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Oh No! Another multicopter!

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narfi

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3- Four high reliable motors with extreme reliable cables and wires and connections.
I think most are approaching this with more motors for stability when one or more fail. Either an under over layout with 4 (or more) sets of upper/lower motors, or a wider 'net' of 6+ motors spread out.
 

Bigshu

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It seems like the transition from hover to forward flight was figured out pretty well back in the 50's. It just never made commercial sense. Tilt propellers and ducted fans accomplished it using commonly available engines and materials. I'd love to reverse engineer a Doak 16, and build one!
 

Aerowerx

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One solution short time:

1- A conventional combustion engine only for generation energy working like a generator.
2- A battery only for support an emergency landing if the engine fail. (works better than BPS)
3- Four high reliable motors with extreme reliable cables and wires and connections.
4- Rotors positioned high enough to avoid ground accidents.

What do a electric motor fail? I think only if the energy is cut off, the bearings stuck or some internal wire disrupt.

With these solutions I think we can have an aircraft with 1-3 hours of flight with some reliability. But how fast would it be compared to a car? How much more fuel would it consume?
You need at least 5 motors/rotors, each one operating completely independently.

With only 4 you are in a hopeless situation if one fails. As an example of what I mean, sit in a chair with 4 legs. Then cut off one of the legs, without changing your position in the chair.

With 5 or more motors/rotors, when one fails the adjacent ones can take up some of the load, and at least keep you upright long enough to get to the ground.

Notice I said "each one operating completely independently". You do not want any single point failure to disable more than 1 of the motors/rotors. As for the electronics, it would have to be multipoint redundant, like the NASA space shuttle which had a 5 way redundant control system.
 

Dusan

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Or, you can make transit inter-modal, and have one airfield per town, and monorails from there
into and around the city. Or busses. Lots of ways to skin the people mover cat. There's even on demand transit system designs that take the pinch out of only one access point with lots of places to go around it.
I'm not sure that will work. If I want to go to another town 200km away, I need to get into my car, get to my town's airport, get through security, wait to get on the plane, fly to the other town, disembark, get to the bus station, and ride the bus to my final destination, all this enchilada is more expensive and takes longer time than driving directly. Studies have shown than flying is less convenient if the destination is less than 3-400km away. Only flying directly, point to point there is potential time savings for shorter flights.
 

Dusan

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It seems like the transition from hover to forward flight was figured out pretty well back in the 50's. It just never made commercial sense. Tilt propellers and ducted fans accomplished it using commonly available engines and materials. I'd love to reverse engineer a Doak 16, and build one!
The transition from hover to forward flight was figured in 50's, but what wasn't figured yet, is how to fly in both modes as efficient as possible. A VTOL capable of transition is a compromise. It has much more disk loading than similarly sized helicopter, so power for hovering it's much higher. In cruise mode the large rotors and large engines (sized for hovering not efficient cruising) are an impediment for high speed performance.

There are 4 basic forces acting on an aircraft: weight(W), opposed by lift(L); drag(D) opposed by thrust(T). Flying straight and level, at constant speed, L = W, and T=D. An important parameter for an aircraft is the L/D ratio (or glide ratio). This is true for all heavier than air aircraft, airplanes, helicopters, VTOL, whatever. A fixed wing aircraft, a general aviation airplane as Cessna 172 has a cruise L/D of about 10, that means it's propeller needs to generate a thrust force that is only one tenth of the airplane weight. The engine and propellers are basically sized to deliver that thrust effectively. To design a comparable VTOL, you'll need to up-size the rotor and engine to generate a thrust value of at least 10 times more. Needles to say that the performance in cruise is taking a big hit with such a large engine and rotor.

Well, there's this...https://youtu.be/HGFOkvHPyB4
The Ryan VZ-3 Vertiplane, was a proof-of-concept experimental aircraft using blown flaps to achieve a short or near vertical take-off. From the test data I read, the designers were happy to achieve 80% of downward thrust using the flaps, 20% lost in various flow effects. The experiment was considered a success, in the sense that proved that not tilting the rotors downward (as in tilt-rotors) would not achieve 100% thrust, so next efforts were on tilt-wings and tilt-rotors.

