[altusmetrum] Min diameter 38mm J1026 launch - early drogue or rocket tumble?

[Bryan Duke]

Hello List-

I flew a rocket a few days ago in search of the J altitude record. The rocket teleported off the pad & quickly got to over 3000ft/s. Very quickly after that, the telemetry reported the drogue firing (at around 10k ft) and then the rocket peaked a few thousand feet later. The accel data show a deceleration momentarily maxing out the G meter. So, about a 100G accel followed by a 100G decel. Ouch.

I’m still trying to figure out exactly what happened. I think the motor made it all the way through burnout, then some “event” happened. The rocket and all the recovery gear are still in great shape, so it’s tough to point a finger at anything from just looking at the rocket. Can I please get some thoughts on what happened based on the data? Is the “drogue” callout on the flight replay matched to the TeleMetrum firing the drogue? If so, why did it fire it so early? I’m definitely not ruling out the rocket tumbling, but the motor exhaust looked straight until we couldn’t see it any more.

FWIW, this was the first flight on a new TeleMetrum. The telemetry page showed that v1.8.5 is loaded. I’ve flown an EasyMini before to about Mach 2, but not a TeleMetrum and not anything approaching Mach 3. This was the maiden flight on this rocket. The chute was in the nosecone & that’s the only thing that gets ejected (single chute at apogee was the plan). My drag & decel calcs show that the nosecone should have plenty force holding in place throughout the flight. It was a fairly tight fit and held on by a single 0.060” styrene rod as a shear pin. I’m not ruling out a drag separation either.

Here’s a Dropbox link for the data file:
https://www.dropbox.com/s/fomf36le9yaeec2/2018-05-28-serial-4989-flight-0001.eeprom?dl=0 <https://www.dropbox.com/s/fomf36le9yaeec2/2018-05-28-serial-4989-flight-0001.eeprom?dl=0> (just click the 3 dots on the top right corner of the screen & select download - you don’t need to be a Dropbox user)

Thanks!
-Bryan

[Plugger Lockett]

That's quite strange Bryan, one would expect if you popped the NC early
you'd at least have some damage on the airframe and/or fins from the (I'm
assuming) kevlar cord you used to connect the NC and airframe. The lack of
damage is somewhat strange when taking that into account. Did your chute
fray from the high speed deployment?

I'll have a look at your data but I probably won't be able to until early
next week as we've got our biggest launch of the year coming up this
weekend.

Better luck next time!

Cheers,

drew

Post by Bryan Duke
Hello List-
I flew a rocket a few days ago in search of the J altitude record. The
rocket teleported off the pad & quickly got to over 3000ft/s. Very quickly
after that, the telemetry reported the drogue firing (at around 10k ft) and
then the rocket peaked a few thousand feet later. The accel data show a
deceleration momentarily maxing out the G meter. So, about a 100G accel
followed by a 100G decel. Ouch.
I’m still trying to figure out exactly what happened. I think the motor
made it all the way through burnout, then some “event” happened. The rocket
and all the recovery gear are still in great shape, so it’s tough to point
a finger at anything from just looking at the rocket. Can I please get some
thoughts on what happened based on the data? Is the “drogue” callout on the
flight replay matched to the TeleMetrum firing the drogue? If so, why did
it fire it so early? I’m definitely not ruling out the rocket tumbling, but
the motor exhaust looked straight until we couldn’t see it any more.
FWIW, this was the first flight on a new TeleMetrum. The telemetry page
showed that v1.8.5 is loaded. I’ve flown an EasyMini before to about Mach
2, but not a TeleMetrum and not anything approaching Mach 3. This was the
maiden flight on this rocket. The chute was in the nosecone & that’s the
only thing that gets ejected (single chute at apogee was the plan). My drag
& decel calcs show that the nosecone should have plenty force holding in
place throughout the flight. It was a fairly tight fit and held on by a
single 0.060” styrene rod as a shear pin. I’m not ruling out a drag
separation either.
https://www.dropbox.com/s/fomf36le9yaeec2/2018-05-28-
serial-4989-flight-0001.eeprom?dl=0 (just click the 3 dots on the top
right corner of the screen & select download - you don’t need to be a
Dropbox user)
Thanks!
-Bryan
_______________________________________________
altusmetrum mailing list
http://lists.gag.com/mailman/listinfo/altusmetrum

...

[Keith Packard]

Post by Bryan Duke
Hello List-
I flew a rocket a few days ago in search of the J altitude record. The
rocket teleported off the pad & quickly got to over 3000ft/s. Very
quickly after that, the telemetry reported the drogue firing (at
around 10k ft) and then the rocket peaked a few thousand feet
later. The accel data show a deceleration momentarily maxing out the G
meter. So, about a 100G accel followed by a 100G decel. Ouch.

