Why Airplanes Look Alike

I was sitting waiting to go at an airline airport the other day when I realized how closely I had to look to know if it was a Boeing or an Airbus. Aging descendants of the DC-9 were easy to spot with their fuselage mounted engines, but a Boeing 777 looks a lot like an Airbus A330.  An Airbus 320 series looks very much like a Boeing 737 that doesn’t have the graceful Aviation Partners winglets.

Yes, it’s still easy to spot the Boeing 747 with its fuselage hump, and the sheer size of the Airbus A380 is unmistakable, but the overall design of airliners has homogenized. And it’s continuing into the smaller airliners where the new Bombardier C-series jets look very similar to the wildly successful Embraer E-jets. Even the ATR and Bombardier Dash-8 turboprops now look a lot alike as they have stretched under their high wing.

What’s happening is aviation has matured. When different groups design an airplane for the same mission the results come out about the same. People have been designing, building and flying airplanes long enough to know what works best for specific missions.

For example, do you see any low wing bush planes? The Thrush and Air Tractor agplanes that dominate the world of crop spraying look very much alike. And with the exception of the HondaJet the configuration of purpose-built business jets is essentially the same.

The maturity of aviation extends down to personal aviation where the low wing design with conventional horizontal tail placement dominates. And in aerobatic flying a mid-wing design with a very narrow fuselage wins the championships despite the unbelievable air show performances of Sean Tucker in his biplane.

If you want a glimpse of aviation design in its youth before trial and error drove it to maturity just look at the antique airplane area at Oshkosh. There you will see airplanes in all manner of configurations that were certified and built in at least enough numbers for a few to survive. Every design idea got a chance in those early days and the market picked the winners.

You can see the same level of design maturity in the homebuilt area at Oshkosh, too. There you will see one or two examples of just about any airplane design configuration and a vast array of construction materials and techniques. But if you count prop spinners you will see that homebuilding has matured, too, and in maturity it is a Vans RV that dominates.

None of this design maturity has anything to do with what is the best technology but rather what is the best combination of technologies that delivers more of what pilots want than other combinations. A big component of maturity in airplanes–or people for that matter– is compromising on some desires to get more of what we want in other areas of performance and pleasure.

There are still some people creating what engineers call a “point design” because the airplane is focused on a single design point. An example would be an air racer where speed is everything and the only thing. Or extreme short runway capability. Or maximum cabin volume. And so on. But those are niche airplanes.

Decades ago my friend Peter Garrison designed and built a point design with his original Melmoth. Peter’s design point was extreme range with decent cruise speed. He succeeded. Peter flew Melmoth non-stop across the Pacific, to the tip of South America and on other extremely long unrefueled trips.

But few, if any, want to sit in a small single engine airplane over the open ocean for hours on end so there is no copy of Melmoth. And when Melmoth was destroyed when it was hit by an out of control airplane as Peter held short waiting to takeoff even he changed his mind. His second design can carry four instead of two, and has only a fraction of the range. Some aspect of maturity—maybe having been there and done that—removed Peter’s desire to cross vast oceans in his own creation again.

Most new airplane designs are better in useful measurements such as speed, range, cabin room and payload than earlier designs. The gains are not often huge, but cumulatively new airplane designs can deliver more of what the majority seeks than designs of years ago. And those improvements are typically the result of using what worked well before and making it better.

Does this maturity mark the end of aviation innovation? I don’t think so. A long time ago automotive designers settled on four wheels as the optimum for nearly all passenger vehicle missions. Has auto design innovation stopped because all cars have four wheels and use the front two to steer? Of course not.

And then there is the HondaJet. A very big company has invested enormous sums in a different configuration for a business jet with over the wing mounted engines and other unique features. Honda has now told the FAA the airplane design work is complete and has entered the Type Inspection Authorization phase which is the first step in final type certification. Honda expects the airplane to enter service about a year from now. The preliminary numbers from Honda look promising. We will all be watching.

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17 Responses to Why Airplanes Look Alike

  1. Erik says:

    The Lear Jet is still probably the best looking jet airplane out there. And still one of the most efficient. And still one of the strongest. And still one of the most fun to fly. And still very passenger friendly. And still advancing and getting better and better. And still my airplane of choice when I win the lotto.
    Another beautiful deviant from the “Ford Taurus Jet” theory is the awesomely efficient, amazingly safe, fun to fly, super strong, extremely Pax-friendly, highly advanced, and still-advancing Falcon line.
    So there are at least two terrific biz jets aircraft that don’t quite conform to the homogeneity-follows-form-follows-function theory.
    I’m also not convinced that canard design ever got a fair chance to prove its superiority. Perhaps an exegesis on the why not could be a future article from you. Or, if I’m way off and the canard really is quackery (pun intended), you might explain why that is the case.
    Thanks, and keep up the great writing!

  2. Thomas Boyle says:

    Erik,

    I’m afraid the canard design is mostly quackery – and I say this as a one-time fan of the layout.

    Burt Rutan got some great performance out of his canard-layout designs for homebuilders, but this was primarily because of the low-drag design of the composite airplanes, not because of the canard layout. The canard layout provided stall-proofing, a safety benefit, rather than drag reduction.

