My claim to the baddest KestreL in the land took a setback last night. I had just got the got my fins and fillets sanded just how I wanted them after several hours of hand sanding (and some blood I might mention, those fins are S-H-A-R-P). It was after midnight and I was out back with a headlamp and porchlight, so I decided to get ahead by laying down a quick primer coat before I went to bed. Only in my haste and the poor light, I grabbed the gloss white! I was half way through before realizing my mistake. I just spent an hour this morning sanding it all off, and then recoated it with real primer. But wait! what's that? Massive crinkle! I didn't get all the gloss paint off, and now my primer looks like a lichen.

Now I'll have to wait several hours before sanding off all the primer and then wait another day waiting till the undercoat gloss white paint dries. Then more sanding. I'm now rethinking my complicated paint scheme as there isn't enough time to get the whole thing finished with my work schedule next week. Drat.

We'll see how this turns out. I made some "special modifications" as Han Solo would say. "She may not look like much, but she's got it where it counts."

I christen it the "Millennium Kestrel"

See you on the range, assuming the K300 motors from Joe come in when the are supposed to.

Chad Moore

Chad, my advice is to wet sand. And wet sand some more. And then some more.... My least favorite part of building a rocket 😯

My KestreL appears to be a LONG way from being done, but I intend to fly her at MHM (sans paint, of course). I am building one that is 100% stock for MHM. In July, I intend to fly the... modified KestreL. Much shorter, much smaller fins, that sort of thing. CG/CP will be a challenge on that version.

The original KestreL did 24K w/ a Loki K350 - and it had 3" of the motor hanging out the back, as that motor is way very long. Fast forward to MHM and add a tailcone, no motor hanging out? Should be good for a whole lot more than 24K. You just never know. Your actual mileage may vary 🙂 BTW, I am flying w/o a GPS to save some weight....

Only in my haste and the poor light, I grabbed the gloss white! I was half way through before realizing my mistake. I just spent an hour this morning sanding it all off, and then recoated it with real primer. But wait! what's that? Massive crinkle! I didn't get all the gloss paint off, and now my primer looks like a lichen.

Now I'll have to wait several hours before sanding off all the primer and...........
Chad Moore

Dont worry Chad, it wasnt you,... I had Snidley switch the cans when you were not looking. Ba ha ha ha.

And JW, No coller huh. Im training my Dog to fetch white rockets, and head for the border. 😛 "North to Alaska, Way up Nooorth! 😉

Managed to get some color on the rocket today after all my priming troubles. It's about 30 grams heavier than I hoped, but not too bad (with a low thrust motor like the K300, it needs to be as light as possible). Will come in at 1315 grams with transmitter and avionics, or about 46.3 oz.

That is a nice weight, Chad - my proto weighed just a snitch more than that, and I built it pretty light (or so I thought!). I came in just a tick over 48 oz with all recovery and electronics but w/o motor. I also didn't paint mine....

Did you build your kit stock, or did you take a bit off the length?

John,
I took 2.25" off the upper tube, and 0.6" off the lower tube. Made some minor internal changes too. Fins are reshaped and fully airfoiled, but the span is not that much less than stock. Maybe 0.2" shorter. My final CP/CG is about 1.7 calibers- pretty conservative. I didn't want wobbles.

Just noticed this thread. I'm working on a KestreL too, though very much not stock. In fact, my "Sharp Stick in the Sky" flown at MHM used some of the parts, as I sort of kit-bashed a Wildman Jr and a KestreL plus a few other random parts like the conical nose cone that's been on my shelf a while... my KestreL project is "K Up Yonder" and will undoubtedly appear at NCR North no later than O'fest... my big personal goal for 2010 is to "need" the high altitude window at least once, and this is the project that will get me there.

I've commented on other threads about the known/obvious limitations in Rocksim. Some are in the docs that came with the program (yeah, I know, I didn't read them either until I started getting weird results!), and some I've learned by talking to Tim. One of the "rudest" for high dynamic flights is that the nose cone drag model is really simple and based on surface area, so a 1:1 conical nose cone will simulate as the optimal choice for altitude.

There are at least two ways to cope with this. One is to use a tool like RASaero to generate Cd values for your airframe for different velocities and plug those in to Rocksim to see how the results are affected. Since the Cd changes radically as you cross mach, using a single Cd value is at best an approximation of what's going on, but you can at least get more believable results for different nose cone geometries this way.

The other approach is to just change simulators. I'm personally using OpenRocket for all of my new designs now. It's an open source rocket design and simulation tool written by Sampo Niskanen at Helsinki University of Technology. One of the pieces of documentation provided is his masters thesis, in which he describes the approach he took to handling drag at higher velocities. I'm not a real expert on these things, but his approach made sense when I read the text and then the code.

I don't have enough actual flying experience with things simulated using OpenRocket yet to know how great the models actually are, but the results seem much more "believable" to me. Since it's open source, if they turn out to need tuning, we can do that. And I really like the ability to plot lots of attributes through the flight and then pan and zoom on the plots to see what's going on. If you're serious about simulating things like the KestreL, I'd suggest giving it a try. As of version 1.1.0, it even has the ability to import a Rocksim file... though to date I've done all my simulations with it by starting from scratch and so don't know how well the import really works.

In any case, have fun! That's what this is all about... 😉

Bdale

I have found that the import works well, but the estimated drag is really, really high compared to both RASAero and actual flights. IIRC, RASAero predicted my J flight going over 22k, which it did, but Open Rocket was predicting something like 17k. So don't use it to figure out if you're going to bust the waiver if you're close. On another rocket, I had to make the body tube almost zero length in Open Rocket to match the Cd that RASAero was coming up with. Hopefully this will get straightened out.

I love the rocket design interface though, and the way the predicted altitude gets adjusted real-time as you move the sliders for the different part dimensions.

Adrian,

Did you play with the surface finish setting? I noticed that OpenRocket picks something rough as default. You can change that in the general screen of any of the exterior components, ticking a box to change it for all exterior parts. That seems to be the largest "knob" on drag that needs to be set to something non-default to get rational results in OpenRocket that I've run in to so far.

Bdale

Yes, I'm pretty sure that was with the smoothest possible settings.

Very interesting. Makes me wonder just how high my KestreL hack might get, then... hrm.

I'd check it in RASAero and see how that compares to what you got with OpenRocket.

I'd like to keep track (at least in my head) of who breaks 20K for their first time - and did so with a KestreL. I think I have heard from 6 or 7 fliers who had their first 20K+ flight and they did it on a KestreL...

In our club, Chad comes to mind? There were other KestreLs that got up there, but I think they were from guys who had broken 20K previously?

It took me something like 3 or 4 tries to recover from over 20K. While it is getting easier, it is still an achievment!

I'd like to keep track (at least in my head) of who breaks 20K for their first time - and did so with a KestreL. I think I have heard from 6 or 7 fliers who had their first 20K+ flight and they did it on a KestreL...

In our club, Chad comes to mind? There were other KestreLs that got up there, but I think they were from guys who had broken 20K previously?

It took me something like 3 or 4 tries to recover from over 20K. While it is getting easier, it is still an achievment!

Well, it won't be on a KestreL, but I'm taking my first legit shot at 20k at the July launch, using my L3 rocket. I've got an M1939W, which sims to ~19.5k, and so far every supersonic flight has exceeded the sim.