To be honest...
If I had carte-blanche and could design any plane I wanted, I'd probably design some kind of Supersonic Airliner. After all, nobody's had the guts to build one other than the Brits and the French. The Concorde may have been impressive, but it wasn't all that impressive compared to the SST designs and the HSCT designs the USA thought up: For one it only had a capacity for 128 pax in a normal airline density, and seat-mile costs that would give most people a heart-attack, it wasn't as fast as the US designs, and had very high takeoff and landing speeds. It's L/D figures weren't quite as good as the US SST designs. Despite this, the Concorde-B would have been nice to see! Not to mention, I hate sitting on an airplane for a long period of time, and recent studies have found that Deep Vein Thrombosis can be a serious health risk and can happen when people remain seated on long flights. Shortening flight times dramatically would easily fix that problem right?
(Some of this is meant to be taken in a light hearted manner, except for the parts that aren't, m'kay?)
If I was in charge of designing a supersonic commercial jet, I'd be building it obviously with some degree of economy and safety in mind, but also I'd be building it to 1-up the rest of the world. After all, it's been so long since the idea of a supersonic airliner has been floating around, but other than the Concorde and the Tu-144, none of them flew!
First of all, I'd want it to be able to fly at Mach 3. That's what the SST-program aimed for and for the simple reason that Mach 3 is faster than Mach 2. And considering we've been waiting since 1966 for supersonic commercial flight, we deserve to get Mach 3 after a 41 year wait! Additionally, I'd want it to carry around 320 or so pax in a three-class set-up since that would be the most economical amount to carry. One of the Concorde, and the SST's pitfalls were short range, so I'd want a range on the order of 5,750 nm to 7,500 n/m if not more.
To achieve a desirable speed and range with minimal fuel-consumption, I would want to design the aircraft using airfoils with ultra-low transonic-drag levels of Sonic Cruiser calibur. Whether this would entail designing the aircraft like a long-stretched-out Sonic Cruiser with a thinner fuselage, a sharper nose and increased leading-edge sweep or would allow a somewhat more conventional design with ultra-efficient CFD-taylored wings, I'm not sure (I would obviously prefer the ability to have some more freedom in the design rather than just stretching and thinning the Sonic-Cruiser out -- something which would work, but would take away a lot of design-freedom, may make it unfeasable to make the 320 pax target, and would probably prohibit a more versatile design)
-- assuming that such ultra-low transonic foils could also achieve high-efficiency flight at Mach 3. Reducing transonic drag particularly would allow much more rapid acceleration and allow for more time at Mach 3 -- thus making Mach 3 crusing more economical. It also would also allow for less fuel weight, thus making the plane lighter for the same range. While not a requirement, it would be preferable to have a design who's shift in the C/L could be controlled throughout the speed range using a canard, and some aerodynamic contouring to the airfoil-design used providing it would not increase transonic drag, or at least not increase it significantly and would not have notably adverse effects on the airplane's cruise L/D-ratio.
A big issue with the aircraft's design would almost undoubtably be sonic boom emissions. I've heard of many solutions to this issue, many of which are difficult to implement, however an idea which features a slightly blunter nose than one would typically use could negate the underpressure behind the shock thus preventing shockwave coalescence which amplify greatly the shockwave levels. This idea would work well, however the problem I see with it is that such a design would produce more drag on the nose than would be ideal. I would propose an alternate possibility. One could use a somewhat more conventional long nose which would would utilize the injection of small amounts of hot-bleed air in a precisely release pattern which would quickly kill the underpressure behind the shock by using positive pressure. The exact amount could be very miniscule, and controlled by a computer which for a given mach and IAS reading would inject the correct amount of bleed-air to blank the underpressure behind the shockwave. A porous area located a given distance behind the injection point would skim off excessive turbulence air through an LFC system. Since this would be fairly close to the bow of the nose, it should work okay. The heat adds energy to the flow even though it prevents the waves from coalescing, and actually changes the local speed of sound. To further reduce the effects of sonic boom levels, the inboard wing would use some dihedral. The fuselage would be contoured in various ways to lower sonic-boom emissions. Additionally, the use of laminar flow would be used on the wing's leading-edges with natural laminar flow behind those areas. To provide de-icing funcions, bleed-air could be back-flushed through the pores when on the ground. The tubing and ducting to allow this to work would require some physical flexibility since the leading-edges of the wing may be drooped for takeoff and landing, additionally there is a possibility that the leading edge may be adjusted in small amounts to reduce sonic-booms and to provide extra lift, and possibly some trim-assitance.
