Aerotech I59WN Cato at TriCities Rockeeteers May 2019 Launch

Here it is, my CATO from yesterday's launch.

HISTORY:
The Rocket: A Blue Tube 2.0 minimum diameter clone of Loc Precision's Weasel (always a great flying rocket design), electronics bay and nose cone bays were SMT Designs products (no SMT Designs products were harmed in this event).

The Motor: The Aerotech I59WN Boost-Sustain Longburn motor. Assembly was per instructions (carefully read through multiple times BEFORE starting assembly). Epoxy used for bonding and inhibiting sustain grain was Bob Smith Industries 15min cure. Not only were the instructions read multiple times and closely followed, but I also reviewed this thread https://www.rocketryforum.com/threads/aerotech-i59-issues.135548/
Motor date code is 081611 01 (Aug,16,2011 Batch 01, if I understand correctly) and it was purchased at last years SodBlaster event on Labor Day weekend as one of the auction items that had been donated by a vendor. The brand new never flown 38/480 case was purchased from same vendor after winning the auction for the motor.

The Igniter: Stock Aerotech one that comes with the motor, most likely a First Fire.

The scene: 12' 1010 rail and Additive Aerospace FARG, the FARG was almost damaged in the CATO as one of the rods popped loose, but was easy to fix. About .5 seconds into the flight there was a "bang" and parts flew everywhere. The sustain grain of the motor landed about 50-75' behind the pad on the sod and commenced to burn a patch of grass about 12" diameter down to bare dirt. Before the day was over all parts of the motor except the two 1/16" grain separator o-rings was recovered, none of the sustain grain or the section of liner bonded to it survived the grain burning AFAICT. The forward and rear insulators were also missing but both the 1/8" and 3/16" O-rings were found in perfect condition, to be exact the forward closure O-ring is pictured in some of the pictures. The rear closure was the last part found on the field, however the nozzle was not found. Both closures appear unscathed (not that I would trust them anymore).

View of carnage, casing burst just about where the Boost and Sustain grains meet, boost grain and the only chunk of liner found to right of "fin can".



View of one end of boost grain.


View of other end of boost grain, none of the 1/16" o-rings were recovered and this is the only section of liner found. The rest of the liner I assume was consumed when the sustain grain tried to set the ground on fire, literally there was almost nothing left of the sustain grain.









More to follow in a little bit (I have 29 photos and a 6 second video clip shot with my phone)

Page 2 of pictures.


Blue Tube 2.0 is tough stuff, the entire lower section of the rocket was still in one large chunk. The section seen below was after I had broken the fin can away from the rest of it. The rocket will fly again as all the fins survived, it will just be about 10-12" shorter.



AFAICT this is a straight up overpressure event, however the cause is unknown to me. This picture is before some of the rest of the motor pieces were located (mainly the o-rings).


Forward closure and its O-ring still in the case.






Boost grain, the following photos are as I rolled it to the left <

Page 3.


Boost grain continue from previous post.





The fins were definitely not planning on coming off, I was eventually planning to Tip-to-tip laminate, but the 1/8" baltic birch fins attached with JB Weld and JB Weld fillets were on there good. The blue tube was peeled away but the epoxy held great.



A short section of the fins, inner ply can be seen attached to the tube still.

The lone attached fin.


The fin with part of the inner ply pulled out by the epoxy that bonded it to the Blue Tube.

Feel free to ask questions. A MESS Report has been submitted and a warranty claim has been sent to Aerotech.

Video:

Okay, so video sucks when uploaded, not that it was all that great but it was much clearer in its original format.

About the only good part of this flight was that the recovery system operated flawelessly, both drogue and main deployed at less than a 100', the electronics were a Missleworks RRC3 Extreme powered by a Turnigy Nano-tech 350mah 2s LiPo on a SMT Designs modular electonics bay, and tracker was a Eggfinder Mini in a custom designed by SMT Designs nose cone tracker bay with a 950mah Turnigy Nano-Tech 2s LiPo.

Oh, no! Sorry to see that happen, Rich. Hopefully Aerotech will get you squared away.

Great job documenting this, Rich. I hope Aerotech can figure it out.

Steve Shannon said:

Great job documenting this, Rich. I hope Aerotech can figure it out.

Click to expand...

