(Yet Another) 100k Attempt

[FredA]

The only way I can think of to get a clean, BATES-style shutoff is by casting something inert into the space where the slivers would occupy, so the motor runs out of propellant when it is still at a reasonable Kn.

This can also be a way to balance the motor if the inert spacer is low-weight

 

[Spacedog49Krell]

A long tail-off is pretty much guaranteed with a moonburner or D grain, because of the way that the propellant burns away to a sliver. If you want to see why, you can download my openMotor software and use the "grain" tab to see the shape of the propellant grain as the burn progresses. The only way I can think of to get a clean, BATES-style shutoff is by casting something inert into the space where the slivers would occupy, so the motor runs out of propellant when it is still at a reasonable Kn. That would be a bandaid solution that reduces impulse and mass fraction, though if that sliver of propellant isn't helping you maybe you don't want it.

I downloaded your openMotor software. I've seen others using openMotor for their Moonburner development. I want to compare your regression equations to Bill Wood's original equations. I find most tail-off issues result from poor initial core L/D selection.

In my profile picture I'm next to my 6" Moonburner test motor. Tests conducted at the maximum web thickness delivered a 52 second burn time with a significant tail-off at burnout. When using an optimized grain, the burn time was reduced to 36 seconds with a very short tail-off.

 

[eggplant]

I downloaded your openMotor software. I've seen others using openMotor for their Moonburner development. I want to compare your regression equations to Bill Wood's original equations. I find most tail-off issues result from poor initial core L/D selection.

In my profile picture I'm next to my 6" Moonburner test motor. Tests conducted at the maximum web thickness delivered a 52 second burn time with a significant tail-off at burnout. When using an optimized grain, the burn time was reduced to 36 seconds with a very short tail-off.

Hmm, not sure what core L/D would do, but I can see how tweaking the core shape might also help eliminate the tail-off. Maybe instead of a simple circular port, a teardrop with the point towards the center of the grain would eliminate some of the slivers (though it would also make it a faster burn).

Fortunately, openMotor can help answer questions like this, because rather than using closed-form equations for calculating regression, it calculates the distance transform of the core geometry and then finds level-set contours on it to determine the surface area of the grain at any regression depth. This means that in addition to the preset geometries available in other software, it also allows you to load in a custom port geometry from a DXF file and simulate it just as easily.

 

[rocket_troy]

I downloaded your openMotor software. I've seen others using openMotor for their Moonburner development. I want to compare your regression equations to Bill Wood's original equations. I find most tail-off issues result from poor initial core L/D selection.

In my profile picture I'm next to my 6" Moonburner test motor. Tests conducted at the maximum web thickness delivered a 52 second burn time with a significant tail-off at burnout. When using an optimized grain, the burn time was reduced to 36 seconds with a very short tail-off.

The specific impulse losses from (say) geometry tail-offs are full of nuisances from flight dynamics and let's not forget that flow separation *contributes positively* to specific impulse. The primary issue with flow separation is when it's asymmetric and the nozzle is large and flimsy to cope with deformations from the pressure gradients.
Things like a lowering of static Pa with altitude and dynamic Pe from velocity both contribute to suppress flow separation with the former assisting specific impulse directly by pressure ratio terms in the isentropic Cf equation.
Yes, at ground level, you definitely want the highest Pc/Pa ratio (optimally expanded) to maximise thrust coefficient, but the importance of that is proportionally reduced with altitude.

TP

 

[rocket_troy]

This means that in addition to the preset geometries available in other software, it also allows you to load in a custom port geometry from a DXF file and simulate it just as easily.

"Other software" not being GrainsCAD which allows freehand geometry creation without the need to import

TP

 

[rharshberger]

Wonder what effect an aerospike nozzle would have in conjunction with moon burner? Has anyone tried it yet?

 

[pugachu]

Wonder what effect an aerospike nozzle would have in conjunction with moon burner? Has anyone tried it yet?

I watched a Formlabs webinar last week on 3d printed alumina.... i thought that would make a great aerospike nozzle. Problem is it's $1,300 for 750mL of resin

 

[rocket_troy]

Wonder what effect an aerospike nozzle would have in conjunction with moon burner? Has anyone tried it yet?

Not aware of any experiments, but the typical flight dynamics of (say) a 100Kft (say) single stage is actually quite suited to a typical de laval nozzle if coupled with a regressive burn profile. Okay, a moon burner might not provide the optimum profile for that, but it should generally be within the neighbourhood. So, given that aerospike nozzles are generally heavier, more complex and have much more thermal issues to contend with; the practical incentives for exploring that avenue aren't compelling for these kinds of projects.

TP

 

[robopup]

Hmm, not sure what core L/D would do, but I can see how tweaking the core shape might also help eliminate the tail-off. Maybe instead of a simple circular port, a teardrop with the point towards the center of the grain would eliminate some of the slivers (though it would also make it a faster burn).

