Failure Analysis of Hyperion

[blackbrandt]

Hello everyone,
I'd like this thread to be an analysis of what went wrong. Speculation is fine, analysis based off of experience is better.

There were 2 major failures on my L3 attempt.

1. Eggfinder Failure
I had an Eggfinder Tx with the stock antenna on it.

Method of prep for eggfinder:
I used 1x3.7v 500mAH Lipo attached via a JST connector to the Tx. The battery was measured at 3.62 volts the night before. Although I have not used it for flight, I have used it for testing before.

I powered on the eggfinder, wrapped the eggfinder in a layer of foam, then placed the battery on the bottom of the wrap and gave it another wrap of foam. This was inserted into a fiberglass tube with an epoxy plug at one end. the other end was secured with multiple layers of new electrical tape.

This assembly was zip-tied to the shock cord next to the nose cone.


This is the method I have used on all previous tracker flights, including a flight that pulled over 40 G's.


On powering on the tracker, the LCD screen showed coordinates that I confirmed by plugging them into my phone. These coordinates were dead accurate to where I was standing at my tent.


I inserted the tracker into the rocket, added my shear pins, and was at the pad within 15 minutes. There was approximately 15 minutes of prep time at the pad before launch. This means that there was no more than a half hour of the tracker beeping away. The Eggfinder user manual states that 200mAH will be enough to keep the Eggfinder going for about 3 hours. Therefore, I have ruled out battery dying.


After launch, during descent, I lost sight of the rocket. I had left my Rx at the table, so I turn around and take my eyes off of the rocket (this was failure number 1, I needed to keep an eye on the rocket). I grab the Rx, and notice that there has now been 60 seconds since the last signal. Furthermore, the coordinates displayed were the coordinates of the launch pad.

My current best guess as to what happened is that on launch, a wire was pulled loose and powered off the Eggfinder. However, this particular transmitter setup has worked on a 40G flight.




Failure #2, main at apogee.

I'm rather infamous for spitting my main at apogee. Generally, it's due to my oversizing of charges. However, I don't think that this was the case this time.


This was the ground test for the drogue. My configuration for the 30" long by 7.51" diameter drogue payload area was a 6.2 gram charge in a charge well, with 3 x #4-40 nylon pins.
[video=youtube;kbmoEYzBznc]https://www.youtube.com/watch?v=kbmoEYzBznc[/video]


This was my ground test for the main. My configuration for the 46" long by 7.51" diameter main payload area was a 8.2 gram charge in a charge well, with 3 x #4-40 nylon pins.
[video=youtube;lmXDt_gtlIo]https://www.youtube.com/watch?v=lmXDt_gtlIo[/video]


As you can see, the drogue charge was just enough to get the rocket separated. The fit of all parts was a smooth but snug fit.


For electronics, I had an RRC3 for primary, and an RRC2+ for backup. All wires were double and triple checked that they were running to the correct charges. I have ruled this method of failure out.

From wind data that several people have gathered, the winds at apogee were approximately 50 mph (which was another error I should have thought of).


The rocket flew to approximately 6500-7000 feet. When we were able to see it, the main had deployed at apogee.

On talking to Dan Micheal, he explained that some altimeters can fire the main at apogee if it is windy enough. This is my leading theory.




Any insights possible would be greatly appreciated.

 

[jderimig]

I used 1x3.7v 500mAH Lipo attached via a JST connector to the Tx. The battery was measured at 3.62 volts the night before. Although I have not used it for flight, I have used it for testing before.

......

The Eggfinder user manual states that 200mAH will be enough to keep the Eggfinder going for about 3 hours. Therefore, I have ruled out battery dying.

At 3.62V your LiPo battery was significantly discharged, probably well less than 1/2 its capacity. You didn't have 500mah left at launch. The battery probably did not suddenly discharge at launch but you cannot rule this out based on the reasons you posted.

On talking to Dan Micheal, he explained that some altimeters can fire the main at apogee if it is windy enough. This is my leading theory.

No. That should not be your leading theory by any means.

