Embraer's new KC-390 looks like it could fit the job, with mission gear installed.
Alternate Aircraft of Nations
- Thread starter Count of Crisco
- Start date
Sorry to be so late but things have been distracting me from AH lately!
There was just such a project in the works in West Germany in the 1960s.
Dornier Do-31
As you can see from the Wikipedia link provided, Dornier responded to a general NATO call for proposals--remarkably but perhaps in view of the outcome not surprisingly apparently no one else did. The bottom line was that it could be done but it cost a great deal. Perhaps if an American firm had responded they'd have the pockets to persist and then lobby Congress to approve funding the thing? The easiest ATL shortcut would be to have Dornier partner with such a firm. Another approach would be for a British firm to respond using Pegasus engines--or of course any company in any nation could have opted to procure Pegasus engines I guess.
In fact reading the article--I last looked at this many years ago so I forgot--Dornier did rely on Pegasus! though not exclusively; the main heavy lift thrust came from some RR engines installed vertically, the Pegasuses (Pegasii?) were meant to combine main forward flight thrust and fine vector control during takeoff and landing.
Ideally, with a multi-engine installation like this one might want to simplify the Pegasus or some comparable engine to provide just one vectoring output instead of four; the engine was designed for a single engine install where the engine's four nozzles would straddle the airplane center of mass. In effect the Pegasus is a kind of turbofan, where the bypass air exhausts through the forward pair of fans and the core exhaust is vectored out the rear pair, each nozzle having two degrees of freedom (I think)--the slats can be flapped up or down venetian blind style, and the nozzle rotated around its axis. With multi-engine install, you don't need so many thrust points independently controlled, though admittedly if you put them all on the wing some differential between fore and aft is necessary. But say instead you have sets of thrusters on the wing, and also a set forward under the nose and another under the tail, then you have 4 widely separated thrust centers and vectoring each one in unison should give you ample control; the forward engine might not be much use for forward cruise thrust but the need for such thrust is far lower than for jet lift; conceivably the tail engine alone (routing through a different nozzle for efficiency) could be plenty, with the wing engines available to boost flight thrust for rapid climb and other fancy maneuvers--not generally needed for a civil vehicle of course but perhaps crucial for survival in contested air-spaces in combat.
Anyway devoting a considerable amount of weight to engines vertically installed to provide raw lift thrust is a pretty common approach taken for military VTOL aircraft--which except for the Harrier variants have not actually been much deployed due to their absurdly high operational costs and low payloads and short legs. The Pegasus is clever, installed as intended, because it provides good VTOL control authority while also doubling as the main thrust engine for cruise flight, and British and USMC operators soon found the vectoring features came in very handy in combat maneuvering at airborne speeds--including being able to slow down to airspeeds their foes could not match without stalling out and crashing.
A transport is simply not going to be able to outmaneuver an aggressive fighter, but one with these VTOL capabilities could do better than a conventional one at evading shots I suppose.
The scale of this aircraft is just under 28 metric tonnes takeoff weight, using two Pegasus engines each producing just under 7 tonnes and 8 vertical-mounted lift jets producing almost 16 tonnes when employed, with about 6 tonnes of net lift for fuel and cargo. Using four Pegasus engines instead, I suppose the thing would have to be scaled down a bit, but control authority with a diamond mounting (one in the nose, one in the tail, two on the wings) would be pretty awesome I'd think. Perhaps we can imagine Hawker, perhaps with American partners, designing such a competitor?
To scale it up to bigger payloads and/or ranges would be quite problematic of course. The specific power and thrust of the Pegasus was supercharged in an attempt to enable a supersonic-capable Harrier successor but IIRC the hotter, even more intense exhaust blast was a real problem, so we'd be looking at either more effectively moving larger masses of air at lower speeds (higher turbofan bypass ratio, which goes against the intended supersonic cruise capability) or simply using more and more Pegasus engines. Each one weighs a fair amount and each one guzzles down fuel so in terms of economical movement of material and men, this will always be a marginal and costly approach, only justified by the contingencies of combat, though of course we can imagine niche civil uses for an aircraft that has no need of a runway. The Do-31 was also very noisy (I read that the frequency of the jet noise was dangerously close to a resonant frequency of the airframe, so we aren't just talking about the comfort of bystanders or even operational personnel here, but structural problems too) and that seems inherent in any attempt to use airflow to provide lifting thrust one way or another; the more the thrust is a matter of lower masses of air being pushed faster, the more intense the noise must be, along with raw power requirement of course
It is a cool idea but obviously marginal and expensive. So much so no one seems to have tried it ever again.
