plan for first "electric ejection" rocket (PML "Miranda" kitbash)

plan for first "electric ejection" rocket (PML "Miranda" kitbash)

Post by David Weinshenke » Mon, 21 Aug 2000 04:00:00



For my next project, I'm planning to build a
rocket to get some experience with electric
deployment... I'm thinking of a "single event"
deployment setup (the more complex dual event
systems can come after I've got some experience
with this one).

I'm describing the plan below, and would welcome any
suggestions or comments.

-dave w

 - - --- - --- - -

The ingredients:
PML "Miranda" kit (3in. tubing, 3ft. main airframe
plus 1ft. payload section)
1 extra piece of 3in. Quantum Tube
1 extra coupler-bulkhead assembly (+1 in the kit)
1 "Intellicone" (3in. plastic nose cone with built-in
electronics compartment)

The recipe:
Use the rear 18in. of the pre-slotted kit airframe.
Install fins and engine mount per kit instructions,
but do not attach the piston strap to the engine mount
tubing. (Assemble the piston in the normal manner, but
do not connect the free end of its strap to anything at
this point.)
Install 1 coupler-bulkhead assembly (CBA) in the front of
this rear section.

From the remaining tubing, cut 1 24in. piece and 1 6in.
piece.
Fit the coupler of the second CBA into the front end of
the middle (24 in.) piece. Drill screw-holes through the
airframe wall and the coupler tubing. Install T-nuts on
plywood pads inside the coupler behind the holes, enabling
the coupler to be fastened into the middle tube with screws.

Install a terminal block on the rear of the bulkhead, and run
a pair wires from the terminals through a hole in the bulkhead.
Apply glue to the hole to make an airtight seal. Install the
bulkhead in the rear of the prepared coupler. Glue the front of
the coupler into the rear of the front (6in.) tubing section.

Mount the alitmeter in the electronics compartment inside the
nosecone, and insert the nosecone into the front of the forward
tube section with the wires from the terminal block running
to the deployment output of the altimeter.

Assembly for flight:
Connect an ejection charge to the terminals on the rear of
the front coupler. Connect the strap of the piston to the
eyebolt of the front bulkhead, and run the forward end of
the recovery harness through the center tube to the D-ring
on the piston. Push the piston into the front of the center
tube, and attach the front section to the center section with
screws. Pack the parachute and harness into the center section.
Attach the rear end of the harness to the eyebolt of the bulkhead
on the rear section, and slip fit the rear section into the
center section.

The result will be a rocket with the same overall length and
external configuration as the original kit design, but an
altered ejection layout: the chute will eject rearward out
of the center section, with separation between the center
and rear section.

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plan for first "electric ejection" rocket (PML "Miranda" kitbash)

Post by Thosz » Mon, 21 Aug 2000 04:00:00


Build it and see.The set up sounds a little intense but the concept seems
relatively sound.The cool thing about ejection system research is the fact that
it either works or it doesn't.No "almost" here. The bottom line  is to get the
parachute out of the rocket in such a way that it can catch air and open(not
always in that order) without being shredded to pieces or tangled,and thats it!
There are lots of ways to make this happen.In my humble opinion,simple is
better.You'll get both positive and negitive response on your concept.The only
real way to find out for sure is build it and turn one loose.Your idea sounds
alot better than that guy in ohio who wants to train a gerbel to push an eject
button when a little light comes on inside his capsule at 600 ft.

 
 
 

plan for first "electric ejection" rocket (PML "Miranda" kitbash)

Post by TSmith13 » Mon, 21 Aug 2000 04:00:00


David described his plan:

(snip)

Quote:

>The result will be a rocket with the same overall length and
>external configuration as the original kit design, but an
>altered ejection layout: the chute will eject rearward out
>of the center section, with separation between the center
>and rear section.

 Your layout is a sound one, Dave. I use a very similar and reliable one for
drogue ejection. A couple of things to keep in mind:

1) Upwards acceleration will tend to push the parachute and piston aft. When
packing, consider leaving the whole shebang in the aft portion of the airframe.
Use sufficient BP charge to pressurize this configuration.

2) The altimeter will not work if you don't turn it on. If you're like me, use
big, bright neon letters to remind yourself to do so.

Tim Smith
TRA #4907 L2

 
 
 

plan for first "electric ejection" rocket (PML "Miranda" kitbash)

Post by David Weinshenke » Fri, 22 Sep 2000 04:00:00


Quote:

> David described his plan:
> (snip)
> > The result will be a rocket with the same overall length and
> > external configuration as the original kit design, but an
> > altered ejection layout: the chute will eject rearward out
> > of the center section, with separation between the center
> > and rear section.

I flew the beast last Sunday at Lunar... worked rather nicely,
in general. It's hard to make exact comparisons without high
speed tracking cameras, but my impression was that the
combination of rearward ejection and automatic firing at actual
peak altitude made for an unusually smooth, uneventful deployment
(compared to the dramatic gyrations I sometimes see).

The only flaw to the flight was the descent rate - the parachute
was undersized (a Rocketman R3 is small for a 5-lb. rocket, and it
looks like it came down at about 40 ft/sec. (from 810ft. inertial
altitude on an H220T) - the nosecone was dislodged on touchdown,
pulling loose the wiring leads between the nosecone's electronics
compartment and the arming switch panel located in the top airframe
section immediately below.

Notes for future flights:
1. Larger parachute
2. Separately replaceable connector harness
   between safe/arm and nosecone
3. Pin nosecone in place (PML plastic rivets)
   instead of slip fit.

Quote:
> Upwards acceleration will tend to push the parachute
> and piston aft. When packing, consider leaving the whole
> shebang in the aft portion of the airframe.

With everything packed in, there actually wan't that much
lengthwise free space. (I may end up wanting to lengthen the
center airframe section to accommodate a larger 'chute...)

Quote:
> Use sufficient BP charge to pressurize this configuration.

I simply used the "dose" of BP that came with the motor -
instead of pouring it into the little well on the front
closure, I poured it into a plastic sandwich bag and shook
it down into the corner. I pushed the head of a Black Sky
electric match into the powder, gathered the bag around
the leads of the electric match, secured it with a wrap of
masking tape, and trimmed away the excess bag material above
the tape. I then put a wrap of aluminum foil duct tape
around the resulting "powder blob" to protect it against
damage in handling.

It seemed to eject adequately.

-dave w

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