Mini BBX

hi guys i need some help

im getting the PML Mini BBX non CPR verson but i still want to make it dual deployment. first thing do i need to fiberglass it so i can stick big motors in the terrier boster, what chute should i use for the drogue(i think it can go with out a drouge) and last thing
i need help with the ALt bay does anyone know any site on 54mm Alt bays???

thanx

Originally posted by matt_taylor
first thing do i need to fiberglass it so i can stick big motors in the terrier boster,

Click to expand...

Since its a PML kit with Quantum Tubing, I don't think you'll need to fiberglass it. If you thought that it may approach Mach, then I might glass the fin to body tube joint is all.

Just a quick note - PML advises against using Quantum tubing if you are going to go past .85 mach. If you are going to go faster than .85 mach, PML advises using fiberglassed phenolic.

- Ken

I agree with Ken here. If you get anywhere near close to .85 mach then fiberglassed phenolic is the way to go. Hence my decision to kevlar my Sudden Rush kit which will go past mach 1.

Dave

well its ordered last night i ordered the Mini BBX and some stuff from giant leap, the BBX is in QT but i will still fiber glass the fins on.


thanx
P.S. im going away for the next week so there will be no more answers from me

I wouldn't bother with the fibreglassing at all on the Mini BBX. I flew mine several times no problem The Quantum Tubing is outstanding. Remember to (a) clean it well with soap and water - not acetone and (b) sand the surfaces to be glued per the instructions. SANDING is the key to adhesion. Otherwise, I absolutely guarantee you that your fins will fall off and things simply will fall out of your rocket. Guaranteed.

My first kit was the Sudden Rush because I saw it on the Gates Bros. website. I didn't sand faithfully. Assembled the thing for flight and it fell apart on the way to the pad.

SAND SAND SAND. In fact, you will need to sand with 400 or 600 grit lightly before painting if you are so inclined. I tend to fly naked. The rockets that is.

Murray Lampert

Matt, I had a PML mini BBX and tried to do the same things that
you are wanting to do, I would like to inform you that if you use QT tubing you will not be able to use 54mm motors a they get too
hot. Phenolic tubing is the proper way to go also fiberglass does
NOT adhere well to QT tubing despite sanding the surface so your fin joint will be weak.

I do not wish to be sarcastic towards you. It's just that I have been there and tried that.

Cheers Airdale

Does the Mini BBX take 54 mm Motors? I haven't hauled mine out to look... but it seems to me that I could only get 29mm motors into my Mini BBX. I don't even recall flying it on a 38mm motor... but I could be wrong.

In any event, you don't want to glass Quantum Tubing. It is not meant to be glassed. And there's not much that you can put into the Mini BBX (if I have the right kit in mind) that is going to cause sufficient speed to present a problem to properly installed fins. I sand well. I use fillets on all fin/tube surfaces. And last but not least, I use two part expanding foam to fill the cavity - it is relatively light (lighter than epoxy anyway) and sticks like stink. I have never lost a fin on a rocket built like this, but having said that, keep in mind that I am still relatively new to the hobby.

I am presently about to build a Shadow Composites RAVEN which I expect will hit Mach 2 - Mach 3. It is using SURFACE mounted fins and the body is 38mm carbon composite tubing. The fins will be attached and this beast will be built using quality high temp epoxy and fillers. NO GLASSING of the fins. The motor will be in almost direct contact with the airframe directly beneath the fins. The key here is the use of quality high temp epoxy. No glass cloth necessary.

BTW, the use of epoxy without filler in making fillets adds strength but a much better idea is to use some type of filler in the epoxy, like chopped Kevlar. This exponentially increases the strength of the fillets.

For some interesting information on high tech construction have a look at www.shadowaero.com.


Murray Lampert
NAR 79489 L2
TRA 08855 L2

Keep in mind when reading this post that there are almost always multiple opinions about anything and everything. And, just because opinions are different, doesn't necessarily mean that one is dead wrong and the other is absolutely right.

Having said that, I have a different opinion about PML Quantum tubing and fiberglassing. I have two PML kits, an AMRAAM 3 and an AMRAAM 4, and on both of them I fiberglassed the fins on - as well as using fillets and internal fillets and fiberglass.

