Sunday, October 16, 2011

Wig-Wag Monocopter

Ascent position

Descent position [almost]

The Wig-Wag is yet another monocopter with an adjustable pitch wing. Like the two Campitch MC's the wing automatically adjusts from ascent pitch to descending autorotative pitch.

The Wig-Wag employs a weighted arm mounted to the hub and a wire loop mounted to the underside of the wing leading edge which goes around the weightbar. Before ignition, the weightbar dangles down holding the wing down with it. As rpm increases centrifigal force swings the weightbar outward, thus upward, until it's horizontal, pulling the wing up to ascent angle. After motor burn out, as rpm decreases, the weightbar sags downward again, bringing the wing down into autorotation mode. Unlike the Campitch MC's, this pitch control system is more responsive in flight and doubtless more tunable on the ground since it's controlled by the mass [and length] of the weightbar alone rather than the interaction of wing weight and spring strength. This actually works like the weight ball governor on old steam engines [and some early petrol engines], particularly stationary units. So like them, at peak performance, the Wig-wag monocopter is literally running ball[s]-out.

While the Campitch MC's would've been difficult to design without serious drafting, preferably CAD, the Wig-Wag was cobbed together a part at a time with no drafting of any sort. It aint perfect, but it's a good first attempt and entirely functional from first flight on.
The wing and hub are used parts resurrected from the remains of the CP-1. This makes for a wing that is too small and heavy but it does turn in fair flights on C motors. The weightbar is made from an RC pushrod clevis and a piece of 2-56 all-thread with a lead fishing weight nutted on. My biggest conceptual stumbling block was coming up with a suitable weightbar pivot mount on the hub. Installation of an upright piece of G10 fiberglass was easy enough with my bandsaw followed by grinding access for the flybar with a moto-tool. What was actually more difficult was bending a suitable wire loop for the wing and then mounting it in the best spot. I bent two loops and then punched three pairs of holes in the wing before I was reasonably satisfied. I was glad to be utilizing used parts as I had no concern for cosmetic issues.

So far the Wig-Wag has made three flights. First on a C6, then on a D5, followed by a D12. While the two Estes motors were fine, the Quest D5 suffered a case burnthrough. While this is no big surprise anytime you spin one, that recycled undersized wing makes matters worse. This led to replacement of the motor mount tube.

After puzzling for quite a while over a name, I settled on Wig-Wag due to the resemblance between the weightbar and a wig-wag railroad crossing signal

Sunday, October 9, 2011

SpaceX Has A Pipedream

Spaceflight Now has a recent article [Reprinted from CBS Space] on SpaceX's vision of making their boosters reusable. The simulation video is sharp. The stated intention is for direct descent and landing under rocket thrust. Sounds simple enough on the face of it but I immediately saw some flaws in the plans.

First Stage; Slant range puts the booster a long way from the launch site and variable target orbits increase possible descent points over a large arc, typically well out over the Atlantic. The sheer height of the Falcon 9 booster makes me want to install much larger landing legs [and more of them]. This is why all flyback booster designs thusfar have wings, wheeled landing gear and sometimes jet engines.

Second stage, This might actually be a bit easier than the first stage. Because the 2nd stage is itself orbital [or nearly so], one can pick the reentry point and bring it down where desired. A reentry heat shield adds a lot of weight though. At least 2 motor restarts are needed, but restarts are not that uncommon here. Need a lot of spare fuel for both the deorbit and the landing. Second stage motor nozzles are typically optimized for high altitude/vacuum operations and will be inefficient back at sea level.
I believe it was NRL that was ground testing a booster 20 or so years ago that was low-pressure [no turbo pumps] and had a variable expansion thrust bell, kinda like the "turkey feathers" on a fighter jet engine nozzle. This allowed inflight expansion ratio optimization for any altitude.

Capsule and boosters are shown returning on thrust alone. Even with thrust for landing, parachute systems would still be more economical and probably lighter for slowing and stabilizing the vehicles in an upright position instead of relying on attitude thrusters and the mains alone. Parachutes would also add some safety in case of motor failure, or at least reduce the splat.

"We'll see if this works," Musk said. "But it's going to be certainly an exciting journey. And if it does work, it'll be pretty huge. If you look at the cost of a Falcon 9 ... it's about $50 (million) to $60 million. But the cost of the fuel and oxygen and so forth is only about $200,000. So obviously, if we can reuse the rocket, say, a thousand times, then that would make the capital cost of the rocket for launch only about $50,000. ... It would allow about a hundred-fold reduction in launch costs."

Was Mr Musk reading that off a script???
Nobody's gonna get 1000 uses out of any booster, even if there is that large a backlog of flight contracts. Divide flight contracts by; payload production rates, vehicle refurbishment rate, available ground support, optimal launch windows... I'm sorry but I would've scoffed at 100 flights per booster. How about 10 flights each on a 5-10 booster fleet. By then; if the economics are sound, you'll be building a few replacements and/or an improved new fleet anyway.
Note that Elon says a 1000 fold reduction in booster cost relates to only a 100 fold reduction in overall launch costs. That sounds reasonable as other costs go up drastically. Additional flight systems complication, booster retransport, refurbishment, range comm/nav systems, additional facilities...manpower, manpower, manpower.

I have great respect for SpaceX and what they have accomplished. In fact I'd like to work for them, and I can't say that about most of the aerospace industry or NASA itself.

Upgraded PC At Last

My friend Steve recently replaced my PC tower with a much newer one. Not precisely cutting edge as it was assembled from hand-me-down components, but it's a lot more advanced than my old one which I had for over 11 years.

There's a helluva lot of work to do yet, software and tools to transfer or download, and gigs of folders to transfer. Wherever practical, I'm downloading fresh copies or newer versions of software and tools just to be sure they're clean and up to date. Normally I cringe and start to break out in hives every time I'm faced with "Updated" or "Improved" software. Most of the time it has compatability issues or unresolved glitches, or will no longer do what I needed it to do beforehand [Quicktime comes to mind on that score]. Naturally, I totally object to automated updates and block them always. The learning curve is pretty steep, principally changing from Win 98 to XP, and Bobcad 17 to 21.xx. After using dialup all those years, having a hi-speed internet connection sure is nice too.

Steve is a computer professional and I cannot recommend him enough. You can reach him through the following link;
Thanks Steve.

Sunday, October 2, 2011

Don't Forget the Cheese!!!

One of the things I like best about living in south Texas is Mexican food. To be more accurate; Tex-Mex food. I aint talkin' about Taco Hell here. Above all else I love breakfast, I'll have breakfast for dinner even, this includes breakfast tacos. I usually ask for cheese on my breakfast tacos and from time to time the cooks forget to do so. Happens to burgers sometimes too. Over the last 30+ years this has added up to quite a bit of lost cheese. Brings a tear to my eye.

Today I was trying out a new restaraunt, ordered myself some coffee and two tacos; bacon, egg & cheese and chorizo, egg & cheese. When the order was ready the manager brought it out because my server was busy elsewhere. The tacos were large but they looked a bit thin, I peaked under the flaps and there was plenty of cheese but nothing else! No eggs, no porky bits. Without some grilling time, these weren't exactly quesadillas yet either. The manager was all apologetic but I had to laugh out loud, disturb the whole place loud. That was funny!

The Wheel of Cheese Turns Full Circle.