Had no idea quantum tube was so brittle.

[RalPh8]

Took my PML spitfire out to a Tripoli launch recently and my parachute never opened. The end result was that the ground impact caused one of the G10 fins to pop off. On further inspection the quantum tubing is cracked in about 6 places. It wasn’t until afterwards a fellow member told me that quantum tubing gets brittle as the temp changes. I had no idea. I figured it would be stronger than Kraft paper. Guess I was wrong. Now I’m debating even trying to fix it. I feel like I’d be better off pulling the other fins off and ripping out the MMT with rings. I can reuse the fins, nose cone,MMT and recovery gear on a new 3 inch airframe. I looked into blue tube but it looks like ARR doesn’t have any in stock. Would it be worth it to just buy a LOC 3inch airframe and switch to that? Thoughts?

here’s video of the flight:

 

[Buckeye]

Quantum = plastic

I think cardboard, canvas phenolic, and fiberglass are better materials.

 

[Art Upton]

Yes, buy a LOC tube. Build the Fin can stand alone, and slit the LOC tube to fit over the fins of the fin can.

 

[Buckeye]

Bottom Line: You impacted the ground with no parachute. All bets are off regardless of material.

 

[Art Upton]

My Kraft tube rockets hold up for about 2-3 wadded up chute incidents with only minor fixable issues if any

 

[Art Upton]

And I make them so I can replace the tube without destruction of the rest of the rocket. They serve as an AeroSkin only, I never even glue the fins to my kraft tubes in Mid-HPR and even in several model rockets; including my L3 7.5" rocket.

 

[mtnmanak]

Agree with Buckeye that most tube material is going to bust if it hits the ground at terminal velocity sans chute.

However, QT has more issues with temperature than other materials. It expands and contracts significantly, which often messes with the PML piston system. Not sure if that is what happened with your chute failure, but many people have experienced catastrophic failure flying a QT in cold weather. And yes, it becomes very brittle.

Further, QT does not survive high speed flight. Never fly it close to Mach, it will shred spectacularly.

 

[RalPh8]

Agree with Buckeye that most tube material is going to bust if it hits the ground at terminal velocity sans chute.

However, QT has more issues with temperature than other materials. It expands and contracts significantly, which often messes with the PML piston system. Not sure if that is what happened with your chute failure, but many people have experienced catastrophic failure flying a QT in cold weather. And yes, it becomes very brittle.

Further, QT does not survive high speed flight. Never fly it close to Mach, it will shred spectacularly.

part of the contracting you speak of is ultimately what I believe to the piston being destroyed on deployment. If you go back and look at my video frame by frame, during the recovery you can see the piston tube destroyed as it exited the vehicle. Oh well I learned my lesson. Screw PML. From now on I'm just sticking with any other brand and material for kits.

 

[David Schwantz]

Love LOC stuff.

 

[mtnmanak]

Well, if you ever do decide to build another PML rocket, they usually offer a phenolic tube option. Recommend doing that and then glassing the tube. Phenolic is brittle as well, but a glassed phenolic tube is about as strong as a full FG frame.

If you do use QT again, put it in the freezer for a while, then sand your piston down until it slides well in the cold temp. Also, dust the inside of the tube with talc powder (real talc, not corn starch) just before you pack it for launch. I have a PML AMRAAM 4" that has a whole bunch of flights on everything from an H up to small K and it has not failed yet.

 

[Bowman]

during the recovery you can see the piston tube destroyed as it exited the vehicle. Oh well I learned my lesson. Screw PML. From now on I'm just sticking with any other brand and material for kits.

