Minie Magg - How Stable Does it Need to Be?

Minie Magg - How Stable Does it Need to Be?

Post by Mick Spence » Mon, 17 Apr 2000 04:00:00



I just finished the rocket for my upcoming L1 attempt, a Minie Magg.
It's a little overbuilt, especially in the aft area.  Even with about as
much nose weight as I think I can stand to put in, the actual measured
CG (plus simulated H242T motor) gives a CG of 23.045" from the nose.
(Total mass is a whopping 75.445 oz.)   Rocksim computes a CP of
26.306", for a static margin of .59.  Is this stable enough for this
rocket?  I seem to recall people saying that the Minie Magg is a natural
stable flyer with "marginally stable" numbers.  Please tell me if I need
worry about this or not.  "Fortunately" today's launch has been scrubbed
due to weather, so I have a little time to work this out.  Also
fortunately, I used Bob Chmara's adjustable ballast system, so I can add
more weight fairly easily if necessary - but I don't want to do it
unless it really is necessary.  Any helpful advice would be
appreciated.  TIA!
---Mick
 
 
 

Minie Magg - How Stable Does it Need to Be?

Post by Actionxp » Mon, 17 Apr 2000 04:00:00


Mick
I regularly, fly a Mini-Mag, on a I357, with no nose weight. It is built near
stock (before I knew what I was doing) and it weighs almost 4 lbs. It has
always flown dead straight, even if I angle the rod some. I also have flown my
11lbs. Warloc (again, no nose weight) 16 times on J-350s and J-570s The sims
say the margin of stability for this rocket is less than 1/10 of a caliber.
Other than weathercocking in strong winds, it, also flys dead straight. The
secret seems to be to get the rocket moving as fast as you can, so quick burn
motors work best (I have flown the Mini-Mag twice on H-97s. Both wobbled some,
at the beginning, but straightened out and then flew dead straight). I'm not a
fan of adding weight to a nose, unless absolutely necessary (I have done it on
longer rockets, however). Also, I am converting all my rockets over to rails,
and this only enhances the flight by removing rod whip from the equasion(?).I
flew my Mini- Mag today, off a 6ft Black Sky Rail It went 2100 feet and, you
guessed it, perfectly straight. Mostly, I trust the sims, but they don't seem
to be that good for short, fat rockets. You may have more of a problem with the
power to weight ratio than I do, but I think it should still fly. Try it and
see. Make sure that the LCO calls for a heads up flight, because the CP is in
question, and (I'm assuming) that it is the rockets first flight. I think you
will be pleasently surprised.

                            Lloyd

Quote:
>I just finished the rocket for my upcoming L1 attempt, a Minie Magg.
>It's a little overbuilt, especially in the aft area.  Even with about as
>much nose weight as I think I can stand to put in, the actual measured
>CG (plus simulated H242T motor) gives a CG of 23.045" from the nose.
>(Total mass is a whopping 75.445 oz.)   Rocksim computes a CP of
>26.306", for a static margin of .59.  Is this stable enough for this
>rocket?  I seem to recall people saying that the Minie Magg is a natural
>stable flyer with "marginally stable" numbers.  Please tell me if I need
>worry about this or not.  "Fortunately" today's launch has been scrubbed
>due to weather, so I have a little time to work this out.  Also
>fortunately, I used Bob Chmara's adjustable ballast system, so I can add
>more weight fairly easily if necessary - but I don't want to do it
>unless it really is necessary.  Any helpful advice would be
>appreciated.  TIA!
>---Mick


 
 
 

Minie Magg - How Stable Does it Need to Be?

Post by Mullen » Mon, 17 Apr 2000 04:00:00


The MM was my first non Estes rocket that I ever built, and the first rocket in
about 15 years. Not knowing any different I built it stock (w/ Nomex chute
protector) and launched it on a H242 for my level 1 cert on a very windy day.
I've since launched in on different motors from a H97 to an I357 with no
problems. I just ordered a Warlock and hope to launch it on J's.

Good luck,
Todd

 
 
 

Minie Magg - How Stable Does it Need to Be?

Post by Larry W. Hardi » Tue, 18 Apr 2000 04:00:00


RockSim calculates the stability of the rocket at zero angle of attack.  At
zero angle of attack there is no impact of the body tube and it is
effectively
ignored.  (This is implicit in the Barrowman equations also.)  At non-zero
angles of attack, the body tube begins to have an impact on stability.  For
"normal" designs, it is destabilizing because the CP of the tube (mid point)

is AHEAD of the CG.  The rule of thumb that you need the CG one
calibre (body diameter) ahead of the CP generally allows you to handle
modest angles of attack (10 degrees or so) without becoming unstable.
For really long, slender rockets, 1 is not enough.  In the case of the Mini
Magg, the center of the BT is very close to the CG and there is virtually
no impact on stability as the angle of attack changes.  Thus, the Mini
Magg will be stable with much less than 1 calibre separation between
the CP and CG.  The only way to know how much is enough is
experience, preferably someone else's.  I ran RockSim with an I-357
in a Mini Magg and the static margin was estimated at 0.50.  Several
people have stated that they have successfully flown this combination.
To be safe, you'd need to know where the CG was for the rocket as
they had built it.  (The CG in my test case was where RockSim placed
it and was not a "real" number.)  Can people provide known CG
locations for which a Mini Magg is stable?

Larry Hardin

Quote:

> I just finished the rocket for my upcoming L1 attempt, a Minie Magg.
> It's a little overbuilt, especially in the aft area.  Even with about as
> much nose weight as I think I can stand to put in, the actual measured
> CG (plus simulated H242T motor) gives a CG of 23.045" from the nose.
> (Total mass is a whopping 75.445 oz.)   Rocksim computes a CP of
> 26.306", for a static margin of .59.  Is this stable enough for this
> rocket?  I seem to recall people saying that the Minie Magg is a natural
> stable flyer with "marginally stable" numbers.  Please tell me if I need
> worry about this or not.  "Fortunately" today's launch has been scrubbed
> due to weather, so I have a little time to work this out.  Also
> fortunately, I used Bob Chmara's adjustable ballast system, so I can add
> more weight fairly easily if necessary - but I don't want to do it
> unless it really is necessary.  Any helpful advice would be
> appreciated.  TIA!
> ---Mick