Gotta love QT from PML

Discussion in 'High Power Rocketry (HPR)' started by AfterBurners, Jan 18, 2020.

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  1. Jan 18, 2020 #1

    AfterBurners

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    Just finished the first coat of primer on my PML Spitfire. I love that I don't have to fill in any spirals. The QT are nice and offer strength and less weight than the all fiber glass kits. I like FB but these kits are a nice compromise over card board and wood. The only places that ever need much attention is the fin can area.
     

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  2. Jan 19, 2020 #2

    MikeyDSlagle

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    Yep. I agree. Lighter and cheaper than glass or canvas; more durable and easier to finish than paper. I love the stuff. Got a Tethys for Christmas. Really looking forward to getting started on it.
     
  3. Jan 19, 2020 #3

    Donnager

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    X3 Just built an Xcalibur. Qt was very easy to use and very nice to finish.
     
  4. Jan 19, 2020 #4

    manixFan

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    When I first got started I built a number of PML kits using QT. If you aren't already, one issue you need to be aware of is that it shrinks a lot in cold weather, so much that if you use a piston it will likely bind and the nosecone may not fit. PML suggests that if you fly in cold weather to put the tube in the freezer if possible and use that to fit the piston. (Hopefully before building.) Same with the nosecone. (Of course you can always add a wrap of tape to the shoulder if it's too loose when it's warm.) Otherwise make sure to check the fit of everything once out at the field if the temps are cold.


    Tony
     
    Last edited: Jan 19, 2020
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  5. Jan 19, 2020 #5

    Donnager

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    No piston in mine, just standard eject/recovery stuff. I was concerned about the differential thermal expansion, as well.
     
  6. Jan 19, 2020 #6

    AfterBurners

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    Yes Tony I have heard of this, but fortunately for me I live in warm weather. I built their 3" Bull Pup and never had a chance to fly. I had posted some pictures of it and ended up selling it, but I'm considering getting another one and using a slim line retainer system on it. I think it would look really cool because the retainer will tuck up inside the boat tail and not over hang giving it a clean look.

    So Tony a quick question? On the piston can you offer any suggestion as far as fit? When I built the Bull Pup it slid in and out pretty nicely with minimal effort, but is there a way to know for sure when you got it right?

    Thanks!
     
  7. Jan 19, 2020 #7

    aerostadt

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    Even in warm or hot weather I have had pistons tend to stick. I was using a short phenolic tube for the piston. I found that a lot of sanding of the phenolic tube fixed the problem, but it was a lot of sanding and testing and re-testing to make sure the fit was good. I would recommend using an electric sander.
     
  8. Jan 19, 2020 #8

    Mustang67

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    I just skip the piston and attach Kevlar to the MMT or fwd centering. I will normally buy and extra centering ring or two from them. Double up the fwd ring and attach a stainless eye bolt and attach the Kevlar harness. I love the spitfire kit, great kit for the price point!
     
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  9. Jan 19, 2020 #9

    manixFan

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    I did use the piston on several of my early builds. It works very well. My test was to put the piston in the rocket and then see if I could blow it out by putting my mouth over the motor tube. That gave me a pretty good feeling how it fit and what kind of force was necessary. If you already flown it, doing that is not a very pleasant experience. Or so I’ve heard!


    Tony
     
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  10. Jan 19, 2020 #10

    Buckeye

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    Yes, finishing is nice, but I don't agree with "strength." The tubes are plastic and they crack (for me). PML warns that reinforcement is needed if going transonic and above. I think canvas is the better middle ground between cardboard and fiberglass.
     
  11. Jan 19, 2020 #11

    crossfire

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    After each flight you should clean inside of tube to keep piston free to slide on the next flight.
     
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  12. Jan 19, 2020 #12

    AfterBurners

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    I sanded my kit with 150, 220, 320 and 400 before the primer and all it needs now is a few minor touch up and its ready for teh second coat and guide coat then wet sanding....love the stuff. Just awesome and save so much time on the finishing process.
     
  13. Jan 19, 2020 #13

    AfterBurners

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    Thanks Tony. I was thinking a quick burst from the air compressor. Maybe use that method for when its already been flown. As far using a Nomex blanket and skipping the piston to reply to everyone else. I think that is pretty wise to do, but IDK for me I just try to build the kit as recommended and see how it works, because once it does work that's just another option you can use on future builds. I guess you have to take your chances once in awhile. I'm always relieved when I see the laundry deploy.
     
  14. Jan 19, 2020 #14

    AfterBurners

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    I also like the rail guides that come with PML kits. So much easier to align because they conform to the airframe. I might stock up on a few packages to have them for future builds,
     
  15. Jan 19, 2020 #15

    llickteig1

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    I think you'll find a large percentage of experienced builders would disagree with your enthusiasm for Quantum Tube.

    QT is fragile. Bonding to QT won't hold up to Mach flight.

    Other folks have pointed out modifications that experienced builders incorporate into PML builds. Your enthusiasm for their linear rail guides isn't widely shared either. Rail buttons are better.

    Yes it finishes well. I care about other stuff. Fiberglass finishes nice, too.
     
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  16. Jan 19, 2020 #16

    JimJarvis50

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    I agree Lance with your opinions on the tube. I do, however, use the rail guides on minimum diameter rockets where there isn't anything to grab on to. The guides have two screws to give at least a little bite, and you can glue them down as well. I usually open them up a bit so they are not so tight on the rail, and I am very careful when I load the rocket.

