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GameGamerABC

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Hello guys,
a little introduction: I am Nick, i build experimental rocket engine's and maybe rocket soon!
So after a lot of engine builds and tests, i got some nice working engine's. So it is time to go build a rocket powered by my own engine's!

So my question is: What do you guys think of the designs? How is the stability? I don't really understand that Cal.
And will this rocket fly on high G class and mid-low H class?

Thanks Nick van Gemert








IMG-20160718-WA0003.jpgIMG-20160718-WA0004.jpgIMG-20160718-WA0005.jpg
 

timbucktoo

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It looks like your stability is about 1.29 with no motors. Select a motor & see what you get. You want a stability of at least 1.0 with the motor loaded. 2.0 is preferred but anywhere in between 1-2 would work. Higher is better! Lot of opinions on stability!
 

K'Tesh

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A) Welcome to TRF

B) Please post the .ork so we can give it the once over.

Thanks!
 

K'Tesh

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Your aft Launch Lug is hanging off the back of the rocket.

Body tube and Launch Lugs seem a tad thick... Is the selection of the dimensions based on a actual measurements, or default?
 
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GameGamerABC

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Your aft Launch Lug is hanging off the back of the rocket.

Body tube and Launch Lugs seem a tad thick... Is the selection of the dimensions based on a actual measurements, or default?
Launch lugs are changed!
The walls suppost to be 2 mm thick But open rocket keeps changing it to 4 mm

Nick
 

KenECoyote

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It looks like your stability is about 1.29 with no motors. Select a motor & see what you get. You want a stability of at least 1.0 with the motor loaded. 2.0 is preferred but anywhere in between 1-2 would work. Higher is better! Lot of opinions on stability!
I see 5.29, which seems to match the CG CP marks...looks to be an overstable rocket as it is in the pic (without motor).
 

KenECoyote

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Also a "caliber" is equal to the width of the rocket body tube, so if the rocket is 1" wide and the stability is 2 calibers (=2.0), the CG is ahead of the CP by 2 body widths/2", which is stable and good. As Timbucktoo noted, you want between 1.0 and 2.0. Higher than 2.0 is okay; however the rocket may tend to weathercock more...which is still better than unstable.
 

neil_w

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Does it strike anyone else as weird to be making EX motors up into L1 range and then scratch building a rocket to hold them without understanding rocket stability? At this power level, might it not be more sensible to start with a kit if there is any doubt?

To be fair, I don't really know what the OPs level of knowledge is (and feel free to correct me if I'm reading this all wrong), but the first post in the thread really got me scratching my head.
 

Daddyisabar

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Does it strike anyone else as weird to be making EX motors up into L1 range and then scratch building a rocket to hold them without understanding rocket stability? At this power level, might it not be more sensible to start with a kit if there is any doubt?

To be fair, I don't really know what the OPs level of knowledge is (and feel free to correct me if I'm reading this all wrong), but the first post in the thread really got me scratching my head.
A lot of folks start out by watching YouTube. Best to get them good advice and hopefully to the safety of a club launch where you can learn to do it right and with much better results. Amazing how quick you will drop the internet junk when you see it done the right way.
 

K'Tesh

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Ok... More sleep in me. I'm currently living and working in China, and it was late when I first responded.

Like Neil and Daddy are saying, you probably should join a local (and national) club to get the help you need. I realize you didn't ask about building EX motors, but I'll save you the hassle. If you're going to build EX motors, Tripoli is where you'll need to go for being able to launch EX rockets if you want to get certified. Personally, I don't have any experience with EX motors. So, I'm no help there. EX stuff is safely tucked away inside the Restricted Research sub-forum, which I also don't have access to (I like keeping all my appendages right where God put them... Well, at least what I still have left of them). Ex motors are not supported in the general areas of the forum, and you likely won't find anyone who would help you with those kinds of questions here.

About building rockets, that we can help you with.

Your body tube/motor tubes are 2mm thick. However, for a standard (read commercial) 54mm motor, your diameter is too small (I have it as 50mm OD). Your tube couplers/nosecone's sholder are a tad too short (most people want at least 1/2 caliber of overlap (personally, I'm more in favor of 3/4 to 1 caliber)).

You can change one of your fins to freeform, setting the number of fins to 4, then delete the additional trapizoidal fins.

