My 2022 conversion manual is 300 pages in length, but this really isn’t a good measure of its content. Here is a small example of what it takes to develop the content to fill several hundred pages with useful information.
The picture is four Whirlwind “Razor” blades. These were designed to fit in a warp drive hub. I contacted Whirlwind and spoke to their engineering team. There was good reason to think these blades would be a very good option or upgrade for Corvairs. in order to accelerate testing, I bought two pairs of blades and began flight tests on friends Zeniths. The blades were $410 each.
While I am known as ‘The Corvair Guy’, I additionally have a very strong background in propellers for light aircraft. I was mentored by two men, now past, who are recognized as masters of propulsion. I have worked as a manager and a consultant for brands, I’ve been a dealer for Warp Drive and Sensenich for almost 30 years each, and I have worked with a number of propeller artisans. I mention this so you can understand there was very good reason, not marketing, that made these blades seem promising.
Aerodynamically, they are good, however, a serious problem emerged in testing. Simultaneously the blades showed their best performance above 3,000 rpm, and the engineering team said they were uncomfortable with that kind of sustained rpm. ( neither Warp Drive nor Sensenich props have this limitation). Out of caution, I ceased the flight tests, as it was not possible, no matter the pitch used, to keep the rpm limit, particularly in a decent.
After a year pause, I contacted Whirlwind again to see if any data or testing had developed which would make them revise their red line rpm higher. They cam back and said they were now moving it lower to 2800 rpm continuous. I now had some very expensive wall decorations.
I could not sell them in aviation, so I listed them on a Florida airboat site. They sold for $600. Besides the time and effort, this is a straight $1,000 loss. Sounds like a lot, but in the last 34 years I have spent more than 100x that on tests which ended like this.
So when I have the next printing of conversion manuals done, the 300 pages will get a single paragraph added in the propeller section, explaining that where blades look good, but the rpm limit is way too low. It’s essentially a thousand dollar paragraph. Give that some thought when looking at the other 1,500 paragraphs in the manual.