[handsofsteel]

Originally Posted by THE-U-

The AAMs are completely different than V22s due to the wonders of electric propulsion and extreme redundancies. Several companies have flown their AAM prototypes for thousands of miles even autonomously. Below is an example from Wisk (Boeing JV):

https://www.Youtube.com/watch?v=LmkKydWRpZU


I am sure with Mahindra's financial backing, ePlane will be able to get certified in short order. If I recall correctly, they already have test flown their prototypes.

Apologies for the misunderstanding, if any. I was not commenting on the AAMs at all, but digressing and commenting on the V22 Osprey. Just a random and useless fact that came into my mind when I came across this discussion.

[anandhsub]

Initially when I read the news article and the opening post, I thought it was the company M&M or Anand Mahindra himself who is investing in eplanes.

But it looks like he is just more of a chief guest who unveiled the prototype and has nothing to do with the start up.

Very unlikely this reached production stage, let alone retail sales.

[Mystic]

This is nothing but a drone. Even if it is a success as a machine that can fly with humans, it will not work in India yet.

I recently saw a movie “Eye in the Sky” which was very realistic even though it is a fiction ( may be technology does exist and being used at military level. It is a matter of time it is used for civilian purposes ).

In Bangalore it takes 2 hours to commute from electronics city to international airport ( air taxi costs are Rs 3000 per person with only cabin baggage .The checked in baggage comes by road ). This air taxi service was not a success. May be India need to learn from other cities abroad where it is successful for air taxis using proper helicopters which can be extended to drones.

Some countries have haphazard unscientific growth of cities and air taxi is the only saviour for getting to the airport in time with traffic chaos. In Dhaka, Bangladesh for example they have a jugaad way of going to the airport by hiring ambulances to reach in time.

[THE-U-]

Originally Posted by Mystic

In Bangalore it takes 2 hours to commute from electronics city to international airport ( air taxi costs are Rs 3000 per person with only cabin baggage .The checked in baggage comes by road ). This air taxi service was not a success. May be India need to learn from other cities abroad where it is successful for air taxis using proper helicopters which can be extended to drones.

Isn't that amazing though? Rs. 3000 for a helicopter ride from the airport to where ever you want to go in the city in 15 or 20 minutes? I have been paying Rs 2800 one way for the airport pickup by a hotel situated near MG Road. Even Uber charges more than Rs. 1500 for bigger cars. Not only my checked bag gets delayed, I also get stuck in the car for 90 minutes when I go by road to the hotel from the airport. I needed to join a teleconference one day, and I couldn't do it in the hotel car as the jostling and ambient noise in the car caused so much disturbance. I was the only passenger in the car. So, Rs. 3000 for an air taxi is a steal and it will only get cheaper if pilotless flying becomes popular. They could land the AAM vehicle on the roof top of the hotel if the hotel would construct a vertiport there!

On your other note about Drones, as I mentioned earlier, the ICAO nomenclature for air taxis is Advanced Air Mobility (AAM). Drones are always remotely piloted and that is why they are called RPAS. If I recall correctly, ICAO has just approved the RPAS standards and recommended practice (SARP). They are still working through what they need to do for AAMs.

[Mystic]

Originally Posted by THE-U-

On your other note about Drones, as I mentioned earlier, the ICAO nomenclature for air taxis is Advanced Air Mobility (AAM). Drones are always remotely piloted and that is why they are called RPAS. If I recall correctly, ICAO has just approved the RPAS standards and recommended practice (SARP). They are still working through what they need to do for AAMs.

Thanks for the info. I am worried about the chaos the autonomous cars are creating on the ground in SFO with a gridlock etc and just imagine such a light flying machine up in the air especially in a situation like yesterday’s dust storm in Mumbai. I think the light air taxi will go to another dimension like in Bermuda Triangle ( just kidding ). I sincerely hope the technology would be made such that the light air taxis would be safe in all conditions.

