98mm N5800 MD rocket for BALLS

[tedapke]

Did the electronics survive?
Any data from the altimeters?
Ted

 

[CCotner]

I think we're very close to solving this challenge. It looks like your fins and booster were just fine, as was your nosecone. This issue now is the upper airframe. The challenge is to get it as strong as possible while maintaining RF transparency. Perhaps a custom thick walled fiberglass tube, along with a custom fit nose cone?

And that is exactly what we had prepared to fly, before our inexperience with recovery electronics reared it's ugly head.

Chris, I'm still sad to see that it shredded. That nosecone sounds like a tough puppy-I'm impressed. Well done! We've got to get a videocamera on ours for the spring...the pad video was sweet.

 

[CCotner]

Awesome flight, sorry it failed. Better materials...I'm especially glad we didn't fly now: even reinforced, I doubt our front end tube would have been strong enough. Especially since our nosecone design is so much heavier than yours... This is really surprisingly hard to do, isn't it?

What were your recovery plans? Apogee detection/deployment/etc.. I'm curious to see what you came up with, especially since we're re-designing that from scratch right now for our attempt.

 

[cjl]

I missed that part of the build, what I remember was "As kevin said, it's ordinary cf from performance rocketry. I'm not too worried about its strength, since it will actually be shorter than the motor casing. As a result, the casing will act as a full length aluminum coupler, pretty much eliminating any chance of the tube buckling. It also should never have a very high heat load, since it will never be directly exposed to the airstream. Honestly, the tube is the one part of the rocket that doesn't terribly concern me." So the motor did not go all the way to the nosecone shoulder?

Nope - there was a gap of around 1/2" to 1" between the end of the case and the start of the nosecone shoulder, and at the moment, all evidence points to that 1" of unreinforced fiberglass tube as the point of failure. This motor is extremely unforgiving of even small weak points on a rocket.

 

[cjl]

Awesome flight, sorry it failed. Better materials...I'm especially glad we didn't fly now: even reinforced, I doubt our front end tube would have been strong enough. Especially since our nosecone design is so much heavier than yours... This is really surprisingly hard to do, isn't it?

Well, it's definitely hard to do. I don't know how surprising it is - these reach a really, really high dynamic pressure (P_total is over 12 MPa, assuming an approximately standard day, mach 4.2, and 10k AGL over Black Rock - for those of you who are familiar with aviation, that's over 2100KEAS). I think it's definitely doable though - I may try again at BALLS next year, regardless of the status of the CTI prize, since as much as anything, I'm doing it for my own enjoyment and curiosity.

What were your recovery plans? Apogee detection/deployment/etc.. I'm curious to see what you came up with, especially since we're re-designing that from scratch right now for our attempt.

I had a single Raven for deployment, but I was using 3 channels. Primary apogee was barometric plus a ten second delay - this was based on Adrian's suggestion. Apparently, the Raven's baro sensor is nearly good to a vacuum, but when you get really high, the noise in the sensor channel makes it difficult to detect accurately. I really didn't care if my apogee was late, but I didn't want it to be early, hence the delay. Backup apogee was a 95 second timer with the added caveat that the rocket had to be above 2000 feet (just to make sure it couldn't fire 95 seconds after liftoff if it somehow was already on the ground, but the electronics were still working). Main was set to 5500 feet, straight baro.

For deployment, I had a 24mm CF tube on top of my e-bay that was about 5 inches long, and there was effectively a piston consisting of a 24mm CF coupler and a 7/8" (I think - it was whatever size fit) oak dowel. There was a 0.4 gram charge inside the 24mm tube, and the piston was shear pinned in, so effectively, it was 0.4 grams of black powder inside an unvented 24mm tube less than half an inch long. The idea was to contain the pressure to allow the black powder to completely burn at altitude, and as the piston was pushed out, the dowel (which was against a bulkhead near the tip of the nose cone) would push the nose off, so I never had to pressurize the internal volume of the nosecone to deploy. The main was wrapped around this piston setup, and was using a Defy Gravity Tether to keep it tightly wrapped until it was time for it to deploy. This entire setup fit inside the nosecone, hence the extraordinarily short overall rocket length for this motor.

