- This topic has 13 replies, 6 voices, and was last updated 14 years, 1 month ago by
.
-
Posts
-
I had a request on how I did my tail boom, so thought I would just present it here. Then everyone can tell me how bad I am!
You need a form. It is interesting how many tailbooms start out with a pool cue- You do need a straight one- Also, lay a straight edge along its length and make sure that it is truly tapered from end to end- If not, you will be limited to the length of straight taper.
Select some balsa- normally A or B grain- C grain will tend to crack. Determine the length of the boom and cut the sheet about a 1/4″ longer. Next we have to determine how to cut the”chord” side of the sheet. I wrap a piece of paper around the “big” end of the boom and mark it- This gives me the circumference of that end. I do the same for the other. I now transfer these dimensions to the sheet. Normally I will draw a centerline on the templates and lay it on the centerline of the sheet. This I cut a trapizoid from the sheet.
Now ya need to form the sheet. I commonly use our bath tube. I put a few inches of hot water in the tube and place the sheet in it. I add some weight to the sheet to hold it down. Let it soak for about 30 minutes to an hour- You will know when its ready when the sheet will roll on itself without breaking.
Note here that some people will put a layer of Jap Tissue on the inside- This will help reduce cracking- An aluminuim/carbon/aluminuim tube uses very thin aluminum sheet on the inside-This is placed on the form then the carbon is laid on top of it followed by aluminum on top- This is all done to keep the carbon from cracking and adding additional strength. Also, some will just put a few coats of dope on the inside- In my instance, I did neither.
While the sheet is soaking, get some surgical gauze. This will be used to hold the sheet to the form. When the sheet is ready, paper towel off the majority of the water on the sheet. If all is well, the sheet should roll over the form and the edges will line up- If they are not perfect, you can still fix it later. I start sometimes in the middle and will wrap the gauze around the wood, holding it in place possibly with some tape. Then wrap the gauze around the wood and form, working your way to the end. Tape it off. Take another piece of gauze and work it from the middle to the other end. You now are done for about 2-3 hours to let the water evaporate.
When all is dry, remove the gauze and you have the beginnings of a tailboom. All this will take you an hour the first time and less as you do more.
Now is the time to look for fits between the edges. If your initial circumference template was good, the joints will be quite good and all you will need to do is glue it together. I sorta cheat when I do this. I use CA (thin) and will start at one end- This is just so that the ends are relatively square. Hold the joint together (on the form, but not up against it) And put a small drop to hold it together. Then start working your way down the boom, gluing every inch or so.
Note here- Some folks will put some Saran wrap on the form and hold it tight against the form. This will give you a rounder tube initally. Not a bad idea to do this.
After the initial tacking it is time to finish gluing. Again, hold the edges together when gluing- If there are small gaps, push the edges together as tight as you can. But, when all is said and done, the gaps can be filled with sanding dust and CA.
You now will have a tail boom- Ronnie Thompson uses some unidirectional carbon (.007″) the length of the boom, with approximately 8 pieces. These will decrease bowing of the boom. On my, I used some carbon fabric that I had (5 oz- which is probably too thick). You could also use fiberglass for this. What I do is lay down some wax paper. I cut the carbon to approximately the same shape as the wood- you want some overlap- the approxiamte size at this pint is not too critical- just make sure it is bigger in dimension than needed. Lay the carbon on the waxed paper and apply epoxy- I use West Systems 105/205. Coat the entire area with epoxy. Lay another piece of wax paper on top of the carbon. Using a squeegee of some type (I have used popsicle sticks for this), start in the middle and work the epoxy to the edges. You will see it being pushed to the side. Keep working it as you need very little- the common problem is too much epoxy is left on the sheet- Sometimes folks have said that when paper toweling will barely stick to it, it is ready.
With both pieces of wax paper in place, trim the composite to size. Use a new razor blade or X-acto and a staright edge. It will cut very easily. When cut to shape, remove the wax paper from only on side. Lay this on the boom and form. Wrap it around the boom. I left the wax paper on but when I got to the lapped joint, I peeled back the paper so I had the overlap. With a little work, you can get it to be tight against the boom. It can be a bit frustrating, but is doable. Once again, wrap the gauze around the boom to hold the material in place. The gauze should be pulled tight- I have also wrapped over the top of the gause with masking tape to insure it is tight.
Let the epoxy dry. Remove the materials and examine your work. It is not uncommon to have some buildup of epoxy (bumps) but these can easily be sanded off. Be careful not to cut thru the fabric.
