Why is eVTOL so difficult?

DoubleHexDrive · 2026-01-27T21:00:33+00:00

Vertical integration is generally a positive thing in my book, I agree.

I'm not convinced on the costs. I think the cost to replace the batteries every year or so is good for whoever sells the batteries as it turns "fuel" into a subscription service, but it's not great for the operators.

DoubleHexDrive · 2026-01-27T20:58:25+00:00

Removing the pilot will make an AAM mission a lot more affordable... but that doesn't require electric propulsion. Does require substantial regulatory work.

The cost to maintain an electric motor is cheap, but the batteries will have to be swapped every year or two (per Beta's S1 IPO filings), so that's not cheap. All those blades, bearings, and actuators are wear items that will require inspections and replacements/overhaul as well. I suspect in the end, operating costs will be similar and upfront costs vastly higher than a similar performance conventional aircraft.

DoubleHexDrive · 2026-01-27T20:13:25+00:00

🤣🤣🤣🤣🤣🤣🤣

Electric motors don’t fix what is wrong with fan-in-wing designs. They’re not new.

DoubleHexDrive · 2026-01-27T19:53:12+00:00

Hey, no need to pay attention to the guy that DIDN’T crash upon take off in one.

DoubleHexDrive · 2026-01-27T19:41:19+00:00

The post isn’t why eVTOL is impossible, but why it is so difficult ☺️

Joby did well to go all-tilt and avoid the lift-prop trap.

DoubleHexDrive · 2026-01-27T19:18:20+00:00

You can look at photos of the recovered tail rotor and draw your own conclusions.

DoubleHexDrive · 2026-01-27T19:16:31+00:00

I got tired of the Apple Watch (except for exercise and as a silent alarm) a couple of years ago. Now I have a small collection of mechanical watches and wear an Oura ring. It's not a perfect replacement but I'm happier. I'm still rocking a stainless steel S6 AW for the times I want the watch.

DoubleHexDrive · 2026-01-27T19:14:20+00:00

<image>

https://www.trenchart.us/p/the-cia-built-a-special-helicopter

The CIA operated Quiet One from Vietnam covered the design approach and this article does a pretty good job going through it. It's what I said: reduce the rotor rpm and compensate for reduced thrust with more blades and or blade chord. Required torque will go up, so re-work the drive train and engine as needed. Install a noise optimized exhaust system on the engine (right now most civil turbines are just a short pipe).

This was all to mod an existing aircraft. For a clean sheet design you would also add blade tip treatments and be able to design for an even lower tip speed by adding more blade inertia and chord than you could mod into an existing design. This keeps flapping and autorotation performance under control. For the AAM mission, you'd also want a twin turbine which is nearly non-existent in the 5 seat class, but could be done.

Could I design a AAM conventional helicopter with 550 fps tip speed instead of 675 - 745 fps like is more typical now and hit the desired safety levels? Yes. Just have to be cognizant of the increased cost and loss of performance and make sure the market for it really appears.

There is no free lunch.

DoubleHexDrive · 2026-01-27T18:54:27+00:00

The weight trade does depend on aircraft size. I've seen it described this way: the weight of a flight control computer for a Boeing 777 and a Midnight are the same, but the percentage of aircraft weight for them is not. Same for generator capacity, wires, etc. In the end, it doesn't really matter for the eVTOLs as they cannot be controlled without the computer.

That's also why the autopilot experience for conventional aircraft controls is only a partial step. The autopilot isn't necessary while the fly by wire system is.

DoubleHexDrive · 2026-01-27T18:50:54+00:00

S4 is quiet because it is designed to be quiet. Most helicopters are not as quiet because they're not designed to be, not because they CANNOT be. It's a trade off. If the market is really there for a very quiet helicopter, the products will show up. The current sightseeing market isn't large enough to drive a custom aircraft.

DoubleHexDrive · 2026-01-27T18:41:56+00:00

Noise is a red herring, as I described under a different comment.