I don't think you should give up on PML so quickly. They make nice kits, so does Loc.
QT finishes nicely too. No rings to fill. The temp issues have been dealt with by many flyers, it's a shame nobody gave you the heads-up beforehand. I have had many flights in ten-degree and colder with no issues.
One tip for piston survival; reinforce the back skirt with a centering ring to keep the phenolic (brittle) from getting busted if it encounters the edge of the body tube. That makes a huge difference. Another trick is to make the piston with two bulkheads, one front and one aft, and don't glue the strap to either, allow it to pass straight through and slide freely along the cord. Tie a knot in the cord near the exit from the body tube to prevent the piston from sliding too-far down the cord into the rocket.
And be sure to sand the piston for cold fit as mtnmanak mentioned. A good piston makes for a pretty foolproof recovery deployment system.

 

[Bowman]

Agree with Buckeye that most tube material is going to bust if it hits the ground at terminal velocity sans chute.

And yes, it becomes very brittle.

Further, QT does not survive high speed flight. Never fly it close to Mach, it will shred spectacularly.

I think "very brittle" is overstating it.
Just my opinion but I don't think cold QT is any more brittle than plain phenolic in the same landing conditions.
Hasn't been my experience anyhow. In some cases I have seen impact to the end of the body tube cause distortion or stress lines that would definitely would have shattered phenolic.
I definitely agree with the cold weather fit issues though.

 

[mtnmanak]

Agree that QT is definitely manageable and PML makes some cool rockets.

Bowman is spot on with the piston management suggestions. I don't usually use two bulkheads with the pass through concept, but it is a good idea.

The phenolic pistons get very brittle, especially after a flight or two. I use a variation of Bowman's suggestions:

I sew the strap and feed it through:



Then I install the bulkhead in a "push" configuration (bulkhead towards the ejection charge) - this is not an issue if you put in two bulkheads like Bowman suggests, but if you put in one bulkhead, put it towards the charge. When the "cup" portion is towards the charge, it can make the pressure inside the cup uneven and make the piston wobble a bit and get stuck. I like to keep the cup - it makes a nice place to tuck the recovery items.

Either way, I epoxy the snot out of the bulkhead:


Finally, even if you use two bulkheads, reinforce the inside of the cup. I have tried glassing the inside of the cup with some lightweight glass and a balloon, but the easiest method I have found is to just coat the whole inside of the cup with epoxy. This not only reinforces the brittle phenolic, it helps keep the piston rigid and less prone to expansion/contraction due to humidity. The white splotch of epoxy in the photo below is a spot where the piston cracked and I had to repair it.

 

[Conway Stevens]

Agree with Buckeye that most tube material is going to bust if it hits the ground at terminal velocity sans chute.

However, QT has more issues with temperature than other materials. It expands and contracts significantly, which often messes with the PML piston system. Not sure if that is what happened with your chute failure, but many people have experienced catastrophic failure flying a QT in cold weather. And yes, it becomes very brittle.

Further, QT does not survive high speed flight. Never fly it close to Mach, it will shred spectacularly.

I'd disagree. I've flown QT past mach no issues. It's all dependent on the temperature and how hard the motor hits at first. I've seen rockets shred made of plenty of other materials at max Q.

I never fly my Quantum tube rockets in the winter and colder months.

And yes. Any tube that hits the ground hard enough can break.

 

[Steve Shannon]

Further, QT does not survive high speed flight. Never fly it close to Mach, it will shred spectacularly.

That statement doesn’t match my experience. I’ve flown PML QT supersonic many times. Once I even had a shred with a 3” QT PML rocket flying on a K2045, but it wasn’t the QT that broke, it was the phenolic coupler that failed when the QT flexed. Blew every panel out of the chute and sheared some pieces off the altimeter, but the QT survived just fine. Fins all stayed attached (in fact they’re still attached). Motor retention had no problems. The weak point was the phenolic coupler, but the flexing of the QT started it.
I have taken core samples with QT also where I was able to knock the dirt out of the body tube and fly it again. It can be very resilient. But it’s not resilient when it’s cold and it doesn’t always fail predictably . I once had a soft landing in cool (but certainly not frigid) temps where a crack propagated right up the side of a QT rocket that had flown for years with no problems. It was rocky ground.
No tube material is perfect. Each has its own strengths and weaknesses.
Learning to deal with the expansion and contraction of QT and phenolic pistons was just a rite of passage.

