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Post by ironhold on Oct 17, 2015 3:38:16 GMT
I had an idea for a sci-fi series I've been thinking about. In real life, coaxial rotors on helicopters are mounted so that both rotors are on top of the air frame. But what if one of the rotors was mounted underneath the air frame with a duct in place around the rotor? |
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Post by the light works on Oct 17, 2015 5:01:46 GMT
I had an idea for a sci-fi series I've been thinking about. In real life, coaxial rotors on helicopters are mounted so that both rotors are on top of the air frame. But what if one of the rotors was mounted underneath the air frame with a duct in place around the rotor? I'm guessing there would be a stability concern. basically you would be balancing part of the weight of the airframe on the rotor instead of hanging it from the rotor. |
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Post by GTCGreg on Oct 17, 2015 16:20:29 GMT
Keep in mind, the rotors on a helicopter do not produce lift by the thrust of downward air like a hovercraft. They produce the lift by the air flowing over a rotating wing more like the way lift is produced by an airplane wing. I don't see what the advantage would be to a ducted rotor.
They do sometimes use ducted tail rotors on conventional (not coaxial)helicopters. In those cases, the tail rotor is acting more like a fan.
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Post by the light works on Oct 18, 2015 1:03:28 GMT
Keep in mind, the rotors on a helicopter do not produce lift by the thrust of downward air like a hovercraft. They produce the lift by the air flowing over a rotating wing more like the way lift is produced by an airplane wing. I don't see what the advantage would be to a ducted rotor. They do sometimes use ducted tail rotors on conventional (not coaxial)helicopters. In those cases, the tail rotor is acting more like a fan. true, ducted fan thrusters are a different concept than ducted rotors would be - a otor in a ring would more likely be a guarded rotor. but it would be interesting to know if the ring improved the efficiency of the rotor by breaking up rotor tip turbulence. |
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Post by silverdragon on Oct 18, 2015 6:27:43 GMT
I had an idea for a sci-fi series I've been thinking about. In real life, coaxial rotors on helicopters are mounted so that both rotors are on top of the air frame. But what if one of the rotors was mounted underneath the air frame with a duct in place around the rotor? 1] what do you land it on? The duct had better be strong?. 2] how you get in/out?.. especially in a hurry?.. I wouldnt want to bail out of a helicopter with the fan UNDERNEATH the thing.... 3] counter-rotating means you have a prop shaft through the crew compartment?.. hard to "service"?... 4] balance issues. With the two sets of blades that far apart, you cant fit a collective and Cyclic control through one control ring, so would have to fit two, one for each set of blades, and getting that balanced is never going to be easy. With one stacked on top of the other, pushing up one side of the ring pushes up on the same side as the one above by equal amounts. You can never be sure of that if the two sets of rotors are separated, with no mechanical link between the two. In the Chinook, the separation of the two sets of blades allows a different and very useful flight characteristic that allows a very fine tuning of how the thing flies. With bot sets of rotors on the same shaft, separated by an aerodynamic body, I am wondering if it will become unstable.... very quickly.. Its different hanging underneath to sitting on top of the thrust, ask and VTOL Harrier pilot about that. Barrel rolling a helicopter is done by pilots who have wheelbarrows to carry their "steel undercarriage" about in?... I aint saying this is impossible, as the impossible is only something no one has ever done before, I am just saying there is a lot to be considered. |
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Post by the light works on Oct 18, 2015 14:51:51 GMT
I can see it possibly being a useful configuration on a multirotor aircraft. that would allow a rigid rotor to be driven by a double ring and pinion transmission, with the drive speed used to perform the function of the collective on a standard helicopter. similarly, the top and bottom configuration could be used IF there was the ability to have a main drive trunk through the airframe, allowing the collectives to be one-piece assemblies. but Silver has a very good point about dismounting from the vehicle in a hurry.
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Post by GTCGreg on Oct 18, 2015 15:11:37 GMT
I can see it possibly being a useful configuration on a multirotor aircraft. that would allow a rigid rotor to be driven by a double ring and pinion transmission, with the drive speed used to perform the function of the collective on a standard helicopter. similarly, the top and bottom configuration could be used IF there was the ability to have a main drive trunk through the airframe, allowing the collectives to be one-piece assemblies. but Silver has a very good point about dismounting from the vehicle in a hurry. even if all the obstacles SD and TLW bring up could be easily overcome, I am still failing to see any real advantage to such a system. |
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Post by ironhold on Oct 18, 2015 16:16:05 GMT
Yojoe.com - Unproduced Vortex XS-2 vehicle (note: lots of pop-up ads)What I was thinking was something along the lines of the above unit, with the cockpit forward of the ducted fan. A second rotor assembly would be on top (where the prototype has the disc launcher), with a tail extending from the rear. This would hypothetically leave me room for some tricycle gear.
