This thread is to discuss and post news on the USAF High-Speed VTOL program.

The HSVTOL program plans to develop a family of different sized aircraft from a drone to a C-130 tactical transport replacement.

In August 2021 from 218 applicants, the USAF AFWERX team selected 35 designs, which it presented in an HSVTOL showcase.

In January 2022 the USAF selected 11 competitors to move to the proof of concept which include all major manufacturers and engine suppliers.

The original US Army Future Vertical Lift plan included four size categories. JMR-Light, JMR-Medium, JMR-Heavy and JMR-Ultra. The two smaller sizes have competitions running. For the last 2 years there has been silence regarding the two larger sizes.

In my opinion the USAF HSVTOL program is taking over this larger size category of aircraft and they will be flown by USAF pilots.

https://aviationweek.com/aerospace/emer ... l-concepts

https://news.bellflight.com/en-US/20996 ... -milestone

Bell is clearly the front runner in my opinion. I havent been this impressed since the F-35B lift system blew everyone away.

It will be interesting to see how the folding rotor technology progresses into practical application. The in-flight transition will be complex.

I think the in-flight transition has been modeled aerodynamically quite a bit. Now, putting that into practice mechanically/software wise is another matter, but I expect Bell will succeed at that. I just hope the development is much shorter than the XV-17 to V-22 IOC took.

Is the model to…basically make the transition in a slow dive? When would a down-select happen from 11 vendors (sorry, I am out of reads on AWST)?

No dive is required. Besides a change in noise I expect the transition to be unnoticed by the pilot. The rotors will stop and fold as the aircraft passes through 150-175 knots. The wings are now providing lift and the turbofan is providing thrust. The design can then accelerate up to 400 knots.

I think to be worth the extra weight and complexity the folding blade concept will have to be capable of at least 450 knots. The V-22 and V-280 can both already do 305 knots and that's with very old/arguably underpowered engines, and I'm confident they are capable of at least 350+ knots with new/upgraded engines.

Interesting that the USAF is trying this again.

I remember reading about this aircraft once, the USAF's earlier attempt at supersonic VTOL.

https://en.wikipedia.org/wiki/Rockwell_XFV-12

aschachter wrote:

Interesting that the USAF is trying this again.

I remember reading about this aircraft once, the USAF's earlier attempt at supersonic VTOL.

https://en.wikipedia.org/wiki/Rockwell_XFV-12

The XFV-12 is a US Navy aircraft. Look at the F-35B, it is an absolute masterpiece and it only has a tiny performance penalty compared to the A and C models. So the USAF definitely wants to repeat the VTOL success of the F-35B with a different category of aircraft. They are using proven VTOL elements of the F-35B, V-22 and V-280 and combining them to create a transport.

In the 1970's a 400 knot capable VTOL transport would have had dedicated turbojet lift engines and a dedicated engine for forward flight. Because of this it wouldn't have been able to carry any meaningful payload. Efficient VTOL requires large rotor area as it is easier to push a lot of air slowly than a small amount of air really fast to produce the same lift. But a large rotor area can't have a high cruising speed. This is why the F-35B style turbofan with a driveshaft output eliminates the weight of dedicated lift engines. The folding props give the rotor area required for VTOL hover but folds away for high speed flight. The Bell design will definitely work.

In my opinion Bell has a winner just like the Lockheed X-35 compared to the obviously inferior X-32.

Some of the other less known competitors have great ideas. Electric lift fans in the wings have extremely high power to weight. They get electricity off the central turbofan running a generator most likely with a small electricity storage device for the surge during VTOL flight. So all the complex driveshafts are eliminated and replaced by power wires.

The Bell design is a nice CAD exercise, as it stands now, plus some hardware component testing.