[V.Narayan]

Originally Posted by THE-U-

The AAMs are completely different than V22s due to the wonders of electric propulsion and extreme redundancies. Several companies have flown their AAM prototypes for thousands of miles even autonomously.
I am sure with Mahindra's financial backing, ePlane will be able to get certified in short order. If I recall correctly, they already have test flown their prototypes.

Dear @ THE-U-

Thank you for sharing the video which I'm sure readers will find interesting.


Dear All,

For the benefit of readers from outside the aviation community AAM stands for Advanced Air Mobility. This is a new name given to light vertical take off flying devices that have a small footprint, good slow speed manouverability and can carry small payloads in the 100 to 250 kgs class. Something will come of it one day. But....

....the attempt is being made to make these green in both energy source and noise. Here the whole story hits physics - those inalterable laws of the universe. Fuel vs Li batteries are still a ~50X gap. In a car that matters less. in an aircraft it is a challenge of an altogether different dimension. In flying every ounce of weight and drag is a severe penalty. In the video above in post there are separate 12 rotors for lift and one pusher prop for forward thrust. Those 12 rotors are a weight and drag penalty for most of the flight. A single engine for light & thrust as against separate engines for lift & thrust is the reason that the F-35B and the Harrier {referred to by @HandsofSteel} are a success and every other jet fighter attempting VTOL was a failure - Yakolev Yak-38, Dassault Mirage IIIV, Dassault Balzac. Same story with every aircraft with tilting rotors - V-22 Osprey, Hiller X-18, Dornier Do 31, Canadair CL-84, etc.

Till they solve for the energy density, IMHO, payload-cost-range-speed economic will simply not work out. But who knows I could be wrong.

Making a demonstrator prototype is one baby step. To make the payload-range economics work in real life is another whole giant step away. And to get all of this air worthy certified by a flight safety regulator is another dimension away. My best wishes to Anand Mahindra and Indigo. I for one would not bet on it.

Also, how many volunteers to fly in a pilotless machine?

[THE-U-]

Originally Posted by V.Narayan

For the benefit of readers from outside the aviation community AAM stands for Advanced Air Mobility. This is a new name given to light vertical take off flying devices that have a small footprint, good slow speed manouverability and can carry small payloads in the 100 to 250 kgs class. Something will come of it one day. But....

As we tend to be very precise in aviation, the eVTOLs are a sub-class of AAM. There are fixed wing AAMs that are under development that use "runways" too. The FAA defines AAM as "likely electric and autonomous". Some regulators like the FAA are choosing the AAM to be piloted as a first step when all the other ecosystem elements are being refined, but other regulators like CAAC have already certified fully autonomous operations.

So, the technology is here already. EASA has published their certification requirements a while ago. FAA is taking a different approach given the unique characteristics of each AAM aircraft and so the certification basis is tailored to each aircraft.

The FAA is on course to publish a final set of "Special Federal Aviation Regulations" later this year for the operation of these aircraft including pilot training and certification (a draft for published late last year for comments from everyone). Several documents are available online on the design requirements for vertiports and associated infrastructure.

Originally Posted by V.Narayan

....the attempt is being made to make these green in both energy source and noise. Here the whole story hits physics - those inalterable laws of the universe. Fuel vs Li batteries are still a ~50X gap. In a car that matters less. in an aircraft it is a challenge of an altogether different dimension. In flying every ounce of weight and drag is a severe penalty. In the video above in post there are separate 12 rotors for lift and one pusher prop for forward thrust. Those 12 rotors are a weight and drag penalty for most of the flight. A single engine for light & thrust as against separate engines for lift & thrust is the reason that the F-35B and the Harrier {referred to by @HandsofSteel} are a success and every other jet fighter attempting VTOL was a failure - Yakolev Yak-38, Dassault Mirage IIIV, Dassault Balzac. Same story with every aircraft with tilting rotors - V-22 Osprey, Hiller X-18, Dornier Do 31, Canadair CL-84, etc.

Till they solve for the energy density, IMHO, payload-cost-range-speed economic will simply not work out. But who knows I could be wrong.

