Help with PML 4" Amraam and fiberglassing

[rvanstone]

I am new to High power rockerty and notice a prevoius post on the PML 4" Amraam . I have just purchase this kit with the Kwik Switch and the CPR3000 options.
So I hoping to get some insights on building.
I planning on fiberglassing , so the question is.

The section with the fins, do you fiberglass the over the fin section or stop at the fin section ?

If I did fiberglass over the fin section this requires me to then remove the fiberglass where the fins are slotted for I would think kinda tricky.

If I fiberglass down to and stop at the fins slots , then mounted the fins and then fiberglass over the fins this make more sense to me .

Or does it matter ?

:kill:

 

[llickteig1]

It definitely matters on this rocket as well as any other Quantum Tube (QT) & G-10 model. Assuming you're building the QT version, I wouldn't fiberglass it at all. Epoxy resin will not soak into the QT or G-10 like it does coarboard and wood, and it is very hard to get an even, bubble/delam free application of fiberglass / epoxy over QT. One of the big advantages to the extra cost of PML kits is the ease of finishing the BT and fins. You'll lose that if you fiberglass.

QT rockets will take some pretty fair abuse and I just don't think trying to fiberglass this rocket will be worth the aggravation. If you were to 'glass anything, the most sensible part would be to 'glass the canards tip-to-tip for reinforcement since they are surface mounted. Even then, you are glassing over G-10 fins which are a dream to finish. The only real gain is the reinforcement of the joint and I think adding some milled glass fibers to your epoxy would most likely suffice there.

You just don't gain much by 'glassing QT & G10 models.

I do build this type of rocket with PML expanding foam between the two centering rings. The foam will add all the necessary strength to the fin can, which is the part that takes the most abuse.

Also note: it is very important when you build QT and G-10 rockets that you rough all surfaces to be epoxy bonded with medium grit sand paper (I use 100 or 150 grit). PML isn't kidding on this in their instructions. Do that and you'll be glad you did.

HTH, --Lance.

 

[LMazza]

Just recently I fiberglassed over fin slots not knowing how hard it was to remove later. I was pleased to find it wasn't all that hard using a sharp blade. The fiberglass when by itself is not that hard to cut.

 

[g_boxwood]

I do agree with Lance: if you got the QT version then it would be pretty hard and useless to glass it... If planning to glass a PML kit always get the PHENOLIC airframe. If you got the phenolic version then feel free to glass the entire tubes without worrying about covering the fin slots: as Luke said they can be re-opened with a sharp blade or any kind of flat file... just don't let any epoxy drip inside the tube through the slots as it will be definetely a time-consuming job to sand it away (you can mask the slots from inside)!
When reinforcing something it is always better not to stop the reinforcement abrouptly: that would make the reinforcement edge a great stress-raiser line and if something is to get broken then it will break along THAT line.

As a general suggestion (in case you didn't yet) always refer to the well thought-out PML FAQs: not only they help to build their kit better but they also give valuable common sense hints!!!

Ciao,

Giacomo

 

[Austin]

rvanstone,

As they have previously mentioned, if your model is a Quantum tube kit, you do not want to glass the tube. Quantum expands and contracts in size with temperatures and you can restrict the tube's properties by glassing it. Also, I noticied you live in Ca, so if you live in a more moderate climate such as that, simply epoxying fins would be just fine.

Now, I will tell you that there are cases where glass can be used successfully on Quantum and it does work well and adds a noticable ammount of strength. I actually do not glasss the entire tube, but have glassed nearly all my fin areas with Quantum tubes for the many PML rockets I own. Glassing the fin area only really does strengthen the can and helps keep the rocket from damage.

I fly in very cold conditions during the winter, 20-30 degrees, and have seen and had Quantum shatter on landing; when field surfaces are frozen like concrete, it's gonna happen. Glassing the fin area only has prevented this from happening, so in this instance, it is a good idea. Also, if you land on very hard surfaces, glassing only the fin area may be viable. Note I say the fin area only; this allows the rest of the tube to "breath" with temp changes. Also, I use 60 grit paper to really "Cut Into" the Quantum surface, leaving deeper score marks, hence a better surface for epoxy to adhere.

Good luck on your build and let us know how it turns out.

Carl

 

[loopy]

Another thing I've noticed people do with PML kits to help the fins is internally glassing the fins. CTulanko is a big proponent of this method. Basically, after installing the fins, soak strips of fiberglass cloth in epoxy, then run the down the fin tab, across the motor tube, then up the opposite fin tab. You can use a stick to help lay it and smooth it out. Same effect as glassing the fins to the tube on the outside, but a better bond with the phenolic motor tube rather than the Quantum body tube. Do that, and good external fillets, and you should be fine.

Loopy

 

[rvanstone]

Guys,

Thanks for all of the insight given!!!

I didn't mention that my air frame is phenolic tubing. So I started out with glassing the the boster section, not as diffucult has I thought.
I rolled on some epoxy place the fiberglass other the tube and rolled all of the air bubles out.
When I check on the result this morning the expoxy setup nicely.

At this point, if I were to sand I probably would have hit the fiberglass.
Should I give the section another coat of expoy ?
What about a filler to smooth out the suface ?

Thanks

Ron

 

[LMazza]

A lightweight sanding filler would yield a much lighter result than a coat of epoxy, not to mention MUCH easier to sand. You can get such fillers that mix with epoxy and sand off easily...(maybe someone else can suggest a specific kind.)

Often times people will just put 1 more layer of a lighter fiberglass over the previous layer and the weave is tight enough to easily fill with primer. This of course would add weight.

 

[LampertRocketry]

I had several flights on my 4" PML Amraam before it burned to the ground in a CATO summer before last. It is a strong kit but not bulletproof. Based on my experience, here is what my next Amraam will be:

1. It will be a Performance Rocketry fibreglass 'kit' using fibreglass tubing. I can't be bothered with the mess of glassing.

2. It will use on of their excellent fincans... I can't be bothered slicing slots in my tube and messing around with fin fillets internally and externally.

3. It will have an electronics bay with redundant electronics, an Adept RDF tracking transmitter AND it will have a loud beeper attached.

I expect it will cost me about twice the price of glassing phenolic tubing myself and messing with through the wall fins. Why mess with 'old technology' when I can use state-of-the-art?

Although not completely bulletproof it will be very rugged. Perhaps an extra wrap of 1" fibreglass tape or kevlar tape around the lips of the body tubes for a little extra strength against hitting the pavement or a rock on landing... or prevening zippering from less than optimal deployments.

I might even put in a 98mm motor mount to open my possibilities for the bigger motors (like HyperTek).

So much I want to do. So little time. I am not going to waste time laying up fibreglass and messing with fin filets if I can avoid it. Rather spend the time messing with electronics and flying.

Murray

P.S. Do NOT glass Quantum Tubing.