Seeking Advice on Stability of 4' Rocket

Seeking Advice on Stability of 4' Rocket

Post by Blockh » Wed, 25 Oct 1995 04:00:00



I've put together a 4' long rocket based on Estes BT-50 tubes (.95"
diameter). It has four fins that seem quite adequate in size (at least to
my untrained eyes). I compare my rocket to the pictures of an Estes "Mean
Machine," and my fins seem much larger. The problem is that I can't get
this model to pass the swing test. I made a longer basswood nosecone in an
attempt to put more weight forwards, but that wasn't enough. The rocket
always stabilizes in a perfectly vertical position, never nose-forwards. I
am now thinking of attaching four more fins to the rocket, but it seems
like overkill.

My question is: how necessary is it for a rocket to pass the swing test.
Some part of me wants to believe that such a long rocket is just too big
to get into a proper trajectory on the end of a tether.... something about
the length extending well well out onto the tangent of the circle, rather
than following the arc tightly.

Another question: how likely is it that a rocket that flunks the swing
test will in fact be stable under power?

And on another unrelated topic: Is there some source of material that will
make sturdy, low-weight launch lugs, for both 1/8" and 3/16" rods? Buying
the Estes lugs seem kind of silly, especially since I take pride in using
non-conventional materials. Any ideas?


 
 
 

Seeking Advice on Stability of 4' Rocket

Post by James J. McLaughli » Wed, 25 Oct 1995 04:00:00



SNIP

Quote:

> My question is: how necessary is it for a rocket to pass the swing test.

Real necessary, and it needs to have motor, recovery device and wadding
in it while you test it.

Quote:
> Some part of me wants to believe that such a long rocket is just too big
> to get into a proper trajectory on the end of a tether.... something about
> the length extending well well out onto the tangent of the circle, rather
> than following the arc tightly.

Some part of me wants to believe I'll win the Lotto America jackpot.

Quote:

> Another question: how likely is it that a rocket that flunks the swing
> test will in fact be stable under power?

Zero.

Quote:

> And on another unrelated topic: Is there some source of material that will
> make sturdy, low-weight launch lugs, for both 1/8" and 3/16" rods? Buying
> the Estes lugs seem kind of silly, especially since I take pride in using
> non-conventional materials. Any ideas?

Contact Magnum, or Countdown or one of those suppliers and order LOC
launch lugs, or just get brass tube at your local hobbyshop.

Quote:
> > Thanks in


You are welcome in advance.

Jim McLaughlin                     These opinions are mine, mine, mine!
                                   And not anybody else's. So there.



 
 
 

Seeking Advice on Stability of 4' Rocket

Post by Kevin Forsy » Wed, 25 Oct 1995 04:00:00



Quote:
> I made a longer basswood nosecone in an
> attempt to put more weight forwards, but that wasn't enough. The rocket
> always stabilizes in a perfectly vertical position, never nose-forwards. I
> am now thinking of attaching four more fins to the rocket, but it seems
> like overkill.

Adding/enlarging fins might just make things worse by moving the CG back.  
Try adding more nose weight.  Lead sinkers (for fishing) work well.

Quote:

> My question is: how necessary is it for a rocket to pass the swing test.

I wouldn't want to be near a launch of an unswung rocket.

Quote:
> Some part of me wants to believe that such a long rocket is just too big
> to get into a proper trajectory on the end of a tether.... something about
> the length extending well well out onto the tangent of the circle, rather
> than following the arc tightly.

You're on the right track about this, but the solution is to expand the
circle.  The longer the rocket, the longer the tether needs to be for a swing
test.

/kevin