Post Mortem on L2 CATO

[dontturn]

Hi all, I just got back from attempting my TRA L2 certification flight. I reused a previously built Apogee Zephyr with motor ejected parachute recovery that I used for my L1 certification and have flown with AeroTech H100 and I284.

View attachment IMG_3161(1).mp4


I attempted my flight with a J340M-14A with a 12-second drilled delay. The launch failed pretty spectacularly which you can see in the attached video. You can see about 1 foot up the launch rail the nose cone vertically separates from the body tube while the propellant is at the beginning of its burn. The rocket and detached nose cone continue to travel vertically until the end of the launch rail, at which point the nose cone cocks 90 degrees and the rocket begins to spiral uncontrolled. The propellant completed its burn then the rocket fell to the ground in an uncontrolled descent.

In a frame-by-frame analysis, you can see hot gasses push the nose cone off the rocket while traveling up the launch rail which would indicate a premature ejection to me. This is further corroborated by the absence of an audible ejection charge after the propellant is consumed or once it has hit the ground. While disappointing, my rocket is in fair shape and will fly again with some repairs but I would like to learn from this. My fear, however, is this may be a scenario where everything in my control I did correctly.

The motor was a reload purchased and built on-site. I built the motor simultaneously with another flier also flying a J340M-14A with identical delay and as far as we know we built them identically. In post mortem, we tore down both motors side-by-side and did not notice and differences or flaws in the assembly of the CATO motor. Here the two motors disassembled side-by-side:



The only differences I noted were:

1. The aft insulator on the CATO motor is significantly degraded as compared to the control motor (looks more like an O-ring now than a
2. When removing the forward closure on the CATO motor, the delay assembly remained and was stuck the forward seal disk while in the control, the delay assembly was rather stuck in the forward closure and had to be removed with tools.
3. The delay grain on the CATO motor is burned incompletely and asymmetrically
   

The launch prefect suggested this could be the result of a cracked delay grain. I've not heard of this before but I don't recall seeing any abnormalities in the grain while loading the motor. I also went though the steps of drilling the charge with the other flier and we identified no differences that could have resulted in the delay grain being damaged. I'm interested to see what others here may think but I suspect this may have been a motor malfunction.

 

[Johnly]

I'm not seeing the forward delay spacer in your parts disassembly layout.

 

[n3tjm]

To me that looks like a pressure separation of your nosecone, cause by the air compressed in the rocket when you installed the nosecone. I've actually seen nosecones pop off rockets sitting on launch pads waiting their turn to launch with this phenomenon. This kind of problem can be solve by a small vent hole drilled through the body just below the base of the nose cone. This will allow the air in the rocket to escape when the nosecone is installed.

I don't see any evidence of a blow by. If the ejection charge did go of prematurely, more than then nosecone would of come off. Also, you will have fire shooting out both ends of the rocket. Also your delay o-ring looks pristine condition. If there was a blow-by it would be roasted to a crisp. Also there will be damage to the touch hole in the forward closure.

 

[justforfun]

Maybe it's just my old eyes, I don't see a CATO.

Roy

 

[mikec]

To me that looks like a pressure separation of your nosecone, cause by the air compressed in the rocket when you installed the nosecone.

I don't think I've ever seen that happen, but I completely agree that it looks like this is the cause. Maybe something about the laundry moving back at liftoff triggered it. A blowby/premature ejection would be much more energetic.

It is weird that the delay stuck to the seal disc. Are you sure you put BP in? Was the BP consumed?

 

[n3tjm]

Its common for the delay assembly to stick to the insulator. I like it when this happens because it gives me something to push on to get the spent liner out of the case. .

 

[mikec]

Its common for the delay assembly to stick to the insulator. I like it when this happens because it gives me something to push on to get the spent liner out of the case. .

This motor uses a seal disc, not a forward insulator like smaller 38mm motors. And I guess the delay sticks like that sometime, but for me it's way more common for it to be stuck in the forward closure and hard to get out, for whatever reason. I haven't flown a lot of larger 38mm motors so maybe it's more common for them?

