Subsequent Flights of Mark Langford's KR2S
N56ML's Subsequent flights
June 15, 2005 - deadstick landing!
Today was the most gorgeous flying day since my plane's been out at the airport. Severe clear, dark blue skies, just beautiful. You could see forever. Things had slowed down at work, so I took off at lunch, leaving a sign on my desk that read "GONE FLYING". I was going to get up to 7000' and do some "cruise speed" runs on the way to Guntersville airport, and then shoot some landings there. There's not much between MDQ and 8A1 other than what passes for mountains (around here), and trees. But it was so clear I flew north and took some pictures of town, and then skirted HSV's airspace south along a mountain ridge down toward the Tennessee river. I was planning on flying up the river to Guntersville, enjoying the view as I went. As always, I was concerned that I would be out of gliding range to an airport, but 7000 ft should give me a few more "fielding" options. And since I was finishing up my 40 hours of "test period", I was also planning on establishing my best glide speed and ratio on my way back down, using the GPS's "glide to target" function.
I'd been crusing at 2700 rpm and decided it was time to climb out to 7000' (I was at about 4300 AGL), so I ran it up to full throttle and watched it hit the usual 3080 rpm. I actually thought to myself "man, what a silky smooth engine I've got here". A few seconds later I noticed that I was down to 3040 rpm. Hmmmm, maybe I'm climbing too steep, so I lowered the nose a bit. The next glance at the tach showed 2900 something or other. I checked all the usual suspects, and found everything in the "normal" position, including mixture. Just for kicks I switched my DPDT switch to swap out the ignition systems, but the RPM dropped a little more. Then I noticed the vibration, fooled with the mixture to get it closer to perfect....and then started a turn back for the airport. In about another 10 seconds the vibration was so bad that I knew I was going down pretty close to wherever I was, so I turned away from my airport, and toward the NEAREST airport, HSV ("the Jetport"). At the time I was over the highest "mountain" in these parts (Monte Sano), but still right next to Huntsville. Maybe 12 seconds after this all started, the engine was shaking bad enough that I thought it might "depart the airframe", which would not be good. Even idling it scared me, so I switched it off. Needless to say, it got pretty quiet in there, and then there was that prop stopped right in front of my face, just in case I forgot.
I nervously fumbled around with the radio trying to switch to 121.5 (emergency frequency) to inform HSV that I was coming to see them, so hold off the jetliners, please. I didn't know their frequency, and figured I didn't have time to punch on the GPS and find it either. All of this while I established best glide (something like 90 mph) and kept that ball centered so I could go as far as possible. Given the situation, I didn't hesitate to "declare an emergency". They told me to squawk some frequency on the transponder and somehow I managed to crank it in, and then told me that I was something like 11 miles out at 12:00. But I could see the runway, and it was at 2:00, and only 6.5 miles away (I was later told). ATC said, "yep, that's Redstone Arsenal Airfield (HUA), and you might consider putting it down there if you can't make it here". I wasn't sure I could even make THAT one, but it looked like it might just be possible, given my limited (none whatsoever) experience gliding in KRs.
One of the areas that my testing has yet to take me is "how far can I glide with the engine idling". I actually thought about doing that Monday near Fayetteville, TN. And oddly enough I thought "you know, even if I could glide there, it's been 10 years since I've been in that pattern, I have no idea of the flying properties of a KR2S with a still prop, and I'm not real good at landing even when I'm perfectly set up for it!" I figured an engine-out landing was going to be a catastrophe, airport or not. But that was Monday, and today my butt was on the line, so I didn't have much choice but to try my best.
