Sunday, February 13, 2011

Valentine's Day Velomobile

For Valentine's Day, I made a cardboard model of a side by side tandem velomobile. The scale is 2 inches = 1 foot, and the wheels are 20" (406 or 451). As with my previous model, the goal is to come up with a reasonably streamlined shape that can be built out of flat panels and simple curves. Here are some pictures.

Saturday, January 22, 2011

Velomobile concept

Today, I made a quick structural mockup for a velomobile. This design could be built in plywood; carbon fiber sandwich panels; or any of a number of other techniques -- but it's mostly designed to be built using conventional aircraft sheetmetal techniques. Among the design influences are:
I built the mockup out of cardboard and a glue gun, around an artist's poseable mannequin. The mockup is scaled to a 6 foot tall person so, given that the mannequin is exactly 12" tall, the scale is 2" to the foot:

This mannequin was from a garage sale, and apparently, some kids had their way with him. He is now the evil brains-eating velomobilist of death from hell. His new ride looks like this:
The body is intended to have three main bulkheads, as follows:
The cockpit, i.e., the area between B and C, has curved sides; everything else is straight. The body is spanned by four longerons at the corners, perhaps made from aluminum angle:
The lower longeron is gently curved in the cockpit area; the upper one is made of two straight sections and one curved one, joined similarly to the Sonex splice plate. Both longeron curves are only in one plane, making them easy to bend.

Since the area between bulkheads B and C is open, we add two "tunnels" to reinforce it in torsion. (In my model, bulkhead B is not quite shaped like it should be.)
The seat can either be a sling, between bulkheads B and C, or a solid structure of some sort. Here is a view with the rider in place:

The front wheel structure (with or without suspension, as the case may be) is built into bulkhead A, and covered with a fiberglass fairing. Here it is with the fairing off:

The rear wheel suspension is not clearly defined at the moment. Perhaps a swingarm attached to bulkhead C, similarly to the Alleweder? Or some further structure aft of bulkhead C? I don't know yet.

Monday, February 15, 2010

A380 wing skins

The secret of the A380 wings is finally revealed. Check out this article. Apparently, each skin panel is prestressed in a custom jig and autoclaved. When it comes out, sproing!, it's the right shape. Nifty, eh?

Sunday, February 14, 2010

My first A380 flight

I recently went on a business trip to Sydney. On the outbound, I chose to go directly from KSFO to YSSY to save time. On the return, I went through KLAX specifically because the YSSY-KLAX leg was on an A380. This is my report of the journey on Qantas flight 11.

At YSSY, I couldn't see too much of the aircraft because of the sheer volume of the three jetways leading up to it.

No matters, though. Welcome aboard!

Notice the nice bright new shiny anodized door latch hardware. It's the details that matter, you see. Once in, the economy class cabin is nice if not ostentatious:

Notice that the plastic parts of the seats are carbon fiber. This is not just a "look": By moving back the edge of the upholstery, I could tell that the reverse side is also carbon, and the edges look black even though the resin is transparent. Most likely: they are real carbon. Nifty!

The seats articulate such that, as the back is reclined, the seat pan moves foward. I would have loved to un-Velcro all the padding to show you how this clever design feature is made possible, but that might have gotten me into trouble, so I chose to demur. Instead, I'll point out that, apparently, the aircraft seatbelt latches of the future are automotive-style, not airplane-style:

Behold the mighty wing that is to hold all this stuff up in the air:

Now on to the star of our performance: The tail-mounted camera. This one thing is so useful, so awesome, that it makes me want to grab a step drill and Jilson snips and add this to every commercial heavy on the planet. Here we are at the gate:

Who wants an entertainment system that shows movies on demand when you have that, eh? Here we are ready for our takeoff roll:

And on climbout, with nifty vortices and Sydney harbor in the background:

Speaking of which, let's look at that wing in flight one more time:

Notice anything? Yes, compared to the ground photo, you can see the wing outboard of the #4 engine pylon. Curved downwards on the ground, the wing straightens in flight.

