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- Dec 29, 2011
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So, some things worked well, some were improvements, and some things didn't work.
I have not grabbed any data from the boards yet. This is just a short report of what happened and what I observed, with not much in the way of analysis.
Turns out there was no long 1010 rail available at the time. John Derimiggio volunteered his tower for the launch with his long rail, but it is 1515 not 1010. He had a 1010 rail for it, but not on the field at that time. 1515 could work, but it is not a wise approach. There is some chance using 1010 on 1515 can cause the rocket to fall off. The RSO team nixed that! So I ended up on a short rail that only extended a couple feet past the upper rail guide. The nosecone was past the end of the rail. But conditions were pretty calm with occasional gusts due to thermal activity. The rocket has some mass, and a good expected thrust to weight ratio. So we all thought it should be ok.
I had been busy with the construction, and had not familiarized myself with the Featherweight Tracker, or the RunCam 2 4K video. So I got help from the rest of our local group with those items. The tracker is in the nosecone (important detail for later) so once the rocket was on the rail but horizontal, the tracker was turned on and the nosecone buttoned up and pinned on. The video was turned on and the rail raised to vertical. We had previously adjusted the rail for a very slight tilt into the winds at altitude.
My recollection of events has it that I turned on the video camera, but didn't start it recording. I hope I'm wrong about that! I'll know when I pull the video card and see what's there. This is where my lack of experience with the camera bit.
We basically manhandled the rail via the rocket. The rail guides stayed solidly in place, so the wet sanding prep work did its job. I can state from experience they would have popped off without that prep. Been there, done that.
The rest of the prep was done, the altimeters were happy, the doubled igniter (each ematch augmented with some BKNO3) was installed on a thin dowel to hold the igniters against the forward bulkhead. I THINK the igniters were against the forward bulkhead, but I didn't mark the dowel. Again, rookie error due to being brain fried. Being all the way at the top is a lot more important with this motor than with most AP motors. If the dowel was a half inch short that would negatively affect the startup. It was probably correct, but I don't have proof.
The nitrous tank valve was opened, and we were ready to start the flight tank fill procedure.
We all retreated to the remote location with the remote control box for the fill and dump solinoids. We had one of the range crew with us for communication with the RSO station. The RSO authorized starting the fill, and we commenced operations.
Temperature was somewhere in the upper 80's I think. This was warmer than during the static test, so I expected to boil off a little more nitrous for chilldown. The cryogenic pressure relief valve popped open sooner than had been the case during the static test, and more frequently. But then when the valve was closed, I thought I was hearing some high pressure gas hiss. We were a couple hundred or so yards away so it was hard to be sure.
I got a pause and went closer to investigate. There were three possibilities. (1) venting at the supply tank plumbing. That doesn't have to be an abort. (2) venting into the combustion chamber. That's an abort. (3) venting at the cryogenic pressure relief valve.
When I got closer I could confirm the high pressure hiss was coming from the area of the rocket and not the supply tank, and there was no visual evidence of haze from the nozzle region of the rocket. So I concluded it was (3). From the sound and the lack of a visible cloud, I thought I could fill the flight tank faster than the venting. I guesstimated I might lose 10% rough order of magnitude total impulse, but elected to continue with the launch. The valve was not a problem I could fix short of replacement and I didn't have a replacement. Nor could I get one in time for this launch.
I went back to the remote station and continued with the filling procedure. When the flight tank was near full and the temperature of the tank lowered, the jet of fog comming from the vent confirmed it was not fully closing when it was supposed to close. So it really was (3). I completed the fill and transferred control back to the RSO for countdown and launch.
There was approximately two seconds of cold flow out the nozzle before ignition occurred. This was better than in the static test, but even this beefed up preheater was not sufficient for instant-on. The loss of two seconds of oxidizer was worth about a third of the oxidizer supply, roughly, I estimate.
This may actually have been caused by the valve failure. Since the valve wouldn't close, the flight tank provided nitrous at a lower temperature than planned, due to the continuous visible boiloff. Lowering the temperature of nitrous has a disproportionate affect on the required ignition energy. The flight tank was definitely well below the dew point on Friday and it wasn't a humid day.
But it did light, producing a beautiful straight climb with visually approximately the expected acceleration. The motor was operating normally once it got going.
The burn was again super smooth, just as in the static test. It is rather loud for its size, but does not have the typical pressure oscillations of a hybrid. That aspect of the design, mostly due to the high turbulence fuel, appears to be working perfectly.
Of course with the boiloff and the delayed pressurization, the motor likely only produced about 2/3 the total expected impulse, if even that. But what it did, it did well.
We witnessed deployment at apogee, but it was too visible. And the tracker confirmed via descent rate that the main was out. For the main to go out, the tether must have failed. I've assigned no cause for that yet. It could have been mis-wiring, mis-configuring an altimeter, gas venting into the electronics bay causing a pressure spike and fooling an altimeter, or hardware failure of some sort. Cause TBD.
We observed the slow descent and slow drift to an off-field landing. We also had the GPS coords from the tracker. Since this is a freebag deployment, the nosecone was not expected to be with the rocket.
When we went to the GPS coordinates for the nosecone, and got permission from the farm owners to retrieve, we found the whole rocket. Turns out the tether bolt in its travel up and out of the upper tube, managed to snag and flip itself into a loose knot that stuck right under the tape I'd put on the kevlar main line to prevent chafing at the top of the tube!
Nosecone under drogue was expected to have similar descent rate as the rest of the rocket under main, so there was essentially no stress to pull out the loose knot. This was a fortuitous occurance!
