Why VTOL jets are generally a bad idea (but would an ESTOL fighter work?)

[Avimimus]

The ability to operate without a runway is attractive. This allows dispersal, making aircraft difficult for an enemy to take out on the ground or predict.

There is also the possibility that a fighter could use a FARP - allowing it to operate in areas without airfields or to operate closer to the front lines (allowing faster responses to threats or calls for CAS).

Theoretical benefits (other than VTOL):

- Excess power (excellent acceleration) is theoretically possible. This is especially true if the lift engines can be engaged for short periods in forward flight.

- A reduction in wing area is possible (theoretically allowing for higher cruising speeds with less induced drag)


Why this doesn't help:

- Complexity and difficulties of design (e.g. correct spacing of thrust, problems with area ruling, control mechanisms at low speed, ground heating, hot air ingestion, the difficulty addressing engine failure).

- Fuel load is limited by the total thrust of the engines at takeoff. Furthermore, the engines add excess weight and volume. So range will fundamentally be much lower than a CTOL design. Similarly, any armament or equipment will be cutting into scarce fuel reserves.

- The actual excess power required for VTOL work isn't used for low-altitude as air-density and supersonic heating will keep your speeds below Mach 1.3 anyway (and then only for short periods of time). So it is basically useless for a low altitude aircraft.

- The excess power could allow high supersonic speeds at altitude. However, the fuel used in climbing to altitude means that interception range will be very limited. In general a CTOL interceptor of equal weight can patrol for longer, can afford a longer climb and can operate off of a conventional airfield further from the front.

As a result, almost every lift-jet design has been a failure.


So what works?

- The Harrier Jump-Jet obviously worked (although typically in a CTOL mode).

- A tail sitter (like the Sukhoi Shkval/Squall studies) might work as a point interceptor (similar to a Komet or Natter but with more efficient turbojet engines).

- What about larger aircraft? Any economies of scale (i.e. how was the YAK-133 a good idea?)


A better solution to the requirements?

A possible compromise would be an ESTOL design - using some lift jets or blown flap technology, but also able to operate as a high speed fighter or attack aircraft. Something like the Sukhoi T-6.

Could a high-subsonic/supersonic aircraft be designed that takes off and lands on an unprepared strip that is less than 200 metres in length (a supersonic OV-10?)


Anyone know of some designs along these lines?

What do you think of the overall problem?

 

[Michel Van]

what stands abbr ESTOL for ?

The use of lift jets have one big problem Dead weight during flight
here was the concept of Harrier Pegasus engine brilliant.

and Harrier show in Falkland war some brillant feature thank it VTOL engine
like waiting on island until Argentines air force arrive, take off and attack them while enemy airplane is running low on fuel.
or transport of Harriers on container ship to battle field

oddly the concept of blown flap technology aka upper surface blowing (USB) was adapted to transporter, not to Fighters !
it would give a fighter bomber STOL capacity or allot payload to be drop on enemy.
i think it was Boeing who made studies about this kind of aircraft.

 

[shedofdread]

I think possibly more could've been made of the Buccaneer concept (see 'Spitfire to Eurofighter'). That used blown flaps to great effect.


As regards the E(extreme?)STOL thing - the BAe P103 always looked interesting but ultimately, the Peggy in a Harrier was a better concept. Work of genius IMO...

 

[Avimimus]

Neat to find out about the P.103

what stands abbr ESTOL for ?

Extreme short take-off and landing. Think 200-300 metres (or even less), rather than 500-800 metres.


Thanks for the thoughts. How would you guys go about designing such an aircraft? Lift-jets, blown flaps, thrust vectoring (at less than 90 degrees), a box/tandem wing?


I really liked the original LARA concept (OV-10 requirement) , but this is obviously a role for a much larger and faster aircraft.


Btw. I suspect that lift-jets might not be so bad in terms of dead-weight - once the aircraft is in forward flight the wings usually generate more than enough lift (at least if the aircraft has anything remotely like VSTOL power to weight ratios). It would seem that loss of volume and added complexity (multiple engines to maintain) are the real killers of such concepts.