Fortunately, openMotor can help answer questions like this, because rather than using closed-form equations for calculating regression, it calculates the distance transform of the core geometry and then finds level-set contours on it to determine the surface area of the grain at any regression depth. This means that in addition to the preset geometries available in other software, it also allows you to load in a custom port geometry from a DXF file and simulate it just as easily.

I like the teardrop idea, and didn't realize you were behind open motor. I've always been a burnsim guy but I'll give open motor the 'ole college try.

Wonder what effect an aerospike nozzle would have in conjunction with moon burner? Has anyone tried it yet?

Interesting. I poked around a bit looking into this, RCS even sells a 54, but sounds like our hobbyist level implementations wouldn't take the heat which is why you only (as far as I know) see them on fast motors.

 

[MClark]

A long tail-off is pretty much guaranteed with a moonburner or D grain, because of the way that the propellant burns away to a sliver. If you want to see why, you can download my openMotor software and use the "grain" tab to see the shape of the propellant grain as the burn progresses. The only way I can think of to get a clean, BATES-style shutoff is by casting something inert into the space where the slivers would occupy, so the motor runs out of propellant when it is still at a reasonable Kn. That would be a bandaid solution that reduces impulse and mass fraction, though if that sliver of propellant isn't helping you maybe you don't want it.

My old boss worked on design of the Mercury escape tower motor. It used was a star grain with inert inserts so there was no tail off. Could damage the parachute. IIRC he said they cast a grain without inserts and severed ends at desired burnout. Propellant snuffs and what remains is the shape for insert.

 

[Chad]

Camera window

I had a little extra time and wasn't quite happy with my first try at the payload tube with the camera hole so I took another shot at it. Original goal which worked on round two was to have the window and not use any screws to hold things together. This ended up being harder than I expected and I didn't find many detailed pictures showing how others did there windows so figured I'd throw these here.

Mount for the window is 3d printed and glues into a section of body + coupler tube:
View attachment 602570

Window is held by a lip in the above picture, and by the blue press fit piece below which will be siliconed in place:
View attachment 602571

I found this thread last night while looking for something else. First of all, what an amazing accomplishment! Very inspiring to see projects and results like this.

Do you have CAD or stl files for your camera window mount? I want to do something similar as I haven't flown with a camera on board yet.

 

[robopup]

I found this thread last night while looking for something else. First of all, what an amazing accomplishment! Very inspiring to see projects and results like this.

Do you have CAD or stl files for your camera window mount? I want to do something similar as I haven't flown with a camera on board yet.

Thanks! See attached for the CAD, let me know if you need anything else.

This project is still very much alive for another attempt - the 100k goal hasn't been met yet! Not sure whether it will be in 2024 yet, but it will remain my rocketry focus for the foreseeable future.

 

[robopup]

I made another attempt this year at XPRS with last year's airframe and backup propellant I'd casted for the original attempt. Boost was straight and second stage lit ~15s into the flight. Unfortunately, I had the same second stage motor failure as last year (lit, and very quickly after let go). I've lit 5 motors of this design now (1 static test, 1 single stage, 1 second stage motor successful, 2 second stage failures). It's a little disappointing this happened again as I'd knew it would be a challenge and made a point of testing as much as possible (with my limited rocketry time) last year. Fortunately, I recovered most of the propellant grains from this year's attempt which confirmed two suspicions I'd had since last year's failure.

With that said, although a failure, I'm about as pleased as I could be with this attempt and where things are headed based on where I left off last time. Off the top of my head:

• Minor improvements to my tower made for easier setup+teardown, rocket loading, angling, stiffness and helped with a very straight boost off the pad
• Two small tweaks to the airframe made prep much easier than last year
• I've spent the last year or so working a new simpler and hopefully more reliable propellant for future attempts. It also should specifically address one of the causes of failure on this motor. I have about a dozen static tests and now two flights, including next year's booster motor on a single stage this year.
• New drogue and main parachutes which are stronger, pack smaller, and have worked well this year.
• New fin construction, alignment, attachment and materials which worked well on the 3in single stage test rocket above
• Corrected and again tested ignition circuit per feedback in this thread
• Improved camera settings
• Close on a composite case design for future second stages

View attachment IMG_9300.MOV

Unfortunately, both closures failed on my second stage rather than just the nozzle this year so my fincan came in hot. Shout out to @tfish for his snazzy lake stake puller!

 

[pugachu]

Sorry about the upper stage CATO and loss of the upper stage airframe.

I'm curious about your next gen upper stage motor design. I believe you had indicated that you want to move away from a moonburner, as the off-axis CG causes the corkscrewing that you saw last year.