 

[n3tjm]

I know it uses the seal disk . It is more common for it to stay in the closure, but once in a while I get lucky

 

[rcktnut]

Maybe it's just my old eyes, I don't see a CATO.

Roy

+1 No CATO

 

[OzHybrid]

Were there shear pins in the nosecone?

 

[dontturn]

Thanks for your help everyone!

I'm not seeing the forward delay spacer in your parts disassembly layout.

Forward delay spacer is stuck in the forward closure along with the delay O-ring, can kind of be seen in the photos.

To me that looks like a pressure separation of your nosecone, cause by the air compressed in the rocket when you installed the nosecone. I've actually seen nosecones pop off rockets sitting on launch pads waiting their turn to launch with this phenomenon. This kind of problem can be solve by a small vent hole drilled through the body just below the base of the nose cone. This will allow the air in the rocket to escape when the nosecone is installed.

I don't see any evidence of a blow by. If the ejection charge did go of prematurely, more than then nosecone would of come off. Also, you will have fire shooting out both ends of the rocket. Also your delay o-ring looks pristine condition. If there was a blow-by it would be roasted to a crisp. Also there will be damage to the touch hole in the forward closure.

I forgot to mention this in the post and couldn't find this post to edit since it was pending approval, but there's a 1/4" hole drilled in the body tube about 2" below the nosecone shoulder. The nose cone was friction fit with layered tape just to the point where the entire rocket including motor can be suspended by holding the nosecone without any give.


For the nose cone to pop off, there'd need to be a higher pressure inside the body tube than outside. right? I'd expect any pressure from putting the nosecone on to have equalized, as the only things inside that could have blocked the hole are the shock cord or nomex chute protector. The rocket sat fully assembled for at least 20 minutes which I'd imagine to be more than enough time for pressure to equalize through such a porous blockage.

However, even if the hole was blocked, I'd really expect this to manifest at altitude when external air pressure decreases. The pressure inside the rocket should not increase as a result of motor ignition, and no altitude had yet been gained, plus there should be additional downward force on the nose cone at launch as a result of acceleration and increasing air resistance. I can also see in the video that the acceleration of the nosecone outpaces that of the rocket itself until about 1ft from the top of the launch rail.



I haven't done any back of the envelope math but intuitively I'd think that'd need a big delta P.

The other thing I've noticed is that there's a visible outgas when the nosecone pops.

The gas appears to be white in color, which is typical of black powder smoke. If it popped due to pressure differential, I wouldn't expect visible gas. I've never used any white substance when packing so the only stuff in the tube is kevlar, nomex, and soot from previous launches.

I don't think I've ever seen that happen, but I completely agree that it looks like this is the cause. Maybe something about the laundry moving back at liftoff triggered it. A blowby/premature ejection would be much more energetic.

It is weird that the delay stuck to the seal disc. Are you sure you put BP in? Was the BP consumed?

BP definitely in, and see above reply about possible consumption. I did not see any BP left in the body tube but I did just notice that the ejection charge cap was lodged in the bottom of the rocket between the motor mount and body tube. Here's some photos:

Burn marks and pitting suggest that the BP did likely ignite, but the asymmetrical burn pattern and the fact that the portion that sits directly above the BP is not singed/destroyed is very suspicious. However, I'm not sure what this part would normally look like after a successful launch because I've never found one after a launch.

Thinking back to previous flights, one of the main differences is I installed a motor retainer ring rather than friction fitting the motor and sealing with tape. When I inserted the motor this time, it slid in readily and did not have to be forced. I'm wondering if what could have happened is this: ignition, exhaust gasses are reflected by the ground, the gas travels up a gap between the motor and motor mount, where they blow off the ejection charge cap before continuing up to pop off the nosecone or even igniting the BP causing the cone to pop. My evidence for this are that the gases shown escaping when the nosecone pop in the screencap above appear to be the same color as the exhaust and that the ejection charge cap is singed asymmetrically its outside and inner wall, but not on the portion that would have been sitting directly above the BP.