My biggest complaint about my recovery system was that it could only be armed with the nosecone off. This necessitated that I basically do the final prep, including main chute packing, once the rocket had already been put in the tower (as can be seen in Ed's picture of my dad and I doing final prep a couple pages back). I'd like to think about some way to arm it with the nosecone on if I do this again, as that was a real pain in the neck. That having been said, the priority with a project like this was always performance over practicality or ease of prep, so I would only change it if I could think of a good way to do it that would not increase the overall length or weight of the rocket. I do have a number of interesting ideas though, and I do think substantial improvements could be made over my design in a number of ways. After I've fleshed out my ideas a bit more, I may post them here, as I really don't mind sharing them - my goal for next year (or whenever I get around to doing this again) would simply be to make it work, not necessarily to be the first or even the highest (although I would certainly optimize it as much as I possibly could).

 

[cjl]

Did the electronics survive?
Any data from the altimeters?
Ted

For the most part, no, they did not. The Beeline and telemetrum are toast for sure. The raven may be salvageable though - the USB connector is trashed, and it's missing the cap and buzzer, but other than that, it seems to be mostly OK. I'll post any data I get if it proves to be recoverable.

 

[cjl]

Now, I have little experience with this.... but.... what if instead of the nose cone coming off, the laundry came out the rear end? Then you could simply secure the nosecone on (or even mold it into the body tube). Just a random Idea I had.

That's actually one of my more...um...ambitious? Yeah we'll go with ambitious here. That's one of my more ambitious ideas for a future project. Make the entire rocket one solid, glued-together piece, with no seams at all, and then eject the entire motor casing out the back for recovery. It has substantial structural and aerodynamic benefits, since there's no external seams at all, and the nose cannot possibly wobble, but there's the difficulty of kicking 4 feet and 10 pounds or so of motor case out the back reliably, with as minimal of a chance of binding as possible. I think it would be doable though. It also introduces some unique headaches with the electronics design, but at least at the moment, it's my leading contender for my next design when I get around to rebuilding. I'll need to figure out a full recovery schematic, but I'm cautiously optimistic about the possibilities here.

Shame this didn't work. I should point out I've been checking here almost twice a day waiting for a flight report...

Now I feel really bad about how long it took me to get around to posting a flight report :blush:

 

[edwinshap1]

The best thing about pulling the laundry out the back would be that it would all be pulled by 10 lb or so of motor, instead of a few oz of nosecone.

 

[cjl]

Yep. It also makes for a much nicer weight split for a drogueless descent - mine would have had around 16-17 pounds of booster on one end of the cord, with 1.5 pounds of nose on the other end. This way, you would have more like 7-9 pounds of rocket on one end, and 10-12 pounds of motor on the other. As I said, it's currently my strongest contender for my next attempt, I just have to work out some of the details first...

 

[cjl]

Gotcha, and I was giving you a hard time on the rebuilding bit.

-Kevin

I know

I do want to redo this at some point though, as I do think it should be possible to make a really nice, optimized N5800 rocket with no metal structural components aside from the motor casing.

 

[donperry]

I hope you find the time and money to do this. Also, an onboard keychain camera of some sort

 

[5x7]

Wouldn't a magnetic switch work?

 

[JLRockets]

For deployment, I had a 24mm CF tube on top of my e-bay that was about 5 inches long, and there was effectively a piston consisting of a 24mm CF coupler and a 7/8" (I think - it was whatever size fit) oak dowel. There was a 0.4 gram charge inside the 24mm tube, and the piston was shear pinned in, so effectively, it was 0.4 grams of black powder inside an unvented 24mm tube less than half an inch long. The idea was to contain the pressure to allow the black powder to completely burn at altitude, and as the piston was pushed out, the dowel (which was against a bulkhead near the tip of the nose cone) would push the nose off, so I never had to pressurize the internal volume of the nosecone to deploy.

Chris,
Sorry to hear about the shred. Great try, and I hope you do try again. The rocket looked awesome coming off the pad.

Your deployment system sounds very innovative. Nice way to handle the issue of BP burn at altitude. It sounds like you just shear pinned the piston, and not the nose itself. How big was your vent hole? Could the problem have been pressure separation, or at least enough separation to have caused the imperfection in the fit that you hypothesized in post #428?

