(Yet Another) 100k Attempt

SilicdyneTRF
Advertise with us
madcow rocketry
The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Spacedog49Krell said:
Bill,

The second stage grain design, on this rocket, is "Moonburner". It has an inherent large mass offset during the burn.
Click to expand...

I did notice that; “…assuming the rest of the vehicle is axisymmetric in mass.”

Look, this thread has been hijacked long enough: I understand why moonburner grains seem the right answer for sustainers on high performance vehicles. But that choice will *always* lead to coning, that’s just physics. A BATES (or any other axisymmetric) grain design with a slower burning propellant will avoid coning and get the longer burn time desired for an upper stage.

Bill
 
Last edited:
cerving said:
Congratulations! 75K isn't anything to sneeze at, now you can set your sights on that 100K goal for next time.
Click to expand...
I completely agree. 75k is amazing, and you desiged and built everything yourself, including the motors and electronics, even sewed your own 'chutes. I enjoyed following this thread.
 
wclaybaugh2 said:
I did notice that; “…assuming the rest of the vehicle is axisymmetric in mass.”

Look, this thread has been hijacked long enough: I understand why moonburner grains seem the right answer for sustainers on high performance vehicles. But that choice will *always* lead to coning, that’s just physics. A BATES (or any other axisymmetric grain design) with a slower burning propellant will avoid coning and get the longer burn time desired for an upper stage.

Bill
Click to expand...
I think the important thing to keep in mind is that this is a system and compromises have to be made. I'm not particularly interested in optimizing any single component but I'm VERY interested in optimizing the system. For example, it seems like a lot of Ex-ers chase maximum Isp, with effects on altitude due to issues like volume loading and burn times be damned.

It's not that I didn't consider bates grains in the second stage. I even flew (successfully) 27" of orange sunset (as far as I know, about the slowest propellant there is) as an L-800 last year in a mockup of my second stage. It's that it seemed likely it wasn't the correct answer for the system: sims suggested that the choice of that same motor in a second stage would result in 15k ft less altitude than the second stage moonburner I used (even with 4" more propellant!), while also raising the maximum speed by an additional mach number (something I was and am very concerned about).

I accepted that there could be some penalty due to coning because it seemed likely the overall system would still perform better. And I still think that there were likely other factors which caused the majority of my problem - looking at data and video I have two theories (one being that I simply didn't get a fin on straight enough). If you look at Kip's or Curt's big flights, both used moonburners in their second stages and, while there was some spin+coning, it didn't dramatically effect the final altitudes compared to expected from straight flight sims.

And many thanks all for the kind words, it means a lot!!
 
JimJarvis50 said:
Rob, you got it off the ground, got a decent altitude and got it back. Not bad at all.

For what it's worth, I've flown moonburners in second stages over 100K multiple times without coning.

Jim
Click to expand...
Yes, I'm a little surprised and quite pleased that so much worked. Thanks a bunch for all the documentation you've posted over the years, your threads were goldmines for me.

Speaking of, I have a question I've been meaning to ask you: what is the specific usecase you're trying to handle by having a shunt which can take the full output of the battery without firing the igniter? My best guess is to last longer than the altimeter FET in case it's locked?

My ignition circuit was as below, but I ended up omitting the low ohms resistor in series with the igniter for the flight - accordingly, my igniter would fire with if both the inline and shunt switches were closed. I did bench test this circuit with the resistor in place and had things working, but decided to leave it out in favor of simplicity for the flight. The reasons being:
  • Open/closed switch meant to handle any bad altimeter altimeter output on powerup
  • Shunt meant to handle any weird static stuff etc, just like I always twist my igniter and ematch leads together until immediately before use.
  • Checked before mounting electronics that all FET outputs were behaving as expected with light bulbs, then didn't fire any more ematches until the actual launch
  • Could test my full setup without disassembly (but outside motor) - 1) turn on altimeter, 2) close open switch, 3) open shunt, 4) wait for 30 seconds, 5) if nothing lights, reverse the process then install closure in motor.

1695218859121.png
 
Last edited:
wclaybaugh2 said:
I did notice that; “…assuming the rest of the vehicle is axisymmetric in mass.”

Look, this thread has been hijacked long enough: I understand why moonburner grains seem the right answer for sustainers on high performance vehicles. But that choice will *always* lead to coning, that’s just physics. A BATES (or any other axisymmetric) grain design with a slower burning propellant will avoid coning and get the longer burn time desired for an upper stage.

Bill
Click to expand...
One last post here on @robopup's thread ...

I am interested in your ideas and the dynamics of coning due to radial imbalance, @wclaybaugh2, but this is not the thread.

Please open a thread or I will if you prefer so we can talk about coning due to radial balance in smaller rockets ?

Thanks Bill looking forward to learning something concrete about something I've always suspected might be the case.

