Yes - the flap angle is probably programmed with rotor tilt, angle of attack, airspeed, etc. to get rid of the drag in transition to and from airplane mode. The tilt wing VTOL got the wing almost completely out of the down wash but that was a handicap when descending to land because of the drag and the need to keep the propeller thrust high to keep the wing from stalling.

As likely as not, but I suspect that the certification battle for that project looked a bit daunting and they were trying to get 525 done and certified...I expect that a lot of factors went into that decision.
(You may be amused to learn that a bit over 20 years ago the USN was looking into maybe getting a 609, or something like the 609, as their primary trainer for V-22 pilots, but after a bit of due diligence decided "no, that's not going to work" and boy am I glad that they did, when you look at what has transpired since then).

Except in an apples to apples gross weight comparison a large diameter, low-disc-loading 2-rotor conventional tiltrotor platform with low tip speeds will absolutely have a lower acoustic signature (at lower frequencies that humans are far less sensitive to) than any of the current crop of eVTOL multirotor platforms.

A wholly unscalable concept due to the astronomic bending loads and moments at the wing attachment. Will perpetually live in the mostly-impractical done space.

Sorry for the thread drift.

I share your sentiment regarding bending moments as concept is scaled up, and looking at the original thread about Transwing (under Military Aviation), it is clear others have similar reservations:

https://www.pprune.org/military-avia...l#post11771177

Well thats not what NASA determined after their UAM flight research project in 1996 and subsequent acoustic testing. However, this is not the thread to discuss it given there are dedicated threads to eVTOLs.

Regardless, if you believe you can design a conventional tiltrotor to operate in the same environment and at a lower noise signature than current eVTOLs, you should definitely move on that idea before the GEN2 eVTOL versions move off the drawing board.

?? I guess two points. Firstly when did GEN1 eVTOL move off the drawing board in any relevant way beyond being technology demonstrators. Two what barriers are these GEN2 versions going to break that is currently stopping the GEN1 versions from flying (say) across Central London?

Since several eVTOLs started commercial ops in China last year and the Joby and Archer production versions continue the FAA type certification process with FAA pilots to perform the final Type Inspection Authorization flights on the Joby this year.

No idea why no London flights now since they've been flying in other countries. For example, the Joby, Archer, and EHang aircraft been flying demo/test flights in and around Dubai since last year. As to the GEN2 versions, its my understanding they will be larger with a move toward hybrid-propulsion vs straight battery packs.

But again I think this discussion should move to the eVTOL thread which has more relevant info on the topic.

Fear of litigation, perhaps?

I think operation in China is something different to UK and US. In China you’ll see film of first stage rocket boosters fall into residential areas to zero concern or consequence. Personally I think the barrier to eVTOL in mature aviation markets are not the aircraft technology but the wider infrastructure and that is beyond individual manufacturers but a question for nation states and how much they wish to adopt this technology.

No clue. But a quick check finds the UKCAA has an established UAM plan, CAP3169, along with an AIN article on eVTOL use around London airspace with a start date of 2029.

Except eVTOLs are not competing in any mature aviation market. Their sole development is to advance a long stagnated market that could not be fully serviced by conventional aircraft: street level urban ops or UAM.

As to nation states and infrastructure, there are currently 60+ countries with established UAM plans and about 200+ cities with UAM infrastructure projects completed, or in work, or proposed to start in the next 2-3 years.

Is it stagnant or non-existent because there is no customer? I’m not sure those most enthusiastic/ have a commercial interest in eVTOL fully understand the latter. London is a great example because you have obvious potential customers and yet even conventional helicopters are not commonplace. Battersea is the main rotary facility and it is neither especially convenient nor threatened by those wishing to compete.

Why is eVTOL going to change that? The plans that any country may have infrastructure wise are all based upon the hope commercial funds will flow, but that remains speculative until and unless authority creates a clear pathway to how and what can be allowed to work.

I don’t see that in the UK today.

At this stage it’s all kite flying. XYZ plc can produce all the PR it likes about 100s of air taxi in 2029. It’s meaningless. Someone needs to commit billions of GBP in infrastructure (UK city real estate is expensive) and be confident those in the vicinity of these “vertiports” aren’t going to complain about noise, air traffic perceived dangers and planning around associated infrastructure (after all service, customer facilities and onward transport aren’t divorced). Even if the CAA manage to pull together all of these threads for the end of 2028 (which they won’t), things still need to be built and the public managed - all of which is beyond the control of the regulator.

Its a 60+ year old concept and market. However, it became severely limited by 1980 and not because for lack of customers. NASA was put to task in the 90s to come up with a solution to those limitations. End result was that the UAM concept was solid, the urban airspace could be managed, and customer street-level access was paramount. But its actually more than just a simple market concept and the reason UAM/AAM has been studied and applied for so long. Plenty of references out there to expand on the topic if you so choose.

Basically because it provides a solution to the two main limiting factors: noise and accesibility. The same limitations which kept helicopters from performing the role.

I know that we've had some thread drift here, and we seem to have strayed from the discussion of the 609. I apologize for that. But the 609 and these new eVTOLs are similar in that certifying them for civilian commercial use is not easy. If it was, the 609 would be already flying oil company workers out to deep water rigs, and important businessmen from a vertiport in NYC to a comparable one in Washington D.C. And this is why nobody else on the planet - like the Russians or the Chinese - are attempting to build and operate a tilt-rotor. (Oooooh, speaking of vertiports, I would bet real money that, given Adam Goldstein's big mouth, there are already groups quietly forming out in California that will oppose ANY effort to build and install vertiports in their neighborhoods. You just watch!)

