Tracking Progress to Air Taxis

Advanced Air Mobility (AAM) is defined by NASA as “an air transportation system that moves people and cargo between places previously not served or underserved by aviation – local, regional, intraregional, urban – using revolutionary new aircraft that are only just now becoming possible.

SMG tracks hundreds of advanced drone, eVTOL and air taxi companies and startups in an Advanced Air Mobility Reality Index (ARI).

The ARI helps assess the industry entrants’ progress toward the delivery of a certified product at mass-scale production.

SOURCES- AAMRealityIndex
Written By Brian Wang,

12 thoughts on “Tracking Progress to Air Taxis”

  1. Mass, mostly. 

    Things in-the-air scale terribly with increasing payload. Basically, one has to make an airframe not just strong enough to support the mass of everything, but to support itself, and the larger-in-turn powerplant, larger props, and and and and….

    Also they become progressively more noisy. Just imagine a big ol' military grade 2 rotor people mover. This is not the airport friendly thing you are going to take to downtown SF to drop off a few well heeled CEO customers on one of the 5 or 6 available helipads.  WAY too large for that.  

    That's basically the conundrum.
    mass raised to some power.  

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  2. It seems at least some of the UAM groups that are at least considering non-battery only approaches are looking at diesel or Jet-A powered generators (except for the hydrogen fuel cell diehards). There are a few aviation diesels available now in the light plane category that may be suitable, and there have been interesting advances in compact motor/generators that may be suitable. Honeywell is a big player in the aviation APU market, and typically uses microturbines for that application. They had a fully built prototype 1MW compact generator they were gonna pair with a big turbine for their DARPA LightningStrike demo program, before that got cut off at the knees at the full scale demonstrator stage unfortunately.

    With a distributed electric propulsion approach fed by a generator and boosted by batteries for the VTOL work, you get a decent setup in theory. The quadplane format is well suited for this (using 4 VTOL rotors that get feathered/stowed and a regular propeller for forward flight), especially with a gas turbine for the generator, as the jet exhaust can help forward flight if you had variable turbine bypass.

  3. While I ⊕1'd you and Dr. Pat, I think the real answer is '3 meter clearance' (above ground level) is the only hopeful answer.  

    Solves a lot of problems too. Problems of motor-loss instabilities, with maintaining a more-or-less vertical orientation in wind; it significantly lowers the center-of-gravity, well above the axis of lift. Intrinsically stable.  

    3 m clearance allows complete morons to spring out of the craft while the rotors are still rotating.  In the real world, door-interlocks would prevent exit while they're rotating. And with modern DC phase-shift tech, the rotors would stop in a handful of seconds.  Active braking, and all that.  

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  4. Dunno. 
    My Greek friend asked if that was a self-making sandwich… ouch.

    Basically, since the word 'hybrid' is BIG (in, hip, OK, talkable, no-downside) then in my humble opinion, the only only solution is one that capitalizes on the 3 kWh/kg ( minus all the motors and shît ) energy density of diesel fuel. A very small diesel turbojet generator, batteries, motors. The most powerful turbojet generator I saw was about 100 kW in a 50 kg package.  Not bad, not bad.  

    The plastic gas tank for 100ℓ might weigh in at 15 kg. The fuel, 85 kg.  

    That at least gives about 250 kWh of electricity in a similar 200 kg 'battery mass' solution (see my analysis below), but with 6× the entrained energy reserve. Lemme tell you, having a (6 × ½ hr) or 3 hour aloft energy store is WAY more attractive.  

    Moreover, the hybrid approach 'recharges' at over 25ℓ/min or 4 minutes, all up. Doesn't require a charging infrastructure, right? And since it is 'hybrid', all the greenies will be amused. 

    At least if I were the CEO of a company actually trying to make a serviceable air-taxi, this'd be the approach I would have the engineers follow.  There isn't a battery technology anywhere near commercial on this mass scale. 

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    ⋅-=≡ GoatGuy ✓ ≡=-⋅

  5. Yep… to paraphrase, "then there's the noise".  

    I can't reduce this to anything practical less than

    100 kg occupant
    + 25 kg of parachutes, protective stuff
    + 15 kg of seat, belts, 
    + landing doohickey (shocks, struts)
    + 200 kg of batteries (40–50 kWh)
    + ??? kg of motors, rotors, electronics, 
    + an airframe capable of holding all this shît, along with cowlings, sheeting
    + FAA certification

    Well that last bit not technically part of the mass. But I don't see a way to lighten the overall thing from what, 500+ kg at takeoff or landing. 

