Nescorna Rocketworks

I finished painting Die Fledermaus, added the rail buttons, and threw some epoxy onto the eye bolt on the nose cone to close it off.  The pictures:

The plan had been to fly at the Ranch on Saturday (May 5, one of my favorite days to launch rockets, especially at the Ranch: the anniversary of the MR-3 flight, Freedom 7, carrying Al Shepard on his first space flight). I scrubbed.

Die Fledermaus, Painted and Ready

Despite the wind forecast, I went out to Snow Ranch. I had promised my daughter to drop her off at my cousin’s place to spend the day with their horses, and that was not made conditional on the weather.  I was about halfway out to Snow Ranch, so I continued. Besides, wind forecast or not, a) it was a gorgeous day, and b) the forecast is not the weather. Unfortunately, in this case, the forecast held fairly true, and we had winds of about 10 gusting 18, with an occasional gust nearing 20 mph. Some of my fellow LUNARtics chose to fly despite the winds, and there were some great flights.

But, some of the flights were, well, not so great. One long, slender rocket probably caught a gust or buffet just as it came off the launch rod, before it was going quite fast enough to get good, solid vertical penetration, and it veered hard over, nearly to horizontal and heading downwind (away from us!) fast. Many of the others weather-cocked hard into the wind, resulting in a high horizontal component of the velocity at parachute deployment (ideally, the horizontal and the vertical components will both be very nearly zero). I fully expected Die Fledermaus to weather-cock some, and, though this thing is, I think, built very solidly, especially for a G-powered bird, launching in those conditions was a needless risk.

I had a pretty good idea that Delta Echo Fox would be even worse in those winds, given its asymmetry.

So, instead, I worked as Low Power Safety Check Officer, checking rockets for safety and assigning pads, and also as Forward Observer on the Hill, watching for aircraft that might impinge on our airspace that could not be seen from the range head. And Die Fledermaus will fly another day.

Old pilot’s saying, adapted to this occasion: better to have the rocket down here, wishing you had it up there, than having it up there wishing it was down here.

Much progress of late on Die Fledermaus (even though all the parts for BAAH-1, my L1 cert bird, have arrived—though I have not yet ordered the parachute and heat shield).

The rocket’s built, and now primed. As I type, the primer is drying. The rocket has very much become a prototype vehicle for the build techniques I’ll use on BAAH-1, to the point that, though Die Fledermaus will initially fly on G motors, it’s probably strong enough to take an I motor, maybe more. Rather than a verbal blow-by-blow, here are the pictures construction pictures.

Finally, repeating the overall picture of the rocket ready for painting. (Why are so many of my “pictures of rocket ready for painting” taken at night?)

Die Fledermaus ready for painting

Die Fledermaus Takes Shape

Continuing on the interlude build project, even though all the parts for BAAH-1 have arrived. The picture shows the rocket as things are taking shape. The MMT is installed, except for the aft centering ring. There are two centering rings now in place: forward and mid; the mid will serve as the forward structural element in the equivalent of the fin can assembly, and the aft CR, which will go on after the three fins are attached, will do likewise, since both are (or will be) epoxied not only to the MMT and the airframe, but also to the fin tabs. A U-bolt as attached to the forward CR, serving as the mount point for the recovery system.

Just forward of the mid CR, a nylon lock nut is epoxied to the inside of the airframe. A rail button will be screwed into that nut after the rocket is painted.

The three fins are all cut out and shaped, along with a spare. One fin slot is cut, allowing for a general idea of how the rocket will look.

The latest sims show about 300 meters altitude on a G64, allowing for a nice flight at NASA Ames if the winds are calm. Up at the Ranch, an H97 (once I get the L1 cert with BAAH-1) should yield right around 500 meters. If I’m really confident in the build techniques and materials, an H268 will hit nearly 900 meters.

I got a small scroll saw: small hobby size, nothing huge, nothing fancy. It fits on the workbench, with a nominal 16″ throat depth. It’s from Craftsman, got reasonably good reviews: in fact, from my combing and reading, about the best of anything in its general price class (I was not in the market for a $500 DeWalt saw [harumph!]). With the saw’s arrival, I thought it would be fun to take some parts I already had in the Rocketworks (“project fodder”), design some odd-shaped fin, and build a rocket.

Die Fledermaus's First Fin

Besides, I needed something to occupy my time productively while awaiting parts for BAAH-1.

As the project evolved, it’s become a good proving grounds for some of the detailed construction techniques I’ll use in BAAH-1: for example, securing the middle rail button when it’s between two centering rings from the motor mount. And, as it evolved and I got a better sense of the shape of the fins, it acquired a real name—along with a paint scheme.

Meet the first piece of Die Fledermaus.

Not all was sweetness and cream, though. Part way through the project, it seemed as if my saw had broken. It’s not that it was in pieces, but it stopped working correctly after I changed the blade. I had changed blades before, so I could not, at first, figure out what had gone wrong. The problem was that the saw’s upper arm was whacking the underside of its housing at the top of the up-stroke, something that, pretty clearly, was not a good thing.