 

[Syclone]

What does the touch hole between the delay element and ejection charge cavity look like? Typically when there is a delay burn-through at the beginning of the burn, the hole will be eroded and melted.

 

[dontturn]

What does the touch hole between the delay element and ejection charge cavity look like? Typically when there is a delay burn-through at the beginning of the burn, the hole will be eroded and melted.

Are you referring to the small hole in the forward closure that separates the delay grain and BP? It was undamaged as was the entire forward closure. I just made a post above yours that gives some additional details but it's pending approval right now.

 

[rfjustin]

What does the touch hole between the delay element and ejection charge cavity look like? Typically when there is a delay burn-through at the beginning of the burn, the hole will be eroded and melted.

Agree on this 100%.

OP, picture inside the well of the forward closure please?

 

[n3tjm]

How much space did the laundry have in the rocket? Like was there hardly any room and your nosecone packs it down? That could of done it?

I still not 100% convinced the charge went in flight because the laundry didn't deploy. If it did go off, you didn't have enough powder. If the flight was normal, you may be purchasing another J motor for another try anyway because your recovery system may not deploy.

Another theory? Maybe Somehow there was a Static Discharge? Was that plastic cap in contact with the BP or did you have any wadding between the powder and the cap?

Can that happen, I doubt it, but I still don't see evidence of a blow buy. That "puff of smoke" can simply be a camera anomaly.

 

[OzHybrid]

If the ejection charge had gone off, the washing would have been deployed and smoke out the top. If the forward closure had failed, flame would have come out the top. Cannot see any scenario where pressure could escape the motor and not show smoke at the front. Any leak of flaming gas tends to be spectacular. Especially with a sparkie. Didn't see any of that in the video. So it's unlikely the motor had anything to do with the failure.
I'd be looking at how you packed your washing and put the nosecone on.
I've seen plenty of scenes where the launcher gets go fever and rushed packing the chute and putting the nosecone on. You could have had a pocket of air trapped in the chute that got compressed when you pushed the nosecone on and the launch shook the nosecone loose enough that the compressed pocket of trapped air in the chute had enough force to push the nosecone off. Or a bunch of randomly packed kevlar which can be quite springy. That would be my best guess on the evidence presented.
Norm

 

[dontturn]

Agree on this 100%.

OP, picture inside the well of the forward closure please?

How much space did the laundry have in the rocket? Like was there hardly any room and your nosecone packs it down? That could of done it?

I still not 100% convinced the charge went in flight because the laundry didn't deploy. If it did go off, you didn't have enough powder. If the flight was normal, you may be purchasing another J motor for another try anyway because your recovery system may not deploy.

Another theory? Maybe Somehow there was a Static Discharge? Was that plastic cap in contact with the BP or did you have any wadding between the powder and the cap?

Can that happen, I doubt it, but I still don't see evidence of a blow buy. That "puff of smoke" can simply be a camera anomaly.

It's quite roomy in there, the chute package sits far below the nosecone and pressure relief hole. I agree that BP should have knocked everything out but I definitely poured it all in there. See my post above about the ejection charge cap, I suspect it may have been blown off by some force other than the BP and have a theory explained in that post.

The plastic cap was placed tightly over the forward closure with the included paper sticker between it and the BP. Wrt the smoke, it appears as soon as the cone pops off, appearing to leave tangential to the centerline as shown in my previous post. Then for several more frames, as the cone continues up, the smoke is visible spanning the gap, as if it's being pushed out of the body tube by pressure, then it eventually dissipates near the top of the launch rail.

