4" Drago rapid dis-assembly

Wayco

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Here is the last shot of my 4" Drago before it's shred at Holtville Havoc March 3rd:
022.jpg


This was the third flight for this rocket, first was on a k456 dark matter. Nominal flight to 5450 ft. with a normal recovery. Second flight was the drag race at ROCstock on the K850 dark matter. Awesome flight to 7614 ft. which won the drag race.
I liked that motor so much, I bought another one and flew it at Holtville, with disastrous results. Lost two fins at 4546 ft. Just about burn out of the motor, and close to 10,000 fps.


I downloaded the altimeters today, and think I have found an answer as to why this event happened.
drago%20rrc3%20failure.jpg


Both altimeters had that strange sine wave before spiking up, with the Stratologger indicating a normal sequence of events after the incident. The RRC-3 fired the drogue, which sheared the pins on the N/C and deployed the main chute. Both of the fins were recovered, and amazingly, the main chute was undamaged. The drogue was destroyed, and the swivel on the main will never be the same again.
Originally, I thought that my epoxy failed when the rocket got some fin flutter or something, but with the downloaded data from the RRC-3, now I'm thinking that my static ports didn't vent right due to the twist and tape wires blocking them. I'm open to any other ideas on this....
 

mikec

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So you had an early deployment? Not sure how that would cause you to lose fins...
 

Wayco

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Curious as to the sampling port config, how many, how big and where where they located?

Three ports 120 degrees apart on the switch band. They are 3/16" in diameter, and two have two strands of 24 gauge wire through them for twist and tape switches. This is a HED rocket, so the switch band is right below the nosecone.
 

blackjack2564

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Here is the last shot of my 4" Drago before it's shred at Holtville Havoc March 3rd:
022.jpg


This was the third flight for this rocket, first was on a k456 dark matter. Nominal flight to 5450 ft. with a normal recovery. Second flight was the drag race at ROCstock on the K850 dark matter. Awesome flight to 7614 ft. which won the drag race.
I liked that motor so much, I bought another one and flew it at Holtville, with disastrous results. Lost two fins at 4546 ft. Just about burn out of the motor, and close to 10,000 fps.


I downloaded the altimeters today, and think I have found an answer as to why this event happened.
drago%20rrc3%20failure.jpg


Both altimeters had that strange sine wave before spiking up, with the Stratologger indicating a normal sequence of events after the incident. The RRC-3 fired the drogue, which sheared the pins on the N/C and deployed the main chute. Both of the fins were recovered, and amazingly, the main chute was undamaged. The drogue was destroyed, and the swivel on the main will never be the same again.
Originally, I thought that my epoxy failed when the rocket got some fin flutter or something, but with the downloaded data from the RRC-3, now I'm thinking that my static ports didn't vent right due to the twist and tape wires blocking them. I'm open to any other ideas on this....


LOL.....first off I think you meant 1,000fps...10,000 would be M-8.93!!!!

I would like to see graph from Strato [or other than one shown.] Something is wonky.You show 0 altitude from lift off to 2.25 seconds then it leaps up to 4,000 ft instantly. Velocity is also 0 and drops negative before shooting up instantly.....some else is going on.

That sure doesn't look like a 4 in rocket either...hmmm 5.5 or 6?

I Twist & tape using those size holes all the time never had that cause this mayhem.

EDIT: did you have pressure relief vents in the tube and nose cone?
 
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robbdm

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Remember you asked me to turn the camera toward your rocket....

This doesn't help the Diagnosis but here is the video.

[YOUTUBE]R7V-NWDXmCE[/YOUTUBE]
 

Wayco

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LOL.....first off I think you meant 1,000fps...10,000 would be M-8.93!!!!

I would like to see graph from Strato [or other than one shown.] Something is wonky.You show 0 altitude from lift off to 2.25 seconds then it leaps up to 4,000 ft instantly. Velocity is also 0 and drops negative before shooting up instantly.....some else is going on.

That sure doesn't look like a 4 in rocket either...hmmm 5.5 or 6?

I Twist & tape using those size holes all the time never had that cause this mayhem.

EDIT: did you have pressure relief vents in the tube and nose cone?

Yep, 968 fps according to Thrustcurve, one little mistake and you caught me CJ!
I will see if Sharon can convert the Stratologger graph, I'm not having any luck with it. It shows much the same, a wonky line for about two seconds, then suddenly it's at 4000 ft.
It's a 4" Drago, Tim shipped it to all the entrants in David Reese's ROCstock drag race last year in November. We all flew the K850 Dark matter single use motor in stages:
p2jII0t.jpg


I did drill 1/8" holes in the fincan and nosecone too.

