Mail Sack – Troglodytes


I typed “Lifestyles of Troglodytes” between 3 and 4 a.m. last night.  Vern and I worked on Zenith Motor Mounts all day. He rode his motorcycle home at sundown to avoid the projected 25F temperature slated for midnight. I worked in the heated shop, putting crank and cam gears on a 2,700cc engine that will be run at Corvair College #22 in three weeks.  At 10 p.m. Alex called and said he was going to have a late cookout. He is the sailer in the “Mail Sack – Sterling Hayden” post. It was a fun night with 10 people there, including a guy from England and one from South Africa. A lot of good conversation fueled by beer and interesting people. As I was planning on flying at dawn (the weather looked like visibility was going to be 100 miles), I was just drinking a small river of coffee.

I walked across the runway back to our place at 2 a.m. To wired to work or sleep, I spent some time looking at airfoils, toying around with shrinking the Tailwind chord from 48″ to 42″, getting the same spar depth in a 15% thick section, ending up with the same area, but several more feet of span and a better aspect ratio.  The evening’s conversations had sparked a lot of thoughts, and I ended up typing the Troglodyte story.  I looked at it for 10 minutes before sending it.  Would builders think it was funny? Offensive? Plain old weird? I sent it after realizing that it is a little late in my life to suddenly get concerned about being thought of as weird or offensive by middle of the road types. I was too tired to fly at dawn, I went to bed instead. I got up when Vern came back at 9:30 a.m. By this afternoon, the counter on the story indicated that 535 different email addresses had been to the story. In came a long stream of letters, many of which required a lot of thought. Evidently it touched a nerve or a funny bone in a lot of people. As a final note, I want everyone to understand that I have many more friends that are Tech-Geeks than Troglodytes, and I meant no offense to people who are smarter than I am. Maybe one of you Tech guys could explain the hierarchy of the tech world, it would be entertaining, but please, use small words for us Troglodytes.


601XL builder and Pilot Andy Elliott, Phd, aerospace engineer from MIT wrote:      


“As a long-time member of the geek tribe, I mention the classic book “Theory of Wing Sections,” Abbot and von Doenhoff, 1948, that is the standard reference for any of the NACA series airfoils. It includes both ordinates and performance data. It is republished by Dover Books in paperback and is available new from Amazon for <$16!
Another good resource it the Univ. of Illinois airfoil data base, which is found at The Clark series are all there in high precision. Note that this database uses the geek-standard approach of providing the airfoil ordinates in the zero-lift orientation. This obfuscates the flat-bottomed nature of the Clark Y. Again, referring to old data to get away from modern misrepresentations, you can find NACA Report 502 online at This report has the Clark Y coordinates in the troglodyte reference frame, that is with the flat bottom flat. There you can easily see that the airfoil is 11.7% thick!   FWIW,   Andy”

Andy, As an owner of a giant collection of aviation literature, I have most of the stuff you reference right on the back porch. believe it or not, the Clark Y is not in Theory of Wing sections. I have the Troglodyte ordinates in the back of a number of old books, but the references you mention are good assets. Thanks-ww


Builder Jerry McFerron wrote:
Hi William, I have written a program that will convert an Excel file containing the airfoil coordinates to an AutoCAD drawing of the airfoil in one second. The program could certainly use some “real world” testing if you are interested. Take care, Jerry.

 Jerry, Thanks for the very kind offer, and I may take you up on it.  Here is the only issue: I am a genuine Troglodyte of the first order, and I hate to say this in public, but I don’t know how to write up a spreadsheet on Excel.  I would need some help from Grace on that one. I think that if I learn to use Excel, then I might be jeopardizing my status, and before you know it, people will start thinking of me as a Neandertal.


