My first experience with modifying a plane was in 1965. I had just bought a Lockheed AL 60-b, which was a rare large single engine, kind of like a Cessna 208. It was supposed to cruise at 150 MPH but it only did about 107 indicated, which fell real short.
Lockheed AL 60-B (Photo from: http://www.jitterbuzz.com/lockheed_patents.html#stogy)
So, I wrote to Lockheed and they sent an engineer down to Mexico City to help find some answers. His name was Tom Lawrence, and he spent about 3 months working with me on the project. We eventually got it to cruise about 14 mph faster, and that was all that could be done, short of adding pants or putting an intercooler in the turbo system.
I was experimental by nature and had modified everything I had ever owned… sometimes successfully.
What we did on the Lockheed was to remove all the pan head rivets on the upper side of the wing, and substitute them with countersunk ones. There were over 2000 of them. I was happy with the result.
Pan Head Rivet vs. Countersunk Rivet (Pop Rivet)
Nothing more happened in that that field until I bought a Seneca I when I was flying air charter out of St..Thomas, US Virgin Islands. I thought the Seneca would perform as advertised, and again, was cruelly disappointed that it did not. I could only get 157 mph economy cruise, when I was hoping for at least 20 mph more. My previous Piper twins (a Doyn Apache and an Aztec) had done exactly as I expected, or more, so I started to fret about the Seneca. I was especially disgusted to read that the Partenavia twin, with exactly the same engines and the same size fuselage was about 20 miles an hour faster than my Seneca, even though it had fixed landing gear!
Then I saw a Partenavia, and the reasons became clear. It’s wing was glass smooth on the upper surface instead of covered with rivets and screws as the Seneca’s was. My previous experience with the Lockheed suddenly became relevant. I was desperate for a better cruise because most of my flights were long distance… over 500 miles per leg, and I was getting bored. I decided I had to act, so I bought a can of Bondo and some flashing aluminum.
A Partenavia (Photo from: http://commons.wikimedia.org/wiki/File:D-GHAN_Partenavia_p.68_Victor_(P68)_01.JPG )
By carefully fairing the upper surface of the wing, I got an increase in cruise speed of over 8 mph, and my future as a modifier started from that moment. I knew if I could get 8 MPH on the top of the wing, simple things like gap seals and hinge fairings would give me another 7, and that was enough with which to get started in business.
I spent a year testing all kinds of bits and pieces which I made. Seventeen different mods in all. During that time, we down to eating roadkill! Then I presented my results to the FAA. Nothing happened for like 8 months, and I was even more frustrated. But one day I got a charter from Grenada to Nassau, so I picked up my wife in St.Thomas on the way, and continued to Virginia, where we had a son to pick up from his summer vacation. By chance, an old friend of my wife’s was very high up in AOPA and she introduced me to the head of the Atlanta ACO, by telephone. We flew down to meet him the next day, and he was incredibly helpful. He in turn introduced me to Piper’s chief of structures, with whom I had lunch the following day in Vero Beach. It seems everyone wanted to help me, because I was nice, naive, and so enthusiastic… “throw that good dog a bone”.
Four months later, the FAA flight tests were all passed, and I was issued my first STC… for the Piper Seneca.
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