Ouch indeed. It looks like you were just shy of maxing the
accelerometer, which is an impressive feat.

Post by Bryan Duke
I’m still trying to figure out exactly what happened. I think the
motor made it all the way through burnout, then some “event”
happened.

I think the pressure curve is probably the most interesting part. At
about 0.8 seconds after boost, the pressure starts *dropping* rapidly,
then "something" happens, which generates a tremendous amount of noise
on both pressure and acceleration curves, then at about 1.8 seconds,
things return to "normal" and the flight carries on with what looks like
a completely nominal decelleration curve (starting at about 10g, then
tapering down to 1g as the speed decreases).

Post by Bryan Duke
The rocket and all the recovery gear are still in great
shape, so it’s tough to point a finger at anything from just looking
at the rocket. Can I please get some thoughts on what happened based
on the data? Is the “drogue” callout on the flight replay matched to
the TeleMetrum firing the drogue? If so, why did it fire it so early?

I don't see it firing early; looks like it's right on top at 24 seconds.

Post by Bryan Duke
I’m definitely not ruling out the rocket tumbling, but the motor
exhaust looked straight until we couldn’t see it any more.

It definitely didn't tumble -- it would have come apart and then the
rest of the trip to apogee wouldn't have looked clean.

Post by Bryan Duke
FWIW, this was the first flight on a new TeleMetrum. The telemetry
page showed that v1.8.5 is loaded. I’ve flown an EasyMini before to
about Mach 2, but not a TeleMetrum and not anything approaching Mach
3. This was the maiden flight on this rocket. The chute was in the
nosecone & that’s the only thing that gets ejected (single chute at
apogee was the plan). My drag & decel calcs show that the nosecone
should have plenty force holding in place throughout the flight. It
was a fairly tight fit and held on by a single 0.060” styrene rod as a
shear pin. I’m not ruling out a drag separation either.

...

There's no way the rocket came apart or did anything 'weird' externally;
it wouldn't have been aerodynamic enough to survive to apogee at 12600'.

There's clearly something 'weird' going on with the pressure data. Are
the static ports in a nice smooth part of the airframe, far back from
any edges or diameter changes? If I were guessing, I'd guess that
there's something evacuating the ebay, and that eventually that caused
some turbulence, which generated enough drag to slow the airframe down
rapidly, but not enough to tear it apart.

The fact that it happened after motor burn-out makes me kinda wonder if
there's some air leakage around the base of the rocket (which seems odd
for a min-diameter airframe). Imagine the sudden low-pressure area
pulling air from inside the airframe. That doesn't explain how the
pressure returned to normal a second later though.

That's one weird data set, that's for sure.

[Bryan Duke]

Thanks for the great thoughts, guys. This helps a lot.

I didn’t have time to inspect the chute before I left for work this morning, but I took another look at the external structure. One of the fins does have a cracked fillet that I didn’t notice before. The fin still feels firmly in place though. The chute was small on this, so it might have happened on landing. Tough to tell.

The rocket is a flying case design with the bulk of the structure being a Loki 38/1200 case. The fin can is a carbon fiber tube with the solid carbon fins attached to it. The fin can assembly is epoxied directly to the Loki case. On the front end, a short body tube section is epoxied to the Loki case with about a 2” band of Hysol. That’s the avbay section & the only place I see for it to leak is out the static ports. I guess it’s possible it leaked out the plugged forward motor closure, but that was all intact & felt good when I disassembled it.

For the rocket to slow down that quickly, it would have taken something fairly serious going on. How about a fish tail/slide type motion during the “something” time? I ran RasAero II on it, but maybe the predictions there were more optimistic than reality.

It may be possible that something strange happened with the smoke/delay grain. The nozzle still looked good, but maybe there was some low volume gas escaping the nozzle at a weird angle because of something partially blocking it. Perhaps that along with being at the lowest stability point in the flight was enough to make the rocket hunt.

The main reason I was curious about the drogue is that if you replay the flight, I thought it called out “drogue” and showed drogue as the status before apogee. The graphed data showed drogue right at apogee though. I’ll replay it though - I’m probably remembering that wrong. It continuing on after the something doesn’t make sense if the laundry is hanging.

The static ports/vents are roughly 3” back from the nose cone on the flat part of the avbay body tube. They’re about an inch forward of a transition that reduces from the body tube down to the motor casing. That transition shouldn’t matter for those ports while the rocket’s supersonic though.

I’d really love to have 3-axis gyro and accelerometer data. :)

I’m hot & heavy into making rockets to go after the F & G records now. I’m aiming to fly them at Tripoli Colorado’s Springfest in a week and a half. Those will have a TeleMini in them. I didn’t have time to do the external GPS mod I wanted to with the TeleMini, so I’ll have to hunt those rockets down with a Yagi. Should be fun!

