Bass edges on balsa fins

[SolarYellow]

I'm just wondering if anyone else has done a bass (or even harder) wood perimeter around the edges of balsa fins. I haven't seen it. Lots of people doing papering on the flat surfaces, but then rounding or tapering the LE and TE, and just CA infusing the edges for hardness. My biggest durability concern for balsa fins so far has been the dents on the LE/TE/tips that occur when they hit hard ground. I'm thinking that using a harder wood around the perimeter could provide a useful additional dent protection without the weight of full bass or weight and hassle of G10/c.f. It's a little more work, but with my history building model airplanes, no big deal if it makes the rocket hold up and stay looking and flying well longer. Worth it for me to build it durable in the first place rather than having to go back and fill/prime/paint it repeatedly later.

I did some quick searching for maple in appropriate sizes, but didn't come up with anything that looked promising. If I had a hobby-size table saw, maybe, but I don't and would go down another path before I did that.

 

[neil_w]

In my experience basswood edges are pretty durable, infinitely more so than balsa. If you try this please photo-document your process, I for one would be quite interested to see it.

 

[BigMacDaddy]

Why not do whole fin w/ plywood instead of trying to add an outside edge around balsa? Weight difference is likely negligible in most models.

Also I would think that CA soaked fin edges would likely be at least as strong as basswood.

 

[neil_w]

Also I would think that CA soaked fin edges would likely be at least as strong as basswood.

I’m not sure. If you can get the CA really absorbed in it’ll get very hard, but if you don’t have end grain exposed then it doesn’t soak in that far, and it’s like a candy shell around the balsa.

Would be interesting to see some testing.

 

[tsmith1315]

A wrapped edge would have a greater coolness factor, for sure.

 

[Back_at_it]

I have done this once. The Estes Pro Series Impulse had Balsa fins with hard wood strips that wrapped the edges. It worked pretty well.

If I had the hard wood strips cut to the exact width like the kit had then I'd do it again. Otherwise I'd prefer to coat the leading edge in epoxy.

 

[SolarYellow]

Hobby Lobby sells bass wood strips in square and rectangular sections. Might mix it up and do square on the tips, wider for the LE and much wider for the tapered TE. Will definitely test, as @neil_w points out, the results of end grain on the tips soaking up the CA. Maybe that will be enough hardening, and it's a lot less work, probably lighter, with no chance of it getting split off. Also, if I use a router table to contour LE & TE, I won't need to worry about the CA infusion of the end-grain tips getting popped off when the cutter gets to it if it's cutting away from the fin. Need to get that router table up and running, among a dozen other rocket shop projects.

 

[cls]

Instead of basswood, how about spruce half rounds? Make a jig to split spruce dowels with a Dremel jigsaw (or bench bandsaw).

I have made some very odd shaped find out of foam core board, edged with half round 3/16" or 1/8" dowels.

The foam core board really needs protection, balsa and basswood maybe not..

 

[Rob Campbell]

Back in the 90's, I built a couple of mid-power birds using this technique. It worked pretty good.

 

[jim_kc]

Back in the mid-late 90's I built an Estes Pro Series Maxi Force that used that construction with Spruce strips. It worked pretty well. You can see the instructions here:
https://plans.rocketshoppe.com/estes/est2065/est2065.htm

 

[SolarYellow]

Interesting:
https://www.rcuniverse.com/forum/4015764-post6.html

Quote:
Yes, spruce is much better for spars, I would replace the basswood.

The difference is nowhere near as big as you imply. There are the numbers from a wood properties table, in an old 1940's book on aircraft structures:

Wood strength modulus density
Spruce 5000 psi 1.30 Msi 25 lb/ft^3
Bassw. 4500 psi 1.25 Msi 25 lb/ft^3

So spruce is about 10% better. But I haven't seen quality spruce in a long time. Basswood is very consistent and easy to get.

Also: https://sigmfg.com/collections/basswood

 

[BigMacDaddy]

I did a test 3D printing edges for balsa fins - mainly for looks, not for durability. Could be another option...