 

[blackbrandt]

At 3.62V your LiPo battery was significantly discharged, probably well less than 1/2 its capacity. You didn't have 500mah left at launch. The battery probably did not suddenly discharge at launch but you cannot rule this out based on the reasons you posted.

I fail to understand your reasoning. How is 3.62 volts less than half capacity of 3.7 volts?

No. That should not be your leading theory by any means.

I should clarify, it's the only one I have.

 

[Lowpuller]

Jderimig.

I don't understand your comment. I use the same setup and rarely if ever see voltage higher than 3.62volts even at full charge????

 

[djs]

Personally, most "main at apogee" issues I've seen were due to wires being backwards. Not saying this is what happened to you, but with shear pins, it's not as likely to jolt the main out.

Your drogue charge (ground test) video looked good to me- that's what I would hope to see for a drogue test. Good enough to get everything out, but not enough to jolt the rocket too hard.

I use lipo batteries and the voltage is "lower" than a 9v, but they seem to last "forever" for me. I would think the eggtimer failure is probably a wire that decided to come loose. Either that or an antenna issue where it was still putting out signal, but the range was very limited.

 

[Flyfalcons]

3.7V is the nominal voltage of a single cell lipo. It will show well above that when fully charged. My 3-cell airplane packs are 11.1V nominal but show over 12V when charged. I agree that you should not rule out a dead battery.

 

[jderimig]

I fail to understand your reasoning. How is 3.62 volts less than half capacity of 3.7 volts?

Below is a typical discharge curve for a LiPo battery. If you look at the top curve which is the low current discharge line, by the time you get down to 3.6v (with this particular battery) there is very very little capacity left.

 

[blackbrandt]

3.7V is the nominal voltage of a single cell lipo. It will show well above that when fully charged. My 3-cell airplane packs are 11.1V nominal but show over 12V when charged. I agree that you should not rule out a dead battery.

But I thought you weren't supposed to overcharge a LiPo?

 

[jderimig]

Jderimig.

I don't understand your comment. I use the same setup and rarely if ever see voltage higher than 3.62volts even at full charge????

You have a bad battery or a bad charger or a bad voltmeter.

 

[Flyfalcons]

But I thought you weren't supposed to overcharge a LiPo?

A 3.7V lipo does not get charged to 3.7V. That is its nominal rating, not what you see when fully charged.

 

[noffie79]

But I thought you weren't supposed to overcharge a LiPo?

A fully charged one cell Lipo is 4.2V. Most, if not all lipo chargers will automatically stop charging once the battery is fully charged. In the RC world, most have a LVC (low voltage cutoff) and that's usually at 3.2V. Your battery was pretty low and I wouldn't be surprised if a low battery is the reason you lost tracking capability.

 

[AeroAggie]

3.7V on a LiPo is the nominal resting voltage (and long term storage), about in the middle of its charge range. You should see 4.2V per cell fully charged, and 3.0V is the minimum safe discharge. These altimeters don't drain a battery like an R/C airplane can so you're probably still ok there, but 3.7V in the R/C world is almost a no-fly voltage. If you never see more than that, you may need a new charger.

edit - gah...y'all beat me to it.

 

[jpoehlman]

Take a look at this chart: https://s36.photobucket.com/user/eunos800/media/LIPOCHART.jpg.html

A fully charged 1s LiPi battery should be at or near 4.2 volts.

Sorry to hear about your loss. Perhaps your voltage meter is off a bit, and it's was something else.

Jack

 

[blackjack2564]

You should have NEVER made that flight without a RF tracker. You would have rocket back if one was in there.That's the hard cold fact. I would not have allowed you to make that flight with out one, especially when uppers were raging like that.

GPS's lose lock & fail...I have seen it way too many times. In 10yrs of using RF trackers, I have never lost one, nor any of my mates using them. Yes I use GPS & that will get me to a rocket real quick, but there is ALWAYS a RF in there for back up. I can't believe Gus or Jim didn't offer or insist, you one to use. They are the last defense for anything going wrong in a flight other than destruction.

