2-stage J total impulse record attempt

[Adrian A]

I’m getting ready to fly another 2-stage 38mm record attempt tomorrow. This one is using my heavier sustainer since the lightweight nosecone I made for BALLS last year is in need of repair, and I’m probably going to be maxing out the waiver as it is.

The motors are an AT I600 for the boost and then a CTI J94 sustainer. It sims to about 30,000. I have been gathering/repairing/making/prepping for all of the last 2 days and now I have had successful ground tests on my second try. Posting here for future reference on the charge sizing.

First the apogee charge of 0.34g in my nosecone ejector:

Then 0.34g in a plugged cardboard tube for the main ejection:

I’m reducing the main chute charge to 0.30 grams and keeping the nosecone at 0.34
(I’ll edit these later since the videos don’t seem to be loading from my phone)

 

[pugachu]

Good luck, Adrian!

 

[JEtgen]

Second that good luck! I'm sure you will, but take some pre and post-flight pics! Would love to see them.

 

[Adrian A]

George Barnes took this cool photo:



The Aerotech I600 is one of my very favorite motors.

 

[Adrian A]

The CTI J94, on the other hand, is not:



The above photo is looking at the aft end of the sustainer motor post-flight, with nozzle missing.

 

[Adrian A]

Like the Mellow Yellow J150 I was unable to ignite this time last year, the J94 also didn’t light, and blew off the nozzle and bottom grain instead.

So the sustainer only went to 9182 feet.

 

[Adrian A]

This year I threaded the Magnelite-augmented igniter from on the other side of the BP pellet. Maybe I used too much Magnelite?



Anyway, I'm giving up on Mellow Yellow for sustainers

 

[Adrian A]

Downloaded from the tracker recorded data:

 

[kjhambrick]

The CTI J94, on the other hand, is not:

<<snip pic>>

The above photo is looking at the aft end of the sustainer motor post-flight, with nozzle missing.

Ouch !

EDIT: Never mind ... answered in Post #10 ( case burned thru ) ... Were the case and / or the sustainer damaged ?

-- kjh

 

[Adrian A]

The Blue Raven data tells an interesting tale:


The I-600 had some kind of event about 0.8 seconds into the burn. Maybe it spat out a grain liner? There is a missing stage separation charge (more on that later) Ignition of the second stage was just after 2 seconds. The augmented igniter plus the BP pellet gave an initial higher thrust, but the motor survived that at first. But then about 1 second later, the aft closure blew off and all thrust was lost. Here is a zoom in of the sustainer burn:



You can see a little bit of thrust from the igniter and BP pellet and then suddenly a lot more thrust when the motor pressurized. After the flight, the bottom grain was missing or consumed; the other grains looked scorched but unlit.

Here's what the acceleration profile was expected to look like:


0.5 seconds into the sustainer burn, there should have been about 13.5 Gs, but there was about 6 instead. Each stage was weighed before the flight, and the first burn acceleration is as expected. I wonder if only the bottom grain lit and somehow that contributed to burning through the case at the back and failing the aft closure.

But the sudden burst of thrust right before the closure let go tells me that this was an over-pressurization, which is typically caused by a sudden increase in burn area from a crack or void in the grain.

 

[kjhambrick]

Very interesting data !

Does the Blue Raven in the booster show the same sort of event 0.8 sec into the I600R booster motor burn ?

Thanks for the report Adrian !

-- kjh

EDIT: Adrian said: I wonder if only the bottom grain lit and somehow that contributed to burning through the case at the back and failing the aft closure.

Was the motor overhang great enough to avoid damaging your sustainer airframe and fins ?

 

[Adrian A]

Very interesting data !

Does the Blue Raven in the booster show the same sort of event 0.8 sec into the I600R booster motor burn ?

Was the motor overhang great enough to avoid damaging your sustainer airframe and fins ?

Yeah, so what about the booster?

Welllll...

I think I'm good at designing rockets, and I'm pretty good at building them. But when it comes to flying them, I'm honestly terrible at it.

On Friday I spent all day prepping, ground testing the sustainer, prepping again, ground testing the sustainer again, and then prepping again for flight. So on Friday night I felt my skills are sharp, everything is fresh and I'm ready to go. I don't need to spend time on a launch checklist.

Friends, I needed to spend time on a launch checklist.

I pulled out the booster av-bay and turned on the tracker so it could get a lock before I put it back into the carbon fiber booster and its tiny fiberglass window.