Tilt-wings and tilt-rotors are also not achieving 100% thrust from their rotors. As the wings and fuselage is in the rotor's slipstream, wing and fuselage flow interactions create impingement and fountain-flow that reduces lift by 5-10%, a much larger effect than what is experienced by helicopters, due to the higher slipstream velocities of tilt-wings/rotors.
 

Bigshu

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I'm not sure that will work. If I want to go to another town 200km away, I need to get into my car, get to my town's airport, get through security, wait to get on the plane, fly to the other town, disembark, get to the bus station, and ride the bus to my final destination, all this enchilada is more expensive and takes longer time than driving directly. Studies have shown than flying is less convenient if the destination is less than 3-400km away. Only flying directly, point to point there is potential time savings for shorter flights.
I don't know where you fly out of, but my airport is an eight minute drive, there's no security beyond a badge operated door or ramp gate, pre-flight and fly to destination city, then some form of ground transport to final destination. The drive to the airport and drive from the airport plus the flight time is bound to be less than door to door driving, unless you drive on an authbahn.
 

Bigshu

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The transition from hover to forward flight was figured in 50's, but what wasn't figured yet, is how to fly in both modes as efficient as possible. A VTOL capable of transition is a compromise. It has much more disk loading than similarly sized helicopter, so power for hovering it's much higher. In cruise mode the large rotors and large engines (sized for hovering not efficient cruising) are an impediment for high speed performance.

There are 4 basic forces acting on an aircraft: weight(W), opposed by lift(L); drag(D) opposed by thrust(T). Flying straight and level, at constant speed, L = W, and T=D. An important parameter for an aircraft is the L/D ratio (or glide ratio). This is true for all heavier than air aircraft, airplanes, helicopters, VTOL, whatever. A fixed wing aircraft, a general aviation airplane as Cessna 172 has a cruise L/D of about 10, that means it's propeller needs to generate a thrust force that is only one tenth of the airplane weight. The engine and propellers are basically sized to deliver that thrust effectively. To design a comparable VTOL, you'll need to up-size the rotor and engine to generate a thrust value of at least 10 times more. Needles to say that the performance in cruise is taking a big hit with such a large engine and rotor.



The Ryan VZ-3 Vertiplane, was a proof-of-concept experimental aircraft using blown flaps to achieve a short or near vertical take-off. From the test data I read, the designers were happy to achieve 80% of downward thrust using the flaps, 20% lost in various flow effects. The experiment was considered a success, in the sense that proved that not tilting the rotors downward (as in tilt-rotors) would not achieve 100% thrust, so next efforts were on tilt-wings and tilt-rotors.

Tilt-wings and tilt-rotors are also not achieving 100% thrust from their rotors. As the wings and fuselage is in the rotor's slipstream, wing and fuselage flow interactions create impingement and fountain-flow that reduces lift by 5-10%, a much larger effect than what is experienced by helicopters, due to the higher slipstream velocities of tilt-wings/rotors.
Check out the Doak 16. I don't know of any rotor or propeller that's 100% efficient. They all lose something to slippage or interaction with the air frame, etc. The point isn't always efficiency in one mode, but that both modes are actually possible in one vehicle. I'll take some inefficiency in hover mode, to get a decent forward cruising speed. Tilt rotors are in service now, and there were lots of different companies looking at it way back when. The criteria they were using back then to gauge success, or commercial viability might be different in the age of drones and multicopters.
 

