Taildragger conversion of H9 Arrow
07-11-2004 | 12:14 PM
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From: Reading, PA
Taildragger conversion of H9 Arrow
Here are some pics of my attempt to convert my Arrow to taildragger configuration. This has always been a nice-flying airplane, and a great little trainer, if a little faster (especially on landing) than some. The semi-symetrical airfoil allows decent entry-level acro, and inverted flight is a breeze. The only weak point I've found is the nose gear mount, although even that was mostly due to a few of my own "dumb thumbs" incidents. Anyway, the last flight ended after an otherwise smooth deadstick landing wherein the nose gear folded completely back due to some firewall damage in the area of the mount on a previous flight. Enough of that...here are the pics:
1) Main gear. I actually wanted to mount it a little further back but it would have ended up splitting the bulkhead behind which the rx and battery are positioned. CG seems to have worked out OK anyway (after removing the 3/4 oz of lead previously installed in the old configuration). Not sure how it will affect takeoff once there's fuel in the tank (although the tank is actually between the mains and the firewall, so it should work out OK).
2) Main gear internals. Used 6mm ply cut to size, with four trangular pieces of the same ply to brace it. You can sorta see the forward braces up against the forward former, and the rear braces were epoxied in between the foreward and aft bolts. This created a small problem in that I didn't allow enough room for the blind nuts to sit in the ply doubler, but this was solved by cutting one of the points off leaving a flat edge that rested up against the brace on each side, effectively locking them in place. 4 1/4" nylon bolts complete the picture (stripped one of my black ones so had to use a white one from my spares supply).
3) Tail gear from the left. Used a Sullivan mount after failing to make a DuBro setup work. More 6mm ply to double up the mounting point, but for some reason, the assembly, when bolted in, tilted to one side (probably the previously unnoticed result of one of the aforementioned dumb thumbs incidents). Had to shim the right side (internally which forced the mounting bolts to the left and stiffened up the whole structure...no interference with the elevator pushrod, horn, or clevis (whew!).
4) Tail gear from the right. This was the hardest part to engineer. Because the Arrow has the rudder mounted above the stab and well forward of the one-piece elevator, the Sullivan wire/spring setup wouldn't work. I struggled with several ideas, all of which failed, but finally came up with something I hope will work. Turns out a servo horn screw fit nicely into the top of the brass knob at the top of the mount. Normally, the wire/spring arrangement would fit neatly through the small hole in this knob and go back and up to the rudder to provide steering, with the spring isolating the rudder from vibration caused by the tailwheel bumping along the ground. What I've done here instead is to CA 2 popsicle sticks together and tightly screw them into the knob, creating a little homemade control horn. Then I drilled a hole in the side of the model for the nylon sliding tube through which I ran the nylon control...ummm...tube. screwed a piece of control rod wire into the other end, bent it onto the opposite side of the rudder servo from the rudder control, and voila! I want to further secure the popsicle stick "horn" to the brass knob by wrapping some wire through the prevuiously described hole and around the 'horn'...hoping this will allow me to maintain some control if/when the screw comes loose later....time will tell if this solution will last! Worst comes to worst, I may further strengthen the horn by glassing it at some point.
Sorry this was so long but maybe it will help someone. Even if it doesn't, I'm kinda proud of the outcome of my little engineering exercise! Of course, if it all flys apart and I crash, I may have to swallow that pride!
Dave
1) Main gear. I actually wanted to mount it a little further back but it would have ended up splitting the bulkhead behind which the rx and battery are positioned. CG seems to have worked out OK anyway (after removing the 3/4 oz of lead previously installed in the old configuration). Not sure how it will affect takeoff once there's fuel in the tank (although the tank is actually between the mains and the firewall, so it should work out OK).
2) Main gear internals. Used 6mm ply cut to size, with four trangular pieces of the same ply to brace it. You can sorta see the forward braces up against the forward former, and the rear braces were epoxied in between the foreward and aft bolts. This created a small problem in that I didn't allow enough room for the blind nuts to sit in the ply doubler, but this was solved by cutting one of the points off leaving a flat edge that rested up against the brace on each side, effectively locking them in place. 4 1/4" nylon bolts complete the picture (stripped one of my black ones so had to use a white one from my spares supply).
3) Tail gear from the left. Used a Sullivan mount after failing to make a DuBro setup work. More 6mm ply to double up the mounting point, but for some reason, the assembly, when bolted in, tilted to one side (probably the previously unnoticed result of one of the aforementioned dumb thumbs incidents). Had to shim the right side (internally which forced the mounting bolts to the left and stiffened up the whole structure...no interference with the elevator pushrod, horn, or clevis (whew!).
4) Tail gear from the right. This was the hardest part to engineer. Because the Arrow has the rudder mounted above the stab and well forward of the one-piece elevator, the Sullivan wire/spring setup wouldn't work. I struggled with several ideas, all of which failed, but finally came up with something I hope will work. Turns out a servo horn screw fit nicely into the top of the brass knob at the top of the mount. Normally, the wire/spring arrangement would fit neatly through the small hole in this knob and go back and up to the rudder to provide steering, with the spring isolating the rudder from vibration caused by the tailwheel bumping along the ground. What I've done here instead is to CA 2 popsicle sticks together and tightly screw them into the knob, creating a little homemade control horn. Then I drilled a hole in the side of the model for the nylon sliding tube through which I ran the nylon control...ummm...tube. screwed a piece of control rod wire into the other end, bent it onto the opposite side of the rudder servo from the rudder control, and voila! I want to further secure the popsicle stick "horn" to the brass knob by wrapping some wire through the prevuiously described hole and around the 'horn'...hoping this will allow me to maintain some control if/when the screw comes loose later....time will tell if this solution will last! Worst comes to worst, I may further strengthen the horn by glassing it at some point.
Sorry this was so long but maybe it will help someone. Even if it doesn't, I'm kinda proud of the outcome of my little engineering exercise! Of course, if it all flys apart and I crash, I may have to swallow that pride!
Dave