Glad that you made improvements on the design. I hope you'll share your HEI safety circuit, as I see a lot of benefits of HEI, but I'm super paranoid of having an unplanned ignition.

 

[rharshberger]

Keep it up Robo you'll get it sooner rather than later I think!

 

[robopup]

Sorry about the upper stage CATO and loss of the upper stage airframe.

I'm curious about your next gen upper stage motor design. I believe you had indicated that you want to move away from a moonburner, as the off-axis CG causes the corkscrewing that you saw last year.

Glad that you made improvements on the design. I hope you'll share your HEI safety circuit, as I see a lot of benefits of HEI, but I'm super paranoid of having an unplanned ignition.

For the time being, still going the moonburner route, I still like its pros/cons over a center core burner for my flight profile. An end burner would be amazing but I don't have the time or expertise to go down that rabbit hole right now.

HEI circuit is very similar to last year, but with R1 moved to the altimeter side of SW2 rather than the igniter side. This is to prevent a dead short if both SW1 and SW2 are latched and altimeter output is on. R1 is calculated so that nominal current to light the igniter is above the always fire current of the ematch, but that if SW2 is closed the current through the igniter is below the never fire, also taking into account the measured resistance through my wire length, connector and switches. I verified that:

• igniter doesn't fire if I hook up my lipo to the altimeter side with SW1 and SW2 closed
• igniter does fire if I hook up my altimeter and close SW1, leave SW2 open

At the pad, a summary of my checklist is:

1. Forward closure out of motor with SW1 open and SW2 closed. HEI hooked up to altimeter.
2. Test arming of HEI altimeter: Arm altimeter, close SW1, open SW2, wait ~20s
3. Unarm HEI altimeter with reverse procedure: close SW2, open SW1, altimeter off
4. Forward closure installed. I can leave the HEI circuit completely connected, exactly as it was in my step 2 test
5. Arm repeating step 2 on pad.

Before prep, I also verify that all the fets on my altimeter are behaving as they should.

Still open to suggestions on this design and process, but after a ton of testing, practice and now 3 launches, I've felt safe with it.

Thanks @rharshberger ! 100k someday!

 

[Finicky]

HEI hooked up to motor.

Did you mean "HEI hooked up to altimeter" in step #1?

 

[robopup]

Did you mean "HEI hooked up to altimeter" in step #1?

Yikes! Yes I did! Edited my post

 

[Finicky]

Yikes! Yes I did! Edited my post

All good

I have flown many multi-stage flights, and have always avoided HEI. I guess I'm old and "seasoned" enough to realize the many failure modes that can ruin your day. Also, I'm factoring in how scatterbrained I am. I do enjoy the build challenge associated with getting the wiring to the bottom of the rocket when not using HEI, since this gets really interesting with minimum diameter stuff. But with all that being said, I really do appreciate it when someone publishes their technique for doing HEI safely. So thank you.

PS - I remind flyers (particularly college teams) to ALWAYS verify the functionality of the FET pyro outputs prior to use on a two stage attempt. 12V light bulbs and a multimeter are your friend.

 

[Cherrywaves89]

It's been a long term goal of mine to get something over 100k ft. I'd never felt quite confident that I had a reasonable shot a success until now. And, along with other legit prerequisites, watching a few Balls/XPRS attempts I'd always sort of assumed that the motor sizes required were something I wasn't that interested in dealing with, at least for now. But, inspired by a couple friends working on similar projects and, in particular, Kip's recent successful flight, I spun some sims this fall and realized it might be doable with a 75mm -> 54mm. I have enough worked out to post the summary below, but I'm sure I'm going to have a lot of questions: this is a lot of pretty new territory for me...

Edit: That got really long, my apologies. If you actually brave reading the whole thing, maybe some music helps.
View attachment 558227

Goals

• 100k apogee, recovery of both booster and sustainer
• Clear video of launch, through apogee, and ideally through sustainer touchdown
• As much home-rolled as possible
• (Relatively) low budget

Design Summary

• Two full stack rockets going into the season
• 75 mm booster -
  • 26.5 lb full stack pad weight estimate
  • Motor: ~M-1230, orange sunset, 8000 Ns, 6.5s burn time, 9.35 lb propellant, 15.75 lb loaded motor
  • 4 fins, > 3 calibers of stability through flight profile per Rasaero, 0.125 in G10 with no tip-to-tip
  • Structure - composite airframe, ~0.050 in carbon fiber (5 wraps) (plain weave carbon fiber with Adtech 820 from Soller Composites)
  • Electronics
    • single altimeter in ISC to manage dual deploy
• 54 mm sustainer:
  • 7.75 lb pad weight estimate
  • Motor: ~L-325, orange sunset, 2900 Ns, 9s burn time, 3.3 lb propellant, 5.85 lb loaded motor
  • 4 fins, > 2 calibers of stability through flight profile per Rasaero, 0.1 in G10 with no tip-to-tip
  • Structure - composite airframe, ~0.030 in carbon fiber (3 wraps) (same plain weave carbon fiber with Adtech 820 from Soller Composites)
  • Electronics
    • redundant in nosecone for recovery, one of which has telemetry and GPS
    • one to manage staging bolted to top of motor
  • 54 mm 5:1 von Karmen nosecone
  • Jim Jarvis style ignition via copper tape, for the full up arming test before sustainer ignitor goes in the motor. No head end.