Jackson made a vent hole sizing worksheet that uses pressure data from RockSim to calculate a flow rate out of the hole and corresponding pressure over time. I’ll get after him to post it on a new thread, but in the meantime, I can have him PM it to you, if you want.

 

[AlphaHybrids]

Chris,

Very nice attempt. You essentially made a Z-Pard with carbon fiber for your recovery device. Rockets Magazine had these a few years back, but out of aluminum tubes. I have a rocket that I haven't flown that does what you describe - ejects everything out the back. It has been ground tested and works very well. I'm using a 6" post bollard from HERE and ejecting a 40" long 98mm motor with centering rings and fins out of the back. I've tested it sitting the rocket on the ground and tossing the bollard into the air. So far I've only gotten about 25' in altitude out of the bollard, but it comes off very cleanly and shears 3 #4-40 nylon screws on the way up. Since I found out about the Z-Pard, I have used it on all my rockets since. You use .5-1 gram of FFFF and you can really make things move. During ground testing I launched a 4" nosecone that was shear pinned with 3 #4-40 nylon screws over 50'. There is a 54mm minimum diameter rocket at NCR that is being built with this device and method - toss everything out the back, and size the parachute for your heaviest part, the motor. Use enough shock cord that the motor lands first, then the airframe lands second. In my opinion it is much more reliable method because you are applying your force directly to what you want, and that force is very repeatable.

Edward

 

[New Ocean]

I hope you find the time and money to do this. Also, an onboard keychain camera of some sort

I think if one wants to learn more about the limits of composites from a flight like this, an onboard camera is a good idea. It is hard to know exactly what happened this time around, so what new information do we have for the next attempt? The camera would be helpful to confirm that the fins did not come off first, for example.

 

[bandman444]

[Crazy Idea/] Is there any chance of using a high speed ground based camera for data analysis? I mean these failures happen at such low altitude that it must be possible with the right tracking to catch it all on high speed tape. Chris, I know you have done some work at Wallops so I know you must have some experience with the professional world of optical tracking. [crazy idea off/]

Good try Chris. Very proud of you for your efforts.

Bryce

 

[Jeroen_at_CTI]

Chris,

Thanks for posting all your findings and your build. And off course for participating in the contest! There is a lot of information in this thread and I think it will be a classic read for many years to come.

As I said, I do have several ideas, but they will have to wait for that magical combination of funding and motivation.

I think it's definitely doable though - I may try again at BALLS next year, regardless of the status of the CTI prize, since as much as anything, I'm doing it for my own enjoyment and curiosity.

I'm pleased to hear that you seem to have changed your mind a bit since last night ;-). Looking forward to your next built thread. If there is anyway we can help, you have my contact info.

Jeroen

 

[loopy]

I think if one wants to learn more about the limits of composites from a flight like this, an onboard camera is a good idea. It is hard to know exactly what happened this time around, so what new information do we have for the next attempt? The camera would be helpful to confirm that the fins did not come off first, for example.

I think it would have to be an onboard camera feeding directly to a recorder on the ground, as a shred such as this would most likely lead to the utter destruction of the camera.

 

[New Ocean]

Not so sure about that, these cameras are pretty strong. All you need is the SD card anyway!

 

[cjl]

Chris,
Sorry to hear about the shred. Great try, and I hope you do try again. The rocket looked awesome coming off the pad.

Your deployment system sounds very innovative. Nice way to handle the issue of BP burn at altitude. It sounds like you just shear pinned the piston, and not the nose itself. How big was your vent hole? Could the problem have been pressure separation, or at least enough separation to have caused the imperfection in the fit that you hypothesized in post #428?

Correct - I shear pinned the piston together, but the nosecone itself was designed to be held on with drag forces alone. Given that the failure happened while the motor was still putting out over a thousand pounds of thrust, and the rocket was in the neighborhood of mach 3, I doubt that it could have been an internal pressure separation. I have a few more calculations to run on that before I can be absolutely certain, but the nose cone was well vented, and at that point in the flight, should have been held on by more than 150 pounds of drag forces and 100 pounds of inertial forces, which should make pressure separation at that altitude impossible (even if it had been unvented, the pressure differential should have been insufficient to move the cone).

