Something I have been thinking of lately.

Has jet design reached its limits in efficiency and practicality?
We are beginning to see new aircraft rolling off the production line which look no different to the next. No more t-tails or rear mounted engines. No more attempts at delta wings or cone noses. No more wing blended engines etc etc. The Dreamliner is perhaps the only aircraft of any note but it too only looks different from the nose, the rest is pretty standard in respects of the underwing engines, fuselage shape etc etc. Design of the A350 has been finalised and despite early promises of a rather attractive and futuristic design again the finished product actually looks pretty dismal with no remarkable features. The A380 too is simply a beefed up standard design.

So what do you all think? Have we reached the pinnacle of aircraft design? Has computer aided technology thought us all we need to know with regards the most efficient shape of an aircraft? Will we need to wait for a significant leap in technology before we can expect something truly different?

Discuss.

This is just the thought I had first time I saw an A300, long time ago: "Oh my God, all aircrafts are going to look just like that in the future". That thing looked so outrageously normal and rational that it killed all hope any fundamental improvement could be made after that — well, except for the winglets.

I believed some significant cosmetic change would occur with the 787 streamlined tail fin. It turned out to be a big disappointment.

Maybe there is still hope in the smaller commercial jet segment. The BAe 146 /Avro RJ is a fine example of a maverick design that has proven to be efficient within its own niche.

Quoting Tonystan (Thread starter): Has jet design reached its limits in efficiency and practicality?

No. It's perpetually butting up against the technology limit of the day. As technology advances, so will jet design.

Quoting Tonystan (Thread starter): We are beginning to see new aircraft rolling off the production line which look no different to the next.

Not really. The basic form (tube fuselage + conventional tail + wing-mounted engines) is predominant because it's the most efficient given current technology contstraints, but there's quite a bit of variance within that envelope (wing planform and airfoil, fairings, high-lift design, pylon/nacelle design, etc.)

Quoting Tonystan (Thread starter): No more t-tails or rear mounted engines.

That's because t-tails and rear-mounts don't work with large high-bypass engines, and you need that to be fuel competitive at larger aircraft sizes.

Quoting Tonystan (Thread starter): No more attempts at delta wings or cone noses.

Deltas and cone noses are awful for subsonic commercial service.

Quoting Tonystan (Thread starter): No more wing blended engines etc etc.

There's basically no way to efficiently meet the thrown blade requirements with a wing blended engine. Rising diameter of high bypass turbofans also makes this impractical.

Quoting Tonystan (Thread starter): The Dreamliner is perhaps the only aircraft of any note but it too only looks different from the nose, the rest is pretty standard in respects of the underwing engines, fuselage shape etc etc.

The nose and windscreen are quite different, the wing is extremely different, and the whole high lift system is very different (for an aircraft of that size).

Quoting Tonystan (Thread starter): Have we reached the pinnacle of aircraft design?

No.

Quoting Tonystan (Thread starter): Has computer aided technology thought us all we need to know with regards the most efficient shape of an aircraft?

Sort of...if you relax all the technology and regulatory constraints we know how to do some very radical, very efficient designs, but they're either not buildable or not certifiable in today's environment.

Quoting Tonystan (Thread starter): Will we need to wait for a significant leap in technology before we can expect something truly different?

Yes. That's been true of aircraft design since before the Wright brothers. For a given set of technologies and regulations, there is a relatively small design area that efficiently meets all of the requirements. Naturally, all production gravitates over time towards that design area. As soon as a new technology comes along, some of the requirements change or can be met another way and you get step-changes in configuration.

Tom.

Thanks for that Tom, so basically we are limited in our technology.
What amazes me is that the basic model of current aircraft design has been around since the first generation jet airliners first built 50 years ago. This is half the period since the wright brothers first flew. Yes the design has been refined and perfected over the years but a shame that we still seem to be no closer to a truly revolutionary design.

No, as technologies that are currently being used on smaller general aviation and business aviation aircraft will eventually make the leap to the larger passenger/commercial market. Airbus and Boeing are really just now beginning to use materials some of the manufacturers of business a/c have been using for close to a decade.

