Is 69445 m/s and 6281 Gs a good top speed for a Estes D12-5?

[Knuckledragger]

Got to launch my rear eject, Big Daddy today! Almost a year of waiting between burn bans/fire danger warnings, high winds, life, and work. Lift off great, climb out great to about 50ft, weather cocked, and warp speed in to the hill side 150yds away! Lots of ooooohs and aaaaahs changed to oh nooooo three seconds later. The good news is that the ejection charge kicked the laundry out, about three feet before impact with rock solid CO clay. The nose cone, altimeter mount, one rivet, and two inches of the extension got sacrificed. I didn't get any feedback from the tattle-tale thread I wove in to the kevlar shock cord to measure deployment stretch with this one though (both looked a little more compact ). Inspection of the rocket body, centering rings, fins and bulkheads are still intact. The rivets tore back through an inch of the extension and the nose cone upper two inches busted off from a 45 degree impact. A little duct tape, some epoxy, and newspaper; she'll be good to go! jk
Estes Big Daddy
3" forward extension
Rear eject
Kevlar shock cord
Altimeter Two
Estes D12-5

 

[Nytrunner]

Oh gads, I love those Altimeter 2 errors. Dont think ive had one as ludicrous as that

 

[BEC]

How was the altimeter mounted in the model? Those numbers look like it got slammed around a bit....

 

[o1d_dude]

Send the photograph to John Beans at Jolly Logic.

He’ll get a kick out of it.

 

[Zeus-cat]

6281.2 G, gotta love that .2 G for accuracy

 

[BABAR]

Is it possible that was the DEcelleration rate on impact?

 

[tsmith1315]

I don't think it would be in one piece after -6000 G. I've seen an altimeter PCB stripped pretty clean on hard impact. Even most of the tiny surface mount capacitors flew off.

 

[Knuckledragger]

Is it possible that was the DEcelleration rate on impact?

My thought exactly! Had to dig three inches down to retrieve the nose cone piece.

 

[Knuckledragger]

Oh gads, I love those Altimeter 2 errors. Dont think ive had one as ludicrous as that

Ludicrous speed!

 

[Knuckledragger]

How was the altimeter mounted in the model? Those numbers look like it got slammed around a bit....

The balsa pieces to the right of the rocket were the mount in the payload bay. They definitely got slammed on impact! No neoprene wrap was going to absorb that hit.

 

[Knuckledragger]

6281.2 G, gotta love that .2 G for accuracy

JL paid some serious attention to detail.

 

[John Beans]

Sigh.

Will look at AltimeterTwo code—there are "reasonableness" checks in it, but this smells like an overflow-type error where the code looks fine but the math produces nonsense in a certain situation.

Not saying that's what happened here, but just as another example: sometimes if there is a "false launch" triggered by unfortunate jostling and the analysis begins while the rocket is still on the pad, all kinds of logical assumptions about events fail in weird ways.

Fixing this on AltimeterTwo is made harder by not having the altitude and acceleration traces to look at later.

 

[BABAR]

Sigh.

Will look at AltimeterTwo code—there are "reasonableness" checks in it, but this smells like an overflow-type error where the code looks fine but the math produces nonsense in a certain situation.

Not saying that's what happened here, but just as another example: sometimes if there is a "false launch" triggered by unfortunate jostling and the analysis begins while the rocket is still on the pad, all kinds of logical assumptions about events fail in weird ways.

Fixing this on AltimeterTwo is made harder by not having the altitude and acceleration traces to look at later.

I think a ballistic recovery is more than a good excuse for a faulty readout. The REAL test is, did it work for the next flight of the altimeter (obviously not necessarily the same rocket) on the NEXT flight!

 

[BABAR]

Got to launch my rear eject, Big Daddy today! Almost a year of waiting between burn bans/fire danger warnings, high winds, life, and work. Lift off great, climb out great to about 50ft, weather cocked, and warp speed in to the hill side 150yds away! Lots of ooooohs and aaaaahs changed to oh nooooo three seconds later. The good news is that the ejection charge kicked the laundry out, about three feet before impact with rock solid CO clay. The nose cone, altimeter mount, one rivet, and two inches of the extension got sacrificed. I didn't get any feedback from the tattle-tale thread I wove in to the kevlar shock cord to measure deployment stretch with this one though (both looked a little more compact ). Inspection of the rocket body, centering rings, fins and bulkheads are still intact. The rivets tore back through an inch of the extension and the nose cone upper two inches busted off from a 45 degree impact. A little duct tape, some epoxy, and newspaper; she'll be good to go! jk
Estes Big Daddy
3" forward extension
Rear eject
Kevlar shock cord
Altimeter Two
Estes D12-5

So, did the altimeter still work properly on the next flight? If so, that’s a strong kudo to the design.

 

[Zeus-cat]

My thought exactly! Had to dig three inches down to retrieve the nose cone piece.

No. You had a relatively low G impact if you had to dig 3 inches to get the nose. Compare that to hitting concrete or asphalt which your rocket would not penetrate and therefore would have a very high G impact.

 

[Knuckledragger]

I think a ballistic recovery is more than a good excuse for a faulty readout. The REAL test is, did it work for the next flight of the altimeter (obviously not necessarily the same rocket) on the NEXT flight!

