Mail sack

Friends,

On the topic of $59 books vs $1,000 engines and how these often make several cycles through the market; Pietenpol builder/ATP CC#24 grad Terry Hand writes:

“William, Did you at least catch the area code on your caller ID, so when we do see the eBay/Barnstormers listing, we can warn our friends? I had to take my daughter to the “Doc In A Box” on Thanksgiving Day where she was diagnosed with Strep Throat. While I was calling trying to find a clinic that was even open on the Holiday, at least I had the manners to thank them when I called for even answering the phone. Amazing! Semper Fi,-Terry”

Terry, The guy wasn’t really all that bad, he was just typical of people looking for a bargain, not really looking to learn something. If learning building and flying are the goals, reasonable people understand that a better approach would be more productive. – ww

Builder Bruce Culver writes;

“Rinse and repeat………”

On the topic of carb location, Piet builder Harold Bickford writes:

“William, There has been plenty to consider with the last three topics. Gravity feed for a fuel system certainly fits the “simplicate and add lightness” dictum from DeHavilland and others. And we know the system works with the Corvair. A steel tube fuselage is now on the list of changes to the Pietenpol project. I agree we reserve the right to become smarter. Though the whole project will end up representing more time and money than the original estimate (and it was only an estimate) the end product will be a far better aircraft. thanks much,-Harold ”

Harold, don’t take my comments on steel tube fuselages to mean that every aircraft has to have one. I just wanted to get people thinking about these concepts. The wood fuselage on a Piet is fairly stout. The existing plans for Steel tube piet fuselages are not good enough for first time builders to efficiently work from. The Grega plans at massively over built; The flying and glider steel tube plans are for a short fuselage and do not have enough details. I have seen other notes, but they include things like left hand doors. I have spoken with two very skilled aircraft plans draftsmen about the idea of a modern set of drawings, but nothing is in motion.Unless you already know something about welding and are good at planning some details, I would stick with building a Wood Pietenpol-ww

 On the subject of CC#25 California builder Lauren Williams writes:

“William, a bit off subject for this site but on for understanding our machinery…I’m of a mind that everyone should earn their car (or plane for that matter) by building it from parts. If you have to go to school for a year in able to do that, cool. On the other hand if you can’t develop enough mechanical understanding, manual dexterity and respect for machinery to be able to build your own car maybe the whole world would be a safer place if you didn’t drive. Just a wild, alternative reality thought brought on by listening to too much traffic radio. I drove professionally for 15 years and truly believe that a third of the folk out there are exceeding their experience and training levels while another third are borderline psychotic or seriously depressed and just not paying attention. Respect your machinery.-Lauren “

 On the subject of props: International aviator of adventure Tom Graziano writes:

“After studying airfoils for several years (Roncz and Riblett rock!), I turned my attention to props. Anyone wishing to learn about propellers should definitely get a copy of Jack Norris’ book – Propellers, The First And Final Explanation – available at: http://www.propellersexplained.com/ . They should also check out Jan Carlsson’s website: http://www.jcpropellerdesign.com/ . I’ve corresponded with Mr. Carlsson and he has loads of propeller knowledge along with an affordable and very much worth having propeller design program. Using a little Jack Norris lingo, Mr. Carlsson “gets it”. One should also take a look at the articles written by the late Paul Lipps, and the Whirlwind clean sheet RV series propeller http://www.whirlwindaviation.com/props/rvseries.asp (Whirlwind “gets it” too!) Just as I learned when studying airfoils, I discovered there is much misinformation, ignorance, old wives tales, and tradition (“don’t confuse us with the facts”), out there when it comes to propellers.-Tom”

Tom, to add to your comments on prop design, I would like to echo your feelings about Norris’s work. What I particularly like about his work is how it is based on using existing respected information with a new way of working with this data. I have read a lot of his work and it is good. I actually think the website is a little ‘over the top’ with a few dozen exclamation points per page and it doesn’t accurately conviegh that Norris work is based on very sound scientific work. I particularly like the stuff he contributed to the CAFE foundation tests. His position argues that optimized props will have the same thrust distribution curve. Note that he isn’t saying they will all have the same blade shape.

Over the years I have read a number of designers argue that they discovered some particular blade shape that made all other designs obsolete. This argument never grabs me. Besides how unlikely it is that a guy working alone would discover something that eluded all the engineers at NACA, Pememunde, The Soviet bureaus and labs in Great Britain, It isn’t logical to think that one blade shape suits all aircraft. One other point: neither the worlds fastest prop driven aircraft (Tu-95) nor the worlds fastest piston engined plane (Rare Bear) have props shaped like the “secret undiscovered design” these people always claim to have “discovered.”

Above, A Soviet Tu-95 ‘Bear.’ This aircraft has held the title of world’s fastest prop driven aircraft for 52 years. Rarely seen in the west, few people appreciate how big it is, it is roughly the size and weight of an early DC-10, about 80% the size of a B-52. It has eight props that are 18 feet in diameter. The aircraft is capable of 575 mph, (about 140mph faster than a P-51D)  With the airframe going mach .82, the rotating prop tips are essentially sonic. (so much for the theory that prop tips above Mach .90 don’t make thrust) Yet still photos show the blades have a conventional planform. This aircraft first flew in 1952 and entered service in 1956. The Russians still built these airframes in the 1980s. If a dramatically better prop design existed on earth, the KGB probably would have found it in 30 or 40 years of looking. If it was patented, I am pretty sure they would not have cared. 60 years into flying, they still have the same blade shape. There are no ‘magic’ prop designs.

Above is a photo of Rare Bear, the worlds fastest piston engine aircraft. It is a modified Grumman F8F with a Wright 3350 cid radial. Several props were tried, but the three blade shown used paddle blades from a P-3 Orion. If highly tapered blades were the secret answer, someone forgot to tell these people. This plane has made a two way pass at 528 mph.

If you are working on completing your first homebuilt, it is my strongest advice that you work with a proven, ‘off the shelf’, existing prop that has flown on your airframe/engine combination before. Props are interesting, and good information about them is educational. But keep the goal of getting your plane  done and flying focused. There are no props that would offer substantially better performance on a Corvair powered aircraft than the proven models in popular use. Conversely, investing in a radical or new design, or letting someone talk you into an unproved design can have a very detrimental effect on your project. Building and operating an experimental aircraft is a long series of good judgement calls based on proven information. Choosing a known prop for your first homebuilt is one of these calls.-ww

 

About William Wynne
I have been continuously building, testing and flying Corvair engines since 1989. Information, parts and components that we developed and tested are now flying on several hundred Corvair powered aircraft. I earned a Bachelor of Science in Professional Aeronautics and an A&P license from Embry-Riddle Aeronautical University, and have a proven 20 year track record of effectively teaching homebuilders how to create and fly their own Corvair powered planes. Much of this is chronicled at www.FlyCorvair.com and in more than 50 magazine articles.

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