Mach Transition Discussion

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REK

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Hi TRF, recently I went with my former high school to launch 4 rockets on hypertek motors. One of these rockets was going to break the speed of sound. The rocket was a 3" carbon fiber rocket. It took off fast and from there we never saw it again. I am under the assumption that the ejection charges deployed too soon and that the chutes did not come out while it was hauling. The altimeter used was an AIM USB 3.0 with mach inhibits set at 7 seconds.

My assumption is that perhaps 7 seconds was too short, because the motor burns for 5.6 seconds and I pressume it was still going too fast that the altimeter may have been fooled and fired the ejection charges on the way up.

Would like your opinions on this.

Thank you
 
Most modern altimeters use smoothing and aren't fooled by Mach transitions, although I don't know anything about the unit you mentioned.

Without more info, it's hard to say what happened, but since you didn't see it disassemble at Max-Q, most likely it just landed far away.
 
Would like your opinions on this.
You're not giving us much to work with here. What motor? How heavy was the rocket? With no visual, no tracking, and no recovery, it's a bit hard to say anything, but certainly your mach delay was shorter than it probably should have been.
 
You're not giving us much to work with here. What motor? How heavy was the rocket? With no visual, no tracking, and no recovery, it's a bit hard to say anything, but certainly your mach delay was shorter than it probably should have been.

The motor is a hypertek L610 with a 5.6 second burn time. Rocket without motor hardware was 5.36lb. Loaded weight ended up at 11lb.
 
Most modern altimeters use smoothing and aren't fooled by Mach transitions, although I don't know anything about the unit you mentioned.

Without more info, it's hard to say what happened, but since you didn't see it disassemble at Max-Q, most likely it just landed far away.

We were under this assumption as well. The charges that the RSOs put were too violent. We had chutes from the other rockets deploy at apogee.

If this may be the case then lets just hope they find it in one piece. It does have contact info so they will be able to call us and notify us.
 
No tracking in a rocket that sims to 17,000 feet? (Though I get 14# for the loaded mass, maybe your 11# number was without N2O?)
 
No tracking? That makes no sense.

I still fly some older altimeters that require Mach lockout timers. It is possible this caused an issue, but it is also possible it had nothing to do with it. Proper simulation is key to setting the timer. If I had a burn time of that length I would have looked at the sim to see when it dropped to about Mach .75 or so- my swag here is at least 8 seconds maybe 10 of the altimeter supports it.

Unless you saw it come apart I would lean towards it working correctly, but nobody saw it. I had that happen once with a pretty hard accelerating small rocket. My theory is the transmitter mount broke during boost. I saw it until apogee, and saw the apogee charge pop, but lost it afterwards.
 
It's unlikely you would be over mach very long after motor burnout if you expected ~1.15M. Especially with Hyperteks regressive burn thrust is very low till the end. If you had an apogee event shortly after motor burnout you would have heard all the various noises that happen with such an event.
 
No tracking in a rocket that sims to 17,000 feet? (Though I get 14# for the loaded mass, maybe your 11# number was without N2O?)

My bad thats right it was 14lbs with loaded fuel.

Dumb mistake on our end not to put a GPS.
 
No tracking? That makes no sense.

I still fly some older altimeters that require Mach lockout timers. It is possible this caused an issue, but it is also possible it had nothing to do with it. Proper simulation is key to setting the timer. If I had a burn time of that length I would have looked at the sim to see when it dropped to about Mach .75 or so- my swag here is at least 8 seconds maybe 10 of the altimeter supports it.

Unless you saw it come apart I would lean towards it working correctly, but nobody saw it. I had that happen once with a pretty hard accelerating small rocket. My theory is the transmitter mount broke during boost. I saw it until apogee, and saw the apogee charge pop, but lost it afterwards.

We did assume that if the charges went off prematurely due to the pressure spike we would have seen it come apart like you mentioned.

I am starting to think that the main chute opened prematurely at apogee and drifted so far away.
 
