Mach Madness Extreme Flight Failure Analysis

[dixontj93060]

I participated in the Mach Madness contest at Thunderstruck 2012. The contest results are shown here. Although my rocket experienced an anomaly north of Mach 2.65, I used it as a learning experience as I typically am a low-and-slow builder. I thus have written a document that briefly summarizes the design/build (as requested by some TRF members) and, more importantly (for me at least), delves into potential reasons for the failure--where many of the areas are new learning for me. The document, Mach Madness Flight Postmortem, is located here for those that might want to examine (or critique) my conclusions.

Cheers,
Tim

[dixontj93060]

There has been some off-line private conversation from a couple of folks who opine that, given the acceleration spike at the 1s point in the flight, the root cause of the anomaly may be a motor event. This may be true. I did not originally post the Raven2 data in the analysis as it is a bit convoluted given the folding of the airframe (and the reason I sought input from Adrian A. on the results), but, given that I am not experienced in extreme flights, I thought I would go ahead and post it to get additional input.

The fact remains that there was an airframe failure, and I wanted that airframe to survive Mach 2.5-3.0, so the postmortem analysis is still valid, but if it does turn out to be a motor issue (that can be proven), I would be happy to include it in the analysis and give credit to the one providing the input. I will say that I spoke to several observers of the flight and they did not see anything in the flight pattern/profile to indicate a motor problem. But, in any case, you motor experts, have at it!

[Adrian A]

There has been some off-line private conversation from a couple of folks who opine that, given the acceleration spike at the 1s point in the flight, the root cause of the anomaly may be a motor event. This may be true. I did not originally post the Raven2 data in the analysis as it is a bit convoluted given the folding of the airframe (and the reason I sought input from Adrian A. on the results), but, given that I am not experienced in extreme flights, I thought I would go ahead and post it to get additional input.

The fact remains that there was an airframe failure, and I wanted that airframe to survive Mach 2.5-3.0, so the postmortem analysis is still valid, but if it does turn out to be a motor issue (that can be proven), I would be happy to include it in the analysis and give credit to the one providing the input. I will say that I spoke to several observers of the flight and they did not see anything in the flight pattern/profile to indicate a motor problem. But, in any case, you motor experts, have at it!

Did the nozzle look o.k. post-flight?

[dixontj93060]

Did the nozzle look o.k. post-flight?

Adrian, unfortunately, nozzle/motor/fin can has yet to be located.

[Adrian A]

In that case, a CATO is probably the simplest explanation. Otherwise, we would have to assume that the av-bay flipped around 180 degrees before running into the end of a shock cord to produce the 300+ Gs seen. Instead, I bet that the back end of the motor let go.

[Dwatkins]

Having seen the flight. Motor performed as I would have expected. No anomalies in the the flame or smoke trail. Looking at the data I suspect Adrain you are right. Avbay coupling let go. 1st event. Swapping end at 180* starts the the g increase by inertia. Hits booster or end of shock cord for second event.

Dennis

[dixontj93060]

In that case, a CATO is probably the simplest explanation. Otherwise, we would have to assume that the av-bay flipped around 180 degrees before running into the end of a shock cord to produce the 300+ Gs seen. Instead, I bet that the back end of the motor let go.

I certainly could be wrong, but the flip doesn't look to be done until well after the high-g event.

[SS/EA 6BBL 71 Cuda]

Tim, as said before many good thoughts and observations on this but,.....maybe just maybe Justin managed to get a shot of this on video?
If you could coax him out of his cave for a short time to retrieve possible moment....maybe we could see this in a little better detail.
It was through his work a couple years back that i narrowed down the loss of "Dream Evil" when it was determined that either the coupler turned into powder or a slight drag separation issue caused the previously said confetti fest.
At these speeds even a one frame shot may prove your hypothesis.....

Remember what i told you as i was leaving Sunday? "Tim you've got the recipe...now you've just got too learn how to cook it."

I'd give the Farrand-man a shout.

[dixontj93060]

Tim, as said before many good thoughts and observations on this but,.....maybe just maybe Justin managed to get a shot of this on video?
If you could coax him out of his cave for a short time to retrieve possible moment....maybe we could see this in a little better detail.
It was through his work a couple years back that i narrowed down the loss of "Dream Evil" when it was determined that either the coupler turned into powder or a slight drag separation issue caused the previously said confetti fest.
At these speeds even a one frame shot may prove your hypothesis.....

Remember what i told you as i was leaving Sunday? "Tim you've got the recipe...now you've just got too learn how to cook it."

I'd give the Farrand-man a shout.

Gus, good idea!!!

[patelldp]

Admittedly I have not read the entire report. However, do you have a picture of the rest of the parts recovered? I have a hard time believing that a Performance clam shell cone could go sideways at mach 2.65 and remain intact, while damaging the glassed phenolic. In my opinion, the 54mm tube is more robust that the cone you were using.

I just don't know how much is left of this rocket to assess the damage. There of course is a likelihood that the booster tube failed, seeing as that has yet to be recovered.

Additionally, to minimize weight addition, I would be sure to double wall any tubing that is spanning open air within the rocket. For example: from the top of the motor casing to the altimeter bay is a single thickness of tube. Epoxy in a coupler to double wall that area and that should strengthen it significantly.