Most of the rest of the issues lie in the engines and the propulsion system consisting of the inlet, the engine, the sound suppression system and the nozzle. Lockheed to my knowledge was able to demonstrate in the 1960's that a wedge-splitter type inlet with the proper contouring, minimal external cowl angles, and the arrangement of slots and porous surfaces could achieve a high pressure recovery and self-stabilization without the use of moveable parts. The HSCT program went back to a variable geometry inlet since even Lockheed's design could potentially still encounter an unstart-- the inlet could simply recover from it acceptably. Unstarts weren't considered acceptable in the sixties, and now they certainly are not tolerable. However, it is my opinion that a fixed inlet could still be do-able at Mach 3. The HSCT relied on a laser system that could sense clean-air turbulence and adjust the inlet accordingly, such a mechanism (the laser scanner) could be incorporated, with the inlet fitted with the provision for active laminar flow control in addition to passive. When a disturbance is detected, the suction can kick on and it would quickly skim off the turbulent air preventing it from disrupting the inlet. If do-able, the design would allow a fixed inlet to achieve Mach 3 performance, and be able to adjust itself to airflow even ahead of the spike by use of laser-scanning. Since engines are cylindrical, I prefer the conical spike instead of the wedge splitter, however the design could work with either design-- wedge or spike as long as the angles are the same. The engine would be of a variable cycle type which would produce lower noise emissions at low-speed than the turbofan used on the HSCT program, and would provide superior high-speed performance. This would also require less low-speed sound suppression, or greater sound suppression with the same degree of cooling air. The engine would operate as a turbofan at low-speed with light-weight composite scimitar shaped fan-blades with variable pitch and variable guide-vanes to maintain the same flow of air into the compressor regardless of it's operation as a turbofan. To allow this, the blades may even be fitted with vortex generators or a type of "sharkskin" which is basically millions of tiny vortex generators. At higher speeds, the engine transitions into a turbojet. I've been told that as counter-intuitive as it may seem, slight afterburner use at Mach 3.0 would allow a specific range increase-- unfortunately afterburners are generally too fuel thirsty, and even worse, produce horrendous amount of NOx emissions. The solution would be an outer-annular combustor which would get it's bypass off the HP
compresor, and upon combustion would yield an extremely high velocity exhaust which would be conducive for highly efficient high-speed flight. To provide a good compression ratio across the whole engine, the HP
compressor may be able to use variable guide-vanes and even a variable blades like the Variable Stream Control Engine that Pratt & Whitney proposed in the early eighties. The design would essentially be a dual-bypass VCE
utilizing characteristics of the YF
-120, the F-119, the VCE
, and all sorts of new technology available. To maintain acceptable emissions, the combustion chambers would utilize a LPP
-type combustion chamber which use prevaporized fuel, premixed with air in a lean fuel/air ratio in a dropless environment in an antechamber and then ignited and burned up rapidly in the combustion chambers. The primary combustor would be dual annular with the inner annulus only activating past a certain point, and reduced in power under some conditions at high-speed to reduce fuel-consumption while the outer-combustor is being used. The combustors would by necessity use no film air at all, and use no dilution holes. All the air goes in to the chamber itself! To allow such high temperatures without film-air cooling, high-temperature ceramic-matrix composites would coat the combustion chamber, and likely high temperature metallics would be used. The turbines would utilize high temperature single-grain cermets with a CMC coating, and an elaborate air-cooling system to allow for a good pressure-ratio. The sound-suppression of the engine would come partially from the engine's fan-bypass mixing with the high temperature hot-stream air. The rest would come from part of the nozzle. Rather than using a 2D
nozzle, I would prefer to use a 3D cylindrical nozzle. The job can still be done, just you'd use a bunch of smaller span-wise segments that would all interlock together into a cylindrical shape when deployed. They would attach to a axisymmetrical fairing in the duct which would be connected to the walls by a series of struts, and a series of auxiliary doors would open up-stream of the sound-suppression chutes. The exhaust blowing through would draw air in... the outside air, the fan air, and the core flow would all be mixed together, resulting in a slower cooled exhaust flow that would also be considerably quieter. I'm not sure what the current noise levels would permit, but the degree of cooling air would be increased to what is necessary to get the job done while trying to avoid losing excessive amounts of thrust. For high-speed climb and acceleration, the chutes would retract out of the exhaust stream, and the auxiliary doors would be closed. The ducting behind the engine would be configured in a convergent/divergent fasion to achieve supersonic exhaust velocity. The rear of the nozzle would consist of petal-type reversers designed to provide braking on landing and for use in mid-air for speeds up to Mach 1.2 (this figure was derived from the L-2000's specs)