Bigshu

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The transition from hover to forward flight was figured in 50's, but what wasn't figured yet, is how to fly in both modes as efficient as possible. A VTOL capable of transition is a compromise. It has much more disk loading than similarly sized helicopter, so power for hovering it's much higher. In cruise mode the large rotors and large engines (sized for hovering not efficient cruising) are an impediment for high speed performance.
Even given that, we're talking about a vehicle that can perform near or actual VTOl, that can also cruise around at or above the LSA speed limit. I couldn't care less about the effieciency or disk loading if the plane can actually do that. Think of the impact on personal transportation if decent cruise and VTOL capability are merged. Why do you think the black fly and drone area were such big hits at Oshkosh the last few years? It's because VTOL is a game changer for light aircraft. It's coming, we just need to make sure it doesn't cut the pilot out of the loop.
 

Bigshu

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The proof that VTOL capability is the holy grail is that the fastest growing segment in light homebulit aircraft is STOL capable airframes. I was just at the Zenith homecoming, and talked to Sebastion Heinz about when we could expect progress on the SAM lsa. He said it's on the back burner because they are laser focused on providing and improving the 700 series STOL capable kits. That's what people are buying, CH750's, Bearhawks, Carbon Cubs, etc. They buy them not for speed, but to get in and out of tight fields (or sandbars, of whatever). Multirotors do that even better than STOL airframes, so expect it in our lifetimes. The latest update on the LSA rules is definitely going to include electric propulsion (per the FAA), so expect the near future to be filled with short range medium speed VTOL capable designs. Just as an aside, can you imagine how popular a ducted fan Carbon Cub would be? Land on a dime and enjoy low and slow aviating in between landing spots.
 

akwrencher

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I don't know where you fly out of, but my airport is an eight minute drive, there's no security beyond a badge operated door or ramp gate, pre-flight and fly to destination city, then some form of ground transport to final destination. The drive to the airport and drive from the airport plus the flight time is bound to be less than door to door driving, unless you drive on an authbahn.
The way I read this was comparing flying commercial vs driving.
 

pictsidhe

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The proof that VTOL capability is the holy grail is that the fastest growing segment in light homebulit aircraft is STOL capable airframes. I was just at the Zenith homecoming, and talked to Sebastion Heinz about when we could expect progress on the SAM lsa. He said it's on the back burner because they are laser focused on providing and improving the 700 series STOL capable kits. That's what people are buying, CH750's, Bearhawks, Carbon Cubs, etc. They buy them not for speed, but to get in and out of tight fields (or sandbars, of seewhatever). Multirotors do that even better than STOL airframes, so expect it in our lifetimes. The latest update on the LSA rules is definitely going to include electric propulsion (per the FAA), so expect the near future to be filled with short range medium speed VTOL capable designs. Just as an aside, can you imagine how popular a ducted fan Carbon Cub would be? Land on a dime and enjoy low and slow aviating in between landing spots.
The Holy Grail, huh?

 

Bigshu

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The way I read this was comparing flying commercial vs driving.
I realized that after I replied, I didn't get why you'd compare commercial flight in this instance, we're talking about more small, municipal airports, not fewer large commercial airports.
 

BBerson

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I've only flown a helicopter once, but I did do a cut power autorotation from a 6 foot hover, not sure you can get much lower or slower than that. So I guess that "helicopter auto-rotation - if you're low and slow, the energy is not available for safe landing " is not a universally true statement.

I'm a fixed wing pilot, so I'm not sure if that's generally true, but the helicopter I flew (MD-520N) could autorotate when low and slow.
It isn't autorotation from a 6 foot hover. From 6 feet the pilot pulls up on the collective to use the last bit of rotor energy to land softy. Opposite of autorotation.
 

gtae07

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I don't know where you fly out of, but my airport is an eight minute drive,
If we could all be so lucky...

My parents live that close to their airport and it's wonderful. Taking shortcuts through the woods I can ride a bike to that airport just as fast as you can drive there. I was spoiled growing up.

Where I am now, I have a class C airport (with stupid high hangar rent and lots of security because we have a commercial terminal) about 20 minutes from the house. The nearest small airports are at least 45 minutes away. You don't break even on travel time till you hit about 250 miles.
 

Bigshu

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If we could all be so lucky...

My parents live that close to their airport and it's wonderful. Taking shortcuts through the woods I can ride a bike to that airport just as fast as you can drive there. I was spoiled growing up.