If the ejection charge had gone off, the washing would have been deployed and smoke out the top. If the forward closure had failed, flame would have come out the top. Cannot see any scenario where pressure could escape the motor and not show smoke at the front. Any leak of flaming gas tends to be spectacular. Especially with a sparkie. Didn't see any of that in the video. So it's unlikely the motor had anything to do with the failure.
I'd be looking at how you packed your washing and put the nosecone on.
I've seen plenty of scenes where the launcher gets go fever and rushed packing the chute and putting the nosecone on. You could have had a pocket of air trapped in the chute that got compressed when you pushed the nosecone on and the launch shook the nosecone loose enough that the compressed pocket of trapped air in the chute had enough force to push the nosecone off. Or a bunch of randomly packed kevlar which can be quite springy. That would be my best guess on the evidence presented.
Norm

Thanks for your reply, Norm. My post above yours was just approved, so you may not have seen it before writing your post. It has some additional info that might be useful, particularly the ejection charge cap seems to indicate it was not removed by the ejection charge itself.

I'm not immune to get-there-itis. We were itching for a launch, but as far as I know my chute was tightly packed, rolled in the lines, and was not compressed when the nosecone was inserted. In my post above I talk about how quickly the nosecone accelerates, outpacing the rocket. I might try to do some force calculations to see what pressure differential would be required to cause such acceleration.

 

[rcktnut]

The only differences I noted were:

1. 
   
2. When removing the forward closure on the CATO motor, the delay assembly remained and was stuck the forward seal disk while in the control, the delay assembly was rather stuck in the forward closure and had to be removed with tools.
3. 
   View attachment 576657

Been thinking about this which indicates a loose fitting delay assembly in the well. This has been a problem with the Hobbyline 29/40-120 motors. The ejection charges were firing at or shortly after ignition with loose fitting delay assemblies. I've seen it happen 2 times personally. There are also posts here on the problem. I've had an I161 that had a loose fitting delay insulator that I taped to insure a tight fit, motor worked fine. I only taped it because of having to tape some of my Hobbyline insulators and was aware of the problem. Delay insulators should not be a loose fit.
Different designs between the 2 on how they seal but is just another possibility. Starting to look like a good possibility to me.

 

[n3tjm]

With the RMS+ Delay motors, it doesn't matter if the delay insulator is loose. The Delay grain is cast in the smooth tubing and the delay o-ring is oversize, so the seal is made by the o-ring being squeezed between the smooth wall of the closure and the smooth tube of the delay element.

Now with the hobbyline RMS, a loose fitting delay insulator can be bad. The seal is made by the forward end of the delay insulator and delay grain pressing against an o-ring. Poor design imo, and if the delay insulator is very loose, I usually add some tape for some peace in mind.

Now for the ejection charges going off shortly after ignition can be propellant related. If the load is Redline, and they stash the delay element loose in the bag with the propellant, replace the delay grain if the load is older than a year. The catalyst will cross contaminate and make the delay grain burn faster.

 

[n3tjm]

Looking at those still frames, that does not look like smoke to me. I think it may be a very blurry shock cord.

 

[AeroTech]

That does not look like a CATO at all. If the ejection went off at liftoff you would have seen massive flames and smoke coming out of the forward end of the body tube.

Where ejection actually occurs at liftoff it is almost always due to reversing the position of the delay element and the delay spacer.

 

[tsmith1315]

In real time, can you see the rocket in the 14 second range after ignition?

 

[dontturn]

Looking at those still frames, that does not look like smoke to me. I think it may be a very blurry shock cord.

I wondered this could be the case too, but in the stills from my second post you can definitely see some kind of smoke flowing out, tangential to the center line, and even above the nose cone. Also wrt your other post, the delay grain was in a separate bag from the propellant. Have you seen my pictures of the ejection charge cap? I'm interested to hear your take since you seem very knowledgeable about the RMS.

That does not look like a CATO at all. If the ejection went off at liftoff you would have seen massive flames and smoke coming out of the forward end of the body tube.

Where ejection actually occurs at liftoff it is almost always due to reversing the position of the delay element and the delay spacer.