In overall design, the plane would probably feature a cranked-arrow/double-delta esque wing with a moderate degree of wing/body blending with a degree of twist/camber, and some inboard dihedral. The leading-edges would feature a type of variable-droop flap to provide optimal lift across the speed-range. The trailing-edge elevons would be able to droop for use as flaps to some extent. It is likely the plane would feature an upward canted canard. The fuselage would feature, likely extensive and elaborate area ruling to provide low-drag and reasonably low sonic-boom levels. As for the tail design, I'm not sure. The inverted-V tail would probably work quite nicely. Since Lockheed has it patented, the design would need a couple of small changes so that it would circumvent this problem. To provide good yaw control, a portion of the vertical fin can pivot to provide yaw control. The plane would feature four engines placed in individual pods properly placed under the wings. Due to the fact that this airplane would not feature any conventional spoilers due to the elevon set-up, a type of speed-brake or speed-brakes would be required-- the trailing edge of the vertical fin could feature a split break because the motion of the whole tail is what produces the yaw. The thrust-reversers can be used below Mach 1.2 in mid-air. To support the airplane's weight, the plane would feature a triple-legged strut with six-wheels on each, and a traditional nosegear.
In older designs the window-size was pretty much restricted, but lately it seems as long as you can prove that the odds of the given object, in this case the window, are so low as to be considered astronomical you can pretty much do whatever you want. So of course, first order of the day-- bigger windows! I'd like them to be at least 777-sized using an elaborate, but light weight structure (like 3 sets of two ultra thin, light weight high-strength glass with a flexible medium like a gel or a fluid or epoxy or something to make it like bullet-proof)
To make the overall airplane design light, various means would be achieved involving structural engineering techniques that would yield light weight, but extreme strength. This would involve the use of composites of various sorts, various high-temperature metals, particularly those of each that can be superplastically deformed and diffusion-bonded, composite reinforced metals, and the like. It should be of a respectably low weight, and be sturdy as hell. Unlike modern day sissy's who design airplanes just to barely make the ultimate load requirement, I would want this plane to beat it by a long shot before breaking.
Regarding the plane's control surface set-up I have no idea. But the plane should have FBW, artificial feedback, soft-limits, auto-trim, if electrical motors are used, some hydraulic motors should be used for some of the control-surfaces in event of electrical motor failure, and some degree of mechanical signalling in the event of a digital computer problem. The plane should feature a self-diagnostic computer system like the 777 has. The plane should feature cameras located in various areas to provide ease of taxying, and digital entertainment for the passengers. Since the airplane has no droopable nose, the plane requires an elaborate set of clustered-sensors and cameras that provide data to each pilot via viewscreen. The visual system should be able to show high-definition image color view during normal operation. Due to the fact that some of the sensors involve weather radar, it can be set up to see through clouds, due to the fact that data from the aircraft's radar, it can show the location of other aircraft, wether they're closing on them, falling behind, if they're above, below, climbing, descending, etc. Since the clustered lay out involves multiple sets of cameras, even if one set fails, a lower resolution can be displayed. To provide the optimum HUD layout, the display itself should also be able to display Heading, Altitude, Indicated Air Speed, Mach Number, Pitch Ladder, Vertical Speed, Angle of Attack, Sideslip, and Engine Data, and anything else needed, perhaps ILS data when being used. The plane's engines would be controlled by a FADEC with the associated back-up and redundancies. Taxying on the ground would be done by a tiller on both pilot's sides, and by simply using the rudder pedals.
Like most airplanes designed to fly quick for a long time and heat-soak, the plane would use the fuel as a heat-sink. The fuel would be inerted by nitrogen.
Of course, that would be if I had carte blanche, which I don't.