Thanks for posting that video David!
 

DavidMcCann

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wacky thought... an effect from being HED? I realize it's unlikely with the number of people flying them successfully, but something wacky happened there, and I don't think it was a good reading at 4K... no way it dropped that fast after it hit the fan.
 

ksaves2

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Could one or more of the fins contacted the nosecone?

IMG_20180311_215846.jpg IMG_20180311_215738.jpg IMG_20180311_215650.jpg

This one took quite the slice from the fincan of a Talon 2 and the rest of the rocket was destroyed. Lost the rocket and Beeline GPS, the motor
casing survived along with the retainer the and altimeter is behaving nominally though I haven't reflown it yet. I really gobbed the epoxy on the
bulkhead and it held. Kurt
 

Andrew_ASC

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So you had an early deployment? Not sure how that would cause you to lose fins...

Nosecone pops off. Chute deploys then fully inflates for maximum recovery drag force with not symmetric drag force on a very rapidly moving object of high velocity. Drag force is proportional to velocity squared. Unsymmetrical drag forces create a moment arm and turn the rocket in flight off its intended path. Then the fins exceed their rated angle of attack and a fin failure by bending stress occurs. You can find fin angle of attack limits at Mach numbers using AeroFinSim for certain epoxy specs and fillet radii. You can also find fin flutter data.

Epoxy some fin plate to a toss away stump or other object and start twisting it, it'll snap off eventually. The aero forces are doing stuff you just can't visually see it.

NASA and light airplane companies used to use spin chutes to save test aircraft during really botched up spin testing. There was enough drag force by the chute at the wing tip of a long moment arm to get the aircraft to stop spinning when normal control deflections didn't have enough force. Normally the opposite rudder of turn direction puts enough aero force out. But somebody had to risk it all and test it to write a spin recovery section in the pilot operating manual, hence the spin chute incase a test pilot can't correct it. (Cool stories out there of test pilots bailing out of million dollar light planes, and keeping their jobs when spin chute failed to save it). Yeah that itty bitty little chute turned real full scale airplanes in a dime. Of course a rocket will turn when a chute pops out and deploys to the side when the chute is upside down and fully inflated. There's real applications out there. Density of fluid, drag coefficient, velocity, and plate areas make the drag force work. It's a force it can turn stuff when there's a perpendicular distance the same as a torque does. It's a torque in this application.
 

mpitfield

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Three ports 120 degrees apart on the switch band. They are 3/16" in diameter, and two have two strands of 24 gauge wire through them

With two of the three sampling ports partially blocked with wires is it not possible that you had some undesirable turbulence and pressure differential in the AV bay?
 

Andrew_ASC

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Yeah that's possible. It would have the same effect as under sizing the pressure relief hole by 66%. Your altimeter reading is artificially off. There could be all kinds of surface flow interactions. Then the nosecone also would be raised off the body tube by internal pressure changes by an undersized hole from the blocked holes reducing available area.

I'll never personally understand why they say drill 1 or 3 or more holes but not 2. I just don't get that but I follow their advice.
 

Exactimator

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Here is the last shot of my 4" Drago before it's shred at Holtville Havoc March 3rd:

I downloaded the altimeters today, and think I have found an answer as to why this event happened.
drago%20rrc3%20failure.jpg


Both altimeters had that strange sine wave before spiking up, with the Stratologger indicating a normal sequence of events after the incident. The RRC-3 fired the drogue, which sheared the pins on the N/C and deployed the main chute. Both of the fins were recovered, and amazingly, the main chute was undamaged. The drogue was destroyed, and the swivel on the main will never be the same again.
Originally, I thought that my epoxy failed when the rocket got some fin flutter or something, but with the downloaded data from the RRC-3, now I'm thinking that my static ports didn't vent right due to the twist and tape wires blocking them. I'm open to any other ideas on this....

Your graph has me baffled. I've never seen traces like that before. Was it windy when you launched it?

As with MikeC, I'm not sure what about an early event would snap fins. Yours looked like they had plenty of epoxy.
 

Andrew_ASC

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When ice would form on pitot tubes and clog in a plane's pitot, one of the failure modes in a climb was the expanding gases trapped in the mechanical pitot tube would cause an altimeter/airspeed error where the altitude and also airspeed indicated would continue to falsely climb and also affect other static source instruments. So the rocket electronics thought they hit an altitude they didn't hit then Recovery charge. Airbuses usually rapidly deconstruct from that d*** flight control auto speed brake logic too because it can't sense between a ice/dirt clog or a real overspeed. I hate Airbus products by that reason.

