Fiberglassing necessary for H-I power rockets???

[Murrill]

I'm planning on a Level 1 attempt in January, and I will probably build either a PML Patriot (1/4) or BSD Horizon for the occasion. Both kits have 38mm motor mounts. I have never fiberglassed a rocket before, and I'm wondering whether glassing is necessary for a rocket that will be flown on "H" and "I" motors? (I suppose it's possible that if my Level 1 is successful, I might get carried away one day and try a "J," but first things first.) Breaking that question down a bit more, is fiberglassing the tube itself necessary for that range of motors? Or would it be overkill? What about fiberglassing the fins? I found lots of info about fiberglassing techniques, but I haven't found anything about when fiberglassing becomes necessary. Any info would be very much appreciated, I would also appreciate any feedback on the two kits I mentioned.
Thanks in advance!
John

 

[Zippy]

From what I've read on PML's own FAQ and picking things up here as well, fiberglassing the tube isn't needed unless you plan to break mach. Not all mach breakers are glassed though. Glassing the fins on is a nice touch at any speed. If you just want more durabillity glassing the whole thing no matter what engine your using is done often enough by lots of people. Don't glass Quantum tubes.

 

[Rocketmaniac]

Fiberglassing is not needed for a "H" motor......... I build my ISP Caliper pretty much stock and did my L1 on a Pro38 H153 and then used it again for my L2 with a Pro38 J285...........

 

[Juerg]

As others said allready, fiberglassing isn't necessary to fly "H" to "I" power motors, but it may make sense to have recovery without damage!
After all, with the same time you are spending on filling the spirals you also do the fiberglassing and you get a nice, hard surface that heavily reinforces the rocket, without adding more weight than a thick layer of filler.
Both phenolic and paper tubes are very sensitive to impact and zipper, fiberglass helps a lot here.
So what reason should one have NOT to fiberglass?

I even fiberglass Aerotech rockets (because of the spirals )! On a typicall 4" rocket I use 2 layers of 160g/m2 glass and I also reinforce the forward end of the tube by shaving off the outer layers (0.5mm) on a length of about 30mm and filling up the void with some layers of glass before applying the final 2 layers of glass over the whole tube.
The result is a nice, heavy "anti-zipper" ring that is completely invisible.

Juerg

 

[Johnnie]

Murrill,

Think of Phenolic like an egg shell...The sides of an egg are weak and brittle, but the end to end strength of an egg have excellent properties. Same with phenolic tubing...from end to end of the tube, phenolic has great strength, for those hard landings...but if it landed more to it's side, you will damage the side wall from the brittle properties that phenolic is known for. Case and point, I saw a PML 4" Black Brandt leaning against a car fall over, and the coupler broke through the side wall of the rocket...it was not even a hard fall. Craft paper tubing has a lot more give and flexibility in their side walls, and will not allow this to happen. On the other hand, Craft paper tubing tends to accordian over time from repeated hard landings to the end of the tube.

To me, all phenolic tubing gets at a minimum of (1) layer of 2 oz. glass, just to shore up the side wall integrity. This has nothing to do with the power of the motor, but only the propertities of the tube.

(disclaimer)...of course this is just my $.02 worth, results may very from flier to flier

 

[Austin]

John,

Lots of good tips, but no one mentioned the tubing you would possibly be using, which is Quantum tube on the PML kits. As mentioned, there are certain instances to use glassing, most of which are not absolutely necessary unless you go supersonic.

You forgot to mention where you live...if it's cold, etc... This will impact what you do. In warmer climates, the PML kit would be fine, but in colder climates, I recommend you glass the Quantum fin can area only. Quantum tube becomes brittle in cold weather and glassing the fins adds a ton of strength to the rear end that will be hitting the ground. On cold days, I have seen Quantum shatter. Also, the piston ejection will need to be sanded to fit on cold weather as the chamber does shrink and the piston ejection becomes tight. I always fit my piston for the coldest day I plan on flying and it works well for everything!

Tip: on PML kits, get a second coupler with the kit, cut it to the length of the piston, then split it and fit it inside the piston to "Double-Wall" the piston assembly. this will prevent cracks from too much ejection charge; I have seen pistons litterally blown apart from the inside out from too heavy an ejection charge, while the model faired fine. It will give you much more material for strength, as sanding to fit may make the outer piston a bit thin, so adding another layer inside gives you your thickness back. A second thing you can do...make the piston detachable with a quick link. this way you can use the piston in the summer and stock deployment with a nomex cloth in the winter.

Don't let some of these tips on PML change you over to BSD only....PML has some of the best kits on the market imho, and I and many others here own several of them. The Quantum tube that PML uses for body tubes is smooth as glass, is made from a 1/16" thick plastic polymer and paints like a dream! It's very strong and very flexible...good stuff. Also, the piston ejection works very well if tuned in...a great concept and design.

Keep us up to date on your progress and pics...we need pics!

Carl

 

[Juerg]

For rockets bigger than 3" one might consider not to use quantum tube at all but to stick to phenolic.

