Jeff said,
"While many seem to poo-poo the RAF-48 airfoil, mostly for it's unknown data points, it is a gentle airfoil with plenty of warning for stalls." That's certainly been my experience. Maybe it's just an OWT but I read or heard many years ago that it's the same airfoil as the Spitfire. That's probably a meaningless statement since there were several Mk Spitfire designs and could easily have had different airfoils . . . but in any case, my Diehl skins have nary a ripple or dent or bubble since Dan and Ken Cottle put them on my plane in 87 or '89. (N335KC is the plane used in the Diehl installation video.) That's a testament to the original good work that went into them, and also to the care and good luck I've experienced in keeping them safe over 33 years. What I want to mention is just how predictable the airfoil is. It also produces a lot of lift. Lots and lots of cushion - one reason we float so far if we haven't crossed the fence very near the stall. Where there is lift there is its opposite - drag. Induced drag. That's one of the many and several reasons I use oxygen and fly at 11 to 14 when going anywhere beyond my local area. This subject can prompt endless discussion about the different kinds of drag (interference, induced, form, parasitic, etc.) but long story short is the higher I go the less resistence I encounter, thus less drag, better fuel efficiency since less power and fuel (assuming NA) pushes the plane along just as fast as below. Thus, longer range, cooler engine on hot days and . . . well, the benefits are practically endless . . . all part of why I go high. If the RAF-48 creates, along with its greater lift, a greater amount of drag, I'm guessing the drag is negligible when I'm up high since I'm sailing along at a lower angle of attack and thus less induced drag. (I'm not up to speed on this particular point so please forgive the error in my thinking if I'm not correct on this particular point). Some of you can correct this if I'm wrong regarding the "less angle of attack, thus less drag" aspect. Overall though, possible minor aerodynamic theory errors aside, in a nutshell it's just plain a lot more efficient to go high. And if you catch some good high altitude winds . . . . :-) Not to mention, at 13K above sea level I can glide about 150 miles if the engine goes south - plenty of time to figure out what's wrong with the engine and, if nothing can be done, have practically endless choices regarding where I want to land. On a short appreach to the main runway at KSEE, I've got a big hill covered with houses which, if I want to land on the numbers or before (which is an old bush flying habit of mine) forces a big loss of altitude on base as soon as I've cleared the backyard BBQ yards on the hill. This situation forces me to initiate some severe cross-controlling to get the plane sideways enough to reach the threshold at the right speed and altitude. These airfoils make such shenigans completely safe and predictable since the wings tell my rear end exactly how close I am to a spin or stall. Stick pressure and the "feel" of what the wings are doing renders a perfect kinesthetic picture of what the plane is doing and/or is about to do. It must look fairly extreme from the ground but in the air it's just a routine maneuver. Just nice solid predictable behavior all the way. That big KR rudder is the key player with these maneuvers, that and the gentle, predictable wings that so reluctantly let go of lift. With enough practice I suppose I could get a good stall break but with normal slow flight practice all I've ever gotten is some slight mushing. That's the normal "KR stall", from what I've read and heard from others - plus, this is my second KR and my other one was the same. Having said all that extolling the virtues of flying high, Max Conrad once wrote me mentioning that I can get the very same efficiency by flying low - like 100 feet above the ocean. It's true. You're dragging it along at barely above stall, but fuel consumption - extreme lean and extremely low power - you can get just as much range (still wind conditions) as up high. Of course it'll take all day to get there and you better not be burning oil or you'll run out, but if one isn't in a hurry, it works. Interesting thing to remember. Maximum range in this instance is equal to maximum endurance. There might be a need to wait out a passing storm or waiting for dawn to see the runway, or for some other reason . . . pulling the throttle back to just enough to stay in the air and mixture back to just above the point that the engine dies, will give hours and hours of waiting time. That's very interesting that Jeff hasn't noticed any noticible improvement in speed between the old and new airfoils. What would be nice would be to have a slight up-deflection on those long beautiful ailerons in cruise configuration. Without really digging into the subject, I'd guess that would add a few MPH. For anyone still building, something to look into. Actually, on second thought, just using normal adjustments neutral can be set for 2 or 3 degrees up deflection so that might be something to try. Mike KSEE _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/krnet@list.krnet.org/. Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change options. To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org
