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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.
As far as I can tell, the main advantage of an ornithopter--the reason that birds use that design--is that it doesn't require spinning parts, and it doesn't require literally burning fuel ie high temperatures. Living creatures don't spin very well or very fast and have no ball bearings, so living propellors would be out of the question, and throwing away some of your own mass isn't a good survival strategy, plus high temperatures have all kinds of problems. Bird wings are very useful if you don't have metal or oil, but past that? Probably no advantage at all.
My friend had been an engineer on the flapper project for years and it was only recently that the booster was added. As far as I understand, the wings do flex and have successfully propeled the plane on the runway to significant (~60kph) speeds without need for a boost, however, the plane kept oscillating into the ground. More than one interesting test day was the result. All I can say is "congratulations" to those on the flapper team...its been a long time coming. :) (I hope there will be an alumni party for those who have put so much effort into this project over the years.)
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
A bird's wing is an aerodynamic lifting body, and model ornithopters were flying before the Wright Brothers. They don't "fight against the lift" of the wing, but use it in a pretty sophisticated way.
We don't have human-carrying ornithopters because scaling effects get in the way. The ability of a wing to produce lift (and the muscle power available to it, in the case of a bird) goes up as the square of the size, but the weight goes up as the cube.
This is what limits the size of birds. A hummingbird can fly all day, even hovering motionless. A robin needs to rest once in a while. An eagle can only fly under muscle power in bursts; most of the time he has to soar on rising thermal currents like a sailplane. An ornithopter big enough to carry a human is going to need a LOT of power.
rj
Sorry but if you had taken the time to RTFA instead of looking for a witty way to take a stab at the editors then you would have noticed that the article WAS about Mr. Bill. Mr. Bill was thier first remote controlled ornithopter. Maybe not the Mr. Bill you're referring to but Mr. Bill none the less. So you've violated your point #5 allowing ME to find that witty way to stab at the editors thusly proving they still are asshats. Thanks for the assist!!
All logical conclusions. When anything migrates, it has to stop and refuel and rest eventually. Also, it's not like there's one bird flying his ass off for 3000 miles all by himself. Ever notice the reverse V formation geese use when migrating? It's the most efficient formation for distance flying. The lead bird does most of the work, and each bird in sequence behind the lead does less and less work to stay aloft, because they're in a drafting chain. The birds at or near the back of the V are working the least while the lead works the most. They often rotate the lead bird out from one of the rear birds.
Another advantage ducks and geese have is that they are able to build up great fat reserves which is converted into energy for long endurance flight. Simply compare the meat of a chicken to the meat of a duck and it becomes obvious which one has more fat content. Ducks and geese also need these fat reserves to survive colder climates for short periods of time as well (pre-migration).
You're correct on your point of wingspan/size ratio of ducks/geese/swans. It seems the longer a bird must fly the greater the wingspan is needed. See the albatross for the best example of this. They have a wingspan of up to 11' 11" (no that's not a typo, 11 feet 11 inches total wingspan).
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."
It had been said for many years that bees to not posess large enough wings to fly, and therefore they don't.
Recently, it was discovered that the bending of the bees' wings helped to create and pull vortecies of air from the base of the wings out to the tips, tripling the effective lift for the same surface area.
My guess is you're quite correct... until we move to a soft-wing design, we're going to have a heck of a time getting advantage to ornithoptor flight. And non-rigid industrial quality materials isn't exactly what our society is known for producing right now.
The ______ Agenda
It comes from an internal combustion engine.
Theres a fairly complex mechancial system that it drives to flap and twist the wings.
I went to a presentation by him a few weeks ago (I got the Institute), and had no idea they were this close to flying it!
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.