RE: Extreme speed 1966 style
Maynard Hill desribed his efforts with the Tortoise in the April 1967 issue of Flying Models. The first one was built in 1965, with two different wings. The first wing was 6% thick, but it was determined that it would flutter so it was never flown. The second wing was 7/8" thick at the center, down to 1/2" at the tips with a span of 45". Unfortunately the airplane was lost on a flight when they broke an aileron horn on a landing, and then pinned the aileron in place to continue test flights. But they missed getting it centered and lost control after launch, so it was crashed with a touch of down elevator.
The next Tortoise was built that winter, pretty much the same as the first. The following June 26, they got in one flight and it was good enough to set the world record at 140.28 mph. The record used a more or less stock TF 9-12 prop and was run on 50% nitro, 25% methanol, 25% castor oil for the ST .60 engine. In the air recordings of the engine determined that they were running at about 15,000 rpm.
The radio was a DeeBee Quadruplex 21 which at the time was considered a pretty reliable radio, though the servo performance was anemic, slow with low torque. I actually had met the guy that designed that radio system several years ago, and found out that we both graduated from the same university, some 28 years apart with degrees in Electrical Engineering.
Hill wrote a number of articles for FM back then. He also described a method to determine speed from recordings of Doppler Shift, as well as other parts of his record attempts for altitude, distance, and speed. He did attempt another speed attempt with another version of the Tortoise with a rear rotor engine, achieving around 160 mph, but not low enough for an attempt.
One of the more interesting things he developed was a system that would automaticly level the wings and hold a climbing angle for his altitude attempts, since he knew that watching an model and controlling it above 10,000 feet would be impossible. Hill had a PhD in Physics, and knew that there is a very weak electric field that extends from the Earth upwards tens of thousands of feet. This electric field is roughly 100 Volts per meter, so the problem is how to take a reading since it has almost no current sourcing ability. The way he did it was to use small radioactive devices to ionize the air right at each of three (or four) probes. The leads from these probes went to very high impedance amplifiers to sense the voltage, and differences in the voltages from each wingtip were nulled out with a circuit that drove the servo. For pitch control a small offset was selected to set the climb.
World Engines (it's their ad in the first post) was going to sell Hill's circuit to modelers shortly afterward, but it was only advertised once and then pulled from the magazines. Word eventually got out that the government decided that it would not allow the sale of that technology, since it would make building a small cheap cruise missle too easy. They envisioned someone taking out a dam by having a cruise missle that would self center up a canyon. Of course, since the concept had been published a year earlier, this only kept the general public from using one, any engineer would be able to do what Hill had done. Of course you need a radioactive source which most people might think is hard to come by, but for about $10 you can buy a smoke detector that has one inside of most of the cheap detectors on the market. $100 would easily build such a devise today, but GPS and MEMS technology has passed it by. But such an achievement in the mid-60's was a huge step forward by a one of a kind modeler. No wonder we made it to the moon.
45 years later, very few know or remember about this phase of modeling history. I hope you found it interesting.