[SS-VehDev] Re: composite short stack/instrumentation section

[william colburn]

Yes, it is an excellent way to go for piping. For our
use it would add diameter, not a great thing because
of the increase in drag. I suppose with some custom
made parts, the diameter increase could be minimized.

Bill Colburn

--- Lakestake Rocketry <lakestake at gmail.com> wrote:

> Hi Bob,
> 
> For the tapered joint: would it then use cement to
> hold the
> two tapers together?
> 
> Matt
> 
> On 10/13/05, william colburn
> <space1space at sbcglobal.net> wrote:
> >
> > Excellent, all.
> >
> > A prime requirement and one that is not trivial is
> the
> > ability to attach successfully with the same
> safety
> > factor to the ends for closures. That is why I
> > suggested a 40 inch length for the test piece. It
> can
> > be hydrotested and then used, if we wish, for the
> > short stack burn.
> >
> > Generally a single simple bolt circle is not going
> to
> > do the job. Here are some solutions that have
> worked
> > for others:
> >
> > Tapered joint- frequently seen on composite piping
> > systems- the outer surface of the end fo the pipe
> is
> > ground to a taper to fit the same taper on a
> fitting.
> > The length of the taper is roughly one diameter of
> the
> > pipe.
> >
> > Insert and bolt circle- The closure is inset a
> bit,
> > perhaps 1/2 diameter and retained with an insert
> made
> > from the same tubing by removing a strip
> > longitudinally. The insert is held in place with
> epoxy
> > and a complex bolt pattern of several circles.
> >
> > Pinned- seen on composite rocket motor cases- the
> > closure is about 1/2 diameter in length. hundreds
> of
> > small roll pins are used in holes which are
> drilled
> > and then reamed for optimum bearing strength.
> >
> > Those techniques are used on unmodified composite
> > filament wound tubing. If the ends are reinforced,
> we
> > might get by with a lesser intense method. But we
> have
> > to prove that early on as it is crucial to the
> success
> > of the motor.
> >
> > BC
> >
> > --- Lakestake Rocketry <lakestake at gmail.com>
> wrote:
> >
> > > Thanks Colin,
> > >
> > > Great information.
> > >
> > > The whole airframe would not have to match the
> specs
> > > for the motor casing,
> > > at least the top half can be a lot lighter
> > > construction.
> > >
> > > I was told (by my vendor) that uni was harder to
> get
> > > and thus more
> > > expensive.
> > > That was several months ago. It sounds like
> either
> > > that was *? or the
> > > landscape has changed in the carbon supply
> world.
> > > Good to hear.
> > >
> > > How do we figure a liner into your calculations?
> If
> > > it has some mechanical
> > > properties as well as providing insulation
> during
> > > the second stage burn we
> > > may be able to build a lighter motor casing.
> > >
> > > Richard, can your group recommend a liner for a
> > > composite airframe
> > > that we can use to refine our model?
> > >
> > > Colin, if you will be able to provide a wound
> tube
> > > how would it compare
> > > with the current fabric design in terms of
> weight at
> > > the same strength?
> > > Would you recommend that we use it as a motor
> casing
> > > only with a light
> > > fabric airframe over the top, or would it be
> both
> > > the casing and aft
> > > airframe which we attach the forward fabric
> airframe
> > > and fins to?
> > >
> > > Matt
> > >
> > > On 10/13/05, Colin Hutchison
> > > <colin at carboncopies.com.au> wrote:
> > > >
> > > > G'day all,
> > > >
> > > > Sorry for the delay. I've run some number on a
> > > range of lay-ups. I
> > > > guess it comes down to Margin Of Safety and
> how
> > > close you would like to
> > > > get
> > > > to the limit. I've attached a screen grab of
> the
> > > Excel spreadsheet I've
> > > > been using. The ply count runs from 15 to 32
> > > plies, however, the braided
> > > > tube was modelled using two separate uni
> > > directional plies. Therefore, for
> > > > example, lay-up for ply count 29 is actually 5
> > > layers of uni-directional
> > > > and 12 layers of braid, totalling 17 layers.
> The
> > > braid angle was also
> > > > modelled at +-60deg instead of the optimum of
> > > +-55deg. This makes the
> > > > calcs a whole lot easier. I'll attach the
> complete
> > > lay-ups at a later
> > > > stage. Each ply (as seen in the calcs) is a
> 200gsm
> > > layer of uni. So the
> > > > braid would be equivalent to 400gsm.
> > > >
> > > > There are a few factors that affect all the
> calcs.
> > > One of them being
> > > > the breaking strain of the Carbon. I've done
> the
> > > calcs for 4000us and
> > > > 6000us. Typically Boeing use a value of around
> > > 4000us. This allows for
> > > > there own safety factors, one of them being
> holes
> > > drilled in the
> > > > surface. Another is the Young's Modulus of
> Carbon.
> > > I've used a slightly
> > > > reduced value from typical pre-preg so this
> should
> > > be ok, but it comes
> > > > back
> > > > to my point that the supplier and quality of
> the
> > > carbon does matter. Also
> > > > the quality of the epoxy will affect the final
> > > product.
> > > >
> > > > If you want to go to bare minimum the you
> could go
> > > as low as ply count
> > > > 17 (1 layers of uni and 8 layers of braid).
> > > Allowing for 6000us then the
> > > > minimum MOS is 0.1219. (Btw, the MOS is
> calculated
> > > for each ply in the
> > > > laminate and then the minimum value is the MOS
> > > stated). The casing would
> > > > come out at around 12.1lbs. If this were to be
> the
> > > lay-up then I would
> > > > probably recommend that the ends be beefed up
> a
> > > little by adding more
> > > > plies. Basically because you are going to be
> > > drilling holes in it.
> > > >
> > > > I'll also just not here that the holes should
> be
> > > at least 3 times the
> > > > diameter of the hole to the edge of any
> composite.
> > > >
> 
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