Okay, my final thoughts about these eVTOLS, then I'll shut up. And again I apologize for getting off-topic.:

wrench1, we can appreciate your enthusiasm for the eVTOL concept. You seem to be very, personally invested in these things. And you obviously believe that FAA certification for the Archer and Joby aircraft is imminent. Sorry to break this to you, but it is not - at least, not as a STANDARD Category aircraft. By calling yourself "wrench1," does that imply that you're an FAA certified A&P? If so, you must be familiar with the term, "FAA Approved." As you may know, there is a reason that EXPERIMENTAL Category aircraft are not approved for Commercial operations. The FAA has standards and requirements for aircraft and the accessories attached to them (e.g. engines, propellors, etc.). With regard to the Archer, we look at AM1.2800 to see what is required for those little carbon fiber propellors to get the big stamp that says, "FAA-APPROVED." Holy cow. Some of the requirements are the same as in FAR 35.15. How will we know for instance, what the finite life of those propellors will be? Unlimited? On Condition? It will be up to the propellor manufacturer to provide that proof to the FAA. If the FAA requires that the Archer's propellors survive the same 4-pound bird impact test as for conventional propellors, it's probably a show-stopper, I would guess. And how about those electric motors that power the Archer? What is their finite life or overhaul interval? The FAA won't simply ignore or waive that standard, and they won't accept the explanation of, "Oh, they run forever!"

Bottom Line: Just because some FAA test pilots are out flying the Archer M001, that doesn't mean it's "this close" to certification in the STANDARD Category. Like Bell found with the 609, there are a lot of hurdles that must be jumped, and some of them may not be easily overcome. The FAA will not relax those standards, no matter what the POTUS wants. There's too much at stake from a public safety standpoint. Trust me, the FAA is not ever going to approve an aircraft for Part 135 operations unless they are satisfied that it meets the notorious "equivalent level of safety" that they've applied to every airplane and helicopter that has come before.

Keep up:

​​​​​​​https://www.twz.com/air/chinas-first...raft-is-flying

Had you understood why the Part 21.17 Airworthiness Criteria linked in Post 98 were published in the Federal Register you would have realized those are the “FAA-APPROVED” methods to type certify the Joby and Archer eVTOLs and by extension to issue a Standard Airworthiness Certificate. So perhaps take a moment and read up on why the Part 21.17 Special Class certification method was used in this situation and it may make more sense to you. Or maybe it won't. The EASA is also using a similar eVTOL approval method as well. And to note, Joby and Archer already have their 135 certificate and once their eVTOLs receive their AWC they can finish the necessary requirements to add them to their certificate.

As to my personal interest, I’ve been following this topic since I was a participant in the NASA HeliSTAR project and have simply followed the progress of UAM and eVTOL technology since then. However, in recent times I have leveraged those contacts to get an insiders view which I share here and other places. Beyond that, not much more to write about..

If you are referring to HeliSTAR, there was no assessment of alternate rotary wing designs (like tiltrotors) as a variable - it was a study of urban acoustics as a result of normal helicopter air operations in Atlanta during the Olympics and specific testing of an FAA S-76 and Bo-105 out of local heliports.
https://cimg2.ibsrv.net/gimg/pprune....3fbab18f9e.png

The HeliSTAR acoustic data provided the baseline for the subsequent testing I mentioned which compared data from alternate aircraft designs and I believe included XV-15 data. So based on that combined acoustic data along with the other operational data from that project and previous testing, the consensus was a new distributed propulsion system was needed to meet all the requirements for a street-level UAM system to succeed. And it seems to me if there were any UAM viable alternate rotor wing designs out there we would have seen one or two in the past 30 years?

And to note, not all heliports used were existing with a number specifically placed in the city at street-level areas for this project. So the acoustic and other data collected provided a unique insight than previously collected.

I will say one thing: These new eVTOLs are amazingly quiet - especially compared with the V-22 which has a very odd and distinctive noise signature that is discernible well in advance of its arrival...or even a CH-47, one of which departed our local airport today and gave me flashbacks of living in NYC in the 1960's and having those noisy New York Airways BV-107s fly over. Personally, I loved that sound, but not all New Yorkers did. Anyone trying to get an inner-city tiltrotor shuttle service going will be faced with a "challenge," given the current, fearful, sky-is-falling, anti-aviation culture we live in. Using an eVTOL will be bad enough; proposing to use a tiltrotor like the 609 would be a show-stopper.

Comparing current 5000lb eVTOLs to the smallest tiltrotor in XV-15 is a gross weight discrepancy factor of 3. This results in immense blade loading and thickness noise differences which makes that point moot.

I addressed this in a previous post - we might have seen one if any of the following were true:
.

• The SPAC-bro driven startups had any idea of how to design a working rotary wing platform that uses conventional flapping, low-disc-loading tiltrotors. It has been sad to witness how these guys couldn't (and many still don't) realize that you simply can't use large rigid 2 blade lifters in high advance ratio flight (see: any tail rotor). Neophyte limited experience of hobby scale drones and rigid props strikes over and over again.
• The OEMs who are capable of actually building the proper tiltrotor technology did not succumb to the idea from their marketing departments that an eVTOL design must be seen as avant-garde by the investment public and that the conventional tiltrotor layout is considered too....conventional (see: Nexus)
• The OEMs who are capable of actually building the proper tiltrotor technology did not also astutely realize that the entire eVTOL premise and market is a financial non-starter and participating in the dog and pony show is an immense capital waste (see: Bell, Leonardo, Airbus)
• Battery technology improved at anywhere near the rate the breathless extrapolations promised