EJF Composite A-10 Construction

[Arthur Knowles]

Yes. I'm currently building a form/mold so I can build new glass wheel covers. The kit has some ABS ones, but they are way to small for a retract installation.

My first attempt at a mold failed using lightweight Hydrocal for the mold. Too porous and fragile. As soon as I have the mold done, I'll post pictures.

In the meantime, I'm finishing up the rudder & elevator assembly and then it's on to the motormount.

[Ed Waldrep]

I'm suprised the Hydrocal didn't work. Maybe there's different version of it but a friend of mine uses it and it's definitely not lightweight. I've made quite a few molds of parts with plaster of paris, the 25 lb bag from Home Depot. I've always had problems with air bubbles and rarely get a mold with none but the other day I mixed a batch with a bit more water than normal and molded the cowl of my GWS Corsair. I poured the mix in and started pounding on the table to get the air bubbles to vibrate/rise to the top and I used a stick to stir the plaster and dispense air bubbles. I got the vibration idea from seeing shows on the discovery channel about concrete pouring in the Hoover Dam and bridges, they used these vibrating jackhammer type things with cylinders on them that vibrate the air out of the concrete. Well, it works...not a single visible air bubble this time.

I had some other molds that I made from the Wattage F-86 parts that I finally got around to experimenting with. I put 3 coats of release wax on the bare plaster mold and then sprayed with mold release and layed up a part with 2 oz glass and West Systems Epoxy. The part released fine, no sticking. I had painted another part mold with black spray paint to see if that would give a nicer surface or help with releasing. The epoxy stuck to the paint...the paint stuck to the epoxy better than it did the plaster! There was hardly any paint left in the mold. The plaster must have a really smooth surface.

The plaster of paris molds are pretty strong, but you wouldn't want to drop them of course.

[Arthur Knowles]

Ed,

Thanks. I have some plaster of paris in the garage and I am going to try and make a new mold tomorrow. We'll see how that one works out.

Art

[Arthur Knowles]

Well, thanks to Steve Neil I now have a pair of glass wheel covers for my A-10. I had to make three molds as the first one with leightweight Hrydrocal was too soft. The second I didn't leave enough thickness for the bootom and it peeled up the first time I cast the mold. The final mold worked well (I baked it at 175 for 8 hours as Steve suggested). I also used candle wax in the mold. PVA (even three layers) still would soak through into the mold.

I pulled 6 covers in total. The first two were thowaways as the molds were bad. The last sets were good, but I sanded the first good pair two low to fit over the retract mounts.

Speaking ot that, if you build this kit, ignore the retract mount height suggestion. It's just too high and wide. Make them only as tall and wide as the retract mounting requires. Then your wheel covers may be a bit shorter than mine.

I'll post some picks in the next day or two after I finish filling and cut out the reliefs for the landing gear strut and wheel.

[Arthur Knowles]

OK, here is a picture of the new landing gear blister in comparision with the original ABS bottom (middle image) and top (bottom image) covers. The plan is to mate the original ABS top to the new glass bottom.

Note how high the new one has to be in comparison to the original version. This is why I state you should disregard the instructions in this area and make your landing gear blocks only as high as you need to. I could cut another 1/4" off the original blocks without any problems. That would place the glass cover at just the right height.

FWIW, I do now have a plaster mold where I can make many more fo these if needed.