Walking away and thinking about it more, while the Do-31 is the only attempt to design a VTOL subsonic jet transport, we are all generally aware I suppose of many forms of prop/helicopter forms attempted. At low subsonic speeds props and rotors are superior because the wider air intake moves a greater mass--for a given power output this means lower reaction airspeed but the math works out to more or less converge on the ideal thrust/power curve where a given power produces more thrust when moving a larger mass. There are offsetting factors but generally speaking one trades off a lower maximum airspeed attainable for more oomph at low airspeeds. No practical VTOL has ever gone supersonic to my knowledge; at high airspeeds one wants the faster more concentrated power exhaust of a pure turbojet (or rocket!) When we near the speed of sound from below we also encounter issues of first rotor and then propeller blade tips pushing sonic speed before--in the case of rotors providing vertical lift as with helicopters or say the Osprey, long before--the aircraft as a whole is approaching it. There we would want our props to be ducted perhaps. As for rotors, in addition to the advancing tips hitting near-sonic speeds with their issues of higher drag and rapid changing of airflow characteristics early on, the net lift of a given blade varies a great deal depending on whether it is advancing or retreating versus general airspeed, so some high-speed helicopter proposals involve dual counter-rotating rotor sets so that there is always a balanced pair of blades advancing on both sides.
Restating the problem for subsonic transports operating well below sonic speed, at say 400 knots or less, we would be looking at variations on the theme of propellers, rotors or ducted fans moving large masses of air (relative to what jets or even conventional turbofans move) at relatively low airspeeds in the same 200 meters/sec or less ballpark, and as noted there are dozens of proposals along those lines.
Bearing in mind the subsonic transport concept only requires the VTOL capabilities just for takeoff and landing when airspeed of the aircraft is very low, minus its vertical climbing component generally zero in fact, I do recall another proposal which I don't know how to look up right now, wherein very large circular fans built in to the roots of the wings would be spun by a set of auxiliary turboshaft engines (four, six or more surrounding the central fan) to lift an otherwise largely standard jetliner type plane off the ground, and after a transition with the plane gaining horizontal airspeed these ducted fans, their thrust now vectored somewhat backwards and with partial lift on the outer wings, would be closed and shut down while conventionally mounted standard turbofans would provide forward thrust and the plane would then fly much as a conventional jetliner, and thus be able to attain somewhere between 75 to 90 percent of sonic speed. Obviously the volume of the wing interior taken up by the fan would not be available as on a conventional jet of this type to store fuel, therefore range and endurance in flight would suffer unless we used fuselage volume to store the fuel instead. Also with this scheme, three axis control of the lifting thrust is pretty poor!
Anyway the above scheme has been proposed much as I outlined it, but I forget by who and just when, I believe it was again in the mid-1960s.
For lower airspeed not pushing the sonic limit so closely we have of course the famous Fairey Rotodyne; one reason given for abandoning this was its excessive noise but again for combat tactical front line uses this might not be so objectionable--it certainly would need to move in airspace where the "friendlies" have at least air superiority and for that matter over terrain where few to no guerrilla or commando units bearing arms capable of bringing down such a helicopter variant could operate. Choppers generally are terribly vulnerable even to small arms at low altitudes.
The clever trick of the Rotodyne was to omit the requirement for a central turboshaft engine to turn the central rotor, by using a turbine engine core as a turbofan of sorts to route somewhat pressurized and heated air through the rotor blades to the tips where a simple form of jet engine using this pressurized warm flow initially and later substituting ram air somewhat would produce inefficient thrust--but on a long moment arm, it produced a lot of torque. This would spin up the rotor and provide power for helicopter lift at zero horizontal airspeed; transitioning to higher airspeed by using the central turbofans for forward thrust combined with tilting the rotor as with conventional choppers, eventually the airspeed would provide autogyro torque to sustain the rotor spin, allowing the tip jets to be shut down. Also a stub wing set would provide airplane-style lift lowering the load on the rotor which permitted higher airspeed and I suppose greater lift/drag efficiency too. Thus we have a vehicle that takes off like a helicopter and transitions over to being largely a turbofan propelled airplane, then can slow down and land vertically as a chopper again.