At this point I used a layer of 1/32″ over the top. Use all the same techniques and use epoxy to bond the 1/32″ to the carbon. Wrap it with gauze and let dry. Pull it apart and do all your final sanding. This boom is now ready for assembly.
You now have a boom. This technique worked very well for my C gas model- I have used just the 1/16″ with no other materials for booms on 1/2A’s. Plus, if a glider, it could be 1/32″ and maybe some .5 oz fiberglass applied with epoxy paint (I used to use Hoby Poxy).
Good luck- it really is not hard to do, once you have done one!
“bath tube” 😕 😕 I knew you FAI types were a bit strange. Most of the rest of us bath in a tub or shower stall. Much less confining. 🙂
Yeah, but when you drink as much as we have to to remain sane, the tube keeps ya upright and head outta the water- would drown in a tub….
Luddite Dan would probably agree. I am waiting for him to chime in. Probably not back from sweeping the competition at KOI.
Ahem…..
What is this ‘bathtub’ that you speak of?How do you attach the second balasa tube to the first? Form it and then glue? Or just glue it during the initial wrap phase?
King Orange
ya shoulda been there.hey Man!! Howdja do at the KOI? Bet the weather was nicer there than here…
I preform it, fit it, and then apply the epoxy to the main boom and gauze it in place…Nothing fancy…
To make a “custom” tapered mandrel see” Rolling your own”, by Bob Lipori, page 4 of the NFFS Digest for May 1999.
Cheers; d-gI don’t have that NFFS issue…”refered to”custom” tapered mandrel see
” Rolling your own”, by Bob Lipori, page 4 of the NFFS Digest for May 1999.Would someone be willing to copy it, scan it and/or email or snail mail it to me? I’d pay any costs.
John! John! Come on man! Warm up!
Good, good. There ya go.
Ok back to the topic. Do you make the seam on the outer tube before gluing it to the inner tube? Seems like the potential for a partial glue joint or excess glue would be high. I’m interested in trying to do it.King Orange was a good time. I had some success. I did have a flyaway with the B Marval. It went about 6 miles. 35 feet up a tree. Walston tracker and no real problem. It is a good feeling when you finally pass the plane. Its direction was toward the Atlantic Ocean.
Trees suck….I think we all should carry a chain saw and when ya see one….brrrrrrr timber!! Firewood….when John and I were at the WC in Slovakia we had a wakefield model in a tree and it was cut down to get it down- I won’t say that the Gunders did it, but the Gunders did it!
I did not glue the seam before installing it (this is the outer piece)….I apply the epoxy thinly, push the preformed piece in place, and then tightly wrap the wood- Any excessive glue is forced out of the seam- BTW, my seam was not perfect and thus the glue had a place for it to flow out. I think the final weight was about 40 grams- The single, inside piece of 1/16″ was 23 grams. The rest was carbon, epoxy, and the 1/32 sheet…It is very simple to do and I know you will like it!
35 feet up wasn’t so bad. I had a 50 foot pole.
I missed a line about wood sizes. —1/16 on inner and 1/32 on outer with CF weave in between? That sounds rigid. Do ypu put any disk-type formers inside? I have a couple inside the B Marval. I know that one came loose, I can hear it rattle.
I’ll bring you a really tasty beer if you’ll make me one 58″ long and 2 1/8 diameter at the front. Ok, 3 beers.
Nope, no formers- No reason for them. Too hard to string the lines when ya do that also…and yup, 1/16″ inside, carbon, 1/32 outside. Also, I bet you could get rid of the 1/32 on top if you wanted to do the thin aluminum deal. The carbon cloth was unidirectional 5 oz. I bet you could get away with 3 oz without a problem- It is just what I had laying around.
I am afeared it would take more than three beers to do that!
John
OK. 5 beers. I’ll make ’em Old Rasputin RIS.
I’m thinking of a 1/2A fuselage now.
1/20″ ,rolled and formed. Then add 3/4oz glass with West System epoxy and wrap with Visqueen and Ace bandage to squeeze away the excess epoxy.
My other thought was just dope the 3/4oz cloth and then paint with epoxy.
This is for a 270″ 1/2A Marval for a Cyclon 049.Hello all,
If you can’t find a used cue that’s straight, Many billiard rooms have used cues for sale at a reasonable price. You don’t need a pro cue. Ask for a cue that has a European taper. These have a constant taper from the thick part of the stick all the way to the end. Much easier to get a nice straight boom. No I don’t play billiards! 😉
Dan A
- You must be logged in to reply to this topic.