I searched. I searched some more. I checked the manual, tried innumerable online queries in the search engines, and came up with nothing to give me a solid hint as to what was wrong. Finally, I stumbled on something: a suggestion from an experienced scroll sawyer that the tension knob, used to adjust the tension on the blade, can come completely out of its receiving nut (or threaded fixture). I found this just before I was going to throw in yon towel and endure the travails of calling Craftsman Tech Support.

Upon removing the tension knob, I found that the specific tip provided by that experienced scroll sawyer did not apply to my saw. I fiddled with the mechanism, moving the actuating cam-arm, watching how things moved, and trying to figure this out without taking apart the entire upper portion of the saw—or more. I discovered that the tension knob’s mechanism seemed to raise and lower the upper arm: the upper arm, when under any tension (even a small amount), moved in conjunction with the lower arm. This made sense: the two arms wave up and down together, holding the blade between them. As I tightened the tension knob, the upper arm pivoted up—and up—and up.

Maybe I had just tightened the tension knob too far!

I loosened the tension knob, re-inserted the blade, tightened the knob back to what seemed a good tension, and hit the power switch.

Voilà!

It’s time: the bug’s bitten me.  It’s time to work on a certification project so I can fly larger motors.

Why?  No: this is not a case of, “Why not?” nor a case of, “Because it’s there.” I have a Vostok 1 model that I want to build. Lots of detail, complicated, a great project—that flies on H motors. That was—is—a problem: if I build it, I won’t be able to fly it. Though I toyed with the idea of using that as my L-1 cert bird, it didn’t take me long to stop toying.

BAAH-1 will, though, be based on an historical rocket.  In fact, it will be a full-scale model of that rocket: nearly 2 meters (a little over 6′) tall, 6.8 cm (almost 2¾”) in diameter, about BT-80 size. Not a big rocket: my Saturn 5 is much bigger in diameter, and Bedknobs and a Broomstick was just about this same size (built on BT-80, in fact).

I’m planning to over-design this rocket, in order to allow it to handle not just H and I motors, but to perhaps use it for my L-2 cert project, too, if the time comes I ever decide to venture into J and larger motors. Besides using thicker-walled tubes, more appropriate to high-power rockets than the Estes-compatible components—I’ll probably use Blue Tubes from Always Ready Rocketry—I’ll upgrade to aircraft plywood fins, bulkheads, and centering rings, U-bolts, a Fruity Chutes recovery system, and an Aero Pack motor retainer. I’m also going to include an avionics bay and dual-deployment capability, though the certification flight will almost certainly be single-deployment.

Side View of BAAH-1

It doesn’t take a very astute eye to notice that the static stability margin is large: in fact, larger than I would like. That’s one of the challenges with this model: the original, like this, is very long, with comparatively large fins.  I am considering adding aft ballast to bring the CG back along the rocket, but that will result in other problems, such as needing a motor with more thrust and, therefore, acceleration to ensure BAAH-1 reaches a safe speed before leaving the launch guide. Most likely, I’ll leave it as-is.

Currently, a friend, who has agreed to serve as my project mentor, is reviewing the plans. Once that’s complete, I’ll start buying parts and build.

The mission parameters included the site and the build:

• Build a rocket for 24mm motors, so I can play with the new 24mm reload kits I got.
• Build something that’s fun to fly at Snow Ranch and at NASA Ames.
• Because of the NASA Ames requirement, keep the maximum altitude under 300 meters.
• Be capable of flying successfully on D, E, and F motors (all available in 24mm, some single-use, some both single-use and reload.
• Use parts I already had.

The result: a 5.64 cm airframe (had a nice 86 cm length of BT-70-sized tubing) with a transition to 2.59 cm (BT-50) upper section, and a “space interceptor” style nose cone (the nose cone dictated the upper section diameter).  I used a BT-70 nose cone as the transition, had some appropriate balsa-ply centering rings for the 24 mm motor mount tube, found a 76 cm parachute and a bunch of Kevlar^® shock cord, and I was in business.  I ended up with a rocket that’s about 140 cm long, only slightly conventional.

Delta Echo Fox in Cradle

With some help from Rocksim to verify stability of a chosen fin design (3 small clipped deltas) and altitudes, I was in business. Predicted altitudes:

• D12-3: 70 meters
• D15-4: 100 meters
• E18-4: 280 meters
• F12-5: 310 meters

Slightly over 300 meters, but still within the ceiling at NASA Ames, being realistic.

The results, on an F12-5J, yielded 244 meters, per the on-board altimeter (Jolly Logic AltimeterOne). There was an interesting rapid directional change (wiggle in the flight path) during boost, which accounts, at least in part, for the 70 meter difference between the prediction and the actual flight. (Some of the difference is because of imprecise simulation: the rocket in the specifications is not exactly like the real thing.)