Airbus and Boeing both have been a bit hesitant to step outside of the box when comes to jet designs. With few exceptions, airliners have not changed from their basic shape since the 707 (While the Comet was the first passenger jet, many of the aspects of its' design did not carry over to future jet designs.). I guess they don't really want to step out of their comfort zones and also feel as though if they develop an a/c that strays too far from the basic design that many passengers are comfortable with, that the a/c won't sell. Another thing to remember is that for the most part, airports are designed with the "standard" idea of how an airliner is shaped, especially when you throw in the fact that many airports are refusing to upgrade their infrastructure in order to handle the A380, while still a "standard" a/c design, its' size isn't exactly "standard". The Concorde was able to use a typical gate because despite its' non-standard design, it was small enough a/c to use a typical gate. If Boeing or Airbus decide to build a BWB airliner, that potentially could affect what airports would accept the a/c, as the design may not be fully compatible with the typical airport gate.

Quoting Tonystan (Reply 3): What amazes me is that the basic model of current aircraft design has been around since the first generation jet airliners first built 50 years ago. This is half the period since the wright brothers first flew. Yes the design has been refined and perfected over the years but a shame that we still seem to be no closer to a truly revolutionary design.

That's partly because there haven't been any truly huge changes in *visible* technologies since then. The change to turbofans drove us to bigger nacelles, but fundamentally a jet is a jet. Transonic aerodyanmics haven't done much other than tweaking (which is visible but subtle) and the introduction of the supercritical airfoil (which is almost invisible unless you really know what you're looking for). Developments in low-speed aero are what got us from the triple-slotted flap of the 727 to the single-slot's that are on most new design but, again, that's kind of a subtle change.

Systems have changed radically, but that's all buried in the fuselage so you don't "see" it, although it shows up in ticket price and aircraft comfort and amenities.

The change to composites is a material swap that didn't enable any really new shapes so, even though it's a massive engineering and manufacturing shift, it didn't change appearance too much.

A lot of promising changes died or never were realized due to regulations. BWB's still have a major problem meeting cabin egress requirements that haven't been solved. Rising fan sizes killed most engine mounting except under-wing.

Sonic Cruiser was the closest we got to a radical change using today's technology, but the market wasn't there.

Tom.

What ever happened to supersonic business jets? Weren't there a couple of projects going on in that direction?

The next step we will see in 5 to 10 years are Geared Turbofan engines. Design studies for a delta wing plane are already underway. So that might be something we will see in 50 years.

Overall the current shape of the aircraft body is pretty refined for the flight speeds. The B787 is having a major change in material used but not in overall shape. The A380 has a different shape of sorts but nothing really dramatic same basic shape just bigger.

We would probably need a major leap forward in engines before much else dramatic happens. Something along the lines of the F/A-22 Raptor which is the first jet to do non afterburning supersonic speeds.

Refining current designs is more the way of the future, changes in materials used and and the like. That being said, a sudden and unexpected advance in technology could change that fairly quickly. This could potentially be dramatic game changer for one of the manufacturers if that change came along same just after one started manufacuring the latest aircraft and the other one was more in design phase and could adapt much quicker.

When it comes to looks, I think that boredom will rule, 2- or 4 engines underneath the wing, no more big 3-engine, no more big 2- or 4-engined airplanes with the engines in the rear.
As for technology, very advanced developement with GTF engines being the latest in engine technology.

I think the next step forward will be the blended-wing body jet combined with large-diameter front fan geared turbofans, both of which could happen within the next 15-20 years. This could result in a dramatic reduction in seat-kilometer costs, since the BWB design is far more efficient aerodynamically for carrying large loads and using geared turbofans will improve that even further.

Aircraft, historically, have a conservative application of technology. As RayChuang has noted, the BWB is one of the obvious steps.

But much of the refinement will only be seen by the trained eye. CFRP, organic structures, and other incremental improvements add up to revolutionary drops in fuel burn.

Not to mention one of the big drives during the period of low oil prices was to drive to maintenance costs. Quite a bit of work was put in that area and its paid off. Now the pendulum swings to fuel burn.

Quoting RayChuang (Reply 10): combined with large-diameter front fan geared turbofans, both of which could happen within the next 15-20 years.

Soon on smaller thrust engines!    Your timeframe is about right for high thrust. Its a game changer.

But the GTF combined with CFRP

Quoting Tonystan (Thread starter): No more t-tails or rear mounted engines.