[dixontj93060]

Admittedly I have not read the entire report. However, do you have a picture of the rest of the parts recovered? I have a hard time believing that a Performance clam shell cone could go sideways at mach 2.65 and remain intact, while damaging the glassed phenolic. In my opinion, the 54mm tube is more robust that the cone you were using.

I believe the term I used in the report was that the pictures of the av-bay/coupler combo were "unreadable" (or something like that), this is true, but actually doesn't tell the whole story... I had taken pictures of the debris at the launch and read/loaded it on computer desktop the Monday after Thunderstruck when I got into the office. Early that morning I had been cleaning up some other files on the desktop when somehow I picked/selected those three pictures also and they went into the trash without me knowing. And yes, you guessed it, I emptied the trash without looking. When I realized what I had done I was sick. I ran back to my house to go dumpster diving as only that morning I had cleaned out the truck I took to the launch, but to no avail, as my trash carrier just happens to come on Monday and I missed him by about a half hour .

In any case, no reason to mis-represent. As described in the analysis, the top part of the payload was jagged and it was easy estimate from overall length of 14.5" that I had lost about the first 2.5" which coincides with the shoulder length on the nosecone (actual shoulder length is 2-5/8" with bulkhead plus break varied +/-1/4" or so distributed pretty evenly around the circumference of the payload frame). I would agree that you may think the nosecone shoulder would be weaker (and there was only about a 1/4" chip in the bottom of the shoulder), but there are three things to note: 1) as stated in the analysis, to save weight I only had one layer of 6 oz. glass on the phenolic--that isn't much. My grandson put a big hole in my PML Bulldog with two layers of glass and that was just a tip of the rocket while it was standing on the floor, 2) when the nosecone came off likely it was still protected by the bulkhead on the end 3/16", 5 ply and the 1-1/4" aluminum studs which themselves were attached internal to the nosecone shoulder with epoxy/chopped carbon mix which strengthened those two sides considerably, and, 3) the fiberglass layering on this particular nosecone, again an older one from Performance Rocketry, seems much thicker than the more recent stuff I have received from them (non-wound nosecones I mean).

I just don't know how much is left of this rocket to assess the damage. There of course is a likelihood that the booster tube failed, seeing as that has yet to be recovered.

This is actually true. I assume the booster airframe also had an internal radial failure but I have not seen the booster. There was damage on the aft coupler of the av-bay where the booster attached. When I say damage though it was more of a shear/twisting/scraping type mark on about 1/4 of the outside of the coupler on the av-bay and a sheared off charge location (wires broken/cut). Again though, there was no BP residue of any kind on the aft bulkhead indicative of a charge going off.

Additionally, to minimize weight addition, I would be sure to double wall any tubing that is spanning open air within the rocket. For example: from the top of the motor casing to the altimeter bay is a single thickness of tube. Epoxy in a coupler to double wall that area and that should strengthen it significantly.

Please explain this. Again, I am no expert in extreme flight profile rocket design. In my mind double walling the phenolic is going to add much more weight than if I added a couple more layers of FG, and, in fact, would be even heavier than if I went to a G12 Profusion airframe.

[patelldp]

Please explain this. Again, I am no expert in extreme flight profile rocket design. In my mind double walling the phenolic is going to add much more weight than if I added a couple more layers of FG, and, in fact, would be even heavier than if I went to a G12 Profusion airframe.

My hypothesis is that you experienced a radial failure of a single walled section of your rocket. I will first explain how I arrived at this, and then I will describe my remedy that I posed before.

You explain in the report that you desired a lightweight tube and you achieved this by designing the rocket around phenolic with a single layer of 6oz glass. Radially, as you showed in your report, phenolic with a single layer of glass is not all that strong.

This leads into my assumptions:

1. The booster section was of a standard design and not zipper less. I assume the rocket was designed in the standard HPR scheme where the rocket separates at the altimeter bay and also at the nosecone.

2. There is some damage that makes it appear as though you "scraped" the altimeter bay against the inside of the booster.

3. Your altimeter bay coupler is more robust than a single thickness of phenolic tubing.

4. The altimeter bay is intact, as is most of the upper section of tubing apart from the zipper.

So now for my idea:

Your airframe experienced a radial failure just above your motor case.

This would explain the relative good condition of everything north of that point, especially the altimeter bay. I would assume that your CG of this rocket was somewhere near or just below the top of the fore end of the motor casing. Should there be any radial force, say a crosswind or any other turbulence, this is the approximate location that the rocket would "rotate" around.

Your rockets' initial failure was right at the top of the motor, just ejecting everything above that point. In this EXTREMELY turbulent environment, the insane deceleration, and centrifugal force experienced by the cord and main chute, it easily sheared the pins in the nosecone and ejected. The quick inflation of the chute resulted in the zipper, but this ejection scenario explains the relative good condition of the nosecone shoulder.

So, how do we fix this given the current material selection?

1. Add more glass (you knew this)
2. Epoxy a coupler into every area of the rocket that is only a single layer of phenolic tube.

I think #2 is a lightweight option that will help significantly. Basically, install a coupler of the appropriate length such that the motor butts up against one end of said coupler, and the altimeter bay butts up against the other end. Further up, the fore end of the altimeter bay butts up against the second coupler, and the nosecone shoulder butts up against the fore end of the second coupler. Essentially, it's a "rocket within a rocket."

Or, you can redesign the rocket in a very minimal matter using a design that Tony A. uses, but using better materials.