Princeton University attempt at a suborbital space shot?

Eyesinthesky said:

Do you mean like these?

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The first one shows corkscrewing until booster motor burnout. If someone put a gun to my head and told me to guess the cause, I'd go for fin misalignment, but it could be other things. Other people here have far more experience diagnosing staged flights. I didn't see the airframe flexing in the third one, but I was also having trouble sorting out camera motions vs. rocket motions.

boatgeek said:

The first one shows corkscrewing until booster motor burnout. If someone put a gun to my head and told me to guess the cause, I'd go for fin misalignment, but it could be other things. Other people here have far more experience diagnosing staged flights. I didn't see the airframe flexing in the third one, but I was also having trouble sorting out camera motions vs. rocket motions.

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I am definitely not an expert, but why would the effect of misaligned fins cease on burnout? I would suspect off center thrust or motor mount misalignment.

Steve Shannon said:

I am definitely not an expert, but why would the effect of misaligned fins cease on burnout? I would suspect off center thrust or motor mount misalignment.

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It's of questionable worth, but from shooting ****-tons of photos, if something stops at motor burn-out, it's motor related. On an MD, mount misalignment is hard to pull off...but off center thrust....thats easy. If it was fins, you'd see the coning get horrific as it slowed.

Like the design of other small sounding rockets (e.g. Terrapin), due to manufacturing tolerances and small roll moment of inertia, it was felt that the vehicle would roll sufficiently without intentional fin cant angle. We estimate the equivalent of about a 0.1 degree cant angle for each stage, which produced ~3 Hz peak roll rate at booster burnout and somewhere around ~7 Hz during sustainer flight (even smaller roll moment of inertia).

We do have data from our IMU confirming that the "corkscrewing" motion observed was actually just a short period pitch oscillation that was poorly damped because the fins were relatively small. We have compared the roll rate from the IMU with the undamped pitch frequency and the vehicle did not pass through resonance and thus it wasn't inertial coupling.

We are not yet sure the source of the inital destabilizing pitching moment, but I personally suspect uncompensated wind shear. It could have also been flexible body dynamics. Assuming it is wind, to make our pitch oscillations match up with the flight data trajectory it seems there was a fairly strong wind shear of about ~15 kt just above the launch tower.

If you read our FAA waiver application, we tried to get away with not actually measuring the winds above the launch pad with balloons during our wind-weighting procedure, instead, we tried to use NOAA wind forecasts. It turns out these were probably not accurate at all at lower altitudes, below the mountain range to the East and West some of which peak out at nearly 8000 ft MSL. At lower altitudes orographic wind effects dominate. Next time we will do wind-weighting properly.

We will also likely go with slightly larger booster fins to increase our damping ratio for the next flight to damp out any short period oscillations more quickly, and have a wider launch commit criteria in terms of peak winds allowed. We may also want a somewhat longer and stiffer launcher, not only to decrease impact dispersion but also to have a reduce the angle of attack due to any wind shears just above the rail due to higher rail exit velocity.

I am working on a flight data report and it will be released soon. The priority is getting an anomaly report with estimated booster impact location to WSMR and FAA/AST, as I'm required to under the conditions of the waiver.

saadzmirza said:

We are not yet sure the source of the inital destabilizing pitching moment, but I personally suspect uncompensated wind shear. It could have also been flexible body dynamics. Assuming it is wind, to make our pitch oscillations match up with the flight data trajectory it seems there was a fairly strong wind shear of about ~15 kt just above the launch tower.

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Before searching for this alleged shear, you should consider the possibility that this is a case of unmodeled system dynamics.

Steve Shannon said:

I am definitely not an expert, but why would the effect of misaligned fins cease on burnout? I would suspect off center thrust or motor mount misalignment.