The energy density is the reason why all eVTOLs are short range, short endurance and with limited payloads. The physics has all been worked out in this space. If one wants to go long distances and carry a lot more cargo, then of course gas turbine based motors are the way to go. There was a Master's thesis from Embry Riddle Aeronautical University, Daytona Beach a few years ago that addressed this whole issue and the design space for electric aircraft.

It also is well known that electric motors can produce enormous torque at low rpms. So, the props can produce the same thrust/ lift at a much lower rpm than conventional engines (be it gas turbine or IC). Because of this, the noise issue associated with helicopters has also been mostly solved. Joby Aviation had done a demonstration in New York City in 2023 and people couldn't believe how quiet the aircraft was. As long as the electricity is green, we have green aircraft doing short flights with as many as six people.

Engineers have also been pointing out that the electric trainer aircraft with two seats are fully viable. But, once the size and payload increase, then one would need to go to liquid powered aircraft for the reasons you mentioned. There haven been integrated plans in the USA as outlined nicely in the below webpage (might be a bit outdated since it goes only until mid-2023).

https://www.faa.gov/air-taxis

Originally Posted by V.Narayan

Making a demonstrator prototype is one baby step. To make the payload-range economics work in real life is another whole giant step away. And to get all of this air worthy certified by a flight safety regulator is another dimension away. My best wishes to Anand Mahindra and Indigo. I for one would not bet on it.

Also, how many volunteers to fly in a pilotless machine?

I think the industry recognizes that the economical aspects will be hard with a pilot on board. But, once they get to autonomous flying, they seem to think they can fly anywhere within a metroplex for what Uber Black charges. This is why companies like Boeing's JV Wisk want to start with full autonomous flying although the FAA's first phase in their "crawl, walk, run" is only focused on piloted aircraft and VFR operations with a max altitude of 4000ft. Wisk says their aircraft can be fully charged in 15 minutes. Amazing isn't it?

Given that the majority of accidents are due to human error including those of pilots, autonomous flying is going to end up more safe in my opinion. This is different than on-road automous driving. The four-dimensional (x,y,z and t) flying doesn't have as many constraints (within reason) as three dimensional driving (x,y and t). The US is also seem to be focused on safely scaling up these operations in the future.

I think many esteemed folks on team-bhp are technically inclined and would appreciate this information!

[WD-42]

Originally Posted by V.Narayan

Fuel vs Li batteries are still a ~50X gap. In a car that matters less. in an aircraft it is a challenge of an altogether different dimension.

In flying every ounce of weight and drag is a severe penalty. In the video above in post there are separate 12 rotors for lift and one pusher prop for forward thrust. Those 12 rotors are a weight and drag penalty for most of the flight.

Not just energy density but power density too.

Power required for hover in VTOL craft is inversely proportional to the square root of the disc loading (thrust/area of rotor). Which means larger the area of the rotor lower the power you need.

Theoretically at MTOW a 640kg Lillium jet prototype with 36 rotors (EDFs) needs ~7x the power of a 620kg Robinson R-22 helicopter with a single large rotor just to take off. In practice it's around 3.6x.

These multicopter's were initially used by the likes of DJI for three reasons:

1. ~17 years ago when DJI was getting started power density of the inital motors used was low, so you needed 4 of them for lift
2. Control systems are much easier since can achieve everything by just controling the RPM of the motors differentially
3. Mechanicals were easy, no need for a swash plate etc.

It makes no sense to do that on larger rotorcraft neither from a design standpoint, nor an economic standpoint.

Originally Posted by THE-U-

It also is well known that electric motors can produce enormous torque at low rpms. So, the props can produce the same thrust/ lift at a much lower rpm than conventional engines (be it gas turbine or IC). Because of this, the noise issue associated with helicopters has also been mostly solved.

I'm sorry, what now? This doesn't make sense.
You would need high torque only if the rotors were heavy and hard to move.

Thrust is a function of change in the momentum of air passing through the blades. You either push more mass or a smaller mass faster.

