reinforcing cardboard airframes

looking to build something of a moderate size that will accomplish two goals:

- fly on a full H to 1800ish feet (about as high as I really want to fly in our local "obstacle" filled field) allowing for all around fun without breaking the budget.

- fly a high impulse and short burn motor (AT K2050 / CTI K940) proving the ability to withstand very high G loads and near instant mach numbers. this flight will either be my Cert 2, or directly after my Cert 2. There is a field a little further out that is available in the winter months where this flight can take place.

right now I am looking at the classic LOC EZI-65. IMHO there really isn't anything not to like about this kit. the lines are classic HPR, and the kit has truly stood the test of time. that and it (like the caliber ISP that I'm finishing right now) is one of the rockets that I really wanted when I flew back in the 90's, but never had the resources to add to the fleet. with the addition of an electronics bay and a few modifications this kit should fit the bill quite well.

my question comes to strengthening the cardboard airframe as this will be needed for most anything above a moderate J. many would simply glass and be done with it. I am ok with this, but what about "sleeving" the airframe by inserting a full length blue tube coupler? this would extend the entire length of the airframe and the actual coupler attaching the payload to the main airframe would be the LOC stiffy A/V bay set-up that I am using in my Caliber ISP (see build thread https://www.rocketryforum.com/threads/build-thread-loc-caliber-isp-38.152201/)

I am also contemplating either glassing the factory fins or having PML cut me some out of G10

so whatcha' all think? is the blue tube sleeve a good way to go?

Full length coupler is a great idea, potentially lighter than sleeping or glassing. Your issue then becomes fin flutter

Theory said:

so whatcha' all think? is the blue tube sleeve a good way to go?

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Why blue tube? A full-length paper coupler ought to be sufficient.

jlabrasca said:

Why blue tube? A full-length paper coupler ought to be sufficient.

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And the blue tube is heavier, and it might be to loose or too tight to fit the cardboard airframe. Finding full length loc couplers is hard to do, but many have used regular couplers to do the same thing.

Blue tube due to the ease of sourcing a full length piece. IMO a single piece is key. Also, a. quick glance at the measurements indicates that it’s workable

Fin flutter will be calculated and addressed. It is one of the things drawing me to the EZI “platform,” as that fin shape is well proven.

This project will be a good one for me. Lots to learn on. True many others have done this and have flown higher and faster, but this will allow me to work it all myself.

Looking forward to it!!!

I bet the Jason at LOC will cut you a full length coupler. I have got custom sizes from him.

David Schwantz said:

I bet the Jason at LOC will cut you a full length coupler. I have got custom sizes from him.

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Good thought, I will ask. If possible that will prove to be several ounces lighter than the blue tube piece

Theory said:

Blue tube due to the ease of sourcing a full length piece. IMO a single piece is key. Also, a. quick glance at the measurements indicates that it’s workable

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John Coker might have some useful advice



Tim VanMilligan, too.

making a coupler from a tube isn't a bad idea, but I'm thinking having LOC cut one is best as I will be 100% sure that the "stiffy" coupler will easily fit inside.

thank you all for the ideas

jlabrasca said:

John Coker might have some useful advice



Tim VanMilligan, too.

Click to expand...

I am building a custom rocket and will have to do this to make my coupler and tubing.

I do not recommend Blue Tube. I just got bit again. I was going to fly my Deuce for the first time in 6 months but the Blue Tube had shrunk again. Couldn't get the motors in or the coupler into the booster airframe (where the plywood bulkhead was tight and needed sanding). Its going to take a while with drill and drum sander to get the motors in and a lot of sanding to the get the coupler to fit. I have had shrinkage issues with both version 1 and 2. I thought the dimensions had stabilized after a year but no such luck.

hhhmmmm, sorry to hear about that but good to know. looks like the fully length LOC coupler is the way I will go.

Theory said:

hhhmmmm, sorry to hear about that but good to know. looks like the fully length LOC coupler is the way I will go.

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iirc Loc doesn't offer longer couplers than listed, still contact Jason to be sure. I wanted a full length section and was unable to get one. Many of the vendors have the couplers pre-cut as they get a better (clean and square) and more consistent cut from the tube manufacturer.

Theory said:

hhhmmmm, sorry to hear about that but good to know. looks like the fully length LOC coupler is the way I will go.

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In a PM exchange about this very topic -- L2 with a cardboard rocket -- Nytrunner suggested I look up build threads by Eric Cayemberg (ECayemberg on the forum). I was already committed to a blue-tube build, and searching the forum didn't really take me to any thing immediately useful. I also didn't have any specific questions, so I didn't want to bother Eric with a PM. So, I will pass along the advice to you, and in the open so that maybe someone can point you (and me) to a relevant thread <smile>.

Very well. The broken pic links don't help matters, but the build remains solid
@ECayemberg , what's your image hosting site?
https://www.rocketryforum.com/threads/loc-n-load-build-thread.143463/