Golden Era of Aeronautics, Part One

Image of Patrick Stoliker, Deputy Director of NASA Dryden Flight Research CenterPatrick Stoliker

Deputy Director 
NASA Dryden Flight Research Center

On May 2, 1952—virtually 60 years ago—36 people boarded BOAC’s De Havilland Comet DH 106, known as “Yoke Peter” to its crew for last letters of its registration G-ALYP, took their seats and readied for a long journey. These were the first paying passengers of the modern jet age, departing London for a 7,000-mile trip to Johannesburg, South Africa. Powered by four Ghost jet engines (also made by De Havilland) and with a cruise speed listed at about 500 mph, the passengers rode in pressurized comfort. About the only significant difference between that day and now was the legroom and the ratio of passengers to fight attendants. But if we pay too much attention to the similarities we’ll miss what is remarkable about the span of time involved. It’s been 60 years since the first passengers rode on a jet airliner and we’re still flying at the same speeds and the same altitudes.

There was a brief interval during which the wealthy could travel at Mach 2 on the Concorde (slightly faster if they wanted to fly the Soviet Tu-144), but neither airplane was ever a commercial success: both were just items of national prestige.

If it seems as though little has changed in the last 60 years—I said seems—consider how much changed between 1903 and 1952: call it the first 50 years of flight. It was on a wintry day in 1903 that two brothers from Dayton, Ohio, succeeded where no one else had, on the sand dunes of Kill Devil, North Carolina. Wilbur and Orville Wright were hardly the only ones trying to figure out flight at that time; there were quite a few in the US and in Europe, and most were further along than the two brothers. Even worse for the brothers, their competitors seemed to be better educated or better funded, as in the case of Samuel P. Langley of the Smithsonian Institution, or at least further along in the quest. 

The brothers made up for this with an intellect that the made their lack of a high school diplomas irrelevant. They learned the value of a wind tunnel by building their own, and they were smart enough to figure out that everyone before them had been wrong about the relationship of lift, wing area, and velocity, to say nothing of airfoils shapes. They had that rarest of talents, what Eugene Ferguson called “engineering in the mind’s eye,” the ability to move back and forth between the abstract and the concrete when trying to solve an engineering problem. They recognized propellers as rotating wings in the process. They understood wing warping and, more importantly, figured out the vertical stabilizer as the solution to adverse yaw, which they encountered on their glider, and they managed to do so largely because of how they mingled the abstract and the concrete. With Charlie Taylor, they put together a 180 pound, 12 horsepower engine with a good enough thrust to weight ratio to fly. It was an ungainly airplane, unstable in all axes, and I’m certain that only the hours of practice with the gliders gave them the skills needed to control the airplane. Then again, the same goes for riding a bicycle: it too, is unstable and takes time to learn how to ride, but you are then rewarded with a contraption that is nimble as can be, as opposed to a four-wheeled wagon. Progress came quickly. Although canard configurations have returned, the Wright’s pursued their original aircraft configuration until 1909, when they added an elevator and larger vertical tails. The 1910 Wright Model B had no canard and engines with 28-42 hp (with a production run of about 100 airplanes).

Their competitors settled into the more conventional wing/rudder/elevator configurations and everywhere advancements in capabilities and performance quickly followed (ditching wing warping in favor of ailerons was a way to control the airplane and try and avoid the Wright’s patent). Aircraft manufacturers proliferated across Europe and the United States. Although we think of this as the era of the biplanes (and triplanes), monoplanes like the Nieuport 2 were being built by 1910! The Loughead Brothers (later Lockheed) formed their first aircraft company in 1912 in Santa Barbara. The first aviation meet in America was held in Los Angeles (Dominguez Hills) January 1910 and airplanes were still so relatively new enough that dirigibles were a huge draw even then.

The speed with which aeronautical technology developed is astonishing and I consider this first decade one of the golden eras of aeronautics. We made big steps from the first ‘practicable’ airplane to modern aircraft. War had much to do with this, as it often does–in this case it was WWI. That war brought the first monococque fuselage, the interrupter gear, vastly improved flight instruments, the first UAV (the Kettering Aerial Torpedo, whose flight was made possible by Lawrence Sperry’s autopilot of 1914), the first all metal aircraft (Junkers J1, J2, and finally, the truly functional J4), just to name a few. The rapidity of the developments and their dramatic appearances likely makes us think war is the prime driver in such changes. But if we look at the bigger picture, this seems to be less the case.

