Rocket tube assembly

[merouane]

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

 

[tim cubbedge]

What is the diameter? Many people use push-in plastic rivets but have also seen them screwed using a backing plate.

 

[Titan II]

I use screws all the time. Drill and tap the tubes. Screw size typically depends on tube size. Sometimes I epoxy t-nuts or tapped hard wood to the inner tube.

 

[Banzai88]

Mostly for fiberglass I've used PEM nuts and 2-56 or 4-40 screws/washers. Never had a single issue. The key is getting the correct drill bit for the PEM nut installation and the correct drill bit for a 'close fit' of the chosen fastener.

 

[merouane]

the diameter is about 6 inches we were thinking to screw them directly to the couplers with selftapping screws but never thought of drilling and tapping the fiberglass tubes but the pem nuts are interesting first time to hear about them can you tell the maximum mach number of your rockets and maybe show some pictures of because the vibration due to the supersonic speed is what concerns us and also I have a team to convince so pics would really help thank you so much

 

[neil_w]

Friendly suggestion: divide your text into sentences, it will make it much easier to read than one giant run-on.

 

[watheyak]

What vibration? You're worried about a problem that doesn't exist.

 

[TheBru]

the diameter is about 6 inches we were thinking to screw them directly to the couplers with selftapping screws but never thought of drilling and tapping the fiberglass tubes but the pem nuts are interesting first time to hear about them can you tell the maximum mach number of your rockets and maybe show some pictures of because the vibration due to the supersonic speed is what concerns us and also I have a team to convince so pics would really help thank you so much

The vibration I think you are referring to is just normal stresses on the airframe of a "thing" going very fast. In a fighter jet, according to my dad, the ride is the worst right before you break the sound barrier and then things get super smooth. The difference in model rocketry is that the motors we use can be very high thrust and will get a rocket from 0 to mach in no time flat (relatively speaking), vs a plane that needs to really work up to it. The G forces associated with that acceleration tend to be the concern, from what Ive seen, and that tends to be the determining factor to how you build your rocket and what you build it out of, not so much the vibration that could be associated with aerodynamic forces acting on the object as it travels.

The great news for you is that model rocketeers have been going mach 2+ for a bit now and you can purchase off the shelf kits that will allow you to do just that. Many fliers use removable rivets and screws to hold the airframe together when it needs to be removable and if it doesn't need to be removed, epoxy it in place. For me, the first question is always, do I actually need to remove this at a later date?

Where the joint is in the airframe can also help to determine what to use. If it is going to be a section that experiences high pressure during ejection then you will want a strong item such as a screw to hold it in place or you will want to do an ejection test to ensure your rivets will hold, but again, this all assumes it has to be removed.

Can I ask what parts you are looking to hold together with screws? Is there a reason that it can't or shouldn't be permanently affixed in place?

 

[Nytrunner]

screw them directly to the couplers with selftapping screws

Self tapping screws could chew up the fiberglass walls. Drilling and tapping for machine screws should be a much cleaner installation. (or using PEM nuts or rivets)
Regardless, use a tube or something on the isnide of the tube when drilling so that the inner wall is supported. That should help prevent tear out or stripping of the inner wall fibers as you break through with the drill bit.

 

[thzero]

I've been using PEM nuts on both fiberglass and carboard builds. But yeah, I've pretty much dedicated a coupler per tube size to drill duty; certainly helps with minimizing tear outs.

 

[JoePfeiffer]

First, some advice you didn't ask for: find a mentor. You really need someone you can go to, one-on-one, to ask questions and get advice. For success, you really need someone with experience with this size of rocket to turn to for help. I'm guessing you're not in the US so you'll have to communicate by email and virtually which isn't ideal, but is better than nothing. It's my understanding (so I haven't re-verified this since seeing your post) the Cup is actually requiring all teams to have an L3 certified mentor this year; whether this is actually a requirement or not reach out to the organizers to see if they can help you find someone. Unfortunately, I'm not eligible since I'm only an L2.

As for your actual question, it sounds like you aren't talking about the removable parts of your rocket but rather assembly of things like attaching fins. For this, use epoxy and where appropriate (like fin fillets) use thickened and/or glass reinforced epoxy. These are things your mentor will be able to give you concrete help with.

 

[prfesser]

I fully agree with JoePfeiffer's post but will add just two words: even if you have to communicate electronically, a mentor "... is much, much better than nothing." There are essential details which can be provided by a good mentor. Example: fiberglass may have a thin film of release material or something else when it comes from the dealer. Wash thoroughly with soap and water, and rinse well and dry before using. There are other important points that a mentor can share with you.