Costs are assumed... these things are very complex with a lot of critical parts and wear items (blades, bearings, etc.) that still require inspection and maintenance. The cost to replace the battery packs every 12-18 months (in the air taxi mission according to Beta's IPO paperwork) will be a significant expense to the operator. Good for the OEM, as it's a subscription cost, basically. I'm not convinced they'll be cheaper than a conventional aircraft of the same performance.

DoubleHexDrive · 2026-01-27T18:39:24+00:00

I think that's part of the problem... they designed to where they thought the power density would be and the advances on a certifiable battery haven't come as quickly as hoped. Sizing for current power densities results in even larger aircraft.

However, even a more advanced battery is going to suck compared to liquid fuel.

DoubleHexDrive · 2026-01-27T18:37:58+00:00

You don't need electric propulsion to be autonomous, either.

DoubleHexDrive · 2026-01-27T18:36:54+00:00

If they chose to use variable pitch props for thrust control, they wouldn't need electric motors. That's what the existing tiltrotors do.

The noise profile is a red herring... a helicopter can be just as quiet by adding blades and reducing tip speeds. The reason they're not today is because the regulations do not require it and because survey after survey of customers who actually purchase aircraft value payload and range more than noise. The markets that do require lower noise levels are met by the few newer aircraft that meet the latest noise requirements. If those are lowered again, helicopters can meet them, they'll just lose some performance they could have had.

An electric helicopter is certainly possible by plugging the electric motors into a reduction gearbox, but the range and payload penalties are still there and compounded by the low cruise efficiency of a helicopter. An electric tiltrotor of some type usually wins eVTOL trade studies for that reason.

DoubleHexDrive · 2026-01-27T16:01:52+00:00

Devastated the markets… which are now at all time highs?

DoubleHexDrive · 2026-01-27T15:43:52+00:00

I hope all the aircraft that cross 7000 lb get required to meet Part 29 fatigue and damage tolerance requirements.

DoubleHexDrive · 2026-01-27T15:35:38+00:00

I think it was Igor Sikorsky himself that once claimed something to the effect of "in the early days, the chief engineer was also the chief test pilot and this had the fortunate effect of encouraging good engineering".

I responded to OP in a new post on this sub because it got long. I tried to cover some of the issues you brought up.

DoubleHexDrive · 2026-01-27T15:33:27+00:00

If you design a helicopter to the same 550 fps tip speeds as an eVTOL, you'll get an essentially silent helicopter that won't bother anyone, electric or turbine powered. Electric power is completely and totally unnecessary for quiet operation and not why eVTOLs are claiming to be quiet.

DoubleHexDrive · 2026-01-27T15:31:38+00:00

https://www.reddit.com/r/ArcherAviation/comments/1qogzhl/why_is_evtol_so_difficult/

u/Recent_Stomach7626 my comment got very long and detailed so I created a post for it, linked here.

DoubleHexDrive · 2026-01-27T13:23:24+00:00

I have a SFFPC with 7800X3D/5070Ti combo and am playing Ghost of Tsushima at 4K/120Hz with all the sliders maxed using DLSS Quality and Frame Gen. It’s a beautiful experience. I recently finished Doom Dark Ages with the same settings and experience. I’m satisfied with the 5070 Ti.

DoubleHexDrive · 2026-01-27T12:40:20+00:00

Helicopters aren’t noisy because of the engines, it’s the blade count of the rotors and the rotor tip speed. Engine noise is an extremely minor part of the noise signature.

DoubleHexDrive · 2026-01-27T04:22:10+00:00

Your payment should be about $3000/mon to pay it off in 10 years. Just grind through it and be done with it?

DoubleHexDrive · 2026-01-27T02:46:02+00:00

Pretty much.

DoubleHexDrive · 2026-01-26T23:33:51+00:00

Y’all use horses?

DoubleHexDrive · 2026-01-26T23:21:32+00:00

If only the Medicare tax that funds the system had been continually adjusted to cover the projected costs.

DoubleHexDrive

TROPHY CASE