    For a canard design to work, the canard has to be more heavily loaded than the main wing. Therefore, in practice, the main wing cannot be operated at high lift coefficients, because the canard – being even more heavily loaded – would stall first. This means that, for a given main wing area, a canard cannot be flown nearly as slowly as a conventional design. It must either have poor (“hot”) landing/takeoff performance, or a wing that is very large and therefore too big to be optimal in cruise (large wetted surface -> high drag, and large area -> low wing loading -> unpleasant in turbulence). Rutan’s designs have the wing sized for comfort in fast cruise, but they takeoff and land fast and flat – watch one, sometime.

    The design of a canard is tricky too: it must be loaded heavily enough in all CG conditions to ensure that it will stall well before the main wing, but lightly-loaded enough in the forward CG condition to provide reasonable runway performance. And laminar flow canards are more or less out of the question, because of the potential consequences of rain drops or ice on the canard (if the canard stall alpha falls below the alpha required for level flight, the airplane will dive).

    In the end, the conventional design offers a wider speed range (higher cruise speed for a given runway performance requirement, or better runway performance for a given cruise speed) – especially because it can handle large flaps; lower cruise drag for a given level of runway performance; lower structural weight (smaller wing); and greater ability to design for a wide CG range. On the other hand, the canard design offers stall-proofing (if loaded properly), better visibility for most light aircraft layouts, and “cool”.

    Runway performance is much less of an issue for small, light aircraft: for them, most urban airport runways are very long, and it is easy to accommodate the longer takeoff/landing runs of “fast” canards like Rutan’s. For business jets, runway length is much more of an issue, and the drawbacks of a canard layout become more significant. In addition, inadvertent stalls are not a common problem with business jets, so there’s not much advantage to the canard’s stall-proof layout. We’re not likely to see many canard business jet layouts (the Piaggio Avanti, an apparent exception, has both a canard and a conventional tail).

  3. Harold Bickford says:

    In simple terms form follows function and thus an optimized configuration for aircraft will result for a given mission. In our arena the RV series shows how that plays out. Different configurations make sense only where a performance advantage can be had, at least at the logical level. Beyond that there is the emotional or visceral appeal of design which at the least is expressed in paint schemes or trim. Sometimes folks just want something different, ergo the rationale for experimental aviation. As an example a Dyke Delta is quite different and performs well and a Pietenpol is not even close to an RV while having a continuing appeal for some people. Vive la difference!

  4. Erik says:

    Thanks Thomas.
    That makes lots of sense.

  5. Jaxs says:

    The takeaway? EAA is no longer needed. Experimentation is officially over. R.I.P.

    • Phil G says:

      Seems that way, Jack Pelton being the head of a certified aircraft company doesn’t seem interested in the Experimental side of the EAA.
      EAA is now just known to kids for running a big airshow.

    • Mac says:

      Hi Jaxs,
      The reality is EAA has never been more relevant for those who wish to fly airplanes that are not part of the mainstream. A designer/builder can select whatever capabilities he desires and create an airplane to match. It doesn’t matter what anybody else thinks of his design, it’s totally personal. That is the heart of E-AB.
      It is a different situation for kit makers because they are under market forces just as any other manufacturer. To succeed as a business a kit must satisfy the largest possible number of builder-pilots in its segment. That is the same as for a standard category airplane manufacturer.
      So the freedom to design and build your own airplane becomes critical for those who want to satisfy their own list of important qualities in an airplane. Now, more than ever as aviation matures EAA continues to support the designer-builder who wants to lead a parade, even if it is only a parade of one. Thanks to decades of work by EAA the designer-builder has near total freedom to build the airplane of his choosing no matter what other pilots think, or what over pilots would buy.
      Mac Mc

  6. Tom Davis says:

    At various times in the history of aviation, designers have “settled” on a norm. There were the fighters of WWI, which were almost all biplanes of similar stature, with but a few exceptions. Then the small transport planes of the 30′s, which looked quite similar to each other (Lockheed Electra, Beech 18.) Look at the fighters of WWII, whether radials (P-47, Zero, FW-190, F4f – F6f) or inline-powered (Spitfire, P-51, Bf-109) and note how similar they are. Or consider the first “mature” jet fighters (F-84, F-86, Mig-15 and-17) with their yawning nose air intakes. At each of those points in history, people probably thought they had finally arrived at the ideal shape of the modern airplane. I have a feeling today’s airplanes will someday look old-fashioned, too.

  7. Tom Davis says:

    Regarding homebuilt aircraft, I think Mac oversimplifies the situation. Sure, the RV’s are quite popular and thus numerous, but there are many, many builders and pilots who want something else (such as the ability to watch the countryside unfold beneath them.) For them, the Kitfox, Tailwind or Bearhawk better suit the design requirement. Or two engines, like the Aircam. And some people, bless them, prefer to put their energies into building an aircraft of their own design. Nothing against RV’s; those are terrific planes, but I’m glad EAAers have broader tastes.