So my former high school teacher is not convinced about a pressure spike that can fool the baro sensors. I remember reading a good artical on it that explained it very well. For the life of me, I can not find it anymore.

Does anyone have a link that explains the sudden decrease in pressure during the transition from sub-sonic to super-sonic speeds?
 

Thanks Bob,

That is very interesting data. Will discuss this further with my former high school teacher to persuade him that mach transition should be something to consider in a mach 1 flight.
 
How high should the rocket have been at 7 seconds? I'm guessing something like 8-10K feet? You mentioned that a few of the other rockets had mains deploy at apogee. Were those pretty clearly visible? If so, at what range and were they the same size chute as the lost rocket? Could you hear the ejection charges on those rockets? I'm leaning toward a successful up with no deployment on the down or possibly main deployed at apogee and it drifted away unseen. Deploying at M0.8 even at a fair altitude would make some noise and also a rain of parts that should have been visible.
 
How high should the rocket have been at 7 seconds? I'm guessing something like 8-10K feet? You mentioned that a few of the other rockets had mains deploy at apogee. Were those pretty clearly visible? If so, at what range and were they the same size chute as the lost rocket? Could you hear the ejection charges on those rockets? I'm leaning toward a successful up with no deployment on the down or possibly main deployed at apogee and it drifted away unseen. Deploying at M0.8 even at a fair altitude would make some noise and also a rain of parts that should have been visible.

We had clear visibility of the other three rockets that werent meant to go mach 1 and the chutes were being deployed at apogee. We set the main to deploy at 700 feet for all four rockets.

We are looking into shear pins for next year.
 
It has not been easy to figure out what happened without reading all the OPs reports, but with the OPs shear pin statement in the preceding post, the root cause of the failure to recover the rocket is quite apparent.

The root cause of the failure to recover the rocket was the apogee deployment event resulted in the main being deployed at apogee due to the lack of shear pins on the rocket. There is no convincing evidence to suggest the rocket did not reach apogee and the altimeter did not activate the apogee deployment sequence. With the main deploying at apogee, the descent at 15-20 fps from a nominal 17 Kft apogee took between 14 to 19 minutes and resulted in the rocket landed several downwind of the launch pad.

Contributing to the failure to recover the rocket was a rush to launch all 4 rockets and the lack of a check list which resulted in forgetting to install the GPS tracker in the rocket. If the tracker was installed in the rocket, it is highly probable that the rocket would have been located and recovered after it landed.

It is highly probable, but not absolutely certain that the altimeter performed as designed. There is no evidence that a mach transient triggered early deployment occurred. No puff of smoke from an ejection charge was observed, no debris generation was observed as would be expected at a high V deployment near mach, and no audible boom from an ejection charge or main charge which would be expected if the ejection charge was activated at ~7 seconds (~7 Kft) after launch on a clear day.

It is unclear how much BP was used in the ejection charges based on the statement of the OP. While this should not be an issue if shear pins were present, however it is an indication that preflight planning, preparation and ground testing were insufficient for the flight.

The OP is an L1 and the rocket used was a L2 hybrid so he was not the official flier unless it was an L2 cert flight. The flier of record who signed the launch card is ultimately responsible for the flight.

Bob
 
Contributing to the failure to recover the rocket was a rush to launch all 4 rockets and the lack of a check list which resulted in forgetting to install the GPS tracker in the rocket.

How did you deduce this, Nancy Drew?

The OP made no mention of rushing anything, and it seems like the tracker was not part of the plan, not simply forgotten.
 
How did you deduce this, Nancy Drew?

The OP made no mention of rushing anything, and it seems like the tracker was not part of the plan, not simply forgotten.

You are correct Buckeye, we were well aware of GPS, but chose not to go with it. Again, a mistake on our end, but that choice was not up to me unfortunately. Trying to get students to understand that a rocket going to 14K needs a GPS is difficult.
 
It has not been easy to figure out what happened without reading all the OPs reports, but with the OPs shear pin statement in the preceding post, the root cause of the failure to recover the rocket is quite apparent.

