Non-finned projectiles

Non-finned projectiles

Post by Allen Ro » Sat, 06 Oct 1990 00:17:11



I am interested in finding out about methods of stabilization of
model-rocket-driven
projectiles that do not require fins on the outside.  I want to launch
these from a
tube; so there are (i think) basically two ways to do it.. 1: make a
sub-tube to hold the
engine, fins, and then a larger, all-encompassing tube to make contacte
with the
launch tube,
or 2: get enough spin on the sucker that it is gyroscopically stable
like a rifle bullet.
using ducted exhaust.  Any ideas??

Thank you for your support

The Human Chameleon Returns!!!

  Please feel free to respond to any comments I make... I am outspoken and
enjoy debate.

 
 
 

Non-finned projectiles

Post by Trevor Smedl » Sat, 06 Oct 1990 00:42:16



Quote:
Rout) writes:

|> I am interested in finding out about methods of stabilization of
|> model-rocket-driven projectiles that do not require fins on the outside.  I
|> want to launch these from a tube; so there are (i think) basically
two ways |> to do it..
|>
|> 1: make a sub-tube to hold the engine, fins, and then a larger,
|> all-encompassing tube to make contacte with the launch tube, or

I'm not sure what you hope to gain this way.  You'd have even more drag
from the outer tube.  If your purpose isn't to reduce drag, but just get
a "cool" looking rocket, than I think this is the best idea.

|> 2: get enough spin on the sucker that it is gyroscopically stable
like a |> |> rifle bullet.  using ducted exhaust.  Any ideas??

Spinning a rocket (or a bullet) doesn't actually make it stable.  It can
make it react very slowly to de-stabilising influences, so for the short
duration of a rocket flight, it will behave reasonably.  However, if the
spin rate is too close to the rockets resonant reequency, disaster can
result.  Also, it's pretty tough to get it spinning enough by the time
it gets off the launch rod.  You could have a first stage with fins at a
slight angle, and then upper stages with no fins at all, but getting a
totally finless rocket could be pretty tough.

Things shaped like bullets (short and stubby) take to this better than
things shaped like rockets (long and skinny).

One book that talks about this, and a lot of other rocket physics things is:

     Topics in advanced model rocketry by Gordon K. Mandell, George
     J. Caporaso and William P. Bengen.  Cambridge, Mass., MIT Press, 1973

I found it in the University Library here.  Very interesting stuff.

You could also try "tube fins".  Just gluing a bunch of drinking straws
on the side of the body tube (with the straw parallel to the direction
of travel, and positioned near the tail end of the body) will often
work, I am told.  You could also use body tubes, with both ends open.

Good Luck.

Trevor Smedley


 
 
 

Non-finned projectiles

Post by Andy Hon » Thu, 11 Oct 1990 12:33:06


Quote:

>I am interested in finding out about methods of stabilization of
>model-rocket-driven projectiles that do not require fins on the outside.
>I want to launch these from a tube...

Back when I was a juvenile-delinquent in high school (now I'm an irresponsible-
***), I developed a tube-launching system for firing rockets at cars, dogs,
and other objects of hatred.

I used a PVC pipe that was about 1/4" wider in diameter than a T-engine.  It
was about four feet long.  Mounted on the pipe were two handles.  Both ends of
the pipe were left open.  A trigger on one handle connected a Polaroid
instant-film battery to a pair of metal strips that were folded into the rear
opening of the pipe.

To prepare the rocket-engines for my home-made bazooka, I would first take a
hand-drill and drill into the nozzle of the engine through the propellant--
making the engine into a "core-burning" rocket--while being careful not to
drill into the delay.  An Estes solar-igniter was placed as far up the core as
possible (this required removing the tape off the igniter).  Each of the ends
of the igniter leads were then wrapped in a folded piece of aluminum foil, and
the foil was taped down to the body of the engine.

Then I would use a strip of duct tape to attach an 8" bass-wood strip as a
stabilizing rod, with a piece of folded-over-itself scotch tape at the end as a
fin.  This construction would place the center of pressure behind the center of
mass.

        *************************************************###



      T-engine             bass-wood stabilizer       scotch-tape

Loading the projectile took almost no effort and could be done in less than a
second--all I had to do was shove it into the end of the pipe, and the aluminum
foil tabs would contact the metal strips on the pipe.  As soon as a pulled
the trigger, the rocket would literally explode out of the pipe, with enough
accuracy to hit the neighbor's dog at 75 yards.