I cyphered your flight, by the way...[I've been all over that field in 9yrs] Checking the layered winds from 6,000 [39mp] 5,000 35mph 3000 [24mph] 2000 22mph surface 7-17 gusts[] that day....using a very forgiving 30/sec rate I figured rocket is 3.7-4.5 miles from launch......we'll see how close I come..LOL

RF tracker or lack there of, is your failure. Everything else was "matters not'' , you would know where it is/have it back . :wink:

 

[kevinkal]

I'm sorry to read of your lost project. I hope you recover it soon!

A single cell LiPo battery should be 4.2 V when fully charged. A cell at 3.62 Volts is nearly discharged. I grabbed this table from an RC model group thread.. I can't say it's 100% accurate.. but a reasonable guide:
4.20v = 100%
4.03v = 76%
3.86v = 52%
3.83v = 42%
3.79v = 30%
3.70v = 11%
3.6?v = 0%

Also, if I'm not mistaken, doesn't Chris recommend that the Eggfinder Tx be used with a 2S LiPo? Here's what I found in the Eggfinder_Users_Guide_RevB6:
"Eggfinder Quick Reference Guide
Eggfinder TX (Transmitter):
Battery: 300 mAh (min.), 7.4V (2S) LiPo battery recommended"

 

[DavidMcCann]

If it's windy on the ground, it can trick some...some... altimeters into thinking a gust is a liftoff, and then when the gust ends, that the increase in pressure is a return to earth, and it'll pop on the pad.

I don't think the RRC series suffers from this, and I don't think the effect would happen at altitude.

I could be wrong on those, but I'd look to other issues as wind is an unlikely culprit... people fly into 70-100 mph winds at altitude far too often for it to be typical.


Without data from an accelerometer, this one may be hard to get a likely cause.

 

[Wingarcher]

((EDIT)) Much of this is repeated above, I'm too damn slow typing replies sometimes.... ((EDIT))

Standard LiPo charging routine runs constant current until the voltage reaches 4.2V per cell for multi cell series packs, then maintain voltage and trail the current down to zero. A fully charged LiPo comes off the charger at 4.2V per cell.

Looks like the EggFinder manual recommends a 7.4V (a 2 cell, series wired pack) battery of 300mAh capacity.

Does the EggFinder incorporate a low voltage cutoff to protect the battery?

N

 

[mccordmw]

I'll second that a fully charged LiPo is higher than the nominal value on the label. I use 2S 7.4V LiPos for my Eggtimers and my Eggfinder. When fully charged, they measure 8.3 to 8.4 V. I would think your Eggfinder might have had a nearly dead or bad battery or a bad charger. How long was it plugged in while waiting for launch? It could have died.

And I'll also second what djs said, that most main at apogee issues are:

- from wires being backwards
- or the payload bay being in backward
- or (not in your case) no shear pins and the nose cone knocking off when the drogue deploys

You won't know for sure unless it can be recovered. Everything else is just speculation.

 

[blackbrandt]

I'll second that a fully charged LiPo is higher than the nominal value on the label. I use 2S 7.4V LiPos for my Eggtimers and my Eggfinder. When fully charged, they measure 8.3 to 8.4 V. I would think your Eggfinder might have had a nearly dead or bad battery or a bad charger. How long was it plugged in while waiting for launch? It could have died.

And I'll also second what djs said, that most main at apogee issues are:

- from wires being backwards
- or the payload bay being in backward
- or (not in your case) no shear pins and the nose cone knocking off when the drogue deploys

You won't know for sure unless it can be recovered. Everything else is just speculation.

I've considered the first 2 methods of failure. I just know for a fact that my wires were correct. I connected the wires at my hotel room in a peaceful area.

The payload bay fits exactly 1 way inside the rocket (it's another check I do).



Thank you all for the input.

 

[djs]

the real answer:

 

[mccordmw]

The Kerbal Kraken!

 

[SS/EA 6BBL 71 Cuda]

You should have NEVER made that flight without a RF tracker. You would have rocket back if one was in there.That's the hard cold fact. I would not have allowed you to make that flight with out one, especially when uppers were raging like that.

