Not quite sure if this was a cato or shred...

[Tim51]

Still trying to understand what happened yesterday to my LOC Fantom EXL. Suddenly broke apart after launch with a muffled double bang. My son was was videoing it on his iPod but didn't get the moment of explosion as such. The motor was still burning after the fin can detached, and the motor ejection charge fired at that point. The attached screen caps give a visual sense of what happened.

Salvage details:

Payload bay, Av bay and electronics, shock cords, nose cone all intact.
Drogue shredded.
Main chute intact.
Fin can, 6G casing destroyed / not found (after extensive search on foot and by drone)
A portion of the forward CR was recovered, still attached to the drogue shock cord, with the steel quick link badly twisted.

This was the rocket's seventh flight - the hardest acceleration it's undergone, but it's flown well previously on a motor with a bigger total impulse but lower average (i.e. a CTI J410)

Points I've been wondering about:

1) this was the first time I'd flown it with a camera (Veho Muvi, in a case, streamlined with a nosecone (as in picture 1), screw attached to the hard point I'd built into the forward CR. Did this put too much stress on the airframe under that sort of acceleration? Fellow club members who saw before hand thought not..

2) All the ejection charges (this was a DD flight) had fired, including the motor charge (which was seen to fire in the air after the rocket came apart). This would, I assume, rule out any problem with the motor delay grain (..?)

I assuming this was a shred - that somehow the airframe crumpled. However, it blew at a very strong point - the fin can...Anyway, I thought I'd put this out there for any thoughts / feedback..

 

[FredA]

What electronics? How programmed? Could this be your first Mach transition without proper Mach inhibit?
A "Double Bang" sounds like deployment charges as I've never heard a CATO produce more than one bang.....
Just a guess....

 

[REK]

How fast was this rocket simulated with that motor?

Can you please give details on the construction of the fin can and adhesives used.

 

[Tim51]

Thank you both for your questions.

What electronics? How programmed? Could this be your first Mach transition without proper Mach inhibit?
A "Double Bang" sounds like deployment charges as I've never heard a CATO produce more than one bang.....
Just a guess....

How fast was this rocket simulated with that motor?

The altimeter was a stratologger CF, with a fresh duracell 9v battery. As a 4" weighing 3.3 kg it would not have reached Mach transition speeds - OR indicated Mach 0.54 / 183m/s, max acceleration 186m/s2

Can you please give details on the construction of the fin can and adhesives used.

Fins were aeronautical standard 3mm Birch ply TTW bonded and fllleted with Devcon 2 ton epoxy. 6mm LOC stock CRs front and aft, filleted. Extra middle 3mm CR bonded with Devcon to front edge of fin tabs. Rear CR filleted and coated with JB weld. Retainer was a screw in alu Rowes retainer securely fixed with inserts as on all previous flights. I've attached the OR file.

View attachment HPR Fantom EXL variant.ork

 

[fyrwrxz]

Kinda sad whatever the reason- that was a pretty bird.

 

[Salvage-1]

What size are the sample holes in the AV bay?
Yes, the double boom sounds like the electronics firing the deployment charges. The StratoCF is a new altimeter, but it is based on the SL100, which has been successfully used 1000's times.
My primary thoughts are that
a) the sample holes are missized and this lead to misreading on that altimeter. Not likely as you have had multiple flights on this one.
b) damaged altimeter. Is there any chance that the altimeter has any damage, it may lot seem like you may, but I have had one in the past that looked fine after coming in hard, but on the next flight, it failed. Luckily I had a second. Checking the first, it looked like pins had come away from the solder.

 

[SpaceManMat]

Can you please post pictures of the recovered parts?

It appears to me that one shot shows the motor falling with part of the body/retainer. I don't have access to OR at the moment, can you post a picture showing fin can side one? Also do you have any data from the altimeter?

 

[Tim51]

What electronics? How programmed?

Just to add - the SLCF was programmed to deploy drogue at apogee and main at 700' AGL

 

[Tim51]

Kinda sad whatever the reason- that was a pretty bird.

Thanks - I hope to at least fly it with a new booster section.

 

[Tim51]

What size are the sample holes in the AV bay?
Yes, the double boom sounds like the electronics firing the deployment charges. The StratoCF is a new altimeter, but it is based on the SL100, which has been successfully used 1000's times.
My primary thoughts are that
a) the sample holes are missized and this lead to misreading on that altimeter. Not likely as you have had multiple flights on this one.
b) damaged altimeter. Is there any chance that the altimeter has any damage, it may lot seem like you may, but I have had one in the past that looked fine after coming in hard, but on the next flight, it failed. Luckily I had a second. Checking the first, it looked like pins had come away from the solder.