If we provided a dual synchronized counter-rotating pair of rotors to guarantee symmetric advancing blades, I suppose the airspeed could be pushed up considerably closer to sonic speed, perhaps to match the airspeed of conventional subsonic jetliners, to Mach 0.8 or more. The fact that the dual-role turbofan, acting initially as a sort of supercharging afterburner pneumatic turbo"shaft" (without the shaft!) and later as a thrust engine, ought to be mounted on top of the aircraft body for greatest efficiency in the take off and landing role, puts loud jet engines just above the payload below, but also means the air intakes are mounted far up to minimize risk of foreign object debris being sucked into the intakes.
So, I suppose something like that would be the practical solution if NATO or someone else were to again desire something as fast as a subsonic jet to be able to land and take off again from a zero-runway length landing zone. Versus the Do-31 jump jet approach, it would not have the enhanced jinking ability at high speed flight but the economics of operating it might not be so ruinous, provided we could haveroutes to the LZ and back again to rear bases with low hazards of interception or surface AA fire--nor would the enhanced dodging ability of a Do-31 enable it to survive long engaged by a high quality fighter nor taken by surprise by hidden AA fire from below!
OTL of course, wisely or foolishly as the case may be the solution adopted by the US military, for applications where a simple heavy helicopter will not do, is the Osprey, whose engines are essentially a hybrid between turboprops and helicopter turboshafts, and with rotors also a hybrid between high speed propellers and low speed rotors, mounted so as to swing between vertical and turned to an intermediate angle between vertical and horizontal propeller style attitude. The rotors demand more power for a given lift thrust than helicopter rotors would, but provide more thrust at a given power than conventional propellers would. It took a long time and a whole lot of money to develop, and last I heard it remained expensive to operate and also very risky even by combat aircraft standards. But there it is, your tactical transport. It isn't a "jet" in that little of its thrust comes from jet exhaust, but certainly the engines are turbine core things. Arguably my advanced Rotodyne evolution is more of a "jet."
But why is it important that propulsion should be accomplished without some kind of visible spinning prop/rotors?
Restating the problem for subsonic transports operating well below sonic speed, at say 400 knots or less, we would be looking at variations on the theme of propellers, rotors or ducted fans moving large masses of air (relative to what jets or even conventional turbofans move) at relatively low airspeeds in the same 200 meters/sec or less ballpark, and as noted there are dozens of proposals along those lines.
Bearing in mind the subsonic transport concept only requires the VTOL capabilities just for takeoff and landing when airspeed of the aircraft is very low, minus its vertical climbing component generally zero in fact, I do recall another proposal which I don't know how to look up right now, wherein very large circular fans built in to the roots of the wings would be spun by a set of auxiliary turboshaft engines (four, six or more surrounding the central fan) to lift an otherwise largely standard jetliner type plane off the ground, and after a transition with the plane gaining horizontal airspeed these ducted fans, their thrust now vectored somewhat backwards and with partial lift on the outer wings, would be closed and shut down while conventionally mounted standard turbofans would provide forward thrust and the plane would then fly much as a conventional jetliner, and thus be able to attain somewhere between 75 to 90 percent of sonic speed. Obviously the volume of the wing interior taken up by the fan would not be available as on a conventional jet of this type to store fuel, therefore range and endurance in flight would suffer unless we used fuselage volume to store the fuel instead. Also with this scheme, three axis control of the lifting thrust is pretty poor!
Anyway the above scheme has been proposed much as I outlined it, but I forget by who and just when, I believe it was again in the mid-1960s.
For lower airspeed not pushing the sonic limit so closely we have of course the famous Fairey Rotodyne; one reason given for abandoning this was its excessive noise but again for combat tactical front line uses this might not be so objectionable--it certainly would need to move in airspace where the "friendlies" have at least air superiority and for that matter over terrain where few to no guerrilla or commando units bearing arms capable of bringing down such a helicopter variant could operate. Choppers generally are terribly vulnerable even to small arms at low altitudes.
The clever trick of the Rotodyne was to omit the requirement for a central turboshaft engine to turn the central rotor, by using a turbine engine core as a turbofan of sorts to route somewhat pressurized and heated air through the rotor blades to the tips where a simple form of jet engine using this pressurized warm flow initially and later substituting ram air somewhat would produce inefficient thrust--but on a long moment arm, it produced a lot of torque. This would spin up the rotor and provide power for helicopter lift at zero horizontal airspeed; transitioning to higher airspeed by using the central turbofans for forward thrust combined with tilting the rotor as with conventional choppers, eventually the airspeed would provide autogyro torque to sustain the rotor spin, allowing the tip jets to be shut down. Also a stub wing set would provide airplane-style lift lowering the load on the rotor which permitted higher airspeed and I suppose greater lift/drag efficiency too. Thus we have a vehicle that takes off like a helicopter and transitions over to being largely a turbofan propelled airplane, then can slow down and land vertically as a chopper again.
