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Thread: Airliners, Aerodynamics, & Efficiency

  1. #1
    Moderator Speedy1's Avatar
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    Airliners, Aerodynamics, & Efficiency

    This is a geeked-out propeller-head thread. Fair Warning. If you're not interested in such things, then just "click out of here."

    I got involved in a discussion with an old friend, earlier this evening, regarding aerodynamics and airliners. Basically the discussion was centered around the subject of "Why do airliners look the way that they do?" In other words... "Why the two wings, the long tube, and the horizontal and vertical bits on the tail?" And what is the deal with "winglets", swept wings, the little "fins" on the wings and engine cowlings, and several other issues?

    First... the short version... Why DO airliners look the way that they do?

    1) The basic design is proven. Two wings, a long tube (fuselage), a vertical tailfin (stabilizer) and a horizontal tailfin (either one fin or two symmetrical fins... stabilizers). That basic design has worked for over 100 years.

    2) The basic design is much easier to get approved by the regulatory agencies. Getting an airliner designed, built, and approved for service takes years, even when the design is completely conventional.

    3) The flying public responds well to a familiar and proven design. If you build something that looks like an alien spacecraft, nobody will want to fly on it.

    4) This familiar "Basic" design is almost "Idiot-Proof." The concepts of fixed-wing flight for the basic design are very easy to understand. With adequate training and experience, a competent pilot can operate a basic design with practically zero error. In fact, almost every major aircraft accident which has occurred without any external factors (weather, being shot down, turbulence, etc.) has occurred due to a mechanical or automation failure. A "Basic Design" airplane practically flies itself... the pilots just tell the airplane where to go.


    The Wright Brothers got it right... in a way...

    The Wright Brothers "stumbled upon" many of the secrets of efficient fixed-wing flight purely out of necessity. Proving sustainable fixed-wing heavier-than-air flight with an airplane carrying its own weight plus the weight of the pilot with only a 12 horsepower engine required a lot of innovation. Most of those innovations were awesome for efficiency, but not so good for reliability and controllability...

    1) The Wrights used a "Canard" configuration, which places the "Elevator" in front of the wing instead of behind it. Almost all airliners use a horizontal "stabilator" or stabilizer with "elevator", located on the tail of the airplane, behind the wing. Any aeronautical engineer would tell you that, in an ideal situation, the "Canard" configuration is more efficient, but that it presents a few problems. The "Basic" configuration, with the stabilator on the tail of the airplane, is more "bullet-proof", and is certainly more familiar to engineers, pilots, and passengers. A few modern airplanes have incorporated the "Canard" design, either supplemental to the Basic design or as a stand-alone pitch-control surface.

    2) Intuitively, the Wrights knew that the only purpose of a Rudder (and vertical stabilizer) is to hide the mistakes of the aircraft designer. The Wrights didn't even have a rudder control... the rudders moved in conjunction with the "wing warping" mechanism. A very few modern airplanes have incorporated this feature.

    3) The Wrights definitely understood the value of wind. The airplane cares nothing for its speed across the ground, only for its speed through the air. This is one of the primary reasons the Wrights chose Kitty Hawk/Kill Devil Hills for their test flights. The other main reason was the large sand dunes, which provided the altitude, slope, and relatively soft landing surface needed to test their gliders.

    4) The Wrights understood that aerodynamics was a complex issue, although they never fully understood the exact nature of the aerodynamic issues which they encountered. Probably the single greatest factor in the Wrights' achievement of manned, powered, fixed-wing flight was their construction and use of the world's first documented "wind tunnel."

    5) The Wrights were quite surprised to discover that boat propellers were extraordinarily inefficient and poorly designed, despite the fact that powered, propeller-driven water vessels had been in use for many years. The Wrights used their wind tunnel and other tools to construct propellers which were significantly more efficient than the boat propellers which were currently in use. In addition to making powered fixed-wing flight possible, the Wrights' propeller designs also quickly advanced naval technology in that regard.

    6) By using twin counter-rotating propellers, the Wrights greatly reduced the controllability issues associated with single-engine propeller-driven aircraft, as well as twin-engine aircraft with propellers and engines which rotated in the same direction. The Wrights did still have to deal with the fact that their aircraft was only driven by one engine, an issue which they did not document very well. It is likely that the Wrights did not fully realize the effect that their single engine had on the controllability of their aircraft. At any rate, it was a minor issue.

    The "Wright Flyer" airplane managed to lift itself and a human pilot into the air in sustained powered flight, with only a 12-Horsepower Engine. Even today, over 100 years later, it takes a very sharp mind to design and build an airplane that can perform the same feat. Because of the design features necessary to allow this airplane to fly with such little power, the Wright Flyer remains one of the most difficult-to-control airplanes ever built. Various replicas have been flown over the years, and many of them have crashed.


