[AR] Re: Sounding Rocket Fin Analysis

From: Ben Brockert <wikkit@xxxxxxxxx>
To: arocket@xxxxxxxxxxxxx
Date: Wed, 4 Sep 2019 14:52:58 -0700

Line scanning/rolling shutter cameras like almost all popular CMOS will
make that harder, in that camera position relative to spin direction will
give very different results. An upright camera looking radially will smear
horizontally, while a horizontal camera looking radially will stretch or
compress the view vertically in each frame depending on if the rocket is
spinning clockwise or anti-.

Here's one with a camera looking axially if you want some source material
to make an attempt on. https://www.youtube.com/watch?v=g-1aVW0pvqQ You can
see the horizon curve, which is an effect of the spin, not the lens.

Here's another one with severe spin distortion:
https://www.youtube.com/watch?v=aS7C5OVLTBA The donut dust cloud on liftoff
of that rocket is one the coolest videos I've ever captured.

Requiring global shutter to make post processing easier would make it much
harder to buy cameras for a rocket. But if I was doing it I'd also want
correlated IMU data, similar to how the app Hyperlapse works.

On Tue, Aug 27, 2019 at 11:40 AM Jaba Adams <jaba.adams@xxxxxxxxx> wrote:

@Charlie I was thinking of this as purely off-board post-processing. Also,
more of a project for me than a project for you. :)

@DHBarr I was just thinking of a single-camera. Wasn't familiar with the
term "despin". Will look up... Even if a single camera is not as good as
multiple, it might be neat to have single-spinning camera -> panoramic/360
view in the COTS toolbox.

- Jaba

On Tue, Aug 27, 2019 at 12:55 PM DH Barr <dhbarr@xxxxxxxxx> wrote:

Better to use an off-the-shelf 360 video rig for the raw footage, then
despin in postprocessing.

On Tue, Aug 27, 2019, 11:32 AM Charlie Garcia <dragonrider.hhcc@xxxxxxxxx>
wrote:

Jaba
Spin stabilization also add load to the fin, and has an energy cost.
Since we're already concerned about the fins being overloaded, I hesitate
to make that the first solution we run to for the possible dynamics
problems. If we did do spin stabilization I'd love to do a Yo-Yo despin
system.
I have no thoughts on post-processing video. I have a hard enough time
getting one camera to work on the way up, let alone enough cameras to do
pseudo-360 footage stabilization. That is a problem beyond my current
abilities.
Sincerely,
Charlie

On Tue, Aug 27, 2019 at 12:21 PM Jaba Adams <jaba.adams@xxxxxxxxx>
wrote:

Charlie,

Impressive. Is the video issue the only reason not to do spin
stabilization?

I was thinking that it should be possible to post-process video from a
spinning camera into a stabilized panoramic shot. Might even be able to get
360 video out of it.

@Everyone would this be useful software to have? Sounds like an
interesting computer vision problem.

- Jaba

On Fri, Jul 12, 2019 at 7:46 PM Charlie Garcia <
dragonrider.hhcc@xxxxxxxxx> wrote:

@Carl It was indeed last Saturday.
We have also used FinSim to estimate our flutter velocity, and we
should have had significant margin, unless the fins significantly softened
due to aeroheating. Thanks for the link, I'll read up! Tapered fins are an
interesting suggestion, possibly more doable than ever thanks to
CNC/Additive

@Ben We pulled values from a Monte Carlo run of OpenRocket (not great,
not terrible) and used 3 degrees at M3.5 as our design case. I believe we
did supersonic thin airfoil estimation of the C_L and then integrated over
the span of the fin. Our data shows very dynamic responses, it's already a
target for improvement. I'm not sure what our solution will be, spin
stabilization is unpopular since it wrecks the video. Control systems are
challenging, but maybe a single axis reaction wheel is doable?

Here's our tilt angle and roll rate, salvaged from the dead telemetrum
chip (Huge shout out to Bdale for making his source public so we could
make
sense of the raw chip dump). We've got a few SD cards getting x-rayed now
to see about salvaging them. The memory chip on our MARSA is left
somewhere
in the desert, so we are regrettable out of information there.
[image: image.png]

On Fri, Jul 12, 2019 at 1:27 PM Ben Brockert <wikkit@xxxxxxxxx> wrote:

How did you choose the AoA to base your structural analysis on? The
USC rocket had what looked like fairly aggressive inertia coupling, so if
you had a similar L:D and no roll control I'd expect you to get it as
well.

On Thu, Jul 11, 2019 at 2:53 PM Charlie Garcia <
dragonrider.hhcc@xxxxxxxxx> wrote:

Hi All!
I'm a member of a student engineering team. We recently launched a
'P' motor powered rocket that (probably) lost a fin at about Mach 3
around
10,000 ft. We did some analysis on the expected fin loads before flight,
and added a healthy safety factor to account for the admittedly
lackluster
composites manufacturing quality control process we have in place. Our
design was based off the one that USC's Rocket Propulsion Lab recently
flew
to space.
We've been reading up on load analysis and design load cases for
sounding rocket fins, and we were wondering if anyone on this list has
expertise or favorite texts in this area that they'd be willing to
share.
Sincerely,
Charlie Garcia
[image: Screen Shot 2019-07-08 at 12.23.00 AM.png]

Follow-Ups:
- [AR] Re: Sounding Rocket Fin Analysis
  - From: Uwe Klein

[AR] Re: Sounding Rocket Fin Analysis

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