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Another Ornithopter Takes Off
mnmn writes "Ornithopters have been around for a while, but a professor at the Toronto Institute for Aerospace Studies has made progress with his. It flew for 14 seconds and covered a third of a kilometer. However it landed with a bit of a crash. Interestingly it uses a glow jet turbine from RC aircraft."
My friend invented a flapping paper airplane 20+ years ago in junior high. Of course it's not nearly the same, since it reacts to pressure fluctuations instead of creating them. There are (pdf) instructions so anyone can be an ornithoptrix.
Glow fuel is Nitromethane mixed with a lubricant such as Castor or Synthetic oil.
Actually, it's a nitro/alcohol mix, with the nitro being anywhere from 5% to 50% or more.
-jcr
The only title of honor that a tyrant can grant is "Enemy of the State."
Actually, glow fuel is mostly methanol with some nitromethane added to improve ignition and horsepower, plus the lubricant you mention. The nitromethane content is typically 5-20%, though it was practically zero for about a year after a 1991 explosion that took out one of only two plants that make it in the US.
There are jet models using ducted fans powered by glow-plug engines, but it's a pretty kludgey solution, because it takes very high rpm and power levels for piston engines. The engines have aft-mounted exhaust ports so they can run a tuned pipe down the middle of the "jet" exhaust, and the pipe is tuned for an rpm just a little bit south of disintegration. They perform very impressively, but the noise is extremely obnoxious and excludes them from a lot of flying sites.
True turbojets began to appear in the Seventies and are common now. The big hurdle in making turbojets (or any gas turbine engine) is that you have to make the turbine wheel out of some exotic, hard-to-fabricate materials; the designers got over that one by adapting automotive turbocharger parts. They sound remarkably quiet, partially because a lot of the sound is above human hearing...your dog's mileage may vary.
rj
No, nitromethane is mixed with methanol and lubricants to make model airplane (glow) fuel.
-jcr
The only title of honor that a tyrant can grant is "Enemy of the State."
Sorry, but that is just not true. My Daughter won a four year scholarship by proving that Ornithopters are actually much more efficient in converting energy into flight then propeller driven airplanes. (Jet's are very inefficient compared to piston engined aircraft, it's just that they fly faster on cheaper fuel and have much lower maintenance costs which make them more "dollar efficient.")
Anyway, the point is, during her analysis (which I might add was very impressive and detailed) she concluded that the flapping motion of birds and insects (which actually have two different flight models) were approximatly 300% more efficient at converting energy into aerodynamic fluid motion. Insects being a slight bit more efficient at it in denser air - which dramatically falls off the larger they get. Birds maintain efficiency to much thinner air - hence their ability to fly with increased sizes - with no known theroetical limit based on her limited science.
What insects and most birds both do very well is use the wings motion in either direction to produces both lift and thrust (which is just lift in the direction of flight.)
The real limit to ornithopters is the physical stresses created by the flapping motion. If you can model a birds wings on that large of a scale, the stress on the materials are tremendous, so careful thought has to go into materials selection as well as energy distribution. In fact, in these guy's earlier models, they were suffering breakages at the hinges (weak points.)
Bill
It's my Sig and you can't have it. Mine! All Mine!
I agree. Im 29 and consider myself to be pretty bright, yet I only discovered that misconception a year ago. Both the education system and mass media repeat "popular" junk science, and it was only by accident that I drilled into a deeper explanation on lift and was suprised with the real science.
This site has a pretty good explanation. My favourite sentence is this:
Students of physics and aerodynamics are taught that airplanes fly as a result of Bernoulli's principle, which says that if air speeds up the pressure is lowered. Thus a wing generates lift because the air goes faster over the top creating a region of low pressure, and thus lift. This explanation usually satisfies the curious and few challenge the conclusions. Some may wonder why the air goes faster over the top of the wing and this is where the popular explanation of lift falls apart.
And yet 747s are the most efficient known method for moving people from place to place. Funny how that works.
If you're speaking strictly of fuel efficiency, then bullshit. A 747 cruises at 650 mph. The highest number of seats currently in use on a 747 is 587 (most 747s have fewer seats due to first and business classes). This gives a maximum of 381,550 passenger miles per hour (source: Wikipedia).
A 747 burns, on average, 3,743 gallons of fuel per hour (source: International Civil Aviation Organization). This translates to 101 passenger miles per gallon.
My Corolla, on the other hand, gets between 37 and 40 miles per gallon on the highway. Since we packed 'em in like sardines on the jet, we might as well do the same for the car and stick five people in there. At the low end of the mileage range, that's 185 passenger miles per gallon. Pretty amazing feat Toyota has pulled off, eh? Almost doubling the efficiency of the most efficient mode of transportation ever conceived!
Even taking account the fact that a road route is longer than a great circle route, the car is still more efficient (15 gallons per passenger for the car, 24 for the 747 from JFK to LAX).
And if I recall correctly, trains are quite a bit more efficient than cars.
Now if you want to take time into account, or the infrastructure required to build a road/railroad across the country, then it's a slightly different story. But since the GP wasn't talking about those, it's a bit irrelevant.