Post by LegendLength on Nov 14, 2006 22:38:49 GMT
What is an Ornithopter
From Wikipedia:
An ornithopter (from Greek ornithos "bird" and pteron "wing") is an aircraft that flies by flapping of the wings. Since many examples of flapping-wing flight exist in nature, such as birds, bats, and insects, designers seek to imitate this mode of flight. Ornithopters are usually built on the same scale as these flying creatures. Some manned ornithopters have also been built.
A pure ornithopter:
Has there ever been a manned flight?
There have been reports of successful manned flights as long as 30 years ago, and a recent jet assisted flight by the University of Toronto pdf in USA.
However, there is currently no aircraft that can reproduce flapping winged flight for testing. So it is safe to assume there never was, given todays technology (e.g. carbon fiber, aviation motors, aerodynamics research).
For any remaining controversy, what is most interesting to people is whether we can fly safely and within a reasonable price range (under $20,000) now, rather than in the past.
What frequency do the wings flap at?
A typical flapping speed for a manned sized ornithopter is 1 - 3 cycles per second. A cycle includes both up and down strokes of the wing.
What size engine is needed?
Minimum power needed for level flight, with a single pilot of average weight and an aircraft weighing 100 lb (50 kg) is around 20 hp (15 kW). This equates to a 200 cc motorcycle engine and is about the same power requirement as an equivalent airplane.
How fast do they fly?
For a lightweight ornithopter, cruise speed is similar to a hang glider: 20 - 40 mph (30 - 55 kph). Heavier and more durable designs are able to fly faster, but jet power appears to be much more efficient than wing flapping at speeds above 100 mph.
What is the difference between thrust and lift?
Both lift and thrust are used interchangeably during discussions, which may be confusing. Thrust and lift both describe the same thing, but lift only takes the up and down force into consideration, whereas thrust can be in any direction.
What are the advantages of an ornithopter over traditional aircraft?
What are the disadvantages?
What if a wing fails?
Hang gliders have had to deal with this issue for some time now. Over the last decade, parachutes have become much cheaper and stronger. This allows hang glider pilots to carry a chute with them which will support both them and their glider. The chutes are made to handle 500+ hundred pounds, enough for both the glider and the pilot.
This is the best option for light ornithopters, and possibily heavier ones up to 300 - 400 lb (130 - 180 kg). It provides a secondary backup in case of most types of failure, including motor failure, wing and structure failure, and even pilot harness failure (ie. falling out).
todo: cite existing chutes for heavy gliders.
For motors, what are the advantages of electric vs gasoline / internal combustion engine (ICE)?
What are the disadvantages of electric?
From Wikipedia:
An ornithopter (from Greek ornithos "bird" and pteron "wing") is an aircraft that flies by flapping of the wings. Since many examples of flapping-wing flight exist in nature, such as birds, bats, and insects, designers seek to imitate this mode of flight. Ornithopters are usually built on the same scale as these flying creatures. Some manned ornithopters have also been built.
A pure ornithopter:
- Must get all of its thrust from wing flapping. It cannot include any other propulsion devices such as propellers or jets. Otherwise it is a hybrid aircraft.
In special cases, for example where an engine's exhaust pipe might provide a very small fraction of the thrust as a by-product, it is acceptable. As long as the aircraft can be shown to fly without needing that extra power then it is no issue. - Must be a heavier-than-air aircraft. That is, it cannot be held up using helium or other floatation devices. The reason for this is that it affects the aerodynamics of the aircraft in undesirable ways.
- Should be able to takeoff and land vertically, but this is not a strict requirement of ornithopters. For early test models at least, designers have chosen to focus on gliding flight rather than vertical takeoff with its extra power requirements and irregular flapping motion.
Has there ever been a manned flight?
There have been reports of successful manned flights as long as 30 years ago, and a recent jet assisted flight by the University of Toronto pdf in USA.
