My 1/2A CNC balsa Hyper Viper from Greg Rodney of Southridge CNC is a quick kit. It's a balsa replica of the Cox RTF model, which was a really sharp looking Stunt model except for it's inexplicably anemic engine. Other than that, it was actually capable of flying the whole PAMPA pattern.
Here's what was in the box.
The first thing I needed to do was clean off the grooves scribed into the wood by the CNC tool. I used 60 grit paper and carefully went over the whole fuselage. That and become reacquainted with my shop, which has been mostly inactive for 2 years now. Wow, time passes fast when you're not having fun.
It's a lot of work removing the grooves and making sure not to re-shape anything by accident. I still keep finding some, but I think some of it must be pressure indentations. I lightly spritzed it today from 3 feet away with Windex to see if some of it would swell out. The jury's still out on that. I've rounded the 4 corners of the wing slightly, as well as the flat edges of the wingtips and put more of a radius on the top of the rear fuselage, following up with 220 and 320 paper. This picture still shows some of the scribing that has now been smoothed out. I've also removed 4 grams of wood from inside the fuselage. It's all about 3/16" thick, and I took some wood out where I thought it was structurally safe.
Next are the hardwood motor mounts. I took the option of running them full length and, for the sake of reducing stress risers, rounded the ends to match the existing radius of the CNCd shelves they sit upon.
Here it is with a Tee Dee perched on the crutch. You can see I have removed some thickness from the inside top of the cowl. It had ridges that could have abraded the bladder, plus it makes more room for it to expand with a full load of fuel too. I also made a breather hole for the venturi. The Norvel
may not need it, but this will aid in future engine swapping. I think there is enough room for enough fuel. There certainly is enough for the more efficient Big Mig or AME. The Tee Dee might be close if I want 6-1/2 minutes for a Stunt run. It will be flying PAMPA at 1/2A day in September.
As for cooling and exhaust evacuation... I'm still imagining ways to handle that. The muffler for the Norvel wont fit without butchery that I'm not likely to do. Some sort of deflector and side vents are likely.
Plenty of room for cooling intake, but not the prettiest thing. I'll probably add another vent on the bottom, because the rule of thumb for heat removal is twice as much exit as intake. Merlin 5-fin Cox Texaco heads are no longer available. I do have an old scruffy red one. Cooling the Norvel is more critical than the Tee Dee.
The inside of the nose will be coated with fiberglass and epoxy finishing resin. Where I've thinned the wood in the fuse
could be covered with resin and carbon veil, but I didn't really take that much wood out, and it should still be plenty strong. I've never seen a plane break there. The wing will be covered with doctor paper, and I've stocked up on enough dope for a similar scheme as the Cox model.
So,
thar she blows.
Nice job on the CNC work, Greg. Thanks,
Rusty
P.S. Anyone else working on one of these?
I'd love to see how you guys are adapting your power plants and plumbing to this model.
Topic: Southridge CNC's Cox Hyper Viper replica (Read 1648 times)