VTOL vs STOVL vs STOL for fighter aircraft

[Elysium]

I'd like to discuss what are the respective advantages and disadvantages of said technologies, especially in the context of constrained landing/takeoff spaces, like carrier operations. What circumstances would lead engineers to chose one over the other?

My quick summary:
VTOL has been tried a few times, with the most prominent examples being the Yak-141, the X-32 and X-35. My memory is fuzzy on the history, but I think all 3 have been conceived as true VTOL aircraft, but the significant technological and practical issues have stopped them from entering service. The F-35B is the only active example, and afaik its capability when used as a true VTOL aircraft is severely reduced, and I'm not sure if anyone uses them operationally like this. On the engineering side, this requires a ton of extra hardware, complexity, and the nasty effects that occur during takeoff/landing, such as aerodynamic suckdown, exhaust reingestion and exhaust velocity (just to name a few), make it dangerous for both the pilot and its environment.
It also drives design decisions like moving the engine exhaust closer to the center of the aircraft, leading to more awkward layouts, and diminishing the effectiveness of thrust vectoring.
I feel like this scheme is more trouble that it's worth, unless I'm missing something. Though it is undoubtedly cool, I'm not sure if future designs can make this practical.

STOVL seems to me like the worst of both worlds. You pay for most of the complexity, yet you take on most of the risks, without getting most of the benefits.
The argument for this scheme is obviously the existence of the F35B. If US engineers went for this, they probably did the math and found this scheme most advantageous. Or did they? It seems the US is planning to procure 4x as many CTOL F35Cs as F35Bs.

STOL is my preferred choice, with the advent of technologies of thrust vectoring and advanced aerodynamic high-lift devices, either dedicated, like Kruger flaps or not, like canards, or barn-door sized horizontal tails, like on the F35, I feel like it's possible to construct an aircraft that could rival a STOVL aircraft in takeoff distance. Another advantage compared to STOVL, is that afterburners are available during takeoff, giving the aircraft more thrust to work with.
Unlike VTOL, where the extra equipment is dead weight for most of the flight, while in this scheme, the thrust vectoring and increased low speed maneuverability it a boon throughout the flight.

Considering all this, I'd clearly go with STOL if I were to design a new naval fighter.
Anyway, these are my opinions, feel free to disagree with me, if you've come to disagree with my conclusions, I'd love to hear your reasoning.

 

[hagaricus]

Once again, I think technology has matured to the point where we need to revisit the tail-sitter. It minimises the weight penalty of vtol, and can be combined with stol characterisics.

 

[uk 75]

Apart from navies that do not have nuclear carriers there is no longer any demand for VSTOL aircraft.
Airports and airbases that can operate CTOL aircraft are in plentiful supply. Apart from the Falklands no conflict has needed land based VSTOL.

 

[riggerrob]

Apart from navies that do not have nuclear carriers there is no longer any demand for VSTOL aircraft. …..

Are you talking about Argentina, Brazil, France (?), Great Britain, India, Japan, South Korea, Spain, etc.?

Truth be told, the US Navy has more aircraft carriers than the rest of the world combined, but the USMC still wants the VTOL F-35B variant to fly from their helicopter carriers.
Also remember that AV-8 Harrier development was driven by lessons-learned by the Egyptian Air Force during their 1967 war versus Israel. After the Israeli Air Force “shortened” …. er …. bombed all the major Egptian air bases, the Egyptian Air Force was grounded for the duration of the war.

 

[paralay]

Once again, I think technology has matured to the point where we need to revisit the tail-sitter. It minimises the weight penalty of vtol, and can be combined with stol characterisics.

A drone could be. But there are still difficulties with maintenance and storage. An obligatory condition will be the independent transfer of the fuselage from the vertical to the horizontal position after the flight and back before the flight

 

[hagaricus]

A drone could be. But there are still difficulties with maintenance and storage. An obligatory condition will be the independent transfer of the fuselage from the vertical to the horizontal position after the flight and back before the flight

Drones are already, even hobbyist models can do vtol now , I'm thinking a conventional vectored-thrust fighter with only the addition of some bleed-air RCS and a tripod landing gear at the tail. Flight control software does the rest. Conventional landing gear for normal operation, transitioning to vertical either in flight or with the use of a crane. there is still a weight penalty, but far less than in existing vtol designs.

