So, maybe I'll try a three-stager

[boatgeek]

I believe you're right, but more than 4 is not going to happen on this flight. At least it's 4 and not 3. Pretty hefty altitude penalty to go to 6.

Anyway, the guy that's making the motors, who isn't really involved, has an interesting way of assembling the motors. Basically no casting tubes. I asked him how it works and he offered an explanation, to which I said "huh?". Second explanation... "huh?". Finally, I said just draw me a picture, and keep it simple. He did that, and I get it!

Jim

Nothing like a drawing in crayon to make you feel judged!

Though it's not as bad as getting markups on a drawing back in red sharpie. That one hurt.

 

[tfish]

I believe you're right, but more than 4 is not going to happen on this flight. At least it's 4 and not 3. Pretty hefty altitude penalty to go to 6.

Anyway, the guy that's making the motors, who isn't really involved, has an interesting way of assembling the motors. Basically no casting tubes. I asked him how it works and he offered an explanation, to which I said "huh?". Second explanation... "huh?". Finally, I said just draw me a picture, and keep it simple. He did that, and I get it!

Jim

Looks like the same guy that came up with my checlist!



Tony

 

[OverTheTop]

Though it's not as bad as getting markups on a drawing back in red sharpie. That one hurt.

Nah. I'm used to that. In the railways we had scale plans that were up to 30' long. A color system was used that worked really well, and I still use to this day. Anything to be added to the drawing is written/drawn in red. Anything colored yellow is deleted. Anything ticked or highlighted blue has been checked. There were also other colors used when staging works were needed (orange or green highlights). At a glance you could see where the changes were and what had to be done.

 

[boatgeek]

Nah. I'm used to that. In the railways we had scale plans that were up to 30' long. A color system was used that worked really well, and I still use to this day. Anything to be added to the drawing is written/drawn in red. Anything colored yellow is deleted. Anything ticked or highlighted blue has been checked. There were also other colors used when staging works were needed (orange or green highlights). At a glance you could see where the changes were and what had to be done.

Red pen, no problem. When they bust out the wide markers, someone's frustrated.

 

[JimJarvis50]

Well, it turns out that John's crayon drawing was spot on! We were unable to fly our Q to O two-stager at Balls, but we were able to fly it at UR NUTS (also at BlackRock, but a few weeks after Balls). The Q motor performed very well, but unfortunately, the sustainer motor didn't come up to pressure even though the igniter fired. Crap! But, we had fun and we flew a big rocket on a big motor, and we still have an O motor to play with.

I put together a video just to document the flight and show some of the video we had. "Kate" controlled the entire flight, and her commentary is included.

Jim

 

[bad_idea]

Was sorry to read of this recently, Jim, and sorry again to see it (though grateful for the upload). That is some hard luck.

Six months now I've been back into rocketry, and composite sustainer ignition seems to me to be the toughest nut to crack in the whole hobby. I've seen more fail than succeed, even for extremely experienced flyers like yourself, and the credits list in your video is a veritable Who's Who and has to catalog a century or more of high altitude flight experience. (Rather daunting given I have hopes of staging composites within the next year.)

Was the data collected from the flight any help to pinpoint the source of the ignition problem?

 

[JimJarvis50]

Was sorry to read of this recently, Jim, and sorry again to see it (though grateful for the upload). That is some hard luck.

Six months now I've been back into rocketry, and composite sustainer ignition seems to me to be the toughest nut to crack in the whole hobby. I've seen more fail than succeed, even for extremely experienced flyers like yourself, and the credits list in your video is a veritable Who's Who and has to catalog a century or more of high altitude flight experience. (Rather daunting given I have hopes of staging composites within the next year.)

Was the data collected from the flight any help to pinpoint the source of the ignition problem?

Well, the amount of "fire" to use to light a sustainer is a bit of a guess at best. We tried to take a little of the guess out of it by using a burst disk in the sustainer motor. However, the combination of the burst disk pressure and the quantity of BKNO3 pellets used was not enough to get the job done. We have a little more homework to do before the next try.

Jim

 

[OverTheTop]

Have you thought about using the grain of a smaller motor in the top of the large motor? Light the small motor first . I have used this successfully.

 

[JimJarvis50]

Yes, I have thought of that (or was advised of that). The application where I have considered this is to use a 38mm white thunder grain in the smoke well of a CTI motor. It's a perfect fit as it turns out. This was suggested by someone who knows quite a bit about CTI propellant and hardware. White Thunder is pretty easy to light, and I can visualize it providing an extended period of heat/fire.

Jim

 

[Joshua Smith]

Have you thought about using the grain of a smaller motor in the top of the large motor? Light the small motor first . I have used this successfully.

Only tangentially related, but has anyone ever lit an APCP with a black powder motor? I'm not looking for a blueprint or anything, just curious if it's been done or tried

 

[3stoogesrocketry]

Only tangentially related, but has anyone ever lit an APCP with a black powder motor? I'm not looking for a blueprint or anything, just curious if it's been done or tried

Yes . Bruce Lee launched his Bomb Pop rocket on 2 M1315's , using C6 motors as initiators .