   Rear mounted engine incur a large weight penalty moving the thrust of the engine up to the primary drag source (the wing). Not to mention the structure and support units that have to be plumbed back to the tail.

Quoting Tdscanuck (Reply 2): No. It's perpetually butting up against the technology limit of the day. As technology advances, so will jet design.

   We'll see new materials, new concepts, and new designs. Think about how long the biplane ruled the skies. Then it was the low wing monoplane... then we evolved to low wing turbines.

Quoting RayChuang (Reply 10): I think the next step forward will be the blended-wing body jet

This is the next leap forward. It will revolutionize air travel in the same way the 747 did.

If aircraft had reached their pinnacle, I would have no career. (I'm in aerospace R&D.) Engines I worked on the concept in 2000 will see (in a much evolved form) the light of day in ~2010 through 2015. Since then, new concepts have been worked on for launch in 2020... some concepts will be obvious solutions that will become green-lighted for earlier fleet introduction (e.g., integrated blade rotor compressors).

One expects a new design airframe to have a 15 year sales life without a huge engineering investment to improve it. (Airframes like the 777 that have had billions in improvements invested in them will have longer sales lives.)

Lightsaber

The next big leap in aircraft design has nothing to do with engine configuration, it has to do with propulsion. That is, FUEL.

The following is a line from my book (the title of which the moderators do not allow me to repeat here)...

"...The border between subsonic and supersonic, near which most planes cruise, is not an aerodynamic triviality. In a poor man's version of Einstein's speed of light conundrum, required energy increases dramatically as you near the threshold. Though not an outright obstacle of physics, it's a huge pain in the wallet. Leaving the sound barrier behind, a completely different wing is required and fuel use soars. That a Concorde looked and flew vastly different from a 747 was more than a quirk of design, as were its ghastly operating costs. For this reason, despite all the other technological advances we've seen, the cruising speeds of commercial jets have not really changed since their inception. If anything, the 21st century airliner travels slightly more slowly than those of 30 years ago..."


The minute a new and affordable propulsion system is developed, this all changes, I think.


- PS

[Edited 2008-10-04 18:53:00]

Quoting RayChuang (Reply 10): BWB design is far more efficient aerodynamically for carrying large loads and using geared turbofans will improve that even further.

A step further, it is anticipated that open rotor will improve significantly on GTF.

Quoting Tonystan (Thread starter): No more attempts at delta wings

IMHO delta wing is not a good idea! for the simple fact that it would be very hard for me to pick a window seat away from the wing!!  I want to look at our beautiful planet from FL350 not a piece of metal.

If the question is whether the technology has hit the ceiling for wing-and-fuselage jet aircraft, that may be the case, or close to it. Others would know better than I.

However when it comes to new body types, one example of the previously mentioned blended-wing concept is the Silent Aircraft Initiative (www.http://silentaircraft.org/). The project has proposed the SAX-40 design, which embodies several blended-wing concepts such as rear mounted engines.

Whether or not the development of such an aircraft is commercially viable is another question, but it shows that there is a wide world of possibilities out there and that the next generation is being addressed. A and B have taken large risks on new designs such as the 747 and the A380, but the only other project that represented such a large leap that I can think of is the Boeing 367. The 367 was was of course based heavily on military-funded technology (the B-47).

Due to the enormous amount of risk involved in developing a brand new body style for commercial production, I think it would take a military or other impetus on a governmental scale to fund the R&D and assume some of the risks. I think we are several decades away from a major change towards blended-wing technology in civil aviation.

Furthermore I think there is a serious question as to whether or not the flying public would adopt airplanes with significantly wider cabins. Blended-wing designs may increase the fear of flying and claustrophobia factors due to the placement and quantity of windows.

The promise of ramjet technology has seemed to stagnate recently, but the same principles apply - there's just too much risk involved in the design to make it commercially viable.

But the answer is clearly no, we have not hit a ceiling from a purely technological perspective.

Yes, airplanes have reached the end of their design evolutions and their performance envelopes. In fact, commercial airliners reached this pinnacle 50 years ago.

With the exception of fuel efficiency, there has been little change in the last 50 years. The first 50 years of aviation saw a paradigm change every 10 years. The last 50 years have seen none.

