Nodd

Dishes, dumbbells, socks, kitchen sink... I've used it all *grin*

Plan A
Well after my success carving out the fuselage battery hatch I was looking forward to trying the hot-wire gizmo again. I pinned balsa template ribs to both ends of a block of foam...



You maybe wondering what the notch in the rib is all about. Well the Cub's wings use a carbon fiber tube as the main spar. I couldn't come up with an easy way to drill a hole span-wise down the wing piece I was about to make so I decided instead to just cut a slot. I'll use expanding foam or something to fill the slot later on...



So it was time to use the spiffy hot-wire cutter. This was the unfortunate result...



Apparently this isn't as easy as it looks. I'd love to play with this more, definitely want to master this process but in the interest of getting this bird done I switched to...

Plan B
Starting with a new block of foam I broke out the router & cut a slot for the wing-rod...



Now that's a nice clean slot, MUCH better...



Then it was back to my trusty belt-sander to shape the airfoil...



Here's a comparison of the hot-wire wing on the right & the sanded wing on the left...



Don't get me wrong though, I have nothing against hot-wire foam cutting. I'm just not very good at it yet. There's lots of great threads on the subject, I'll read-up on it, practice some & hopefully next time will yield better results.

So here we are test fitting the sanded center section. Looks pretty good to me...



Yellow & Black
Meanwhile back in my wood-shop/paint-booth more progress was made...



While the finish is far from perfect its about what I expected having painted directly on foam. Its certainly plenty good for this silly project...



I'm going to let this paint dry overnight then I'll mask out the rest of the windows & the lightning-bolt graphic & lay down a couple of coats of black.

Slope Pilot

That ought to be a good glider. I have a 1/4 scale cub, Landing it is a pain, the long wing and airfoil design make it not want to come down, it just glides. I must say, you are a great scratch builder.

rhall999

Hi Nodd, that little feller is looking pretty good. I like it!!

About foam cutting, Ihave cut many foam wings in my day, right from small free flight (12 inch span) up to 60" span R/C stuff. Still not an expert at it!! Here is one thing I picked up on that may have been a small part of the problem.

In my experience balsa is way too soft to use as a foam cutting template. Light ply works much better. With the balsa, it is soft enough that the wire can dig into it a bit which causes the exact problem that you can see in your wing, nasty ridges. This is especially so when the wire is hot.

Ialso don't like to pin the templates to the foam, Ifind that there is too much possibility of movement because the pins can pretty easily "wobble" in hte foam. Iuse a LIGHT spray of 3M 77 aerosol contact cement on the foam and template, then stick them on. It does smell a bit more as the hot wire goes through the glue, but the template will not move.

The other thing I like to do which will help is use guide pins on the leading and trailing edge. Ipoke T pins in the leading edge and trailing edge, one at each end of the panel (4 pins total). Then, Iget the hot wire going, and start on the LE pins, pulling it along the pins until I get to the template and then follow the template. This is especially helpfull when you get to the trailing edge, you slide off the template and onto the pins to finish our cut. By doing this, you are actually "starting your cut" before you actually touch the foam and "finishing the cut" after you have left the foam. I find this makes much smoother starts and ends to the cut. (A simple drawing below how this is set up.

Spar slots, Inever use the hot wire to cut them, especially not at the same time as cutting the airfoil. Never had any success with that. I usually cut the wing "blanks" first, and the router or x-acto out the spar slot after.

Here are some pics....the drawing of my "start and finish" guide pins, and my latest foam cut project.

Nodd

Yeah before I vertically introduced this Cub to the ground she did like to float around. There certainly are better sailplane airfoils out there but I expect this wing should serve well enough to goof around with.

Although I'd like to avoid turning this into a "how to use a hot-wire foam cutter" thread I totally appreciate the tips. That all makes a lot of sense. You're right, balsa wasn't a good choice. The wire did snag on it & actually started to burn its way into the wood, leaving nasty indents all over my wing in the process. As soon as I cut the spar notches in the template ribs I realized that was probably a mistake too. Much better to either cut that before or after, using the router. I love the T-pins start/finish idea also, especially for the start of the cut. Good stuff, I'll read up on it some more & hopefully get a clue.

One question about your foamie project there. It looks like it has a nice red shinny finish to it. How did you achieve that?

rhall999

Hi Nodd,didn't want to hijack your thread, just throwin a couple of tips at you For the most part, with those few tips, and a bunch of practice, foam cutting gets easier.

That red jobby is just painted with this stuff: (except in red, this was the first ink that came up on a google search)

http://www.walmart.com/ip/Krylon-12-...-of-6/21065879

Now, with this, Ididn't even prime before painting. The only reason.......the store was out of the primer for this paint and I didn't have time to wait for it to come in!!! In person, the paint is not quite as shiny as it looks in the pictures, but it is still pretty good. I suspect that with a bit more time and a coat of primer it would have come out even better. Heck, I didn't really even spend a lot of time sanding the foam smooth, justknocked teh lumps off with the 220 grit, smoothed'er out with some 400until it was decent and sprayed her with the redcolor coat.

See, here's the quick background to that glider. My Father-in-law also flies, and he phoned me one sunday afternoon and said him and the missus were coming for a visit to get a "grandkid fix" the following weekend (September Long). He said he was going to bring his glider so we could try out the new slope soaring site Ifound. Ididn't have a good slope glider, so I set out to have one built by the time he got here. That Monday, I brought a scrap chunk of foam home from work, and the following Saturday afternoon we flew it. So, you see, I didn't really spend any time making it pretty, just get'er in the air!!

It has a 64" span, aileron and elevator control. I did the wing in 2 chunks, each 32".

Now, back to the Cub.................

Ron

PS....Forgot to mention, the nice shiny red tail on the glider is because the balsa tail is covered in Monokote.