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."

Comments

sturdy? as opposed to a helicopter?

[lecithin]

I know the Marines still have CH-46 helicopters in service that took battle damage in Vietnam. Some are 40 years + and none are less than 35 years old.

Saying "The design is sturdy (as opposed to a helicopter)" is really quite a statement since the design is not in service.

Seems pretty cool though.

Re:sturdy? as opposed to a helicopter?

[localroger]

How many of those helicopters that are still flying were flown a wall at any point during their service life?

Re:sturdy? as opposed to a helicopter?

[Hijacked Public]

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.

Re:sturdy? as opposed to a helicopter?

[forrestt]

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).

Re:sturdy? as opposed to a helicopter?

[drinkypoo]

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...

Re:sturdy? as opposed to a helicopter?

[modecx]

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.

Re:sturdy? as opposed to a helicopter?

[Profane MuthaFucka]

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.

Re:sturdy? as opposed to a helicopter?

[BostonPilot]

I beg to differ - I think the parent was probably correct about what the author meant. First of all, the design did NOT look that stable. Also, the fact that the fan is ducted means gentle collisions won't destroy the rotor system which is a pretty good feature for a small UAV. It also has a safety benefit if the rotor is ducted.

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?

Re:sturdy? as opposed to a helicopter?

[comp.sci]

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.

Penguin on a treadmill

[electrofreak]

I like the story about penguins on a treadmill more.

Excellent!

[Vexor]

Now we have our own device to abduct aliens from their homeworlds.

Hmmm...

[ProteusQ]

It just won't seem real to me until it fires laserbeams from its undercarriage at passing motorists and pedestrians while the words "De-stroy! De-stroy!" are chanted from its external loudspeaker system. If its targets all looked 50's retro, that would help too.

Amazing opportunity...

[cno3]

For a new breed of modern warfare. Simply fill the device with eels...

Re:Amazing opportunity...

[LouisZepher]

I will not buy this record, it is scratched...

Re:My one question

[Anonymous Coward]

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.

Re:Maintenance?

[the_wishbone]

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.

Re:Maintenance?

[jandrese]

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.

Re:seems inefficient?

[jhfry]

Hovercraft's that use the technique you describe would be required to move a lot more air, and do not do so well at higher altitudes where the air is thinner. This is due to their lift being generated entirely by creating a low pressure zone above the craft by moving huge quantities of air from one side of the craft to the other.

This craft moves a smaller amount of air across it's surface, like the wing of an airplane, the way the air flows across it's surface creates the low pressure zone necessary to create lift.

The method you discuss, works well in situations where the rotors are very large in relation to the body of the craft, while this method works even when the rotors are much smaller in relation.

I am sure someone with a little more understanding of the physics involved could improve upon what I just said, but I'm pretty sure this is the way it works.

Re:Maintenance?

[mhall119]

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.

Re:Sturdy vs surveilance helicopters, perhaps

[djdavetrouble]

So what you are saying is that we need to build a new super shotgun that shoots wet wads of toilet paper ? ;)

Re:More of a flying hovercraft, not a helicopter

[Anonymous Coward]

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 :)

Re:Coand effect

[barakn]

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.

Re:Maintenance?

[radtea]

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.