[AR] Re: Intertank coupling design
- From: Paul Mueller <paul.mueller.iii@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Tue, 29 Oct 2013 13:18:45 -0600
Carl,
Wow, beautiful work! Did you heat-treat the tanks to T6 after welding or
were they strong enough as is?
Paul M
On Tue, Oct 29, 2013 at 10:26 AM, Carl Tedesco <ctedesco@xxxxxxxxxxxxxx>wrote:
> The end caps were hydro-formed from 1/8" thick 6061-T0 aluminum using a
> paint sprayer to generate the high pressure required to deform the domes.
> We were trying to make the ends as close to 2:1 elliptical domes, but in
> reality they came out as a spherical segment about 2" tall. We machined
> them to a perfect 8" diameter then butt welded them to the seamless 8"
> diameter tube. We then added an additional 4" section of the 8" tube to act
> as a tank skirt.
>
>
>
> Here's an inter-tank adapter with an access hatch:
>
>
> We routed all plumbing and electrical lines outside the tanks and made a
> fiberglass faring. Here are a few pics of the faring:
>
>
> https://www.facebook.com/photo.php?fbid=525688197501822&set=pb.287398957997415.-2207520000.1383063222.&type=3&theater
>
>
> https://www.facebook.com/photo.php?fbid=525689307501711&set=pb.287398957997415.-2207520000.1383063220.&type=3&theater
>
> --- Carl
>
>
> <https://www.facebook.com/photo.php?fbid=525689307501711&set=pb.287398957997415.-2207520000.1383063220.&type=3&theater>
>
> On 10/28/2013 7:39 PM, Robert Watzlavick wrote:
>
> Carl,
> Since your tanks were also part of the airframe, how did you handle the
> tank end caps? What was the shape and were they welded? Also, did you
> route cables and feedlines through the tanks or around the outside?
>
> -Bob
>
> On 10/25/2013 02:04 PM, Carl Tedesco wrote:
>
>
>
> Sent from my iPhone
>
> On Oct 24, 2013, at 8:47 PM, Robert Watzlavick <rocket@xxxxxxxxxxxxxx>
> wrote:
>
>
> Carl,
> Thanks for the info and link to Richard's page. I haven't decided on the
> exact coupler configuration yet so there's still room to improve the
> design. I assume one "caliber" means one diameter?
>
>
> Yes, one caliber = one diameter.
>
> I saw that on many other HPR websites where the construction materials
> were composites or fiberglass. Some of them even suggested two or three
> diameters. I can't believe that you would need a 5-10 inch long coupler to
> hold two 5 inch diameter tube sections together.
>
>
> In hindsight, they may be talking about the sections that separate for
> parachute deployment, since these sections usually have 2 to 4 nylon shear
> screws. The one caliber rule insures the section stays put during high
> speed flight.
>
> An airplane fuselage is many feet in diameter and they usually only
> have a single frame section with a few inches on either side. Of course
> there stringer section running the length of the airplane.
>
>
> Ours was about 2-3 inch long coupler for our 8-inch diameter airframe. If
> I do it this way again I would probably use two rows of fasteners offset;
> still the same number of fasteners.
>
> I can envision alignment issues though, especially if the ends aren't
> completely round and the fastener holes aren't drilled perfectly square to
> the ends. I was hoping to mitigate some of that by making the coupler a
> bit thicker than needed so it wouldn't deform as everything is bolted
> together.
>
> Was your fuselage skin also the pressure tank?
>
>
> Yes, the pressurized tanks were also the airframe.
>
> ---Carl
>
>
> I had to go with 16 #10-32 screws on the 5 inch diameter to keep from
> exceeding the bearing allowable stress on the skin. With a conservative
> 2.0 factor of safety, the tank end caps have to withstand around 18000 lbf
> each (which works out to about 1100 lbf per #10 fastener in shear).
>
> -Bob
>
> On 10/23/2013 02:17 PM, Carl Tedesco wrote:
>
> Bob,
> Just getting to this post...
>
> Here are some comments on the couplers on our SDSU
> rocket<http://eon.sdsu.edu/%7Erocket/>
> :
>
>
> 1. Our SDSU rocket was 8" diameter, 0.072" wall.
> 2. The coupler was made from the same tube; we slit the tube
> longitudinally to remove enough so that it could be fit into the original
> 8" tubing.
> 3. We riveted the coupling to the airframe/tank tube for sections that
> we did not intend to seperate.
> 4. For sections we wanted to separate we used twenty (20) 8-32 screws.
> We had a few screws strip in the thin 0.072" wall, so your method with
> inserts is appealing.
> 5. Our big problem was alignment of airframe sections, which many on
> this list gave some good tips.
> 6. Picture of our inter tank adapter
> here<http://4.bp.blogspot.com/-y9c5oqkLSw4/URW_PgeNrnI/AAAAAAAAAFc/Wpq8c8LMobA/s320/Rocket+project+1.jpg>
> 7. An HPR guy once told me to make the coupler insertion length at
> least one caliber. We did not follow that advice and hence could have
> contributed to our alignment issues given the tolerances of our "rolled"
> couplers.
>
> Why could you not use your "inner sleeve" as the coupling tube? Seems like
> one extra part.
>
> Richard Nakka has a nice little webpage on calculating loads on your
> airframe here <http://www.nakka-rocketry.net/fusestru.html>. It doesn't
> address loads at if your rocket has any angle-of-attack, but it's still a
> nice guide.
>
> --- Carl
>
>
>
> --
> Carl Tedesco
> Flometrics, Inc.
> 5900 Sea Lion Place, Suite 150
> Carlsbad, CA 92010
> tel: 760-476-2770 ext. 515
> fax: 760-476-2763ctedesco@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
>
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