Thanks for the consideration. To take up your points -

a) There were 4 sample holes, drilled to .101" as per the Perfect Flite instructions. As you say, I've flown it twice before.
b) I hadn't thought of that. I'll have another look at the altimeter tonight.

 

[Salvage-1]

Check vent hole size against this https://www.vernk.com/AltimeterPortSizing.htm taking into consideration the length of your altimeter bay. This was your highest thrust flight. I could imagine a situation where the port sized were maybe a little too small and the algorithm in the altimeter got confused with the acceleration... you would think that this problem wouldnt exist with the Kalman filters that the altimeters have, but, if the port size is too small, then the pressure sensing would be off as well.
Just a thought.

Thanks for the consideration. To take up your points -

a) There were 4 sample holes, drilled to .101" as per the Perfect Flite instructions. As you say, I've flown it twice before.
b) I hadn't thought of that. I'll have another look at the altimeter tonight.

 

[Tim51]

Can you please post pictures of the recovered parts?

It appears to me that one shot shows the motor falling with part of the body/retainer. I don't have access to OR at the moment, can you post a picture showing fin can side one? Also do you have any data from the altimeter?

Yes you're correct - one shot just shows the fin can with a white smear of smoke coming out of the front - that was the motor ejection charge going off. The flame from the motor then threw the fin can back across towards what would have been the left of the picture - but that wasn't captured on video.

I've posted a shot of the mangled forward CR with twisted quick link (I don't think I'll try repairing that..) and also a shot of the whole rocket which I happened to take as I was prepping it, just to give you a sense of the shape and size. I didn't take a shot of all the wreckage, as I didn't find the fin can. Basically the section of booster tube I did find (but again, didn't photograph) had broken at the top of the MMT, which in this case was the standard LOC one for this kit - 50cm long.

I haven't downloaded any data from the altimeter. I think I need a lead I don't have for that... so far I've just listened to the beeps and decoded the data that way. Agree it would be helpful if I could download more.

 

[Tim51]

Check vent hole size against this https://www.vernk.com/AltimeterPortSizing.htm taking into consideration the length of your altimeter bay. This was your highest thrust flight. I could imagine a situation where the port sized were maybe a little too small and the algorithm in the altimeter got confused with the acceleration... you would think that this problem wouldnt exist with the Kalman filters that the altimeters have, but, if the port size is too small, then the pressure sensing would be off as well.
Just a thought.

Thanks that's useful to know. I'll take a look at that.

 

[dixontj93060]

Yes, results look like early drogue charge to me. The reason, can't be sure. Sounds like the sampling holes were sufficient. If this is the first time with the camera, where was it mounted in relation to the sampling holes?

BTW, beautiful rocket!

 

[Tim51]

Yes, results look like early drogue charge to me. The reason, can't be sure. Sounds like the sampling holes were sufficient. If this is the first time with the camera, where was it mounted in relation to the sampling holes?

BTW, beautiful rocket!

Thanks - the static ports are distributed evenly around the red band, which you can see in the picture, so they were well in front of the camera mount.

...we're changing our ways, taking different roads.

I did wonder if my timing was that wrong.. but certainly watching it there was a taste in my mouth as desperation took hold, I can tell you.. (bless you, Ian C.)

 

[vance2loud]

If it was a Cato the second bang might have been the flames setting the drogue charge off. Without finding the casing to inspect it for damage or seeing the altimeter data it's difficult to know for sure.

 

[3stoogesrocketry]

The bangs could have been your chutes .where they recovered and were they intact?
Eric

 

[Tim51]

If it was a Cato the second bang might have been the flames setting the drogue charge off. Without finding the casing to inspect it for damage or seeing the altimeter data it's difficult to know for sure.

Thanks. What would a cato look like in terms of the altimeter data?

 

[Tim51]

The bangs could have been your chutes .where they recovered and were they intact?
Eric

The drogue was completely shredded. The main was fine and completely intact, so I assume it was deployed at a point where the rocket was no longer moving upwards or downwards at any significant speed. When I recovered the Av bay and payload section, both deployment charges had been fired.

 

[rharshberger]

Friction fitted or pinned lower airframe? This might also have been a drag seperation, first bang was drogue charge firing, second bang was motor charge or main firing. A similar event happened to me, the drogue was damaged, and the drogue charge fired immediately after seperation, and because the rocket was still below the 1000' the main was set at it automatically fired the main charge as well. My alt was a RRC3. A cato could have the effects of the above and motor destruction too.