    500 kg × 9.81 N/kg ≈ 4900 N of lift. Moving air (1.27 kg/m³) at 25 m/s (55 mph) from the above physics is

    № 1.2a: F = mΔv
    № 1.2b: 4900 = 20 m
    № 1.2c: Vol = ( m ≈ 250 kg/s ) ÷ 1.27 kg/m³
    № 1.2d: Vol = 200 m³/sec

    № 2.1: Area = Vol / rate
    № 2.2: Area = 200 ÷ 20
    № 2.3: Area = 10 m²

    № 3.1: P = ( Ek = ½mv² ) ÷ 1 sec
    № 3.2: P = ½ × 250 × ( 20² → 400 )
    № 3.3: P = 50,000 W

    Of course, with vortexes, noise, heating, turbulence, motor inefficienceis, propwash and the rest, its VERY likely to be closer to 75,000 W. Our 40 kWh or 40,000 Wh battery at 90% discharge is going to give ½ hr of flight time. 

    See? IT IS DO-ABLE!
    No pilot.

    Basically needs way lighter batteries.
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    ⋅-=≡ GoatGuy ✓ ≡=-⋅

  6. Not physics, but basic sociology indicates that nobody else will be upset by the culling of the sort of people who walk around taking selfies.

  7. Can the physics determine if I'll be OK if I walk into those naked propellers while taking a selfie and not paying attention?

  8. For a semi-modern take on superSTOL aircraft, looking at what Boeing was working on for the Frog ATT is a good starter point.

  9. Rotor size is a core issue, as that defines all sorts of parameters, such as the landing pad size, and the amount of air blast. There's the added headache that just making rotors larger is not an immediate win for tilting propulsion systems, as forward flight ups the RPM's so high that you risk making the rotor (now propeller) tips supersonic. Allegedly variable length rotors have been researched, but no full size prototypes recently.

    The only semi-decent workaround seems to be autogyro systems, but they have their own headaches as well. The rotor is unpowered during forward flight so that cuts down on the power needed, but they also need a fairly big rotor, and can't launch on a pinpoint landing pad (needing to roll a bit to get up to speed), and while than can do vertical landings, you can't easily recover from a botched landing if pure vertical (preferring a rolling landing).

  10. eVTOL designs optimize rotors for low power consumption @ hover, but cruise leg range/payload/speed suffer horribly (hence eVTOLs w/wings & axial props). Another option is optimize for cruise and instead use some STOL variation (e.g. ASTOVL, SSTOL, ESTOL, STOL) which basically trade vertical for short horizontal takeoff & landing balanced field lengths. Even at SSTOL conditions (say rotate @ 200', then over a 50' obstacle w/single engine/lift-post out by 300'), this mayconsume more than 5X LESS energy (thus less cost). These can also have very low fan pressure ratios, thus low exit velocity (large mass flow), to make them MUCH quieter than a comparable eVTOL needing 5X more power (translating to noise, which bedroom communities will legislate against). Check this out …

  11. So… a refresher for anyone kind of intersted in the physics of LIFT and flight. 

    № 1.1: Ek = ½mv² … and

    № 1.2a: F = m Δv/Δt with Δt = 1 sec becomes 
    № 1.2b: F ≈ mΔv

    [1.1] sez that the kinetic energy contained in a moving mass is related to the square of its relative velocity. The [1.2b] equation says that we cannot expect to get more force from an accelerated mass than 'mΔv'.  

    To lift a helicopter, quadracopter, airplane (or boat, space ship!) requires accelerating a mass of stuff, be it air, water or rocket fuels to a higher velocity by PUSHING on it. For every ACTION is an equal-and-opposite REACTION: a gun has recoil 'cuz it pushes the bullet out the front end. Rockets, boats, bullets, and yep… aircraft. 

    I looked up ALL of the STOL aircraft listed in the article, and sure enough … they're all converging on the same problem. [1.1], the energy problem. 

    Take [1.1 and 1.2b] and put 'em together:

    № 1.3a: Ek = ½ FΔv and invert that
    № 1.3b: F = 2Ek/ Δv

    Ek is a proxy for power, so for a given power, lift force is REDUCED with greater downward 'wind' speed. Moving more air more slowly, delivers same lift at reduced power.  

    Hence why conventional helicopters have such large rotors.  
    Maximum air, minimum velocity.  

    This I believe is the crux of the whole air-taxi problem.  
    In a nutshell. 

    ⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
    ⋅-=≡ GoatGuy ✓ ≡=-⋅

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