth, who did a nice job (as per usual) finishing the welds. For reaming to final size, I had purchased an adjustable reamer specifically for the task. I welded a two foot tube to the end of the reamer for leverage. It actually took me half a day to ream out the two sockets since I was removing only a thou at a time. By lunchtime I had arms like Popeye and was covered in sweat and cutting oil.

Now here came the tough part, I needed to drill the locating AN5 bolt hole at the top of each leg socket. Drilling through the socket and the leg meant I had only one chance to get this right. The first thing I needed was a nice flat surface, so I had to make one. I basically made an MDF box with supports, all cut at the same table saw fence setting for consistency. With the gear and truss laid out on the box, I clamped down the axles tightly, so they would be in the same plane. Initially I was scratching my head as to how to drill square and true, the whole work piece was too heavy and big to set up on the drill press, then it dawned on me...take the mountain to Mohammed. I set the drill press up on the floor, and voila. I started with 1/16, then basically worked up to a .300 bit. Then I finished with a 5/16 'under-size' reamer (AN5 bolts are well under at around .308-.310 it seems). There is probably a little run-out on the drill press, so it transpired that a AN175 close tolerance bolt fitted perfect for a snug 'tap-it-in' fit, phew!.

I have been making full use of the rotisserie on the fuselage, lots of welding tabs here and there and cutting off the legacy steel from the old bungee gear (gear truss, and ears for the leg attachments etc.).

The next step is to remove the fuselage from the rotisserie and jig everything back up ready for dry fitting/cutting the engine mount along with the landing gear and truss for its final fit, then tack weld everything.