DD Woes. The Tragic StratoLogger Event.

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Except for one thing. The rocket weather cocked away from us and drifted back to us. When it reached approx 200', it was less than 25 yds away from us. So distance 75", elevation 200". Well within distance to hear a report.
I've conducted hundreds of analysis to discover what anomalies occurred during a rocket flight. The process involves the compilation of as much hard data (flight recorder data, videos, photos, etc. and as many first hand observer reports as possible, and developing a self-consistent event line of the flight and one or more possible explanations for the flight anomaly.

Hard data provides a permanent record of what happened while the first person accounts provide supplementary or confirming information to assist in the development of possible scenarios. A problem with first person accounts is that they may not be complete and the resulting time-line or analysis may be inaccurate because information was left out. In this case, the original description of the flight was incomplete. The reported wind at launch was 12-15 mph and it was reported the rocket exhibited slight weather cocking on ascent. From the altimeter the descent rate of the rocket from a 1344' apogee to 200' is know to be ~14 fps. Using the maximum estimated 15 mph wind speed (22 fps) and the altimeter's 80 second difference between time markers, a calculated maximum 1760' downwind drift of the rocket could have occurred. If the rocket exhibited only slight weather cocking, the downwind drift would have caused the rocket to be far away from the observers, most likely well over 1000' downwind. This was a key element in the previous analysis.

Now after is added the rocket was less than 100' from the observers at ~200' altitude, the conclusions obtained in the original analysis must be reassessed.

  1. Was the wind velocity actually 12-15 mph, or was it lower?
    1. If yes, then the description of slight weather-cocking is incorrect based on the new information.
    2. If no, it was lower, then the observation of slight weather-cocking would be consist with the new observation of a recovery relatively close to the observers.
    3. Neither result would effect what happened, but will effect the analysis of what most likely caused the anomaly.
  2. If the rocket was indeed close to the observers when the 200' main deployment charge was commanded to fire as confirmed by the altimeter, then it should have been heard.
    1. This puts more credence to the initial observer initial statement that the apogee charge seemed louder than usual that could indicate both charges fired at apogee.
      1. This leads to the possibility of there was problem with the connections of the e-matches to the altimeter and both the apogee and main deployment charges fired at apogee by the apogee pyrocircuit.
      2. Or the bulkhead flanges of the altimeter compartment are not gas tight and the apogee ejection charge pressurized the altimeter compartment and fooled the altimeter to into believing that the rocket had descended to 200' agl which caused the main to fire.
      3. Or the charges were wired backward and the apogee charge was wired to the main, fired and the apogee charge wired at the same time.
  3. Of these possibilities, the only one consistent with the StratoLogger data is:
    1. The apogee pyrocircuit fired both the apogee and main e-matches at apogee.
      1. Both charges had a common connection to the switched side of the apogee pyrocircuit.
      2. All preflight beeps would have appeared normal.
      3. Since the main pyrocircuit triggered at 200' as recorded by the altimeter, the other 2 possible explanations can be eliminated.
So the new observation alters the original conclusion. The probable cause of the flight anomaly is:


  1. Either a wire end or heavy soot deposit formed a bridge to enable the cross-connection.

The corrective actions to avoid the same event from occurring in the future is:


  1. Conducting a visual inspection of the altimeter pyrocircuit connections and any other wiring connections prior to each flight.
  2. Developing and using a written check list prior to each flight to insure that proper procedures and sufficient inspections occur before each flight to avoid these issues.

Bob
 
Was the wind velocity actually 12-15 mph, or was it lower?

Yes it was at or near that velocity but also with obvious various at different altitudes. I've often seen winds at our field vary noticeably at varying altitudes due to the surrounding landscape. By observation of the drift during decent, you could see times of great drift and times of near stall. Not uncommon on that field.

Or the bulkhead flanges of the altimeter compartment are not gas tight and the apogee ejection charge pressurized the altimeter compartment and fooled the altimeter to into believing that the rocket had descended to 200' agl which caused the main to fire.

Based on your in depth analysis, and my personal inspection of the bay, this seems the most viable of the listed causes. As I am human, I *could* have failed to tighten the nuts as securely as I should have.

Before disassembling the bay to pull the altimeter, I checked all connections for stray wire strands, secured set screws, carbon residue and damage to the bay or bulkheads. All was in order.

Pressure change in the bay caused by the drogue charge seems the most logical conclusion based on my inspection here. Barring that, a fault in the altimeter itself is the only logical conclusion.

Next launch, I will be putting the altimeter in my least "painful" to lose rocket. If it fails and the rocket is lost to damage, I won't be heartbroken.

The last unexplained riddle is the drastic change in the locator siren sound. If you are familiar with the StratoLoggerCF, you know the standard warble the siren makes. After landing, it sounded very distinctly like a group of crickets. After rebooting it, the startup tones sound as they always have. Obviously I can't trigger the locator without a flight, so I won't know until I fly it again. Unless you know a way to trigger it that I am unfamiliar with.

Thanks for the help everyone. Especially Bob. It has, at least, given me somewhere to start my physical testing.
 