Jackson made a vent hole sizing worksheet that uses pressure data from RockSim to calculate a flow rate out of the hole and corresponding pressure over time. I’ll get after him to post it on a new thread, but in the meantime, I can have him PM it to you, if you want.

I would be very interested both in seeing it and in seeing the methodology behind it (what assumptions and equations are used, mostly - flow through a hole can be a non-trivial calculation)

 

[cjl]

Wouldn't a magnetic switch work?

I had a magnetic switch. The electronics were too far towards the middle of the rocket though, so the E-bay could be assembled just fine, but the nose had to be off to arm. As I said, this will definitely need a better design for next time.

 

[cjl]

I think if one wants to learn more about the limits of composites from a flight like this, an onboard camera is a good idea. It is hard to know exactly what happened this time around, so what new information do we have for the next attempt? The camera would be helpful to confirm that the fins did not come off first, for example.

The orientation of debris in the debris cloud plus the appearance of the debris seems to very, very strongly indicate that the fins did not come off first. It's not perfectly conclusive, but it's pretty good, and I'm very unconvinced that an onboard camera would have survived, given the violence of the disassembly. It tore surface mount components off of circuit boards that were inside multiple layers of protection.

 

[cjl]

[Crazy Idea/] Is there any chance of using a high speed ground based camera for data analysis? I mean these failures happen at such low altitude that it must be possible with the right tracking to catch it all on high speed tape. Chris, I know you have done some work at Wallops so I know you must have some experience with the professional world of optical tracking. [crazy idea off/]

Good try Chris. Very proud of you for your efforts.

Bryce

That would be awesome - the ground based optical tracking produces some incredible results, and you're correct that I've seen it used at Wallops. Sadly, it's way beyond my (or I suspect any other amateur) capability in terms of both equipment and cost.

 

[AlphaHybrids]

That would be awesome - the ground based optical tracking produces some incredible results, and you're correct that I've seen it used at Wallops. Sadly, it's way beyond my (or I suspect any other amateur) capability in terms of both equipment and cost.

Doug Gerrard mentioned at one MHM or O'Fest that he might bring an optical tracker to the next event. He was looking for fast, high altitude rockets and was putting the tracker on the hill.

You might contact him.

Edward

 

[Adrian A]

I had a magnetic switch. The electronics were too far towards the middle of the rocket though, so the E-bay could be assembled just fine, but the nose had to be off to arm. As I said, this will definitely need a better design for next time.

A big magnet should have been enough for that. Did you have one?

 

[5x7]

I had a magnetic switch. The electronics were too far towards the middle of the rocket though, so the E-bay could be assembled just fine, but the nose had to be off to arm. As I said, this will definitely need a better design for next time.

Stronger magnet? Oops -Adrian beat me to the post.

 

[cjl]

A big magnet should have been enough for that. Did you have one?

I did at one point, but I managed to lose it during the packing (oops). Regardless, the next design (when I get around to it) will have substantial changes, so it shouldn't require a large magnet anyways.

 

[MaxQ]

The upper tube was actually the older style (cloth based) PR FG tube, not the newer filament wound stuff. As for rebuilding? As I said, I do have several ideas, but they will have to wait for that magical combination of funding and motivation.

I don't know about the rest of you guys, but I'm sufficiently intriqued enough to see some team sponsoring of the next project by Chris.
In fact, if he keeps us posted for next year, I'll ante up $ome.

I won't be doing any Mach 3 flights myself anytime soon, but I wouldn't mind seeing this one suceed.

One or two provisos...HE designs it - we offer advice and only advice that he picks and chooses.
He keeps receipts and we get to see it fly.

 

[BLKKROW]

I don't know about the rest of you guys, but I'm sufficiently intriqued enough to see some team sponsoring of the next project by Chris.
In fact, if he keeps us posted for next year, I'll ante up $ome.

I won't be doing any Mach 3 flights myself anytime soon, but I wouldn't mind seeing this one suceed.

One or two provisos...HE designs it - we offer advice and only advice that he picks and chooses.
He keeps receipts and we get to see it fly.

I would be willing to donate to a project of his also.

+1 from me.

 

[MaxQ]

I would be willing to donate to a project of his also.

+1 from me.

We can all wear plaid, the team color.