Strengthening fins on a Quantum airframe?

What are some ideas for strengthening G10 fins when attaching them to a Quantum airframe? I'm getting ready to start on a 1/4 scale Patriot kit (PML) and was hoping to listen to any new ideas before I start in on it.

I'm thinking glassing must be pretty much out of the question as the epoxy won't have much to bite into (quantum) (making a weak bond).

Is strengthening the bond where the G10 fin meets the motor tube (inside airframe) a better place to focus strengthening efforts when working with a quantun airframe?

Thanks in advance!

Westy

What will make the most difference is to sand the areas of contact inside and outside of the tube with 60 grit sandpaper.
Then make your normal epoxy inside and outside fillets to the tube and fillet at the engine tube.
I have not found that adding glass to these joints adds much but weight.

Originally posted by Westy
What are some ideas for strengthening G10 fins when attaching them to a Quantum airframe? I'm getting ready to start on a 1/4 scale Patriot kit (PML) and was hoping to listen to any new ideas before I start in on it.

I'm thinking glassing must be pretty much out of the question as the epoxy won't have much to bite into (quantum) (making a weak bond).

Is strengthening the bond where the G10 fin meets the motor tube (inside airframe) a better place to focus strengthening efforts when working with a quantun airframe?

Thanks in advance!

Westy

Click to expand...

Drill small holes through the fins just above the line where they come out of the body. Drills other small holes through the body very near the slot. When you lay in your fillets, allow it to seep through these holes. You'll get small bumps inside the body like rivet heads. The same will happen going through from one side of the fin to the other. But when you lay the fillet on the opposite side, it'll cover and surround those. You will have "sewn" your fins to the quantum. If you want to make sure not too much drips through into the fin can, place stripes of tape loosely along the lines of holes in the tube. But if you drill them small enough, that shouldn't be a problem. And not too may or it'll be perforated and get weak, and tend to crack there.

I just used something very like this to reattach a surface mount carbon fin to a carbon tube. Worked like a champ. Couldn't go through the body because it's minimum diameter, but I drilled holes at an angle through the existing fillet that was still on the fin. Slopped epoxy on the bottom of the fillet, pushed it on, and the epoxy oozed right through the holes. When they'd dried as bumps larger than the holes, I covered them over with a smoothing fillet.

Westy

Quantum Tube kits are designed for sport flying. They are not designed for high performance rocketry, or mach busting, or fiberglassing. PML specifically states this on the following web page: https://www.publicmissiles.com/images/PMLAirframesFAQ.pdf

Standard epoxy preparation techniques such as sanding the QT and the G-10 are important to get a good bond to both surfaces. Additional fiberglassing is unnecessary for the QT version of the Patriot, which is designed to fly on G, H, and I motors only. Simply follow PML's excellent directions and you'll have a fine rugged rocket.

If you want to fly it on J's, PML recommends purchasing the the phenolic airframe version and glassing.

Bob Krech

On the Quantum tube rockets I've built, I use 80 grit paper to sand all fillet areas inside, and outside the tube, and to rough up the motor mount. I also sand the fillet areas on the fins. Next, I drill 3 or 4 holes along the inner tab part of the fin. Then I attach them as normal. After they are attached, and all fillets are done, I pour two part expanding foam in the fin can. As it expands, it will fill in the holes in the tabs, "locking" the fins in place. Next, I carve off any excess that might stop the rear centering ring from going on, then spread some epoxy over anything the ring will contact inside. Slide the ring on, turn it up and let the epoxy set. Finally, apply the external fillets to the rear ring. I've not had a fin come loose, or even crack a fillet yet (knocking on wood).

Just rough your G-10 and QT well with 60 grit and bond your fins on with 30 minute epoxy. They won't break on you. I have a QT-based rocket with .093" G-10 fins, and it has handled motors up to "K" power (~1400NS) with no problems.

I just rough up the areas of QT real good and epoxy as normal, but I don't really push the envelope much. I know that CTulanko fiberglasses his fins to the motor mount on his PML kits - he soaks a strip of fiberglass in epoxy, then wraps it around a wooden dowel. Place one edge against a fin, then unroll the strip to the bottom of the fin, across the motor tube, and up the adjacent fin, then press it into the corners of the fin/mmt joints. I've never seen that man lose a fin.

Loopy

Excellent! This is exactly the info I was hoping to hear.....it sounds like there are many startegies to help strengthen this build...I'll employ a few of these during my build and I'm sure I'll be just fine!

Thanks gang!

Westy

I built my PML 1/4 scale Patriot using West Epoxy. I added fillets inside and outside the Quantum Tube and on the motor tube.

I added some of the West Colloidal Silica to add strength to the epoxy.

I have built three quantum tube rockets one of them, the Tetyes I flow a J-350 for my Level two flight without any major damage. I too use the 60 grit sandpaper, and then I take a pointed metal object like a nail and deeply score the tube where I know the fillets are going to cover them gives a good bite. The other key to success in my opinion is the fillets you put on the inside of the frame and againest the motor. It takes patience(I need to work on this anyway!!!) but is key to a strong bond.

I also love DynoSoar's idea of drilling the holes through the fins, my next Quantum tube project is a custom design that my Grandson came up with and I'm going to use his idea on it.

I wish I would have asked for my project below.

GOOD LUCK

IRV