If we provided a dual synchronized counter-rotating pair of rotors to guarantee symmetric advancing blades, I suppose the airspeed could be pushed up considerably closer to sonic speed, perhaps to match the airspeed of conventional subsonic jetliners, to Mach 0.8 or more. The fact that the dual-role turbofan, acting initially as a sort of supercharging afterburner pneumatic turbo"shaft" (without the shaft!) and later as a thrust engine, ought to be mounted on top of the aircraft body for greatest efficiency in the take off and landing role, puts loud jet engines just above the payload below, but also means the air intakes are mounted far up to minimize risk of foreign object debris being sucked into the intakes.
So, I suppose something like that would be the practical solution if NATO or someone else were to again desire something as fast as a subsonic jet to be able to land and take off again from a zero-runway length landing zone. Versus the Do-31 jump jet approach, it would not have the enhanced jinking ability at high speed flight but the economics of operating it might not be so ruinous, provided we could haveroutes to the LZ and back again to rear bases with low hazards of interception or surface AA fire--nor would the enhanced dodging ability of a Do-31 enable it to survive long engaged by a high quality fighter nor taken by surprise by hidden AA fire from below!
OTL of course, wisely or foolishly as the case may be the solution adopted by the US military, for applications where a simple heavy helicopter will not do, is the Osprey, whose engines are essentially a hybrid between turboprops and helicopter turboshafts, and with rotors also a hybrid between high speed propellers and low speed rotors, mounted so as to swing between vertical and turned to an intermediate angle between vertical and horizontal propeller style attitude. The rotors demand more power for a given lift thrust than helicopter rotors would, but provide more thrust at a given power than conventional propellers would. It took a long time and a whole lot of money to develop, and last I heard it remained expensive to operate and also very risky even by combat aircraft standards. But there it is, your tactical transport. It isn't a "jet" in that little of its thrust comes from jet exhaust, but certainly the engines are turbine core things. Arguably my advanced Rotodyne evolution is more of a "jet."
But why is it important that propulsion should be accomplished without some kind of visible spinning prop/rotors?
Bit of confusion here. The DO-31 was submitted to the NMBR-22 requirement, which was a modification of NMBR- 4. NMBR-4 was for a V/STOL transport, and though the committee selected 5 designs for further study, they basically came to the conclusion that joint production of a NATO transport was impracticable. NMBR-22 was then launched with the requirements widened. Dornier were not the only ones to submit. NMBR-4 had 25 submissions from 6 countries, at least some of which ended up in NMBR 22. Some of aircraft associated with the process are:
Breguet 941 -STOL, not VTOL. Marketed by Breguet to the French Airforce and McDonnel Douglas, who bought the license, in the US. No orders presented and only one prototype and 4 production aircraft were ever built
De Haviland Canada DHC-4 Cariboo - STOL as well. 150 some built for the US Army as a tactical transport, also operated by Australia, Canada, India, Malaysia and Spain, among others. Also found a niche in civilian transport in rough areas.
Ling-Temco-Vought XC-142- American Tilt Wing V/STOL. Five prototypes built but the three American services pulled out of the program one by one and the project was cancelled.
Armstrong-Whitworth AW.681. Jet V/STOL transport that actually won a similar contest in Britain but was killed by the 1957 white paper
Fiat G.222 - Twin Engine STOL Turboprop. When the NATO requirement fell through it was adopted by the Italian Airforce. It is still in service and over 100 have been sold to 9 other Airforce's around the world.
There were also about a dozen other designs from British companies submitted (it was a hard time in the British aircraft industry) with at least 3 just from English Electric. Some of these were STOL but others were V/STOL or could be converted to be.
Some third thoughts---
What if we take the Lockheed "Hercules," which has after being deployed in the 1960s become a mainstay ubiquitous machine around the world, accomplishing pretty high subsonic speed and high payload and good short/poorly developed STOL capabilities, and try to stretch it into having VTOL ability?
