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A vertical take-off and landing (VTOL) aircraft is one that can hover, take off, and land vertically. We have several military fighter jets, which can takeoff and land vertically (like the Harrier Jump Jet).

Would it be possible to design an airliner (for example as big as a A320 carrying over a hundred people and travelling at 0.85 mach) to perform VTOL?

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  • $\begingroup$ If your plane as big as an A320 is only carrying 100 people, it is doomed. An actual A320 carries 150-190 people, so you're talking about something that's much more expensive to run than a conventional plane but only earls 50-65% of the revenue. $\endgroup$ – David Richerby Apr 19 '17 at 9:25
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The closest to what you ask was maybe the Do-31 experimental VTOL transport.

Dornier Do-31 in hover

Dornier Do-31 in hover. Picture Source

It was developed to fly supplies to VTOL fighter bases. Makes no sense to have a VTOL fighter fleet if you cannot supply them, right? That was what the Do-31 was for, and the technically successful program folded when NATO abandoned the VTOL strategy in the Sixties.

Compared to regional airliners of its time, the table below shows how much the installation of sufficient thrust has cut performance:

Performance comparison between Do-31 and F-28

I used the Fokker F-28 for comparison, because it is of similar size and age. As you can see, VTOL easily costs half the payload. 36 fully equipped troops may weigh more than 36 passengers, but they will sit on much lighter seats and have much more frugal accommodations. Note that I used the reduced take-off mass for VTOL flight, but have no information if that mass would have included the full payload. The range is valid only for the higher maximum take-off mass of 24.5 tons, for which a conventional take-off was necessary.

The Do-31 could have fitted the Belgian airline SABENA, which at the time (the Fifties and Sixities of the last century) had the most advanced VTOL strategy of all airlines. They operated regional connections with helicopters, but eventually reverted to regular aircraft well before the Do-31 would had been available. Heli-Air Monaco is still in operation after almost 40 years, but this is more a taxi service than an airline.

Considering not only the increased fuel consumption, but also the increased maintenance cost on more and diverse engines (most VTOL airplanes have dedicated lift engines), the operating cost even at the times of cheap fuel were too high to make the convenience worth it.

I think it is possible to develop a VTOL A320, but it would look very different, would cruise at a lower speed and have a much reduced payload and range. Tickets would be horrendously expensive, though.


EDIT: Thanks to @egid for his suggestion to use mass fractions for comparison. Unfortunately, I found detailed mass data of the F-28 only for a later version, but the expanded table shows the point clearly:

enter image description here

The useful load fraction is the result of dividing the difference between take-off mass and operating mass empty by the take-off mass, showing the sum of payload and fuel as a fraction of take-off mass. Adding lift engines, slow-speed controls and a rear loading ramp clearly reduced what could be carried in VTOL flight.

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  • $\begingroup$ Your comparison is pretty good but the mtow seems drastically different. Is it that surprising that payload is smaller? What about payload as a fraction of mtow? $\endgroup$ – egid Jun 27 '15 at 22:26
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    $\begingroup$ @egid: The best I have is payload+fuel as a fraction of MTOW, but you're right, this helps. $\endgroup$ – Peter Kämpf Jun 28 '15 at 4:32
  • $\begingroup$ Nice, definitely still helps. $\endgroup$ – egid Jun 28 '15 at 16:19
  • $\begingroup$ Another factor not mentioned is the far higher maintenance cost of the VTOL aircraft (more engines and moving parts) and higher fuel cost. Thus the operating cost per passenger/mile is even more out of whack with conventional aircraft than the numbers based purely on number of passengers and range would suggest. $\endgroup$ – jwenting Jun 29 '15 at 6:26
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    $\begingroup$ The V-22 Osprey is similar: 32 troops, MTOW 27.4 tons, useful load fraction 12.4/27.4 = 0.4526, range 1600 km, but cruise speed only 446 km/h. $\endgroup$ – MSalters Jul 1 '15 at 11:48
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A big part of making an aircraft that can take off and land vertically is the thrust to weight ratio has to be greater than 1 so that it can work against the force of gravity. The Harrier Jump Jet can only take off vertically when it isn't loaded to full capacity (in which case STOL is used).

For a commercial airliner to perform VTOL, taking the A320 as an example, it would require more than 765 kN of thrust, which is 3.2 times the thrust it currently has. Such engineering is infeasible with current technology.

  • Maximum A320 mass is 78 tonnes, so the weight is ~765 kN.
  • The two CFM56-5B4's produce 240 kN.
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  • $\begingroup$ Since the duration needed is relatively short you probably could use rocket engines which have better thrust to mass ratio without the mass of fuel burying you. Especially since you'd only need the lift near the ground. Obviously it wouldn't make any sense, though. Using runways is much cheaper and you'd never get permission to fly passengers with such a contraption. Rocket fuels being dangerous almost by necessity and all. Then again the VTOL version of F-35 doesn't make any sense to me either, so what do I know... $\endgroup$ – Ville Niemi Jun 27 '15 at 2:44

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