Any program of record would have to start from a detailed mission analysis, which I doubt the USAF can do now as the rotorcraft expertise in the US resides with the Army and the Navy (for its specific problems), which will drive the technical specifications for the aircraft. If speed and range are the priority, presumably the aircraft would look like an F-35B on steroids, i.e., paying the penalty of very low hover and low speed efficiency, and with a very powerful and hot downwash. If hover and low speed are the priority, presumably the aircraft would have big propellers, and pay the penalties of low speed, high drag, and high transmission weight.

Trying to address both with lift fans plus foldable rotors, apart from the high complexity, would leave the aircraft with big draggy and, especially, heavy objects at the wing tips (plus cross-shafts and transmission somewhere on the aircraft). I bet that the structural wing modes would end up in the flight dynamics frequency ranges, making the design of an effective FBW system a nightmare. Also, I am not an engine expert, but I would assume that an engine that has to be able to switch from jet power to shaft power is not going to be optimal in any sense.

I'm not saying that it's impossible. In fact, personally, I'd welcome such a project because, with so many unproven technologies, people like me in R&D would have job security for a long long time.

It seems China also has a high speed VTOL program.

China's helicopter makers have reportedly conducted test flights for at least two types of helicopters with innovative designs: one is a blended-wing body multi-rotor vertical takeoff and landing aircraft, the other is a helicopter with a completely different, innovative design

https://www.globaltimes.cn/page/202204/1259635.shtml

I thought your first post is a really nice introduction.

We've written about this before, and I'm sure you know several of us fear the operational cost is not worth the additional benefit. What I'm asking now is somewhat technical so maybe no one knows .. when are estimates of running costs created? Surely they don't spend many billions of $$ on multiple prototypes before deciding they can afford to run the thing. So how does that happen?

kitplane01 wrote:

I'm sure you know several of us fear the operational cost is not worth the additional benefit.

This simply comes down to bit understanding how great the additional benefit is. The elimination of helicopters and aviation fuel at a FOB would be a huge initial benefit.

kitplane01 wrote:

What I'm asking now is somewhat technical so maybe no one knows .. when are estimates of running costs created? Surely they don't spend many billions of $$ on multiple prototypes before deciding they can afford to run the thing. So how does that happen?

They would have the costs of the FOB during the war on terror. They would know what assets could be moved to a safer/cheaper operating area if they had a long range VTOL aircraft. They know how many
fuel truck convoy deaths.

Over 3,000 American soldiers or contractors were killed in fuel supply convoys between 2003 and 2007 in Iraq and Afghanistan, officials said. Eighty percent of all supply trucks operating in the region are carrying fuel.

https://money.cnn.com/2011/06/14/news/e ... /index.htm

A fleet of a few hundred C-130 sized VTOL aircraft could have removed 90+% of these fuel truck convoys.

Now imagine if the enemy was more advanced and each FOB was getting attacked daily. Thousands of extra deaths all because the helicopters have short range. There is no alternative besides retreating. With high speed VTOL and/or a large tilt rotor fleet the bases can be moved to a safer location.

To form an argument from an operational cost basis another operating metric would be "operating cost per kg of payload delivered to a distance of 1,000nm to a location with no runway".

A Chinook would have to conduct the flight as a ferry flight and might be able to carry a 500kg of payload. A V-22 would be able to comfortably deliver 5,000kg that distance. The V-22 would have a significantly lower operating cost per kg than any helicopter.

A high speed VTOL aircraft even if it had a hourly operating cost as much as an F-22 it would still be cheaper per kg than any helicopter at that distance.

It is like saying a A321 has a lower operating cost than the A350 which is not worth the additional benefit. But if the flight is to carry passengers 8,000nm away the A350 is far cheaper per passenger.

RJMAZ ...

We understand your point. You're explaining it well. We disagree for the reasons already described. viewtopic.php?f=10&t=1472017&p=23270345#p23270345 starting about post #37.

I was actually just curious at what point in the development process the operational affordability decision is made. I've read a lot about defense procurement and never read about that.

kitplane01 wrote:

I was actually just curious at what point in the development process the operational affordability decision is made. I've read a lot about defense procurement and never read about that.

