Archive for April, 2012
One of the things that I thought may have caused the crash was the horizontal stab fluttering. It was actually bowed and pretty flexy, so I slit the under side and inserted a 3/16" CF strip and CA'd it in place. This straightened it out and made it a lot stiffer. I'm hoping that helps flight characteristics.
The whole plane was stripped of original paint...at least as much as I could get off. Dents and holes filled with lightweight spackle, primered, then painted several coats with Rust-Oleum "Aluminum" metallic finish spray paint. It came out really nice and looks like metal. I am planning on modeling after a different squadron altogether. Callie Graphics will be ordered. I replaced the stock motors with Turnigy Park 480 Dubro 2 1/2" 3-blade spinners and MAS 9x5x3 props.
With the mold ready, I pre-heated it to 200 degrees in the oven prior to doing my first pull on the vacuum form. I made two frames from MDF that sandwiched a 11x12 sheet of .020 PETG held together with a bunch of binder clips. Placing that assembly on the oven rack under the broiler, i heated it until it began to sag about 1 inch below the bottom of the frame...moved it out and quickly centered it over the mold, turned on my shopvac and...voila! Instant canopy!
When the canopy's inside plaster is set, I removed the cast, then, after wetting the base, turned the mold over onto a pile of fresh mixed plaster to make a thicker base. Clean around the edges and smooth them while also trying to create an edge that will be visible as the bottom of the canopy when the original is removed.
Base for interior mold is made and smoothed. Be careful not to make a negative bevel. I almost did here. When the soft plastic is drawn down over the mold during vacuum forming, it will lock the mold in and be kind of hard to remove.
Here is the completed mold ready for vacuum forming.
I made an exterior plaster "cast" by carefully laying strips of gauze that were dragged around in dry plaster over the canopy, then spraying the whole thing with water til it was wet, then left it alone. After it was hardened a bit, I carefully added more until it was good and sturdy enough to resist distortion when the inside was filled with plaster.
The broken canopy was a real disappointment. It is thin plastic and can't be glued back together...I needed a new one, but they aren't available. I started reading about vacuum forming and figured I could make my own pretty easily. After watching about a dozen YT videos and RCG blogs, I came up with my own.
It looked like most of the pieces were there and should Gorilla Glue/epoxy back together ok. Props were broken, but the motors and all servos still worked. The canopy was broken and replacements were not available. Seeing other similar crashes of these planes, a common breaking point was at the tail booms. I decided to beef them up a bit with some 1/16" balsa sheeting over the broken joints to use as also a joiner. These were glued in place with epoxy.
In October '11, I bought this Banana Hobby P-38 from a friend. I was excited about owning my first multi-engine plane, plus it's definite cool factor! He had flown it so I assumed it flew well. Unfortunately, on my maiden flight, it took off very nicely, but as I brought it around on the downwind leg of a planned touch and go, it started to oscillate very badly. I tried to calmly get it under control, but nothing seemed to work. I passed my radio to a friend who is more experienced than me, but after 3 failed landing attempts, the plane finally spun in. We gathered all the pieces together and I took it home to fix it but more importantly, try to figure out what went wrong.