 

[JohnR]

- The Harrier Jump-Jet obviously worked (although typically in a CTOL mode).

Hardly CTOL, a short rolling take off to benefit weapons load and fuel usage, and a very short rolling landing or in the case of a sea borne operations vertical landing.

Whilst on the subject of Harriers/Vectored Thrust. Has the potential developments reach its end in light of the F35B and its lift fan? What happened with regard plenium chamber burning was it a dead end?

Regards

 

[Sundog]

You'll see VSTOL advances, IMHO, in concert with electric propulsion developments. NASA is already flying a model using distributed propulsion for VTOL and flight. However, I don't know that you'll see it in a fighter type aircraft due to the volume distribution requirements. Maybe that "pulse jet" lift technology Boeing was working on could be used for a fighter type aircraft. However, to be efficient in vertical propulsive lift you want a low velocity delta distributed over a large area (Like helicopters, tilt-rotors, etc.) to be efficient and lift fans still require a large amount of internal volume. Eventually, lift fans will probably be driven by electric motors, but you're still going to have packaging problems.


As for blown flaps, those were also used on the TSR.2, F-104, and other aircraft. The problem with them is they're tied into engine speed. USB flaps are great at low speeds, but tend to have a penalty at higher cruising speeds. Which is why the C-17 just drops the flaps into the jet efflux to increase it's lift.


The problem with Harrier type installations, is once again, the packaging. For a supersonic aircraft that is area ruled, it's really better to have the powerplant in the tail (F-35B). The P.1216 style designs from BAe were probably the epitome of a harrier style engine layout for a fighter.


The problems with PCB were noise and heat effects on the aircraft structure. Once again, not so much of a problem if the engine is in the tail. Also, if you really wanted that style of engine, with all of the advancements we have made in turbomachinery technology, you could probable develop an engine today that would put out dry thrust equivalent to those older designs that were to use PCB. Though you're still going to have the packaging issues; which also goes into how difficult it is to change it out. Don't forget, to change the powerplant on the Harrier they had to remove the wing. With a conventional layout, you just pull it out the back, though the Navy would prefer if it could just be dropped down.

 

[CiTrus90]

I'm not an engineer, but i think you would need to better define the role of such an aircraft.

Are we thinking along the lines of an air superiority fighter, a point interceptor, a CAS/COIN aircraft or a cargo?
What are the mission requirements, except for the VSTOL/ESTOL capability? Supersonic/subsonic speed, short/medium/long range, payload, etc.? What kind of threats is it meant to face and be able to survive?

If you need a point interceptor, that's what SAMs are for.
For a CAS aircraft instead, supersonic speeds would be unnecessary and even detrimental, in my opinion.
For a cargo, a part from the interesting designs for SOFTA, if VTOL is a must you could always revert back to helicopters and tiltrotors.

Other interesting concepts though, could be Lockheed VARIOUS, the already mentioned P.1216 and the AIT.320, but it all really comes down to what mission requirements such an aircraft is going to have.

 

[pathology_doc]

Tailsitters are probably viable now that we have inherently unstable aircraft and electronic systems which can keep the thing stable and back them down under thrust. Perhaps it's time to revisit that concept. Ground erosion would still be an issue, but the other problems they had all seem soluble now.

 

[Avimimus]

I'm not an engineer, but i think you would need to better define the role of such an aircraft.

Are we thinking along the lines of an air superiority fighter, a point interceptor, a CAS/COIN aircraft or a cargo?
What are the mission requirements, except for the VSTOL/ESTOL capability? Supersonic/subsonic speed, short/medium/long range, payload, etc.? What kind of threats is it meant to face and be able to survive?

I guess that is basically what I was trying to get at here:

What requirements does this technology actually offer an advantage for? Is jet VTOL technology actually appropriate for any role?

Do the design tradeoffs involved in making a VTOL jet (e.g. high thrust to weight ratio) benefit any other capabilities? Or will having VSTOL always lead to an overall weaker design?