    Jim
     
  17. Jan 19, 2020 #17

    Mustang67

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    I simply think they are great every day kits, easy to build and at an excellent price point. They give you the opportunity push it some when you want to with out having to go to fiberglass. Sure if you want to target Mach + speed you are talking high power and the need for a stronger air frame. Our club is in the North East, our last launch in November so really no concerns with too cold of temp to fly when using QT. Great kits for someone just getting into the hobby and wanting a bit of room for growth. I started with the Spitfire... love that kit. Endeavour is another favorite, I have a 6 inch glassed I need to put together yet. I like the fin design.
     
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  18. Jan 20, 2020 #18

    manixFan

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    Interestingly, I have found that in smaller diameters, say less than 3", QT is reasonably strong. I have a nearly 20 year old Tiny Pterodactyl that has probably close to 40 flights on it, including a couple of lawn darts into plowed dirt. (I think the long strakes probably help a lot.) But larger tubes don't seem to fare as well. And to echo what Mustand67 said, I found the PML QT kits gave me the kick start I needed to get stated in HPR. The instructions are well written, the kits are very complete, there are lots of motor suggestions, and the piston, while it has it's drawbacks, is very reliable for beginners. PML has been a great vendor for many years.


    Tony
     
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  19. Jan 20, 2020 #19

    AfterBurners

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    Its been a fun build so far. I'll post some finished pictures later. I haven't had much time to build, but trying to manage my time and make the most of it.
     
  20. Jan 20, 2020 #20

    AfterBurners

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    I agree and maybe clean the piston up with a lite sanding perhaps?
     
  21. Jan 20, 2020 #21

    AfterBurners

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    I've been high powered certified for a few years or more now, so not new to the hobby and I don't disagree with what has been said about fiberglass and also the disadvantages of the QT. I just haven't used it enough to see this, but I guess what I am saying is I like it over cardboard because of its finishing properties. Yes fiberglass is by far better all around, but from a price point the QT is pretty decent.
     
  22. Jan 20, 2020 #22

    H_Rocket

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    One thing I found helps is to make it so you can disconnect the piston from the strap. I use a short length of strap for the piston and them connect with quick links. This facilitates cleaning the main tube.

    Another is to fiberglass the inside if the piston. The edges will get damaged after a while no matter how careful you ar.

    Another is to install the piston upside down - gives you a bit more room for the laundry

    Finally, I would put the Quantum Tube in the freezer to chill and fully contract - then sand the room temperature piston to slide easily.
     
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  23. Jan 20, 2020 #23

    JimJarvis50

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    One thing not to overlook is the PML fiberglassed phenolic. I have a clone of the quantum leap that I fiberglassed myself. I did this about 15 years ago, and that rocket has flown dozens of time, landed in lakes twice, and it's still kicking (flew it last month). No problems with pistons fitting either.

    Jim
     
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  24. Jan 20, 2020 #24

    Donnager

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    PML pretty much kibashes mach flights in the recommendations for their stuff, or at least with the instructions I've seen.

    I like it because it is easy to paint, and easy to work with. I don't intend to break mach with my PML QT stuff, so I don't concern myself with it.

    Your and Jim's concerns are well noted, but probably not applicable for H-I motors for fun, rather than trying to attempt an altitude/velocity records, where I'd agree it is a poor choice.
     
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  25. Jan 20, 2020 #25

    AfterBurners

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    Not everyone flies fiberglass or can afford the prices of some of the materials and kits.
     
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  26. Jan 20, 2020 #26

    AfterBurners

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    I'm not using it for Mach 1 flights and as I recall PML has recommended suggestions on their website stating which tubes are best for certain application.
     
  27. Jan 20, 2020 #27

    JimJarvis50

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    My only concern about the QT, assuming the guidelines are followed, is with the fit of the piston. I'm a big fan of pistons (based on early experience with PML pistons), but I like my pistons to have a close tolerance and not "rattle". If you have to sand the piston so that it fits in cool weather, than it might be loose normally. I've only had one QT rocket and it was long ago, and I don't recall if that particular rocket (a Phobos) even had pistons. But I hear about the temperature concern a lot.

    One thing that I've learned in rocketry is that most people will tend to build and fly larger rockets over time as their skills develop. That may or may not be the case with you, but if that is taken as the general trend, then I try to advise people to avoid rocketry dead ends. These are things that you might do for a particular rocket that will never scale up beyond a certain point. So, why develop skills with them if you are more than likely to outgrow them. I buy lots of stuff from PML. But, PML sells some dead ends IMO. CPR is one example (learning to design and build altimeter bays that will allow redundant deployment is a better use of time) and QT is another. No problem using them on a given rocket for whatever reason.

    Jim
     
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  28. Jan 21, 2020 #28

    AfterBurners

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    Thanks Jim. Well said and point taken
     
  29. Jan 21, 2020 #29

    aerostadt

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    I agree with Crossfire on cleaning out the inside of the QT for good piston movement! I have been flying my 4" diameter 4xOT since 2008 with 16 flights so far. Actually, the very first flight without a piston had a bad crash, because the parachute was not pulled completely out of the tube. Thereafter, I have used the piston with no problem for the piston. The QT for this demonstration flyer with a parasite glider works great. (Finishing was easy.) I don't need Mach performance. I did put screws through the QT into the forward motor mount bulkhead, which also has the attachment for the shock cord.
     
  30. Jan 21, 2020 #30

    Voyager1

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    Indeed! I’m one of those not using QT anymore. Yes, it’s great to work with, BUT it is not as durable as FG, and it also suffers from differential heating resulting in body tubes bending when on the rail waiting for launch in a hot sun.
     

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