 

[carvalho2008]

According to the laws of physics, a vtol aircraft will never be as efficient as a stol. The energy spent to either take off or land vertically is enormous, as in this modality only engine power and zero aerodynamic thrust are used. Ditto when landing, where famous maximum landing weight limits may even arise, I try to discard loads or burn a lot of fuel. The British are masters of avoiding waste and maximizing resources in their doctrines and developed the SRVL or SRL...where the F35 comes in a short rolled landing. I can't understand the obsession with vertical landing and takeoff on jets, because in practice, I never see this type of action (except landing). So, it would be and has always been much smarter to vector the nozzles for a short roll, whether during takeoff or landing, without requiring complex controls. I can give a true example, in which the XF5U could have been the Harrier of the 40s until the 80s...after all, it flew at almost 800 km/h and took off at 200 meters without wind. It was estimated that it would be possible to take off from an aircraft carrier practically vertically with a wind of 30knots....

 

[hagaricus]

According to the laws of physics, a vtol aircraft will never be as efficient as a stol. The energy spent to either take off or land vertically is enormous, as in this modality only engine power and zero aerodynamic thrust are used. Ditto when landing, where famous maximum landing weight limits may even arise, I try to discard loads or burn a lot of fuel. The British are masters of avoiding waste and maximizing resources in their doctrines and developed the SRVL or SRL...where the F35 comes in a short rolled landing. I can't understand the obsession with vertical landing and takeoff on jets, because in practice, I never see this type of action (except landing). So, it would be and has always been much smarter to vector the nozzles for a short roll, whether during takeoff or landing, without requiring complex controls. I can give a true example, in which the XF5U could have been the Harrier of the 40s until the 80s...after all, it flew at almost 800 km/h and took off at 200 meters without wind. It was estimated that it would be possible to take off from an aircraft carrier practically vertically with a wind of 30knots....

I see your point, and with sufficient access to runways, even emergency rough fields & roads it may be a dead concept, my only point is that if desirable, there is now the tech to do so more easily.

There is still the matter of deployment to sub-aircraft-carrier size ships, however, which might be a worthwhíle niche.

 

[carvalho2008]

I see your point, and with sufficient access to runways, even emergency rough fields & roads it may be a dead concept, my only point is that if desirable, there is now the tech to do so more easily.

There is still the matter of deployment to sub-aircraft-carrier size ships, however, which might be a worthwhíle niche.

 

[Scott Kenny]

As to the specific question? STOL fighters all the way.

VTOL is usually too much of a performance penalty outside something the size and weight of a Harrier. Or maybe the P1214 or P1216 on the upper limit.

I see your point, and with sufficient access to runways, even emergency rough fields & roads it may be a dead concept, my only point is that if desirable, there is now the tech to do so more easily.

There is still the matter of deployment to sub-aircraft-carrier size ships, however, which might be a worthwhíle niche.

Not sure how often you'd be deploying fighters on those ships, though. (Because I mentally file the gator-freighter LPHs as carrier-sized)

Tilt rotors or helicopters, sure, all the time.

=====

In all honesty, the F-35 could/should have been two separate aircraft. One for the USAF and USN, and one for the USMC. The USMC do not absolutely require supersonic capabilities, they ran Harriers for decades without that. That said, the B model's VSTOL work did greatly help the -A model, all the weight reductions they did for the -B made the -A a much better fighter.

 

[carvalho2008]

Ryan Rogallo F-104....why not?

Or by Carvalho2008 version....hahahaha...

 

[Scott Kenny]

Man, I love the Flying Flapjack...

Of all the roads not taken, I so wish we HAD taken this one! Turboprop fighters with T38 cores (to hell with the T40 units, the combining gearbox just was not up to the task!)

 

[carvalho2008]

Ryan Rogallo F-104....por que não?

Ou pela versão Carvalho2008....hahahaha...

Usando a ideia inicial de Pete Girard, algo semelhante ao F-104 seria interessante como ponto de partida. Era uma fuselagem estreita que permitia força vertical e combinada com o empuxo tradicional, poderia proporcionar uma decolagem e pouso curtos, sem a necessidade de buscar enfaticamente modos verticais.

Fiz uma versão que na minha opinião seria melhor, desalojando o motor interno e colocando dois em posição dorsal ligados ao mecanismo giratório. O espaço interno poderia ser ocupado por muito combustível, conferindo-lhe, de alguma forma, um alcance muito maior.

 

[carvalho2008]

Man, I love the Flying Flapjack...

Of all the roads not taken, I so wish we HAD taken this one! Turboprop fighters with T38 cores (to hell with the T40 units, the combining gearbox just was not up to the task!)

It was predicted that the XF5U could take off and land vertically if the Essex were at 30 knots.

I'm not kidding, with a speed of 750km/h, it could easily be the Harrier from the 40s to the 70s....

View: https://www.youtube.com/watch?v=A-wstZacb58&t=450s

 

[Scott Kenny]

It was predicted that the XF5U could take off and land vertically if the Essex were at 30 knots.

