Slightly crushed airframe tube.

Hi, I'm building an EZI-65 with 4 inch airframe and when it arrived in the mail I noticed that the airframe was apparently slightly crushed at
some point. It is not very noticeable and the tube appears to be round since a coupler can easily slide down the entire length. The only noticeable thing is that there is a very slight crease on the outer paper covering and maybe the tube is a little more flexible than it should be. I have never worked on a 4 inch diameter tube so it's hard to judge if the tube is too flimsy. I'd rather not go to the time and trouble of returning the merchandise if possible. Is there a way to strengthen the tube and ensure that its structural integrity is sound? I intend to prime and paint the rocket on completion and I am willing to experiment with composites if this is practical. I noticed the bulkhead had a similar defect which is slightly more obvious, but before I notice the airframe also had a problem I ordered a replacement bulkhead. Also, what do you all think of the phenolic tubes and the unfortunately named "Stiffy". This rocket will be used for L1 certification so I need it to be dependable and not to far from specs since I already ordered the 38/240 rms. Thanks, Laura
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I would ask whoever you got it from to replace it. THat is because a kink in the airframe is a weak spot where it may fail. If you've ever seen a rocket that seems to fold in half during boost, either that (a failed airframe) or a weak coupler are usually the cause.
Phil
wrote:

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lizardqueen wrote: > Hi, I'm building an EZI-65 with 4 inch airframe and when it arrived in > the mail I noticed that the airframe was apparently slightly crushed > at some point. It is not very noticeable and the tube appears to be > round since a coupler can easily slide down the entire length. The > only noticeable thing is that there is a very slight crease on the > outer paper covering and maybe the tube is a little more flexible > than it should be.
From your description the tube is "probably" OK--certainly for most H or I motors. But an easy way to reinforce the tube is to glue a coupler inside at the crease. Use epoxy, as white/yellow glue will be difficult (epoxy will "lubricate" the tubes allowing you to slide the coupler into place while white/yellow will "grab"). The coupler might be in the way of a centering ring; if so, see if you can move the centering ring up or down to clear it.
You said the "bulkhead" was also creased and that you ordered a replacement. Do you mean "coupler"? (Bulkhead usually means a disk--a centering ring without the hole--and I don't see how it could get creased.) If you mean coupler, then use the creased one to reinforce the tube--just don't align the creases together.
At this point in your HPR career I'd keep things simple. While composites can be lots of fun :-) you don't need to go that route yet.
> what do you all think of the phenolic tubes and the > unfortunately named "Stiffy".
The, uh, "Stiffy" is more than you need at this point, but it could certainly serve to reinforce the tube as I described above. It adds weight and some complexity. Remember, keep it simple.
Phenolic is fine--prone to cracking & shattering and you must use epoxy and prep the surface well--but it serves the purpose. I lean slightly toward using paper over phenolic as it takes adhesive easily, but I'm not really fussy.
--
Steve Humphrey
(replace "spambait" with "merlinus" to respond directly to me)
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Maybe I should have said bulkhead assembly. What I was referring to was basically a payload section tube, part PL-3.90. It looks more seriously damaged than the main body tube. I purchase the kit from Red Arrow Hobbies, so they would probably not give me a problem in replacing it. I'm just impatient and want to start building. The thought of waiting another week or so for another kit bums me, but since I won't be able to launch until winter in my area (no clearance above 1500 or F engine) I should probably just replace the kit.

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lizardqueen wrote:

You can reuse the creased payload section to reinforce the creased main tube, by slotting the PL-3.90 so it can conform to a smaller diameter. Here's how: Cut the PL all the way down the side. Collapse the PL enough so you can slide it into the main tube. Now expand it again as much as it will go against the inside of the main tube. Use a sharp pencil to mark where the cut edge of the PL overlaps itself on the inside. Remove the PL and cut it again, following the line you drew. This removes a thin slice from the side of the PL. Now close up the gap and it should slide nicely into the main tube. Epoxy it inside the main tube where it will overlap the crease.
Replacing the kit is certainly an option--Red Arrow Hobbies is a reliable shop. But the kind of repair I described is a useful technique you should get some practice doing. :-)
--
Steve Humphrey
(replace "spambait" with "merlinus" to respond directly to me)
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lizardqueen wrote:

All this talk about cobbling things together. Laura just paid good money for a kit. She should get her money's worth. Cobbling the damaged parts together are going to produce an over-weight, yet still damaged, kit. If I paid for a kit in good condition, I'd want a kit in good condition.
It's like buying a new car and getting in a wreck. All the insurance in the world, paid to the best repair shop in the world, and you are still driving a wrecked car yet paying for a new one.
Laura, get a new kit.
--
Visit Rocketry Planet - http://www.rocketryplanet.com

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Thanks for the input everyone. The idea of cutting the payload to strengthen the airframe is excellent, and I am sure that I will remember that tip in the future, but the more I discuss, the more I think I should just negotiate with the store for a new kit or replacement parts. I appreciate also the explanation of what the "stiffy" is. I wasn't sure if it was made differently, or of a different material. It didn't even occur to me that it might just be thicker. Darrell and Philip are correct, if I didn't ask for a proper replacement I would not be satisfied, and always wonder if it could have been better. Also, I'm sure I'll get to use Steve Humphrey's repair soon enough, but I hope not until the ezi has had a few good flights . :-)
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Exactly. Laura paid for an undamaged kit. Any decent vendor will replace either the kit or the parts with a problem.
Phil
On Sun, 03 Sep 2006 13:58:15 -0400, "Darrell D. Mobley"

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Call them up and complain and have them ship a new kit next day air. That way you won't have to wait a week.
KT
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Thanks everyone, I spoke to Red Arrow Hobbies and they were very nice. I did not ask for next day air, but I was told that a new airframe would be sent.
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Replacement airframe received in good condition and surprisingly quick. I can't ask for more than that! Can't wait to get started.
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Wow, that was quick.
~ Duane Phillips.

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I noticed the bulkhead had a similar defect which is slightly more obvious, but before I notice the airframe also had a problem I ordered a replacement bulkhead. Also, what do you all think of the phenolic tubes and the unfortunately named "Stiffy". This rocket will be used for L1 certification so I need it to be dependable and not to far from specs since I already ordered the 38/240 rms. Thanks, Laura
Laura As others have suggested a coupler can be used to reinforce the air frame as can the split piece of body tube. All would work well but add weight and this would have to be factored into the motor selection. A Stiffy Tube is just a thicker coupler that goes inside a standard coupler. I used them when I built a "clone " of a PML Endeavour with LOC parts. I built it "Anti-Zipper " per http://www.rocketryonline.com/modules.php?name=Guiki&MODE=SHOW&PAGE=Anti-Zipper%20Design or http://www.info-central.org/construction_antizipper.shtml These are the same article just in different locations. I did not use the baffle part of the design but I did use the U-bolt just placed it to the side of the MMT. I used a regular coupler and a stiffy tube to strengthen the coupler area and the motor mount tube ran through the coupler. I will try to post some pictures on alt.binaries.models.rockets. BTW Info central is a great place to find construction hints. Good Luck
--
William Richardson ENC USNR Ret.
TRA 8703 L2
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If your kit arrived crushed then return it.... you can reinforce it with another coupler but it adds weight. Another option is to peel the outside off and fiberglass it, but if this is your first time doing HPR then I dont recommend it because it adds to complexity. Unless you live outside of the USA (like me) where return shipping would make returns a hassle, go ahead and return it.
--
TAI FU
"lizardqueen" < snipped-for-privacy@gmail.com> wrote in message
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