Would an ESTOL design always be superior?

 

[Jemiba]

... Do the design tradeoffs involved in making a VTOL jet (e.g. high thrust to weight ratio) benefit any other capabilities?

Am I wrong, or would for example the F-15 have been (theoratically) able to take off vertically,
given its thrust/weight ratio ?
- For quite a time there were thoughts about launching fighters from ships fitted just with heli
pads, probably unsuitable even for ESTOL.
- Several VTOL aircraft were designed for beingn launched from forrest glades, as giving them
the most secure cover, when on the ground.
- VTOL passenger jets were seen as a high speed replacement of helicopters for inter city routes.

....

What has to be taken into account are the reasons that were seen for real VTOL. So I cannot fully
agree to the title. Reasons and tactics are changing regularly and I wouldn't be that sure, that we
won't see pure VTOL coming up again one day.

 

[CiTrus90]

I suppose ESTOL gives and will give always overall better performances over VTOL with current technology.

The only role open for a VTOL jet now, in my opinion, is in close air support because that's the only role for which an aircraft is absolutely necessary in an all out war.

If we're to consider a peer to peer conflict, worst case scenario, i suppose every airfield close to the front line will be pounded to rubble in the first hours of it. This would mean game on for ground operations, and given the number differencies between NATO and opfor countries with peer capabilities to NATO's, it wouldn't be acceptable from a western point of view.

This means you need to be able disperse and launch tactical air support from pretty much any suitable space without giving away your position to the enemy. One way to do this, could be the one Sweden and Switzerland (just to name a couple of countries) have come up with: make your higways compatible with aircraft operations. The other option is to proceed with a VTOL attack aircraft.

What's needed in my opinion, is an aircraft with the same mindset that was behind the A-10 but mixed with Harrier capabilities. Nothing too technologically complex avionics wise, as much heavily armed as possible for a VTOL platform. Not at all necessarily supersonic.

The VTOL requirement arises from a need, and in any other role it would limit too much the design.

 

[RyanC]

The reason VTOL looked like a good buy in the early 1960s is that they were projecting in the future 100 to 1 thrust to weight ratios for liftjets; meaning that if you had a F-105/F-35 sized aircraft of 50,000+ lbs; then taking off vertically would with a T/W of 1.15 would need only about 600 pounds of parasitic mass for the liftjets.

 

[mz]

Even though an F-15 can have T/W greater than 1, it would not be controllable at low speed. However with thrust vectoring and computer control a lot of things have become possible.
https://www.youtube.com/watch?v=N2o6Ks55xvw
https://www.youtube.com/watch?v=uxRhWiTlra0

I think with a modified gear and software you could take off or land a Raptor on really short runways? Probably not a lot of payload or fuel though.

 

[riggerrob]

What about VTOL executive transports?

 

[shin_getter]

The ability to operate without a runway is attractive. This allows dispersal, making aircraft difficult for an enemy to take out on the ground or predict.

There is also the possibility that a fighter could use a FARP - allowing it to operate in areas without airfields or to operate closer to the front lines (allowing faster responses to threats or calls for CAS).

The minimum operating space requirements of conventional designs can be seen in STOBAR carriers (engineers can put up a ramp and arresting gear), which is merely a few multiple length of aircrafts already. If damage so so serious that even this level of operating surface is unavailable, it is unlikely that supporting infrastructure survived at all either. Ramps is after all, thrust vectoring for free so a neat solution.

As for FARP in general, forward refueling from the air is safer and faster than landing, while fast rearm turn-around time hasn't been a big thing in air combat, with point defense interception mission done by SAM while offensive missions gets done by huge strike packages that require coordination with a lot of different and often large airframes. The need may be show itself if two equivalent air force go at it but it is a very unlikely situation and hasn't happened.

If forward based CAS is needed, helicopters and STOL ground attack aircraft is available. Alternatively, modern "artillery" simply have enough range. to provide support without using aircraft.