• If the blades have a smaller radius (smaller blades) like these AAMs all do then you need higher RPMs and consequently higher power not higher torque.
• If the blades have a larger radius (longer blades) like helicopters, then you can get away with lower RPMs, and trade off power for torque.

So ideally you would use electric motors for helos, not for multi-copter style AAMs.

Originally Posted by THE-U-

This is why companies like Boeing's JV Wisk want to start with full autonomous flying although the FAA's first phase

I'm sure you are aware that Wisk was offloaded on Boeing by Kitty Hawk right? Sebastian Thrun has publicly stated that it is very hard to make UAMs a profitable proposition.
________________

I do hope the FAA and EASA take the certification aspect very seriously and don't delegate it to DERs like the FAA did and we end up in a Boeing like fiasco sitation.
________________

One of the biggest annoyances of this I would like to highlight is the noise.

One of the retail quick commerce companies was testing a 5min drone delivery to home and was flying that over my house to their test drop point every few minutes. The buzzing noise drove me mad so much that I drove to their base and gave them an earful.

As if dealing with the constant traffic noise on the streets wasn't enough for those of us living in cities, we will now have to deal with noise from above too.

[THE-U-]

Originally Posted by WD-42

It makes no sense to do that on larger rotorcraft neither from a design standpoint, nor an economic standpoint.

You are comparing drones to Advanced Air Mobility. Drones were toys before we got smart about them. We are past the point of talking about AAM viability. These technologies have been proven to be viable. As noted earlier, helicopter air taxies are operating in Bengaluru right now and they used to operate in New York and LA from 1950s to 1970s if I recall correctly. The Bengaluru operator is a subsidiary of a US company.

Also, the design space for electric propulsion is well understood. I am sure many of these AAM companies have performed advanced calculations - the ERAU thesis I mentioned is available publicly and lists all the battery technologies based on energy density vs weight/ volume compared to the liquid jet fuel and hydrogen (IIRC).

Originally Posted by WD-42

I'm sorry, what now? This doesn't make sense.
You would need high torque only if the rotors were heavy and hard to move.

Thrust is a function of change in the momentum of air passing through the blades. You either push more mass or a smaller mass faster.

• If the blades have a smaller radius (smaller blades) like these AAMs all do then you need higher RPMs and consequently higher power not higher torque.
• If the blades have a larger radius (longer blades) like helicopters, then you can get away with lower RPMs, and trade off power for torque.

So ideally you would use electric motors for helos, not for multi-copter style AAMs.

Follow through what you wrote and consider the weight of the aircraft, number of propellers, pitch of the propellers and other factors that determine the angle of attack. At equivalent low rpm, gas turbine/ IC engines will not be able to sustain combustion and will stall. A correctly designed electric motor on the other hand can produce enough torque to keep the props moving at a very low rpm. This is the fundamental difference. The rotary wings of helicopters actually run at a much higher rpm causing terrible noise issues. Not the case with AAMs. But, for the range, endurance and payload a helicopter provides, liquid fuel is the only option - not batteries.

Originally Posted by WD-42

I'm sure you are aware that Wisk was offloaded on Boeing by Kitty Hawk right? Sebastian Thrun has publicly stated that it is very hard to make UAMs a profitable proposition.
________________

I do hope the FAA and EASA take the certification aspect very seriously and don't delegate it to DERs like the FAA did and we end up in a Boeing like fiasco sitation.
________________

All these issues are irrelevant to the discussion. Many of the US based AAM manufactures have deep pockets behind them as many of the established companies also want to diversify and invest in up and coming technologies. Surely, some of these start ups will go out of business. I hear there are more than 30 different companies with different types of AAM designs trying to bring them to market. There will obviously be consolidation in the near future.

Originally Posted by WD-42

One of the biggest annoyances of this I would like to highlight is the noise.

As if dealing with the constant traffic noise on the streets wasn't enough for those of us living in cities, we will now have to deal with noise from above too.

