faceman

Anyone have any suggestions or tips in getting balsa sheeting to bend around a contoured pitts 12 fuse. Seems as though Im having a tough time with this. The plane im working on is a Bob Trueworthy Pitts 12. Any help would be appreciated.

BMatthews

First off all balsa is not created equally. The cut and density will make a GREAT difference in how easily it takes bends. Pick through all the balsa you can find of the correct thickness and flex the sheets across the grain looking for the more flexible sheets. When bending into place a little water on the outside of the sheet will help a lot with getting it to form easier. For more serious curves swabbing on some amonia straight from the bottle will soften the wood up a lot more. You'll want to do the last bit outdoors and with gloves on for obvious reasons.

Most important. I found out the hard way that if you glue the wood while it's wet it will shrink a bit and pull things out of shape. Wet, bend into place and clamp, rubberband, or otherwise fix into place to dry and then trim and glue for the final step.

At least this is my story and I'm sticking to it....

FHHuber

Yep... get the wood wet. Adding some amonia tothe water allows sharper bends with stiffer grades of balsa.

Just getting it wet and immediately bending can shatter the wood... let it soak 30 min to 1 hr. The stuff willl bend almost unbelieveable curves.

faceman

Thanks for the help. I'll give it a try.

Spicoli

Strip planking is the way to go over tough curves.A 1/2" wide sheet bends a lot more than a 3" wide sheet

CurtD

My Feedback: (1)

Here's how I did it on my Pitts M12. Instead of trying to sheet it with one or two large pieces, I sheeted each section from stringer to stringer seperately, butting each piece up the the previous, starting on the bottom. Use a sheet of paper to get the exact shape for each section. Pick your wood carefully and use "A" grain balsa if you can, with straight grain and flexible across the piece. This is actually easier to do than it sounds and goes pretty quickly. I used a combo of slow and fast CA, and pins to attach the pieces. Wetting the outside side of the wood will help it make the compound curvatures easier. I don't really have any photos showing the process but here's a couple of the final results. Gonna go fly it some more tomorrow!

rchawaii

I have used a combination of all these methods. If you go look for planking a wooden model boat hull, you will find a good way to plank an airframe. All these fine folks are right. Make templates with paper as mentioned and use that to make your "planks". Take the strip planks whatever width you're comfortable with or need. Soak in ammonia/water for the time mentioned above. I Use Medium CA to hold the piece in place mindful that moisture acts as a kicker (accelerator) with cyano (CA). Use the thick CA for filler for larger spaces. Pin the "planks" or strips in place with whatever pins you have. Tape doesn't hold it to shape (The wood while drying wants to go back to its shape) so get some good "T" pins or similar. (From sewing dept in some places.)

You can do very very fine and complex shapes with this method, as long as you soak the wood long enough. I have planked planes and boat hulls with these methods sometimes the angles very steep (As in the fore of a tug boat) and with practice and skill you will come out with a great finished airframe. (BTW I have used up to 1/8" Mahogony ply using this method with no problems.)

rchawaii

I'm sorry I forgot to mention, leave the pins until it's completely dry and make sure your airframe is straight before adding planking. Also if you can, do the oddest shaped places first (like inside corners which will be hard to get to in the end of the process). When dry (Dont try to speed it up), use needlenose pliers to remove the pins, being careful not to pull anythign out but the pins.

hookedonrc

Here is another little trick that I have used that has worked quite well. I take a dull pencil like object (you do not want it sharp) and on the back side, using a little pressure, draw parallel lines in the balsa. Start at one side and move to the middle about 1/16" to 1/8" apart. Then draw parallel lines from the other side and move to the middle again. Then when you add the water/ammonia on the outside of the piece, the dents on the backside squeeze together and it curves much easier. I really don't know whether or not this damages the wood, but is sure seems strong to me after it is in place. (The distance between the dented lines also depends on the size of the piece. The bigger the piece, the farther apart they are.

faceman

Thanks again guys for all the help. This website is great. Hey CurtD I am curious what pitts 12 plane that is that you have pictures of there. It looks very similiar to the one that I am building. Mine is a laser cut short kit from Robert Truworthy. His website is bigairplanes.com. What I was having trouble with was gettting the balsa to bend around the round and tapered fuselage. I see that yours came out very nicely. Check out Roberts website he has some good pictures and some nice links to Pitts 12 info. Here is a picture of mine.