 

[Fighterreaper97]

Super extremely short take off and landing fighter aircraft that can have a take off and landing distance of 100 feet would be much safer than vtol aircraft

 

[Nik]

From post #5 "with regard plenum chamber burning was it a dead end?"

My friend 'Mr. Rowe', who claimed his small team solved the supersonic Pegasus / Harrier issues that had thwarted the big, official crew, said 'PCB' was a dead end. My later reading suggested this was due to over-heated nozzles, eroded run-way/pads etc etc. Bit like after-burners make really bad neighbours due to their extended, almost-rocket exhaust...

Sadly, after he finished chortling about the shortcomings and limitations of PCB, he went 'full-NDA' and that was that...

 

[T. A. Gardner]

The single biggest issue with VTOL aircraft is you need a greater than 1 to 1 thrust to weight to take off. That means you need a lot of thrust and have to keep weight low. The result is an aircraft with limited load capacity that has a lot of engine and not much else. This in turn, limits range, performance in flight, and mission flexibility. Sure, range to some degree can be mitigated by in-flight refueling but that takes time and has limitations.

I really don't think that can be gotten around completely.

 

[uk 75]

Rather like aircraft carriers the problem for vstol aircraft is that modern airfields and airports with decent runways are readily available in most places. They are more difficult to put out of action than they used to be but usually our opponents have lacked air power anyway.
A high performance land based aircraft offers better capabilities in most cases than a vstol or carrier based equivalent.
West Germany used the G91 and then the Alpha Jet with a much smaller tail of ground support equipment than RAFG Harriers. But both like forward deployed US A10s were more effective if they used their parent airbases. Elaborate use of paved surfaces like taxiways and roadways at airbases could keep these planes flying and runway repair crews had become pretty good too.
China aims to use large quantities of missiles (as Russia has tried in Ukraine) to deny allied forces use of airbases. But this has never been demonstrated in actual wars. Saddam's missiles made little impact on his opponents' airbases.

 

[Desertfox]

Airfields are ntoriously difficult targets to take out of action. The allies tried repeatedly against Iraq during the Gulf War with limited success, despite dedicated airfield denial weaponry. Except for very niche applications, STOL aircraft can do almost everything a VSTOL aircraft can do and do it better and cheaper.

 

[riggerrob]

What about building an A-10 style airplane with turbo-fans that can swivel to vertical?
This reminds me of a NASA study of a bizjet that resembled an early Cessna Citation with straight wings and an extra lift fan in the nose. The goal was to extend executive transport beyond the 300 mile limit of helicopters.

An even more bizarre concept is reviving the Pogo CTOL but installing the cockpit in a tip tank. That location would make it easy to tilt the cockpit to horizontal for vertical landings. Counter-balance with a similar-sized electronics pod on the opposite wing-tip.
As an aside, what is the disadvantage of moving contra-rotating propellers to the trailing edge of a VTOL delta? this would move them closer to the ground. Would they kick up too much FOD?

 

[Nik]

"As an aside, what is the disadvantage of moving contra-rotating propellers to the trailing edge of a VTOL delta?"

I'm sorry, I'm struggling to visualise this: So, like a compound helo with 'pusher' prop(s) for speed, but the static lift provided otherwise ??

 

[riggerrob]

"As an aside, what is the disadvantage of moving contra-rotating propellers to the trailing edge of a VTOL delta?"

I'm sorry, I'm struggling to visualise this: So, like a compound helo with 'pusher' prop(s) for speed, but the static lift provided otherwise ??

No, I am only talking about a pusher delta similar to the Convair XFY Pogo that the USA experimented with during the 1960s.
Pogo and most of its competitors had contra-rotating propellers on their noses, well above the ground.
I am asking about a delta-winged airframe with a pusher propeller(s) mounted center rear of the trailing edge. This has been proven impractical for light deltas because of pitch control problems during lift off.
In a VTOL delta, this would put the propeller(s) almost at ground level. I am wondering if mounting propeller(s) this close to the ground would create additional problems with down-wash and FOD.
All the static lift would be provided by the pusher propeller(s), since the prop shaft would be vertical in landing configuration.

