Skylark sounding rocket (pt. 2) HPR

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wrad

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I already have a skylark sounding rocket / build thread that I have been flying for a few years now relatively successfully. (https://www.rocketryforum.com/threads/skylark-sounding-rocket.145395/) and a couple of months ago I promised a part 2, HPR upscale version, as although I greatly enjoy flying the MPR version, and intend to continue to do so, its small scale has made it a real challenge to prep/fly. So I wanted to build an upscale version, that would fly comfortably on HPR motors, and be a bit easier to prep.

Another big factor was wanting to push my skill level up a bit further and this was the obvious next step.
Finally 2 stage HPR flights are extremely rare here in the UK, I have personally only seen one in the last 5 or so years. So thought it was about time they were flown more regularly, and had the motivation of this years Midland sky launch event (my big launch of the year) being in only a few months, and nothing new to fly to get it done.

So here is the thread, its gonna be a bit in retrospect as I was in such a rush to get this done in time, reporting on it took a back seat.
Spoiler alert! the launch was last weekend, and boy did she fly great.
Lots of build photos, 3D models, renders, launch photos/videos and data to come soon.
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waltr

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Looking forward to the build and launch info.

I built a Skylark with 24mm BT and 18mm motor. Made it single stage but with the finless Goldfinch booster. Always flew great and even had Dual deploy ebay. Last flight had a Quest motor noozle fail and it went horizontal at about 200 feet up into the woods. Never found it.
Been thinking of a slight up scale, maybe a 38mm BT and still single stage.
 

wrad

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Ah thats a shame to loose it like that! my mid power skylark is 32mm tubes and 24mm motor mounts, but I used clear fins on the goldfinch after the first flight which was unstable. With the forward fin position and higher thrust motors, even with it siming relatively stable it just didnt seem to have enough control authority to fly straight. Nose weight would have helped but i didnt have room to add any with that build.
 

wrad

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Ok, to start with I directly scaled my smaller skylarks open rocket file to 65mm tubes. This gave me as pretty good idea of the performance expected, roughly what motors it could fly on and size of materials/layout.

As with all my builds I took the opportunity to jump right into making a 3D model, this time of the complete model from the ground up (previously I modeled the scale rocket, then cut pieces out to modify into 3D prints). The model then contains all the parts to print as well as providing all of the measurements etc for the build.

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wrad

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Jumping straight into the build. The boosters construction is pretty straight forward, 3 fins through wall mounted. The centering rings were printed, including fin slots, so it all clips together straight. The motor mount overhangs the back and has a slimline snap ring retainer, hidden within a small printed piece to make it look more like a nozzle.

The interstage and av bay was pretty complex however, with a 3D printed skin to look like the real thing, and internal av bay for an egg-timer apogee made from 54mm coupler and 2 bulkheads (the forward bulkhead is also the sled for the apogee).
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wrad

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For the sustainer (the skylark itself) the fincan was built as a zipperless design, built as a self contained unit, with the drogue separation point just above the fins. This was built much the same as the booster with printed centering rings, however also including the wiring passthrough tunnels, also printed into the centering rings. The only quirk with this was i slotted the body tube in the opposite direction to "normal" so that it slid up over the motor mount rather than down, this was to keep the interstage section solid. This meant I had to fill the slots above the fins to make them flush.
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I didnt get many good pics of its build but here are a couple with the body tube off then on, and the finished by the booster.
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waltr

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Wow, that looks great.
Love the details you did with the 3D printing.

My Skylark was stable due to the weight of the ebay.
 

wrad

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The nosecone was printed with a large threaded compartment in the shoulder to take an egg-finder mini. The cone was wrapped in aluminium tape to finish it and looks great but i realised i had turned the whole thing into a faraday cage, so i printed an extension to move the egg-finder fully into the shoulder. The egg-finder sled is again printed and screws directly onto the back of the eye bolt used as a shock cord mount.
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RocketScientistAustralia

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The nosecone was printed with a large threaded compartment in the shoulder to take an egg-finder mini. The cone was wrapped in aluminium tape to finish it and looks great but i realised i had turned the whole thing into a faraday cage, so i printed an extension to move the egg-finder fully into the shoulder. The egg-finder sled is again printed and screws directly onto the back of the eye bolt used as a shock cord mount.
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Beautiful example of the power of 3D printing. Watch out for the metalised nose cone reducing signal strength for anything in there. Both for Tx and Rx. Foil, carbon fibre or even metallic paint can significantly reduce transmission/ reception.
 

wrad

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Beautiful example of the power of 3D printing. Watch out for the metalised nose cone reducing signal strength for anything in there. Both for Tx and Rx. Foil, carbon fibre or even metallic paint can significantly reduce transmission/ reception.
Im not sure how you build rockets without a printer to be honest! Yes, im expecting a complete blind spot directly in front of the antenna , and generally reduced signal strength/ range. On launch day it maintained a good gps lock and the ground station continuously received packets throughout the launch and recovery, so for my purposes, where I am generally using it to help receiving from tall crops where I already had a rough line of sight on it I am more than happy with the performance. I wouldnt trust it so much if it was going a lot higher/out of sight.
 

wrad

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I also have a working theory that any rocket with GPS tracking will recover easily within direct sight of the launch pad, guarantied. Im yet to be proven wrong with my admittedly small data set.
 