Ok, here's a quick weekend project. Design a reliable, strong and lightweight mounting, articulation and actuation system for the wing control surfaces. This must take into account the flexure of the wing, and specifically, should maintain proper slot geometry for flaps and slats all along their length at all aerodynamically significant conditions. Remember that, if your mounting is off the neutral axis of the wing, the spanwise distance between your mounting points will change as the wing flexes.

(Yes, I know this is a previously solved problem: all large aircraft must be designed with wing flexure into account. But, in this case, it's particularly dramatic.)

Another weekend project: Design a wing that is curved downwards when unstressed. Now manufacture it. Notice that, strictly speaking, your unstressed top and bottom skins are actually double-curved.

And now on to the only way to go flying, as ordered by Doctor Awesome:

This is me programming, while keeping tabs on our status. :) Unfortunately, there is one source of silliness: the "warning" on the display. This comes up, and makes the rest of the screen "grayed out", whenever there is a PA announcement. How annoying. Hrmph. Incidentally, the power connector is on the back of the armrest of the seat in front of you (it took me a while to find it):

There are RJ-45 and USB sockets on the end of your own armrest, but on my flight, these did not provide any useful connectivity (though perhaps the USB was powered).

One of the "problems" with this ship is that it is noticeably quieter than the average commercial heavy. Why is that a problem? Because the all-night chit-chat of the flight crew in the nearby kitchen was audible enough to keep me up! D'owww! :) It did not help that I was consuming uppers and downers together:

Obligatory potty shot: The faucet is temperature adjustable and activated by a proximity sensor, like all decent bathrooms worldwide. Why it took so long for aircraft to adopt this "new" idea is totally beyond me.

Finally, we arrived, a little bleary-eyed but none the worse for wear. Here is an awesome, if blurry, shot of us approaching the California coastline with spoilers deployed:

Flying what looked like a downwind for KLAX 24R:

Turning final, likely over PALAC, with downtown LA in the distance:

And braking on the ground:

Finally, it's time to say goodbye to my ride:

Monday, May 25, 2009

Another little airplane

On Saturday, May 21, we drove to Rio Linda Airport for the 6th Annual Northern California Sonex Fly-in. Wow! The Sonex is one of the most amazing light aircraft designs out there. The airframe is filled with cute little tricks that make the construction simple yet strong. The design has an excellent track record and many dedicated followers. One aircraft that taxied in was powered by a Jabiru 3300 engine. For reference, for those who haven't been there: it sounded no louder than a lawn mower; clearly, this is a very refined and well-muffled engine.

Unsurprisingly, today, my son Aden (6yo) wanted a Sonex of his own. I copied the 3-view from the Sonex website into my CAD program and made some very simple cutting diagrams. We then cut stencils out of paper:

We cut the parts out of balsa:

We then attached everything with a glue gun:

I then made him a quick and dirty nose with scrap balsa. The result is a happy little Sonex fan:

Sunday, January 4, 2009

Trim blues

I suspect I might be genetically unable to trim model gliders.

I tried and tried with the little homebrew FF glider (see previous post). I moved the CG forward then experimented with all possible variations of wing and tail incidences. I was not able to get two consecutive consistent flights: with what seemed like the exact same settings, one flight would be lovely, floating down to a nice pretty flare, and the next twenty would either climb and stall, or dive.

Perhaps it's my launching method. I mean, I can't really say I was consistent in my (hand) launches, and the six feet from my hand to the ground does not give the glider lots of room to settle into a nice trimmed attitude and speed. But still.

I suspect I should just buy some RTF (better than a Guillows toy, but not necessarily the fanciest) and follow the instructions (especially about CG settings) religiously, hoping to build experience in how a properly constructed glider should feel. Or maybe I should join the AMA and get someone to teach me. Or something.