CTI M840 nozzles

[jondub]

The nozzles on CTI M840 motors flown at XPRS last September and again this June at Mudrock have shown a strange charring effect. The nozzle on the right is the one from my XPRS flight and the left is from Wilson Allness' flight at Mudrock on 21 June, 2020.
I personally have never seen a nozzle look like this nor has anyone I have shown it to, including Gary and Karl at Aerotech (although they offer a thought that it could be the mysterious "Hibachi Effect"). I can't find anything on the Hibachi Effect that makes sense.

I inquired with CTI after my flight but have heard nothing from them. I also sent photos to Robert DeHate at AMW where both motors were purchased. He was at a loss as well.

I was willing to write this off as a corner case but after Wilson's flight my curiosity has been rekindled.

Anyone seen this before?

 

[tfish]

Jonathan. Is it OK if I post this on a Research forum on Facebook? I'd let you know if there was any good info there.

Tony

 

[jondub]

Sure...wherever you like.

 

[BF Rockets]

Long burn motor... Nozzle deteriorated over the course of the motor burn, what's more to it is there.. As long as the thrust was nominal what difference does it make.

 

[Cameron Anderson]

I think that level of nozzle deformation qualifies as "off nominal."

 

[Reinhard]

Is acceleration data available form the flights? I'm wondering if it contains small discrete drops in acceleration, coincident with loosing parts of the nozzle.

Reinhard

 

[Handeman]

My first though would be faulty materials in manufacturing, but BF Rockets could be right also.

 

[eggplant]

I assume the long burn of the motor significantly weakened each nozzle, and then hitting the ground (even under main) was enough to fracture off the charred phenolic. Consider that the nozzle is typically the aft-most component of the rocket and ones that protrude through the aft closure like these do probably sustain a decent impact when hitting anything other than the softest field.

 

[jondub]

I have flown a lot of long burn motors albeit most have been Aerotech with Medusa nozzles. The exception to the Medusas are the K270 and N1000. None of these nozzles look anything like the 2 in question, in fact, none have been deformed in any way. Nor could landing, even a hard landing directly on the playa have caused this. Wilson's clearly landed nozzle first on the playa but mine did not.

I was expecting close to 40k' on my XPRS flight and was shocked when I heard the max alt of ~34. And my initial thought when I saw the nozzle was that had to be the reason for the short fall.

Attached are the Raven and Telemetrum eeprom files from the flight. The Telemetrum registered mach 2.9 while the Raven was considerably lower.

 

[3stoogesrocketry]

I have flown a lot of long burn motors albeit most have been Aerotech with Medusa nozzles. The exception to the Medusas are the K270 and N1000. None of these nozzles look anything like the 2 in question, in fact, none have been deformed in any way. Nor could landing, even a hard landing directly on the playa have caused this. Wilson's clearly landed nozzle first on the playa but mine did not.

I was expecting close to 40k' on my XPRS flight and was shocked when I heard the max alt of ~34. And my initial thought when I saw the nozzle was that had to be the reason for the short fall.

Attached are the Raven and Telemetrum eeprom files from the flight. The Telemetrum registered mach 2.9 while the Raven was considerably lower.

You are absolutely correct. The nozzles expansion ratio took a hard fall to almost nothing.

 

[Jack Hydrazine]

The nozzles on CTI M840 motors flown at XPRS last September and again this June at Mudrock have shown a strange charring effect. The nozzle on the right is the one from my XPRS flight and the left is from Wilson Allness' flight at Mudrock on 21 June, 2020.
I personally have never seen a nozzle look like this nor has anyone I have shown it to, including Gary and Karl at Aerotech (although they offer a thought that it could be the mysterious "Hibachi Effect"). I can't find anything on the Hibachi Effect that makes sense.

I inquired with CTI after my flight but have heard nothing from them. I also sent photos to Robert DeHate at AMW where both motors were purchased. He was at a loss as well.

I was willing to write this off as a corner case but after Wilson's flight my curiosity has been rekindled.

Anyone seen this before?

My guess is that the nozzle was defective in some way possibly in its manufacture.

 

[Rocketjunkie]

The M840 is a moon burner. Asymmetrical erosion is not unlikely. Both nozzles got over cooked and the exit cone failed.
I make long burn (17 sec) 98 mm motors using Aerotech hardware and nozzles without issues.
This was in 2008, Gary Rosenfield was there and saw it.

 

[BF Rockets]

Well, I take back my earlier comments. I didn't zoom in and see how badly the nozzle deteriorated when I posted. I also came across this post which shows an M840 nozzle post flight, in much better condition.

https://www.rocketryforum.com/threads/airfest-xxii.132104/post-1617281

 

[Cameron Anderson]

I have two M840s...I'm flying one that is 10 years old in a month. The other is 3 months old and I was going to save it for LDRS next year but I might fly it sooner just because I am curious now about the erosion. I will definitely post pictures of the nozzles post flight.