 

[SolarYellow]

I did a test 3D printing edges for balsa fins - mainly for looks, not for durability. Could be another option...

I wouldn't do that for just half-rounds, but it might be a neat way to get an airfoil LE if you had a resin printer that would provide a reasonably smooth surface. I also really like the idea of the fillets, if you find a glue that does a good job holding on to your prints. You could design them to the curve of the body tube and get a really nice joint. Can probably even get the ends nicely tapered/faired, if you want to get fancy.

Evergreen and Plastruct have polystyrene half-rounds in standard sizes. I was hoping they might have wedge strips that would work well as TE, but no luck with either.

 

[Dane Ronnow]

I don't have a pic of the unfinished fins, but these are .125" balsa with a bottom-edge strip cut from a coffee stirring stick, glued with carpenter's wood glue. I fly off a dry lake bed—a very unforgiving surface on touchdown—and I have yet to see a chip.

If you want heavier wood, go with a popsicle stick.

 

[SolarYellow]

I fly off a dry lake bed—a very unforgiving surface on touchdown—and I have yet to see a chip.

Cool. Dinging up the fins on the very first landing of a new rocket at Lucerne is the reason for this thread. For some reason, just crazy luck, perhaps, the second landing hit the same point on the same fin, dinging it a little worse.

 

[kjhambrick]

Thanks everybody !

I really like compund fins !

And I have to say that I like the ideas that have come out here.

I never thought of reinforcing the perimeter of the fins but what a great idea !

I did buy one package each of 1/16 x 1/16 inch and 1/16 x 1/8 inch basswood strips at Hobby Lobby for my latest build.

I didn't use them but I'll try basswood LE, tip chord and TE on a Hobby Lobby / Estes Olympus sitting in my pile.

Thanks for that idea !

Now you've got me pondering whether I could bend wet basswood around the perimeter of the fins of a Cherokee E also sitting on my pile

As for my gratuitous anecdote from 'the olden days' ...

I was and I still am a fan of composite fins built up from different wood in turned in different orientations joined with epoxy and maybe including a layer of 0.75 oz fiberglass.

For example, I destroyed the plastic shell fins on my Estes Maxi Honest John after just a couple flights.

But I really love that rocket so I built 'fat' replacement fins with a basswood core and balsa 'skins' joined with epoxy and sanded to more-or-less the original diamond airfoil.

Finally, I painted the 'skins' with epoxy.

They have lasted a long time, even after flying tens of AT RMS 24/40 F39T's and a few F24W's ( but mostly on the soft Fiesta Island sand ).

I'll get him out of the attic for an inspection and I'll take a picture after work.

-- kjh
.

 

[samb]

I've done alot of edge reinforcement (leading and trailing) on models with balsa fins with relatively long spans. Adds rigidity as well as edge protection insurance for relatively little effort or weight penalty. Hardwood dowels and half-rounds matching the fin width are my tools of choice. I've done a bunch over the years but the ones that come to mind are old Fatboy and Solar Sailer.

 

[jqavins]

There are stores that sell basswood millwork, aimed at dollhouses and dollhouse furniture and the like. I first found this stuff when I was thinking about using miniature cove molding for fillets. Here are a couple of sources; there are more, and these are not recommendations.

https://freedomminiatures.com/collections/woodhttps://jeepersminiatures.com/building-materials/wood-trims/
Hey! AC Supply has some, so you can combine shipping with all that other rocket stuff!
https://www.acsupplyco.com/midwest-doll-house-wood

 

[kjhambrick]

Yikes !

I didn't remember how heat up the balsa skins on my ex-Estes Honest John had become until I got it down from the attic last night.

Here they are:

The best:



The worst:



The motor mount showing the ttw fins.



Note that I cut off the fwd end of the engine hook to accomodate G55's in the 24mm motor mount tube ( whee ) !

Also note that as bad as the balsa skins look, the basswood core, including the LE and TE is fairly intact, even after numerous repairs.

-- kjh