Remember, there was no need to certify drones- they were only approved for VLOS (Visual Line of Sight) operations first. Now, everyone is clamoring for BVLOS (Beyond VLOS) operations. Even with drones, I am told the fixed wing Zipline drone was very quiet and one doesn't hear it approaching and dropping off the package.

Several people live under departure paths of large aircraft in many urban areas and they have to put up with much higher level of noise than what these AAMs are going for. There are already noise regulations at the ICAO level and I am sure there are discussions to fine tune these regulations for AAMs. Either way, I have no skin in the game here - but expect the AAMs to be much quieter based on what I know from the technologies.

[WD-42]

Originally Posted by THE-U-

We are past the point of talking about AAM viability. These technologies have been proven to be viable.

Sure...

• Do we know the mTBO for these motors?
• Do we know the reliability of these?
• Can an A&P mechanic service these?
• Can they auto-rotate and land safely in case of a power failure? Single motor out trim cases, can they still land safely?
• How do they handle rain, gusts, wind shear? What about inadvertant entry into IFR? What about (de)icing in electric motors and batteries?
• How do they handle bird strikes?
• How do they handle landing between tall buildings (venturi effect of wind)?
• How do they handle landing between high tension cables in a city i.e. visual identification systems?
• Can the airframe handle the number of cycles? Joby is predicting a 10 year life with 13000 cycles per year! No aircraft today does 13000 cycles per year and then does that over 10 years.
• What about ATC?
• What about collision avoidance, terrain avoidance?
• What about TCAS implementation in such a crowded airspace?
• Are they going to have ATS-B style transponders or something new in dense airspace, how does that work?
• Who will operate the ATC network in a city, the "cab company", the government, the local muncipality?
• What about radio operations in such a crowded airspace, do radios even make sense?
• What about human factors? In order to stay profitable Joby, Lillium etc. expect to do 35-50 flights/day. Will pilots be under pressure to complete trips like our Uber Ola drivers today? Do they have targets of number of trips to complete for their incentives? What happens to safety then?
• Are pilots going to be limited to 8 hrs duty time, which means 3 shift pilots which increases the costs 3x unlike an Ola/Uber driver who does an 18 hour shift and sleeps in his cab.

None of these have been proven.

There's a vast chasm between them being technologically viable as prototypes with test pilots or unmanned prototypes and them being technologically viable for paying passengers, and being certified to Part 135/121 safety standard operations, which needs to be grasped.

They can be FAA/EASA certified for all that, but it remains to be seen whether those will pan out in real life.

There is no doubt that all of these questions will be answered over time. But that adds cost & complexity to the entire system. Throw in the cost for all of this and the cost will be nearly the same as a helo operation, maybe 25% lower, which isn't nearly enough to create an entirely new market.

Originally Posted by THE-U-

Follow through what you wrote and consider the weight of the aircraft, number of propellers, pitch of the propellers and other factors that determine the angle of attack. At equivalent low rpm, gas turbine/ IC engines will not be able to sustain combustion and will stall. A correctly designed electric motor on the other hand can produce enough torque to keep the props moving at a very low rpm. This is the fundamental difference.

Gearboxes, heard of them?
Given the power density of gas turbines and the energy density of dead dino-juice. The weight of the gearbox + fuel < weight of batteries.

Originally Posted by THE-U-

Even with drones, I am told the fixed wing Zipline drone was very quiet and one doesn't hear it approaching and dropping off the package.

Zipline is a fixed wing UAV AND has a propreitery rotor designed for noise reduction which none of the UAMs have.
____________

Originally Posted by THE-U-

As noted earlier, helicopter air taxies are operating in Bengaluru right now and they used to operate in New York and LA from 1950s to 1970s if I recall correctly. The Bengaluru operator is a subsidiary of a US company.

Yep, Blade, their Indian subsidiary is here.

From their own investor report:

AAMs are not that much more cost-efficient than a helo.
Also swap out that Bell 407 for even a Bell 206 suddenly you are approaching the CASM/RASM of an AAM.
So why hasn't Blade been running 206s or a similar cheaper helo all over Manhattan?