    Supersonic Flight...

    1) Supersonic flight was once the "Holy Grail" of air travel, and air combat... but no longer. Today, there is almost no need to "be there." We have the Internet and other tools. Why pay $12,000 to fly an executive round-trip between New York and London, when he can Video-Teleconference anywhere in the world, with people in places all over the world, for pennies? Concorde became nothing more than a Rich Man's toy almost the moment that it entered commercial/airline service. Concorde was a state-of-the-art masterpiece, but it was never truly Useful... or, at least, only for a short time. The world doesn't need supersonic commercial flight. So what if it takes 11 hours to fly to Japan? There's free WiFi aboard, and a tiny USB drive can hold 50 or more movies, books, etc.

    2) Concorde proved a lot of things that the military already knew. Concorde was long and thin, with an ogival delta wing... an ideal shape for a supersonic supercruiser. Concorde was the first aircraft actually capable of supercruise (supersonic flight without afterburner). The SR-71 (A-12) technically came first, but it wasn't really intended to supercruise as part of its mission. Concorde was specifically designed to supercruise on a regular basis. Concorde's shape and wing were a big part of this. There is a reason why the U.S. Air Force's F-22 is the very first U.S.-built fighter built with the ability to supercruise... It's difficult to build an aircraft that flies well at supersonic speeds and at subsonic speeds. Fighter aircraft rely upon low speed capability to win dogfights and avoid enemy attacks. It's hard to build a fighter that can maneuver at low speeds and supercruise efficiently. The F-22 is a decent compromise... the result of over 100 years of aerodynamic research and empirical evidence.

    3) Other than bragging rights, there is no point in manned supersonic flight in the military. Modern-day fighters, bombers, and attack aircraft are truly only weapon platforms. The days of dogfighting are over. Here... in 2016... if you actually see an enemy aircraft... you're already dead. The future of air combat is unmanned, subsonic, remotely-piloted aircraft... sometimes inaccurately referred to as "Drones." Or maybe one day the robots and computers will be autonomously flying the aircraft... and they really will be drones...

    4) Flying on the airlines, adjusted for inflation, is the cheapest that it has ever been. Over the past 40 or so years, since deregulation, airline travel has gone from a perk for the rich, to a cutthroat business where shaving pennies off of airfares can make or break an airline. The airlines are definitely not going to be investing any money in supersonic flight at any time in the foreseeable future... the market for it simply does not exist.


    That's enough for now. I might post more later.
    Last edited by Speedy1; 07-23-2016 at 02:54 AM.

  2. #2
    Moderator Speedy1's Avatar
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    Another reason that airliners look the way that they do...

    I mentioned in my last post that a proven design is much easier to build, and also much easier to get approved by the governmental authorities, especially when you're seeking approval for an airliner that will carry 200-600 paying passengers.

    A lot of airliner designs are based upon older airliner designs. Case in point... The Boeing 737. Boeing has built so many versions of this aircraft that I can't even count them all with my shoes on and my pants zipped up. Boeing knows... it's much easier to get a new "version" of an existing aircraft approved than it is to get a totally new aircraft approved. Of course, Boeing does occasionally develop a new aircraft, but it's never radically different from the "Basic" design. Baby steps... A great man said, about 80 years ago...

    "Aviation in itself is not inherently dangerous. But to an even greater degree than the sea, it is terribly unforgiving of any carelessness, incapacity or neglect."

    It's really hard to complain that we haven't seen any "radical or great leaps forward" in the airline industry. We probably never will. We can look back 100 years and say "Wow... look how far we've come." Our great-great grandchildren will look back at us from 100 years in the future and say, "Wow... look how far we've come." But all we will see is baby steps... practically imperceptible.

    That's because all it takes is just one tiny little fuck-up... and 600 people are shark food, or implanted into the side of a mountain. There are no "fender benders" in the airline industry. That's why we move at a snail's pace, and I think that's a good thing. Of all the things that government bureaucracy brings to a slow crawl, this one they actually got right.

    In fact... I think it's time for a bit of a "pause" in airline industry development. And why not? We're paying the lowest prices that passengers have ever paid, in the history of commercial aviation, when those prices are adjusted for inflation. We're also flying on airliners that are so remarkably safe that it's extremely rare to here of one just "breaking."

    Our biggest problem right now is getting the airline pilots and the airline maintenance folks up-to-speed on the technology that is already in commercial service. I'm getting tired of reading about accidents that occurred because someone didn't understand how this high-tech flight computer or other gizmo works. And I sure as hell don't want to be "Passenger #74" on the next airplane that flies itself into the ground while the pilots are saying, "What is it doing NOW?!"