 

[jsdemar]

Well, the amount of "fire" to use to light a sustainer is a bit of a guess at best. We tried to take a little of the guess out of it by using a burst disk in the sustainer motor. However, the combination of the burst disk pressure and the quantity of BKNO3 pellets used was not enough to get the job done. We have a little more homework to do before the next try.

It looked good on paper. Maybe I should have done the igniter calcs in crayon. ;-)

We'll follow up with some more tests and report back to everyone. The amount of BKNO3 pellets followed the calculations I've used on many successful ignitions (including this flight's Q booster). Two differences, though, were the burst disk and the head-end igniter basket.

I did minimal ground testing for the burst disk sizing. The requirement for the disk is to maintain the igniter pressure while the motor transitions to self combustion. The motor's critical pressure should burst the disk, not the pressure from the igniter. The risk is that the igniter pops the disk and the motor chuffs. I believe that's what happened on our URNUTS sustainer.

The head-end igniter calculations also assume there's a basket or pouch about 3/4ths the diameter of the propellant core. We re-used the same steel screen basket design from the 2019 flight (which worked then). But the core was 1.75" diameter in the previous sustainer and only 1.2" diameter in the latest sustainer. It was a tight fit, not allowing the flame and heat to spread. My guess is that the containment forced most of the heat down the core and popped the disk too early. (Slaps forehead!)

Many good things came from the project, though. It was the fourth burn on the same full P/small Q bolted 6" hardware (made by Jim Long). Is that a record? It was also the first test of my new propellant binder and process which allowed me to make 120 lbs of propellant alone, with 2 hours of pot life, 99% theoretical density (0.065 lb/in^3), and a delivered Isp of about 220.

And, most important, we all had fun!

 

[FredA]

John -- I would guess the smaller core volume caused the igniter to achieve a higher pressure and pop the burst disc.
Where are you sourcing your burst discs?

 

[manixFan]

…<snipped for brevity >… It was also the first test of my new propellant binder and process which allowed me to make 120 lbs of propellant alone, with 2 hours of pot life, 99% theoretical density (0.065 lb/in^3), and a delivered Isp of about 220.

And, most important, we all had fun!

Wow, that’s very impressive! I’ve seen your other posts on mixing, but that sure sounds like it warrants a good write up on its own.

Hint Hint.


Tony

 

[jsdemar]

John -- I would guess the smaller core volume caused the igniter to achieve a higher pressure and pop the burst disc.
Where are you sourcing your burst discs?

The igniter mass calculation was done using the new smaller core. So, not over-sized for the burst disk.

I make the disks out of polystyrene sheet of different gauges. Either captured above the convergent section of the nozzle, or captured between the nozzle and nozzle washer on snap-ring cases.

 

[RGClark]

Well, it turns out that John's crayon drawing was spot on! We were unable to fly our Q to O two-stager at Balls, but we were able to fly it at UR NUTS (also at BlackRock, but a few weeks after Balls). The Q motor performed very well, but unfortunately, the sustainer motor didn't come up to pressure even though the igniter fired. Crap! But, we had fun and we flew a big rocket on a big motor, and we still have an O motor to play with.

I put together a video just to document the flight and show some of the video we had. "Kate" controlled the entire flight, and her commentary is included.

Jim

Thanks for the update. Getting the upper stage to maintain stable burn at high altitude seems to be a common problem. (Irony: its called the “sustainer”, but it’s difficult to get it to sustain stable burn.) One cause is the low pressure at high altitude. A solution would be for the ignition of the upper stage engine take place in a pressurized tube. This is what happened with the Stanford University launch described here:

https://www.rocketryforum.com/threa...rbital-space-shot.145647/page-18#post-1959109
Their purpose in doing this was not to get high altitude stable burn (in fact the ignition altitude was not particularly high) but to get a stable launch platform. But it occurs to me this could also work to get reliable burning at high altitude, low ambient pressure.

I was thinking about this as a separate tube around the base of the upper stage. But if occurs if the lower stage stays attached for a short-time after upper stage ignition to allow pressure to build up, and then is jettisoned, this might allow stable burn for the upper stage to take place.

Robert Clark

 

[Joshua Smith]

Thanks for the update. Getting the upper stage to maintain stable burn at high altitude seems to be a common problem. (Irony: its called the “sustainer”, but it’s difficult to get it to sustain stable burn.) One cause is the low pressure at high altitude. A solution would be for the ignition of the upper stage engine take place in a pressurized tube. This is what happened with the Stanford University launch described here:

https://www.rocketryforum.com/threa...rbital-space-shot.145647/page-18#post-1959109
Their purpose in doing this was not to get high altitude stable burn (in fact the ignition altitude was not particularly high) but to get a stable launch platform. But it occurs to me this could also work to get reliable burning at high altitude, low ambient pressure.

I was thinking about this as a separate tube around the base of the upper stage. But if occurs if the lower stage stays attached for a short-time after upper stage ignition to allow pressure to build up, and then is jettisoned, this might allow stable burn for the upper stage to take place.

Robert Clark

In place of the burst disc I assume?