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The main av-bay was a pretty simple build, with a fairly standard setup of 2 threaded rods holding the two bulkheads together along with the sled. Flight computer wise i build the sled to hold a quantum for the staging events and a quark for dual deployment. 2 300 mAh batteries and 2 micro switches in a 3d printed pull pin housing that puts both altimeters on 1 pull pin. this was all designed to take the flight computers as they are set up for my small skylark so i can swap the computers between them in seconds if i so wished.

I used jst connectors for all of the connectors, as well as for the break point in the staging wiring. The 2 connectors for the separation charge and second stage ignition had their female housing trimmed down so they disconnect without too much force, but still have a nice positive connection. For the staging wiring all the connectors were colour coded, or had reversed connectors so as to make connecting up the wires quick and simple on the day, without having to double check every wire was connected to the right point.
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The final part of the build was just the 2 body tubes, which i dont rely have anything more to say about, they are tubes.

Finally the fin can got some beautiful decals to finish it of thanks to Wizard rocketry for sorting these out on super short notice!
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The decals were literally the last thing to go on the rocket before flight (30 mins before), with everything else, motors and all prepped. Im never putting decals on at the launch site again though, they were tiny and a right fiddle!
 

wrad

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I got the build done with just enough time to test all 4 of the pyro events (separation, drogue, main, booster main) and get them dialled in before flight. (0.4g, 1g, 1g, 0.8g pyrodex p respectively). And vacuum tested all the altimeters/ av bays with all the wiring harnesses connected to check everything was working as expected.
 

wrad

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In preparation for the first flight I fully updated the sims to exactly match the built rocket, and started looking at potential motor combos.
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Motor choices for the first flight were relatively straight forward. I have both cesaroni and aerotech 38mm reloads available to me, I currently don't hold level 2, so need to stay under 640Ns total for the combo. I wanted to fly close to that though with both motors being high power, so chose to go with an I in the booster and a H in the sustainer. For the sustainer I wanted to stick with cesaroni due to the reputation for quick lighting, especially the blue streak and skidmark, which were the number one choices. I wanted a skidmark just for the visuals, but couldn't get one on the day so went with the H152bs. For the booster I wanted to keep the thrust to weight above 5:1 but didnt want to absolutely hammer it of the pad, especially for the first flight. So wanted an average thrust of over 150N and below 364Ns total impulse. In the end I went for an aerotech I161 white lightning.
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The sim for the first flight looks great, and fell exactly into the performance and altitude bracket I was looking for.
For the staging parameters I had a play around and picked timings that would play it relatively safe on velocities and timing.
The booster motor burns for 2.2 seconds, separation is set to burnout +0.5 seconds.
Second stage ignition was set to T+5 seconds (2.8 second coast) with the rocket predicted to be 850ft and 130fps.
Events were programed into the quantum based on the sim, along with a staging lockout altitude of 600ft at 5 seconds.
 

wrad

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Ok, so that's the build complete. So on to the flight.
'There were a few loose ends to tie up on launch day, the decals for the fin can as discussed, installing pins to lock the body tubes to the av bay, and then installing parachutes.
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all stacked and ready to go.
 

wrad

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The maiden flight was fantastic, and nearly picture perfect (just 1 or 2 small issues to iron out for its next flight)
The boost was dead straight. separation occurred perfectly with the booster continuing to coast dead straight behind the upper stage. The second stage ignited perfectly after coasting for about 3 seconds, and flew dead straight up to just over 3000ft.
So the small issues were all on the way down. The booster ejected its parachute at apogee, however the fire blanket it was wrapped in slid up the shroud lines, reefing the parachute, stopping it from deploying properly. Thankfully although it had a relatively heavy landing, the booster survived unscratched. Secondly the second stage nosecone shook itself loose, just after apogee, deploying the main (which was oversized) at almost 3000ft rather than the planned 500ft. Fortunately the winds were kind and the rocket came down in an open field only 100m or so past my tent. The only damage to the rocket was a small crack in the end of the lower body tube, that i can easily trim off.
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waltr

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Great photos of the launch and recovery.
What Tim said- Congrats on the build and flight.
 

wrad

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wrad

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I put this in the other Skylark thread as well, but I will add it here too for anyone interested in the history of the Skylark:
This is a fantastic lecture, Robins book rely is a fantastic resource I would highly recommend to anybody with any interest in rocketry/space history.
 

Tim51

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This is a fantastic lecture, Robins book rely is a fantastic resource I would highly recommend to anybody with any interest in rocketry/space history.
+1 His book is excellent historical scholarship and at the same time almost a technical manual. It's a pity there aren't more books like his devoted to other rockets.
 
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