 

[riggerrob]

"As an aside, what is the disadvantage of moving contra-rotating propellers to the trailing edge of a VTOL delta?"

I'm sorry, I'm struggling to visualise this: So, like a compound helo with 'pusher' prop(s) for speed, but the static lift provided otherwise ??

I was thinking of a Convair XFY Pogo, but with pusher propeller(s) mounted at the aft end of the fuselage. This would put Prop(s) at the center of the trailing edge of the delta wing, very close to the ground.
This configuration has proven impractical for light pusher deltas taking-off with their delta wings horizontal.
My question is about pusher deltas taking off vertically. IOW with the propeller shaft vertical for VTOL landing and take-off.

 

[T. A. Gardner]

Probably one of the most practical, would be going with the ESTOL, to coin a term. That is, the Extreme STOL aircraft. The historical example is the F5U Flying Pancake.



While it had some mechanical issues in 1944 -45, I think with modern technology you could make this one workable today as an attack / ground support aircraft with limited fighter capability. It might make a great helicopter killer and could certainly be used as an escort and complement to the V-22 Osprey.

 

[Nik]

( Apologies if a stub just posted, my ISP / Browser is glitching..)

Would a modern version, using turbo-props, place the jet-engines in line with those props rather via zig-zag gear-box / drive train ??

Or safer to politely shrug and consign to history. Given they could literally launch/land on a tennis court, original would have been so-handy instead of 'Hurricats' for convoy escort carriers, sorta flat-topped merchant ships. I reckon they'd earn an "Oh-Fook !! It's a 'Deadly Dee' !!" from any Condor or U-Boot crew sighted, but missed the niche...

 

[_Del_]

I am still surprised that after all the money we threw at tandem fan stovl studies, that the F-35 ended up with a (more technically and mechanically complex) lift-fan, and we got nothing from tandem fans.

Image courtesy of Mark Nankivil:

BAe P.115:

https://www.secretprojects.co.uk/attachments/p115a-jpg.139823

Vought TF-120 (and other):
https://www.secretprojects.co.uk/threads/vought-ltv-v-stol-tandem-fan-fighters-tf100-to-tf300.783

 

[_Del_]

What about building an A-10 style airplane with turbo-fans that can swivel to vertical?

View: https://www.youtube.com/watch?v=kwDVHaghawQ


Or more seriously, something like the Grumman 698?

As an aside, what is the disadvantage of moving contra-rotating propellers to the trailing edge of a VTOL delta? this would move them closer to the ground. Would they kick up too much FOD?

Well, a few potential issues that come to mind quickly would be: prop clearance and the necessity for longer struts and/or structure. The prop is also getting dirtier air in forward flight. Being that close to the ground has the potential to set up nasty resonance when the air comes bouncing back into the prop and aircraft. And mostly, if there is a fire while oriented vertically and the pilot wants to exit the aircraft, he wants to go down and quickly (which will now be towards a spinning prop).

 

[Fighterreaper97]

Airfields are ntoriously difficult targets to take out of action. The allies tried repeatedly against Iraq during the Gulf War with limited success, despite dedicated airfield denial weaponry. Except for very niche applications, STOL aircraft can do almost everything a VSTOL aircraft can do and do it better and cheaper.

Thank someone that finally speaks my language. Canard foreplanes act as a lift generator to shorten take offs and landings

 

[riggerrob]

What about building an A-10 style airplane with turbo-fans that can swivel to vertical?

View: https://www.youtube.com/watch?v=kwDVHaghawQ


Or more seriously, something like the Grumman 698?

As an aside, what is the disadvantage of moving contra-rotating propellers to the trailing edge of a VTOL delta? this would move them closer to the ground. Would they kick up too much FOD?

