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Fliskits and other shrouds

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JRThro

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I picked up 3 Fliskits kits recently, the Triskelion, the ACME Spitfire, and the Nantucket Sound. 2 of the 3 have large shrouds and nose cones made from rolled cardstock that's supplied with the kits.

On both the ACME Spitfire and the Nantucket Sound, the fins attach to the shrouds with no other support. I'm concerned about the strength of the shrouds in general, and especially when the fins will be glued to them.

Any recommendations on strengthening the shrouds would be appreciated. I've already built the ACME Spitfire except for the fins, but the Nantucket Sound is pretty much just started.
 

El Cheapo

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EDIT: I would contact Fliskits first and foremost. It seems the guy is available 24/7 when it comes to his product. One thing you could do is CA the heck out of it and call it a day.
 
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powderburner

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First, let me say that we seem to have a recurring theme here on TRF (so no, I'm not picking on you, JRThro) to "beef up" first and ask questions later. Many of us seem to think that the kit manufacturer must not know what they are doing (to design such a flimsy structure) or that they have never actually built and launched (as in "testing") their designs.

Maybe we should give the kits a chance, as designed by the manufacturer?

I have done the exact same thing (overbuilt). I looked at the paper shrouds on the Spitfire and immediately reached for some BT80 stock instead. I have no idea whether I really needed to do that. I know Jim Flis understands how to build model rockets (he's done one or two), so I have no excuse.

OK, enough of that.

If you really want to reinforce, you could:
-- fit some fin tabs between the paper shroud and some other substructure, positioned to line up with the external fins
-- re-cut new fins with integral TTW tabs
-- foam the (empty?) space inside the paper shroud with something dense enough to provide support
-- cut some custom CRs to sit under the fin root (and inside the shroud) in several places
-- use a heavier material than the cardstock...but be sure it can be smoothly bent, or you will end up with some ugly creases and wrinkles showing

El Cheapo has another possible approach that works on the shroud but then you are kinda stuck using CA or epoxy to attach the fins (white or yellow glues don't bond well to "plasticized" cardstock).
 

El Cheapo

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I was thinking, build it, CA it, sand it, prime, paint, etc.

I do have to say in an honest apology....really bad day, here, tough times and my post should not have been such an outright attack.
 

Luv2launch

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I picked up 3 Fliskits kits recently, the Triskelion, the ACME Spitfire, and the Nantucket Sound. 2 of the 3 have large shrouds and nose cones made from rolled cardstock that's supplied with the kits.

On both the ACME Spitfire and the Nantucket Sound, the fins attach to the shrouds with no other support. I'm concerned about the strength of the shrouds in general, and especially when the fins will be glued to them.

Any recommendations on strengthening the shrouds would be appreciated. I've already built the ACME Spitfire except for the fins, but the Nantucket Sound is pretty much just started.
Having seen both of those kits fly myself and one of them being the prototype for the Nantucket Sound I would say that building them stock per the instructions is the way to go.A bit of CA probably wouldn't hurt but stock they are just fine.
 

chanstevens

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With the Acme, the nose shroud really doesn't get much stress on it (at least, it shouldn't), so no reinforcing is needed. Maybe a thin film of white glue if you're paranoid, just to stiffen the very point.

The Nantucket shroud that's provided is decent cardstock and needs to reinforcement, so should be fine. Where you cut out for the launch lug, though, I'd apply a drop of very thin CA to prevent additional tears or fraying. Now if you choose to print your own decorated shroud, as I did, you might have trouble finding single-piece heavy cardstock in 11x17, so either have to go lighter or 2-piece. I went lighter, and did reinforce with a very thin bead of dilluted white glue while I was forming the shroud, but I also used a couple of centering rings (and wax paper) to keep the shroud round while the glue dried. You could probably reinforce just as well after forming, but with such a large area I wanted to just apply it quickly and smear it fast, flat.