I was dismayed that after I got the booster assembled, the GPS lock didn't come back. When I had tested my RF window to make sure it big enough, I did it with the newer Featherweight trackers that use the UBlox M10 receiver. And I had marginal signal strength with only a 3/4" diameter hole for it, but it was o.k. But when I assembled the booster this time I happened to use an older tracker of mine, with the M8 receiver, and it wasn't quite good enough to keep a lock through that small hole when I tried it yesterday morning. But I wasn't too worried, because the whole av-bay gets ejected at apogee, and since it already had a lock and downloaded ephemeris from satellites in view, it should be able to regain lock quickly. The wind was rising during the morning as forecasted, and I needed to go as soon as I could after the waiver opened. I installed the sustainer nozzle (which had been off for safety), Vic helped my stack everything inside the tower, and I used the app to verify that the sustainer deployments had good continuity, and then I armed the airstart with the screw switch, and saw those continuity voltages come in, and then I software-armed the airstart, made sure I still had good tracking on the sustainer, re-checked that I was getting LoRa signal but no GPS in the booster, and then walked away to get ready for the launch. What didn't I do? Turn on the booster's Blue Raven.

So with no GPS on the way up, and no deployments to eject the av-bay, I never found out where it went. I searched along the sustainer flight path, looking for a carbon fiber fence post, but I never saw it.

I resolve to never again try to fly a multistage rocket without carefully following a good launch-day checklist.

 

[robopup]

Like the Mellow Yellow J150 I was unable to ignite this time last year, the J94 also didn’t light, and blew off the nozzle and bottom grain instead.

So the sustainer only went to 9182 feet.

Bummer about the booster, and I can't imagine how frustrating that must be to not get those sustainers lit.

When I was doing my big project last year, I spent a day and 4-5 motors (1 full up 2nd stage motor, several other smaller 38's) static testing to dial in my ignition system. If these were commercial motors, it would have felt ridiculous and wasteful, but I also can't imagine consistently lighting second stages without that little exercise. EDIT: And I still didn't quite get it right on the first flight.

You'll get this!

 

[mperegrinefalcon]

Yeah, so what about the booster?

Welllll...

I think I'm good at designing rockets, and I'm pretty good at building them. But when it comes to flying them, I'm honestly terrible at it.

On Friday I spent all day prepping, ground testing the sustainer, prepping again, ground testing the sustainer again, and then prepping again for flight. So on Friday night I felt my skills are sharp, everything is fresh and I'm ready to go. I don't need to spend time on a launch checklist.

Friends, I needed to spend time on a launch checklist.

I pulled out the booster av-bay and turned on the tracker so it could get a lock before I put it back into the carbon fiber booster and its tiny fiberglass window.

View attachment 643936

I was dismayed that after I got the booster assembled, the GPS lock didn't come back. When I had tested my RF window to make sure it big enough, I did it with the newer Featherweight trackers that use the UBlox M10 receiver. And I had marginal signal strength with only a 3/4" diameter hole for it, but it was o.k. But when I assembled the booster this time I happened to use an older tracker of mine, with the M8 receiver, and it wasn't quite good enough to keep a lock through that small hole when I tried it yesterday morning. But I wasn't too worried, because the whole av-bay gets ejected at apogee, and since it already had a lock and downloaded ephemeris from satellites in view, it should be able to regain lock quickly. The wind was rising during the morning as forecasted, and I needed to go as soon as I could after the waiver opened. I installed the sustainer nozzle (which had been off for safety), Vic helped my stack everything inside the tower, and I used the app to verify that the sustainer deployments had good continuity, and then I armed the airstart with the screw switch, and saw those continuity voltages come in, and then I software-armed the airstart, made sure I still had good tracking on the sustainer, re-checked that I was getting LoRa signal but no GPS in the booster, and then walked away to get ready for the launch. What didn't I do? Turn on the booster's Blue Raven.

So with no GPS on the way up, and no deployments to eject the av-bay, I never found out where it went. I searched along the sustainer flight path, looking for a carbon fiber fence post, but I never saw it.

I resolve to never again try to fly a multistage rocket without carefully following a good launch-day checklist.

That really sucks Adrian. Sorry to hear that it didn't go well.

 

[kjhambrick]

Dang !

I feel your pain, @Adrian A !

I crashed more than my share of rockets in the olden days when I forgot to "Arm the AltAcc" because who needs a checklist for a simple dual deloyment rocket ( I do, that's who )

-- kjh

 

[pugachu]

Sorry it didn't go as planned, I have several long 'mellow yellow' 38mm and 54mm motors that I got for sustainer stages. I guess I should do some practice single stage flights first.

Better luck next time!

 

[Adrian A]

Bummer about the booster, and I can't imagine how frustrating that must be to not get those sustainers lit.