Honestly John if you look at the impact crater, I didn't think the altimeter survived, we haven't had rain in a month and the ground is almost as hard as concrete. When the rocket weathercocked, it was at approximately 50ft but man did it appear to accelerate toward the ground. The only parameters I have is a Big Daddy modified with a 4" forward extension, D12-5, really sweet parabolic flight in to a 15 degree embankment 150yds away

I think a ballistic recovery is more than a good excuse for a faulty readout. The REAL test is, did it work for the next flight of the altimeter (obviously not necessarily the same rocket) on the NEXT flight!

Hope to find out Tues/Wed. Winds are gusting 15knts so no flight unless it calms down this evening. Mars Lander and BBertha are next up. Pretty certain the mount I made for the altimeter helped save it, as the blue tape holding the mount had to separate, the balsa mount had to absorb the hit inside the NC and break apart before the device could bounce and exit the smaller opening of the broken NC.

 

[Knuckledragger]

Thank you John Beans for a quick response to my post and email. I truly mean the post to be a testament as to the build quality of the Jolly Logic Altimeter. When I saw the shattered NC I thought for sure the window/case on the altimeter would be toast. Your quick response sir, in my eyes, reinforces that commitment to quality. If weather cooperates, I hope to fly again this week, possibly the same rocket. Since it rained 1.5 inches last night and the sprinklers on the field have been on, the ground might be a little more forgiving but either way I have a spare NC and more just ordered! Thanks again.

 

[jrap330]

I think a ballistic recovery is more than a good excuse for a faulty readout. The REAL test is, did it work for the next flight of the altimeter (obviously not necessarily the same rocket) on the NEXT flight!

I wish guys that ask questions, start doing a little math 69000 meter/sec is about 43 miles per second, which is 2582 miles per hour...as a rocket person.....is that achievable.

 

[Reinhard]

I wish guys that ask questions, start doing a little math 69000 meter/sec is about 43 miles per second, which is 2582 miles per hour...as a rocket person.....is that achievable.

The Parker Solar Probe will be about three times as fast. So ... as a rocket person ... it IS achievable.

Reinhard

 

[John Beans]

Knuckledragger shared the data with me:

Altitude	Speed	Burn	PeakAcc	AvgAcc	C2Ap	Apogee	Ap3Ej	Descent	Duration
3	69445	0.5	4.0	6821.0	0.0	0.0	3	0	0.5

This is the signature of a "false launch." Very low altitude for apogee and ejection, and nonsense data otherwise.

AltimeterTwo senses launch by sensing acceleration. It tries to ignore normal handling, but it's not perfect. It seems especially sensitive to being dropped down the rod/rail.

The solution, until it gets smarter, is to take a little extra care once it's armed and perhaps consider taking a quick peek at it right before you close it up.

 

[Reinhard]

AltimeterTwo senses launch by sensing acceleration. It tries to ignore normal handling, but it's not perfect. It seems especially sensitive to being dropped down the rod/rail.

Here is my currently preferred approach, maybe it's interesting for you:
Continuously write acceleration data into a circular buffer. The buffer should hold maybe about 500ms of data.
Average the acceleration (minus gravity) in the buffer after every update. The average acceleration in the buffer is equivalent to the delta_v gained within that time frame. If this is bigger than a certain threshold, lets say 12m/s, launch is detected.
12m/s within 0.5s is 2.4g, something that every rocket launch should be well above of. On the other hand 12m/s is equivalent to tossing the rocket 7m into the air (or dropping it from the same height), which is well beyond rough handling of a rocket.

There are some details, that need to be taken care of, but then the algorithm should handle pretty much all scenarios, including things like strong thrust oscillations as they occur in some hybrids.

Reinhard

 

[neil_w]

Woohoo, D altitude record! Gonna be tough to top that.

 

[Knuckledragger]

Woohoo, D altitude record! Gonna be tough to top that.

Torn between acknowledging the significance or going higher, faster, or deeper

 

[Knuckledragger]

Knuckledragger shared the data with me:

Altitude	Speed	Burn	PeakAcc	AvgAcc	C2Ap	Apogee	Ap3Ej	Descent	Duration
3	69445	0.5	4.0	6821.0	0.0	0.0	3	0	0.5

This is the signature of a "false launch." Very low altitude for apogee and ejection, and nonsense data otherwise.

AltimeterTwo senses launch by sensing acceleration. It tries to ignore normal handling, but it's not perfect. It seems especially sensitive to being dropped down the rod/rail.

The solution, until it gets smarter, is to take a little extra care once it's armed and perhaps consider taking a quick peek at it right before you close it up.

I loaded the laundry/rear CR, turned the rocket nose up and loaded the altimeter, NC, and installed the rivets that hold the NC in place, and then turned the rocket tail up to load the motor and ignitor before putting it on the pad. Will change that process next launch. Thanks again John

 

[prfesser]

That D motor must have had some of that propellant that a guy posted on the web about 20 years back. He was claiming a two-grain 29 mm motor was a J motor. That would be consistent with Isp around 700. I can only assume that some U-235 or Pu-239 was in the mix... (Found out later that he was multiplying *peak* thrust by burn time; it's supposed to be *average* thrust x burn time.)

Best -- Terry