Well, a few potential issues that come to mind quickly would be: prop clearance and the necessity for longer struts and/or structure. The prop is also getting dirtier air in forward flight. Being that close to the ground has the potential to set up nasty resonance when the air comes bouncing back into the prop and aircraft. And mostly, if there is a fire while oriented vertically and the pilot wants to exit the aircraft, he wants to go down and quickly (which will now be towards a spinning prop).

That's why ejection seats were invented.

 

[Archibald]

Probably one of the most practical, would be going with the ESTOL, to coin a term. That is, the Extreme STOL aircraft. The historical example is the F5U Flying Pancake.

View attachment 682902

While it had some mechanical issues in 1944 -45, I think with modern technology you could make this one workable today as an attack / ground support aircraft with limited fighter capability. It might make a great helicopter killer and could certainly be used as an escort and complement to the V-22 Osprey.

Yeeees ! I dream of a modern day variant with plain good PT-6 turboprops. It would be a complete killer.

 

[Desertfox]

Theoretically, an XF5U with turboprops could be capable of full VTOL capability.

 

[Dick]

I am still surprised that after all the money we threw at tandem fan stovl studies, that the F-35 ended up with a (more technically and mechanically complex) lift-fan, and we got nothing from tandem fans.

Image courtesy of Mark Nankivil:

BAe P.115:

https://www.secretprojects.co.uk/attachments/p115a-jpg.139823

Vought TF-120 (and other):
https://www.secretprojects.co.uk/threads/vought-ltv-v-stol-tandem-fan-fighters-tf100-to-tf300.783

Lockheeds original concept was to have a tandem fan. Supposedly, they hated the idea of using multiple exhaust nozzles, front and back having a different "stealth" profile. I'm sure a solution could be found but they cheaped out.

That entire procurement didn't make sense. MD was offering a lift fan with tip driven turbines. Like the Ryan XV-5, but in the same orientation as the F-35. It would have cost 1/3rd the price to build compared to Lockheeds shaft driven lift fan. The lift fan was Yakovlev's idea. Clearly no one had anyone intention of picking the X-32. And MD already had a massive contract with the F-15 and F-18 with a less expensive lift fan. But for some reason Lockheed got their shaft fan.

I don't think we'll ever see a tandem fan. Poor, poor tandem fan

 

[Dick]

The ability to operate without a runway is attractive. This allows dispersal, making aircraft difficult for an enemy to take out on the ground or predict.

There is also the possibility that a fighter could use a FARP - allowing it to operate in areas without airfields or to operate closer to the front lines (allowing faster responses to threats or calls for CAS).

Theoretical benefits (other than VTOL):

- Excess power (excellent acceleration) is theoretically possible. This is especially true if the lift engines can be engaged for short periods in forward flight.

- A reduction in wing area is possible (theoretically allowing for higher cruising speeds with less induced drag)


Why this doesn't help:

- Complexity and difficulties of design (e.g. correct spacing of thrust, problems with area ruling, control mechanisms at low speed, ground heating, hot air ingestion, the difficulty addressing engine failure).

- Fuel load is limited by the total thrust of the engines at takeoff. Furthermore, the engines add excess weight and volume. So range will fundamentally be much lower than a CTOL design. Similarly, any armament or equipment will be cutting into scarce fuel reserves.

- The actual excess power required for VTOL work isn't used for low-altitude as air-density and supersonic heating will keep your speeds below Mach 1.3 anyway (and then only for short periods of time). So it is basically useless for a low altitude aircraft.

- The excess power could allow high supersonic speeds at altitude. However, the fuel used in climbing to altitude means that interception range will be very limited. In general a CTOL interceptor of equal weight can patrol for longer, can afford a longer climb and can operate off of a conventional airfield further from the front.

As a result, almost every lift-jet design has been a failure.


So what works?

- The Harrier Jump-Jet obviously worked (although typically in a CTOL mode).

- A tail sitter (like the Sukhoi Shkval/Squall studies) might work as a point interceptor (similar to a Komet or Natter but with more efficient turbojet engines).