When I was doing my big project last year, I spent a day and 4-5 motors (1 full up 2nd stage motor, several other smaller 38's) static testing to dial in my ignition system. If these were commercial motors, it would have felt ridiculous and wasteful, but I also can't imagine consistently lighting second stages without that little exercise. EDIT: And I still didn't quite get it right on the first flight.

You'll get this!

Thanks. When I originally wrote the post you're responding to, I hadn't looked closely at the accelerometer data yet. Now I think I did get at least one of the grains lit, but then the motor just had a CATO 1 second into the burn in that snuffed out whatever was still on.

 

[robopup]

Thanks. When I originally wrote the post you're responding to, I hadn't looked closely at the accelerometer data yet. Now I think I did get at least one of the grains lit, but then the motor just had a CATO 1 second into the burn in that snuffed out whatever was still on.

Same comment from me if the ignition was too hard. I think I had the same failure mode as you on my sustainer motor on my first attempt last year - I knew from the static test and single stage data I was pushing things with the igniter. Backed off on the second attempt igniter and that one (happened...?) to work.

Sorry if I missed this somewhere above, but had this second stage propellant already flown as an upper stage?

 

[Adrian A]

Same comment from me if the ignition was too hard. I think I had the same failure mode as you on my sustainer motor on my first attempt last year - I knew from the static test and single stage data I was pushing things with the igniter. Backed off on the second attempt igniter and that one (happened...?) to work.

Sorry if I missed this somewhere above, but had this second stage propellant already flown as an upper stage?

This was the first flight for this particular motor. My previous similar attempt a year ago had a smaller booster and the J150 Mellow Yellow instead of this J94.

 

[pugachu]

Adrian, was the sustainer damaged from the motor burn thru? Did you need to turn down the plastic thrust ring to get it to fit into the booster? If not, I'm curious as to how you attached the two stages.

Sorry about the loss of the booster. Hopefully the sustainer cam be flown again

 

[Adrian A]

Adrian, was the sustainer damaged from the motor burn thru? Did you need to turn down the plastic thrust ring to get it to fit into the booster? If not, I'm curious as to how you attached the two stages.

Sorry about the loss of the booster. Hopefully the sustainer cam be flown again

The sustainer recovered without a scratch. I sand down the knurled part of the CTI aft closures so they can be the interstage coupler.

 

[Adrian A]

I'm getting ready to fly this again this weekend at NSL, maybe Sunday. I'm planning to fly a Loki J474 (great initial thrust for a lot of speed out of the tower) for the booster, and a CTI I470 for the sustainer. Not your classic long-burn sustainer, but they are available, it should light easier, and the total impulse came out right.

My most recent booster is still missing, so I repaired a carbon fiber booster I first made in about 2011.

I cut removed and replaced 2 cracked fins.



The fins have unidirectional carbon fiber reinforcing the fillets, like the original one did. It seems pretty symmetrical.

This afternoon I cut out the radio window so hopefully the GPS will keep reception in the tower this time. This was a pretty thick tube that I built as the 2nd stage of a 3-stage attempt, and I wanted it to be beefy so that the whole skinny rocket wouldn't flex much. Later reinforced it with another secondary layup, so it's quite thick and heavier than it needs to be. But it's reassuring to have more meat for the fiberglass window to grab onto.

I used a scrap 1.5" aluminum tube to provide support for drilling with the 3/4 hole saw. Then I used a dremel with a sanding wheel to enlarge the hole and taper the edges:

I covered the aluminum mandrel in flash tape and slid it back into the tube, then laid up the fiberglass window over the hole, with quite a few layers of medium-weight FG fabric, some cut out as ovals to match the hole, and some rectangles to go over everything. Then I wrapped peel ply over it and it's curing now.


Most of the work was in the innards, which I don't have photos of. I may take more photos during prep.

 

[2-0turbo]

Interesting idea on the RF window. Curious to see how that will work.

 

[Adrian A]

Interesting idea on the RF window. Curious to see how that will work.

This was the third carbon stage I have modified this way. Unfortunately I forgot the recipe yesterday and had my release tape facing the wrong way (should have been outward) and so I glued the rocket to my mandrel. I had to cut out the window and pry the rocket off of the mandrel and then pound it out and start over again. This time the hole was necessarily larger.

I cured it on my dashboard and had no problem this time with removing the mandrel or the release masking tape. I sanded it flush on my belt sander and then tested out the tracker. It works great looking through the window, almost as good as unobstructed. Yesterday’s mistake cost me about 2 hours today. I didn’t have time to go up to the site to set up my tower; I’ll go early tomorrow and try to catch a predicted brief window before the wind becomes excessive.