_____________

Let me reiterate my points clearly:

• Multi-rotors have a lower efficiency than a large single rotor.
• eVTOLs are less power efficient than helicopters.
• Multi rotor eVTOLs are consquently less economically efficient than helicopters => an unsexy electric helicopter would be more economical than the sexy multi-rotor eVTOLs today.
• The economics are questionable today.
• The operations scope is questionable today.
• While eVTOLs have an overall dB level lower than helos they their noise is mostly in the high frequency range (buzzing noise) which makes it more annoying than a low frequency noise of a large rotor.

[THE-U-]

Originally Posted by WD-42

Sure...[list]
Let me reiterate my points clearly:

• Multi-rotors have a lower efficiency than a large single rotor.
• eVTOLs are less power efficient than helicopters.
• Multi rotor eVTOLs are consquently less economically efficient than helicopters => an unsexy electric helicopter would be more economical than the sexy multi-rotor eVTOLs today.
• The economics are questionable today.
• The operations scope is questionable today.
• While eVTOLs have an overall dB level lower than helos they their noise is mostly in the high frequency range (buzzing noise) which makes it more annoying than a low frequency noise of a large rotor.

With all due respect, please read some of the materials that FAA has on the link I posted. You would see how operations are being specified to avoid some of the complex situations you are posing. Fundamentally, these aircraft are not going to land some place randomly like military helicopters – that is not the intent. Even chartered helicopters/ air taxis don’t land in random places. The AAMs need vertiports and other infrastructure as I posted in the very beginning (the ecosystem). I posted also about the upcoming FAA SFAR. Much of these are based on the current capabilities. On vehicle reliability, folks have already worked out the necessary system redundancies and that's why you see "cert basis" for these aircraft.

If you don’t want to accept that China’s CAAC has already certified an AAM type and those have begun operations in China, then consider the following. We are halfway through 2024 and are likely to have multiple certified AAMs by middle of next year by other authorities. You don't need to wait until then to know these technologies are already here and are viable (in a technical sense).

All other things being equal, your first bullet above is true (same fuel, similar technologies). Your second bullet is not true. The overall efficiency of thermal energy conversion (heat to mechanical) if it exceeds 60% it is a great achievement. Whereas, electricity to mechanical is upwards of 95% efficient (all things being equal). This is why even with all of the difficult manufacturing processes, life cycle impacts of electric cars (at similar capability, not comparing a Corolla to a high-performance Tesla) tend to be lower. Gear boxes tend to be heavy and at higher rpms, engines (either gas turbine or piston) tend to produce a lot of noise too. So, your hypothesis there is incorrect although it sounds good on paper.

It is also well known that rotary wing aircraft are terribly inefficient compared to fixed wing aircraft. This is where eVTOLs are making their case with the "wingborne" cruise phase that employs aerodynamic lift. So, it is not correct to say an eVTOL will be less efficient than a helicopter. I have no idea what the data Blade uses for "electric vertical". I already pointed out earlier, the economics of AAM operations are a little dicey with a pilot on board but will be much better when automated.

You are also mistaken in saying that the noise will be at a higher frequency - may be for a toy drone (I agree those are very annoying). All these AAMs are being designed not to be a noise nuisance (like zipline? ) because these companies like everyone else knows they cannot annoy people out of their homes if they want to survive as a viable urban transportation. Commercial helicopter operations are subject to extreme limitations over many of the US big cities due to noise.

Finally, I want to point to the history of Joby from their website- it contradicts many of your suppositions. They say “In partnership with NASA, we confirmed the revolutionary noise footprint of our aircraft, demonstrating it will blend into the existing soundscape of cities”. I am sure it is similar for other AAMs. As you can see, Joby has already received military certification and has sold their AAM to the US DoD. They should be receiving their civil certifications soon enough. They say they also have their Part 135 approval from the FAA already.

https://www.jobyaviation.com/about/

This is all from my end. Greetings to all the aviation nerds out there! Peace out.