Yes.
Now how--given a specific set of fins--does one analyze the problem to
establish what tab sizing will always provide the minimum required roll rate
while not exceeding some maximum?
Leaving the launcher, the vehicle needs--for the FAA--to spin up to around 8-10
hertz; that can be accomplished w/ a fin tab. My question is whether there
exists analysis that can decide whether the spin momentum so induced is
sufficient to assure FAA compliant thrust averaging after the loss of induced
spin that comes w/ transonic and supersonic flight...and w/o generating
excessive spin later in flight.
This is a problem that has been addressed at Wallops and White Sands wrt canted
fins; I'm asking if anyone, Ben, is aware of an extension to fin tabs or some
low cost alternative.
Bill
Sent from my Commodore 64
On Jul 17, 2016, at 7:55 AM, Ben Brockert <wikkit@xxxxxxxxx> wrote:
If you assume a spherical cow then there is no fin setup that can give
a constant roll rate other than 0 for any accelerating rocket. An
ideal fin tab or canted fin will spin the rocket through the air at a
constant "thread pitch", nominally with 0 spin rate at launch and
apogee and maximum spin at maximum velocity, though in reality inertia
would slow the spin up and spin down.
On Sun, Jul 17, 2016 at 1:29 PM, William Claybaugh
<wclaybaugh2@xxxxxxxxx> wrote:
Yep, supersonic. Still interested in a non-canted fin solution theory, if
any one knows of one.
Bill
On Saturday, July 16, 2016, Ben Brockert <wikkit@xxxxxxxxx> wrote:
I imagine your rockets go supersonic, so you'd be better off with a
canted fin (or a trim fin at the end of a fin) than a trailing edge
fin tab due to the change in behavior of a trailing edge control
surface in the transonic and supersonic regimes.
On Sat, Jul 16, 2016 at 11:37 PM, William Claybaugh
<wclaybaugh2@xxxxxxxxx> wrote:
I'd be interested in a theory to describe this problem. My own interest
is
in using fin tabs to assure spin at a specific rate (9-10 hertz), which
appears--to me--to be cheaper and more reliable than trying to carefully
align the fins to just the correct offset. Aligning them dead straight
and
using a fin tab appears to be much simpler....
Does anyone know of such an analysis?
Bill
On Saturday, July 16, 2016, Ben Brockert <wikkit@xxxxxxxxx> wrote:
Gary Cooper posted this to the FAR facebook page, though he's flying
in northern California:
https://youtu.be/I-FhXvLtk-U
A homebuilt motor that appears quite reliable, and trim tabs on the
fins to get rid of the tiny amount of roll the rocket was doing.