Once the first commercial jet was created, the performance envelope was maxed out. That means a jet that travels between 30-40,000 ft, for about 8 hours, at about 550 mph. If you were to ride in a 707 in 1958 and a 777 today, with the exception of the cabin furnishings, you would notice very little difference. Perhaps a few less decibels. All the change in the last 50 years has been change that you can't see. Now, imagine flying in a plane in 1908, and then one in 1958, what a difference there was in that time frame. One is like a UFO compared to the other. But from 1958 to today, almost no change in the basic performance envelope or flying experience, or basic look.

Speed wise, there has been no improvement. Altitude wise, no improvement. Range there has been some improvement, but nothing that changed the face of aviation. In fact, range is only better because of better fuel efficiency. Comfort wise, again virtually no improvement. A climate controlled, pressurized cabin was already flying by 1958. Some would argue that comfort has devolved from 50 years ago. Certainly service has.

Even the navigation system used is the same one used in 1958. We are still using the old radio navigation beacons and the old transatlantic tracks from 50 years ago. We are still using the same fuels as we did 50 years ago. We are still using the same basic turbine propulsion technology of 50 years ago.

All that has changed in the second half of the 100 years since airplanes were first invented, is improvements to make planes more automated and more fuel and labor efficient. The advances are almost all economical. In the first half of the 20th century, the advances were in size, speed, propulsion technology, shape, wing configuration, and comfort. In the last half of the century it was all economic.

The irony is that with 50 years of squeezing every last drop of fuel out of the engineers' efforts, airlines are less profitable today than ever. So even the economics of airlines have not improved in the last 50 years. They have remained static or declined.

If there ever is a new phase in the design of commercial airliners, and I doubt we will see such in the next 30 years, will be the BWB concept.

So in short, yes, commercial airliners had long ago reached their zenith with the introduction of the 707 - 50 years ago.

Quoting Flexo (Reply 6): What ever happened to supersonic business jets? Weren't there a couple of projects going on in that direction?

They won't happen. The economic downturn in America will see to that. It's doubtful that they'll be able to turn it around and prevent another great depression.

What does have possibility of happening is engine designs like mid-tandem fans which has some of the benefits of a modern turbofan (quiet) and the high exhaust velocities that are desirable.

The Concorde shape probably won't be radically altered for future supersonic airliners - but I do think there will be small improvements and refinements. I also doubt that "virtual" windscreens will be the replacement for variable geometry nose configurations, I suspect those will remain - if only because they are more trustworthy (and because they work well).

Quoting Jbernie (Reply 8): We would probably need a major leap forward in engines before much else dramatic happens. Something along the lines of the F/A-22 Raptor which is the first jet to do non afterburning supersonic speeds.

Unless I'm not mistaken, that was done in the 1970s with the Concorde prototypes, and subsequent production planes in service for 27 years. They didn't use afterburners for supersonic speeds (they accelerated from M1.7 to M2.0 without them, climbing at the same time from 43,000ft to around 49,000ft respectively, and from there on, drifting ever higher).

The MTF engines seem to be the most logical solution at the moment - everything else looks complicated and costly to build.

Quoting Art (Reply 13): A step further, it is anticipated that open rotor will improve significantly on GTF.

On shorter missions only. Due to the open blade tips, flight mach numbers must be reduced on open rotor designs.

Quoting Cpd (Reply 17): Concorde prototypes,

Concorde required afterburners ('augmentors') for supersonic speed.

Quoting Hmmmm... (Reply 16): Altitude wise, no improvement.

Aircraft are slowly increasing their cruise altitudes. 'No improvement' is a bit of a bitter interpretation.

Noise is *way down*. Field performance, cargo, reduced crews, etc. There have been numerous improvements. Airlines are a business. We can only spend the funds to engineer what customers desire. There is a reason older airframes fade from the fleet when a new equivalent is introduced.

The explosion of air travel over the last 50 years shows how important those efficiency gains have been. They've allowed for air routes that require airframes with range almost twice that of the 707.

The CFRP frames are a leap forward in maintainability and a nice step in range (once they optimize the weight).

But I think we can come to a consensus, the BWB is needed for the next great step.    Due to the ranges BWB's will be operated on, I've *never* seen a concept that didn't have shrouded fans. (No airline would be competitive adding 2+ hours on a long haul mission; the time penalty that would result in the unshrouded fan's cruise mach number limits.)

