|TD to FT Conversion: (click here for newest entries)|
(page 1 of 2)
I retrofitted my tail dragger to a fixed-tricycle Glasair. The process is to remove the small tail wheel and fuselage mounted main landing gear and to install new main gear in the wing and a large nose gear assembly to the firewall. Well, at least I wish it were that easy. I've scanned and posted the fixed tricycle gear installation instructions in the library to use while at the hangar. You can take a look at them if you care to see the depth of the operation.
Due to the Subaru engine installation, the engine mount I designed had no consideration for a fixed tricycle gear. On a Lycoming equipped Glasair, the nose gear mounts to the firewall and to the lower portion of the engine mount just below the lower vibration mounts. The lower portion of the Lycoming mount carries the truss load from the engine.
My mount design has the truss load being carried across the top structure with no triangulation side to side on the lower structure. This was ok because the lower mounts are only supporting the engine level. The upper portion handled swirl motion, up down and right left.
I settled on this design to handle the impending loads of the engine and the nose gear:
Dec. 8th, 2004 Concept:
May 20th, 2005 Reality:
As you can see I decided to completely remove the engine mount from the plane and weld in new cross braces for proper support. These braces will mount half way up the side of the firewall and attach at the same location as the original upper tail dragger main gear. These reinforced areas worked out great because I can't run the tubes to the top mounts due to the radiator assembly taking up the space below the upper mounts.
The stock Glasair upper shock mount plate will be replaced with a new part that is four inches longer to line up with my lower engine vibration mounts. This replacement will make my design the same as the Glasair, except that my main engine support is still carried across the top of the engine mount frame. You could say that I will have an "overbuilt" engine mount now.
This combination will give the best support overall. It will require an estimate of twenty additional hours to completely remove and reinstall the engine. It will also add the weight of the two tubes and the slightly longer upper shock support, but that's acceptable to me now that I'm confident that it is strong enough to do the job.
The drawing at the left is comparing the Glasair 1 and Glasair 2 trunnion attach plates. I built my firewall with 1/2" fiberfrax. This makes the overall thickness of the firewall over 1". You can see by the drawing that the old style plate is too short. I had to use the larger Glasair II plates to make it work. I have Deltacad .dc and Autocad .dxf versions of the trunnion attach plate (suggest right-click and "save as" to download)
02/12/2005 Task Hours: 7.0: Disassembly:
Before I started removing all the stuff that would be in the way of the FT conversion, I took several pictures of the engine plumbing and electrical layout to aid in reassembly.
These next three pictures are of the device (sheet of aluminum) I placed under the thermostat housing to collect the coolant and direct it to the drain bucket:
It's amazing how little time it takes to remove three years worth of assembly.
Parts have all arrived:
The nose gear strut, wheel, tire, both main gear legs, main gear leg clamps and "A" rib bracket were purchsed used. I had to purchase new "B" brackets, nose gear trunnion attach plates, various bushings and bolts. I calculated needing about 35 yards of UNI and a few yards of bi-directional cloth for the install.
03/3/2005 Task Hours: 2.0: Started removing foam for the "A" rib and both "B" rib reinforcement laminations.
The first step in the FT conversion is to lay out the UNI-directional reinforcements on the inside of the "B" ribs and the left side of the "A" rib. I used a pin router in my Dremel tool to cut through the first two layers of existing laminates. Removing the foam was relatively easy with a small gasket scraper. The ridge that remained along the wing skin laminates was removed with an orange tapered stone bit in the Dremel. The most difficult part was removing the Q-cell that bonded the original foam rib reinforcements to the wing skins. This had to be done without damaging the wing skins. I kept a vacuum running on the area to keep the skins visible while grinding the Q-cell out and moved slowly to prevent skin damage.
04/9/2005 Task Hours: 16.0: Removed the remainder of the foam and ridges in the reinforcement lamination locations. Sanded back of rib laminates in preparation for applying laminates. Sealed all exposed areas of foam with a q-cell and resin mixture. Started cutting uni-directional mat and ran out after cutting the lower b-rib layers. Discovered that the other 112 feet I need is on backorder. I guess I should read the invoice :-|
04/25/2005 Task Hours: 8.0: Received the remainder of my uni-directional cloth this week. Finished cutting all of the A-rib strips and the upper B-rib strips. The lower B-rib strips will get cut as I install them. Each one is a custom width. Once the cutting was done, I laminated the 3-layer lower B-rib horizontal strips and then I started laminating the lower A-rib strips. By the end of the day I had completed all 18 uni strips and the 6 bi-directional strips of the lower A-rib only. This part of the A-rib took 3.5 hours to complete. The 18 strips fit with no problems and I will have to laminate another 3-4 to fill the remaining gaps flush with the A-rib face.
This all means that the remaining upper A-rib and both upper and lower B-ribs will take at least another 17.5 hours just to complete the minimum laminations. I estimate another hour for the final fill laminates and yet another hour for the 2-layer bi-directional laminates over the three completed ribs. That means I will probably be done by ... oh... next January!!!! ;-)
05/5/2005 Task Hours: 10.0: I took this week off from work to allow time for this next step. Monday I set up the work area and laminated the upper A-rib strips. This 21-layer lamination took 4 hours to complete. Tuesday I laminated the upper B-rib reinforcements. After about 2 hours, I realized that my back wasn't going to take it. I went to the hardware store for some steel to make a lifting jig for the aircraft jacks I built. This allowed me to raise the wing a little more than counter height as well as any level that my back could handle. It was quite a relief. These laminates took me a little over 6.5 hours to complete. Wednesday, I cleaned the paint off the back of the firewall in the area of the vertical nose gear ribs. I marked the locations of the ribs. Next I cut the foam for the ribs. This included the two middle 40lb foam pieces and the four 5lb foam pieces. Then I bonded the 40lb pieces into place with a 2x4 jig to hold them square and properly spaced apart. Thursday I bonded the remaining four pieces of the nose gear ribs into place and applied the q-cell radius along the edges. Then I set out to laminate the lower B-rib reinforcements. These laminates had to be cut just prior to lamination because the size of the space they were going into was shrinking as each layer was applied. This took another 7 hours to complete both of these. The last thing I did was sand the rear edges of the nose gear ribs with a nice radius for laminating over. MY BACK IS KILLING ME!!!!
(page 1 of 2)
HOME | WEB LOG | SUBARU ENGINE | AIRFRAME CHANGES | PROPELLER | ELECTRICAL | INSTRUMENT DASH | BUILDERS LOG | LINKS | CONTACT