  8. John Patson says:

    In some ways it is sad to see the great, big, draggy engines hanging from the armpits of modern passenger jets (you can tell if they are Alitalia because they don’t shave under the wings is the old joke…)
    British design had a period of in-wing nacelles, where for given engines, the aeroplanes were noticeably faster than suspended engines.
    The story goes that they were abandoned for the Airbus (originally a Franco-British bird) because at the time the unions in the UK were too strong and the mechanics could not be bothered to climb a ladder or use a lift and open a hatch for basic maintenance such as oil tank checks.
    Now of course the giant fans probably make in-wing designs impractical, although most military jets hide the engines.
    The other British alternative, the VC10 with four engines on the tail giving a very clean wing was fast but suffered from the same reluctance of mechanics to use lifts.
    Assuming that passenger jets remain low wing for ease of manufacture, the next move may be to have the engines on top a la Honda, to allow space for the ever larger fans, lazy mechanics or not.

    • Jeff Boatright says:

      Could you point us to sources that support your hypothesis that lazy union mechanics drove design decisions?

      • John Patson says:

        Conversations with British aeronautic designers, airport authorities and trade unionists!
        The web did not exist then.
        And heaven help any company which put anything like this on paper for formal discussion…. Come to think of it, it is a bit like Boeing in Seattle today.

        • Jeff Boatright says:

          No memoirs? Nothing? And what large jets allowed maintenance without some use of lifts, ladders, or stairs? This just doesn’t hold much water. I’m not saying that these people didn’t make statements to you along these lines, but it’s not clear why these statements are believable.

  9. Thomas Boyle says:

    Experimental aviation is far from finished, and the RVs are not the final form of sport aircraft – although they may be some of the most-refined examples of what can be done with current technologies.

    Experimental aviation has 3 directions it can go: new powerplants (which often produce large changes in aircraft design); new structural technologies (ditto); and electronics, which change function but not form. At recent AirVentures I’ve seen exciting – if not always entirely successful – efforts to introduce small turboprop engines, electric propulsion, and powerplants based on automotive/marine engines. Rutan introduced composites years ago, although the high labor content and unpleasant chemicals involved have kept these from being as successful as we once hoped – but new composites may change that. I expect we’ll see 3D printed parts showing up before long. And electronics have just begun to demonstrate their exciting potential: purists may hate the idea, but we will have autopilots capable of “cruise control” all the way through the landing (or with Big Red Button functionality that takes over if the pilot is incapacitated or out of his/her depth), autopilots capable of flying sailplanes, electronics capable of providing aerobatic instruction (including demonstrating the routines themselves)…

    The RVs are a great thing. But experimental aviation has lots to do.

  10. Hod says:

    Mac probably isn’t aware of:
    http://www.synergyaircraft.com/
    Just goes to show the “maturity” of his thinking as he flies around in his Baron, which has not changed much since its introduction in 1961. The reality is that people become comfortable with what they know and are familiar with, not what necessarily works best for a particular mission. In large part, it is precisely this kind of thinking that has led to stagnation in general aviation and aircraft certification.

    Of course a thoughtful person won’t fly a low-wing airplane into the brush and risk ripping the wings open, which is obvious and goes without saying.

    However, in general, aviation is risk-adverse and has far too few early adopters to make new technology accessible or feasible. Internal combustion aircraft engines are a perfect example of stagnant technology (and in-the-box thinking) that has cost general aviation dearly.

    Both Boeing and Airbus have radical and innovative designs (by current standards) on the drawing boards that will lead to increases in efficiency in the years ahead, and certainly do not resemble the current crop of airliners.

    As you walk around general aviation airports, notice how old the pilots you see are getting. General aviation is operating rotary-dial technology and thinking, in the iPhone age, and is shrinking as a direct result. It doesn’t have to be that way.

  11. Thomas Boyle says:

    What Hod said.

    It’s been my observation that pilots are both extremely risk-averse about innovations (which is understandable) and highly xenophobic (which isn’t). There’s a lot of – there’s no other word for it – hate expressed toward pilots or aircraft that are different. I have been horrified, over the years, by the number of aggressively negative, usually ill-informed rants directed at LSAs/Sport Pilots, ultralights, engines not manufactured by Lycoming or Continental, pilots who would like to see the 3rd Class Medical eliminated, airframe parachutes, autopilots, airplanes manufactured in China…

    Little wonder, in some ways, that we see so little change. Hard enough to take the risk of trying something new, without being scorned for it.

  12. Tom Davis says:

    I agree with Thomas Boyle, that there is a strong resistance to newer facets of aviation that don’t fit the traditional model. But I think there’s reason to be optimistic. There is a newer generation of aviators –maybe call it the Brady Lane crowd — who didn’t grow up with Continental and Lycoming as the only engines; for whom LSA has always been an option; who don’t revel in the good ol’ days of NDB’s and etc. I know that participation is meager, at least now, but as the years go by aviation will come to be dominated by people born much later than most current EAA and AOPA members. And they will fly, and they will visit Oshkosh, and they will introduce ideas we haven’t thought of yet.

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