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

  • From: Rick Maschek <rickmaschek@xxxxxxxxxxx>
  • To: ROC-Chat <roc-chat@xxxxxxxxxxxxx>
  • Date: Mon, 25 Jun 2012 02:39:56 -0700

Hi Richard,
 
While slightly different, we are considering pre-pressurizing our motor (that 
also serves as our airframe) for sugar shot. Since sugar propellant can be 
brittle, one of the reasons for CATOs is the expansion of the grains when the 
motor lights due to the combustion pressure. APCP is more forgiving and usually 
doesn't crack when firing since the propellant has some stretch to it. To over 
come this problem, we have our grains 'free floating' in the motor case with 
the idea that the combustion pressure will act both from inside the core 
pushing out and from between the grains and motor casing pushing inward and 
thus equalizing the pressure on the propellant. Resent tests we have done with 
our six inch DoubleSShot motor indicates this cracking may be happening with as 
low a pressure differential as under 500 psi. If the combustion gases are not 
getting around the ends of the grain assembly quick enough it might be causing 
the grains to crack leading to our CATOs. Too large a gap and we loose 
propellant mass or the weight and drag of a larger airframe.
 
For us, the extra mass of a thick flat bulkhead isn't a problem since the 
bulkhead needs to be strong enough to contain the 1,000 psi combustion chamber 
pressure (our CATO occurred at ~2,000 psi). A possible solution we might be 
trying involves installing a Schrader like valve in the nozzle acting like a 
burst disk. We pump up the motor with approx 500 psi with the valve designed to 
'blow out' of the nozzle at say 700 psi. While this is different than what you 
are asking, the project I'm working on below is somewhat 'similar'.
http://sugarshot.org/downloads/dss_bps_data_curves.gif 
http://www.youtube.com/watch?v=NuxTAv71Xac 
 
I've been working on a $99 M-class motor/rocket combo. The case bonded motor 
will be standard 3" PVC pipe. To withstand the chamber pressure, this motor 
will be inserted into a pressurized 4" PVC pipe serving as the air frame. The 
space between the two will be pressurized to ~250 psi which means the inner pvc 
motor case will only see a net pressure of 250 psi if we run the combustion 
chamber at 500 psi. 
 
Not exactly what you are thinking about but it is pressurizing the rocket into 
a 'balloon'.
 
Rick

 



From: allen.farrington@xxxxxx
Subject: [roc-chat] Re: High Alt, Multi-staging, and Balloon Structure
Date: Sun, 24 Jun 2012 20:54:48 -0700
To: roc-chat@xxxxxxxxxxxxx

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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