As noted, though, these are both fine stock, no additional reinforcement unless you're planning on overdoing the motor, and for the Acme that's a bad idea--it can barely handle the D ejection charges as it is.
 

Micromeister

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Don't really understand why folks have this precieved Strength problem??? Particularly on LPR models of the type we are discussing here.
Shroud attached fins are really no more of a stress problem then those attached to a rigid body tube. If fact they offer some stress releif advantages.

I've been building and flying such models for a very long time with absolutely no ill effects on the models at all. If you look back in time you'll find a few examples of Non-reinforced should mounted fins as well. the X-24 bug Leaps to mind.
I have several models that sport butt joint, cardstock transition mounted fins Which all have many flights without a single crack or broken fin or damaged shroud. I think you underestimate the bonding power of properly applied glued joints.
To be perfectly honest. I believe a fins is LESS likely to suffer landing damage on a body that provides a little Give, then one super rigidly attached to an overbuilt model. A sort of semi shock absorber if you will;)
Hope this helps a bit
 
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jflis

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Interesting question that has come up from time to time. :)

In the case of the ACME there is no structure under the shroud, other than the lower centering ring. In this respect, yes the fins rely almost entirely on the shroud for strength. The advantage of the design 3 of the 4 fins are above the base of the model and don't get much landing stress and there is little boost stress as the model doesn't really go all that fast (despite the word "Spitfire" in her name :D )

I've built and flown over a dozen of them and have never had a fin pop off. I've heard of one case where the builder said the fin attachment "felt weak" and I suggested strong fillets with epoxy.

In my opinion the fin attachment and chance of popping a fin off is about the same as a fin attached to a body tube.

As for the Nantucket Sound, we have two things to consider:
  1. All of the fins hang down below the base of the model and take a lot of landing stress
  2. The shroud is much larger

As a result of this we use a very high quality card stock (110# stock) for strength. Additionally, there is internal structure (support fins) that are attached INSIDE the shroud, right under the locations for the fin roots. The centering ring is cut with alignment tabs so that you can locate these internal fins when attaching the aero fins so there shouldn't be any problem getting a solid structure there.

I have had one customer who, after attaching the fins, realized that he didn't get any adhesion of the shroud to the internal support fins and asked for suggestions. I recommended that he prick holes at the fin root and through the shroud, press the shroud onto the internal fin support and hit it with thin CA. This did the job and the result was rock solid.

Hope this helps! :)

jim
 

mjennings

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I'm thinking about coating the shrouds of my Spitfire with thin CA after installing the fins, because of where I fly there are a lot of large shrubs / small trees and I've had some damage from pointy sticks.
 

JRThro

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Thanks, Jim and everybody else.

I was concerned because the shrouds aren't as strong as a normal body tube, but it sounds like I don't really need to worry.

For the ACME Spitfire's nose cone, I did run a blob of white glue into the tip and let it dry, as well as coating the inside with a layer of white glue per the instructions. I'll do the same with the Nantucket Sound's nose cone if I remember to.

I may still soak the Spitfire's larger shroud with some thin CA just to make myself feel better, but it sounds like the internal fins/ribs in the Nantucket Sound will support the actual fins nicely enough.
 

gpoehlein

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I build a LOT of competition models out of nothing but cardstock (either 67# or 110#). I glue the fins (which are usually cardstock wrapped around a mattboard core) directly to the cardstock using the double glue method (thin coat of white glue on both glue joint surfaces, let dry then another thin coat of white glue to glue them together). After the fins are dry, I give them a traditional white glue fillet. They rarely go anywhere, and I have flown them on everything up to C motors. (I have a cardstock version of the Big Bertha that is a 1.5" diameter shroud around an 18mm motor tube. Centering rings are all that hold the shroud around the outside, and the fins are glued directly to the shroud. I've not had a failure yet on C6-5 motors.) You should be fine gluing fins directly to the shrouds.
 
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