I'm thinking we start with what can be done with its installed standard turboprop engines plus some auxiliary turboshafts fore and aft. If we can modify the main engines on the wing to collectively drive a shaft running to the wing tips, this shaft can drive a ducted fan mounted there. We might want to make it swivel around to rotate from its axis being vertical to horizontal, but maybe we don't have to do that. Say it is fixed flat in a shrouding duct, perhaps with venetian-blind style slats to cover the duct above and below during forward full wing borne flight speeds, perhaps without relying on duct detail design to prevent any bad effects, or anyway limit them to simple drag. Now we can get some lift at takeoff straight up. Can we vector it? Well, say we can't for the moment. The main standard props can't develop anything close to their full design thrust with the power being routed to the wing tips like this, but we don't need that thrust yet.
At the nose and tail, we have similar duct-shrouded fixed vertical axis fans in pairs straddling the fuselage, the forward pair behaving like a canard , the aft pair might be buried near the roots of a stretched rear tailfin. Also at the rear, buried in the root of the vertical tail fin (a la the "Fenestron" arrangement in some French helicopters) we have a reversible vertical fan that can provide thrust sideways. These fore and aft fan sets are each driven by auxiliary turboshaft engines.
Now with all seven of these added fans, in principle if we can get the design to close, six of them provide fixed-axis vertical lift thrust that is meant to add up to the weight of the loaded aircraft plus some maneuvering margin. What about the other 5 dimensions of control--forward and aft translation, side translation, and the three turning axes?
Well forward is easy enough. The power available to the main standard propellers is anemic due to most of it being siphoned off to the wing tip fans--and come to think of it, having adopted the "Fenestron" buried fan-prop model, we could put the wing lift fans at the root of the wing instead, though that would as noted in the prior post cut badly into fuel storage volume which we have to relocate or do without. But anemic or not, at low horizontal airspeeds we should have considerable thrust available on fractional power just the same. These advanced turboprop blades are I believe reversible, called "Beta Control," and so we can back up aft as well as ease our way forward.
Pure sideways motion is also available, funny to say! This is the main reason I put that seventh fan in the vertical tail root. By itself, if we crank the blade pitch out of neutral either way, we get sideways thrust that also acts with strong torque on the center of mass to spin the aircraft around--but if we counter that torque by forward thrust on one wing's set of main engine/props and reverse thrust on the other wing, the net thrust of both wings is zero, and the sideways thrust in the tail-fenestron operates, leverged over to the center of mass by the opposing torques, to thrust the aircraft sideways (once we have lifted off the ground that is of course). Again the net thrust might be kind of weak versus the mass for low accelerations, but moving sideways is a matter of fine positioning anyway, not something we want happening at high airspeeds! We can also regard it as a way of opposing side winds.
That takes care of the 3 translation axes; with an aircraft we need control of roll, yaw and pitch as well. Pitch is controlled by differential thrust between the fore and aft lift fans, obviously--depending on the axes of thrust of the main engines versus the vertical height of the center of mass, their thrust might also affect pitch so even if we don't need the fore and aft fans for much lift, they do have to be strong enough to counter any such deviations.
Yaw is the rotation of the aircraft around its vertical axis, and again as already noted the main engines provide some considerable yaw input if they are not thrusting in unison, and we have the vertical tail Fenestron for that too. Once clear of the ground the craft can pivot around its center of mass--for instance, to bring its fore-aft axis in line with the wind, fighting drift due to that wind with a combination of fore-aft and sideways thrust.
Roll is around the fore-aft craft body axis, and clearly by varying the ratio of thrust of the two wingtip lift fans, we can get powerful authority here--during takeoff rise, we mainly want to keep the craft level. The four fans at the nose and tail also can provide differential lift but the lever arm is pretty short so we can ignore these.
Takeoff then is a matter of pouring in enough power into suitably sized lift fans, six of them as conceived here, while using finer control to counter any adverse winds and turn them into favorable ones by yawing around to face it nose on, then when we have achieved enough clearance from the ground, bring the nose up and raise the forward thrust while maintaining enough fan lift to avoid sinking, and accelerate into the wind to gain full lift on the wings; we will have gradually shut down power to the lift fans once airborne on the wings. We don't need to vector any of the seven fans, and the Fenestron points the way to mounting these fans so that they are not too adversely affected by the high speed slipstream nor producing too much drag. Presumably they do produce some drag--I proposed stretching the three tail fins to provide for mounting the three fans there, which increases the drag of that assembly by raising its wetted area, plus any extra increase due to the ducts themselves. In the nose, as noted the assembly is sort of a canard, which tends to destabilize the pitch of the aircraft now acting as an airplane, but I suppose the larger tail fins tend to compensate for that, the main thing is the added drag, which also applies to the wing tip fans. The upshot is that to maintain the same cruising speed we'd need more powerful engines, which the math of transitioning from fan lift to wing lift might already have shown needed to be multiplied anyway, possibly by considerably more than needed for cruise. And of course the operation of takeoff and landing on fan thrust will be guzzling some fuel, and any increase in cruise power requirement also translates into higher fuel consumption.
