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Combined Hovercraft and Helicopter
An anonymous reader writes "Has British engineer Geoff Hatton brought us the best of two worlds with his UFO-looking machine? The US military thinks so and are investing in it. The design is sturdy (as opposed to a helicopter) and can fly high (as opposed to a hovercraft). It is based on the Coanda Effect."
I think they base that primarily on the fact that the rotor is protected. Many helicopters can take hits in non-critical areas but a rotor strike is almost always catastrophic.
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What they are saying is that the hovercopter (for lack of a better term) has the rotors protected and can bump into things and still fly. What it basically is is a small inverted squarish bowl with a fan on top that forces air down and around the sides. The fan is protected and therefore, more stable. It is controlled with fins that direct the downward air in various directions for steering. This isn't being designed for movement of people or cargo, but rather as a means to carry a small camera for recon missions. (think the small machines sent out by Skynet in the Terminator movies).
They won't be much larger, or made out of much more durable materials (they can be flexible) because they are planning to use them as UAVs and not as manned aircraft, at least for the time being. If you RTFA they specifically talk about the design's suitability for this purpose in light of its ability to survive collisions with walls.
I'm afraid I'm going to dream of manhacks tonight...
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
I'm an aerospace engineering student.
Note the scoops on the sides. They're all directing the airflow clockwise (as seen from top). If your rotor is also spinning clockwise (as seen from top), the airframe will be torqued counterclockwise, and those little scoops will counter the torque.
Just my guess.
FTA:
"'Unlike a helicopter, though, this is aerodynamically neutral and you can bump into walls and not smash the rotor,' said the inventor.
"And, unlike a hovercraft, you can fly it as high as you want.'
The dome-shaped object is powered by an electricity-driven propeller on top that pushes air over the outer surfaces, and has controllable flaps.
Geoff's Flying Saucers - the original name for his GFS Projects company - are based on an aerodynamic principle that has been around for nearly 100 years.
Known as the Coanda Effect, after a Romanian jet-engine pioneer, the principle is today used primarily in helicopters that have no tail rotors."
Sounds to me like it's even less complicated than a traditional helicopter. The blades in a traditional helicopter go through some incredibly complex motion. From the pictures in TFA, it looks to me like this is a simple propeller. Rather than relying on complicated mechanisms on the blades, it exploits the properties of the working fluid (air in this case). The adjustable flaps over that outer surface look simple enough.
Seems to me like a lot less complex, mechanically, than the helicopters we've been deploying to wars for decades.
I bet they direct the thrust to counteract the torque of the motor.
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It's far more efficient than a helicopter. It's getting lift both from the airflow over the rotating blades, and from the flow of the downwash over the body. In a traditional helicopter, most of that downwash is simply wasted.
If you were blocking sigs, you wouldn't have to read this.
No. The Coanda effect is different than regular wing aerodynamics. The Coanda fallacy, the first external link on the coanda effect wikipedia article, explains the differences.
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He is referring to its ability to handle midair crashes
I don't think that's what he's referring to at all. Helicopters are very unstable machines, especially in hover mode, which is arguably the most important and most distinguishing feature of a helicopter. A helicopter requires hundreds of very precise control inputs a minute to remain in a hover. If you change one of the variables, you pretty much have to change all of the rest. For example, if you adjust the cyclic, you have to adjust your engine's torque and collective a tiny amount so you don't fall out of the sky, or alternatively, go flying up too fast, and you'll also have to nudge the tail rotor to account for the increased torque form the main rotor. You can think of it as a loop in a computer program that operates very quickly.
It looks like this guy's hovering craft aims to make the most advantageous feature of a helicopter much, much easier to preform, and hence the vehicle is "more stable" than a helicopter. It's probably more sturdy, too, but that's a side effect of not having blades swinging around in an arc that is considerably larger than the aircraft.
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There's a little goblin inside who spins it the other way.
Not funny, not informative, but at least it's not another dupe.
If you were blocking sigs, you wouldn't have to read this.
That's because it isn't new. The Avrocar was using a very similar system in the early 60s. While I'm sure the scale model pictured in the article has no trouble going up or down, I bet it has a lot of difficulty building up linear velocity while maintaining stability. That has always been the trouble with these aircraft. They're great if you only want to go up or down, but most people want lateral movement as well.
As an aside, I'm not sure why using the Coanada effect is better than just building a ducted fan with internal control surfaces. Putting that big blockage in your airflow just seems like it's going to sap power from your engine.
I read the internet for the articles.
Actually, half the tags come across as heavily opinionated comments. Questions are answered "yes" or "no" or often, both. A product that might not work quite right or a company that gets its come-uppens gets tagged "haha".
Ya, these are really going to help anyone search.
If your RTWA (Read the Wikipedia Article) you'll learn that the "blockage" isn't at all a blockage, and the air blown down by the fan runs along the side and then straight down, instead of being deflected back up, which means there is no "sapping" of power. This gives you the entire center cavity for payload, instead of making it a hollow cylinder like a ducted fan would require.
http://www.mhall119.com
Yeah, but physics says that if your airflow is being redirected it's not only losing power from changing the direction of the flow, but also from friction between the airflow and your surface.
I read the internet for the articles.
It looks like it turned into this http://www.defensetech.org/archives/002723.html
Close, but not quite right. Im being picky here, but IAAAE (i am an aerospace engineer) and it bugs me to see all the incorrect definitions of lift.
:)
The main lift mechanism for this vehicle is the Coanda effect. The acceleration of the fluid as it curves around the body of the "ufo" generates the majority of the lift. The fluid curves because it is a viscous fluid and experiences boundary layer attachment, ie there is friction between the fluid and the surface which keeps it "attached" to the convex shape. I assure you that the thrust generated by his tiny propeller is not nearly enough to lift the vehicle vertically by itself.