Multiple studies have already been done.

You will really enjoy the following link

https://dsb.cto.mil/reports/2000s/ADA473069.pdf

Page 68 has the costs.

Costs for a 30t payload tilt rotor in 2007 dollars.
$750 million R&D
$1.5 billion for new engine development
$2.5 billion for two prototypes
$190 million per aircraft with 100 aircraft ordered

The MVM estimates $250 million per aircraft. So we are looking at more than double and close to triple the cost of the C-130J.

The analysis even calculates the sustainment levels for battalions in combat to work out the number of VTOL aircraft are required. It directly compares it to the C-130 with runway construction in what they call an "enclave landing zone" or what we call a FOB.

Most of the concerns in the report regarding technical, reliability, safety and development risk have since been eliminated. The V-22 has proven itself. The V-280 development was fairly rapid.

RJMAZ wrote:

kitplane01 wrote:

I was actually just curious at what point in the development process the operational affordability decision is made. I've read a lot about defense procurement and never read about that.

Multiple studies have already been done.

You will really enjoy the following link

https://dsb.cto.mil/reports/2000s/ADA473069.pdf

Page 68 has the costs.

Costs for a 30t payload tilt rotor in 2007 dollars.
$750 million R&D
$1.5 billion for new engine development
$2.5 billion for two prototypes
$190 million per aircraft with 100 aircraft ordered

The MVM estimates $250 million per aircraft. So we are looking at more than double and close to triple the cost of the C-130J.

The analysis even calculates the sustainment levels for battalions in combat to work out the number of VTOL aircraft are required. It directly compares it to the C-130 with runway construction in what they call an "enclave landing zone" or what we call a FOB.

Most of the concerns in the report regarding technical, reliability, safety and development risk have since been eliminated. The V-22 has proven itself. The V-280 development was fairly rapid.

I wonder if you're missing our point. We're not arguing there are no circumstances where a tilt-rotor is not the best way to move payload. We're arguing that if you cannot maintain a FOB you're already losing the war. And the solution might often be more soldiers to keep the peace, not more tiltrotors to fly over the territory we fail to control.

RJMAZ wrote:

[...]
Most of the concerns in the report regarding technical, reliability, safety and development risk have since been eliminated.
[...]

No, they have not.

The V-280 is a scaled down version of the V-22. Big problems appear when you scale up.

And this is for a tilt-rotor, which is a relatively well known technology.

kitplane01 wrote:

We're arguing that if you cannot maintain a FOB you're already losing the war.

A country can win a war and still suffer high casualties at their FOB. The whole point of heavy vertical lift is to reduce casualties. 3000+ fuel truck convoy drivers deaths is a start.

You're not arguing against me but the high quality research and plans of the US military. Page 19 shows the operational geometry. Intermediate supply bases contain all of the logistics but are located in a safe area. Battlefield enclaves do all the hard work done by a traditional FOB. No capability is lost.

kitplane01 wrote:

And the solution might often be more soldiers to keep the peace, not more tiltrotors to fly over the territory we fail to control.

That shows that you completely miss the point. The whole point of that document is to improve the US effectiveness again asymmetric adversaries, distributed war, insurgency and terrorism.

If territory can't be controlled it would just get bombed by the air. So the fact they are talking about soldiers on the ground means this is about controlling territory and reducing casualties.

50 soldiers tasked to protecting 100,000 litres of highly explosive jet fuel at a FOB contribute nothing to keeping the peace. Move that fuel to the ISB.

RJMAZ wrote:

kitplane01 wrote:

We're arguing that if you cannot maintain a FOB you're already losing the war.

A country can win a war and still suffer high casualties at their FOB. The whole point of heavy vertical lift is to reduce casualties. 3000+ fuel truck convoy drivers deaths is a start.

