Rocket tube assembly

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watheyak

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You should do some actual research before you post. Or you can continue arguing with me and prove you have no idea what you're talking about.
My, you're awfully salty.

Ok I'm game.

It's clear you don't understand the issue with the elevator. Or maybe you do, and you're just not explaining it well? Regardless, not an issue with vibrations.

I guess that's the first step. Prove your understanding there, or I'm going to call it a win for me.
 

gldknght

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My, you're awfully salty.

Ok I'm game.

It's clear you don't understand the issue with the elevator. Or maybe you do, and you're just not explaining it well? Regardless, not an issue with vibrations.

I guess that's the first step. Prove your understanding there, or I'm going to call it a win for me.

I'm done with this stupidity. I don't have to prove anything to you and you can call it anything you like.
 

watheyak

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And, by the way, yes I have experienced trans-sonic vibrations. A while back when I was in the Air Guard doing maintenance on F-16s, I got an incentive ride in the back seat of an F-16D. As we approached mach 1, in that trans-sonic velocity range, I could REALLY feel how our speed was affecting the stability of the aircraft, bumping us around, causing... much more vibrations in the cockpit. Once we got about mach 1, the vibrations went away, and the ride was soo much smoother.
The only way you know you're going Mach 1 is by looking at the airspeed indicator. There is no "speed affecting stability". Especially on an F-16. I'm not saying you didn't do that, it sounds like an awesome opportunity. I'm just saying that's not what you were feeling.

I'm done with this stupidity. I don't have to prove anything to you and you can call it anything you like.
Wait, I thought you said I'd you were going to prove I have no idea what I'm talking about.
 
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mtnmanak

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While this thread has gone completely sideways, let's try to answer the OP's original question. Everyone needs to learn how to do these things the first time.

Drilling and tapping into an FG airframe is perfectly feasible, but it is not my preferred method for rockets using large motors. Eventually, the FG will wear out against the screws and they will become loose. You can keep reinforcing the hole, but I personally opt for PEM nuts - they provide a lot more long term stability.

Regardless of what kind of stress supersonic flights put on an airframe, I have flown a number of rockets above Mach 1 and have never had a PEM nut fail.

Feel free to get some pointers from any of the build threads I have or ask any questions - we all want you to succeed. In this thread I use a couple different kind of PEM nuts: https://www.rocketryforum.com/threads/darkstar-series-build.162848/

Here are some pics of the Lumadyne PEM nuts I used on my last build. These were 4-40 nuts/screws on a 3" frame. Good luck on your flights:

PXL_20201225_192515810.jpg


PXL_20201225_220343405.jpg


PXL_20201225_220241508.jpg
 

JimJarvis50

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Hi everyone,
I am a student and my team and I are participating in the spaceport america cup and we are using fiberglass tubes and we are concerned that if we screwed them or revitted them directly to the couplers that the vibration will chatter the fiberglass tubing and break the tubes so I want to know this senario is real and how were you assembling you rockets and by the way our rocket apogee is 10k feet and it reaches mach 1.3, thanks in advance for your precious help
I can show you how I do this. It won't win any high tech awards, but I have never had it fail (and I have tried). I use socket screws to attach things like altimeter bays to the air frame. The socket screw screws into a plywood bulkhead. The larger head of the socket screw distributes the force so that the air frame doesn't tear (like might happen with a smaller diameter screw shank). They are the easiest to make if you use a pilot-tip drill head to make the larger hole. That way, you have a centered hole for the smaller hole. I use lots of these connections around the rocket. Some examples are attached.

Jim
 

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MikeyDSlagle

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I've had zero success with PEM nuts, yes I have the correct drill but, but admittedly I may not be using them correctly. I usually use a piece of wood sanded to ID and a threaded insert.

Maybe I missed it but where are you? Tripoli is a worldwide organization with Prefectures sprinkled around the world. Maybe you'll get lucky and be close to one.
 

Evolvant

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I can show you how I do this. It won't win any high tech awards, but I have never had it fail (and I have tried). I use socket screws to attach things like altimeter bays to the air frame. The socket screw screws into a plywood bulkhead. The larger head of the socket screw distributes the force so that the air frame doesn't tear (like might happen with a smaller diameter screw shank). They are the easiest to make if you use a pilot-tip drill head to make the larger hole. That way, you have a centered hole for the smaller hole. I use lots of these connections around the rocket. Some examples are attached.

Jim
Jim,

Thanks as always for your willingness to share. :)

What size have you found gives the best result to "flush" for each size tube? What I mean is the head is flat and the OD of the body tube is round. When you screw it in I'm assuming you're trying to get it as "flush" as possible to the OD of the tube. Do you have a rule of thumb like 2-56 for 2.2", 4-40 up to 4", 6-32 up to 6"? Or something like that?

I've been working on something and have another idea I'd like to run by you. What about countersinking the holes and using flat head screws. I had planned on putting heat set inserters into the AV Bay, then using a flat head screw in a countersunk hole from the outside. If I do it right and size it right, the surface area of the countersink will carry the load. Better, worse, different? Thoughts on this?