Lightsaber

Quoting Flexo (Reply 6): What ever happened to supersonic business jets? Weren't there a couple of projects going on in that direction?

They're still in the works. The economics of supersonic travel only work in the biz jet realm, so they're our best hope, but they're small companies with very large projects so progress will be slow, at best.

Quoting Caspritz78 (Reply 7): Design studies for a delta wing plane are already underway.

Why would you do a subsonic delta? The aerodynamics just don't make sense.

Quoting Jbernie (Reply 8): Something along the lines of the F/A-22 Raptor which is the first jet to do non afterburning supersonic speeds.

Concorde did that. Concorde used afterburners to get over the drag hump around Mach 1 but didn't use them to cruise supersonically. Afterburners burn *way* too much fuel to use them continuously for commercial ranges.

Quoting Aviateur (Reply 12): The minute a new and affordable propulsion system is developed, this all changes, I think.

The problem is that any propulsion system that makes supersonic travel economical makes subsonic travel *really* economical and there aren't enough routes where the extra speed can justify the extra cost.

Quoting Zudnic (Reply 15): The promise of ramjet technology has seemed to stagnate recently, but the same principles apply - there's just too much risk involved in the design to make it commercially viable.

Risk isn't the problem with ramjets. In a lot of ways, they're less risky than current engines. However, they're an economic disaster. The cruise speed required for a ramjet is so high that you don't have a hope of being cost competitive with transonic airliners, which can't use ramjets.

Quoting Hmmmm... (Reply 16): With the exception of fuel efficiency, there has been little change in the last 50 years. The first 50 years of aviation saw a paradigm change every 10 years. The last 50 years have seen none.

To be blunt, bull. There have been *huge* changes in airliner design over the last 50 years (analog to digital and safe-life to fail safe to damage tolerant being two of the most obvious)...they're not visible configuration changes, but that doesn't mean there were no changes.

Quoting Hmmmm... (Reply 16): If you were to ride in a 707 in 1958 and a 777 today, with the exception of the cabin furnishings, you would notice very little difference.

Then you're not looking very hard.

Quoting Hmmmm... (Reply 16): Speed wise, there has been no improvement.

Concorde?

Quoting Hmmmm... (Reply 16): Altitude wise, no improvement.

Why would you want to fly higher? Nobody (passengers, flight planners, pilots) cares about maximum altitude, they care about time and cost.

Quoting Hmmmm... (Reply 16): Comfort wise, again virtually no improvement.

Clearly, you haven't flown a nice business class recently.

Quoting Hmmmm... (Reply 16): Even the navigation system used is the same one used in 1958.

GPS vs. sextants. Not exactly the same thing. A CatIIIc landing in 1958 wasn't even remotely possible.

Quoting Hmmmm... (Reply 16): We are still using the same basic turbine propulsion technology of 50 years ago.

If you want to take that tactic, then there has been no improvement in car engines since the Model T. After all, it's still an Otto cycle.

Tom.

It seems to me that things are not moving as far as I would have expected. If you look at the 707, this was designed in the 50's, now we have the 787 which looks very similar, albeit, much more technically superior. That said, if you look at the late 60's and early 70's, we had men on the moon, Concorde entering service, ect. I would have thought by now we would have SST's all over the place, moon bases and men on Mars, it's almost 2010 for heavens sake! Other than computers, I feel we have regressed in a lot of areas. When I look at an aircraft like Concorde or a SR-71 they seems so futuristic, even 40+ years later...Just my thoughts.

Yes, boring is the word unfortunately, unless the BWB makes it into production or technology advances to the point of making supersonic travel financially realistic we are stuck with aircraft as 'exciting' looking as the 777.

I'll agree with the statement that the limits of aircraft design are all dependant on the technology of the day. But, I think aircraft design (along with everything else) will always continue to advance. I don't think we've reached the limits of design, I very much think we haven't reached the limits of design. This thread reminds me of a quote that's in a book I own called "1001 Dumbest Things Ever Said" (no offence to the OP, haha)

"Everything the can be invented, has been invented."
- Charles H. Duell, commissioner, US Office of Patents, 1899

Think how much technology has advanced since then.