-- kjh( a 1990's one-DoF Rip Van Winkle suddenly awakening in the new 6-DoF world of rockets )
 
robopup said:
I think the important thing to keep in mind is that this is a system and compromises have to be made. I'm not particularly interested in optimizing any single component but I'm VERY interested in optimizing the system. For example, it seems like a lot of Ex-ers chase maximum Isp, with effects on altitude due to issues like volume loading and burn times be damned.

It's not that I didn't consider bates grains in the second stage. I even flew (successfully) 27" of orange sunset (as far as I know, about the slowest propellant there is) as an L-800 last year in a mockup of my second stage. It's that it seemed likely it wasn't the correct answer for the system: sims suggested that the choice of that same motor in a second stage would result in 15k ft less altitude than the second stage moonburner I used (even with 4" more propellant!), while also raising the maximum speed by an additional mach number (something I was and am very concerned about).

I accepted that there could be some penalty due to coning because it seemed likely the overall system would still perform better. And I still think that there were likely other factors which caused the majority of my problem - looking at data and video I have two theories (one being that I simply didn't get a fin on straight enough). If you look at Kip's or Curt's big flights, both used moonburners in their second stages and, while there was some spin+coning, it didn't dramatically effect the final altitudes compared to expected from straight flight sims.

And many thanks all for the kind words, it means a lot!!
Click to expand...

Rob:

Before dismissing coning as not much effecting performance you might want to look into the results of the second flight of Mesos.

But enough on coning; it was a remarkable flight, congratulations!

Bill
 
Last edited:
robopup said:
Yes, I'm a little surprised and quite pleased that so much worked. Thanks a bunch for all the documentation you've posted over the years, your threads were goldmines for me.

Speaking of, I have a question I've been meaning to ask you: what is the specific usecase you're trying to handle by having a shunt which can take the full output of the battery without firing the igniter? My best guess is to last longer than the altimeter FET in case it's locked?

My ignition circuit was as below, but I ended up omitting the low ohms resistor in series with the igniter for the flight - accordingly, my igniter would fire with if both the inline and shunt switches were closed. I did bench test this circuit with the resistor in place and had things working, but decided to leave it out in favor of simplicity for the flight. The reasons being:
  • Open/closed switch meant to handle any bad altimeter altimeter output on powerup
  • Shunt meant to handle any weird static stuff etc, just like I always twist my igniter and ematch leads together until immediately before use.
  • Checked before mounting electronics that all FET outputs were behaving as expected with light bulbs, then didn't fire any more ematches until the actual launch
  • Could test my full setup without disassembly (but outside motor) - 1) turn on altimeter, 2) close open switch, 3) open shunt, 4) wait for 30 seconds, 5) if nothing lights, reverse the process then install closure in motor.

View attachment 605327
Click to expand...
Looking at your circuit you really want the resistor to the left of the shunt switch. That way the shunt switch wins in the fight against the altimeter output.
 
OverTheTop said:
Looking at your circuit you really want the resistor to the left of the shunt switch. That way the shunt switch wins in the fight against the altimeter output.
Click to expand...
For my drawn circuit diagram, that's not correct. You need to keep the circuit from altimeter output to shunt as low resistance as possible so that it sucks as much current from the battery as possible. And then use the resistor on the ematch side of the shunt to reduce current through the ematch below no fire. I tested my calculated resistance value for my battery configuration on this circuit and it worked - 1) top left switch and shunt were closed 2) battery connected to left side of circuit directly (rather than through altimeter fet) 3) ematch doesn't fire in this configuration 4) open shunt a few seconds later (before battery lets the smoke out) and ematch fires.

It just wasn't clear to me what the safety usecase was for the shunt having this behavior (other than some corner case like an altimeter fet which latched, but this can be tested beforehand other ways) so I abandoned the resistor altogether. Still curious on Jim's thoughts though.
 
robopup said:
For my drawn circuit diagram, that's not correct. You need to keep the circuit from altimeter output to shunt as low resistance as possible so that it sucks as much current from the battery as possible. And then use the resistor on the ematch side of the shunt to reduce current through the ematch below no fire. I tested my calculated resistance value for my battery configuration on this circuit and it worked - 1) top left switch and shunt were closed 2) battery connected to left side of circuit directly (rather than through altimeter fet) 3) ematch doesn't fire in this configuration 4) open shunt a few seconds later (before battery lets the smoke out) and ematch fires.

It just wasn't clear to me what the safety usecase was for the shunt having this behavior (other than some corner case like an altimeter fet which latched, but this can be tested beforehand other ways) so I abandoned the resistor altogether. Still curious on Jim's thoughts though.
Click to expand...
My preference is to put the resistor close to the altimeter in the wire to the shunt. The logic of this is that the resistor will control the maximum current from the altimeter, and then the relative resistances of the shunt and the ematch will control how much current the igniter sees. Using the resistor downstream can also work, but the difference is that you have a situation where high current is going to the circuit and bad things could happen as a result. For example, if the shunt wire or switch burned out, then the igniter fires. There is no problem with two resistors either.