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Sorry, I wasn't clear. I meant that I could see corkscrewing until burnout because the smoke trail continued to corkscrew. I have no idea what happened after burnout since I couldn't see the rocket anymore.

saadzmirza said:

...
We do have data from our IMU confirming that the "corkscrewing" motion observed was actually just a short period pitch oscillation that was poorly damped because the fins were relatively small. We have compared the roll rate from the IMU with the undamped pitch frequency and the vehicle did not pass through resonance and thus it wasn't inertial coupling.

We are not yet sure the source of the inital destabilizing pitching moment, but I personally suspect uncompensated wind shear. It could have also been flexible body dynamics. Assuming it is wind, to make our pitch oscillations match up with the flight data trajectory it seems there was a fairly strong wind shear of about ~15 kt just above the launch tower.
...

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Was there yaw motion observed as well? If not, is the corkscrew appearance because the rocket was pitching about its own axis, which was rolling? It's been a long time since I was in dynamics class, so I'm trying to resolve the clear corkscrew motion from the video with it only pitching.

Yes, it yawed as well producing the corkscrew appearance.

Doubtful that the destabilizing pitching moment was from launcher tip-off David, because you'd see the initial angular velocity immediately off the rail, and we did not have an angular velocity about the pitch axis immediately off the rail.

saadzmirza said:

Doubtful that the destabilizing pitching moment was from launcher tip-off David, because you'd see the initial angular velocity immediately off the rail, and we did not have an angular velocity about the pitch axis immediately off the rail.

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It is touching to see such confidence in instrumentation. I wish I shared it.

The sample rate available is a maximum of 100SPS which isn't really adequate to capture these dynamics. Worse is that the configuration of the sensor is unknown. The specifications make it look like it could be a MPU-9250. If so, it has issues.

The DLPF is pretty poor and should be configured to no higher than 10Hz when used at 100SPS. That introduces 18ms of delay. Since this is roughly on the order of the time the pitching moment would be applied, the data wouldn't reflect the angular rate until after the rocket was off the rail. (Note also that with 10ms between samples, you only see a couple with one guide on the rail. Wildly inadequate.)

But the configuration isn't stated anywhere I can find so who knows what it is doing. It could have set the DLPF to a higher frequency and just given Nyquist a miss. But there is always delay.

Corkscrew right off the rail can be caused by miss-aligned rail buttons.

Just saw this on the Watering Hole sub:

STUDENTS WANT TO BREAK WORLD RECORD FOR HIGHEST ALTITUDE REACHED BY A ROCKET.

https://news.northeastern.edu/2018/...ord-for-highest-altitude-reached-by-a-rocket/

Likely, they were encouraged by the Princeton attempt. Here's a link to the teams web page:

https://operationspace.org/index.html#about

The team hopes at minimum to break the 144,000 foot altitude record by a student team set by USC. But their actual goal is to reach the 100 km von Karman line for suborbital space.

Bob Clark

I just saw this on Mach5lowdown.com that another student team will attempt the 100 km altitude goal:

28 AUG 2018
The Hound – Our Mission
by Tobias Bauernfeind |
In less than 4 weeks, our rocket „The Hound“ will launch from the Black Rock Desert.
https://spaceteam.at/2018/08/28/the-hound-our-mission/?lang=en

Like the Princeton attempt, they will use two commercial motors. However, they will attach the fin can and nose cone directly to the motor casings without a separate airframe, presumably to save weight.


Bob Clark

RGClark said:

I just saw this on Mach5lowdown.com that another student team will attempt the 100 km altitude goal:

28 AUG 2018
The Hound – Our Mission
by Tobias Bauernfeind |
In less than 4 weeks, our rocket „The Hound“ will launch from the Black Rock Desert.
https://spaceteam.at/2018/08/28/the-hound-our-mission/?lang=en

Like the Princeton attempt, they will use two commercial motors. However, they will attach the fin can and nose cone directly to the motor casings without a separate airframe, presumably to save weight.


Bob Clark

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Launching the weekend of September 21 at Black Rock.
So they are launching at BALLS?

M

Side question: Are RGClark and MClark related?