Against that, if we can get this scheme to work, we do have something almost as capable as a Hercules, with only somewhat reduced range, that can land its payload anywhere it can fit. We can make it amphibious by the simple expedient of installing some floats, or land it on suitably large cleared deck areas of ships.
So I haven't actually done any of the math nor looked up the references to the Hercules itself nor the Fenestron prop installation scheme, but I might do so by and by soon.
Just saying--if you want a tactical combat transport vehicle with VTOL, this sort of thing is probably the most straightforward way to get it; if this can be done we can have airspeeds and cruise altitudes closely competitive with jetliners with a minimum of fuss.
It boils down to how large and how much power the fans need to be and use, and how adverse is the drag and weight of these installations.
What if we take the Lockheed "Hercules," which has after being deployed in the 1960s become a mainstay ubiquitous machine around the world, accomplishing pretty high subsonic speed and high payload and good short/poorly developed STOL capabilities, and try to stretch it into having VTOL ability?
I'm thinking we start with what can be done with its installed standard turboprop engines plus some auxiliary turboshafts fore and aft. If we can modify the main engines on the wing to collectively drive a shaft running to the wing tips, this shaft can drive a ducted fan mounted there. We might want to make it swivel around to rotate from its axis being vertical to horizontal, but maybe we don't have to do that. Say it is fixed flat in a shrouding duct, perhaps with venetian-blind style slats to cover the duct above and below during forward full wing borne flight speeds, perhaps without relying on duct detail design to prevent any bad effects, or anyway limit them to simple drag. Now we can get some lift at takeoff straight up. Can we vector it? Well, say we can't for the moment. The main standard props can't develop anything close to their full design thrust with the power being routed to the wing tips like this, but we don't need that thrust yet.
At the nose and tail, we have similar duct-shrouded fixed vertical axis fans in pairs straddling the fuselage, the forward pair behaving like a canard , the aft pair might be buried near the roots of a stretched rear tailfin. Also at the rear, buried in the root of the vertical tail fin (a la the "Fenestron" arrangement in some French helicopters) we have a reversible vertical fan that can provide thrust sideways. These fore and aft fan sets are each driven by auxiliary turboshaft engines.
Now with all seven of these added fans, in principle if we can get the design to close, six of them provide fixed-axis vertical lift thrust that is meant to add up to the weight of the loaded aircraft plus some maneuvering margin. What about the other 5 dimensions of control--forward and aft translation, side translation, and the three turning axes?
Well forward is easy enough. The power available to the main standard propellers is anemic due to most of it being siphoned off to the wing tip fans--and come to think of it, having adopted the "Fenestron" buried fan-prop model, we could put the wing lift fans at the root of the wing instead, though that would as noted in the prior post cut badly into fuel storage volume which we have to relocate or do without. But anemic or not, at low horizontal airspeeds we should have considerable thrust available on fractional power just the same. These advanced turboprop blades are I believe reversible, called "Beta Control," and so we can back up aft as well as ease our way forward.
Pure sideways motion is also available, funny to say! This is the main reason I put that seventh fan in the vertical tail root. By itself, if we crank the blade pitch out of neutral either way, we get sideways thrust that also acts with strong torque on the center of mass to spin the aircraft around--but if we counter that torque by forward thrust on one wing's set of main engine/props and reverse thrust on the other wing, the net thrust of both wings is zero, and the sideways thrust in the tail-fenestron operates, leverged over to the center of mass by the opposing torques, to thrust the aircraft sideways (once we have lifted off the ground that is of course). Again the net thrust might be kind of weak versus the mass for low accelerations, but moving sideways is a matter of fine positioning anyway, not something we want happening at high airspeeds! We can also regard it as a way of opposing side winds.
That takes care of the 3 translation axes; with an aircraft we need control of roll, yaw and pitch as well. Pitch is controlled by differential thrust between the fore and aft lift fans, obviously--depending on the axes of thrust of the main engines versus the vertical height of the center of mass, their thrust might also affect pitch so even if we don't need the fore and aft fans for much lift, they do have to be strong enough to counter any such deviations.