Jim
 
Thanks Jim. And my apologies @OverTheTop!

I thought I'd looked into this early on and decided I was right on the margins for the no fire and always fire ematch currents. Now that I do the math again (if I'm doing it correctly), it doesn't seem so bad. Live and learn...
 
Haven't caught the bug yet to really dig through data to understand the under-performance, so no update yet. I did put this little diddy together though; it doesn't hold a candle to Kip's stuff but I enjoyed editing it.

 
Last edited:
Great flight,
At the start of this build, it looked like the 2 sustainers had slightly different fin shapes. Were they? Did they stay different? Was the second one launched? Or was that at ARLISS?
 
OzHybrid said:
Great flight,
At the start of this build, it looked like the 2 sustainers had slightly different fin shapes. Were they? Did they stay different? Was the second one launched? Or was that at ARLISS?
Click to expand...
Other than one manufacturing snafu on one of the booster casings which caused it to be half an inch shorter the rockets were identical. That and the "A" rocket got all the parts which I felt were meaningfully better. Both were flown at XPRS, somewhat ironically "B" was the one that worked. Long story short the second stage motor on "A" cato'd shortly after ignition. Moderately disappointing as I'd made a point of testing this motor and its ignition beforehand, but high L/D motors and acceleration are... a challenge. Still trying to understand what exactly happened - second stage of "A" was recovered with no damage (motor sheared at aft snap ring grove).
 
Last edited:
robopup said:
Haven't caught the bug yet to really dig through data to understand the under-performance, so no update yet. I did put this little diddy together though; it doesn't hold a candle to Kip's stuff but I enjoyed editing it.

Click to expand...


Phenomenal flight and video! Love the black sky towards the end of the ascent.

As for performance, you mentioned that you didn't think that the the coning was the biggest reason for the departure from the simulated altitude, or that the moonburner caused the coning. Though Kip's first flight of Mesos and Curt's flight are evidence that you can successfully fly a high-performance two stage rocket without substantial coning or loss of performance, the fact that those flights worked isn't enough to prove that a moonburner can't cause performance problems, or wasn't the source of them on a specific flight. Though it is a complex problem that I can't claim to understand fully, I think Kip's second flight of Mesos was evidence that using a moonburner for a sustainer can cause issues. From what I've heard, it was an identical rocket launched at a different launch site (a bit lower MSL) and underperformed the first flight by 200kft, as in it reached 90kft rather than 290kft. The video showed extreme coning, and considering it was going M4 by burnout, the energy lost to the extra drag and vectored thrust must have been huge. I think it is safe to say that the coning caused the performance issue for Kip, and my hunch is that the offset mass of the moonburner caused the coning. As for why it didn't cone on the first flight and did on the second, it could be as simple as differing wind conditions on different days at different sites putting the rocket into a regime where coning is more likely.
 
@eggplant Thanks! And I'm probably going to be reaching out to you shortly on details about your closures on your composite case; I think that's where I'm taking this next.

I need to go through the data to verify, but I suspect the primary cause for under-performance WAS the coning. I'm just not at all convinced that the dominant cause of the coning was the off axis mass of the moonburner. I've flown several moonburners in min diameter rockets with very little coning, as have many others on this forum. My bet right now is that "B's" particular fincan simply had at least one fin which wasn't on quite straight enough. I think Kip's two flights (with two different fincans) also support this guess - if the cause was dominated by off axis mass, why wouldn't those two flights be similar?

There's definitely dynamics here that I don't really understand right now, I just think there are too many clean flights floating around the forums at least for me to write this configuration off and be okay with hammering this thing on a long bates motor.
 
Last edited:
robopup said:
@eggplant Thanks! And I'm probably going to be reaching out to you shortly on details about your closures on your composite case; I think that's where I'm taking this next.

I need to go through the data to verify, but I suspect the primary cause for under-performance WAS the coning. I'm just not at all convinced that the dominant cause of the coning was the off axis mass of the moonburner. I've flown several moonburners in min diameter rockets with very little coning, as have many others on this forum. My bet right now is that "B's" particular fincan simply had at least one fin which wasn't on quite straight enough. I think Kip's two flights (with two different fincans) also support this guess - if the cause was dominated by off axis mass, why wouldn't those two flights be similar?

There's definitely dynamics here that I don't really understand right now, I just think there are too many clean flights floating around the forums at least for me to write this configuration off and be okay with hammering this thing on a long bates motor.
Click to expand...