I can absolutely guarantee you this - you canNOT separate the fiberglass from the Quantum tubing. The two are joined for life.

I am in the process of building a scratch built rocket with 4" Quantum tubing, and the fins will be glassed on it as well. The fins also have internal wooden pieces epoxied to the "through the wall" part of the fins to act as additional retainers. And, the fin can has two part foam. Sooooo.... The fins are retained by:
- being epoxied to the 75mm internal phenolic tube
- having internal wood pieces epoxied to the "through the wall" part of the fins
- the fin can is filled with two part foam
- tip to tip external fiberglassing
- external fillets

Overkill?? Probably. On the other hand, I have some rockets that are older than a lot of the people that subscribe to this forum. And I still fly them all. I don't believe in "hangar queens."

When I epoxy *anything* to Quantum tubing, I first rough the surface of the Quantum tubing that is going to be bonded with 80 grit sandpaper. That has always worked really well for me.

At any rate, there are always multiple ways to do things. I say that you can fiberglass fins to Quantum tubing, and if done correctly, there is no way that you will be able to separate the two (short of outright breakage) once the epoxy is hardened.

As a rule, should you fiberglass a whole Quantum body tube? In my opinion, no. PML's catalog states that Quantum tubing should not be used for applications that will exceed .85 mach. The only reason that I would ever want to fiberglass a whole body tube would be if I was going to exceed mach. If/when I decide to do that, I'll use phenolic tubing that has been glassed, or maybe go the fancy composite route that others have talked about.

Just another opinion.
- Ken

Why are we all talking about fiberglass? Hello here people!

I know we are all better than this...does kevlar ring a bell...carbon fiber [yelling like a drill sargent]

Wake up and smell the composites here people!

David

PS- I really wish we could use aluminum airframes

would smuthering the QT with epoxy resoned and rolling some fiberglass mess work i think that would strenthin it up but i think it would be expensive to find that mush resoned

hi
well im back from holiday and i see there have been a few more posts. Im going to fiberglass the fins on ok! so we can end the bit. Know one has said anything about the deployment issues.
Its first flight will be with motor depolyment only(i dont have anymore money for a alt.


thanx

if you use QT tubing you will not be able to use 54mm motors a they get too

Click to expand...

Are u sure? there is a guy at my club that has flew the top stage of a thunder and lighting on a K550W to about 10,000 feet with no problems and he did fiberglass the fins on as well (im sure that would go over .85 mach)

yay it has arrived now im just waiting for my stuff from giant leap to get here, for all the owners of mini BBX's what did you do about motor retention???? looking at that tail cone it might be a bit hard??? also i havent brought the terrier boster so i might get that in Phenolic tubing



thanx

I can say from experience that in at least some cases Quantum Tubing <U>will not</U> survive mach, even with the fin joints glassed and good internal and external fillets.

I flew a Quantum Leap on a K550 to a K550 in August, and all hell broke loose as it approached mach. All four fins were ripped out at the roots. The glass cloth was pretty much peeled off and didn't appear to have formed a very strong bond with the tubing even with the tubing roughed up pretty well prior to glassing.

Details of the flight are at:

https://www.eebert.com/Rockets/2002-08-02/ql-2002-08-03-K550W-K550W.html


-- Erik Ebert, L2
TRA #09105
NAR #79868

QT TEST(right click on the link and click "save as") here is a link of a video of the top stage of a thunder and lighting on a K550W going about mach 1.2 to about 10,000 feet with no problems and he did fiberglass the fins on as well.
i half finshed my Mini BBX still waiting for the stuff from giant leap to come.


matt

Matt,
It's not that the QT won't take Mach, it's that transition to Mach that is the problem. Once the rocket reaches about .85 mach, the air in front of the rocket begins to compress into a shock wave. When the vehicle breaks through that barrier, that's when the sonic boom is generated. However, the ride just before breaking through that barrier can be pretty bumpy. Apparently, the T&L that you reference must have broken through the barrier rather quickly. The biggest problem is when the rocket only achieves .85 mach or greater but less than mach 1. The turbulence will probably tear it apart. Glassed Phenolic will hold up much better in these circumstances.

what kind of stress does the build up of air pressure and when it's released wouldn't that be the largest stress on the airframe