Me too Steve, that motor has great potential especially in the lighter 38mm MD rockets. It has a 173ns kick off the pad then a 60-something NS sustain. Not sure now if I want to fly the I49's that I have.

Looks like an overpressure event that split the case. (duh, I state the obvious alot....) If the top end isnt inhibited enough or the grains are not epoxied well enough it happens. I blew up a G69 which is another warp 9 end burner because I didnt inhibit the top of the grain well enough. Looked just like that.
Steve

SDramstad said:

Looks like an overpressure event that split the case. (duh, I state the obvious alot....) If the top end isnt inhibited enough or the grains are not epoxied well enough it happens. I blew up a G69 which is another warp 9 end burner because I didnt inhibit the top of the grain well enough. Looked just like that.
Steve

Click to expand...

Karl has said he has an idea of what happened and will contact me via phone. But AT has already said they will warranty the load and hardware.

Dang, Sorry to see that your auction winnings went rogue on you rich! maybe a little bad karma after smoking the rest of us that day

Regardless, It's nice to have a great example of how to document a CATO. Hopefully, Aerotech can sort everything out!

Awesome customer service from AeroTech once again, not only have they said they will warranty the hardware and reload but Karl contacted me yesterday and we discussed what may have occured based on the evidence I was able to present. Obviously it was an overpressurization event, most likely cause was insufficient bonding of the sustainer grain. Karl recommends prepping like we do for any epoxy bonding process, scuffing the liner lightly, and wiping with a solvent such as acetone. Then don't skimp on the epoxy put epoxy on the inside of the liner and wipe epoxy on the outside of the sustainer grain, insert sustainer grain into the liner and push through until flush on the forward end as per instructions, the excess epoxy can be used to inhibit the forward end of the sustainer grain then the additional excess wiped away. One thing Karl did say was DO NOT sand/rough the end of the sustainer grain and I forgot to ask why, however I believe its due to the fact that little bits of propellant would be raised up into the epoxy and provide a route for forward end ignition if the flame gets past the glue between the casting tube and liner or the grease on the outside of the liner. Karl also recommended bonding the boost grain (he did say that my boost grain looked pretty normal after the CATO), the reasoning behind bonding the boost grain is so that the casting tube for it will act as a column support under the sustainer grain preventing it from moving rearward, if for some reason it was inclined to do so and prevent occluding the nozzle (Karl's words not mine, my choice would have been Blocking instead of Occluding).

Now I have a path forward with the replacement motor and simply need to put the fins back on the Rabid Weasel and shorten the airframe about 8 to 10" due to the destruction but it will fly again maybe as early as next month. The rest of the flight after the CATO was pretty text book, the altimeter did its job perfectly and fired both apogee and main charges at about a 100' (just a guess until I pull the altimeter and see if it has any useful data) this time it was a Missleworks RRC3 Extreme altimeter with a Eggfinder Mini in a SMT Designs custom nosecone bay with 950mah 2s Lipo, chutes deployed and rocket was recovered safely less than 50' from pad.

Edit: actual aiframe will be shortened 8.72", no more 38/720 motor options and a 38/600 might not work either unless there is room to get the shock cord in it too. I may just order another section of Blue Tube and return to the 26" fincan size I had before.

That type of failure should not happen. NFPA 1125 7.4.4 says that any separated bits should travel longitudinally. Which is hard to do when you blow out the side.

But that is a tricky design. The nozzle needs to work both while the boost grain is burning (higher pressure) and after. Also, the core of the boost grain needs to be large enough so it doesn't look like a nozzle to the sustainer grain. That could boost pressure between the two grains which would be bad and hard to detect.

The core of the boost grain is about .5" or so, and the sustain grain is a solid stick of propellant (no core), the nozzle is fairly small compared to the core. The parts were spit out the rear of the casing as the rear closure was blown out as the case split, and the grains with liner, nozzle, insulators, all went out the rear of the rocket in a typical failure, if the sustainer grain had failed to light we might have more information of what went wrong but it lit and was totally consumed on the field.

Sorry to hear that!

You did a really great job documenting it all. We're working on an update to motorcato.org that will allow easier submission, including pictures. It will also allow everyone to view the data collected.

Just a reminder: when anyone has a motor failure (cato, wrong delay, etc.) please submit a report so they get tracked.