You're not arguing against me but the high quality research and plans of the US military. Page 19 shows the operational geometry. Intermediate supply bases contain all of the logistics but are located in a safe area. Battlefield enclaves do all the hard work done by a traditional FOB. No capability is lost.

kitplane01 wrote:

And the solution might often be more soldiers to keep the peace, not more tiltrotors to fly over the territory we fail to control.

That shows that you completely miss the point. The whole point of that document is to improve the US effectiveness again asymmetric adversaries, distributed war, insurgency and terrorism.

If territory can't be controlled it would just get bombed by the air. So the fact they are talking about soldiers on the ground means this is about controlling territory and reducing casualties.

50 soldiers tasked to protecting 100,000 litres of highly explosive jet fuel at a FOB contribute nothing to keeping the peace. Move that fuel to the ISB.

I do not think I miss the point at all. I disagree with the point, which is quite different.

I do believe in the value of expert opinion, and totally acknowledge these people know more than me. That experts in the US military agree with you is evidence you're right. That they also thought the B-2 and LCS was a good idea reduces the strength. No other nation thinks this is the best way to spend money (but no other nation except MAYBE China has the US military budget).

I doubt this is a good idea partially because I believe the US military, when making advanced technology systems, always and significantly underestimates the cost. Consider the early pre-prototype estimate for the MV-22 (or F-35 or Zumwalt destroyer or pick any other program). Their track record is SO BAD at estimating costs at the pre-prototype stage of high technology systems, that I just don't believe them (and I bet you don't either).

The problem was the US military tried to add extra capability towards the end of development causing big cost increases on these projects. They have learnt this lesson and it will not occur on the T-X, V-280, B-21 or 6th gen fighter. One thing the US is good at is predicting the future. The US has the guts to cancel expensive programs when it no longer suits the future B-2, F-22, Commanche, FCS, LCS, Zumwalt etc. They will presist with troubled expensive developments that clearly suit the future such as the F-35 and V-22.

https://sites.utexas.edu/nppp/files/202 ... -April.pdf

Here is another report that provides a key piece to the jigsaw puzzle. When you read all of the research you can clearly see what the future entails. Alaska already has a military base powered by the first of these micro nuclear reactors. They even go as far as calculating the electricity cost.

The army Future Combat System was killed so far into development because in 2009 the Tesla roadster clearly showed battery electric propulsion was the future. So the US army had to start from scratch. By 2050 I expect 1-2 megawatt micro nuclear reactors delivered to the battlefield enclaves by VTOL. All the forward deployed vehicles are fully electric that recharge from the reactor. No fuel delivery is then required beyond the intermediate supply base or sea base.

Front line forces will be delivered and moved around by VTOL and will consist of:
1) Medium weight, manned, electric armoured vehicles.
2) Light weight, agile, manned and unmanned electric tactical vehicles.
3) Electric unmanned aerial drones that deploy from the vehicles to provide situational awareness and return to recharge.

The USAF highspeed VTOL program is key to making this happen.

https://www.nationaldefensemagazine.org ... roits-help

RJMAZ wrote:

It seems China also has a high speed VTOL program.

China's helicopter makers have reportedly conducted test flights for at least two types of helicopters with innovative designs: one is a blended-wing body multi-rotor vertical takeoff and landing aircraft, the other is a helicopter with a completely different, innovative design

https://www.globaltimes.cn/page/202204/1259635.shtml

You do know that the Global Times is a CCP nationalist daily newspaper.
https://en.wikipedia.org/wiki/Global_Times

They've been spreading all kind of misinformation from covid-19 to Xinjiang to HK protests to the ongoing war in Ukraine.

https://www.bbc.com/news/world-us-canada-58273322

Another popular theory, pushed by the nationalist tabloid the Global Times, attempts to connect the virus's origins to a US coronavirus expert, Dr Ralph Baric, and researchers at Fort Detrick.
The newspaper suggested that Dr Baric created a new human-infecting coronavirus, citing a paper the North Carolina-based researcher co-authored about the virus's transmission from bats in Nature Medicine.