I headed for the end of the 7300' runway, figuring if I ended up high I could round it out and slip it, but if it was close, I'd be glad I was there. It took several minutes of glide time to get there, the longest few minutes of my life! On the way I wondered if the engine would still run, because if I needed it at the end, I'd rather know now whether or not I could call on it. It fired right up, so I switched it off and put it in my back pocket for later. Out of habit I switched the master off too, so I disappeared off of radar and they lost radio contact. Needless to say, ATC became a little concerned about me. I was seriously wondering if I'd make it the last mile or so, and at the very end I had to fire it up for about 5 seconds preserve enough altitude to get me into a position that looked like I was really going to make it. That saved me enough altitude to allow me to drop the flaps to slow it down a little. [They are split flaps and provide more drag than lift, which is why waited]. At that point, I wasn't even looking at the airspeed indicator (who needs one anyway?), so it was "just another landing". I did the most beautiful sweeping turn you've ever seen, and slid it down there in what several folks called "a really nice landing, considering", but with a bounce.
I really suspected that my ring gear had come off the harmonic balancer, judging by the ringing sound that's still seared into my memory, but after I hopped out and looked, the oil and aluminum chips on the outside of the cowling told me something different. I think it was the spinner backplate that was ringing. I coasted to the first turn off, where I was met by two of the really nice folks at Redstone Army Airfield. I started to pull it toward the hangar with the prop, and it was clearly broken and flopping around. The cowling was chewed up a little, and I could see the crank sealing surface (that ain't right!), and the seal itself was trashed. I guess that's why there's oil on the cowling. The stuff hanging down under the cowling is Thermo-tec tape that was wrapped around the exhaust system. In 40 hours of flying it's stayed right where I put it. In 20 seconds of crank failure, it shook the tape and the hose clamp off the exhaust pipe!
In the last few weeks I learned that there have been three Corvair crank failures in the last year or so. In all cases, they were KRs running prop extensions on top of William Wynne's prop hub, but with either a 2" or 4" extension between the hub and the prop. Mine is a prop hub of my own design, but 2" longer than William's hub. This has been at the back of my mind for a few weeks now. WW assured me that he wasn't too concerned about mine, since my engine was so perfectly balanced, and my hub is all one piece, and it's been a smooth running engine. The other common thread with these engines is that they all were running rear starters, with the ring gear running off the inner hub of the harmonic balancer...just like mine. This was not completely lost on me, but I figured I'd gone too far to turn back now, and it's running great, right? And it's hard to say if adding that extra rotating mass back there is a good thing or a bad thing, unless you have the equipment to measure torsional vibration. The only other difference I can see between us and the "typical" Corvair engine is that KRs run them at higher rpm than most installations, but I really don't think that's a factor (but what do I know!). I had about 50 hours on the engine.
So what now? My 3100cc "big boy" case is junk now, and since it takes so long to get a case and heads machined, I'll consider building a 2700cc while I wait on the machine work. I've learned a lot more about building Corvair engines than I knew five years ago when I built this one, so my next one will be better...and I have quite a head start already!
There are several other things that I needed to do to my plane anyway, that will be a lot easier to do at home than at the planeport, so it's not a totally bad thing. I now have the opportunity to use what I've learned about my engine installation and cowling to do it again, but smarter this time around. I'll probably also go ahead and do all those little jobs that I was reluctant to do before, like wheelpants, fairings, gap seals, nav lights and strobes, and maybe even paint. I can also finish up the interior, relocating some instruments and that sort of thing. I've answered a lot of questions about the plane by flying it for 40 hours, so I'm somewhat satisfied for the moment.
For those others considering running a prop extension and the "rear starter" setup, you might consider doing it differently. William Wynne thinks that the rear starter has nothing to do with the problem, and that the prop was more likely the culprit. It was not CNC machined, and had been repitched by hand (as well as built by hand), and could have put assymetrical thrustloads on the crank. I don't know, but my next prop will be a CNC'd Sensenich anyway. I have not lost faith in the Corvair at all, but am seriosly wondering about rear starter drive and prop hubs longer than WW's. For more information on possible causes as it unfolds, check the broken crankshaft investigation page. In case you're wondering, I had all reciprocating and rotating parts of the engine dynamically balanced at a speed shop before assembly (except for prop and flex plate), and the crank was magnafluxed.