After all, the Wrights achieved flight in a period of peace and were themselves not driven by any war, even if their first customer was the US Army Signal Corps. The first four-engine aircraft, Igor Sikorsky’s Ilya Mourometz appeared in 1914 in Russia, before The War. It was during the interwar years, the period between WWI and WWII, that NASA’s predecessor agency, the NACA (National Advisory Committee for Aeronautics) developed or assisted in developing some of the most fundamental changes to aeronautics, including retractable landing gear, the variable pitch propeller, deicing boots, engine cowlings, and the world famous NACA airfoils. It was in this same era that the first superchargers were developed to allow piston engines to gain higher altitudes (and speeds), and we saw the first genuine pressurized fuselages. It was in 1928—long before WWII began—that Englishman Frank Whittle conceived of the turbojet, and still before WWII that German Hans von Ohain succeeded in flying the world’s first turbojet, developed independently of Whittle. And while people first paid to travel by air before the War, it was in the interwar years that commercial aviation actually took off, so to speak.

Image of X-1WWII drove more aeronautical developments, of course, one of the subtler ones being the abandonment of seaplanes as the preferred way to carry passengers on long routes. The war resulted in plenty of new runways all over the world as well as an abundance of multi-engine aircraft with long range, making the big seaplanes a dying breed. It also helped that long-range navigation and radar approaches were improved and created, respectively, because of WWII. Piston engine/propeller aircraft had been having trouble with the transonic realm before WWII; figuring out supersonic flight was the next big challenge, and while folks in the Army Air Corps and the NACA expected it to be a big challenge, I don’t think they realized just how big the leap into the unknown would be. Getting to Mach 1 could be done with a turbojet engine, but if you were in a hurry to do it—and the AAF was—you were going to need a rocket plane. Jet engines of the era simply weren’t powerful or reliable enough to do the job-yet. This led to the Bell X-1, two X-1s actually, and the quest for supersonic flight. This was dawn of the golden age of flight research and X-planes, of almost infinite questions and purpose-designed aircraft like the X-3, the X-4, and the X-5.

Change came fast.

In 1961 TWA introduced in-flight movies on its Boeing 707s. By 1964 we had gone Mach 3 in a jet powered aircraft (A-12/SR-71), faster in rocket planes; we’d been to space and back in capsules and a space plane (the X-15), and supersonic flight was routine, at least for the military. In 1970 Boeing introduced first the “jumbo” airliner, the 747, and we’ve been packing in more and more passengers ever since. Yet we’re still flying at virtually the same speed and altitude as those 36 passengers on “Yoke Peter” in 1952. Have things really not changed? Are we in the doldrums, and if so, why?

Birds, TEDx, and the Mind's Boxes

Watch Al’s TEDxNASA presentation, “Toward More Bird-Like Flight: Thinking Outside the Box,” here.

By Al Bowers
Associate Director for Research
NASA Dryden Flight Research Center

It’s been a couple of weeks since the TEDxNASA@SiliconValley event now. I’ve had a little time to decompress and reflect. I have some thoughts to share…

An incredible amount of work was done by the NASA Ames folks putting on their first TEDx event, and the NASA Langley TEDx crew did an equally incredible amount of work in support of the event, helping out and getting everything spooled up. There were a number of NASA Dryden folks helping out as well; many kudos and thanks to everyone who was doing a lot more than pulling their own share.

Image left: Al Bowers takes the stage for his 8 minutes of fame at the recent TEDxNASA event in San Francisco. Image courtesy Michael Porterfield.

Wow, TEDxNASA. What an event. In the lecture/conference world, the TED name (stands for Technology, Entertainment, and Design) has huge gravitas. And it is well deserved. Some of the most mind-blowing ideas have been presented in a public forum at TED, and to put all those great ideas together in one place like TED does is simply amazing beyond words. TEDx is the way TED shares their ideas worth spreading with a broader audience. Bravo!

So I knew what TED was before I was asked to be a TEDxNASA speaker. And when the question came up of who should speak for NASA Dryden, the fact that my name got mentioned was a huge compliment and honor. To be honest, I view myself as a pretty regular person. Not very noteworthy, and having little to add to a thought or conversation. But once in a great while, a few times in my life, I’ve had these glimpses of incredible insight. I could see connections between GREAT ideas from the great thinkers that I’ve read about, and thought about their ideas. And suddenly I can see how these amazing ideas work in the vision of my mind.

So TEDxNASA was an opportunity to share one of the really big ideas that I was able to grasp. I chose the last paper by Ludwig Prandtl on the spanload of wings. Prandtl was the founding father of the science of aeronautics. His formulas were the first practical tools by which we could calculate lift, induced drag, and spanload – the distribution of load across a wingspan. John Anderson, the great professor of aeronautics and noted historian, speaks of how Prandtl should have won the Nobel Prize for Physics because of his contributions to aeronautics. And I completely agree. Prandtl’s last paper on spanload and induced drag has languished, almost completely unnoticed, and would be not even a footnote were it not for two brothers who used his idea to build a few wooden gliders and sailplanes. These two brothers, Reimar and Walter Horten, built some of the most beautiful man-made aircraft to ever fly – pure flying wings. The Hortens had to integrate all the components of flight into a single unit, and eliminate everything that did not contribute to their singular idea. Prandtl’s last paper on spanload was the germ of that idea.