However, there is currently no aircraft that can reproduce flapping winged flight for testing. So it is safe to assume there never was, given todays technology (e.g. carbon fiber, aviation motors, aerodynamics research).
For any remaining controversy, what is most interesting to people is whether we can fly safely and within a reasonable price range (under $20,000) now, rather than in the past.
What frequency do the wings flap at?
A typical flapping speed for a manned sized ornithopter is 1 - 3 cycles per second. A cycle includes both up and down strokes of the wing.
What size engine is needed?
Minimum power needed for level flight, with a single pilot of average weight and an aircraft weighing 100 lb (50 kg) is around 20 hp (15 kW). This equates to a 200 cc motorcycle engine and is about the same power requirement as an equivalent airplane.
How fast do they fly?
For a lightweight ornithopter, cruise speed is similar to a hang glider: 20 - 40 mph (30 - 55 kph). Heavier and more durable designs are able to fly faster, but jet power appears to be much more efficient than wing flapping at speeds above 100 mph.
What is the difference between thrust and lift?
Both lift and thrust are used interchangeably during discussions, which may be confusing. Thrust and lift both describe the same thing, but lift only takes the up and down force into consideration, whereas thrust can be in any direction.
What are the advantages of an ornithopter over traditional aircraft?
- Vertical takeoff and landing.
- Slower and safer takeoff speeds (close to zero mph).
- Much smaller takeoff area needed.
- Extra wing control allows different ways of flying.
- Virtually no propulsion noise (wing vs propellor).
- Efficent at normal speeds unlike a helicopter which does not benefit from large wings.
What are the disadvantages?
- High speed travel is difficult, and anything approaching the speed of sound is out of the question.
- Only single passenger ornithopters have been proposed. This is mainly due to the larger forces that ornithopters encounter during normal flight (5 or 10 times that of an airplane).
- Much higher mechanical complexity because of the wing flapping mechanism.
- Ornithotpers are prone to heaving which bounces the pilot around with each wing flap cycle.
- Traditional aircraft have a century of practical safety testing and R&D behind them, whereas ornithopters have only a handful of people working on them.
- Wing flapping puts a lot of load on the motor due to the high forces involved. The engine must push a large lever (each wing) very close to it's attachment point. Each wing already has 200 lb of force pushing on it, but the motor ends up getting 5 or 10 times that amount because of the lever attatchment position.
What if a wing fails?
Hang gliders have had to deal with this issue for some time now. Over the last decade, parachutes have become much cheaper and stronger. This allows hang glider pilots to carry a chute with them which will support both them and their glider. The chutes are made to handle 500+ hundred pounds, enough for both the glider and the pilot.
This is the best option for light ornithopters, and possibily heavier ones up to 300 - 400 lb (130 - 180 kg). It provides a secondary backup in case of most types of failure, including motor failure, wing and structure failure, and even pilot harness failure (ie. falling out).
todo: cite existing chutes for heavy gliders.
For motors, what are the advantages of electric vs gasoline / internal combustion engine (ICE)?
- No noise from both the motor and the propulsion (wing flapping).
- Cheaper running costs (gasoline is about 4 times the cost of electric to run).
- Instant on and off.
- Electric motors give maximum torque at any RPM whereas ICE motors develop torque only at high turning speeds.
- Lightweight. Only 3 pounds for enough to power a light ornithopter with pilot.
- Brushless electric motors last forever. They have no parts that move except for the rotor which floats on a magentic field, preventing any wear.
- No pollution except at the electric power station.
- No need for motor oil.
- Electric motors do not lose power at higher altitudes whereas gasoline becomes less efficient with the thinner air.
What are the disadvantages of electric?
- Motors are more expensive than equivalent ICE ones (by a factor of 3)
- Batteries are very expensive ($5000 for 10 minutes of flight)
- Batteries are also heavy (20 lb for 10 mins of flight)
- High voltages and currents are needed to power the 10 - 20 kW motor. This creates issues for crash testing where wires may be cut or batteries deformed. Fire and electric shock can easily occur in those situations.