There's a real world altimeter static source fault for yah. Unpressurized light planes, break the VSI gauge also connected to pitot static system and a new static port is generated. There's three holes for most pitot tubes. Altimeter, airspeed, and Vertical speed indicator. That's kinda how pressure differentials can screw up a altimeter by static source fault.
 

Andrew_ASC

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As with MikeC, I'm not sure what about an early event would snap fins. Yours looked like they had plenty of epoxy.
Most fins only like 3-8 degrees angle of attack at max Mach. If that nose popped at boost then bad stuff happens by high aero forces on an upside down chute putting a massive torque on airframe short perpendicular distance but very high drag force loading at high velocity enough to tilt rocket off course enough to snap fins at joint. Most rocket airframes structurally hate violent turning. Then it's all fin bending stress analysis.
 

Wayco

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With two of the three sampling ports partially blocked with wires is it not possible that you had some undesirable turbulence and pressure differential in the AV bay?

So the graph would indicate. I finally got an acceptable copy of the Stratologger graph, and it shows a similar pattern:
perfecttry2.jpg


With both altimeters showing strange pressure variances in the avbay, I have to suspect the static ports. I'm like CJ though, I have eight other rockets with this same setup, and none of them show these symptoms. On the other hand, this is the only HED setup with twist and tape wires through the static ports. So the first thing I'm gonna do is remove the wires and install magnetic switches.
I will rebuild the fincan with some fiberglass reinforcement where the body tube is damaged at the fin slots, and fly it on some smaller motors.


 

blackjack2564

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Wayne this look familiar?.....................

Screen Shot 2015-11-01 at 9.56.59 PM copy.jpg

I knew I had a similar flight few years ago [2015] took me awhile to find it. After much brew..ha..ha.. driving myself nutz trying to figure out what happened I gave up.
Just one of those 'flukes'...never happened again.

Same thing just took longer it was sustainer [why 10 sec] shortly after lighting while still burning both events happened at same time. Some weird pressure thing.

This is raw data [you should have that too]
time...altitude...velocity....temp....voltage.

Notice it goes wonky 8 seconds in velocity starts going all over the place where finally at 10.45 it goes 33,000ft per sec...lol
Note from 8-11.5 positive to neg & back couple times...I'll bet your raw data looks the same.

Screen Shot 2018-03-12 at 10.52.34 PM.png

Something caused a major pressure spike. This resulted in re-writing the lock-out of the RRC3 firmware [?] to cover a longer time issue. I don't know how Perfect flight handles that. I was using 1 of each, same as you.

Here's the re-work based on my flight, note the time stamps correspond to my issue.

'':: copy.png

I'm thinking you had the same thing happen, BUT as you can see, charges did not fire till long after the event. What ever caused the pressure spike..."popped' off the cone and all hell broke loose. There were bad gusts and wind shear at altitude the day I flew.
How about you?

It was one of those things that has not happened since. it was a 3 in Punisher, it also deconstructed, but I re-built.
It would be nice to figure out, but I don't find fault in anything in the set up.
 
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farsidius

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With both altimeters showing strange pressure variances in the avbay, I have to suspect the static ports. I'm like CJ though, I have eight other rockets with this same setup, and none of them show these symptoms. On the other hand, this is the only HED setup with twist and tape wires through the static ports. So the first thing I'm gonna do is remove the wires and install magnetic switches.
I will rebuild the fincan with some fiberglass reinforcement where the body tube is damaged at the fin slots, and fly it on some smaller motors.


I also use twist and tape on most of my rockets, including a few HED kits. I always use three port holes but I oversize one of them and run both altimeter wires through that same hole. I'm not sure I would feel comfortable interfering with two of the three ports. Just food for thought - I'm not suggesting that my experience is evidence that it's a better approach.

-brant
 

jd2cylman

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I also use twist and tape on most of my rockets, including a few HED kits. I always use three port holes but I oversize one of them and run both altimeter wires through that same hole. I'm not sure I would feel comfortable interfering with two of the three ports. Just food for thought - I'm not suggesting that my experience is evidence that it's a better approach.

-brant

I do this also on a lot of my dual deploy rockets. On a few new rockets, I have added a fourth hole for just the wires. But haven't flown many of them yet to get any sort of database. But, I'm not a data junkie either. If the flight is successful and the altimeters beep out the altitude, that's all I'm after.
 

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I'll never personally understand why they say drill 1 or 3 or more holes but not 2. I just don't get that but I follow their advice.

It's about consistency. I don't like using one hole, because there is nowhere for the air to go once it is in the bay. With two holes, assuming they are 180* apart, then crosswinds could blow through the AV bay, then if there is a sudden wind shear, now the wind is missing the ports altogether. With three holes, you have a reasonable expectation that at least two of them are sampling correctly at any given time.