 

[Charles_McG]

Has anyone tried flooding the core volume of the motor with O2(g) before sealing with a burst disk? The O2 partial pressure would be about 5x higher than air at any given pressure.

 

[Joshua Smith]

Has anyone tried flooding the core volume of the motor with O2(g) before sealing with a burst disk? The O2 partial pressure would be about 5x higher than air at any given pressure.

wouldn't that be...more than a little dangerous?
I would just like to add that I love cider

 

[Charles_McG]

I don't know. It would be a fixed, limited volume of oxygen at launch pad atmospheric pressure - at most. There's a lot more oxidizing potential in the grain - but you've got to get it up to temperature and pressure.

 

[JimJarvis50]

I was thinking about this as a separate tube around the base of the upper stage. But if occurs if the lower stage stays attached for a short-time after upper stage ignition to allow pressure to build up, and then is jettisoned, this might allow stable burn for the upper stage to take place.

Robert Clark

It would be interesting to go through a calculation of how the pressure would change if the stages stayed connected but began to separate as the motor came up to pressure. I've never done it (I think it would be fairly complicated). I've seen what happens when the stage are not allowed to separate (it's not pretty), so I generally try to avoid constraining the outlet of the motor. We just need a properly sized burst disk and igniter.

Jim

 

[TheAviator]

Has anyone tried flooding the core volume of the motor with O2(g) before sealing with a burst disk? The O2 partial pressure would be about 5x higher than air at any given pressure.

O2 isn't the answer, both propellant and igniter contain all the oxygen they need. Low ambient pressure is the problem. The low pressure means that burning rate (and thus the rate of gas produced) is very low and that it's easy for the gas to exit the nozzle more quickly than it's produced, thus snuffing the motor.

 

[Ronz Rocketz]

Well, it turns out that John's crayon drawing was spot on! We were unable to fly our Q to O two-stager at Balls, but we were able to fly it at UR NUTS (also at BlackRock, but a few weeks after Balls). The Q motor performed very well, but unfortunately, the sustainer motor didn't come up to pressure even though the igniter fired. Crap! But, we had fun and we flew a big rocket on a big motor, and we still have an O motor to play with.

I put together a video just to document the flight and show some of the video we had. "Kate" controlled the entire flight, and her commentary is included.

Jim

Still one of the best HPR videos I've seen (despite the lowish altitude and wrong date). Thankfully no Burning Man staff around to drop the rocket on...

 

[JimJarvis50]

Still one of the best HPR videos I've seen (despite the lowish altitude and wrong date). Thankfully no Burning Man staff around to drop the rocket on...

Thanks! Unfortunatly, the way the camera is mounted, I don't have access to the buttons that would correct the time. Sigh....

Jim

 

[RGClark]

Well, the amount of "fire" to use to light a sustainer is a bit of a guess at best. We tried to take a little of the guess out of it by using a burst disk in the sustainer motor. However, the combination of the burst disk pressure and the quantity of BKNO3 pellets used was not enough to get the job done. We have a little more homework to do before the next try.

Jim

Weren’t you able to get stable high altitude burn with your ThreeCarbYen flight to 175,000ft?



Robert Clark

 

[JimJarvis50]

Weren’t you able to get stable high altitude burn with your ThreeCarbYen flight to 175,000ft?

Yes, the third stage motor lit at around 45K. It just used a generous amount of pyrogen. The problem with this approach is that it is unpredictable. It depends on the burning fuel to pressurize the motor and that can take a while. I've had motors take up to 6 seconds to light. Ideally, a burst disk would be instant on.

Jim

 

[RGClark]

In place of the burst disc I assume?

Getting the right sized burst disk appears to be the problem. Is this something that can be tested on the ground in a vacuum chamber?

Robert Clark

 

[Steve Shannon]

Yes, the third stage motor lit at around 45K. It just used a generous amount of pyrogen. The problem with this approach is that it is unpredictable. It depends on the burning fuel to pressurize the motor and that can take a while. I've had motors take up to 6 seconds to light. Ideally, a burst disk would be instant on.

Jim

What about casting a burst disk into the uppermost grain or gluing it between the top and second grain so there’s a much smaller volume to pressurize rather than the full volume of the motor? Maybe even a couple burst disks to pressurize a second larger volume after the first disk bursts?

 

[jsdemar]

What about casting a burst disk into the uppermost grain or gluing it between the top and second grain so there’s a much smaller volume to pressurize rather than the full volume of the motor? Maybe even a couple burst disks to pressurize a second larger volume after the first disk bursts?

Containing a small volume with a burst disk at the head of the motor would cause a chuff. Especially at altitude, the sudden change in pressure upon bursting would likely drop the pressure and heat flux below the critical point.

 

[Steve Shannon]

Containing a small volume with a burst disk at the head of the motor would cause a chuff. Especially at altitude, the sudden change in pressure upon bursting would likely drop the pressure and heat flux below the critical point.

Okay, that makes sense. Is there a way to prevent such a sudden change in pressure, such as perhaps a thermoplastic restrictor in the nozzle that burns out over the same time period the motor comes up to pressure?