I’m busy with work until tomorrow night. I’ll take a better look at my “something” rocket then.

Thanks!
-Bryan

Post by Keith Packard

Post by Bryan Duke
Hello List-
I flew a rocket a few days ago in search of the J altitude record. The
rocket teleported off the pad & quickly got to over 3000ft/s. Very
quickly after that, the telemetry reported the drogue firing (at
around 10k ft) and then the rocket peaked a few thousand feet
later. The accel data show a deceleration momentarily maxing out the G
meter. So, about a 100G accel followed by a 100G decel. Ouch.

Ouch indeed. It looks like you were just shy of maxing the
accelerometer, which is an impressive feat.

Post by Bryan Duke
I’m still trying to figure out exactly what happened. I think the
motor made it all the way through burnout, then some “event”
happened.

I think the pressure curve is probably the most interesting part. At
about 0.8 seconds after boost, the pressure starts *dropping* rapidly,
then "something" happens, which generates a tremendous amount of noise
on both pressure and acceleration curves, then at about 1.8 seconds,
things return to "normal" and the flight carries on with what looks like
a completely nominal decelleration curve (starting at about 10g, then
tapering down to 1g as the speed decreases).

Post by Bryan Duke
The rocket and all the recovery gear are still in great
shape, so it’s tough to point a finger at anything from just looking
at the rocket. Can I please get some thoughts on what happened based
on the data? Is the “drogue” callout on the flight replay matched to
the TeleMetrum firing the drogue? If so, why did it fire it so early?

I don't see it firing early; looks like it's right on top at 24 seconds.

Post by Bryan Duke
I’m definitely not ruling out the rocket tumbling, but the motor
exhaust looked straight until we couldn’t see it any more.

It definitely didn't tumble -- it would have come apart and then the
rest of the trip to apogee wouldn't have looked clean.

Post by Bryan Duke
FWIW, this was the first flight on a new TeleMetrum. The telemetry
page showed that v1.8.5 is loaded. I’ve flown an EasyMini before to
about Mach 2, but not a TeleMetrum and not anything approaching Mach
3. This was the maiden flight on this rocket. The chute was in the
nosecone & that’s the only thing that gets ejected (single chute at
apogee was the plan). My drag & decel calcs show that the nosecone
should have plenty force holding in place throughout the flight. It
was a fairly tight fit and held on by a single 0.060” styrene rod as a
shear pin. I’m not ruling out a drag separation either.

There's no way the rocket came apart or did anything 'weird' externally;
it wouldn't have been aerodynamic enough to survive to apogee at 12600'.
There's clearly something 'weird' going on with the pressure data. Are
the static ports in a nice smooth part of the airframe, far back from
any edges or diameter changes? If I were guessing, I'd guess that
there's something evacuating the ebay, and that eventually that caused
some turbulence, which generated enough drag to slow the airframe down
rapidly, but not enough to tear it apart.
The fact that it happened after motor burn-out makes me kinda wonder if
there's some air leakage around the base of the rocket (which seems odd
for a min-diameter airframe). Imagine the sudden low-pressure area
pulling air from inside the airframe. That doesn't explain how the
pressure returned to normal a second later though.
That's one weird data set, that's for sure.
--
-keith

...

[Keith Packard]

I’d really love to have 3-axis gyro and accelerometer data. :)

Yeah, TeleMega data is nice to have for situations like this.

I guess it could have been coning or some other instability right after
motor burn out. Odd that it seems dependent on both high speed *and*
motor burn out, but...

I’m hot & heavy into making rockets to go after the F & G records
now. I’m aiming to fly them at Tripoli Colorado’s Springfest in a week
and a half. Those will have a TeleMini in them. I didn’t have time to
do the external GPS mod I wanted to with the TeleMini, so I’ll have to
hunt those rockets down with a Yagi. Should be fun!

I'm hoping to finish a 24mm min-diameter airframe to fly up in Hartsel
myself. I'm bringing along some NAR contest folks from Ft Collins; plan
to be there Saturday until the winds come up.

I’m busy with work until tomorrow night. I’ll take a better look at my
“something” rocket then.

You might bring the airframe that did this to the launch; I'd love to
take a look at it.

[Chris Attebery]

Did you sim the rocket in OpenRocket too? It's been noted that RAS is a
little less conservative than OR when it comes to stability. As Keith said,
maybe it got a bit unstable at burnout.

Post by Keith Packard

I’d really love to have 3-axis gyro and accelerometer data. :)

Yeah, TeleMega data is nice to have for situations like this.
I guess it could have been coning or some other instability right after
motor burn out. Odd that it seems dependent on both high speed *and*
motor burn out, but...