 

[Bowman]

it wasn’t the QT that broke, it was the phenolic coupler that failed when the QT flexed.
.
.

No tube material is perfect. Each has its own strengths and weaknesses.

I had a similar experience but the failure started due to fin flutter then once it went out of line it (the QT) folded right at the coupler.

The flexibility and elasticity of the QT is perhaps its Achilles heel when it comes to extreme velocity. I have a couple rockets that I built with the intention of periodically exceeding mach. I used QT but lined it with full-length coupler tube so the only part of the body tube that it QT only is the few inches below the nose cone shoulder. So the QT is really just a skin over all but ~1/4" of the air frame.
Yeah it adds weight but not as much as me glassing the phenolic myself.
So far three trips past mach and no issues.

 

[Bowman]

Agree that QT is definitely manageable and PML makes some cool rockets.

Bowman is spot on with the piston management suggestions. I don't usually use two bulkheads with the pass through concept, but it is a good idea.

The phenolic pistons get very brittle, especially after a flight or two. I use a variation of Bowman's suggestions:

I sew the strap and feed it through:

View attachment 449525

Then I install the bulkhead in a "push" configuration (bulkhead towards the ejection charge) - this is not an issue if you put in two bulkheads like Bowman suggests, but if you put in one bulkhead, put it towards the charge. When the "cup" portion is towards the charge, it can make the pressure inside the cup uneven and make the piston wobble a bit and get stuck. I like to keep the cup - it makes a nice place to tuck the recovery items.

Either way, I epoxy the snot out of the bulkhead:
View attachment 449526

Finally, even if you use two bulkheads, reinforce the inside of the cup. I have tried glassing the inside of the cup with some lightweight glass and a balloon, but the easiest method I have found is to just coat the whole inside of the cup with epoxy. This not only reinforces the brittle phenolic, it helps keep the piston rigid and less prone to expansion/contraction due to humidity. The white splotch of epoxy in the photo below is a spot where the piston cracked and I had to repair it.

View attachment 449527

I put a coupler centering ring in right at that edge that you repaired. Since I started doing that no more broken edges.
I epoxy the inside (and outside) of the piston too. It also helps make residue clean off easier and prevents swelling if you land in a wet area. That paper fiber that the phenolic is impregnated into does absorb a little water, just enough to prevent a subsequent flight until the piston dries and gets re-fit.

Boy the more I type, the the more I realize that I spend a lot of time making pistons work! They're still my preference though.

 

[Handeman]

The only PML rocket I have is a Callisto that is 18 years old. Still all original, including the paint and decal. I've sanded the piston so many times in cold weather that it works year round now. I did fly it once at 26ºF and the Quantum tube broke in half a couple inches above the forward CR when it landed. A coupler and some J-B weld epoxy and it was good as new. I still fly it a lot but not when it's below freezing.

The coupler on the piston is chipped, cracked and worse for wear, but still works just fine. I did learn a long time ago to never put more than 0.5g of BP in the ejection charge.

 

[AstroAbaqus]

Not an expert on QT, but just looking on the speed and the way you hit the ground, I suspect that probably the fin blowing away like that was a salvation. That is essentially a cantilver that hits the ground while rotating at high angular and vertical speed. It failed where it is supposed to happen at the root. I think your main issue is not the material but the fact that you had the free fall. Unless you are flying lpr or very light rockets that crash will produce damage in any way. I saw a member of the forum hitting with a MAC kit, very well build, just hard surface on the retainer causing a sever fractuire in the airframe, and was only an hard landing with a heavy rocket with perfect parachute open.