GPS's lose lock & fail...I have seen it way too many times. In 10yrs of using RF trackers, I have never lost one, nor any of my mates using them. Yes I use GPS & that will get me to a rocket real quick, but there is ALWAYS a RF in there for back up. I can't believe Gus or Jim didn't offer or insist, you one to use. They are the last defense for anything going wrong in a flight other than destruction.

I cyphered your flight, by the way...[I've been all over that field in 9yrs] Checking the layered winds from 6,000 [39mp] 5,000 35mph 3000 [24mph] 2000 22mph surface 7-17 gusts[] that day....using a very forgiving 30/sec rate I figured rocket is 3.7-4.5 miles from launch......we'll see how close I come..LOL

RF tracker or lack there of, is your failure. Everything else was "matters not'' , you would know where it is/have it back . :wink:

Jim- I always fly with two trackers in everything i send up- I'm using a new system right now and, didn't want to give him my "B" transmitter. "A" was in another rockteers rocket prepped and, ready to go. Then he flew it...before Matt. The recovery took longer than expected and, thus we didn't get it back into Matt's rocket. You are right with your comments though and, i do not take it personally.

What do i know?
- I can fly with RF (aka 1800's technology) in MY rockets and, get them back 99.999% of the time.
- Problems with GPS seem to be too rampant.

What did i learn?
- From now on, i will highly RECOMMEND that any L-3 flight i watch/review have TWO systems on board for tracking...Whether it's GPS or RF or a combination of both-

Once again, Jim you are right with your comments and, i respect that. Matt's failure to locate his rocket STILL weighs on me. That's the beauty of hindsight. It can bite you in the arse for sure.

 

[jderimig]

Well you could have had an altimeter failure. If you double the number of altimeters in your rocket you double the probability of an altimeter failure.

 

[terryg]

A flight with a smaller engine would have given a lower maximum altitude and corresponding easier recovery when the main deployed at apogee.

 

[rocketsam2016]

How heavy was the nose cone? 3x 4-40 shear pins will shear at 150lbs, so only 15Gs wouls shear the pins if the nose cone was 10lbs.

Then, it was a windy day, so the rocket could've had substantial horizontal velocity. If your drogue was sized to lower the rocket at 50fps, then if the drogue deployed at 190fps you'd have 15gs of deceleration which would shear the pins (based on the formula Gdecel = vdeploy^2/vterminal^2). Any chance the rocket was weathercocking enough to have a drogue deployment at those speeds, particularly if the drogue fired a little before or after apogee so you have 30-50fps of vertical velocity as well? Or was your nose cone much heavier than 10lbs or your drogue descent rate slower than 50fps? This formula is of course a conservative approximation, things like using nylon instead of Kevlar or having a chute open slowly soften the actual Gs.

 

[blackbrandt]

How heavy was the nose cone? 3x 4-40 shear pins will shear at 150lbs, so only 15Gs wouls shear the pins if the nose cone was 10lbs.

Then, it was a windy day, so the rocket could've had substantial horizontal velocity. If your drogue was sized to lower the rocket at 50fps, then if the drogue deployed at 190fps you'd have 15gs of deceleration which would shear the pins (based on the formula Gdecel = vdeploy^2/vterminal^2). Any chance the rocket was weathercocking enough to have a drogue deployment at those speeds, particularly if the drogue fired a little before or after apogee so you have 30-50fps of vertical velocity as well? Or was your nose cone much heavier than 10lbs or your drogue descent rate slower than 50fps? This formula is of course a conservative approximation, things like using nylon instead of Kevlar or having a chute open slowly soften the actual Gs.

I actually had a 4 pound nose cone, and nylon shock cords.

 

[rocketsam2016]

I actually had a 4 pound nose cone, and nylon shock cords.

Haha ok scratch that idea, you'd have to be going 300-400fps then to have a problem...

Any chance you swapped the charges by accident?

 

[blackbrandt]

Haha ok scratch that idea, you'd have to be going 300-400fps then to have a problem...

Any chance you swapped the charges by accident?

99.99999 percent sure.

 

[5x7]

Do you have a picture of the av bay wiring?

 

[jderimig]

99.99999 percent sure.

So you're telling me there is a chance.