The root cause of the failure to recover the rocket was the apogee deployment event resulted in the main being deployed at apogee due to the lack of shear pins on the rocket. There is no convincing evidence to suggest the rocket did not reach apogee and the altimeter did not activate the apogee deployment sequence. With the main deploying at apogee, the descent at 15-20 fps from a nominal 17 Kft apogee took between 14 to 19 minutes and resulted in the rocket landed several downwind of the launch pad.

Contributing to the failure to recover the rocket was a rush to launch all 4 rockets and the lack of a check list which resulted in forgetting to install the GPS tracker in the rocket. If the tracker was installed in the rocket, it is highly probable that the rocket would have been located and recovered after it landed.

It is highly probable, but not absolutely certain that the altimeter performed as designed. There is no evidence that a mach transient triggered early deployment occurred. No puff of smoke from an ejection charge was observed, no debris generation was observed as would be expected at a high V deployment near mach, and no audible boom from an ejection charge or main charge which would be expected if the ejection charge was activated at ~7 seconds (~7 Kft) after launch on a clear day.

It is unclear how much BP was used in the ejection charges based on the statement of the OP. While this should not be an issue if shear pins were present, however it is an indication that preflight planning, preparation and ground testing were insufficient for the flight.

The OP is an L1 and the rocket used was a L2 hybrid so he was not the official flier unless it was an L2 cert flight. The flier of record who signed the launch card is ultimately responsible for the flight.

Bob

Bob,

We are well convinced that mach transition was not an issue and like you stated, that the main chute deployed at apogee.

Charges used were 0.5grams for the drogue and 0.7grams for the main. The drogue was an 18" chute with a small spill hole and the main was a 48" fruity chutes.

By the way this was under the systems go program. Not launched by any TRA or NAR club. Hence why I stated this was a discussion with my former high school teacher. Trying to get him to understand that mach transition can cause pressure spikes is very difficult and that is why, I brought this conversation here to obtain more info from experienced fliers.
 
Hence why I stated this was a discussion with my former high school teacher. Trying to get him to understand that mach transition can cause pressure spikes is very difficult...
Your altimeter's manual should explain what the mach inhibit is for if it has one. For example, the old MWC RRC2-mini documentation says:
Mach Inhibit mode is used to prevent the barometric “spoofing” that occurs during sonic-subsonic transitions during rocket boost. This is a Bernoulli-based effect and is most pronounced at
motor burnout (typically the largest velocity delta of the rocket flight).
Though this is a bit of an oversimplification it clearly shows what the mach inhibit is for. If the AIM documentation (which I couldn't find online) doesn't explain this, then that's a real problem IMHO.

As to what happened on your flight, deploy at apogee is perhaps the most likely scenario but it's also possible that the rocket deployed early, or came in ballistic, or came in on drogue and failed to deploy the main. Those charge sizes don't sound especially large to me. Without recovery or good visual tracking you just don't have any evidence to prove anything.

I know almost nothing about SystemsGo, but based on this story I question just how well-supervised it is if kids are flying Level 2 hybrid rockets with such major potential issues.
 
Agreed. Rocket was launched and never seen nor heard from again. Pretty hard to say that the root cause of the failure is quite apparent.

Drifting far away is the likely scenario, as JC simply concluded way back in post #3.

0.5 g charge is pretty wimpy for a 3" HPR rocket. That is what you find in Estes and 24mm RMS motors for low-midpower rockets.
 
For that matter, the flight could have gone exactly as planned and the rocket just wasn't found. I've had normal dual deploy flights to these sorts of altitudes land miles away; without radio tracking, I would have never found them.
 
Your altimeter's manual should explain what the mach inhibit is for if it has one. For example, the old MWC RRC2-mini documentation says:

Though this is a bit of an oversimplification it clearly shows what the mach inhibit is for. If the AIM documentation (which I couldn't find online) doesn't explain this, then that's a real problem IMHO.