    Believe it or not... I've been on more than a couple of accident investigation workgroups where the pilots were heard on the "black box" recording, saying, "What is it doing NOW?!" in reference to the airplane flying itself into the ground or ocean.

  3. #3
    Moderator Speedy1's Avatar
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    Here are a few old "Aviation Axioms" that I like to remember, on occasion, along with their relevance to our everyday travels with the airlines...

    1) When your flight is delayed because of weather or a "minor" mechanical issue, and you feel like saying, 'Come On! We can make it! This is a Bullshit Problem!' ...

    "Always remember... If you die when your airplane crashes while flying in a thunderstorm... Your funeral will be held on a beautiful, sunny day."

    2) Takeoffs are optional. Landings are mandatory.

    3) The hard, inescapable reality is that anyone who flies may die in an airplane.


    One sad fact... and I have MANY quotes about this... is that most airliner accidents are survivable. I have been on many workgroups, investigating airliner accidents, and in almost every single case, we have found people who died due to post-crash fire or smoke inhalation. No broken bones... no head trauma... in fact, there are usually indications that the person was trying to exit the aircraft, or at least trying to move in some direction. I'm not joking... almost every accident.

    Some good advice? Sit in an exit row... any exit row... preferably in the window seat (the seat right next to the exit). If you can't sit in the exit row, then sit in the window seat either directly behind or directly in front of the exit row. Read the exit door opening instructions and look at the images on the passenger card. Look at the exit door and imagine how you would open it if your eyes were closed. In a real emergency, chances are that you won't be able to see the door due to smoke, haze, or a press of panicked human flesh. If you are involved in a crash...

    If the aircraft seems to be intact, not on fire, no smoke, not sinking into the water, etc...

    REMAIN CALM. The aircraft has come to a stop and is not on fire or sinking. Try to keep the people around you calm and relaxed, and wait for instructions from the cabin crew. Most likely, you'll all exit smoothly through one of the forward or rear boarding doors. In this situation, your greatest danger is getting trampled in a mass panic. A nosewheel collapsing upon landing is no reason to go diving head-first out of the over-wing exit door.


    If the airplane crashes and it is on fire, sinking, or it's otherwise obvious that an immediate evacuation is necessary, it's time to take action quickly. First of all... look out the window of the emergency exit door. If there's a fire or anything particularly nasty there, turn your head 180 degrees and look out of that window. Almost all emergency exits are located in pairs... one on the left, and one on the right. If the cabin crew isn't already giving instructions, it's time to go... Open the emergency exit, immediately, and get your ass out of the airplane, immediately. If you're sitting in the window seat in front of or behind the emergency exit, it should still be easy to get the exit open and get out of the airplane.

    This is not a selfish act... although it is a self-serving act, it is also a humanitarian act. Not only are you not in the way of the other passengers, you're also probably one of the few people on the airplane who is aware of what's going on and what needs to be done. As you exit the airplane, you should be yelling "Follow Me! Here! Here! Follow Me!" Once you're through the door, keep yelling, "Come On! Move! Move! Move!" Grab any hand that you can and drag them through the exit. Depending upon the circumstances, get the people away from the airplane, or get them to head to a common rally point, or get them to stand on the wing, etc.

    If you're not the first guy out of the exit, head directly towards the exit. NEVER backtrack to grab a child, a handicapped person, or an elderly person, despite your natural instinct. You're only hurting the situation, not helping it. The most important thing is to keep everyone moving in one direction, and ONLY one direction. If you see a child behind you, yell at the person who is about to pass that child, "Grab that child!" If you pass a child, grab the child and drag the child behind you. Yell at the child to "Move! Run!" or whatever you have to do to get his little legs moving. If he starts to cry for his parents, tell him that his parents have already exited the airplane, waiting for him... whatever it takes to keep him moving.

    Injured or unconscious people are a judgment call... an often heartbreaking judgment call. One person can move through the exit every two seconds. If you bungle up the moving line for ten seconds to try to save an injured person, you might have just killed five people. You can go back for the injured people after all of the people who can move under their own power have been evacuated, if there is still time to do so. If you're fortunate enough to be a relatively strong person, and you pass an injured person, and there's another strong-looking person right behind you... Grab the injured guy's legs and yell at the other guy, "Grab him by the armpits and Keep Moving!"

    It is absolutely heartbreaking to see a layout of the crash site and see how many people could have lived. You can see the evidence of panic, confusion, and bad decisions in the pattern in which the bodies are laid out.
    Last edited by Speedy1; 07-23-2016 at 04:22 AM.

  4. #4
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    Good topic. As a former aircraft mechanic there are too few people who even care how and why an airplane flies. Despite knowing the mechanics of jet engines, airframes and structures, every time I see a DC-10, A380, or 747-400 I shake my head in amazement. I'll always have a soft spot for the B727-200 though, it's remains my favorite airframes of all time. Aviation to me remains one of the most, if not the most greatest advancements in human civilization. I can think of nothing else other than perhaps the internet itself that has bridged the cultures and brought humans closer to one another.

