Need advice over airframe tubing....

[el chubbo]

First - a big THANKS to all of you on this forum - by your posts and discussions you have helped our group immensely! This site is a GREAT resource!


O.k. Here is the background.

Our elementary school rocket club is working on plans for a MP cluster vehicle utilizing (4) pro38 1G's. We are carrying payload for other elementary school classes.

Here is the main question(s) : what type of airframe tubing? I have used standard postal tubes with (1) pro38 1g and have had much success. Has anyone had experience with the non-brittle phenolic tubing carried by Giant Leap? What is the difference between this and quantum tubing? Any other suggestions?

Our program is very "hands on" (the students build almost everything) - I would like to avoid fiberglass for now (if possible).

Comments everyone?

 

[lalligood]

Welcome to TRF! Glad you find it to be a fun & informational place, 'cause that's how we like it!

I personally don't know much about Giant Leap's non-brittle phenolic tubing (I'm sure that someone else will chime in about it) but PML's Quantum tubing (QT) is a resilient plastic that's easy to work with & paint.

QT's downsides are that you must make sure to rough up any areas where you are applying epoxy to it, only comes in diameters up to 3.9in, cannot withstand speeds greater than .85 mach, & cannot tolerate direct motor contact (i.e., cannot be used for motor mount tubing).

If that fits within the boundaries of your design, it's awesome to use. Another way of looking at it is as long as you're not planning to use it for a minimum diameter and/or mach buster design, it's worthy of consideration!

And wow...4 Pro38 G69s. That ain't MPR! hehe

 

[jetra2]

Lemme see...you're doing four G's. That's a I class motor. Lotsa power there man. Lets say you're using a 4" diameter postal tube (do they even make those? if so, I'm buying some!). I would say that you would want to give the tube one wrap of 1.5oz or 3oz fiberglass cloth. You can find the cloth at most hobby shops, or online. You can find out more about the technique around TRF. That's my recommendation for strengthening the cheapest tube around. Then again, you could use 4" phenolic tubing, and you'd be fine!

HTH,
Jason

 

[PunkRocketScience]

Hey, just wanted to add my two cents worth. My last big project was build with Giant Leap's 6" flexible phenolic with no fiberglass on J power and it had no problems, other than a small zipper (but I attribute this to the use of kevlar shock cord that was a little on the thin side...)

All in all though, this sounds like a relatiely advanced project for elementary school students... Good luck!

 

[bsexton]

Originally posted by el chubbo
Our elementary school rocket club is working on plans for a MP cluster vehicle utilizing (4) pro38 1G's.

Having worked with Cub Scouts (elementary school) this sounds like a pretty aggressive project for young people. I hope there is some serious adult supervision. Sorry, but it concerns me a little...

 

[el chubbo]

Thanks for the input -

I was not sure to post in the MP or HP section - type of engine vs total impulse?

I will certainly be ordering phenolic for our first run - has anyone had experience with the fiberglass "sock" ? (i'm sorry but it looks like a condom to me)


I appreciate the notes of caution... our "senior" group (4th - 6th grade) had been quite busy preparing for this challenge... we have quite a zealous group that has been studying all facets of model rocketry since the start of school.... and - yes - we have more supervision, safety guidelines and protocol than I know what to do with...

 

[Ray Dunakin]

Personally I would recommend the paper tubing from LOC/Precision. Giant Leap's "flexible phenolic" has its uses, but is still very brittle IMHO. The only benefit that phenolic has over paper is that it's stiffer, and if you're going to glass it anyway you might as well go with paper and skip any problems with brittleness.

Four G69's is roughly equivalent to an I280. If it's a simple design you might not even have to glass it, but a single layer of 4 or 6 ounce glass certainly wouldn't hurt and would allow you to fly it on larger motors later if you so desired.

Four 38mm motor tubes will only fit into a LOC 3.9" airframe tube if you distort it out of round a little bit. That's do-able with paper tubes, but probably not with phenolic. If you do it, it won't adversely affect the rocket's performance.

 

[Scale Rocketeer]

Definitely stay away from the Quantum tubing.

Freind of mine had a rocket with the Quantum tubing that flew well with the Pro38 G. He then flew it with an Pro38 I and the motor mount broke loose and pushed forward and stripped the plywood fins off.

I t just does not bond well to anything even when sanded. It's OK if you don't put too much power behind.

Interesting though...it looked like a total strip on the flight but the fins, tube, nose cone and all the parts were recovered without breakage and could be reglued and used again.