 

[merouane]

Friendly suggestion: divide your text into sentences, it will make it much easier to read than one giant run-on.

yeah hhh well sorry for that my first post ever in any forum

The vibration I think you are referring to is just normal stresses on the airframe of a "thing" going very fast. In a fighter jet, according to my dad, the ride is the worst right before you break the sound barrier and then things get super smooth. The difference in model rocketry is that the motors we use can be very high thrust and will get a rocket from 0 to mach in no time flat (relatively speaking), vs a plane that needs to really work up to it. The G forces associated with that acceleration tend to be the concern, from what Ive seen, and that tends to be the determining factor to how you build your rocket and what you build it out of, not so much the vibration that could be associated with aerodynamic forces acting on the object as it travels.

The great news for you is that model rocketeers have been going mach 2+ for a bit now and you can purchase off the shelf kits that will allow you to do just that. Many fliers use removable rivets and screws to hold the airframe together when it needs to be removable and if it doesn't need to be removed, epoxy it in place. For me, the first question is always, do I actually need to remove this at a later date?

Where the joint is in the airframe can also help to determine what to use. If it is going to be a section that experiences high pressure during ejection then you will want a strong item such as a screw to hold it in place or you will want to do an ejection test to ensure your rivets will hold, but again, this all assumes it has to be removed.

Can I ask what parts you are looking to hold together with screws? Is there a reason that it can't or shouldn't be permanently affixed in place?

well this is a really valuable information about the smoothness of the ride after breaking the sound barrier this could be a game changer of information thanks a lot.

we are aware of the G forces that comes from the high acceleration and we simulated the inner parts and the body with the cone to see if they can handle the load and it did

First, some advice you didn't ask for: find a mentor. You really need someone you can go to, one-on-one, to ask questions and get advice. For success, you really need someone with experience with this size of rocket to turn to for help. I'm guessing you're not in the US so you'll have to communicate by email and virtually which isn't ideal, but is better than nothing. It's my understanding (so I haven't re-verified this since seeing your post) the Cup is actually requiring all teams to have an L3 certified mentor this year; whether this is actually a requirement or not reach out to the organizers to see if they can help you find someone. Unfortunately, I'm not eligible since I'm only an L2.

As for your actual question, it sounds like you aren't talking about the removable parts of your rocket but rather assembly of things like attaching fins. For this, use epoxy and where appropriate (like fin fillets) use thickened and/or glass reinforced epoxy. These are things your mentor will be able to give you concrete help with.

we know that we need a mentor with a level 3 certification and his help is indispensable but we didn't know how to find one we searched the internet and couldn't find a list of available L3 certified personel if you could provide one or give us some hints it will be amazing and much appreciated but even if we don't find a mentor the competition organizers will be our mentors and we will work with them remotly but it is less ideal situation.

I fully agree with JoePfeiffer's post but will add just two words: even if you have to communicate electronically, a mentor "... is much, much better than nothing." There are essential details which can be provided by a good mentor. Example: fiberglass may have a thin film of release material or something else when it comes from the dealer. Wash thoroughly with soap and water, and rinse well and dry before using. There are other important points that a mentor can share with you.

are you talking about the tubes or the tissue? because we roll our own tubes from fiberglass tissue.

PS : we are using glass reinforced epoxy

Thanks for all the support you are giving it is much appreciated

 

[prfesser]

are you talking about the tubes or the tissue? because we roll our own tubes from fiberglass tissue.

PS : we are using glass reinforced epoxy

Sorry about that, I meant fiberglass tubes, fins, etc. need to be washed.

I hadn't heard of fiberglass tissue before. My understanding (correct me if I'm wrong) is that the thicker fiberglass mat is to be used only with polyester resin and not epoxies. The mat has a coating that is dissolved in polyester resin (my guess is by the styrene that's in the resin and gives uncured resin a strong smell). The coating prevents epoxy from sticking well to the glass. Fiberglass cloth does not have that coating.

Best -- Terry

 

[watheyak]

well this is a really valuable information about the smoothness of the ride after breaking the sound barrier this could be a game changer of information thanks a lot.

This notion of vibrations approaching the speed of sound is a myth. Perhaps this is alluding to stability issues on early supersonic aircraft, but it's certainly not something that happens today. The only way you know you're supersonic or not is by looking at your airspeed indicator.

In a rocket a sparky motor might induce some vibration, but other than that I can't imagine why there would be any vibration during flight.

 

[JoePfeiffer]

we know that we need a mentor with a level 3 certification and his help is indispensable but we didn't know how to find one we searched the internet and couldn't find a list of available L3 certified personel if you could provide one or give us some hints it will be amazing and much appreciated but even if we don't find a mentor the competition organizers will be our mentors and we will work with them remotly but it is less ideal situation.

As I understand it, it won't just be a matter of the organizers trying to help you, they'll be assigning you someone if you haven't been able to find one yourself. I'm guessing you're not in the US -- if you are, say where and there's a good chance someone on here will step up and help you. It's unfortunate that the laws in many countries make it very difficult to pursue hobby rocketry at all, let alone high power.

are you talking about the tubes or the tissue? because we roll our own tubes from fiberglass tissue.

