Flight 1 Summary:
I'm not going to get through all the analysis I want to do in a reasonable amount of time, so I figured I'd at least get some data up.
I spent Monday - Sunday on the playa, for both ARLISS and XPRS. ARLISS is amazing - Becky, John, Tony and all the other volunteers don't mess around; it's a great crowd. Flying dozens of nearly identical rockets, prepped in similar ways and seeing the different flight results (most successful, but a few failures) was interesting, and also a foreshadow of what was to come for me.
I also appreciated having the extra time to get my tower dialed and do final button up on the rockets - because of work, in past years I was traveling, then rushing onto the playa Thursday afternoon for a Friday morning flight and it always felt like I couldn't quite catch my breath. I think the slower pace really helped make for cleaner, accurate final prep.
The weather for the full week was also unbelievably good. No wind (Windy was forecasting something like < 15knts at 50k the days I flew), good temps and a new moon which led to some killer starlink and ISS passes.
Flight 1 ('A' airframe):
After a couple friends got their big two stagers off, I was in the tower late morning on Friday.This flight was a little bit of a CF - I had two separate failures:
- My booster came in hot. No charges fired and my suspicion is that one of the power wires solder directly to the altimeter (didn't have the height for terminal blocks) broke. One of the wires was very thin stranded and was kinda weak, the other was thicker solid, both of which I'd had trouble with previously. On flight two, I potted everything in silicone just in case. While the rocket gods didn't exactly smile on me, it sure felt like it when I drove up on the crater on my way back from retrieving the second stage - I'd spent a couple days at each of the previous XPRS events driving grids without success. My uncle and I got it all dug out (using his patented post hole technique), and I found most of the altimeter so we'll see what else I can learn here...
- My second stage motor cato'd shortly after ignition. The aft snap ring grove failed, the propellant and nozzle were dumped and the rest of the rocket continued to apogee at 24.5k and successful recovery. Due to the cato, I'm having some trouble getting the full data set off my altimeters but I think there's still a chance. My suspicions at this point are that it's one or more of:
- Long (for me anyway) motor, likely errosive burning which I'd also seen in tests, tight cores and nozzle, not a lot of margin
- aggressive igniter (one full pyrodex pellet + ematch with ~.25g magnalite in a 3/8 x 23.5in core) - this had worked successfully twice, but potentially not this time.
- grain cracking due to acceleration - I've figured my group has been curing propellant too hard for a long time, but we've also had a lot of success with the version of OS we used so why change it? Maybe this is why...
- burn rate changes due to acceleration - I don't know much about this at this point, only that burn rates seem to go up.
It's too bad the second stage motor let go on this flight - the booster burn was much straighter than 'B's, and I had made some minor tweaks on how I made the 2nd stage fincan - I believe the fins on this one were on straight (and it's recovered so I'll be able to double check).
Flight 2 ('B' airframe):
My first reaction after 'A's failure was to bail on the second flight. After some long talks with the DAWG Pack, Becky and some final convincing by Tony (much appreciated), I was prepped and in the tower again Saturday morning.
Other than some hard coning, previously discussed, and a torn seam on my 2nd stage main, this one worked. Some altitude/velocity/acceleration data:
A few comments on this:
- I'm still looking into what exactly happened at ~28 s; a few seconds after second stage burnout. You can also see in the video that something... significant happened which put a big aoa of the rocket
- Not surprising, but the speed on descent from apogee to about 10,000 m is fast, not a lot of air up there
- You can see at lower altitudes that there is a fair amount of change in descent speeds. From the video, this is the rocket transitioning between the fincan tumbling/spinning, about 90deg from the flight path and it becoming ballistic, dragging the nosecone behind it. Unfortunately, it was in the later state when my main fired which tore a seam. I'd used a very small streamer (sorta the shape of a nomex pad), because I was concerned about the descent rate from my June test flight. Lotsa work to do on drogue descents I'm realizing...
- Looks like instant on of the second stage again which I'm really happy about. Instant on, or at least repeatable time-delay-on makes altimeter programming so much easier
Spinning and conning - I posted the video here already. Just adding the rotation data. The rocket spends 20 seconds pegging my 2000deg/s sensor, lovely... Like the acceleration plot and video, this plot also shows something intense happened at ~27 s, about 5 s after second stage burnout.
Because I had altimeters in the nosecone with vent holes that were still in the curvy part, as well as an altimeter with vent holes several inches behind the shoulder of the NC, I figured I'd make this plot comparing baro pressures. No major surprises - you can see that the pressure in the NC becomes increasing higher the faster the rocket goes, and also some difference as the rocket passes through mach 1.
It's not in the same ballpark as some of the flights on the forums, but the Interlux boat paint and G10 fin leading edges held up well. The rocket spent 36 seconds > M1 (including the brief dip below mach 1 before staging) and 10 seconds > M2. Max was mach 2.8. Albeit this was at altitude so much less intense than
these crazy cats.
One spot on the fillet where it looks like the primer melted (and maybe a clue to something else going on like crooked fin or flutter...?). All others are pretty clean.
This is the one leading edge with a little noticeable damage of the fin material - the rest just have small paint bubbles like towards the tip on this one.
The nosecone just has some minor bubbling. Much improved from the BBQ paint I used to use (shown here flown on a K250 to ~M2.1:
I did not get drag separation, it occurred 3 seconds after booster burnout at the programmed separation charge firing. Speed was M1.4. The charge was passed through a small hole in the side of the ISC 54mm tubing, sealed with rope caulk. You can see what a terrible job I did sealing things from the pressure plot below - nothing a good kalman filter can't handle though! Booster continued on it's way to apogee at 19k ft.