- What about larger aircraft? Any economies of scale (i.e. how was the YAK-133 a good idea?)


A better solution to the requirements?

A possible compromise would be an ESTOL design - using some lift jets or blown flap technology, but also able to operate as a high speed fighter or attack aircraft. Something like the Sukhoi T-6.

Could a high-subsonic/supersonic aircraft be designed that takes off and lands on an unprepared strip that is less than 200 metres in length (a supersonic OV-10?)


Anyone know of some designs along these lines?

What do you think of the overall problem?

What do you mean by "basically useless for a low altitude aircraft"? Helicopters are low altitude vtol designs. Attack helicopters are entirely used in low altitude operations. So maybe a compound helicopter would be more suited for that idea. Which brings everything back to "what are your operating requirements?"

Lift jets are a cheap solution, but largely useless. Totally works, but why bother when there are better options? Blown flaps put huge thermodynamic strain on engines. You could try getting the desired effect with an axillary unit or with a multicycle engine but then two problems appear. 1) why not use that excess power and complexity for vtol? 2) blown flaps are constantly getting clogged and very hard and costly to clean. That's why they didn't catch on. So why bother with that? The "rolling takeoff" used by Harrier is already an ESTOL configuration. So solved.

Tail sitters are bad ideas because this drift way too much in even the slightest headwind. Ryan did a lot of work with the tail sitter concept and even though solutions could be found, they were not worth the cost as rotating the plane 90 degrees lowers the frontal area and thus eliminates the need for said solutions.

The overall problem is there is no clear design parameter. Multiple types of vtols exist and each one is better suited for a particular operational parameter. You wouldn't use a rotating prop vtol for a supersonic application. When the USAF issued a competition for the A-10 they specifically listed a subsonic design. So highly swept wings and afterburners were out. A solution X for any problem Y requires parameters. If loitering is a requirement, like an attack aircraft, different engines, intakes and even propulsion is required. So what is you airplane going to do?

 

[Scott Kenny]

Hardly CTOL, a short rolling take off to benefit weapons load and fuel usage, and a very short rolling landing or in the case of a sea borne operations vertical landing.

Whilst on the subject of Harriers/Vectored Thrust. Has the potential developments reach its end in light of the F35B and its lift fan? What happened with regard plenium chamber burning was it a dead end?

Regards

Had significant issues with hot gas reingestion (which kills thrust) and surface erosion/FODing adjacent aircraft.

The reason VTOL looked like a good buy in the early 1960s is that they were projecting in the future 100 to 1 thrust to weight ratios for liftjets; meaning that if you had a F-105/F-35 sized aircraft of 50,000+ lbs; then taking off vertically would with a T/W of 1.15 would need only about 600 pounds of parasitic mass for the liftjets.

I don't think any engine has gotten a 100:1 T:W...

As an aside, what is the disadvantage of moving contra-rotating propellers to the trailing edge of a VTOL delta? this would move them closer to the ground. Would they kick up too much FOD?

In flight, the props would suffer from differential pressure on the upper and low halves of the arc.

They may or may not kick up too much FOD, that probably depends on just how high the disc loading is. Lower is better here.

Yeeees ! I dream of a modern day variant with plain good PT-6 turboprops. It would be a complete killer.

Needs more power than a PT6, you'd want T700s or equivalent in the 2000hp range, if not something in the 3000hp range for twin engines. Using a single T56 or Osprey engine for a single-engined solution.

 

[uk 75]

solution looking for a problem.

In low intensity warfare airbases are nearly always available (Gulf, Kosovo, Serbia, Afghanistan etc)

In high intensity warfare airbases are at risk from air or missile strike. But hardened shelters, dispersed locations on big sites and the ability to use roads etc as well as repair runways.

Which leaves small carriers as the main user, hence F35B/Yak 141 replacing Harrier.

Civilian use may come with skycabs but the 60s idea of VTOLports still has safety issues even if new technology makes engines quieter. A Chinook size VTOL crashing on take off/landing on a city or suburban street is a real headache