So, maybe I'll try a three-stager

[Charles_McG]

Cold gas RCS.

 

[daveyfire]

Jim, congrats on another incredible achievement. What a journey it's been... and I thought you were crazy for L3ing with a minimum diameter N4000!

I was looking at the EasyMega data for the period after the rocket started tumbling (at 75 seconds) to the point where the sections were blown apart (at 130 seconds). A plot of the yaw, pitch and roll data is attached. Isn't it facinating how regular the motion is for an extended period of time?

I'm not a dynamics guy and I didn't stay in a Holiday Inn Express last night, but both yours and Kip's went so high (i.e., into thin enough air) that it gives me a good excuse to take the old Spacecraft Dynamics reader for a spin, so I'm gonna try and give this a shot. Please disregard the speculation, highlighting, and sarcastic pencil comments in the margins of the scanned document... it was a long time ago and the lectures were 2.5 hours each.

In theory, the rocket is happy spinning about either of its two principal axes. If it gets nudged a little (like by a motor shutting down), it'll start to nutate/cone. Equations 2.2-2 and 2.2-3 describe the possible nutation frequencies for all rocket body shapes. Pages 8-11 walk through what's happening from the Easymega's perspective, and pages 12-14 are how I'm supposed to envision it in my mind's eye.

If there's electronics or cameras offset from the center axis, then the momentum vector doesn't line up with the body tube (Eq. 3.1-3 or example 3.1-2) and you get nutation/coning at an angle offset from the rocket's body tube axis.

As OverTheTop pointed out, the spinning behavior is most stable about the axis with the highest moment of inertia, and that's usually not aligned with the body tube of the rockets we fly. The transition from one principal axis to the other happens when its spin energy crosses the "separatrix" (what a name), as described on the bottom of page 6 and the top of page 7. If the nutation/coning remains within the little circle at the top of the globe in Fig. 2.1-1, then we're good. And in theory, it can.

But the stability of the long-axis spinning is only guaranteed for constant energy. If energy is dissipated by, say, a tiny bit of air over the fins or recovery gear shifting around inside the rocket or the airframe bending a little, then the spin will always transition to its lowest energy state, i.e. a flat spin (Eq. 6-3 and the two after that). This happens slowly for spacecraft in benign environments, but for rockets flying at Mach 3.3, things happen a lot faster.

So, best practices would seem to be:

• Stiff rocket: minimize joints, use long couplers, add shear pins, etc.
• Balance mass around the centerline of the body tube: mount avionics symmetrically, add cameras in pairs (or with other masses)
• If possible, despin the rocket once it's out of the air with a yo-yo mechanism or something
• Bundle shock cords and use deployment bags to minimize energy loss from recovery gear shifts

I think. Ok, yeah, I'm sticking with propulsion. Thanks for indulging me

 

[OverTheTop]

Spin-stabilisation can work, but the key is stopping the rocket flexing (think banana) do it takes longer to degrade to the tumble. A good spin-stabilised rocket is quite stiff and will also be axially balanced do it is less inclined to banana, thus delaying onset of tumble.

Oops. Just updated the page and read the thread above. More techie explanation of what I said , so my comment may or may not be superfluous!

 

[dhbarr]

Nutated Banana sounds like a great name.

 

[JimJarvis50]

Nutated Banana sounds like a great name.

That might be a pretty good name given the motion that occurred. Here's what I think it looked like.

Jim

 

[CoyoteNumber2]

That might be a pretty good name given the motion that occurred. Here's what I think it looked like

What software are you using to create that visualization?

 

[JimJarvis50]

What software are you using to create that visualization?

Nothing special at all. Just powerpoint and a video editor.

Jim

 

[JimJarvis50]

Hey, as long as my thread has re-emerged, should I take the opportunity to refresh the link to the video of my Balls flight? Sure, why not.

Jim

 

[Steve Shannon]

What’s next, Jim?

 

[Leo]

4

 

[JimJarvis50]

What’s next, Jim?

4

4 - Nooooooooooo .....

Hard to say, Steve. Stu says he wants to fly his almost-Q rocket again. We had fun doing that (P to O) project, but he would have to promise not to collide with my sustainer. I would have to build a new sustainer, so I've been giving that a little thought. We'll see.

Jim

 

[Nytrunner]

Would there be any way to apply the stabilizer module to that flight!?

 

[JimJarvis50]

Would there be any way to apply the stabilizer module to that flight!?

We tried the P to O flight in 2016 and we used the stabilization module for that flight. It didn't get a chance to work because Stu's booster knocked it off the bottom of the rocket (I'll put a link to that video below - it was, um, a highly entertaining flight). I know a lot more about how it works now, so I will probably reevaluate its use and then decide. For the three-stage flight, there was a good match between the flight and the use of the stabilization module. Specifically, the booster took the rocket to just short of Mach 1, such that vertical stabilization could occur as the rocket velocity fell from around 1000 to around 700 ft/s. The timing was ideal. For the P to O flight like what we tried before, the booster velocity is much higher, and all stabilization would occur above Mach 1, I think, so more simulations would be needed to see if there is a good window in the flight profile. I just haven't looked at it in detail just yet. At present, I have zero experience with supersonic control, so that would require some test flights. So, maybe, maybe not.