Quick loading... quick firing.  It was an ideal... and cheap system.

If you decide to try out this system... keep in mind that the launching pipe
can't be metal--or you'll short out the metal ignition strips.  And PVC is
*much* lighter, and therefore more portable (i.e. you can run faster with it
when you get chased by the angry owner of the car with the shot-out window).

The bass-wood stabilizer isn't too important if your pipe is long enough and
you don't need pin-point accuracy.  As long as you core-burn your
rocket-engines, the propellant will burn *completely* while the rocket is still
inside the pipe--so once the rocket has left the piep, it will travel in a
relatively straight line.  (If you've experimented with shooting finless
rockets out of pipes, you've probably figured out that if the propellant is
still burning once the rocket has left the pipe, the rocket will spin
uncontrollably.)

The rockets were tested with/without the tape on the end of the stabilizer.  It
*seemed* like the tape increased accuracy.  (At least it never seemed to
decrease it.)  And unbelievably, it was never burned off by the exhaust.

If you need more detail, send me a quick note and I'll try to answer whatever
questions you might have about this system.

--andy--
skate safe.  andy.

 
 
 

Non-finned projectiles

Post by Nur Iskandar Ta » Fri, 12 Oct 1990 01:28:31


Quote:
>Back when I was a juvenile-delinquent in high school (now I'm an irresponsible-
>***), I developed a tube-launching system for firing rockets at cars, dogs,
>and other objects of hatred.

Hehehehe I wonder how many others have tried this. My
variation was a bazooka that fired six bottle rockets.
It had a craft paper tube from the core of a bolt of
cloth, an attachment at the back for a six-pack magazine
of bottle rockets (expendable, cardboard, quick-loading),
a cone in front to catch the exhaust gases, pistol grips
and sights...

This was a secret weapon for our numerous bottle rocket
battles. The opposition used bottles as launchers, re-
sulting in mediocre (non-existant?) accuracy. Need I say
they were routed? The bazooka cound land two or three
rockets on a person at fifty yards. Even near misses were
quite effective. And another magazine could be in place
in seconds!

To stabilize the rockets, it was necessary to leave
about six inches of stick. Experiments with stickless
rockets proved dismal, with rockets shooting off at 60
degree angles...

The usual disclaimers apply.. don't try this! (the
bottle rockets involved were the relatively harm-
less 2" long by 3/16" diameter size that you buy
by the gross...)

-------------------------------------------------------------------------------
Iskandar Taib                        | The only thing worse than Peach ala


 
 
 

Non-finned projectiles

Post by Eric Shaf » Sat, 13 Oct 1990 07:47:15



Quote:
(Andy Hong ) writes:
> Back when I was a juvenile-delinquent in high school (now I'm an
irresponsible-
> ***)
[...]
> As soon as a pulled
> the trigger, the rocket would literally explode out of the pipe, with
enough
> accuracy to hit the neighbor's dog at 75 yards.
[...]
> And PVC is
> *much* lighter, and therefore more portable (i.e. you can run faster
with it
> when you get chased by the angry owner of the car with the shot-out

window).

What an incredibly fun guy you must have been.  I hope you have
grown up some since then.

Regards,
Eric

 
 
 

Non-finned projectiles

Post by Jordan K. Hubba » Wed, 17 Oct 1990 23:54:01


Sounds like fun, though I can't say that the dog and/or car owners must
have liked it much. Still, my main question is whether or not you ever
experimented with some sort of warhead on them there bazooka rockets.
I can see where a compact cardboard rocket case would have provided some
impact effect at 75 yards, but not much. Figuring out some way to attach
an M-80 type of warhead to the projectile would be very interesting,
especially if you could both get it to balance properly and to explode
at different ranges. Too bad we could never get estes rocket engines
where I grew up (now I think I know *why*!), I would have tried some of
these things.. 'course, I was able to buy really good quality fine grain
black powder (for my, um, muzzle loading rifle) and that led to some nice
cannons.

Ah, youth.

                        Jordan
--
                        PCS Computer Systeme GmbH, Munich, West Germany

        EUNET:          unido!pcsbst!jkh