As to what happened on your flight, deploy at apogee is perhaps the most likely scenario but it's also possible that the rocket deployed early, or came in ballistic, or came in on drogue and failed to deploy the main. Those charge sizes don't sound especially large to me. Without recovery or good visual tracking you just don't have any evidence to prove anything.

I know almost nothing about SystemsGo, but based on this story I question just how well-supervised it is if kids are flying Level 2 hybrid rockets with such major potential issues.

The kids are no longer even allowed to go near the launch pads or take the rocket to the launch pads. Loading black powder charges are done by RSOs. Loading nitrous oxide is also done by the program. They take safety very seriously.
 
Agreed. Rocket was launched and never seen nor heard from again. Pretty hard to say that the root cause of the failure is quite apparent.

Drifting far away is the likely scenario, as JC simply concluded way back in post #3.

0.5 g charge is pretty wimpy for a 3" HPR rocket. That is what you find in Estes and 24mm RMS motors for low-midpower rockets.

Indeed no proof no telling how. However, we want to consider every possible scenario in order to prevent this in the future. It seems to me that ground testing is one of those options to consider.
 
For that matter, the flight could have gone exactly as planned and the rocket just wasn't found. I've had normal dual deploy flights to these sorts of altitudes land miles away; without radio tracking, I would have never found them.

Yes gps or a form of tracking is required when going that high, no exceptions next time.

Speaking of tracking, what would you guys recommend for a non-altimeter type gps or tracker without the need for a HAM license?

Unfortunately the trackimo from giant leap can not be used due to the monthly fee's after the one year free service. This is something the school will not support.
 
Yes gps or a form of tracking is required when going that high, no exceptions next time.

Speaking of tracking, what would you guys recommend for a non-altimeter type gps or tracker without the need for a HAM license?

Unfortunately the trackimo from giant leap can not be used due to the monthly fee's after the one year free service. This is something the school will not support.

It's difficult to beat Walston trackers for simplicity, but for a more sophisticated solution get the ham license and then get one of the Altus Metrum or Big Red Bee(BRB) solutions. Kurt Savegnago (ksaves2 I think) has done many very interesting reports on using the BRBs. I've watched Keith Packard do some really cool things with the Altus Metrum products.
Another option, which is not inexpensive, but is a full on commercial quality product that does NOT require an amateur radio license is the Telemetry Pro, from https://www.multitronix.com. I've seen it in operation. It's nearly idiot proof and a hoot to listen to. That Kate has an attitude.
Finally, you owe it to yourself to look at the Missileworks RTx. I don't know much about it, but I think Jim Amos is one of the nicest guys around and I've used other products made by him for sixteen years without any failures that I didn't cause.
 
I watched a number of the flights on the live stream for Saturday.
While the coverage was pretty good, they didn't seem to get much of the flight besides the ignition and lift off.
You could tell if the flight went well due to the announcer saying it was under chute, or recovery system deployed.
But there were a number of flights that you just saw long faces on the kids from the school launching, and not much commentary other than that.
Would have liked to have known, or seen what went wrong with those flights.

Does look like a very cool program for the schools.
 
It's difficult to beat Walston trackers for simplicity, but for a more sophisticated solution get the ham license and then get one of the Altus Metrum or Big Red Bee(BRB) solutions. Kurt Savegnago (ksaves2 I think) has done many very interesting reports on using the BRBs. I've watched Keith Packard do some really cool things with the Altus Metrum products.
Another option, which is not inexpensive, but is a full on commercial quality product that does NOT require an amateur radio license is the Telemetry Pro, from https://www.multitronix.com. I've seen it in operation. It's nearly idiot proof and a hoot to listen to. That Kate has an attitude.
Finally, you owe it to yourself to look at the Missileworks RTx. I don't know much about it, but I think Jim Amos is one of the nicest guys around and I've used other products made by him for sixteen years without any failures that I didn't cause.

We might look into the license, but for now a tracker with no license needed would be great.

All that you posted except the missile works products are way too expensive. I should have mentioned somewhat cheap, my apologies.
 
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