That concludes the quick look report. I'll take pics and post analysis over the next few days.
I have not grabbed any data from the boards yet. This is just a short report of what happened and what I observed, with not much in the way of analysis.
Turns out there was no long 1010 rail available at the time. John Derimiggio volunteered his tower for the launch with his long rail, but it is 1515 not 1010. He had a 1010 rail for it, but not on the field at that time. 1515 could work, but it is not a wise approach. There is some chance using 1010 on 1515 can cause the rocket to fall off. The RSO team nixed that! So I ended up on a short rail that only extended a couple feet past the upper rail guide. The nosecone was past the end of the rail. But conditions were pretty calm with occasional gusts due to thermal activity. The rocket has some mass, and a good expected thrust to weight ratio. So we all thought it should be ok.
I had been busy with the construction, and had not familiarized myself with the Featherweight Tracker, or the RunCam 2 4K video. So I got help from the rest of our local group with those items. The tracker is in the nosecone (important detail for later) so once the rocket was on the rail but horizontal, the tracker was turned on and the nosecone buttoned up and pinned on. The video was turned on and the rail raised to vertical. We had previously adjusted the rail for a very slight tilt into the winds at altitude.
My recollection of events has it that I turned on the video camera, but didn't start it recording. I hope I'm wrong about that! I'll know when I pull the video card and see what's there. This is where my lack of experience with the camera bit.
We basically manhandled the rail via the rocket. The rail guides stayed solidly in place, so the wet sanding prep work did its job. I can state from experience they would have popped off without that prep. Been there, done that.
The rest of the prep was done, the altimeters were happy, the doubled igniter (each ematch augmented with some BKNO3) was installed on a thin dowel to hold the igniters against the forward bulkhead. I THINK the igniters were against the forward bulkhead, but I didn't mark the dowel. Again, rookie error due to being brain fried. Being all the way at the top is a lot more important with this motor than with most AP motors. If the dowel was a half inch short that would negatively affect the startup. It was probably correct, but I don't have proof.
The nitrous tank valve was opened, and we were ready to start the flight tank fill procedure.
We all retreated to the remote location with the remote control box for the fill and dump solinoids. We had one of the range crew with us for communication with the RSO station. The RSO authorized starting the fill, and we commenced operations.
Temperature was somewhere in the upper 80's I think. This was warmer than during the static test, so I expected to boil off a little more nitrous for chilldown. The cryogenic pressure relief valve popped open sooner than had been the case during the static test, and more frequently. But then when the valve was closed, I thought I was hearing some high pressure gas hiss. We were a couple hundred or so yards away so it was hard to be sure.
I got a pause and went closer to investigate. There were three possibilities. (1) venting at the supply tank plumbing. That doesn't have to be an abort. (2) venting into the combustion chamber. That's an abort. (3) venting at the cryogenic pressure relief valve.
When I got closer I could confirm the high pressure hiss was coming from the area of the rocket and not the supply tank, and there was no visual evidence of haze from the nozzle region of the rocket. So I concluded it was (3). From the sound and the lack of a visible cloud, I thought I could fill the flight tank faster than the venting. I guesstimated I might lose 10% rough order of magnitude total impulse, but elected to continue with the launch. The valve was not a problem I could fix short of replacement and I didn't have a replacement. Nor could I get one in time for this launch.
I went back to the remote station and continued with the filling procedure. When the flight tank was near full and the temperature of the tank lowered, the jet of fog comming from the vent confirmed it was not fully closing when it was supposed to close. So it really was (3). I completed the fill and transferred control back to the RSO for countdown and launch.
There was approximately two seconds of cold flow out the nozzle before ignition occurred. This was better than in the static test, but even this beefed up preheater was not sufficient for instant-on. The loss of two seconds of oxidizer was worth about a third of the oxidizer supply, roughly, I estimate.
This may actually have been caused by the valve failure. Since the valve wouldn't close, the flight tank provided nitrous at a lower temperature than planned, due to the continuous visible boiloff. Lowering the temperature of nitrous has a disproportionate affect on the required ignition energy. The flight tank was definitely well below the dew point on Friday and it wasn't a humid day.
But it did light, producing a beautiful straight climb with visually approximately the expected acceleration. The motor was operating normally once it got going.
The burn was again super smooth, just as in the static test. It is rather loud for its size, but does not have the typical pressure oscillations of a hybrid. That aspect of the design, mostly due to the high turbulence fuel, appears to be working perfectly.
Of course with the boiloff and the delayed pressurization, the motor likely only produced about 2/3 the total expected impulse, if even that. But what it did, it did well.
We witnessed deployment at apogee, but it was too visible. And the tracker confirmed via descent rate that the main was out. For the main to go out, the tether must have failed. I've assigned no cause for that yet. It could have been mis-wiring, mis-configuring an altimeter, gas venting into the electronics bay causing a pressure spike and fooling an altimeter, or hardware failure of some sort. Cause TBD.
We observed the slow descent and slow drift to an off-field landing. We also had the GPS coords from the tracker. Since this is a freebag deployment, the nosecone was not expected to be with the rocket.
When we went to the GPS coordinates for the nosecone, and got permission from the farm owners to retrieve, we found the whole rocket. Turns out the tether bolt in its travel up and out of the upper tube, managed to snag and flip itself into a loose knot that stuck right under the tape I'd put on the kevlar main line to prevent chafing at the top of the tube!
Nosecone under drogue was expected to have similar descent rate as the rest of the rocket under main, so there was essentially no stress to pull out the loose knot. This was a fortuitous occurance!
That concludes the quick look report. I'll take pics and post analysis over the next few days.