Honored to get a reply from AeroTech! Yeah, after thinking through this more and learning from replies on this thread, I'm convinced it's not a premature ejection. However, I don't think I'm convinced it an issue with the pressure relief hole being blocked. Maybe you would have a better idea, does the ejection charge cap look like it underwent ejection? I'm starting to think it was knocked off somehow, the BP flew out, and there was no ejection.

In real time, can you see the rocket in the 14 second range after ignition?

Yeah it's in frame 14 seconds after. By that point, it's on the ground. There's not a clear view since the nosecone ends up sitting at the start of the body tube, perpendicular to it. I don't see any smoke or hear any sound that would indicate an ejection charge. I can post that part if you want, I had to clip the video due to the forum file size limit. The RSO held us for 30 seconds since no one heard an ejection charge. When I reached the rocket, the chute was still in the body tube and pulled out easily when I yanked the shock cord.

 

[Tractionengines]

I'm wondering if what could have happened is this: ignition, exhaust gasses are reflected by the ground, the gas travels up a gap between the motor and motor mount, where they blow off the ejection charge cap before continuing up to pop off the nosecone

I think you may be onto something here.... is there any path for the motor exhaust to "reflect" off the "stuff" below the motor at ignition, causing a short but significant pressure surge? What was the space between motor nozzle and blast deflector? Is blast deflector angled or flat?

It looks like no space between and the initial surge at ignition rebounded and pushed just hard enough to pop the nosecone.

Next launch support the rocket at least 6-9" above the (preferably angled) blast plate. Shear pin ( or 2) on the nose would help too.

(That forward closure is too pristine, and there is no sign of smoke flames or anything coming out the front of the body tube after that first fraction of a second; to be any type of forward seal CATO .)

 

[dontturn]

I think you may be onto something here.... is there any path for the motor exhaust to "reflect" off the "stuff" below the motor at ignition, causing a short but significant pressure surge? What was the space between motor nozzle and blast deflector? Is blast deflector angled or flat?

…

We don’t have a blast deflector at this site, but usually there’s a crater below the rocket about a foot deep. However, at this weekend’s launch a university class was there to fly some very powerful rockets so our launch site was 100ft further back than usual. They dug a small hole under the pad but it was only about 4 inches deep. The motor nozzle itself is suspended about 4-6” above ground level (not counting the aforementioned hole).

 

[cbwho]

I watched it over and over. There is no smoke by the cone. I can see the lines/shock cord popping out. I think the vibration of liftoff popped the cone loose from the laundry under compression.

I think you mentioned you added tape to the cone for a snug fit. If you remove that tape and repack the rocket as you did before, does the cone pop up?

 

[rfjustin]

@dontturn, here is my .02 for what its worth.

Was this a CATO? No...

Was there pressure in the tube causing the nose cone to fly off right when the motor came up to pressure? Yes there appears to be as seen in the video. For some unknown reason, some gas got through the delay stack when the motor came up to pressure. I would bet the delay was "cocked" meaning not in perfectly straight in the delay insulator tube.

Again, just my .02

Best,

 

[KenECoyote]

Doesn't "CATO" mean "Catastrophy At Take Off"?

I know it's mostly used to describe major motor failures since those are pretty catastrophic, but this one did have a catastrophy at take off to me.

Very impressive video too!

 

[Tractionengines]

Rocket CATO - Yes
Motor CATO that Manufacturer should warranty - I don't think so.

I wouldn't file a MESS report, or warranty claim... just review the notes here, evaluate everything, then try the flight again.

 

[waltr]

My question is: was there enough grease on the inside of the forward closure to ensure the delay O-ring sealed properly.
Thinking it may be possible a tiny amount to propellant gas passed the delay O-ring to ignite the BP charge. Then Sealed so that no additional gasses pasted during motor burn.

Amount of grease in the FWD closure can not be check after burn.
When assembling, was the Delay O-ring very tight and slide smoothly into the FWD closure?

Any difference of the Liner's length between the COTO motor and the one the fired nominally.