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Post by GTCGreg on Oct 18, 2015 18:01:08 GMT
Yojoe.com - Unproduced Vortex XS-2 vehicle (note: lots of pop-up ads)What I was thinking was something along the lines of the above unit, with the cockpit forward of the ducted fan. A second rotor assembly would be on top (where the prototype has the disc launcher), with a tail extending from the rear. This would hypothetically leave me room for some tricycle gear. As I mentioned a little earlier, this is more a hovercraft design with the downward thrust of the "fan" supplying lift. One major disadvantage of this design is the lack of auto-rotate capability. If you lose power, it turns into a rock. At least with a helicopter, as long as you have some forward airspeed, you can "glide" to a controllable landing using auto-rotation. It makes for a nice si-fi looking craft, but other than that, I don't believe it's beneficial. |
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Post by wvengineer on Oct 19, 2015 1:03:41 GMT
The primary reason for the rotor on top is a matter of stability. It is much easier to hang something from a single point than to balance on one. Think about it this way, a crane lifts from a single point and usually not from below. Pushing it up from below would be a major challenge to maintained stability. Anything happens to loose stability and you flip over and are in a traditional top rotor setup, not something you want in the middle of a flight.
The problem with the single large rotor like you have is that a large engine like that will make the craft want to spin. you either have to have some form of dual, counter-rotating rotor that cancel each other's torque out, or some form of tail rotor or vectored exhaust to control the torque.
A dual rotor setup would cancel the torque, but it would be a challenge to control roll along the axis between the two. You are still fighting the stability problem.
Purely from an engineering standpoint, I would suggest a quad rotor platform for stability reasons. That would give the most stable platform without major design . You could do a tri-rotor setup with two smaller and one large one. They would need to be sized so they balance out the torgue from the single large engines would cancel the torque of the two smaller ones.
There is a issue with ducted fans. They are good at focusing air in one direction. A helicopter maneuvres by tipping the rotor forward and back. A ducted rotor would either need fins to direct the air to maneuver the craft, or a gimble setup to change the direction of the of the whole fan setup.
So looking at the link posted, trying to make it work, I am thinking counter rotating rotors and some form of fin setup to allow for movement.
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Post by the light works on Oct 19, 2015 1:23:50 GMT
The primary reason for the rotor on top is a matter of stability. It is much easier to hang something from a single point than to balance on one. Think about it this way, a crane lifts from a single point and usually not from below. Pushing it up from below would be a major challenge to maintained stability. Anything happens to loose stability and you flip over and are in a traditional top rotor setup, not something you want in the middle of a flight. The problem with the single large rotor like you have is that a large engine like that will make the craft want to spin. you either have to have some form of dual, counter-rotating rotor that cancel each other's torque out, or some form of tail rotor or vectored exhaust to control the torque. A dual rotor setup would cancel the torque, but it would be a challenge to control roll along the axis between the two. You are still fighting the stability problem. Purely from an engineering standpoint, I would suggest a quad rotor platform for stability reasons. That would give the most stable platform without major design . You could do a tri-rotor setup with two smaller and one large one. They would need to be sized so they balance out the torgue from the single large engines would cancel the torque of the two smaller ones. There is a issue with ducted fans. They are good at focusing air in one direction. A helicopter maneuvres by tipping the rotor forward and back. A ducted rotor would either need fins to direct the air to maneuver the craft, or a gimble setup to change the direction of the of the whole fan setup. So looking at the link posted, trying to make it work, I am thinking counter rotating rotors and some form of fin setup to allow for movement. that particular design would probably require counter rotating impellers inside the duct with controllable venting, or auxiliary thrusters to spill or create thrust for motion control. looks to me like one of those designs that is only good for proving you are creative enough to make such a design get off the ground. |
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Post by wvengineer on Oct 22, 2015 2:06:48 GMT
I am wondering what the application for something like this would be. Helicopters rotor work by moving lots of air over a large area to generate the lift needed. Something like this has a much smaller fan area, so the air would have to be moving a lot faster, requiring more powerful engine(s), fuel etc. Also, Ironhold I would suggest a 2nd cockpit, cargo area, or something in the back to ballance out the weight.
For a fighter, this setup would have a large target area and radar signature for what it does, making it easier to shoot down.
It maybe practical for a recon/observation platform in non-combat areas or a transport of some kind.
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Post by silverdragon on Oct 22, 2015 5:56:30 GMT
Been doing some asking in my world of friends of aviation....
Quad Rotor is in investigation... as in "Up-sizing" a drone.
