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

  • From: Richard Dierking <richard.dierking@xxxxxxxxx>
  • To: "roc-chat@xxxxxxxxxxxxx" <roc-chat@xxxxxxxxxxxxx>
  • Date: Mon, 25 Jun 2012 08:52:42 -0700

Yes, not exactly the same as what I was considering - but still interesting.
Richard

Sent from my iPhone

On Jun 25, 2012, at 2:39 AM, Rick Maschek <rickmaschek@xxxxxxxxxxx> wrote:

> 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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