    Now I do have one disagreement: Air-to-Air combat. "They" have been saying air to air conflict is outdated since at least the end of the Korean War. "They" were wrong in nearly every conventional air battle the US has fought since. We lost a lot of good airmen in Vietnam because some forward thinking, paper pushing dipshit was convinced that there's no good reason to put a gun on an F-4 Phantom. The reasoning was all that was needed was missiles to stop Soviet bombers. There were no Soviet Tu-95 bombers used in Vietnam. That meant US forces had to adapt to the situation; fast. As any combat aviator will tell you, once you see HIM(enemy) and he's to close... Once he sees YOU and you're to now have direct conflict; A dogfight.

    So here we are in 2016 and "they" still think that some flying robots are gonna change the battlefield as we know it. Thankfully nobody is really buying it. That's why they're putting resources into the F-35. They're is even talk of restarting the F-22 program although that's just speculation at this point due to enormity of cost. The Pentagon is very concerned over China's recent incursions. Sure they're buying drones but only as a compliment to manned aircraft. Flying a drone does not give the operator 360 degree situational awareness. You need a pilot. If a sortie involves bombing a target and providing close air support in addition to that. Guess what? You need a pilot. A pilot flies for ego, for pride, for honor. An "unmanned attack vehicle operations specialist" flies because he thinks its cool that he gets a 30 min lunch break after blowing up the enemy so he can get back to playing his Playstation 4. You think you can entrust winning a techno-war with just drones that can be hacked by the enemy? Tsk, still need a pilot.

  5. #5
    Moderator Speedy1's Avatar
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    I understand the missiles versus guns discussion. That was, quite simply, an idea that turned out to be flawed. But taking the pilot out of the airplane is an eventuality that can't be stopped, as long as there are no other humans aboard. That limits the concept to warfare and cargo. This is a lot different from what is coming down the pipe. I've seen some of this stuff in action, and it's amazing. I'm not giving away any secrets here. The basic concepts are common knowledge. Within 50 years, there will be no reason to have a pilot, or any other human, aboard the aircraft, for several reasons. There will still be pilots... they'll just be on the ground.

    1. 360-degree situational awareness is coming quickly. UAV's don't use it, because it's unnecessary. UAV's are very difficult to shoot down, and they will only become more so as they become smaller and more efficient. UAV fighter pilots of the future will have full 360-degree views, unimpeded by even the aircraft structure itself. The pilot will see everything as if he were flying an invisible jet, with his view unimpeded by any weather or other obscuring phenomena. True "Superman" vision, while safely on the ground. The tech is already there. The USA just doesn't use it because it's far cheaper to just take another Predator out of the box than it is to build the ground-based pilot suites.

    2. Which brings up the next point... The USA is already almost there as far as this one goes... It will soon be cheaper to flush a UAV down the toilet than it is to sortie an interceptor. It costs Iran more to sortie an F-14 for an hour and fire a couple of missiles than it costs the USA to blow up a UAV, and guess who has the bigger budget? As cold and as callous as it sounds, the harsh reality is that the USA can keep putting UAVs in the air until the enemy is completely bankrupt and can no longer afford to wage war.

    3. The advantages of UAVs over piloted aircraft are undeniable. A pilot can "die" in combat a dozen times, and keep coming back, now with more actual combat experience. It would be like being able to resurrect Richard Bong or Eddie Rickenbacker over and over again. UAVs capable of pulling 20+ Gs will exist in a couple of decades. To the enemy, it will be like trying to kill a hummingbird with a broadsword. As technology advances, with no need to carry a pilot or the necessary life support and interface equipment, the USA will soon have UAVs that are smaller than motorcycles. At this point, the ordnance is the limiting factor. If the missile wasn't so big, the UAVs would already be smaller. That size, in combination with stealth and other technology, would make a UAV indistinguishable from an average-sized bird. Even a pilot less than one mile away wouldn't be able to see it with his own eyes on a perfect day.

    It's coming. I'm a pilot too, I don't ever want to give up flying. But taking pilots out of warplanes? I'm all for that. I don't want to take the pilot out of the cockpit, just out of the airplane.

    One big problem... and this is a real discussion that I have actually witnessed... is that this threat is as great as the threat of nuclear weapons. If the genocide of a race or an entire country's population is as easy as taking a couple of Billion dollars out of the U.S. Air Force bank account, with zero risk to U.S. personnel, there is no incentive for the enemy to show restraint. The enemy literally has "nothing to lose" at that point. Russia would launch their nukes just the same as if the USA had launched their nukes... at least that's how the theory goes.

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