 

[cwbullet]

Not an expert on QT, but just looking on the speed and the way you hit the ground, I suspect that probably the fin blowing away like that was a salvation. That is essentially a cantilver that hits the ground while rotating at high angular and vertical speed. It failed where it is supposed to happen at the root. I think your main issue is not the material but the fact that you had the free fall. Unless you are flying lpr or very light rockets that crash will produce damage in any way. I saw a member of the forum hitting with a MAC kit, very well build, just hard surface on the retainer causing a sever fractuire in the airframe, and was only an hard landing with a heavy rocket with perfect parachute open.

Nice Banana.

 

[cls]

I think poop pipe is terrible stuff. brittle, doesn't glue well, not stable with temperature. all my QT rockets have died. the piston system is not the best, either.

 

[rharshberger]

Nice Banana.

Its not a banana its a boomerang!

 

[aerostadt]

I like the ease of no-filling the spiral of QT tube. I have QT in my 4x OT. It has flown 17 times over a period of more than 10 years. The launches have been in warm weather. I think the latest I ever launched in Utah was October or November. I had a bad crash landing on the very first flight at the summer Hellfire launch on the Utah Salt Flats. The QT was destroyed above the wing. I cut the QT back to the undamaged section and made a paper trace of the irregular cut. I sent the paper trace to PML and they custom cut a section of QT to match the lower good section. I then used a coupler tube to put the two QT tubes together. I am not sure PML would be agreeable today for such a customization, but this method worked like a charm.

 

[sharkbait]

I think poop pipe is terrible stuff. brittle, doesn't glue well, not stable with temperature. all my QT rockets have died. the piston system is not the best, either.

I have taken QT past Mach 2, somehow a small shard of QT was stuck in the harness on my Mongoose, since there was no piston, it landed safely with the chute deployed perfectly also

 

[David Schwantz]

I have seen QT shatter on several flighs. last one, QT was used as MMT and she let go and shot the motor through the NC.

 

[dpower]

I fly a QT PML Endeavour with piston - works great - never had a crack - never had the piston stick. Haven't flown it near mach, and avoid flying in winter - same as my AT kits with plastic fins.

 

[Antares JS]

last one, QT was used as MMT and she let go and shot the motor through the NC.

PML specifically says not to use QT for motor mounts, and common sense should dictate that plastic will soften next to a hot rocket motor case. That one is definitely on the flyer, not on PML.

QT has limitations like any other material. It glues fine if you scuff it per the instructions, and yes, it's not advisable to fly it in cold weather. It works well if you use it within its limitations. There's no need to dump on QT or on PML.

Disclosure: I got both my level 1 and level 2 on QT PML kits.

 

[DaHabes]

Either LOC or Blue Tube is more than sufficient for any 54mm or smaller motor you put in a 3" airframe. I use LOC and BT exclusively on all of my scratch builds.

ARR has 3" in 'MMT Only' in stock. They are blemished but should be usable as airframe with some extra finish work and they are half the price....

 

[Handeman]

I think poop pipe is terrible stuff. brittle, doesn't glue well, not stable with temperature. all my QT rockets have died. the piston system is not the best, either.

My QT tube Callisto was my first HP rocket I built in 2003. I fly it almost every launch and it's still going strong, guesstimate 150- 200 flights. It did break in half on landing on a 26 deg. day, but a coupler fixed that. The piston is worse for wear but still going strong.
QT might not be the best BT for a rocket, but it certainly isn't the worst.

 

[Tommie D]

Handeman, The Callisto was my first HP rocket too! Used it for my level one. I have flown PML quantum tube rockets for over twenty years and never had a problem with them. My Level two was a 1/4 Scale Patriot on a J350, what a hoot! Lost it two years later at the NSL in McGregor Texas in the early two thousands. Built another one to replace it. Thunder & Lighting, Tiny Pterodactyl , Ariel, Bull Puppy and just started a 1/6 Scale Patriot Missile last week. Everyone has their favorite, and to each their own because rockets are like cars, some like fords and some like chevy's. Me I drive a pos Ram but it's mine and it does the job.