Incendently, we carry the Pro38 G's at:

https://www.scalerockets.com/motors.html

The standard G can be shipped by US Parcel Post without restriction and without hazmat. The purchaser must be at least 18. We sell a lot of these to those who want to fly the biggest motor you can purchase without LEUP or Level 1 Certification.

However, the regulations still apply regarding launch distances and FAA waiver for the rocket your planning on launching. It will be classified as a High Power Rocket with an I rating.

I would highly recommend that the launch be supervised by someone with Level 1 Certification at a regular launch where a FAA waiver is already in place.

 

[el chubbo]

Thanks for the 411...

I missed my L1 last week because of a pesky thing called "unexpectedly having to work"....

Your advice on the FAA part is right on.... we have already been in contact with the locals - they are (suprisingly for gov. people) helpful and seem to be on-board...

1-G Reloads can be shipped without hazmat? I did not think that was possible....

Thanks!

 

[Scale Rocketeer]

The Pro38 Standard G reload is under the 62.5 gram limit and can be shipped without hazmat by US Parcel Post. The smokey Sam G reload is above 62.5 grams and must be shipped with hazmat by either UPS or Fed-x.

 

[powderburner]

Originally posted by el chubbo
. . . has anyone had experience with the fiberglass "sock" ? (i'm sorry but it looks like a condom to me) . . .

I have to agree with bsexton, this looks pretty ambitious, are you guys SURE you want to bite off this much rocket? Keep in mind that you are also going to have to master the art of simultaneous ignition of clustered motors, you will need a fairly high-powered ignition system, you will need a rather large launch field to safely fly this thing----I'm sure there are other cautions that should be brought up.

I am even more curious what the payload is. How much weight do you plan to hoist? Are you aware that rockets over 3 pounds total lift-off weight require clearance with the FAA? I hope this payload does NOT include live animals: that area is ripe for all the bunny-huggers to protest and scream "ANIMAL ABUSE" and get your project shut down. This problem is real, and so severe that the NAR specifically recommends against animal passengers. Be careful.

And welcome to TRF!

 

[Scale Rocketeer]

Correction, Any rocket over 3 pounds or having more than 160 newton seconds of impulse. Four 133 newton second G's is 532 newton seconds!

It sounds as if he's already getting the waiver in place. He'll need it to about 5000'! Also he's indicated he's going for level 1 and he'll have this in place before the launch of the project.

He's doing it right even if it is a little much!

I have to agree on the clustering. Make sure that a relay controller is being used and the distance should be 100ft from the the launcher and the spectators. Usually 50ft is OK, but the clustering doubles the distance.

Plan for the contingency that 1 of the engines may not ignite and put a some spin angle into the fins to keep the flight straight if one of the engines does not ignite. Another trick is to offset the engines alla "dueces wild" so that the flight is straight no matter how many engines ignite.

 

[powderburner]

I completely overlooked the impulse-thing (I am not accustomed to launching at such lofty power levels)

Another thought here: it would probably be a good idea to do a little practicing with a smaller cluster, maybe four x 18mm? This would get you some inexpensive practice with clusters, cluster ignition, and all the fun little quirks and foibles that come with. And you could probably launch your practice bird much closer to home (wouldn't have to wait for scheduled national events to fly).

 

[el chubbo]

You guys are right.... this is an ambitious project for our group...

I have been working on the front end of this project for the better part of (3) months before we ever started talking with our students...

Nothing alive, nothing flamable and nothing metal (except necessary component parts). These are the general rules for payload.

We have (4) pages of range safety that students, parents and staff have to sign off on before they start. We sent up 97 LP rockets at our fall launch without a single range safety violation on the part of our students (PARENTS are another thing!)

We've been stand testing cluster configurations for a week.

I have a group of 5th and 6th graders also starting to design a machbuster.

We're in the beginning stages of the FAA waiver.

The field is 180 sq. acres surrounded by 500+ acres of additional rural land adjacent.

I will post more tomorrow - I have to do the "work" thing....

Thanks for your input! I hope that I have covered all the bases! If anyone can think of something that I have missed PLEASE let me know.

 

[powderburner]

I am impressed.

That sounds like quite an accomplishment for ANY school class, let alone an elementary grade! Is this effort supported/funded through the school system, or do you have an independent benefactor?

Sounds like you have the situation well in hand. With a launch site of that size, you should be good for some fairly big stuff.

Other than airframe construction, are there any other questions from your gang? Any needs for equipment or building supplies?

 

[rstaff3]

Starting with BP clusters is a good idea. But remember that they are MUCH easier to ignite than AP-based motors. If you really want to try high power, you might check with the local clubs to see if some LEUP-ed flier will help with the motor end of things and let the students emphasize the rocket/payload.

Sounds like a great program.