Balsa verses Basswood and Ply

[AfterBurners]

Just recently I built the Dynastar Snarky kit and currently halfway through the build on the LexxJet. I like the kit designs, but not really fond of the balsa. I know that there are different grades of balsa and some of the better grades are much denser than others. Balsa does sand and shape nicely, but with certain kits like the ones mentioned it can pose a problem. For instance everyone knows that when you trim the pieces off the sheets it's always a good idea to clean up the edges including the root edge. Not the case with these kits. By cleaning up the rough root edge edges you can change the shape and even the size of the wings, which include from two to three pieces each. The vertical stabilizer on the Lexxjet has a slight curve that conforms to the shape of the tail cone section. By sanding either the root edge of the vertical stabilizer or the tail cone itself you ruin the shape and mating surfaces leaving a gap. It's just a "Gotcha" you have to be aware of. On the Snarky if you sand any of the "mating or glue" edges of the wing you can change the angle resulting in a wing that is off set and smaller size leaving a root edge that is way off.

I would like to build the kits again, but use upgraded wood. I'm considering basswood because I think it's a good in between choice. It's stronger and not much difference in weight and correct me if I'm wrong less grain to fill verses balsa and lite ply.

Has any here built these kits or worked with similar kits.

I was also considering just doing a 4" version of each kit....

 

[Gary Byrum]

There's no golden rule that says you need to sand the root edges. Maybe get rid of the little nubs left behind by the cutter. I never sand root edges unless I have to clean up all my "hand cut" pieces. That's not often either. Basswood prolly be a better option regardless.

 

[Daddyisabar]

Swapping out basswood for balsa in a tricky kit like the lexjett is not a simple proposition. The added weight of the basswood could throw off the CP-CG relationship and require more nose weight. I don't know how much margin for play there is in the lexjett, but from the one flight I have seen I bet there is not much. Not much of an "idiot factor" built into the kit like you find on a traditional 3-4FNC kit. Build light and build strong. Use some old school gluing technique and sanding sealer and yer balsa should be quite strong!

 

[Steven]

Perhaps applying paper and CA to the fins might work here. The CA will strengthen the fins and the paper will reduce finishing including the elimination of any sanding sealer.

 

[dr wogz]

https://www.dave-cushman.net/aircraft/balsa_selection.html

This can help identify and choose the right balsa sheet for the project at hand.. I usually will pull out all the pieces in the shop bin, and select / choose the few I want, for any given project. As for basswood, haven't really used much. I have papered a few 'less quality' sheets of balsa to get stiffness. I've also added Monokote to a few fins in the past.

I have used a lot of ply in various thicknesses to get stiffness & a smoother finish. I have use an almost half thickness sheet of ply instead of the stock balsa to get the stiffness / strength, and reduce the overall 'frontal area' & weight of the ly. but we're only talking LPR type builds.

I have, also built up fins as they've done recently for the Mega Mosquito & MDRM. I've even gone as far as to fill the voids with Styrofoam meat tray pieces. And, I've once cut holes in a balsa fin, filed it with meat tray foam, and then papered over it. Mind you, that was years ago!!

 

[AfterBurners]

All very good suggestions. Balsa does play a role in these and I thank you all for opening my eyes to other techniques that I knew about but never considered applying on these kits. The Snarky main wings can be tricky when gluing if you sand the edges or just slightly clean up the rough spots on the glue edges. The 3 root edges have to align straight as an arrow and if one glue angle is off it changes the entire root edge of the wing. The Lexxjet for me seems more straight forward. The only procedure I think is difficult is following the original paint scheme. I haven't got there yet, but in order to do it the side pods have to be painted separate and CA on after the jet is painted completely, not to mention the amount of time involved in masking that ridiculously cool paint job. I think I will focus more on the build techniques of using lite ply and cutting out sections for weight reduction then coming back to skin the frames of the wings and stabilizers with balsa and possibly skinning them when I do a 4" upscale of the Snarky. I still want to build both kits again, but appl to some of the techniques you guys mentioned.

 

[dr wogz]

One thing a lot of people overlook is a good / reliable sanding set up. A sanding bar is good., but a proper sanding station is key.

I have a 2" x 2" x 10" block (and it happens to be balsa!) that is square. On one side, I have glued a length of sand paper. I then place my 'intended to be sanded' part on a riser, typically a scrap piece of (again) balsa sheet, 3/16" to 1/2" thick (so it's not flat on the table). I then gently bring eh sand paper side of the sanding block to the edge / face I wan tot sand / smooth, and carefully move back & fro to sand the edge / face. Usually only a few passes is all that's needed..

Sometimes, with the same set up, but on a harder material riser (an old machined metal plate) I'll make sure the edge /face I want opt sand is flush to eth edge / face of eh riser. I'll then carefully move the piece out a smidgen, then again, move the sanding block to & fro. When the sanding block 'bottoms out' against the riser, I know I've sanded off the 1/32" or whatever I want. . Also, with the piece on a taller riser, if I'll put a scrap stick under the sanding block to give it an angle. Depending on the size of eth stick under the sanding block, I can get pretty much any angle I want. and Voila, a beveled (not 90°) sanded edge / face.

 

[AfterBurners]

One thing a lot of people overlook is a good / reliable sanding set up. A sanding bar is good., but a proper sanding station is key.

I have a 2" x 2" x 10" block (and it happens to be balsa!) that is square. On one side, I have glued a length of sand paper. I then place my 'intended to be sanded' part on a riser, typically a scrap piece of (again) balsa sheet, 3/16" to 1/2" thick (so it's not flat on the table). I then gently bring eh sand paper side of the sanding block to the edge / face I wan tot sand / smooth, and carefully move back & fro to sand the edge / face. Usually only a few passes is all that's needed..

Sometimes, with the same set up, but on a harder material riser (an old machined metal plate) I'll make sure the edge /face I want opt sand is flush to eth edge / face of eh riser. I'll then carefully move the piece out a smidgen, then again, move the sanding block to & fro. When the sanding block 'bottoms out' against the riser, I know I've sanded off the 1/32" or whatever I want. . Also, with the piece on a taller riser, if I'll put a scrap stick under the sanding block to give it an angle. Depending on the size of eth stick under the sanding block, I can get pretty much any angle I want. and Voila, a beveled (not 90°) sanded edge / face.

I use to make sanding jig out of card stock. I pick it on Apogees website.

[video]https://www.apogeerockets.com/Advanced_Construction_Videos/Rocketry_Video_2[/video]

Something that I would consider doing on future builds. The Lexxjet main wings are joined by the root edges, but by having the tips of the wings raised. The right angle is determined by gluing on the winglets and then allowing the two root edges to join together foaming the correct angle. The problem you have is the gap it creates on the opposite side. The correct way to do this is to bevel or sand the correct angle. Following the instructions do work, but you have to fill the gap and sand the wing until the gap is gone.

 

[Steven]

You know, consider using sheet styrene plastic to skin the wings, say like 0.010 thick rather than 0.030 to reduce weight and finishing. I used a similar approach on Sheri's Mercury Redstone.

 

[AfterBurners]

I wanted to add up the cost to scratch build each kit and if you include the shipping cost on the items you need to purchase well you're only saving $3-4. For instance I have someone that will lazer cut the balsa pieces for say the Snarky kit. Total $6 but again it's $7-8 to ship. Body tubes are around $4 for the pair and nose cone is $12.95 you're looking at $30 right there. There's other miscellaneous stuff center rings, shock cord, motor tube etc. Seems smart just to buy the kits and get free shipping, if you buy on BRS. I figure whatever parts I don't use from the kits I can sell cheap. I would get better body tubes.