Just read what they have to say about the Russian invasion of Ukraine

bajs11 wrote:

[...]

You do know that the Global Times is a CCP nationalist daily newspaper.
https://en.wikipedia.org/wiki/Global_Times

They've been spreading all kind of misinformation from covid-19 to Xinjiang to HK protests to the ongoing war in Ukraine.

[...]

From that same article:

" Since Wu gave a general time frame of 10 years for most helicopters to achieve high speed, it can be expected that China could also reveal its high-speed helicopters within 10 years, a Chinese military expert told the Global Times on Monday, requesting anonymity. "

"China's helicopter makers have reportedly conducted test flights for at least two types of helicopters with innovative designs: one is a blended-wing body multi-rotor vertical takeoff and landing aircraft, the other is a helicopter with a completely different, innovative design."

There have been dozens of VTOL contraptions in the last ten years or so in the Urban Air Mobility arena, most of which were very useful to fool venture capitalists but ended up nowhere. So hopefully (for them) the Chinese hackers hit the right computers.

The hard reality is that VTOL capabilities are very expensive and subject to very tight engineering limitations arising directly from physics, which have been known for decades. An inescapable fact of life is that to fly fast and efficiently you need to accelerate a little air a lot (=jet engines), to fly slow and efficiently you need to accelerate a lot of air a little (=big rotors).

Also, the USAF does not know anything about accelerating a lot of air a little, so they wouldn't even know where to begin in assessing how a given design would satisfy their operational requirements. In the US, that expertise resides with the Army. I have no idea about how easy it would be for the two services to seriously talk to each other, but my (informed) guess would be: not very.

This might sound crazy, but how feasible would it be to use the F35B engine and lift fan for these larger VTOL projects? Maybe a blended wing body aircraft with two, four, or even six (depending on size) F35B engines and lift fans would be feasible.

The MTOW of a F35B is 60,000lbs.
The MTOW of a C130J is 155,000lbs.

At first glance, a C130 size aircraft with four F35B engines and lift fans would appear to provide more than enough lift, possibly even with an engine or lift fan failure.

Ok, maybe far fetched, but at the same time, why not? A blended wing body with four F35B engines and lift fans in the wings sure would be neat. Much cheaper than developing a whole new lift system too.

RJMAZ wrote:

One thing the US is good at is predicting the future. The US has the guts to cancel expensive programs when it no longer suits the future B-2, F-22, Commanche, FCS, LCS, Zumwalt etc. They will presist with troubled

We super-a-whole-bunch don't see the world the same way.

You REALLY believe the LCS was cancelled when they understood it was a bad idea?

Did you know there are still 11 ships under construction and/or waiting to be commissioned?

https://en.wikipedia.org/wiki/Littoral_ ... mbat_ships

flyinggoat wrote:

This might sound crazy, but how feasible would it be to use the F35B engine and lift fan for these larger VTOL projects? Maybe a blended wing body aircraft with two, four, or even six (depending on size) F35B engines and lift fans would be feasible.

The MTOW of a F35B is 60,000lbs.
The MTOW of a C130J is 155,000lbs.

At first glance, a C130 size aircraft with four F35B engines and lift fans would appear to provide more than enough lift, possibly even with an engine or lift fan failure.

Ok, maybe far fetched, but at the same time, why not? A blended wing body with four F35B engines and lift fans in the wings sure would be neat. Much cheaper than developing a whole new lift system too.

This is effectively the plan but with a larger lift fan/blades.

The lift fan on the F-35B is very inefficient. It has a small diameter for packaging as it is a supersonic aircraft. This small diameter is why it needs 21,625kw (29,000hp) going into the fan yet generates only 8,900kg of thrust/lift. An Apache helicopter by comparison has 10,433 kg takeoff weight with only 2,818kw

You can see how important rotor diameter is. The tilt rotors usually require around double the engine power of a conventional helicopter due to the disc loading.