"As such, the wing develops lift by forcing the majority of the air over the top of it to create an area of low pressure over the top of it as it rotates."
There is no majority or minority of flow over an airfoil. In fact, boundary conditions for the freestream are generally positive and negative infinity. If lift was only generated by more flow going over the top, airplanes would have a really hard time flying inverted!
Lift is indeed generated by the integration of an asymmetric pressure distribution, but the interesting thing is what causes the asymmetric pressure distribution. Simplified a bit, lift is a reactionary force on the wing, generated by the downward change in momentum imparted to the fluid due to the airfoil's shape.
Or you can explain lift with circulation theory, which is a mathematical model that makes no practical sense to anyone
I've heard that some of our attack helicopters can lose significant percentages of the rotor surface and still stay aloft, specifically the Apache and the Comanche (project abandoned once it was complete, your tax dollars at work.) Was I lied to? :)
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
In forward flight, the main rotor thrust is tilted which pulls the helicopter to the side. As the helicopter moves to the side, the vertical fin at the rear of the helicopter provides weathercock stability, much like the fins on an arrow. This yaws the helicopter in the pro-turn direction. Some helicopters need a little bit of pro-turn anti-torque pedal, but this is a minor correction to keep the aircraft in trim. Most of the yawing force in forward flight is being provided by the (fixed) vertical stabilizer.
In a HOVER, a conventional helicopter uses tail rotor thrust to yaw the aircraft. As a previous poster pointed out, this is done by changing the angle of attack of the tail rotor, not by changing the speed. As he pointed out, in full size helicopters, the main rotor and the tail rotor are connected by drive shafts and transmissions, meaning their speed is always at a fixed relationship to each other. This is done so that during unpowered flight (autorotation) the main rotor can keep the tail rotor turning, to give the pilot yaw control during the glide and landing.
Also, you are incorrect about how counter-rotating helicopters generate yaw forces. A tandem rotor helicopter like the CH-46 and CH-47 generate yaw forces by tiling the front and rear rotors in opposite directions. To yaw left, the front rotor is tilted to the left, and the rear rotor is tilted to the right. Coaxial and intermeshing helicopters generate yaw forces by changing the relative pitch of the rotors. This causes the rotor turning in one direction to generate an increased torque force, while the rotor turning in the opposite direction generates decreased torque forces. The imbalance causes a yawing force. Note that these systems need to work backwards when in autorotation. I've never flown one of those systems, so I only know what I've read - someone who has flight experience in a Kaman or Kamov might comment?
Back to the particular device in the article, the anti-torque force seems to be generated by a combination of fixed fins around the circumference (note how they are all bent in the anti-torque direction) and the (4?) moving fins which are probably there to provide yaw control to the operator.
Yeah, but physics says that if your airflow is being redirected it's not only losing power from changing the direction of the flow
Fluids is a tricky subject, and not just grammatically. So long as the force doing the redirecting of the flow is everywhere normal to the direction of the flow there is no power expended in the process of redirection. This is not quite the case in the Coaanda effect, which seems to be mediated by frictional effects, but one of the startling things about it is that the normal forces are much larger than the frictional forces, so you do get substantial redirection with very small losses.
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If you had checked at the end of the page and http://jlnlabs.imars.com/gfsuav/gfsuav.htm you would had seen that the guy is giving credit to Hatton and gives a brief history of machines based on the same physics.
... the "blockage" isn't at all a blockage, ... there is no "sapping" of power. This gives you the entire center cavity for payload, instead of making it a hollow cylinder like a ducted fan would require.
It also causes the lift (and thrust) to appear distributed over the surface of the fuselage (except for the very center), where it can be easily transferred to support the payload.
With a helicopter lift appears on the rotor. It must first be focussed on the rotor shaft, then passed through a bearing, and finally distributed to the airframe via a skeleton that is hung from the bearing. Here there is a local tug-of-war between the rotor and the center of the fuselage, then the lift appears in a ring around it.
Same idea as the "flying wing". Or Bucky Fuller's "all the strength is distributed through the skin" geodesic designs, with their fantastic strength-to-weight ratios.
Also:
- The system is more stable with the lift appearing in the outer regions rather than at the center.
- With a broad lifting surface (like an airplane wing) more ordinary control surfaces can manage the craft's flight - or you can modulate the lift in patches by valving in air leaks to selectively break the airstream attachment.
- In a helicopter much of the control is done by dynamically adjusting the pitch of the blades using a complicated control structure and shafts in bearings that constantly dither once per rotor rotation - then the forces must be transferred by applying bending stress to the rotor shaft! With the coanda saucer the blades are a solid structure that only creates an airflow, while the control structures only move when the control parameters change.
- Unlike a helicopter, lift can be adjusted to trim out major offsets of the load's center of gravity.
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Unless equally sized bits break off of every blade or a *very* small piece breaks off a blade, the helicopter is almost sure to immediately literally explode from the created imbalance. And that's not a joke.
Many RC-Helicopter pilots know this from own experience -- a loud bang and the helicopter rains down in pieces (and those blades only weigh ~150g).
Also a report of this happening to a real helicopter.
bla
> That would be news to the high voltage tower service pilot. I've watched as a helicopter
> hovered absolutely still (+/- 6-12") for over 5 minutes while a tech harnessed to the
> side and hanging down attaches the insulator on top of the tower in 30 mph wind.
Hovering with respect to the ground in a 30mph wind is the same as moving 30mph in still air.
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