[AR] Re: Intertank coupling design
- From: Paul Mueller <paul.mueller.iii@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Tue, 29 Oct 2013 16:06:40 -0600
Ahh, very helpful, Ben. And as long as we're on the subject, I assume you
(Carl) used T0 temper for the pieces to be hydroformed to make the process
doable with lower pressures, etc.--correct?
Paul M
On Tue, Oct 29, 2013 at 3:48 PM, Ben Brockert <wikkit@xxxxxxxxx> wrote:
> Bringing 6061 tanks up to T6 is a pain in the ass because it involves
> solution annealing, which requires getting the tank frighteningly close to
> melting and then quenching rapidly with water or a lot of cool gas. Doing
> it without collapsing or warping the tank requires careful setup and
> skilled operators. The tank can be straightened after the quench, but that
> requires another, possibly complex, setup.
>
> Instead, skipping the solution anneal and going straight to artificial
> aging can give you results of 6061-T5, without nearly as much hassle. It's
> an improvement of about 50% in tensile strength. It just requires an oven
> that the part can fit in, which for tanks those size could probably be done
> at a powder coating shop. There are a lot of different formulas for
> artificial aging, usually two heats of two to eighteen hours each, at
> temperatures between 300 and 400F. Higher temperatures take shorter times;
> normal aging would be to let the part sit at a warmish room temperature for
> a year or two.
>
> Still well short of the state of the art in 6000 series rocket tanks but a
> useful and achievable improvement over as-welded condition.
>
> Ben
>
> On Tue, Oct 29, 2013 at 2:56 PM, Carl Tedesco <ctedesco@xxxxxxxxxxxxxx>wrote:
>
>> No heat treating was performed. I would have liked to, but budget
>> wouldn't allow it. We did hydro test the complete welded tanks to 450 psi
>> for 5 complete pressurize/depressurize cycles (MEOP 350 psi).
>> --- Carl
>>
>>
>> On 10/29/2013 12:18 PM, Paul Mueller wrote:
>>
>> 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
>>>
>>>
>>>
>>>
>>> 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
>>>
>>>
>>
>> --
>> 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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