question about fillets

[Jarik C-Bol]

So I'm slowly building a estes kit, and as I'm just getting back into the rocketry thing, i want to do a nice job on everything, especially finish (i looked at some of my old rockets from when i was a kid, and it was a bit embarrassing, the quality of finish was, shall we say, bad.) anyways, i did fillets on the fins with white glue, but the glue seems to have been absorbed largely into the balsa fins. i am wondering if it would be a good idea to use a fill-and-finish type substance to fillet the fins, or is it better to leave them the way they are?

(I'm actually using red devil onetime lightweight spackle, because nowhere in town sells Elmer's fill'n'finish)

just experimentally i used the spackle along the launch lug, and it seems alright, but i dont know if it would be good on the fins.

 

[m85476585]

Spackle won't add much strength, if any. You don't need aerodynamic fillets unless you want to add them for looks (you will get a little bit less drag with aerodynamic fillets, but it won't make much of a difference on a small rocket. There is an optimum ratio of fillet radius to root chord length, but I can't remember it). I would just do another layer or two of white glue fillets since you will probably get the most benefit from extra strength.

 

[doug_man_sams]

i did fillets on the fins with white glue, but the glue seems to have been absorbed largely into the balsa fins. i am wondering if it would be a good idea to use a fill-and-finish type substance to fillet the fins, or is it better to leave them the way they are?

(I'm actually using red devil onetime lightweight spackle, because nowhere in town sells Elmer's fill'n'finish)

just experimentally i used the spackle along the launch lug, and it seems alright, but i dont know if it would be good on the fins.

Spackle should be OK. The glue fillets will generally add all the strength you need for model rockets, but the glue tends to shrink as it dries, so it doesn't look very good. And it takes many applications to build up a nice aerodynamic/cosmetic fillet. So using FNF or spackling makes that much simpler. It won't add much strength, but, with glue fillets underneath, that's not needed. Just make sure you sand the glue a bit before adding the fillet.

One key when applying the FNF (or spackle) is to use a wet finger to tool it. I keep a wet rag on the bench, and dab my finger on that. You can get the fillet nearly perfect and thus won't need to do much sanding later. Also, make sure you wipe off all the excess while it's wet - no need of making extra sanding work for yourself later.

With spackling, some of it - depending on the type - is rewettable, so be careful applying your primer - you don't want to soften the fillets.

HTH.

Doug


.

 

[Jarik C-Bol]

thanks, i may fillet with the spackle then. I'm still debating with myself if i want to or not, mostly because I'm a little nervous about the area where the fillets come together at the top of the fin. the spackle i have gets REALY hard when it drys, and if i botch anything, it'll be hard to correct.