Someone please correct me if I am off-base.
 

Buckeye

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Where did you tape the wires? Above the hole, below the hole, or to the side of the hole?

The pressure measurement is seriously wacked, confirmed by two baro altimeters, so compromised static ports is a good guess. Altimeter instructions make a big deal about "clean" ports with no frayed edges, etc. Sticking wires through them makes them "unclean" and disrupts the airflow. I don't like twist and tape.
 

DavidMcCann

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Where did you tape the wires? Above the hole, below the hole, or to the side of the hole?

The pressure measurement is seriously wacked, confirmed by two baro altimeters, so compromised static ports is a good guess. Altimeter instructions make a big deal about "clean" ports with no frayed edges, etc. Sticking wires through them makes them "unclean" and disrupts the airflow. I don't like twist and tape.

I don't disagree that clean ports are ideal. But the vast number of flights that do twist and tape out one hole, and have baro agree (reasonably) with accel and GPS leads me to believe it's not that bad either.
 

Wayco

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Thanks to CJ for additional data related to the incident. I didn't notice any wind shear in the smoke trails of previous flights, but the wind was picking up as the day proceeded.
With HED, you have to tape the wires to the switch-band beside the hole that they come out of, everything else separates from the avbay.
I like Brant's idea with the wires through one enlarged hole, I might go back and retro-fit this on some of my other rockets. I did go back and download the graph for the two previous flights on my Drago, both were normal.
I'm like Adrian, not really a data junkie. If a flight is normal, I might not download the altimeters, just read the beeps and record the altitude in my log.
I don't really like to repair rockets if they are seriously damaged, but this one should be fairly simple. I will probably get to it this summer, when flying season is over here.
I'm also reconsidering a couple of builds we have in our build pile that are HED. I might add a payload tube to the 4" Punishers, making them easier to prep and more in line with the other sport fliers we have.
 

cerving

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Enlarging the vent holes to compensate for the twist and tape wires might be a good idea. Those graphs look like the vent holes somehow were restricted, then the blockage opened up.
 

Wayco

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How big is the vent hole in the booster (long fin can section) and where is it placed?

Because this airframe is a bit larger than the normal 3" I fly most often, I went to a 9/64" hole vs the 1/8" I normally use. The hole is in the forward part of the booster, in the gap between the aft end of the avbay and forward of the drogue pocket.
If you look at my first post, you will see that the RRC-3 fired the drogue charge 2.2 seconds into the flight. I can't blame the altimeter for this, it was sensing a decrease in barometric pressure, and did what it was programmed to do. I'm pointing this out so we are clear on what caused the failure.
I want to thank everyone who commented on this thread. This is why we are all here on TRF, to share ideas.
Right now, I'm thinking that I must have upset the Rocket Gods, and they are seeking retribution for some offence... I might have to sacrifice that LOKI L2050 and burn it in an appropriately small rocket...
.:y:
 

Wayco

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I suppose another option would be leave the holes alone, ditch the twist and tape, and use a switch of your liking.

Considering the number of redundant dual deploy rockets that I fly with Featherweight magnetic switches, and my comments in post #16, it shouldn't be hard to figure out where I'm going with this rocket.
One final thing that might be relevant, I noticed that I had put a half hitch in the wires where they come through the holes in the switch band. Not sure if that was done on the first two flights. I do remember that I added fresh electrical tape for it's last flight.
Sharon had a 2.6" Blue Iguana come it ballistic a while back, after a flight to 20k ft. on an L935. We decided that twist and tape was the culprit. Flights in the neighborhood of Mach 2 tend to strip off anything (including tape) on the outside of the airframe.
 

mpitfield

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Considering the number of redundant dual deploy rockets that I fly with Featherweight magnetic switches, and my comments in post #16, it shouldn't be hard to figure out where I'm going with this rocket.

I am a fan of the magnetic switches, especially the new version.

Flights in the neighborhood of Mach 2 tend to strip off anything (including tape) on the outside of the airframe.

Makes sense to me.
 

blackjack2564

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Sharon had a 2.6" Blue Iguana come it ballistic a while back, after a flight to 20k ft. on an L935. We decided that twist and tape was the culprit. Flights in the neighborhood of Mach 2 tend to strip off anything (including tape) on the outside of the airframe.

Yup.......I always tuck the wire inside for those type [high mach] flights. But they are few and far between for me, living on the East coast.
I now add a second small hole next to vent, so I can tuck the wire back into that hole and tape over it with aluminum tape. That stuff never comes off!....lol

If you are doing many high mach flights, using a switch is the best solution. :smile:
 
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