Image right: The Horten H VI sailplane, built by Reimar Horten.Image courtesy Doug Bullard.

Many years ago, I had the great honor to listen to Bob Hoey, the retired Edwards Air Force Base engineer. Bob had been studying the flight of birds. And Bob was talking about the spanload of birds and how, if you got it wrong, nothing worked, but if you got it right, everything worked. Bob didn’t know about Prandtl’s last paper, or details of the Hortens’ work. But I did. And suddenly I connected the dots between them, realizing how Prandtl’s idea could solve the three great problems of aircraft in a single integrated solution: maximum performance (that is, minimum drag for maximum efficiency), minimum structure (if you’re limited in structure, what is the wing that is optimum?), and controlled coordinated flight (minimizing the added clutter of control surfaces we take for granted). And I could see the connection between Prandtl with his ideas, the Hortens with their sailplanes, and Hoey with his birds, and everything came together.

Graphic at left: The elliptical spanload (dashed line) and the bell spanload (solid line), with the centerline at the left and the wingtip at the right. At the top are the spanloads, and at the bottom are the induced drag curves (note the bell spanload induced drag goes negative at the wingtip).

TEDxNASA gave me only a few minutes to get my idea across. Normally, it takes me a full 40 minutes to develop the background of how we got to where we are (mostly developed by the Wright brothers and Prandtl), but this was unacceptable for TEDxNASA. Enter the person who could distill the entire talk to what it needed to be, Hayley Foster. Hayley is a Langley person, and her job is speech coach. I’ve never had a speech coach before. Man, was she good, and wow, did I need it! Hayley was not exactly an aero person (she knew some of the jargon and the background), and she could see the germ of the idea I had. And when she edited my first draft, I think there was more red than there was white left on the page! There were seven complete rewrites, and many dozens of edits in there. But it came out. And it fit in the time slot. Hayley is a miracle worker; thank God for her…

TEDxNASA@SiliconValley was in San Francisco, near Moscone Center. It was tagged on the end of the IT Summit, so there was a certain amount of teardown activity for the summit and buildup for TEDxNASA going on. We had our pre-meeting for the speakers, and that was our first walk-through of the venue and familiarization with where the Green Room was, when we needed to be where, the final details on the schedule, and the real indoctrination of what it means to be a TEDx speaker. All the folks doing the prep were running around in these cool black TEDxNASA shirts. All of us speakers were sort of milling around in the middle of this huge hubbub of people running to make things happen. And then, it started.

The first few speakers gave their talks. Things were going pretty well. We had the usual GLITCHes (GLITCH = gremlins living in the computer hardware), but the presentation was moving very well. It was time for me to get ready. Now, I have a confession to make. The worst time for me, for any talk I give, is the last five minutes before I walk out to start talking. I am a total nervous breakdown, train-wreck of stomach-churning, introverted, hands-shaking nerves. I know none of you believe that of me, but it’s true. And then I walk out on stage, and I start, and suddenly…the moment flows. I can connect with people; I can open their mind’s eye to new ideas, to concepts that are really the secret truths of the universe. For a moment, this frail, failing, human mind of mine can do that with others.

“Assumptions are a fact of life…” I begin to share what I have learned. The boxes our minds live inside of…the flight of birds…the Wrights and their success…Prandtl thinking the great thoughts…explaining induced drag…Horten figuring out the implementation…and my stumbling into the implementation (with help!)…my disbelief of the analysis, and Mike Allen’s unwavering belief that it MUST work…how much we could reduce the carbon footprint of aircraft (about 40%). All of this because of the flight of birds. I glanced at the clock twice, right at the last quarter of my talk (1:24 to go), and again just before the summation with 0:24. “When we distill an idea down to its minimum, it is simple and elegant. Prandtl had to rethink his assumptions to find superior solutions. We, too, must rethink our assumptions to solve the problems of today. And I believe this is an idea worth spreading. Thank you.”

Wow. It’s over. Is it really over? Did I get all my ideas in? Was it okay? Faces are coming up to me to shake my hand and congratulate me. Friends are giving me the thumbs-up, slapping me on the back and saying how great I did. Really? Did I do that? Everyone smiles at me. I sit down again and listen to the other speakers. Ilan Kroo (Stanford professor) comes up, says I need to present the derivation to his graduate students. (Wow! Really?) My wife walks me back to our hotel room. I’m in too much of a daze to do anything; it’s a good thing I didn’t have to drive.

The days pass. Life returns to “normal.” The video is posted now. The talk is not perfect (not by a long shot). But it’s good. I’m glad the idea – Prandtl’s idea – is being talked about.

Yesterday afternoon I was working out in the yard, clearing some branches. The sun was hot, and the afternoon breeze was blowing. I watched a raven slope, soaring as he flew by. His tip feathers stretched out against the afternoon’s azure sky…