No. I'm wrong. Had a seal been the issue, the altimeter would have logged the main deployment at an earlier time stamp. And there should have been a sudden drop then spike in the altitude log to show it seeing a 200' pressure registering. Back to square one.
 
ue and damage to the bay or bulkheads. All was in order.

The last unexplained riddle is the drastic change in the locator siren sound. If you are familiar with the StratoLoggerCF, you know the standard warble the siren makes. After landing, it sounded very distinctly like a group of crickets. After rebooting it, the startup tones sound as they always have. Obviously I can't trigger the locator without a flight, so I won't know until I fly it again. Unless you know a way to trigger it that I am unfamiliar with.

Thanks for the help everyone. Especially Bob. It has, at least, given me somewhere to start my physical testing.

Build yourself a vacuum chamber, then you can simulate a flight. I use a Foodsaver Marinating Bowl and my Foodsaver. I just place the altimeter inside the bowl with the connected battery and christmas light bulbs connected to the igniter/e-match circuits, activate altimeter, wait for the ready beeping, close bowl, connect Foodsaver/vacuum source, wait for apogee event (when Foodsaver reaches max vacuum) then open the valve to release vacuum and wait for the main circuit to fire the light. When pressure is normalized you should get the locator siren, and the data should show a flight when connected to a computer, it will have errors since there is no change in descent rates, but should work for testing. Its how I preflight test/practice with my altimeters
 
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Per the SL CF manual, you should be able to simulate flight by using your shopvac and building vacuum in the av bay... Review your manual. That'll give you a quick method of testing your outputs. I'd use Christmas light bulbs on your charge terminals as you want to simulate a load as well.

Mike
 
Build yourself a vacuum chamber, then you can simulate a flight. I use a Foodsaver Marinating Bowl and my Foodsaver. I just place the altimeter inside the bowl with the connected battery and christmas light bulbs connected to the igniter/e-match circuits, activate altimeter, wait for the ready beeping, close bowl, connect Foodsaver/vacuum source, wait for apogee event (when Foodsaver reaches max vacuum) then open the valve to release vacuum and wait for the main circuit to fire the light. When pressure is normalized you should get the locator siren, and the data should show a flight when connected to a computer, it will have errors since there is no change in descent rates, but should work for testing. Its how I preflight test/practice with my altimeters

Or, Adept Rocketry sells a very nifty altimeter testing chamber.
 
Per the SL CF manual, you should be able to simulate flight by using your shopvac and building vacuum in the av bay... Review your manual. That'll give you a quick method of testing your outputs. I'd use Christmas light bulbs on your charge terminals as you want to simulate a load as well.

Mike

What he says - assuming you have a shop vacuum. Otherwise, if you haven't already, send it back to Perfectflite!
 
So the new observation alters the original conclusion. The probable cause of the flight anomaly is:

  1. Either a wire end or heavy soot deposit formed a bridge to enable the cross-connection.


  1. If this were the case and the "starter" for the main deployment was fired from the apogee circuit, would you still see the same voltage droop when the main circuit was triggered against an already fired starter?
 
The e-matches I use don't always burn the bridge wire. Most of them still test successful for connectivity after firing.

Amazingly reliable as well.
 
No. I'm wrong. Had a seal been the issue, the altimeter would have logged the main deployment at an earlier time stamp. And there should have been a sudden drop then spike in the altitude log to show it seeing a 200' pressure registering. Back to square one.
That is correct.
What he says - assuming you have a shop vacuum. Otherwise, if you haven't already, send it back to Perfectflite!
Or you can use a regular vacuum cleaner...... What is important is to read the manual so that you know how to check out the altimeter after a mishap to make sure it is operating properly. The screamer should also activate when a simulated flight is conducted.....
If this were the case and the "starter" for the main deployment was fired from the apogee circuit, would you still see the same voltage droop when the main circuit was triggered against an already fired starter?
It depends on the source of the fault.

  1. The pressure trace shows there were no pressure abnormalities at apogee.
    1. This means the main pyrocircuit should not have been triggered at apogee.
    2. There is no marker indicating that the main pyrocircuit did fire at apogee.
  2. The event trace shows the main pyrocircuit was fired at 200'.
    1. Observers stated they did not hear a main event at 200'.
  3. From the rate of descent calculated from the pressure trace and personal observations, the main deployed at apogee.
    1. There is no main event maker at apogee, so the main deployment was not triggered by the main pyrocircuit in the altimeter.
    2. If the pyroshock did not break open the rocket at the separation point, then the only way for the main to come out at apogee was if the main deployment charge was fired by the apogee pyrocircuit.
  4. The only conclusion that can be drawn from the data and observations is that both charges were fired at apogee by the apogee pyrocircuit.
    1. The most probable reason is that the e-matches activating the apogee and main charges were wired incorrectly to the apogee pyrocircuit and both fired at apogee.
  5. Functionality of the altimeter should be checked as suggest in several preceding posts by using the procedures outlined in the StratoLoggerCF operating manual before sending the unit back to PerfectFlite.