Rob:

If coning is induced by pitch roll coupling then there exists some critical spin rate at which the aero and inertial properties of the vehicle will initiate coning. Below that spin rate, the vehicle will not cone.

The obvious example of the latter is a vehicle that is not spinning and accordingly cannot cone.

The spin rate at which coning initiates can be estimated in advance or after the fact given knowledge of the aero and inertial properties of the vehicle.

Bill
 
@robopup congratulations on your flight! This was a huge achievement and I hope you feel that way. I think you can solve the coning issue. I’ve have flown moons over 100k ft with no coning.

Since Mesos is mentioned here, I will chime in on its second flight this May at FAR. There were some differences in the fins between Flight 1 and 2. In particular, Flight 2 had stainless steel leading edge caps which caused some leading edge warp. This topic alone deserves its own thread/YouTube video which I’ll get into someday. The warp, while slight, likely induced most of the spin.

The next culprit was the motor case which was also new for Flight 2 because the one from Flight 1 got dinged (rocky landing site). The nozzle end of the motor case and snap ring grove was actually 0.33 degrees out of perpendicularity from the case axis. This is huge and I am surprised I did not catch it before the flight. So off axis thrust was another factor that contributed to the wild flight.

The rocket actually hung on until the spin rate exceeded 1200 deg/s about halfway through the upper-stage burn which puts most of the remaining propellant on one side of the case. Then the rocket pitched hard and instantaneously to 30 deg AoA. I’m surprised it did not shred. But it coasted to 94,000 ft, popped it’s drogue and landed on a main with no damage 1.5 miles away.

Luckily I got my upper stage back and that helped so much with the detective work this summer. A new upper stage fin can and case are now complete with major changes in terms of how they were made and inspected. And the goal is to fly again in November at FAR.

I learned a lot and it’s my guess that you @robopup can learn a ton from your flight given you recovered it. Good luck and I hope you fly it again soon!
 
@Kip_Daugirdas Thanks! Yes, still pretty dang excited about how much worked.

Interesting on the snap ring grove - that particular problem hadn't occurred to me, but I'll go back and double check. How are you measuring that precisely?

It's definitely a relief to have it recovered and to have to opportunity to review data - I lost projects the two years before this down there (one a definite failure, one likely a success).

Reading your Workbench thread, sounds like you're a skier? If you happen to find yourself in the PNW this winter and feel like spinning some laps and talking rockets let me know.

Good luck on your flight this fall!
 
Last edited:
robopup said:
Interesting on the snap ring grove - that particular problem hadn't occurred to me, but I'll go back and double check. How are you measuring that precisely?
Click to expand...
I use a line laser, v-block, and ruler mounted to the wall. Based on how high off the end the tube the laser is and the measured wobble as you spin the tube you can calculate the perpendicularity. I got this from Jim Jarvis and it’s how I square all my tubes. But now it’s how I check my cases that I have machined too.

The case from flight 2 is “banana-ed” about 12” from the nozzle end. And has a 4mm wobble at ~27”. That is atrocious and translates to the nozzle end being approximately .020” out of square.

The new case is dead on at the nozzle end. No wobble. Below is the booster case getting checked prior to machining a couple yrs ago.

And @robopup yes I love skiing! Likewise if you’re ever in Utah. So many options just 30 minutes from my house!
IMG_0577.jpeg
 
@Kip_Daugirdas I've squared tubes that way but hadn't done casings before, makes sense. Copy that on Utah!

Speaking of squaring (but not measuring) tubes, I meant to post these here a while ago. A buddy turned me on to these things - I think he got the idea from an article in Sport Rocketry. They're... amazing.

IMG_7652.jpg

IMG_7653.jpg

IMG_7654.jpg

IMG_7655.jpg
 
Last edited:
robopup said:
@Kip_Daugirdas I've squared tubes that way but hadn't done casings before, makes sense. Copy that on Utah!

Speaking of squaring (but not measuring) tubes, I meant to post these here a while ago. A buddy turned me on to these things - I think he got the idea from an article in Sport Rocketry. They're... amazing.

View attachment 606380

View attachment 606379

View attachment 606378

View attachment 606382
Click to expand...
I don't know what I'm looking at, but I'm interested ! Do you have more details you can share ?
 

Similar threads

Rocketman_dan
Agena I High Performance Two Stage Pathfinder
Replies
1
Views
360
waltr
W
J
Balls 31 two-stage to 50K attempt
Replies
4
Views
1K
kjhambrick
K
Buckeye
Determining motor ejection delay in booster?
Replies
16
Views
1K
kjhambrick
K
morgandemarigny
building LOC Terrier/IRIS as a two stage dual deploy
Replies
1
Views
410
Titan II
Titan II
S
Airstarts + dual-deploy with single altimeter?
Replies
13
Views
1K
Spurkey
S

Latest posts

Back
Top