Yaw is the rotation of the aircraft around its vertical axis, and again as already noted the main engines provide some considerable yaw input if they are not thrusting in unison, and we have the vertical tail Fenestron for that too. Once clear of the ground the craft can pivot around its center of mass--for instance, to bring its fore-aft axis in line with the wind, fighting drift due to that wind with a combination of fore-aft and sideways thrust.
Roll is around the fore-aft craft body axis, and clearly by varying the ratio of thrust of the two wingtip lift fans, we can get powerful authority here--during takeoff rise, we mainly want to keep the craft level. The four fans at the nose and tail also can provide differential lift but the lever arm is pretty short so we can ignore these.
Takeoff then is a matter of pouring in enough power into suitably sized lift fans, six of them as conceived here, while using finer control to counter any adverse winds and turn them into favorable ones by yawing around to face it nose on, then when we have achieved enough clearance from the ground, bring the nose up and raise the forward thrust while maintaining enough fan lift to avoid sinking, and accelerate into the wind to gain full lift on the wings; we will have gradually shut down power to the lift fans once airborne on the wings. We don't need to vector any of the seven fans, and the Fenestron points the way to mounting these fans so that they are not too adversely affected by the high speed slipstream nor producing too much drag. Presumably they do produce some drag--I proposed stretching the three tail fins to provide for mounting the three fans there, which increases the drag of that assembly by raising its wetted area, plus any extra increase due to the ducts themselves. In the nose, as noted the assembly is sort of a canard, which tends to destabilize the pitch of the aircraft now acting as an airplane, but I suppose the larger tail fins tend to compensate for that, the main thing is the added drag, which also applies to the wing tip fans. The upshot is that to maintain the same cruising speed we'd need more powerful engines, which the math of transitioning from fan lift to wing lift might already have shown needed to be multiplied anyway, possibly by considerably more than needed for cruise. And of course the operation of takeoff and landing on fan thrust will be guzzling some fuel, and any increase in cruise power requirement also translates into higher fuel consumption.
Against that, if we can get this scheme to work, we do have something almost as capable as a Hercules, with only somewhat reduced range, that can land its payload anywhere it can fit. We can make it amphibious by the simple expedient of installing some floats, or land it on suitably large cleared deck areas of ships.
So I haven't actually done any of the math nor looked up the references to the Hercules itself nor the Fenestron prop installation scheme, but I might do so by and by soon.
Just saying--if you want a tactical combat transport vehicle with VTOL, this sort of thing is probably the most straightforward way to get it; if this can be done we can have airspeeds and cruise altitudes closely competitive with jetliners with a minimum of fuss.
It boils down to how large and how much power the fans need to be and use, and how adverse is the drag and weight of these installations.
the OP specified V/STOL, which means at least some vertical lift at zero ground speed capability, which narrows down the field.
And in the long period between their question and today, no one responded with any of these options.
So my "confusion" is to read it as specifying jet propulsion, which the OP most certainly did not do.
Given that various prop/fan solutions such as the Osprey, which was certainly not operational in service in the 1970s but whose antecedent experimental craft was one of these dozens of options, were as you note abounding in the time frame they asked about, where were all these answers then?
Only the Osprey, among strictly vertical options, became operational, but I certainly think a straight adoption of the Fairey Rotodyne might have served some limited tactical purpose, if protected well enough from hostile air and ground based strikes. For that matter your basic combat helicopter seems to fit, more or less, on whatever scale the OP meant to address--the Soviet Halo (NATO appellation) and its immediate predecessors was/is pretty hefty and fairly fast, and certainly operated in combat environments..
For that matter, before indulging in talking about a jump-fan version of the Hercules, I was first thinking of a DC-3. Gooney Birds were already pretty close to STOL, especially by post-war jetliner standards, and they were a glut on the market after the war, to the point that a number of companies trying to market "DC-3 replacements" were finding them impossible to sell even with some nifty modern conveniences because people had faith in their old warbirds which got the job done and could be kept flying pretty cheaply--the only replacement for a DC-3 is another DC-3 they said. So I was thinking first of what it would take to enable an actual wartime vintage Gooney Bird to take off and land vertically, then of one of these ambitious and disappointed firms (including Douglas itself) tacking on vertical take off and landing onto their would-be replacement models--and finally on to "hey, the Hercules became the DC-3 of the mid and later Cold War era, so let's look at that."
Only the Osprey emerged from this cluttered field of proposals, the vast majority of which for sensible enough reasons (in this flight regime; there were quite a few jump jet proposals some of which became operational more or less for fighters) bypassed jet lift.