Another problem of quantum is also that at low temperatures it shrinks more than the phenolic piston, so the piston may get stuck in cold weather.

On the other hand quantum gets quite soft in warm weather and doesn't provide the stiff support needed for the fins. Filling the void between motor mount tube, body tube and fins with polyurethane foam is one cure.

Juerg

 

[shockwaveriderz]

I don't think fiberglassing itself is needed for this power class but in I have used epoxy finishing resin, which is relatively "light" and "thin" to coat body tubes both inside and outside......I either try to peel off the outer glassine wrap or just sand it off.....it will soak into the kraft paper pretty good.....and it create a light hard surface....

 

[Matt]

I hope top be scratch building my new rocket a 4" custom PMl parts rocket and it will run on up to a K700 or larger for experimental motors.
And i plan on Carbon fibreing the whole airframe with a 2.5 oz fibreglass veil on it.
and carbon fibre the fins and Kevlar and carbon fibre the whole avionics bay.
And really it probably will be a complete over kill,
BUT IT WONT BREAK!!
nothing can go wrong with that cinda stuff.
Plus it can handle anything even if the drogue fails and it falls 7,000ft until the main parachute deploys at about 0.85 Mach
nothing will strip.

 

[Juerg]

Matt

If you are after the "sharp look" of carbon, go for it. If you want to really make your rocket more resistant use fibreglass!

Carbon is very light and very stiff but it shatters like phenolic when hit, fibreglass doesn't!

There is only two technical reasons to use carbon, one is if you need the stiffness of carbon (carbon is stiffer than glass), the other is saving weight (what isn't an issue when used as a cover only!).

Juerg

 

[Juerg]

P.S. If I need a "sharp look" I use fibreglass covered with one layer of carbon ;-)

 

[Stymye]

I have a question about quantum tube

would fiberglasing(carbon fibering),be logical on a quantum tube? .It seems that the epoxy would not penetrate very deep and you would be left with a tough outer skin yet
a hard non flexable inner wall that could still crack or break somewhat easily

I can understand it being used around the fin area sucessfully
but If the tube itself shrinks or expands at a much different rate than the outer layer,what would result from a hard landing?

I've never used quantum

 

[Juerg]

By sanding the QT you may get some adhesion between the fibreglass and QT but it doesn't make sense to glass the whole tobe.
For the fin area, using foam is the better way to reinforce.
If you want a rocket capable of high-speed flights, QT isn't really the best choice, specially not on larger diameters (>3")

Juerg

 

[Silverleaf]

All great points. If your like me, someone who can't stand the thought of fiberglassing, simply pay the extra money and have it done for you by the manufacturer - or a specialty designer, or your bestest rocketry pal - you know the guy..the one whom adores seeing the feel of the tube after the glass is just packed on, trying out that new vacuum method.

Sure, its more expensive, but it saves me the single step that I hate. Don't get me wrong here fellas, I admire those that do their own glassing, just that I prefer not to.

Now, who can I find to glass 4 - 30 inch lengths of tubing...or those 2 mega 3 foot diameter tubes...hmmm

Cheers,

 

[Ray Dunakin]

Originally posted by murrill
I'm planning on a Level 1 attempt in January, and I will probably build either a PML Patriot (1/4) or BSD Horizon for the occasion. Both kits have 38mm motor mounts. I have never fiberglassed a rocket before, and I'm wondering whether glassing is necessary for a rocket that will be flown on "H" and "I" motors? (I suppose it's possible that if my Level 1 is successful, I might get carried away one day and try a "J," but first things first.) Breaking that question down a bit more, is fiberglassing the tube itself necessary for that range of motors? Or would it be overkill? What about fiberglassing the fins? I found lots of info about fiberglassing techniques, but I haven't found anything about when fiberglassing becomes necessary. Any info would be very much appreciated, I would also appreciate any feedback on the two kits I mentioned.
Thanks in advance!
John

My two cents: Fiberglassing won't be necessary for H and I motors, and probably not for J either. (Caveat: If you used a really high-thrust motor like a J570 you'd probably need to glass it.)

PML uses phenolic tubes that tend to be brittle, so you may want to glass it just for extra durability. I don't know what kind of tubes BSD uses. Paper tubes such as LOC won't need glassing unless you are using high thrust motors or larger than J motors. Another circumstance in which glassing might be needed is if you have something such as a mirror shroud for a camera payload, which causes assymetrical thrust. I've found that in such cases it's usually a good idea to reinforce paper tubes if I'm using "I" motors or larger.

BTW, there are other ways to reinforce a tube. You can glue in a full-length coupler (be sure to leave room for any "real" couplers that might be needed). With paper tubes, I've often split one tube lengthwise, then glued it around the outside of a second tube. Leaves a small gap on one side, but makes for a very rugged tube without investing much time, money or effort.

Yet another method is to glue thin strips of wood lengthwise on the outside of the tube. I've used four 1/4" by 1/8" strips of wood to add longitudinal strength to a tube on several occasions. The strips tend to look like conduits.