Last question. Have you ever held on to a motor like this? Think some sort of ring the size of the ID of the tube that is bolted to the forward closure. You'd then screw from the outside into that threaded ring to hold the motor in place. This would hold the motor under thrust as well. If you have, how much thrust did you hold on to? What size screws? What was the airframe made of (CF, FG)?

Thank you!

Cheers,
Paul
 

JimJarvis50

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What size have you found gives the best result to "flush" for each size tube?

What about countersinking the holes and using flat head screws.

Last question. Have you ever held on to a motor like this?
I'm not exactly sure what the "number" is for the screws. For the ones that I use the most, the larger hole is cut with a 5/16 drill.

I'm not a big fan of countersinking a hole and using a flat-head screw. I think it weakens the area around the hole and exposes the tube to the smaller shaft of the screw.

I suspect the connection could be made strong enough for a motor, but I would not do it. Per the picture I posted, I use a single, typically 3/8" piece of all thread down the middle. That way, the rocket is connected with a system of either harnesses or all thread. This "central spine" concept holds everything together during recovery or "other" events. As a result of this, the connection holding the bay in place is somewhat less critical in the sense that the structure of the rocket doesn't depend on that connection. This would not be the case if the connection was used on a motor.

Jim
 

Evolvant

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Jim,

So let me ask a different question then. Note, I'm sure this is buried in the many detailed posts you've been so kind to share, but maybe we can focus in on it here.

In the case where you're holding on to the sustainer, in the IC, with the motor hanging out and no thrust ring (which I've read in a couple threads where you talk about this), how do you hold on to the motor in the sustainer? I know there are MD solutions like an aeropak MD for example. What if I want everything to come out?

Do you say, Don't do it, Paul. Come up with another way! Design around it.... lol.....

OR

Do you have some ways you've done this before that would work? Just friction fit with shock cord attached to forward closure, thus "captured". Always design a "glued in" thrust ring of some sort on top of the motor?
Think something like this https://www.badassrocketry.com/product-page/badass-md-retainer

As always, thank you!

Cheers,
Paul
 

JimJarvis50

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Jim,

So let me ask a different question then. Note, I'm sure this is buried in the many detailed posts you've been so kind to share, but maybe we can focus in on it here.

In the case where you're holding on to the sustainer, in the IC, with the motor hanging out and no thrust ring (which I've read in a couple threads where you talk about this), how do you hold on to the motor in the sustainer? I know there are MD solutions like an aeropak MD for example. What if I want everything to come out?

Do you say, Don't do it, Paul. Come up with another way! Design around it.... lol.....

OR

Do you have some ways you've done this before that would work? Just friction fit with shock cord attached to forward closure, thus "captured". Always design a "glued in" thrust ring of some sort on top of the motor?
Think something like this https://www.badassrocketry.com/product-page/badass-md-retainer

As always, thank you!

Cheers,
Paul
Most of my rockets are constructed with "zipperless" couplers. The motor is held in the fin can using all thread into the forward closure. Some pics will make this clear. There are many reasons to use zipperless couplers.

Jim
 

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Evolvant

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Most of my rockets are constructed with "zipperless" couplers. The motor is held in the fin can using all thread into the forward closure. Some pics will make this clear. There are many reasons to use zipperless couplers.

Jim
Do you always epoxy the coupler in the fin can or have you ever made it removeable by screwing into it from the out side of the BT?

Wouldn't design #4 on the drawings cause the cato the "no thrust ring" pic is suggesting?

Thank you,
Paul
 

JimJarvis50

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Do you always epoxy the coupler in the fin can or have you ever made it removeable by screwing into it from the out side of the BT?

Wouldn't design #4 on the drawings cause the cato the "no thrust ring" pic is suggesting?

Thank you,
Paul
I always glue in the coupler. If the fin can is to be used with a motor without a thrust ring, then I design the fin can for the motor I plan to use. On a few occasions, I have used a longer motor and had it extend further out of the bottom of the air frame. No problem doing this as long as the stability is OK.

I have discussed with others the approach of having a removable zipperless coupler, but for use with motors with a thrust ring. As I recall, this was in the context of the coupler holding electronics, where access would be helpful. I haven't done it myself.

Both #3 and #4 would require thrust rings. The drawing shows options for zipperless couplers, not options for zipperless couplers without thrust rings. Version #3 was intended to allow the use of zipperless couplers with longer or shorter motors. The thrust ring and the bolt on top of the zipperless coupler pull everything together. I've never done this either, but I have seen it done successfully.

Jim
 

Zeke Johnson

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Most of my rockets are constructed with "zipperless" couplers. The motor is held in the fin can using all thread into the forward closure. Some pics will make this clear. There are many reasons to use zipperless couplers.

Jim
Jim,

What type of metal are your all-thread rods made from?

Zeke
 
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