The Bell concept is effectively a tilt rotor.
The V-22 has:
9,180 kw of combined motor power.
21,546 kg vertical takeoff weight.
27,442 kg takeoff weight with runway.
6,800 kg maximum vertical payload (with emergency fuel)

21,625 kw from the F135-PW-600 turbofan is 2.35 times the power of the V-22. If we scale the weights that is:
50,633 kg vertical takeoff weight.
64,488 kg takeoff weight with runway.
15,980 kg maximum vertical payload.

But it gets even better the F-35B also produces thrust from the vectored exhaust nozzle producing another 8,000kg of lift. So that should get the vertical payload weight up to 20,000kg. The takeoff weight with a runway to heavier than a C-130J.

I am sure the F135-PW-600 is far from optimised as it must share the size and commonality with the standard version. So there is no doubt room for further improvement.

Most turbofans can be modified to suit Bell HSVTOL application. Traditional turboshafts and turboprops simply extract a larger percentage of shaft power out of any given turbine size. So only a little bit of exhaust thrust remains. As this Bell design actually wants exhaust thrust for horizontal flight then most off the shelf turbofans can have a shaft added to the front.

kitplane01 wrote:

We super-a-whole-bunch don't see the world the same way.

You REALLY believe the LCS was cancelled when they understood it was a bad idea?

Did you know there are still 11 ships under construction and/or waiting to be commissioned?

https://en.wikipedia.org/wiki/Littoral_ ... mbat_ships

The LCS is a favourite punching bag. They were developed for littoral operations with a very shallow draft around 4 metres. South east asia has lots of islands and shallow waters. They are around half the draft of the new Constellation-class frigates. China has simply transitioned from a green water navy to a blue water navy much quicker than anyone expected. Had war started in 2015 the US Navy would have wished for 100 LCS.

By your logic the F-22 is a terrible aircraft. They couldn't cancel it fast enough. F-15's will still be flying long after the F-22 is retired. When the F-22 started production the chance of a near peer war suddenly dropped to zero. The role of the aircraft had just been made redundant for a couple decades. Same with the LCS.

RJMAZ wrote:

[...]
The Bell concept is effectively a tilt rotor.
[...]

If you refer to the full flight envelope, i.e., hover plus forward flight, it's most definitely not.

In the Bell concept, in forward flight the rotor blades fold back and become a lot of dead weight and parasitic drag that you need to carry around at your wing tips, and this is the primary price to pay for the ability to hover. Add to this the weight penalty of the shafts needed to move the rotors, and that of the transmission required to go from turboshaft RPM to rotor RPM, all totally useless in forward flight. Finally (for now), add the efficiency losses in an engine that has to go from being a turboshaft (in hover) to a turbofan (in forward flight).

If the general says: "I absolutely need my transport plane to be a VTOL, no matter what the cost and no matter what the compromises", and Congress (in the US) doesn't kick him/her out of the room, then OK, yes, it can probably be done, but it would take so much time and so much money, that the F-35 ordeal would look like a weekend project by comparison.

RJMAZ wrote:

kitplane01 wrote:

We super-a-whole-bunch don't see the world the same way.

You REALLY believe the LCS was cancelled when they understood it was a bad idea?

Did you know there are still 11 ships under construction and/or waiting to be commissioned?

https://en.wikipedia.org/wiki/Littoral_ ... mbat_ships

The LCS is a favourite punching bag. They were developed for littoral operations with a very shallow draft around 4 metres. South east asia has lots of islands and shallow waters. They are around half the draft of the new Constellation-class frigates. China has simply transitioned from a green water navy to a blue water navy much quicker than anyone expected. Had war started in 2015 the US Navy would have wished for 100 LCS.

Not to go off-topic, but the LCS just deployed to the Middle East for the first time. It was always meant for Littoral operations there and eastern Pacific. So now they are active in both regions.