If they are related, that would make for very entertaining holiday gatherings!

rfjustin said:

If they are related, that would make for very entertaining holiday gatherings!

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Even more so if they're actually the same person, with a split personality.

"I wrote what?!?!"

I disowned him a while ago
https://www.rocketryforum.com/threa...a-two-stage-rocket.145740/page-4#post-1785779

M

MClark seems way too practical for RGClark to duplicate. RGClark is all math theoretical and no engineering sense he struggled with material selection once. Also lacks flight experiences or hadn’t posted flights.

Andrew_ASC said:

RGClark is all math theoretical and no engineering sense he struggled with material selection once. Also lacks flight experiences or hadn’t posted flights.

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Maybe you two are related?

Lol. No. You’ve seen my stupid temper. Bob never really gets mad about stuff or streams posts of thought that piss off entire forum.

Bob never was described as arrogance crashing through kool-aid like a brick. When I post something stupid. People notice and not in the good way.

Andrew_ASC said:

Lol. No. You’ve seen my stupid temper. Bob never really gets mad about stuff or streams posts of thought that piss off entire forum.

Bob never was described as arrogance crashing through kool-aid like a brick. When I post something stupid. People notice and not in the good way.

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Andrew, you should get a picture of Kool Aid and use it as your avatar...would be excellent.

MClark said:

Launching the weekend of September 21 at Black Rock.
So they are launching at BALLS?

M

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At least, that's the plan.

Reinhard

RGClark said:

Like the Princeton attempt, they will use two commercial motors. However, they will attach the fin can and nose cone directly to the motor casings without a separate airframe, presumably to save weight.

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Mostly commercial would be more accurate. Some adjustments (custom closures) have been made for integration purposes, but performance wise, they are stock motors (N5800 to M2245).

Reinhard

Team from Virginia Tech is planning for a two-stage flight with experimental Q motors. Motors are cast into 8-inch casings. I’m rooting for them to pull it all together over the next couple of weeks and then make the long drive to blackrock.

Andrew_ASC said:

Lol. No. You’ve seen my stupid temper. Bob never really gets mad about stuff or streams posts of thought that piss off entire forum.
Bob never was described as arrogance crashing through kool-aid like a brick. When I post something stupid. People notice and not in the good way.

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I’m a veteran of the verbal wars on Usenet in the late 1990’s to early 2000’s. (Anybody remember Usenet?) I decided then to only respond to the scientific content in posts.

The comments here are more humorous than malicious like on Usenet.

Bob Clark

r.m.r.

Good luck to Virginia Tech. Whatever happens they will learn a whole lot more than most of us. They are attempting what very few people try.

RocketHunter said:

...
Our final ignition method used a slow burning igniter and a burst disk on the nozzle to maintain ~ ground level pressure and help the motor come up to pressure faster (recommended by Karl @ AT). Initial analysis of accelerometer looks like both worked as intended, but the disk needed to be sized for more pressure - it ignited and produced momentary thrust then immediately chuffed out.
...

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Just saw this video by the TU Wien team on their attempt at a student altitude record:

The Hound - Mechanics and Test Flights.


They discuss there their work to insure the upper stage does ignite.

Bob Clrk

You got me again! YRB....
There is no discussion of sustainer ignition, just statements of need to work on it.
High altitude [40-50,000 ft] is a byatch & comes with special requirements.

blackjack2564 said:

You got me again! YRB....
There is no discussion of sustainer ignition, just statements of need to work on it.
High altitude [40-50,000 ft] is a byatch & comes with special requirements.

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Yeah, he got me too. Hey, I have an extra pellet....?!

Jim

blackjack2564 said:

You got me again! YRB....
There is no discussion of sustainer ignition, just statements of need to work on it.
High altitude [40-50,000 ft] is a byatch & comes with special requirements.

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I'll inquire of the TU Wien team what efforts they are doing to insure the upper stage lights.

Bob Clark