Rail Buttons are generally considered better than LL's when you're getting into HPR. Launch rods can whip, causing all kinds of bad things, Rails are much stiffer (and I believe that the buttons have less drag).

What kind of method of motor retainer are you thinking of? Tape?
 

jqavins

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It looks like your stability is about [5.29] with no motors. Select a motor & see what you get. You want a stability of at least 1.0 with the motor loaded. 2.0 is preferred but anywhere in between 1-2 would work. Higher is better! Lot of opinions on stability!
This was probably clear already, but I'm just making sure. Even though Tim misread what was on the screen, the key point here is that you need to have 1 to
2 calibers with the motor installed. You need to weigh your motor and measure its CG if it's not a commercial one, and install it in your design, then check that stability margin, otherwise it means nothing. And incidentally, the design does look pretty much OK, but understand that I have not opened the ORK file.

A lot of folks start out by watching YouTube. Best to get them good advice and hopefully to the safety of a club launch where you can learn to do it right and with much better results. Amazing how quick you will drop the internet junk when you see it done the right way.
Wait, isn't this the internet?
 

GameGamerABC

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Ok... More sleep in me. I'm currently living and working in China, and it was late when I first responded.

Like Neil and Daddy are saying, you probably should join a local (and national) club to get the help you need. I realize you didn't ask about building EX motors, but I'll save you the hassle. If you're going to build EX motors, Tripoli is where you'll need to go for being able to launch EX rockets if you want to get certified. Personally, I don't have any experience with EX motors. So, I'm no help there. EX stuff is safely tucked away inside the Restricted Research sub-forum, which I also don't have access to (I like keeping all my appendages right where God put them... Well, at least what I still have left of them). Ex motors are not supported in the general areas of the forum, and you likely won't find anyone who would help you with those kinds of questions here.

About building rockets, that we can help you with.

Your body tube/motor tubes are 2mm thick. However, for a standard (read commercial) 54mm motor, your diameter is too small (I have it as 50mm OD). Your tube couplers/nosecone's sholder are a tad too short (most people want at least 1/2 caliber of overlap (personally, I'm more in favor of 3/4 to 1 caliber)).

You can change one of your fins to freeform, setting the number of fins to 4, then delete the additional trapizoidal fins.

Rail Buttons are generally considered better than LL's when you're getting into HPR. Launch rods can whip, causing all kinds of bad things, Rails are much stiffer (and I believe that the buttons have less drag).

What kind of method of motor retainer are you thinking of? Tape?

Okay, to make somethings clear. I already build and tested successful ex rocket engine's.
I have considered that a H class is to high to begin with. It wil be a G class rocket engine.
I also gonna join a rocket club for experimental rocketry. unfortunately there are not many out here in the Netherlands. But i found one. http://www.navro.nl/en/

About rail buttons. I am going to use them, but i cant find them in open rocket. My ex rocket engine will just fit in there. So i don't need centering rings. There will be a bulkhead with screws to prevent the engine from going up.
I am still thinking about how to keep the engine in while waiting on the launchpad. Maybe you guys have a idea.
I also changed some thing in the design, I'll send the new one's now to. The wight component you see is the weight of the engine. But if all the fuel is burned the stability will change a lot. The weight off the motor is 480 grams with about 243 grams of fuel.

Nick van Gemert

View attachment Rocket design No Name yet (Future).ork
 
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Daddyisabar

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...Wait, isn't this the internet?
TRF is pure, wholesome, high end internet. The Youtube "Here, hold my beer" stuff is simply junk. Once you dabble among the enlightened, rocket science oriented TRF members, you never need to go back to the gutter that is Youtube " make yer own motors and rockets" trash.:)
 

K'Tesh

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So, this is a minimum diameter (MD) rocket, with a nonstandard size motor casing. Good to know, just wanted to make sure about that.

Rocket Design No Name Yet.jpg

Standard Rail buttons are 3/8" OD, and 3/8" tall, I substitute launch lugs of those dimension (with an inner diameter of 0) in their places.

Tape is frequently used motor retention. A wrap or two of tape around the outside of the motor and you friction fit it inside your rocket. I've heard of some people using it for HPR, but I have no experience with it myself (outside of LPR).