The LCS retirement request was due to the cancellation of the ASW mission package, which leaves 9-10 ships without a package. But they have surplus MCM packages, and Congress is unlikely to allow their retirement, so they will likely still be active and useful for some time.

So may not be a good comparison to the high speed VTOL program.

RJMAZ wrote:

kitplane01 wrote:

We super-a-whole-bunch don't see the world the same way.

You REALLY believe the LCS was cancelled when they understood it was a bad idea?

Did you know there are still 11 ships under construction and/or waiting to be commissioned?

https://en.wikipedia.org/wiki/Littoral_ ... mbat_ships

The LCS is a favourite punching bag. They were developed for littoral operations with a very shallow draft around 4 metres. South east asia has lots of islands and shallow waters. They are around half the draft of the new Constellation-class frigates. China has simply transitioned from a green water navy to a blue water navy much quicker than anyone expected. Had war started in 2015 the US Navy would have wished for 100 LCS.

By your logic the F-22 is a terrible aircraft. They couldn't cancel it fast enough. F-15's will still be flying long after the F-22 is retired. When the F-22 started production the chance of a near peer war suddenly dropped to zero. The role of the aircraft had just been made redundant for a couple decades. Same with the LCS.

What a funny way you edited. You left out the part I was replying to: "One thing the US is good at is predicting the future. The US has the guts to cancel expensive programs when it no longer suits the future B-2, F-22, Commanche, FCS, LCS, Zumwalt etc." You're the one who brought up the LCS. I went with your example!

So, answer the question if you want. Do you believe the LCS was cancelled at the right time? There are still 11 building/on-order/waiting-to-be-commissioned.

IADFCO wrote:

RJMAZ wrote:

[...]
The Bell concept is effectively a tilt rotor.
[...]

If you refer to the full flight envelope, i.e., hover plus forward flight, it's most definitely not.

I refer to the tilt rotor for hover efficiency only to calculate potential takeoff weights from the available thrust/power.

The X-35 flew 22 years ago and the V-22 first flew 33 years ago. Computer design as come such a long way. I am sure Bell will develop this high speed VTOL aircraft without much issue.

kitplane01 wrote:

So, answer the question if you want. Do you believe the LCS was cancelled at the right time? There are still 11 building/on-order/waiting-to-be-commissioned.

Yes perfect timing. The only change I would have made would have swapped Freedom-class ships for more Independence-class ships as I think they will be more valuable in the future. The demand for shallow draft and fast ships for littoral operations didn't suddenly disappear. The number of ships required simply reduced as the potential enemy is moving away from the Littoral and the ASW role is moving away from ship based systems.

The Independence-class has a flight deck over 1,030m2. This is double the size of the new constellation class frigates of 520m² and far bigger than any destroyer or cruiser. Being able to land a Chinook or King Stallion or maybe one of these High Speed VTOL aircraft would come in handy.

Sikorsky ought to revisit the X-wing concept that they investigated with the S-72. It would be less draggy, have far superior disk loading, and capable of higher speeds than Bell's folding rotors concept.

https://www.sikorskyarchives.com/X-WING.php

This is Sikorsky's to lose if they go this route.

744SPX wrote:

Sikorsky ought to revisit the X-wing concept that they investigated with the S-72. It would be less draggy, have far superior disk loading, and capable of higher speeds than Bell's folding rotors concept.

https://www.sikorskyarchives.com/X-WING.php

This is Sikorsky's to lose if they go this route.

I’m trying to understand the X – wing concept.

The wings seem very long and thin. How does one build such a thin wing capable of holding the entire aircraft and not going into flutter at high speed?

Either the left or right side depending on which way the rotor rotates, will have airflow in forward flight that is the reverse of airflow in hovering flight. How does one design an efficient airfoil for a lift with air coming in either direction?

It would seem airflow from the forward to branches of the acts would interfere with the airflow to the rear two branches of the X. Doesn’t that reduce efficiency?

