Aircraft design decisions

Decisions, decisions … I think it is safe to assume that a lot more brain power and thought has gone into all kinds of design decisions that people don’t even know about. Just the other day, I was assembling a new IKEA wardrobe for our kids’ room, when I was blown away by the ingeniousness of some aspects of the design. I didn’t even need a screwdriver anymore for that thing, except for the hinges. Click, snap, boom, you have a drawer! I really appreciate these little moments, when I notice some piece of industrial design and it makes me think about how smart the person was, who came up with the idea, and how he or she saved untold numbers of people maybe just a couple of minutes each, but made the world a little bit of a better place by doing so. And don’t even get me started on things like electronics or medicine. Besides all the things that are wrong with the world, I think more things go right and we do live in glorious times.

Anyway, to get back to today’s strip: In contrast, I wonder how many and which design decisions were actually made totally arbitrarily, and just got continued by sheer momentum or inertia. I just can’t come up with an example at the drop of the hat, but there must be tons of examples for those out there too, right?

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7 comments on “Aircraft design decisions
  1. Captain Dunsel says:

    Some companies like to keep using ‘trademark’ shapes (for example, DeHavilland’s graceful tail fin /vertical stab shape). Others just want to same the cost of drawing and jigging new components when ones on hand will do.

    On a MUCH smaller scale, I design and build R/C models. I often re-use wing and tail structures, simply modifying them to fit as needed (For example, adding or removing landing gear mounts, moving aileron servos to the top or bottom of the wing, and so on. Why redraw a whole wing?

    Back in the 30’s, several manufacturers made families of aircraft, using the same basic wing, fuselage, and tail structures, adding/removing components, changing power plants, etc. For example, I believe the Curtis CW-19, CW-21/22, AT-9, etc., shared common parts.


  2. reynard61 says:

    Prop blade count is generally determined by two factors: Horsepower and torque. Smaller engines with low torque were generally given relatively simple fixed twin-blade props. (There were exceptions, of course. Small, fast fighters like the Sopwith Camel got twin-blade wooden props, but they tended to be quite a handful to fly in any direction other than that which their engine’s torque wanted to pull them.)

    As engine horsepower — and torque — increased, more blades (as well as blade specific speed controls) were added. (This accounts for the addition of another blade to the Corsair as the engine size and horsepower/torque increased. Another way to go, as seen on the P-40K, was to add more area to certain flying surfaces.) Eventually, some piston engines became so powerful that 5- and 6-bladed props were needed (Griffon-powered Spitfires and the Avro Shackleton are good examples); or larger, sturdier props that could withstand near-supersonic blade speeds. (The Lockheed L-188 Electra.)

  3. Fbs says:

    « Un bel avion est un avion qui vole bien. » – Marcel dassault

    (An awesome plane is a well-flying plane) – That’s a quote from one of the most talented plane maker….

  4. Speedsix says:

    A friend of mine who is an engineer recently told me several aircraft manufacturers changed from 2-bladed airscrews to 3-bladed ones due to the strain that was put onto the engine crankshafts / transmission gear when doing rapid turning manoeuvres. Seems like the same applies to wind generators, albeit on lower rpms but sooo much bigger blades.
    And don´t forget the contra-rotating double airscrews as on the Avro Shackleton, Tupolev Tu-95, Supermarine Seafang etc. This was to eliminate the massive torque which those huge engines put on the airscrews and which made take-off quite hazardous.- Apart from reducing prop diameter, of course!

  5. Quill says:

    Everyone here is saying that it’s about matching performance, optimizing for the engine and speed of the plane, taking into account the compromises and trade-offs, I think that actually looks and marketing could play a role, cannot be ignored in many airplane design decisions. That’s extremely true for cars, but I think it’s also true for some airplanes – especially Cessnas, such as the 172 line. They want to design what will sell, and buyers buy based on performance – and looks. The swept tail design had no performance advantage over the earlier straight tail, but looked better. Can probably see this in homebuilts as well, both the design from the designer and how builders equip them – they want something they feel cool flying, even if it doesn’t help or even hurts performance – a three-bladed prop could be an example in this.
    As for appreciating design features, as an engineering student I can really see what’s going on, and often how moronic designs are. If I had something similar to that “Deathnote” book, but one that punches the written person in the face rather than killing them, it would be filled with “Person who designed…” But I have seen a few things that amaze me with little genius design features. I think of this especially with my old VW Bug. It was a later model (’73), I figure the engineers had been gradually tweaking a relatively unchanging design for decades, optimizing every tiny little detail, rather than starting from scratch every few years like most car designs. Does have a few stupid design features as well, mostly minor cost-savers – but I have modified it to fix them.

  6. Speedsix says:

    The Piaggio Avanti is an example of how unorthodox design curbes an otherwise fine design. Not a bad aircraft at all, it still suffers from targetting a conservative market that prefers classic layouts.

  7. Captain Dunsel says:

    Having designed several R/C models, I have a lot of respect for designers. The model I keep in mind is the Hershey’s Kiss, with a bit of almond in the center. What I ask myself, is how would I put that bit of nut in the center of a mass of molten chocolate? The concept is simple, but the execution isn’t.

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