Jim

 

[Nytrunner]

Was this the flight with the chuff that gave you that great booster window camera shot of the sustainer nozzle plume?

Good luck with whatever path you take! (although I'll be holding out for a supersonic flight of the stabilizer training rocket)

 

[JimJarvis50]

Was this the flight with the chuff that gave you that great booster window camera shot of the sustainer nozzle plume?

Good luck with whatever path you take! (although I'll be holding out for a supersonic flight of the stabilizer training rocket)

Yep, that was the one. If you look closely at the video, you can see that the stabilization module is attached to the bottom of the sustainer when it first separates, but it is gone after the first collision. What you can't see is the stabilization module whizzing by the booster with its shreded chute on the way to crashing onto the desert floor.

We looked for the stabilization module but couldn't find it. One problem was that the crash has removed the antenna from the tracker, and also separted the tracker from the module as it turned out. We were just about to give up looking, but on the last pass, my wife spotted the module sitting near one of the washes. Whew! Then, we picked up the faint tracker signal and got that back too.

Jim

 

[JimJarvis50]

There seem to be multiple threads going on at the moment about lighting motors at altitude. I lit the M1401 at over 40K feet, and so far as I know, that's the highest altitude that a sustainer motor has been lit by a hobbyist. So, just to document what was done, I used a double ematch with approximately 2 grams of magnelite, a 0.9 gram BKNO3 pellet, and about 2 grams of magnelite that was potted into the smoke grain. From testing, the potted magnelite produces a jet of gas for a period of two or three seconds. The motor took about 4 seconds to come up to pressure, and I allowed for that time in the flight profile.

It would be nice at some point to have a way to build motor pressure to avoid the delay in lighting the motor, but I don't have that capability at the moment.

As long as I'm posting, attached is a picture of the barometric altitude from the 3rd stage easymega. The altitude that is reported is off a little, but you can easily detect where apogee actually occured. The tumbling of the rocket started at 75 seconds, but the rocket kept going up for the next 45 seconds.

Jim

 

[Nytrunner]

Is the ematch heads doubled back, or are their tips at the end?

 

[JimJarvis50]

Is the ematch heads doubled back, or are their tips at the end?

I don't have a picture of it before dipping, but the heads were wired in parallel with one head about an inch from the top of the assembly and the other near the bottom of the assembly. At altitude, the ematches themselves don't work all that well, so the idea was to give two chances to light the pyrogen.

Jim

 

[MattJL]

There seem to be multiple threads going on at the moment about lighting motors at altitude. I lit the M1401 at over 40K feet, and so far as I know, that's the highest altitude that a sustainer motor has been lit by a hobbyist. So, just to document what was done, I used a double ematch with approximately 2 grams of magnelite, a 0.9 gram BKNO3 pellet, and about 2 grams of magnelite that was potted into the smoke grain. From testing, the potted magnelite produces a jet of gas for a period of two or three seconds. The motor took about 4 seconds to come up to pressure, and I allowed for that time in the flight profile.

It would be nice at some point to have a way to build motor pressure to avoid the delay in lighting the motor, but I don't have that capability at the moment.
Jim

Simple but effective solution to the problem. Is there a way to adapt COTS motors to this? Unless I've misread something about the installation.

Also, quick thought on building motor pressure - something I've been looking into is installing a burst disc over the nozzle exit (maybe partially ventilated, to prevent it shredding on the way up). I think that might allow for doing away with the BKNO3 pellets by keeping a little of the atmosphere in, but I'd have to progress to bench tests to figure that out. Apparently there's a patent on the concept (with a tungsten alloy burst disc!) as of about four years ago: https://patents.google.com/patent/US20120006001, but I don't think many of us have access to those kinds of exotic materials.

As long as I'm posting, attached is a picture of the barometric altitude from the 3rd stage easymega. The altitude that is reported is off a little, but you can easily detect where apogee actually occured. The tumbling of the rocket started at 75 seconds, but the rocket kept going up for the next 45 seconds.

The tumbling is interesting. Would spin-stab plus a de-spin rig have helped?

 

[ksaves2]

I don't have a picture of it before dipping, but the heads were wired in parallel with one head about an inch from the top of the assembly and the other near the bottom of the assembly. At altitude, the ematches themselves don't work all that well, so the idea was to give two chances to light the pyrogen.

Jim

Holee molee, About 5 years ago I was experimenting with staging igniters in that same fashion. Two parallel wired match heads which I made the matchheads myself from scratch. Did 10 open ground tests. A couple of them only one match caught the pyrogen burning and then it sorta burned like a
sparkler. Certainly more than enough to light a BKNO3 pellet otherwise it would be too slow to light an upper stage on it's own. That flight video was really
wonderful to experience. Kurt

 

[JimJarvis50]

Simple but effective solution to the problem. Is there a way to adapt COTS motors to this? Unless I've misread something about the installation.