Tom Graziano, man of a thousand global aviation adventures, Super DC-3 owner, etc., writes:

“William, You’ll save yourself a lot of trouble by just getting a copy of Harry Riblett’s book GA Airfoils from the EAA. With a Riblett airfoil, you’ll end up with a superior wing. For a Tailwind, look at the GA35A413.5 and GA35A415 airfoils. You can draw out the ordinates & airfoil by hand – I’ve done it for a couple of projects (butcher paper works well) – or use a computer program. I use Compufoil. Works great! Cheers, Tom”

Tom, Great to hear from you.  I have Harry’s book, read it cover to cover many times. The Tailwind has a real funky packaging problem at the butt rib because the root chord is choked down so much, and the area around the rear spar attachment and where the torque tube passes is generally not covered by the footprint of a lot of good airfoils. You can’t use a lot of them because with the correct angle of incidence they would be either too low for the door to open or too high to blend the cabin top and windshield into the wing. I’ll get a look at the two airfoils and see how they lay out.-ww


Harold Bickford, NE, writes:

“Quite a spectrum there William and a very enjoyable read. On the one hand I’m a geek in that I look to the soon to come day when 3D printers allow the fabrication of many parts useful in an airplane and at reasonable cost. Yet the building will still have to occur, however simplified. Still the Pietenpol (Neanderthal Aviation?) has an appeal as an old school, proven idea. The Corvair engine follows suit. Ditto ‘steam gauges.’

“Just like manually plotting an airfoil using accurate information, it is the engagement that makes the experience fun and a learning experience. Whether cutting and milling wood parts to precise sizes (and being willing to try again) or simply researching the engine numbers to determine which engine you really have, the activity becomes a means of involvement that uses all of the senses.

“It is not instant gratification by any means though the process does become continuing gratification as at every step some bit of learning and progress occur and then the stage is set for the next act in what is a real life adventure.”


Joe Goldman, Sprint builder N198JL from Florida writes:

“William, That’s the way my ribblett wing went. Harry Ribblet airfoil GA35U-A315 . Got a long 1/4″ luan plywood, made my center line and went one from the X column, one from the Y, and one from the Z…. Checked it many times. Looks good and allows for a straight up 8.7″ spar. Hope it flies like the original. Joe.”


Terry Hand,  USMC & ATP,   (    Writes:

“William, As a Captain for a major airline and an airline pilot for close to 25 years, I can appreciate your comments on flying and technology. I spent 4 and 1/2 years instructing glass cockpit jumbo jet training, and we worked hard to instill the concept of ‘automation download’. Simply put, automation download means that once the technology gets in the way of flying that keeps you out of risky situations, download to the next level. If necessary, download to the next level, whatever it takes to maintain safe control of the aircraft.

“How about an example? Say you are flying an airplane such as a 767 that has FMS and you set up the FMS to fly the ILS to 27L in ATL. It is in the box, and you are monitoring the systems while actually flying a Visual Approach to 27L. You call the runway in sight, and Tower offers you 27R since it is a quicker turnoff to the terminal. You accept the runway change, but now what? You download the automation, turn off the FMS (because reprogramming it requires a heads down cockpit- not good at 2000 AGL). You kick off the autopilot, and hand fly the aircraft down the PAPI that you see giving you great glide path info. In other words, you fly the airplane, not the technology. That is the trick – teaching pilots when to make that automation download decision, and avoid going heads down, trying to load the ILS 27R approach in the FMS, and ending up flying across the 26L final approach course (look at the ATL airfield diagram – yes that happened many years ago – unbelievable!). Just my thoughts on the subject. Keep up the great writing. You make me think.”


Rob Schaum, Murphy Rebel w/3,000cc Corvair builder writes:

“Yikes….that story is as scary as it is entertaining. You’ve alluded to this before in your writings, but I’m convinced that the greatest challenge any homebuilder faces is knowing which information sources to trust, and which ones to run away from…quickly. This process, for me, takes almost more time than building. It is compounded by the fact that I, like so many of us, am a part-time builder and cannot rely on an Embry-Riddle education – and decades of experience – to immediately identify the flaws in someone’s argument. Nevertheless, the process of screening out the good info from the bad is critical to our being able to one day confidently sit at the controls of our aircraft, lined up for takeoff, and push that throttle forward.”

Rob, Fear not, you can trust the things you read here, and over time you will develop more and more of a sense of good vs. b.s. info. BTW, did you see yourself in the group 2005 photo on the Dr. Ray Post? I’m pretty sure you’re in there.-ww




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