I’m hot & heavy into making rockets to go after the F & G records
now. I’m aiming to fly them at Tripoli Colorado’s Springfest in a week
and a half. Those will have a TeleMini in them. I didn’t have time to
do the external GPS mod I wanted to with the TeleMini, so I’ll have to
hunt those rockets down with a Yagi. Should be fun!

I'm hoping to finish a 24mm min-diameter airframe to fly up in Hartsel
myself. I'm bringing along some NAR contest folks from Ft Collins; plan
to be there Saturday until the winds come up.

I’m busy with work until tomorrow night. I’ll take a better look at my
“something” rocket then.

You might bring the airframe that did this to the launch; I'd love to
take a look at it.
--
-keith
_______________________________________________
altusmetrum mailing list
http://lists.gag.com/mailman/listinfo/altusmetrum

...

[Bryan Duke]

Chris- Yeah, it’s pretty marginal in OpenRocket (1 caliber at M3). Above about Mach 2, OpenRocket predicts the Cp quite a bit more aft than either the Barrowman or modified-Barrowman results that RAS gives. RAS still showed plenty stability at Mach 3 for its worst case. Honestly, I mostly scoffed OR’s results because of several posts Chuck’s made on RAS2’s improvements. Sooo, yeah, maybe that was a bad idea.

It’ll be a while before I can try this rocket again because of our typical Vegas waiver. Maybe next time I’ll bring a couple rockets instead of just one. Having different fin sizes and/or CGs would be nice. I should have some time to run some CFD before then too.

Keith- I just officially started construction on my 24mm rockets tonight. The fins are ready to attach…I’m 3d printing my fin alignment guides now. Long way to go before the 9th. Also, I guess it’s Spring Fling, not Springfest (oops). We’re planning on leaving Vegas next Thursday & getting to the Hartsel area on Friday the 8th. Is it that launch you’re going to or the one this weekend?

I have to build a Yagi and a launch tower before then too. Go, go, go!

-Bryan

[Bryan Duke]

Sorry….above M2, OR predicts Cp quite a bit more forward than RAS. Worse stability. You know.

Post by Bryan Duke
Chris- Yeah, it’s pretty marginal in OpenRocket (1 caliber at M3). Above about Mach 2, OpenRocket predicts the Cp quite a bit more aft than either the Barrowman or modified-Barrowman results that RAS gives. RAS still showed plenty stability at Mach 3 for its worst case. Honestly, I mostly scoffed OR’s results because of several posts Chuck’s made on RAS2’s improvements. Sooo, yeah, maybe that was a bad idea.
It’ll be a while before I can try this rocket again because of our typical Vegas waiver. Maybe next time I’ll bring a couple rockets instead of just one. Having different fin sizes and/or CGs would be nice. I should have some time to run some CFD before then too.
Keith- I just officially started construction on my 24mm rockets tonight. The fins are ready to attach…I’m 3d printing my fin alignment guides now. Long way to go before the 9th. Also, I guess it’s Spring Fling, not Springfest (oops). We’re planning on leaving Vegas next Thursday & getting to the Hartsel area on Friday the 8th. Is it that launch you’re going to or the one this weekend?
I have to build a Yagi and a launch tower before then too. Go, go, go!
-Bryan
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altusmetrum mailing list
http://lists.gag.com/mailman/listinfo/altusmetrum

...

[Bryan Duke]

Sorry….above M2, OR predicts Cp quite a bit more forward than RAS. Worse stability. You know.

Post by Bryan Duke
Chris- Yeah, it’s pretty marginal in OpenRocket (1 caliber at M3). Above about Mach 2, OpenRocket predicts the Cp quite a bit more aft than either the Barrowman or modified-Barrowman results that RAS gives. RAS still showed plenty stability at Mach 3 for its worst case. Honestly, I mostly scoffed OR’s results because of several posts Chuck’s made on RAS2’s improvements. Sooo, yeah, maybe that was a bad idea.
It’ll be a while before I can try this rocket again because of our typical Vegas waiver. Maybe next time I’ll bring a couple rockets instead of just one. Having different fin sizes and/or CGs would be nice. I should have some time to run some CFD before then too.
Keith- I just officially started construction on my 24mm rockets tonight. The fins are ready to attach…I’m 3d printing my fin alignment guides now. Long way to go before the 9th. Also, I guess it’s Spring Fling, not Springfest (oops). We’re planning on leaving Vegas next Thursday & getting to the Hartsel area on Friday the 8th. Is it that launch you’re going to or the one this weekend?
I have to build a Yagi and a launch tower before then too. Go, go, go!
-Bryan
_______________________________________________
altusmetrum mailing list
http://lists.gag.com/mailman/listinfo/altusmetrum

...