 

[vance2loud]

Thanks. What would a cato look like in terms of the altimeter data?

I'm not really sure, but the altimeter data should be able to tell you when or if it fired the drogue compared to what you saw

 

[Tim51]

Friction fitted or pinned lower airframe? This might also have been a drag seperation, first bang was drogue charge firing, second bang was motor charge or main firing. A similar event happened to me, the drogue was damaged, and the drogue charge fired immediately after seperation, and because the rocket was still below the 1000' the main was set at it automatically fired the main charge as well. My alt was a RRC3. A cato could have the effects of the above and motor destruction too.

Thanks for the input - the booster was friction fitted, on a stock LOC 'long' electronics bay. All the parts are LOC so it's a smooth fit, not too tight but not sloppy either. All as previous flights. We saw the motor charge fire once the fin can and motor had been flung sideways of the debris cloud, after the double bang, which happened at break up and was a quick double, slightly muffled report. Would the camera induce sufficient drag to cause drag separation? The break up seemed to occurred whilst the rocket was still under thrust, within the first second of the flight.

A fellow club member who lives close to the field by tells me he takes a walk 'rocket gleaning' later in the summer immediately after the harvest - perhaps he'll find the motor casing at that point, and things will become clearer.

 

[Tim51]

I'm not really sure, but the altimeter data should be able to tell you when or if it fired the drogue compared to what you saw

Sure - I'll have to order one of the USB connector leads to download and take a look.

 

[dixontj93060]

Friction fitted or pinned lower airframe? This might also have been a drag seperation, first bang was drogue charge firing, second bang was motor charge or main firing. A similar event happened to me, the drogue was damaged, and the drogue charge fired immediately after seperation, and because the rocket was still below the 1000' the main was set at it automatically fired the main charge as well. My alt was a RRC3. A cato could have the effects of the above and motor destruction too.

Actually a good point. Maybe the addition of the camera added drag enough now to make it separate early on the way up if pins were not in place.

 

[Tim51]

Actually a good point. Maybe the addition of the camera added drag enough now to make it separate early on the way up if pins were not in place.

Could the booster drag separate if it was still moving upwards under thrust?

 

[rharshberger]

Could the booster drag separate if it was still moving upwards under thrust?

My bet is it was a cato causing sepereation, which in turn led to the altimeter firing the drogue at what it determined to be apogee, then the main deployed normally even if it hadnt reached its set altitude. Some altimeters will fire the main as long as its above the minimum arm altitude as a safety feature, I know my RRC3 as long as the unit goes over 100' or 300' AGL the main will deploy even if it doesn't reach the 1000' its set to deploy at normally.

 

[Wayco]

Thanks for the input - the booster was friction fitted, on a stock LOC 'long' electronics bay. All the parts are LOC so it's a smooth fit, not too tight but not sloppy either. All as previous flights. We saw the motor charge fire once the fin can and motor had been flung sideways of the debris cloud, after the double bang, which happened at break up and was a quick double, slightly muffled report. Would the camera induce sufficient drag to cause drag separation? The break up seemed to occurred whilst the rocket was still under thrust, within the first second of the flight.

A fellow club member who lives close to the field by tells me he takes a walk 'rocket gleaning' later in the summer immediately after the harvest - perhaps he'll find the motor casing at that point, and things will become clearer.

Actually a good point. Maybe the addition of the camera added drag enough now to make it separate early on the way up if pins were not in place.

The camera definitely could have created enough drag to cause the fincan to separate, but not while the rocket was under thrust.
I'm not clear what motor you were flying, was it by chance a 38mm CTI?

 

[H_Rocket]

It may not have been a "CATO" per se. It might have been a premature firing of the motor ejection charge. The first bang being the motor ejection and the second the apogee charge as the upward motion just stopped.

 

[dixontj93060]

Could the booster drag separate if it was still moving upwards under thrust?

It would happen at or soon after burnout. Don't know exact specs on the motor you were using, but in video, looks like you were past a typical 1 to 3 second thrust stage when separation occurred.

 

[mpitfield]

Friction fitted or pinned lower airframe? This might also have been a drag seperation, first bang was drogue charge firing, second bang was motor charge or main firing. A similar event happened to me, the drogue was damaged, and the drogue charge fired immediately after seperation, and because the rocket was still below the 1000' the main was set at it automatically fired the main charge as well. My alt was a RRC3. A cato could have the effects of the above and motor destruction too.

This explanation seems to make the most sense so far. Hopefully you recover your hardware.

Nice looking bird!