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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."
Disclaimer: I'm not aeronautical engineer, but...
I'm curious whether the flying saucer would be stable and not spin around. Helicopters have rear rotors so they can counteract the spin forces induced by the main rotor. Other helicopters have two rotor blades on top of each other, one spinning one way, the other spinning the other way.
Without a design that counteracts the torque caused by the only rotor, what is it that will prevent the UFO thing from spinning around like crazy?
How is forcing the airflow over the body of the aircraft itself an improvment over an open airpath directly through the craft (a hole)?
Interesting how they mentioned this is like the Wright Brothers in terms of being very early in its development.
It sounds like it could work underwater maybe.
It looks like it is made for silicon wafer size engineering, microdrones.
I wonder about the linear speed and turning too. Would it be bad to put wings on it? Is that just a propellor and not a turbine like in the Avrocar? Would a turbine be better, and would tilting it naturally turn the machine's direction through gyroscopic precession?
If you put a rocket on one side, would it stay stable?
Could some kind of electrostatics (perhaps wires suspended above the disk parallel to it) help increase air flow by physically drawing it past the surface? Thinking of the "lifter" models.
If it was rising through a charged fluid you might think it could be leveraged. Usable in high atmosphere?
Is its rate of rise limited by the weight of the cowling it needs as a surface?
Does it use rare earth magnets like in engines inside electric car wheels?
Would a spiral ramp-shaped body like Da Vinci's early helicopter design actually work with a fan on top?
Would another fan help in maintaining stability and speed direction changes, like with helicopters tail blades?
The only thing in the inventor's favour is that the British MOD has a track record of failing to recognise useful inventions (such as RSA encryption, which it had long before R,S and A and ignored) while spending a fortune on torpedoes that don't work, nuclear submarines with no role, tanks with undersized engines, and rifles that don't shoot properly. For long haired left leaning peaceniks like myself half the charm of the MOD is its ability to reduce the risk that we will get involved in a major war by making sure our armed forces are ill equipped to fight one. (that was sarcasm btw). However, my own view is that they regard flying surveillance vehicles as unnecessary. The plan is to cover the entire planet in talking CCTV cameras, which will probably catch speeding motorists as well.
Pining for the fjords
There are two more things which you didn't mention. One is that the fan is inside a duct, which reduces tip vortices. That should make it more efficient.
The second is that it would avoid a problem which helecopters face when trying to hover out of ground effect. When more than about a rotor's diameter above the ground, the downward moving air starts to circulate down, out, up, and back into the rotor. The air moves in a circular pattern through the rotor, around, and back through the rotor again. This creates a downdraft from the perspective of the helecopter. Adding more power doesn't always help, because it just makes the air move in a circular pattern faster. The result is that the helecopter sinks when trying to hover at altitude.
If you observe helecopters hovering at altitude, you'll notice that they aren't actually hovering. They're moving forward very slowly. That's the only way to avoid that problem. You have to keep moving a little bit so you stay out of the circular rotation of air that you create behind your helecopter. If you stop completely, you're in the circular pattern and you sink unless you've got some enormous power source like a jet engine.
When you're in ground effect, the ground itself disrupts the circular movement of the air and limits how fast it can move in a circular motion. It also makes it turbulent as it deflects off the ground. The result is that you don't get a well-formed column of downward moving air that your helecopter is sitting in, thus you can efficiently hover without moving at all when you are fairly close to the ground or some other air-disrupting object like a building that you're carrying materials up to.
I would not be surprised if this device had some advantages over regular helecopters when it comes to hovering out of ground effect.
Fascism trolls keeping me up every night. When I starts a preachin', he HITS ME WITH HIS REICH!
It's interesting that you bring that first link up. The second link, Coanda Effect: Understanding Why Wings Work, is from no less than Jef Raskin, the father of the Mac. It contains a fallacious argument on why the Bernoulli effect can't explain the lift generated by a wing, which he claims he first derived as a child. It contains some child-like assumptions, the most grievous being the assumption that the ratio of the chord lengths (distance over the wing versus under the wing) is the same ratio as the speed of the air over the wing versus under. This implies that two air molecules that separate at the front of the wing, one going over and one going under, will meet at the back edge of the wing, as if joined by some invisible rubber band. In reality the ratio of the speeds is larger than the ratio of the chords, and the top molecule reaches the back long before the bottom one does. This link to a different page on the same website as the first Coanda fallacy link, shows the airflow using smoke pulses and does a great job of describing what is going on.
"I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
As for the stability of helicopters, if you look at the designs in the 50's and 60s, stability was a big goal. Look at Stanley Hiller's demonstration of hands off hovering of his helicopters. Over the years stability appears to have been less and less of a goal. Look at how the flybar on the Bell rotor systems has disappeared. I'm not sure why this has happened, but I'm guessing that agility has won out over stability, especially since stability can easily be added by electronic means.
I read the article, but I wasn't quiet sure how the Coanda effect was utilized by this design. I'm guessing that rather than tilt the rotor there are places where the downwash is attached (or not) and thus generate sideways thrust? I saw the little vanes moving, but assumed that was more for anti-torque - if you noticed, most of the vanes were fixed with a little bend in the direction of anti-torque (and, like the MDHC Notar the anti-torque force would be proportional to downwash and thus to torque). A few of them moved to give you the ability to rotate the machine and account for minor yawing forces not exactly countered by the fixed vanes.
Did anyone else notice where/how Coanda effect was used? Perhaps the moving vanes really are implementing the Coanda effect, but if so it's in a fairly different way than the MDHC Notar system. Did I miss something?
Desite your reply as an AC, I have to give you credit for correcting me on this one. You pointed out something that I did miss. I did recognize that the Coanda effect was redirecting the airflow downward around the edges (I have air knives here at work that do this), but missed that the air movement over the surface would also generate a lifting force as well.
The secret of keeping helicopters in action for years is that due to very frequent checks and tests, almost every part gets regularly replaced.
I talked to a air-rescue helicopter pilot once and he told me they have helicopters in service that are 35+ years old, but the only original parts in them are their skids.
There are plans to build your own version of this aircraft here, along with quite a few videos of it in flight. I'm amazed by how stable and under control it looks in the video of it flying outdoors in a wind.
What kind of helecopter was it? And how long did he have to hover there? And did his boss care that he was burning fuel at an amazing rate to get the job done?
Probably not. The boss probably wants him to burn the gas to the get the job done. On the other hand, the news chopper won't hover in a stationary position because he can save a shitload of gas by moving forwards a little bit. If he's in a jet copter, he'll have the power to do what he wants. But he might not want to burn the extra gas. If he's in a Robinson, his options are more limited for high altitude hover.
Fascism trolls keeping me up every night. When I starts a preachin', he HITS ME WITH HIS REICH!