[roc-chat] Re: High Alt, Multi-staging, and Balloon Structure

  • From: Allen H Farrington <allen.farrington@xxxxxx>
  • To: roc-chat@xxxxxxxxxxxxx
  • Date: Sun, 24 Jun 2012 20:54:48 -0700

Well, first of all, to really do a balloon tank, it has to always be 
pressurized "think the Estes Dude rocket". The mass you save by making it work 
under 1 G only rather than under 10 Gs isn't much.

As for the end-caps, in order to make them withstand the pressure, you can use 
flat ones but the extra mass in them and their epoxy attachments will probably 
outweigh the mass savings in the sidewalls.

For a L3 rocket, I would recommend NOT doing something like a balloon tank. Pro 
rockets don't use them much any longer since they're not especially efficient  
with newer metal alloys (except for the legacy Centaur upper stage). Some 
rockets like the Falcon 9 use monocoque tanks for the LOX, but I'm not sure 
that they're technically balloons..

You're going to have enough new stuff to deal with so I recommend purchasing 
the tubing. You can certainly use a cardboard tube as a mandrel for making a 
fiberglass or CF tube (there are YouTube videos on how to do this, but 
basically you layup the tube and then soak it in a pool for a day or so to pull 
out the cardboard) but it's so easy to purchase these types of tubes. In fact, 
Public Missiles has some 6" tubing that's only about 38g per inch. Very light. 
I've used their 3" carbon tubing and while pricy, it can withstand a LOT of Gs. 
Like crashing nose-first into the playa nearly under power...don't ask me how I 
know this ;-0

Well, my 2 cents...for what it's worth.

Allen
--------------------------------------------------------------------
Allen H. Farrington
818-653-2284
web: http://www.allenfarrington.org

On Jun 24, 2012, at 4:25 PM, Richard Dierking wrote:

> So flatwall ends will not work (i.e. they must be domed)?  Would they create 
> too much stress at the attachment point to the sidewall?
>  
> Please tell me more about this Allen.
>  
> Thank you,
> Richard
> On Sun, Jun 24, 2012 at 3:14 PM, Allen Farrington <allen.farrington@xxxxxx> 
> wrote:
> The hard thing about the balloon isn't the sidewalls but the domes at the 
> ends. Without them, you don't save any mass.
> 
> Allen
> Terseness and mis-spelling courtesy of my iPhone
> 
> On Jun 24, 2012, at 11:05 AM, Richard Dierking <richard.dierking@xxxxxxxxx> 
> wrote:
> 
>> Thank you Jack and Kurt for the great info on the waiver. 
>>  
>> Regarding Kurt's first question, good point.  But, I like to take risk 
>> trying new stuff.  As usual, I will test along the way.  I'm thinking a 
>> level 3 project with properly weighted upper "stages" to simulate the stress 
>> on the booster.  Kramer knows a lot about airframe design, so I'm 
>> considering ribs and stringers.  Dang, it would be cool to try the balloon 
>> structure. 
>> Again, has anyone heard about someone trying this before?
>>  
>> Richard
>> On Sun, Jun 24, 2012 at 10:50 AM, Kurt Gugisberg <kurtgug@xxxxxxxxxxxxx> 
>> wrote:
>> I guess you can save a little weight going with a thin pressurized airframe, 
>> but is it worth the cost to experiment with such an unknown factor 
>> considering that it might collapse under the weight of the upper stage 
>> and/or the strap-ons?    
>> 
>> Also, I don't think there is any problem with the FAA in flying something 
>> like you are talking about.  You do have to submit your plans to have them 
>> approved (at least with Aeropac) if you are going over 25K.
>> 
>> Kurt
>> -----Original Message----- 
>> From: Mike & Nancy Kramer 
>> Sent: Jun 24, 2012 10:40 AM 
>> To: roc-chat@xxxxxxxxxxxxx 
>> Cc: Richard Dierking 
>> Subject: [roc-chat] Re: High Alt, Multi-staging, and Balloon Structure 
>> 
>> For the airframe,
>> 
>> Yes there is there is thin carbon fiber cloth.  4oz cloth will be around 
>> .006 inch thick with a wet layup, 8 oz will be around .012 thick with a good 
>> wet layup.  One thing to think about is having a thin ply on each side of 
>> the paper / cardboard to make a sandwich structure.  Takes some practice but 
>> good solid structure.
>> 
>> balloon construction, are you talking about a pressure stabilized tube?  If 
>> so, by using VERY light ribs and stringers I think you can get a much more 
>> reliable lightweight structure.
>> 
>> Mike kramer  
>> 
>> On 6/24/2012 10:22 AM, Richard Dierking wrote:
>>> I got the high-alt bug at BALLS last year.  I saw some multi-stage projects 
>>> attempt to reach high-alt, and they all didn't seem to do too well.  For 
>>> one thing, I think it's difficult to design/build a stable N to M to M kind 
>>> of rocket.  So, many people just build the P, Q, whatever large single 
>>> stage         rocket or reduce the number of stages to two.  I have ideas 
>>> about a 3 stage rocket with strap-ons for the initial boost, and even have 
>>> done some experimenting, but need some advice.
>>>  
>>> First, are there specific FAA restrictions on launching high altitude 
>>> multistage rockets?
>>>  
>>> Again, I'm not planning minimum diameter, which I understand has some great 
>>> advantages.  But, the method for the strap-ons requires some attachment 
>>> depth.  Additionally, I like the idea of having some through-the-wall fin 
>>> attachment.  So, I plan on using 6" tube with 98 mm mount, and 4" strap-ons 
>>> with 75 mm mount.
>>>  
>>> To reduce weight on the first stage, I'm thinking about thin fiberglass 
>>> over paper tube (I would like to use carbon fiber, but honestly, have no 
>>> experience with this).  Then, stripping the layers of paper out from the 
>>> inside of the tube, adding the motor mount, and being able to pressurize 
>>> the inside to 5 to 10 psi (over ambient of course) for a strong balloon 
>>> structure.  Has anyone ever done this for a amateur-type rocket?  Is there 
>>> even such a thing as thin carbon fiber cloth?
>>>  
>>> I would like to try the 1st stage core with balloon structure for my L3 
>>> project.  Is this too weird? 
>>>  
>>> I've messed around with modifying aquarium check valves and I think I can 
>>> build a very simple and light pressure regulator to prevent over-pressure 
>>> of the airframe.  Strength must be maintained, and it must be very robust 
>>> during launch, because I'm also planning on using 3 or 4 strap-ons attached 
>>> to the centering rings of the airframe..
>>>  
>>> Richard Dierking
>>> Level 2
>>> TRA 11366
>>> NAR 84983
>> 
>> 
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>> 
>

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