I don't think any of the other ones you listed used jet propulsion. As I said it is my goof that I somehow thought the OP meant jets, but I was willing and able to point out that even that extreme solution was taken seriously and actually flown by someone.
Driftless
Donor
This Potez is a nice tie-in with the English translation of the great "France Fights on/Fantastique Time Line(France Fights On)". The OTL Potez 63 series aircraft make some appearances there.
Just to be clear, I am not trying to undermine what you have written here, which is both extensive and interesting. Trying to add to it by giving comparable designs to the same spec.
I can't find much on the English Electric entries but they could also have been VTOL.
www.secretprojects.co.uk
Well, not many, but there were some:
The Osprey didn't really come along until the 80's. Though I don't doubt the earlier tiltrotor designs were dug up for reference when the project started, it doesn't seem to have followed directly from the NMBR 4/22 designs.
AW.681 was, as was at least the de Haviland (later Hawker Siddley) 129:
I can't find much on the English Electric entries but they could also have been VTOL.
Hawker Siddley HS-129 and Handley Page HP.135
Hi Whilst looking through some issues of Air Pictorial there was a picture that caught my eye in a Paris Special from 1965(? not too hand so not sure on the exact issue). The picture was a selection of European military Transport model, one was the Dornier Do28 another was a rather tasty swept...
www.secretprojects.co.uk
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Yeah but can you imagine flying and manouvering something like that, that close to the ground? Also, what a target...
Hammerbolt: Wrong kind of support aircraft
Not the A-10 more like the AC-130 which would make sense given the use of converted C-47s and C-119s but...Monk78: Two major issues was the B-17's left after WWII were pretty worn out and as 'operational' bombers were rapidly replaced, retired and mostly scrapped. Second was up until Vietnam, (and some lessons learned in Korea but not applied till the later conflict) the doctrine of ground support did not reflect the need for a 'gunship' as we think of it but something that was more an 'attack' (A-10-like) mission for which the B-17 was ill-suited.
Now ground forces in Korea very much could have USED either a gunship or attack aircraft but given the budget constraints post-WWII the Air Force opted for a high performance aircraft (the P/F-51) rather than retaining a more balance aircraft (the P-47) which was a shame as the ground-pounders would have loved to have the latter and pilots who had to fly the former in close ground support instead got a more vulnerable thoroughbred instead of a tougher work-horse aircraft.
Have Dewey win in 48 instead of Truman and you 'might' see someone (AF or Army) reacquiring some more capable ground attack aircraft and maybe even looking into a 'heavier' air support platform but my guess is it would be something new with the expanding budget instead of re-treads.
Randy
I know, but you still need to go low and slow and manouver; with such a large plane... well...Hammerbolt: Wrong kind of support aircraft
But yeah by then any B-17 will be too worn out.
Thing was unlike the converted cargo aircraft the B-17 was built for, and very proven to be able to also take a licking while dishing it out so given the right circumstances I think it would have worked out quite well. But the issue is getting it to 'live' long enough to get there.
(Edit) Really the issue would be that the .50s would not cut it and you'd need to mount at least 20mm cannon instead to get any kind of actual utility. The cargo conversions worked out even though they used 7.62mm rifle rounds due to the amount of lead they put 'down-range' per second. The .50 out-ranges the 7.62 but the volume of fire, along with the 'fire-control' is vastly more limited.(/Edit)
Randy
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Can the 23mm dual cannons be mounted in nose and tail ( like soviet Cold War bombers)
And maybe 2 50 cal in the ball turret and 2 50 cal in the waist on each side ?
I would say its likely a quickly drawn from memory based on something the artist thought was a commie jet but may well have been one of a dozen types deals. Basically the show runner said, "I want a sequence animated with some Ruskie jets" and the artists did their best from memory.
Last bit first; Yes they could... and did
That's what the YB-40 was all about putting twin 50s in just about every gun mount. You're problem is still the range on a .50 and it's effectively manually operated shooting at targets the gunnery can't really see. Might have some use against a "human wave" attack but again if you can shoot the enemy you're also in range of his LMG's and HMG's.Cannon were placed in turrets of bombers from early on, (see the XB-19 for example) but again the idea of 'ground attack' was different then than now and more akin to what an A-10 would do, (hence the use of A-20's, B-25 "solid nose" and other twin engine ground attack aircraft) rather than an AC-130-etc.
Randy
Does anyone know of any good sources for Austro-Hungarian aircraft of the first world war?
Ooh, well if I ever get a new computer (is it too late to opt out of this adult thing?) I know what's on the top of my priority list.