PS : we are using glass reinforced epoxy

I strongly recommend you buy commercial airframe components rather than trying to roll your own, particularly if you don't have someone *really* experienced helping you.

Ah, something else -- I assume you're checking the forums on HeroX for information. There's one in particular addressing support for International teams: https://www.herox.com/SpaceportAmericaCup2021/forum/section/73#scroll-to-paginator

 

[cbwho]

yeah hhh well sorry for that my first post ever in any forum

Well, you are not sorry as you are still not using periods.

I usually frown on grammarians but seriously, your lack of punctuation makes for annoying reading. Punctuation was invented for a reason about a thousand years ago. I highly suggest you brush up on it. We are not looking for perfection so meet us halfway.

P.S. Most people get annoyed with liars.

 

[Ez2cDave]

I was "curious" . . .

https://spaceportamericacup.com

https://www.soundingrocket.org/sa-cup-home.html

Dave F.

 

[Nytrunner]

 

[Zeus-cat]

One thing I tell engineering students that they rarely want to hear, learn how to speak and write effectively. You can be the best engineer in the world, but if you can't talk/write so that your boss understands what you are trying to say, your prospects are very limited. In my opinion, it is better to be an average engineer who knows how to communicate, than a brilliant engineer who can't write a coherent sentence.

 

[JoePfeiffer]

https://spaceportamericacup.com

https://www.soundingrocket.org/sa-cup-home.html

Also https://www.herox.com/SpaceportAmericaCup2021

 

[cbwho]

Perhaps the original poster's lack of punctuation is in protest of Aristophanes as he is a strident supporter of Cicero?

One thing that 2020 has shown, notions that we thought were settled science are being rebuked as conspiracies. Perhaps he wants to fire a rocket high enough to see the "edge of the Earth" and peek at the great tortoise?

 

[Ez2cDave]

One thing that 2020 has shown, notions that we thought were settled science are being rebuked as conspiracies.

The problem has arisen from "unsettled" "science" being widely promoted as "settled science", for various motivations.

Dave F.

 

[cbwho]

The problem has arisen from "unsettled" "science" being widely promoted as "settled science", for various motivations.

Dave F.

Mmm... I don't think that's it...

 

[REK]

What vibration? You're worried about a problem that doesn't exist.

I second this, I have used plastic rivets at mach speed with no issues.

 

[merouane]

I really apologize for taking so long to respond to this, also sorry for not using proper punctuation and I appreciate every piece of advise that you guys have given me, even the ones that are not related to the subject of this thread I, really do apreciate it.

as for the forum threads on herox website, yes I am aware of them and I know that they will provide us with a mentor, but it's going to be better if we manage to find one, since the mentors provided by spaceport will mentor us and also, they will have to run the competition so it is better for both of us to find a mentor on our own.

for the last threads, talking about my lack of punctuation and aristophanes.... well I didn't understand a word from what you said but no hard feelings I am writing this with a big smile on my face.

you have been an incredible help to me and I really appreciate it, and if you need my help PM me and I will respond, I study aeronautics and I have a good knowledge with cad modeling with solidworks and fusion360 ans well as cnc machining, don't hesitate to ask me about anything related to those topics, Thanks.

 

[gldknght]

This notion of vibrations approaching the speed of sound is a myth. Perhaps this is alluding to stability issues on early supersonic aircraft, but it's certainly not something that happens today. The only way you know you're supersonic or not is by looking at your airspeed indicator.

In a rocket a sparky motor might induce some vibration, but other than that I can't imagine why there would be any vibration during flight.

Actually that is NOT a myth. It's called "compressibility." It's shock waves moving along an air frame at trans-sonic speeds. Shock waves cause vibration. It is the reason supersonic aircraft no longer have hinged elevators on the horizontal stabilizers at the back of the fuselage. But the trans-sonic shock waves are still present.

 

[watheyak]

Actually that is NOT a myth. It's called "compressibility." It's shock waves moving along an air frame at trans-sonic speeds. Shock waves cause vibration. It is the reason supersonic aircraft no longer have hinged elevators on the horizontal stabilizers at the back of the fuselage. But the trans-sonic shock waves are still present.

Really.

You've experienced these vibrations?

Also the reason there are no longer hinged elevators on supersonic aircraft has nothing to do with "vibrations".

 

[gldknght]

Really.

You've experienced these vibrations?

Also the reason there are no longer hinged elevators on supersonic aircraft has nothing to do with "vibrations".

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.

 

[gldknght]

Really.

You've experienced these vibrations?

Also the reason there are no longer hinged elevators on supersonic aircraft has nothing to do with "vibrations".

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.