I'm not kidding, with a speed of 750km/h, it could easily be the Harrier from the 40s to the 70s....

View: https://www.youtube.com/watch?v=A-wstZacb58&t=450s

Putting a pair of T38 turboprops in there with 2000+hp and half the weight of those R-1830s would help reduce the wind over deck requirements, too.

 

[riggerrob]

Ryan Rogallo F-104....why not?

Or by Carvalho2008 version....hahahaha...

Please be more precise with your terminology.
That proposed F-104 variant might have a delta wing, but it does not resemble most of Rogallo’s flexible wings. Rogallo’s wings were single-surfaced and resembled a pair of half-cones.

This vocabulary advice comes from an old skydiver who has jumped both a Delta II and a Paradactyl.

 

[carvalho2008]

Please be more precise with your terminology.
That proposed F-104 variant might have a delta wing, but it does not resemble most of Rogallo’s flexible wings. Rogallo’s wings were single-surfaced and resembled a pair of half-cones.

This vocabulary advice comes from an old skydiver who has jumped both a Delta II and a Paradactyl.

ok, sorry...Peter Girard by Ryan Aeronautical Company

 

[carvalho2008]

Man, I love the Flying Flapjack...

Of all the roads not taken, I so wish we HAD taken this one! Turboprop fighters with T38 cores (to hell with the T40 units, the combining gearbox just was not up to the task!)

In a modern redesign of the XF5U, the gearbox problem would already be solved by current helicopter technology, but in reality, it would be completely unnecessary. At the time and in the original model, the two propellers had to be connected to the single propulsion group, otherwise, if one of the engines failed there would be a catastrophic imbalance. Nowadays, it would be enough to use counter-rotating propellers on each side. It would be much lighter and more power efficient.



Another point is that the XF5U is a wing body, allowing a lot of internal space for fuel or weapons bays....an airplane that takes off from 200 meters without relative wind would be sensational for any role, fighter, cod, refuel, etc. .

In a new reading of the original project, if you tilt the engines just a little, you will probably be able to take off without wind in 50 meters...

 

[Scott Kenny]

In a modern redesign of the XF5U, the gearbox problem would already be solved by current helicopter technology, but in reality, it would be completely unnecessary. At the time and in the original model, the two propellers had to be connected to the single propulsion group, otherwise, if one of the engines failed there would be a catastrophic imbalance. Nowadays, it would be enough to use counter-rotating propellers on each side. It would be much lighter and more power efficient.

I'm not sure that counter-rotating props on each side would prevent the need for a cross-power shaft. Losing one prop would be really bad, especially when the aircraft design is using the prop vortex to counteract the wingtip vortex.

These days, I'd go for a single T56 or even the Osprey engine, turning through a locked automotive differential and then 2x 90deg gearboxes to the props. That setup provides opposite-rotating props without any extra gears anywhere. Downside is that takes up the space on the centerline of the aircraft that is needed for rockets and missiles to clear the prop arcs. Thicken the belly a bit and you can have a thin bay like the F-22 that can only hold AMRAAMs, with deeper bays off the centerline.

Another point is that the XF5U is a wing body, allowing a lot of internal space for fuel or weapons bays....an airplane that takes off from 200 meters without relative wind would be sensational for any role, fighter, cod, refuel, etc. .

In a new reading of the original project, if you tilt the engines just a little, you will probably be able to take off without wind in 50 meters...

Tilting the props would also allow for tricycle landing gear instead of tail dragging, and that will also simplify the cockpit visibility needed.

 

[helmutkohl]

worth pointing out that Singapore, a country with no carriers, has opted for the f-35b version

 

[carvalho2008]

 

[SteveO]

STOVL or V/STOL is best for fighters

VTOL wastes fuel and aerodynamic surfaces in take off and landing.

STOL needs bigger control services, heavy duty landing gear, afterburner take offs and thrust vectoring and thrust reversers or parachutes for landing in really tight landing zones.

STOVL or V/STOL needs an elegant engine solution (tandem fan with switch in nozzles maybe?). Then it can have pretty much CTOL aerodynamics and airframe and operate however it’s needed STOL or VTOL or CTOL.

Obviously there is a bit more to it than that but the F-35B isn’t the best V/STOL fighter we can come up with. (I like the F-35B by the way!).

 

[riggerrob]

worth pointing out that Singapore, a country with no carriers, has opted for the f-35b version

Singapore is a small city-state with little land available to build long runways.
Re: 1973 atom Kippur War, anyinvader would start by cratering runways to ground the Singapore Air Force.