Jets may look similar these days than they did in the 1960's on the outside, but underneath, they are a completely different animals. Aircraft design has actually advanced quite alot over the past half century in ways that the average flyer probably can't see, mostly to make them more efficient. For example, coming from the table on page 64 of the DOE's Transportation energy data book, http://www-cta.ornl.gov/data/tedb27/Edition27_Full_Doc.pdf, the average aircraft used 10,282 BTU's of energy per passenger mile in 1970, while the average aircraft in 2006 only uses 3,228 BTU's per passenger mile.

I think as we continue to see new technologies developed, we will continue to see aircraft design advance. How they advance, however, is largely dependant on what the economic situation of the day is, and over the past 50 years, that has mostly been to squeeze every last mpg out of an aircraft as possible.

If I had to bet, with this whole climate thing we have today, that the next big advance will probably be to develop some way to power an aircraft in a way that is Carbon-neutral. I'm also fully convinced that in the future we will eventually have supersonic transports that will regularly fly long distances. And then, we'll have vertical take-off and landing, and a Single-stage to orbit space plane and on and on and on. The question is when not if (but admittedly it will probably be a while).

Anyone who says it can't be done, isn't an engineer.  

[Edited 2008-10-04 21:05:27]

Quoting Lightsaber (Reply 18): Concorde required afterburners ('augmentors') for supersonic speed.

No - it didn't. While they were used to get between M0.93 (27,000ft) and M1.7 (43,000ft), they would be switched off at M1.7, where the plane would then accelerate and climb on full dry power alone. Above FL450 - they were of little usefulness.

If it used them all the time, then it would never had flown London-Barbados routes - it wouldn't have even went half-way. Sorry to call you on this - but it's an endless point of mis-information on the internet.

Quoting Jbernie (Reply 8): We would probably need a major leap forward in engines before much else dramatic happens. Something along the lines of the F/A-22 Raptor which is the first jet to do non afterburning supersonic speeds.

Nope. Supercruise has been around for decades.

Quoting Lightsaber (Reply 18): Quoting Cpd (Reply 17): Concorde prototypes, Concorde required afterburners ('augmentors') for supersonic speed.

It did not. They simply made the transition to supersonic faster and IIRC less fuel consuming.

Concorde-B was designed to use non-afterburning engines.

Quoting Flexo (Reply 6): What ever happened to supersonic business jets? Weren't there a couple of projects going on in that direction?

Gulfstream is currently doing research on the very subject- Google "Quiet Spike" and you'll see how they've been able to reduce the sonic boom to a mere whisper.

DeltaGuy

Quoting Cpd (Reply 17): The Concorde shape probably won't be radically altered for future supersonic airliners - but I do think there will be small improvements and refinements. I also doubt that "virtual" windscreens will be the replacement for variable geometry nose configurations, I suspect those will remain - if only because they are more trustworthy (and because they work well).

I do think that an SST will fly again. But first, we need to stop using fossil fuels.

We live today in a society of scarcity. That scarcity is energy. If you think about it, the vast majority of current problems are energy issues. If we had unlimited energy at our disposal, fresh water would not be an issue; we could desalinate whatever we wanted. Garbage would not be an issue; we could just launch it into space on a collision course with the Sun.

If humanity does not do itself in first, there will come a point where we will have a different energy source that is clean, cheap, and renewable. Whether it will be algae biofuels or fusion-cracked hydrogen, fuel will become cheap enough to power a supersonic plane.

That plane will have a geometry so that it will be "boomless." It will have an efficient design so that it need not carry the vast quantities of fuel that Concorde did, but fuel will be far less expensive.

But that day is FAR off in the future. It WILL come, but at best, if anyone is alive today who will live to see it, they probably haven't hit puberty yet.

Burt Rutan has already sat down and figured this out... watch this.
http://www.youtube.com/watch?v=nwfSENkvJXY

The next paradigm shift is aerospace will be to bridge the gap between rocketry and winged flight. Imagine being able to take off like a conventional aircraft, ascend to 60,000ft, accelerate into orbit, complete one revolution around the earth, and then re-enter at your destination.

London-Sydney in 2 hours.

Quoting Wingscrubber (Reply 27): The next paradigm shift is aerospace will be to bridge the gap between rocketry and winged flight. Imagine being able to take off like a conventional aircraft, ascend to 60,000ft, accelerate into orbit, complete one revolution around the earth, and then re-enter at your destination.

As soon as you can figure out how to do it as inexpensively as you can fly a 77L that same route someone will buy it.