Also, quick thought on building motor pressure - something I've been looking into is installing a burst disc over the nozzle exit (maybe partially ventilated, to prevent it shredding on the way up). I think that might allow for doing away with the BKNO3 pellets by keeping a little of the atmosphere in, but I'd have to progress to bench tests to figure that out. Apparently there's a patent on the concept (with a tungsten alloy burst disc!) as of about four years ago: https://patents.google.com/patent/US20120006001, but I don't think many of us have access to those kinds of exotic materials.



The tumbling is interesting. Would spin-stab plus a de-spin rig have helped?

I sort of liked the idea of potting the magnelite. When i first tested it, I was disapointed that it burned for so long. But in the absence of a burst disk, I thought that a longer burn might be a good strategy.

i believe that the BKNO3 is good to use in combination with a burst disk. You want the heat from that in combination with the gas produced.

I suspect spin/despin would avoid the tumbling, but I don't have the capability to do that. Next time, I'll try and be a little more careful about balancing the weight.

Jim

 

[JimJarvis50]

That flight video was really
wonderful to experience. Kurt

Thanks Kurt.

Jim

 

[MattJL]

I sort of liked the idea of potting the magnelite. When i first tested it, I was disapointed that it burned for so long. But in the absence of a burst disk, I thought that a longer burn might be a good strategy.

i believe that the BKNO3 is good to use in combination with a burst disk. You want the heat from that in combination with the gas produced.

It's definitely a field that deserves a lot of study. An easy to replicate, reliable high-altitude start strategy would open up a whole new frontier for rocketeers.

I suspect spin/despin would avoid the tumbling, but I don't have the capability to do that. Next time, I'll try and be a little more careful about balancing the weight.

Jim

Did it present any issues with recovery? I suppose that at that altitude, air resistance doesn't matter too much.

 

[JimJarvis50]

It's definitely a field that deserves a lot of study. An easy to replicate, reliable high-altitude start strategy would open up a whole new frontier for rocketeers.



Did it present any issues with recovery? I suppose that at that altitude, air resistance doesn't matter too much.

i would love to do some igniter testing, but I don't have a location where I can do it.

Did you watch the flight video and the animated video on the tumbling? Both are linked a little earlier here. The tumbling started at around 135 to 140K. Speed was still Mach 1.5 at that point, so it's a good thing there wasn't much air, but you can see the effect of the air that is there in the barometric altitude plot. It probably resulted in enough drag to reduce the peak altitude by around 10K. No effect on recovery though.

Jim

 

[Random Flying Object]

Do you want to pull a vac on an igniter during test or an entire motor?

 

[Charles_McG]

A British group building a ballocket autopiloted glider did testing on CTI motors in a vacuum chamber packed dry ice.

They never found an airspace that would let them fly, but their igniter experiments are still online.

https://www.theregister.co.uk/2014/04/02/lohan_rehab_tests/

 

[MattJL]

A British group building a ballocket autopiloted glider did testing on CTI motors in a vacuum chamber packed dry ice.

They never found an airspace that would let them fly, but their igniter experiments are still online.

https://www.theregister.co.uk/2014/04/02/lohan_rehab_tests/

I wish they published what they made their igniters out of. I haven't been able to find precise details yet.

EDIT: Spoke too soon. Not sure how much I like this setup.

 

[saadzmirza]

Reliable ways to ignite solid rocket motors at high altitude are documented in aerospace engineering manuals. You need an understanding of the physics of the ignition process.

Testing an igniter under vacuum is not the issue; igniters will usually fire under vacuum, but they will fail to light the propellant. The igniter needs to pressurize the motor.

By the way, I'm pretty sure LOHAN used thermite (I wouldn't mess with it personally since it is static sensitive), which does not produce gas, and it failed to light their motor.

 

[Charles_McG]

I didn’t post the LOHAN link for the igniter- but for the effort they put into ground testing. IIRC, they ended up wrapping a heater around the motor casing. A rocket ascends so quickly the fuel doesn’t have time to chill.

 

[JimJarvis50]

Reliable ways to ignite solid rocket motors at high altitude are documented in aerospace engineering manuals. You need an understanding of the physics of the ignition process.

Testing an igniter under vacuum is not the issue; igniters will usually fire under vacuum, but they will fail to light the propellant. The igniter needs to pressurize the motor.

By the way, I'm pretty sure LOHAN used thermite (I wouldn't mess with it personally since it is static sensitive), which does not produce gas, and it failed to light their motor.

This isn't something that I know a lot about, but since I didn't have a method of pressurizing the motor, other than to go with a really big (and untested) igniter, I chose a method that would provide heat over a period of time. By potting the magnelite, I got about 3 seconds or so of a jet coming down the core of the motor. The idea of this is to burn some of the propellant so that it becomes what pressurizes the motor. It took about 4 seconds for the motor to come up to pressure at 45K feet.

It was also suggested to me, by people who really know a lot about motors, that I could have used a section of a 38 mm white thunder grain in the smoke well to accomplish the same thing. It's a perfect fit by the way. I elected not to do that.

One question you have to ask is whether you need instant on or not. I arranged my flight so that instant on wasn't necessary. I think there are more options that way, particularly if you don't know what you are doing with respect to pressurizing the motor. Did i mention that I don't know a lot about this?

Jim