Mike:
Experience differs: when building machines that are going to go from zero
to 2000 mph in six or eight seconds it has been my experience that any
piece part that is not absolutely hell for stout will fail.
With regard to off-axis imbalance, my personal standard is to static
balance the entire payload within 0.5 gram on all three axises. OTOH, I’ve
not yet pushed such a payload past Mach 2, so I am not able to claim that
this rule of thumb is sufficient for flights past Mach 3. I do intend to
find out….
Bill
On Tue, Nov 16, 2021 at 3:14 PM Mike Caplinger <mc@xxxxxxxx> wrote:
On 11/16/21 10:37 AM, William Claybaugh wrote:
If lateral acceleration is normal to the vehicle axis then it seems tobreakup.
me that the curve in Drew’s data is exactly what I would expect for a
buildup of coning induced lateral acceleration leading to vehicle
I guess I'm not sure how coning is defined. What you say would be true
if the lateral accelerometer axis were always in the same orientation
relative to the spin axis, but is this what coning is?
At any rate, Plugger's flight certainly looks "wiggly" but I've had
failures like this that had no particular wiggle, at least as visible
from the ground. For what that's worth.
...I’d suggest that building the rocket so that it does not fail
structurally will show whether the coning is caused by the structural
failure or has some other underlying cause.
Good advice, but easier said than done, at least for me. :)
I've certainly always verified with RASAero II that my rockets have lots
of stability margin at velocity. I suspect there is something about
non-zero AoA and dynamic stability that puts more stress than expected
into the short section of airframe between the top of the motor and the
nose cone joint. Maybe that's related to poor spin balance, maybe not.
I've had it happen on lightweight rockets that simply didn't have enough
mass to be unbalanced very much (or so I thought.)