Electronics

• Homerolled, I've exclusively been flying these the last few years in similar sized single stage projects
• Standard version has low and high g accelerometers, pressure and temperature sensors. Fancy version additionally has a GPS and radio for telemetry (I've been burned now 1 too many times with my Walston and other directional tracker; having time of flight only to never find the rocket after it's landed)
• User defined events
  • Up to 16 user defined events which can trigger pyro output using combinations of AND or OR logic
  • Triggered by liftoff, burnout, apogee, or any other user defined event
  • Greater than/less than/equal to constraints can be placed on altitude, velocity, acceleration, tilt angle, max tilt angle, flight phase, or powered flight counter. Additionally, time after triggering event and time after all constraints met can be specified.
• Simulation - not there quite yet, but I'm modifying post-scripts for testing I wrote a while ago to ingest Rasaero data -> convert to raw sensor output -> run on flight firmware in an attempt to remove surprises encountered by other folks attempting projects like this and to try to dial in my staging logic.
• Staging logic - TBD but I'm leaning away from a simple timer, and more towards a combination of:
  • min_speed < velocity < max_speed
  • tilt_angle < max_tilt and max_tilt_angle < max_tilt2
  • altitude > min_altitude

CAD

• Sustainer ebay:
• View attachment 558248
• Payload - staging altimeter and GoPro Session 5:
• View attachment 558247
• ISC:
• View attachment 558246
• Booster ebay:
• View attachment 558249

Flight Simulation
All simulations were done in Rasaero using weights determined from CAD. Chuck and Kip's new Rasaero thread on skin friction coefficients and simulation has been awesome... Goal is to keep the booster stability at > 3.0 calibers, sustainer at > 2.0 calibers through flight:
View attachment 558237

View attachment 558238

View attachment 558239

Test Plans
I have a number of test flights slotted for the spring; I want to make sure I feel super comfortable with all components before a full up attempt:

• 54 mm sustainer motor static test. My motor making buddies and I have quite a bit of flight experience with the booster motor, so not static testing that one.
• Sustainer single stage on a small H to test all electronics and cameras
• Staging test with small motors - ~I-600 in the booster -> small H in the sustainer
• Sustainer single stage on the full L-325 motor

Current Progress
Winters are usually pretty busy for me with my extra hobby job, but I've made decent progress on several components of this project which I was either more nervous about finishing in time or could be done before finalizing design

• Most of my time so far has gone into a ground up rewrite up my electronics firmware which I've just about finished. Everything is much more modular, I can define the user events described above, I added support for telemetry with a separate ground station I've been working on along with GPS and I have a full suite of unit and flight tests I've been meaning to write for a while. Big remaining item is to finish the scripts to ingest simulation data for full simulated flights
• 8 of 12 75 mm booster bates grains are cast (going for 2 booster motors total). I have my sustainer motor designed, and just took delivery of some of the fancy pants Loki liners but have not cast grains yet. I need to cast 4 sustainer motors: one for static testing, one for a single stage flight, and two flight ready motors.
• Tubing - I have all tubing rolled for two each of: 54 mm sustainers, ISC 54mm and 75mm and 75 mm boosters
• View attachment 558243
• Fin beveling jig - I built a v2, trying to fix everything that was bothering me from v1 https://www.rocketryforum.com/threads/75mm-composite-minimum-diameter-build.173626/post-2312429. I'm sure I'll find new stuff I'm not happy about with this one
• ISC - At some point I'll write a post detailing my intended design, but for now the 3d printed portion of this part has gone through a few design iterations with some cheapazoidal leftover material:
• View attachment 558244

Game on!

Hey what are you using as a mandrel for the two tube sizes?

 

[robopup]

@Cherrywaves89 I've used all sorts of mandrels. Usually they're motor casings - in this project specifically the booster was rolled on a long 3in EX case, the 54mm second stage on a spent K-250 casing. The key is that you select mandrels which are as consistent along the length and as round as possible. If either one of these is off, it can be awful or impossible to get the tube off.

The last year or so I've moved to a dedicated set of mandrels for 29mm-75mm. They're all very consistent diameter, round, much longer than I need which makes it easier to roll, and polished to help slide tubes off.