Mark, Since it seems that your prop is a little too steep in ptich perhaps you should give an old trick a try: Climb out to 200 feet above your test altitude and level off. Let the KR accelerate up to top speed. Then enter a very shallow dive of 50'/min descent rate. After four minutes you will be back down to your test altitude and the engine will be spinning a few hundred RPM faster. In some planes this trick is enough to get the plane accelerated to a speed that otherwise it could not achieve. If this doesn't work try 400 feet above test altitude and a 100'/min dive. Somewhere in there you will find the sweet spot where you get a couple of extra MPH than you could otherwise accelerate to in straight and level flight at a particular test altitude. The point to remember is that you get a higher top speed when you dive on it than when you climb to it. Good luck!
Regards, Bob Lee N52BL KR2 Suwanee, GA 91% done only 65% to go! http://kr.flyboybob.com mailto:b...@flyboybob.com -----Original Message----- From: krnet-boun...@mylist.net [mailto:krnet-boun...@mylist.net]On Behalf Of Mark Langford Sent: Monday, April 02, 2007 11:35 PM To: KRnet Cc: Corvair engines for homebuilt aircraft Subject: KR> Sterba prop data vs Sensenich NetHeads, I should have waited for a 59 degree day, but it was pretty much gorgeous this afternoon, so I flew the 52x60 Sterba prop on the new 3100cc engine for the first time today. Although I didn't really plan it, I did a 0' AGL to 7500' climb test, then leveled off at 7500' for a wide open throttle test, then pulled the throttle back to idle and did a glide test / simulated engine-out thing just to see how far I could glide. My first clue that this was going to be quite different from the Sensenich 54 x 54 was that I had to just about double the engine RPM to get the plane moving away from the hangar. I actually got out to see if I had two flat tires, but "no joy". The Sterba just didn't move as much air at "low" airspeeds. Then I took off, and ate up about 50% more runway than usual getting off, and I started to question touch and goes in the future. Climb rate was down from 1300'/min to about 1000'/min, but it's also a 20 degree warmer day than that test on the Sensenich. The Sensenich allows (maybe begs) you to assume a really steep climb angle just to keep the climb speed down to 100 mph. The Sterba was much shallower to maintain the same speed, with slower climb rate. Top speed at 7500' is 170 mph TAS, about 7 mph slower than the Sensenich, but at a whopping 500 rpm slower! This means I'm still screaming along, but with a lot less load on the engine, lower fuel consumption, and noise in the cockpit, which is not a bad deal. The lack of spinner probably cost me 2 mph also, so we're down to only 5 mph, and it was 20 degrees warmer today than the Sensenich test, so that narrows the gap even more. Not a bad flying experience, actually, but the lack of climb rate means a decrease in safety margin during takeoffs. The glide test raised the glide ratio bar (although this probably has more to do with improved piloting and data gathering) from 11.5:1 to 12.3:1. Ten miles out from the airport at 7500' I chopped the throttle to idle and glided to Fayetteville. Seven minutes later at 3000' I crossed the runway at midfield, and had to do some serious slipping to fly the pattern and drop from 3000' to the runway to put it on the numbers. The average glide speed was about 75 mph at 630 ft/min, about 13 mph above stall speed clean. Any slower and vertical speed increased. I did five touch and goes and flew to M38 and did three more. When I left the gas pump I did my usual business of standing on one brake and increasing to about half throttle, but the plane wouldn't move...not until I wound it out to wide open. Quite a difference in props! I guess what I'm describing is the difference in a climb prop and a cruise prop, except the Sterba's still too coarse to be a cruise prop for my plane. But somewhere in the middle is going to be sweet! I'm not going to worry about it until I get wheel pants and leg fairings, among other things, but it's now clear to me that I can do better in the prop department. More testing is in order... Mark Langford email: N56ML "a" hiwaay.net website: www.N56ML.com _______________________________________ Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net Post photos, introductions, and For Sale items to http://www.kr2forum.com/phpBB2/index.php please see other KRnet info at http://www.krnet.org/info.html