What caused the wiggle? At first, it looked like the rocket suddenly became unstable, or was in the midst of an uncontained engine failure. Neither was the case. My best guess: the rocket encountered a wind shear. The rocket is not fully symmetric: because there are three fins, not four, the flare on the nosecone cannot align with a fin pair. My theory is that this makes the rocket more susceptible to wind shear: if the shear hits perpendicular to the nosecone flare, it cannot also be perpendicular to symmetric fins. The forces will be unbalanced, and it can take the rocket a little time to recover. To correct this, I should probably go to four or six fins (why six? adding three symmetrically will be easy; converting three to four requires removing two fins and adding three).

I finally did more than remove the bulk of the damage on Bed Knobs and a Broomstick, damaged (very bad zipper, and a gussetted centering ring partially torn) at last month’s NASA Ames launch (see the posting). The zipper on the forward portion of the lower part of the rocket went right down into the coupler that joined the two tubes together. I had expected to have to patch at or slightly forward of that coupler. I looked more closely today, and noticed that some of the remaining body tube had, essentially, delaminated from the tubing coupler. It turned out that the forward body tube itself could be peeled away from the coupler, leaving a pretty clean, intact, standard diameter coupler sticking just the right amount out of the aft body tube.

Instead of having to craft a complicated two-part stepped coupler, it was a very simple matter of taking the new forward body tube and gluing it to the coupler!

Fie on burned-through delays. A pox on them and their progeny!

Bed Knobs and a Broomstick Launch, June 26, 2010, NASA Ames

It was an absolutely beautiful day out at NASA Ames Research Center at Moffett Field for the monthly LUNAR launch. Cloudless, light winds (almost no wind until about 11!), pleasantly warm but not hot, fun people, a good crowd. Paul Pittenger started us off with a triple drag race, including a pair of his styrofoam Sputniks. We had plenty of volunteers, so the expected possibility of flying once, if that, before helping didn’t materialize.

Bad, Bad Zipper for Bed Knobs and a Broomstick

I enjoyed chatting with people as a built the G64-4W for Bed Knobs and a Broomstick’s third launch. The rocket got lots of attention while I waited in the check-in line: Dan’s nosecone really is an eye-catcher. After a minor difficulty with the launch controller, up went the Broomstick! I was just settling in for a nice flight and the tension of the ejection charge’s timing when BAM! went the motor and out popped the parachute, with the rocket doing about 100 meters/second and at maybe 100 meters altitude. The chute deployed fine, but—but—when I recovered the rocket after a reasonably gentle landing, I saw the zipper.

Feh. Feh, feh, and fie on that delay charge! I’m not at all sure why the delay charge just burned right through. The zipper is evident in the picture on the right where the red-orange parachute is showing through.

King Tut’s Pyramid flew twice today: once on a single-use F50-4T for a very nice flight, once on a G77-4R. Again, something odd happened with the delay, and it seemed to burn right through, or perhaps the thrust gasses leaked around the seals. Regardless, ejection occurred during or just after boost. The pyramid’s rear ejection (tossing the entire motor mount aft, with parachute attached) prevented damage, though.

Despite the problematic ejections, it was a wonderful day!

Removal of the vast majority of the damage to the forward portion of the S-II is complete. This entailed cutting around the S-II aft skirt wrap, which is the most complicated of the cylindrical (as opposed to conical) wraps, and probably the most complicated of all the wraps. The S-II aft skirt wrap has a large number of LH2 Feed Line fairings, LH2 Recirculation fairings, the LH2 fail and drain fairing, etc., all of which protrude forward of what would otherwise be the forward edge of the wrap. The plan is to avoid replacing that wrap: it’s complicated and difficult to glue the wrap to the body tube, and the masking and painting is also difficult. (In retrospect, it might have been faster to just cut lower and replace it, but that seems also somehow less, well, elegant.)

One of the unexpected challenges was cutting through the forward thrust ring, a very small piece of tubing that lines the inside of the S-II tube and abuts against the forward side of the motor mount centering ring. I did an awfully good job gluing that thing in, and the yellow glue is resilient stuff! That’s done, though, and the remnants of that thrust ring that were on the inner sides of the fairings are also removed. I believe that it’s now time to begin real repairs and reassembly.

I’ve made the first sets of cuts on the Saturn V.  The rough cut to remove the forward, damaged portion of the S-II is done, the body tube for that has been separated from the S-II tunnel cover, and the forward motor mount centering ring, with its gussets, is removed. I’m documenting the work in a photo album.

I’ve been considering rebuilding the rocket in a way that a mild H motor (H97J, H128W, maybe even H180W). If I do this, I don’t want to add much weight: finesse, rather than brute force, will be the goal. While walking the dog last night, a way to increase strength of the forward MMT CR joint (to the main tube, the 144 mm body tube) hit me, so I spent about 20 minutes writing down my thoughts and creating revision 4 of the repair plans. (What’s wrong with this picture? The repair’s barely begun, and the repair plans are already on R4! Maybe nothing’s wrong with this picture, though, and reflects careful thinking. I hope so!)

The reloads that appear potentially viable:

It won’t take much to handle the H97J or the H128W: maximum thrust on the first is less that that of the G64W, that of the second is only (only?) 40% more. Going to the H180W, though, is probably not advisable if I still want to fly on the G motors.