Bob
 
Yes. Functionality is the prime concern now. I'll be performing a test this evening. Just need some Christmas lights. Big Lots here I come.
 
Could the main and apogee be wired up wrong? The main firing is very likely to result in both deploying.
 
No. The wiring was double checked. Plus, the altimeter had not been taken apart since the last launch. And it flew twice as it was during that launch.
 
No. The wiring was double checked. Plus, the altimeter had not been taken apart since the last launch. And it flew twice as it was during that launch.

Humm.... I wonder what the failsafe action is for the altimeter, in the event that there is a low voltage on the battery. Did you use the same battery for both launches, simply replacing the charges?

That's a new detail we didn't know..
 
Voltage looks fine from the altimeter log - minimal droop on both events.
 
The altimeter ticks off the voltage during startup. I used the self check to test the battery before assembly and to reconfirm on the pad.
 
As very much a newb, I'm curious as to why more people don't fly with some type of onboard video? Even a keychain cam or two can shed tons of light on the flight log numbers...
 
Cameras create drag for one. Can affect the flight. The 808 camera shroud cost 3 times what the camera costs. If you love de a rocket, and you have a high end camera, you lose the rocket, the motor case, the altimeter, and an expensive camera.

Plus, cameras are an extra expense. And ones small enough for rocketry are fairly new. Compared to RMS and DD altimeters anyway.
 
As very much a newb, I'm curious as to why more people don't fly with some type of onboard video? Even a keychain cam or two can shed tons of light on the flight log numbers...
For this flight, a camera would not provide any more information than the altimeter data file does. If the rocket lost a fin, or had a mechanical failure then an in-flight video might have been useful.

Cameras create drag for one. Can affect the flight. The 808 camera shroud cost 3 times what the camera costs. If you love de a rocket, and you have a high end camera, you lose the rocket, the motor case, the altimeter, and an expensive camera.

Plus, cameras are an extra expense. And ones small enough for rocketry are fairly new. Compared to RMS and DD altimeters anyway.
You have a $30 3" rocket with a $55 altimeter. A $16 shroud would not be a major expense if you wanted to launch a $35 to $40 808 #16 camera to collect in-flight video, but most folks I know simply attach them with Velcro or masking tape. An AT G75J lists at $22 so that what you spend every time you launch your $85 rocket which could carry an additional $38 to $54 camera investment which is less than value of the rocket if you wanted in-flight videos.

https://www.ebay.com/itm/Mini-DVR-8...-HD-720P-H-264-Pocket-Camcorder-/180776698380

https://www.etsy.com/listing/177473932/808-16-camera-shroud-for-rockets-3d

So the cost of a keychain camera is not really a major impediment to obtain in-flight video. If you want in-flight videos you make a camera investment equal to 2 G motors. If you aren't interest in videos you don't. Either way, you would not have obtained any more data to explain why you main deployed at apogee than you already have now.

Bob
 
Would you not be able to tell if the main was deployed via pyro vs deployed over a second or two via drag, depending on the placement of the camera(s)?

Not arguing for arguments' sake; merely trying to understand.

Thanks.
 
Well I finally took the time to set up a vacuum chamber. The altimeter is testing fine in the chamber. It is doing the a full flight sim and reporting the results. The locator siren is also sounding normal. I'm going to assume it was an odd fluke all the way around.

I had another chance to speak to my club's RSO about the flight. He made a note of something I missed. He has better eyes than I do.

During ejection, he says that he clearly saw two separate puffs of smoke from the ejection charges. I had missed that.

So the known facts here are:

1) The apogee deployment was late based on 4 people's visual observation.

2) Both deployment charges fired together based off visual observation and audible report strength.

3) There was no ejection report at the preset for the main, however both charges had fired.

4) The altimeter was wired properly and the connections were clean and secure.

5) The data logging clearly shows that the main deployed early based on the decent rate.

6) The data log clearly shows two separate events, at the appropriate altitudes.

Final conclusion:

The data and the observed events conflict. The performance of the altimeter and its siren obviously had flaws. No issues can be found in the data or in flight simulation testing.

Sometimes weird crap happens without explanation. Load it back up in a rocket you don't dearly love and see what happens.

We can't prove what we saw and heard but it did happen. Maybe a poltergeist possessed my rocket and had a good laugh. Or the gremlins had a field day during our day at the field lol.
 
Yep. He pretty much approached things same as Bob did. The conversation left me to believe that he had no intentions of having me send it back based on the available data.

So unless there is a recurring incident and hard proof, it looks like I'm on my own and use it at my own risk.
 
Yep. He pretty much approached things same as Bob did. The conversation left me to believe that he had no intentions of having me send it back based on the available data.

So unless there is a recurring incident and hard proof, it looks like I'm on my own and use it at my own risk.

You're not on your own when you fly with the club. :) Perhaps let a few of your rocket buddies who have used this alt observe your set-up and prep next time. Locals rule !
 
Thank you all for this thread it has been very informative let us know how it works after the next launch.
 
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