I’m sure Sikorsky has thought of all of these issues. I am just thinking there are in efficiencies in this design like all the others.

The X concept involved quite thick rotors to make them stiff enough to act as wings. To overcome the drag effect of the thick aerofoils, they were blown with compressed air, on both advancing and retreating sides.

The interaction of front and rear aerofoils would lead to inefficiencies. Those might be made up by the weight savings of using them for lift in forward flight. The project didn't get far enough to find out.

The problem with the X-wing concept was (and is) its extreme complexity.

The airfoils by itself had no trailing edge in the conventional sense. The trailing edge was "recreated" by the airflow pumped through one or both the blade/wing spanwise slots (this was the concept proposed by Prof. Cheeseman) by the Coanda effect, i.e., the airflow sticking to and following a solid surface under certain conditions.

This airflow would have come from and be regulated by (from a caption in the interesting link provided by @744SPX) a circulation control valving system consist[ing] of 48 valves, 24 for leading edge blowing and 24 for the trailing edge. Note the size of the plenum hardware in relation to the technician working on it. It also required a very complex control system to precisely synchronize the airflow in the presence of centrifugal pumping and Coriolis effects. This complicated system was partially fixed (to the aircraft) and partially rotating, which means that some of the seals also had to be rotating.

As a laboratory/research experiment it was fascinating, and it was fantastic that NASA and Sikorsky spent the time and money to study it. As a practical solution IMHO it was doomed to failure. The maintenance effort required to keep the slots on the wing clean and the hub valving system operational must have been staggering, especially because both would have probably been flight critical.

IADFCO wrote:

The problem with the X-wing concept was (and is) its extreme complexity.

The airfoils by itself had no trailing edge in the conventional sense. The trailing edge was "recreated" by the airflow pumped through one or both the blade/wing spanwise slots (this was the concept proposed by Prof. Cheeseman) by the Coanda effect, i.e., the airflow sticking to and following a solid surface under certain conditions.

This airflow would have come from and be regulated by (from a caption in the interesting link provided by @744SPX) a circulation control valving system consist[ing] of 48 valves, 24 for leading edge blowing and 24 for the trailing edge. Note the size of the plenum hardware in relation to the technician working on it. It also required a very complex control system to precisely synchronize the airflow in the presence of centrifugal pumping and Coriolis effects. This complicated system was partially fixed (to the aircraft) and partially rotating, which means that some of the seals also had to be rotating.

As a laboratory/research experiment it was fascinating, and it was fantastic that NASA and Sikorsky spent the time and money to study it. As a practical solution IMHO it was doomed to failure. The maintenance effort required to keep the slots on the wing clean and the hub valving system operational must have been staggering, especially because both would have probably been flight critical.

Call me optimistic, but I'd like to think that these issues could be overcome given 40+ years of technological advancement in miniaturization and control systems

DARPA selects competitors for high-speed vertical take-off and landing aircraft

https://www.flightglobal.com/helicopter ... 17.article

We might have a flying demonstrator in 12 months.

Someone was working hard on making a good acronym.

SPeed and Runway INdependent Technologies (SPRINT)

A quick video overview. They want an aircraft like in the Avengers.

https://youtu.be/y6ymNoWjyGI?si=Sx_v6n1gix588-lM

I like the approach Boeing is taking. It sounds much like the VTOL idea I posted about a while ago. Personally, I think this is the way to go, and the design may provide an option for a non-VTOL aircraft for traditional flight transport and aerial refueling.

Aurora revealed details of its approach on 15 November. The Boeing subsidiary says it will pursue a fan-in-wing design based around a “high lift, low drag” blended-wing-body (BWB) airframe.

Drawing on Boeing’s experimental X-48 BWB type, the Aurora Sprint aircraft will incorporate embedded engines and moderate sweep, with a vertical flight design comprised of embedded lift fans linked to the engines via mechanical drives.