Where I am now, I have a class C airport (with stupid high hangar rent and lots of security because we have a commercial terminal) about 20 minutes from the house. The nearest small airports are at least 45 minutes away. You don't break even on travel time till you hit about 250 miles.
It gets better...The airport where I had my solo is across the river from the one I fly out of now. Side by side airports! They closed mine and turned it into a GM car plant. Talk about paving paradise. In my county, we have The downtown airport, and 3 smaller GA fields, KCI is in the next county over, but still less than 15 minutes to get to. The county south of mine has a couple of nice fields, and The airport down by the Garmin campus is good sized as well, even though its on the Kansas side,
 

Dusan

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Check out the Doak 16. I don't know of any rotor or propeller that's 100% efficient. They all lose something to slippage or interaction with the air frame, etc. The point isn't always efficiency in one mode, but that both modes are actually possible in one vehicle. I'll take some inefficiency in hover mode, to get a decent forward cruising speed. Tilt rotors are in service now, and there were lots of different companies looking at it way back when. The criteria they were using back then to gauge success, or commercial viability might be different in the age of drones and multicopters.
The rotors/propellers are not 100% efficient and cannot be. At most they are around 80-90%, but this is besides the point. The point is conflicting requirements for the driving parameters of cruise and hovering performance for any VTOL aircraft: L/D drives the performance for cruise and that means large wetted aspect ratio and small propeller size. Disk loading and no flow interference drives the hovering performance and that means large rotors and no wings.
 

Bigshu

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The rotors/propellers are not 100% efficient and cannot be. At most they are around 80-90%, but this is besides the point. The point is conflicting requirements for the driving parameters of cruise and hovering performance for any VTOL aircraft: L/D drives the performance for cruise and that means large wetted aspect ratio and small propeller size. Disk loading and no flow interference drives the hovering performance and that means large rotors and no wings.
Except that there have already been successful designs that have made the performance compromise. Theory is theory, but practice is what matters. "If you build it, they will come" is as true of technology as it is of baseball fields in a corn field.
 

Dusan

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If the performance numbers from the theory don't make sense, no amount of practice will fix it. There's this thing with aerodynamics theory predictions - usually it over-predicts performance as there are simplifying assumptions. So performance you got from the theory are an ideal limit that will never be achieved in practice.

Actually only 2 designs have evolved from historical 50's to 'life' to be real aircraft and those are military aircraft. I'm of course talking about the tilt rotor design - the V22- osprey, and the jet VTOL's the harrier and newer F-35, the military specification aspect to perform the mission are the reason of their success, the economic cost is secondary.

The civilian marked is driven by economics, and as long that the aircraft design compromises too much, it will never be a viable option. Some people believe that the electric propulsion solves the problem, because of high inherent efficiency of electric propulsion. Surely the high efficiency of electric propulsion helps a lot, but the overall efficiency of a system is the product of efficiencies of each part, and the part with lowest efficiency has the most weight on overall efficiency. For an electric VTOL, as for any aircraft in fact, that is the aerodynamics, so I believe that should be the focus of any designer.

As an example I will compare the hover performance of two aircraft:
Ehang 184
Configuration: 8 rotor multicopter
Rotors: 8 x 1.5m diameter (Area=14.13m2)
Motor/Engine: 8 x 13.25KW = 106KW (142hp)
Weight: 360Kg
Disk loading: 25.46Kg/m2

Heli-Sport CH-7
Configuration: Classic single rotor helicopter
Rotors: 1 rotor 2 bladed 6.2m (Area=30m2)
Motor/Engine: 1 × Rotax 914 , 84.6 kW (113.5 hp)
Weight (MTOW): 450 kg
Disk loading: 15Kg/m2

The Ehang 184 needs 26% more power than the CH-7, even that the Ehang 184 having 20% lower weight. This is because the aerodynamics for hovering is much better on the CH, having lower disk loading, and higher Reynolds numbers.
 
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