I'm still a little uncertain about your bulkheads/shoulder lengths... Again, most people want at least 1/2 caliber or more of shoulder to prevent a shred (or drag separation).

Here's a link to my .ork files showing how Binder Design does their payload bays:

http://www.rocketryforum.com/showthread.php?123564-K-Tesh-s-OpenRocket-files&p=1595279#post1595279

 
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jqavins

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TRF is pure, wholesome, high end internet. The Youtube "Here, hold my beer" stuff is simply junk. Once you dabble among the enlightened, rocket science oriented TRF members, you never need to go back to the gutter that is Youtube " make yer own motors and rockets" trash.:)
Yeah, I do understand the difference, but don't tar the whole internet with a single brush. It's even possible to find quality advice on YouTube, though a beginner might have some trouble knowing the difference; the actual words "Hold my beer" are a pretty good indicator. And it's also possible to find bad advice here on TRF, but I like to think it's even rarer than good advice on YouTube.
 

GameGamerABC

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I'm still a little uncertain about your bulkheads/shoulder lengths... Again, most people want at least 1/2 caliber or more of shoulder to prevent a shred (or drag separation).

Here's a link to my .ork files showing how Binder Design does their payload bays:

http://www.rocketryforum.com/showthread.php?123564-K-Tesh-s-OpenRocket-files&p=1595279#post1595279

I feel pretty bad not understanding that a 100 % :confused2:
So can you expain it a little bit. You mean with drag separation something like this but than all the way off. It is the first Orange rocket https://m.youtube.com/watch?list=WL&v=cLI9SI3KjHs
 

K'Tesh

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[EDIT] I just watched the video... Right around the 1:30 mark, you can see the forward section try and separate. If they had a short shoulder it would have been quite a problem. It also could have been caused by a lack of venting... As the altitude increases, the air inside expands if it's not vented, and that can also push the rocket apart.

If your rocket is designed to break in the middle for parachute deployment, you need a tube coupler that is firmly attached to one portion of the body tube, and can slip inside the other body tube. If your rocket is designed to pop the nosecone, again, you need a shoulder that can mate the nosecone to the body tube. When a rocket is launched, everything is compressed together, and that's fine, as long as you don't exceed the strength of the materials. However, once the rocket begins to coast, Things with mass like to move forward. Here's an analogy... Imagine you're a passenger in a car, the driver really hits the gas hard, you're compressed into the seat. Once they let off the gas, your body wants to move away from the seat, and the seatbelt is there to catch you. If there's too little tension in the belt, you hit the windscreen. Now, back to the rocket. When the rocket decelerates, the mass objects (your altimeter, your GPS, etc) want to move forward. However, aerodynamic drag, causes the aft section to slow down faster... Too little of a shoulder, and the aft section separates from the forward components, the aft section drastically decelerates due to the increased drag of the now non-aerodynamic front edge (maybe even the parachute deploys), the forward section is still aerodynamic and traveling fast. If the shock cord isn't long enough, or the mounts aren't strong enough, the rocket will tear itself apart (or the parachute may tear open), resulting is a less than desireable return.

Also, if the overlap (shoulder) is short, and there's any kind of play between the forward section and the aft section, the rocket may buckle, causing it to tear itself apart. A longer shoulder helps reduce the likelihood of this happening.

The AV bay I linked to above is sealed from above and below, preventing the electronics from being damaged, and giving you firm mounts to attach your recovery devices.

Rocket Design No Name yet (Future)(mod).jpg

I moved the LLs (and converted them to my interpretation of "rail buttons") to centered between fin, as rails may have a problem fitting between fins and rail buttons.
 

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GameGamerABC

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Okay thanks,
I agree with your changes exept the payload bay. It already was easy to get it out. The bulkheads in the electronics bay where couplers also. And because i will have nose cone seperation. The couplers/bulkheads will e hold in place by screws.

But i understand the change at the nose.
So if i build it like this, exept the payload bay. This should work? And fly stabel

(Wrote this on my telefone )

Thanks
 
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GameGamerABC

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I have on more question.

My stability is around 1.5 caliber with full engine with fuel.
But is the fuel is burned is my stability around 3- 3.5 caliber.
Will i get problems with this?
 

mkadams001

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I vote this thread as the most helpful to someone who seems to be doing it bass-ackwards.
 
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