Main area of investigation is as a sky crane....
You know when something heavy has to be lifted, such as a tree in logging, or putting a new A/C unit on top of a tall building without a crane.... those are the area's where a sky crane is used, a BIG helicopter.
Having a quad-rotor or multi-rotor that has "Geo-stationary" ability?... one that can fly to an area, hands off the main flight controls and leave it in auto-pilot, whilst the pilot does the "Lift"?....
Having six rotors with the ability to loose one and the other 5 start taking up the slack... also priceless.
Being able to do that with "Remote control", as in the pilot is on the ground using "VR" goggles....
Ask a sky-crane pilot the worst part, and its taking up the load the first few feet.
Having the ability to track a moving object, such as a ship, and stay 20ft above the stern deck whilst lifting someone who needs hospitalisation?...
However, the general idea is hanging UNDER the rotors, as much of helicopter work that isnt flying is concentrating on whats below you.
I asked once what the main objectives are in the first parts of getting a helicopter licence.
"Take off, fly over there, land, followed by 'Did he hit anything?..' if the answer is no, he passed."
Erm, ...?... simplified, that works for me?....
Also, they say, the higher the rotors, the less chance of them hitting anything on the ground.
The reason commercial aircraft engine hang UNDER the wings is ease of servicing.
Otherwise, the safest place for an engine is as high off the ground as possible when taking off or landing....
The design of a billion-dollar project such as the A380 then is dependant on how high the spanner-man can climb to service the engines....safely...
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Post by the light works on Oct 22, 2015 14:21:25 GMT
Been doing some asking in my world of friends of aviation.... Quad Rotor is in investigation... as in "Up-sizing" a drone. Main area of investigation is as a sky crane.... You know when something heavy has to be lifted, such as a tree in logging, or putting a new A/C unit on top of a tall building without a crane.... those are the area's where a sky crane is used, a BIG helicopter. Having a quad-rotor or multi-rotor that has "Geo-stationary" ability?... one that can fly to an area, hands off the main flight controls and leave it in auto-pilot, whilst the pilot does the "Lift"?.... Having six rotors with the ability to loose one and the other 5 start taking up the slack... also priceless. Being able to do that with "Remote control", as in the pilot is on the ground using "VR" goggles.... Ask a sky-crane pilot the worst part, and its taking up the load the first few feet. Having the ability to track a moving object, such as a ship, and stay 20ft above the stern deck whilst lifting someone who needs hospitalisation?... However, the general idea is hanging UNDER the rotors, as much of helicopter work that isnt flying is concentrating on whats below you. I asked once what the main objectives are in the first parts of getting a helicopter licence. "Take off, fly over there, land, followed by 'Did he hit anything?..' if the answer is no, he passed." Erm, ...?... simplified, that works for me?.... Also, they say, the higher the rotors, the less chance of them hitting anything on the ground. The reason commercial aircraft engine hang UNDER the wings is ease of servicing. Otherwise, the safest place for an engine is as high off the ground as possible when taking off or landing.... The design of a billion-dollar project such as the A380 then is dependant on how high the spanner-man can climb to service the engines....safely... I doubt they will develop a multirotor skycrane that can lose a rotor without requiring an absolutely phenomenal pilot to manage a good landing. and they have tried multirotor skycranes before - and I think they ran into engineering limitations rather than concept limitations. as for airplane engines under the wings - keeping the thrust in line with the balance points is also important. if you lose one engine of a twin engine plane, a lot of compensation is necessary to keep things in line. |
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Post by oscardeuce on Oct 26, 2015 2:11:49 GMT
Like this contraption?  |
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Post by silverdragon on Oct 26, 2015 10:29:58 GMT
We (UK) Did it this way.....  Ended up with this....  Thats a Kestrel by the way, the R&D project that became the harrier. |
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Post by oscardeuce on Oct 26, 2015 13:45:26 GMT
Those are jets, the flying platform used the proposed props and duct to lift. Here is an even more pure form;  |
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Post by Lokifan on Nov 19, 2015 16:55:13 GMT
Like this contraption? I'm a little late to the party. Ah yes, the Hiller Flying Platform. More info here.The Hiller Museum is just down the peninsula from San Francisco in Redwood City (they were a local company). You can see one there, as well as a lot of coaxial prototypes and other vertical takeoff aircraft. |
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Post by silverdragon on Nov 20, 2015 10:17:31 GMT
Anyone else miss-read that with the first L as a T?....
HiLLer.... or not....
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Post by the light works on Nov 20, 2015 15:37:35 GMT
Anyone else miss-read that with the first L as a T?.... HiLLer.... or not.... yes, I've misread it a couple times, even knowing there was no connection. |
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