The one thing I'm proudest of is that I pulled off that deadstick landing, and did a pretty decent job of landing the thing...and even making the first turnoff. I feel a lot better about that sort of thing now. I was only slightly worried that my wife might say something like "no more planes for you", but instead she said "I figured you could handle just about anything that came up", and I guess I did, so I'm still in the game...
updated June 13th, 2005
I have finally mastered landing N56ML. It's really not that difficult. I was just a rusty low-time pilot that needed to hone my landing skills. Right now I almost have my 40 hours flown off, with almost a hundred landings on it. Some of them have been real squeakers lately!
Initial observations regarding my plane are:
The plane is very stable in all three axes. It is trimmed to the point that letting go of the stick, it will fly straight forever. I can make it turn gradually by leaning left or right.
When trimmed, disturbing the pitch leads to gradual oscillations that are eventually damped out, with the nose returning to the same pitch as before the disturbance.
The MAC elevator trim works great, but I've only used the "up" range so far. Cleaning up the draggy wheels with fairings may correct that, as they cause a nose down moment about the thrustline.
The engine runs great, with low oil temps (around 200F) and reasonable CHTs (usually the hottest being about 350 on a 90 degree day at cruise).
Gross weight is set at 1200 lbs, empty is about 735. It holds 16 gallons of fuel at present, but I will expand that somewhat with another wing tank, probably made from 4" diameter aluminum irrigation tubing.
My prop (a repitched Sterba 52x60, I think) has too much pitch, as 3200 rpm is the best I can do wide open at about 165 mph. It does 3100 rpm static and on takeoff and climbout. But I'll wait until I clean up the airframe (aerodynamically) before I worry about fine tuning the prop.
My plane is still very draggy at this point, with no spinner, wheel pants, leg fairings, aileron or flap gap seals, an aileron bellcrank cover is completely missing (I almost have another one made), and no gap seals underneath the horizontal stabilizer.
The split flaps are just plain wonderful. I get the best of both worlds...drag and lift. Stall speed is lowered by 5 mph with flaps down, and the view of the runway is far better with the flaps than without. They really help with speed control during landing. Full deployment is under 4 seconds using an RV flap motor.
I slow the plane down to 110 mph by the time I'm downwind and abeam the end of the runway, then drop the rpm to 1600 or so and let it start descending, and hold that rpm most of the way down. I'm probably doing about 90 when I turn base, 80 when I turn final, and hold it at about 70 all the way down to flare. When it actually touches down, I might be doing 60, but I'm not looking at the ASI, so I could be wrong.
My VSI problems are more or less solved. I disconnected the static port and it started working correctly, so I still have static port problems. Opening and closing the cabin air vent doesn't seem to affect its operation, so I'll stick with it like it is for a while, pending more static port location experimentation. My original static port was exactly per the KR plans, but drove all the instruments crazy somehow.
My fuel sending unit on my main tank started working, as hoped. It worked when I installed it, but quit working after the tank was sealed up. My theory is that offgassing vinyl ester resin vapor coated the windings, and now the wiper has mechanically cleaned them up again. Next time, I'd eat the weight and install an aluminum mounting plate that would allow access and replacement of the fuel sending unit.
The Ellison EFS-3A is working beautifully. Mixture changes very little from idle to full throttle, and anywhere in between. Ram air is not a problem for it at all.
My canopy could have been a little taller. My seat is an inch off the floor, and I'm using an inch of blue Tempurfoam on top of that, and with my excessively padded headset, I'm right at the canopy, with maybe a quarter inch to spare. The bottom of the canopy is about 17" above the longeron where my head is, and it would have been nice to have more headroom. I'm about 5'-10", so if you're taller than me, consider making it even taller.
My cockpit width is just about perfect. I've flown in stock width KR2's, and they are unacceptably cramped side-to-side. Somebody's going to need to check their shoulder at the door! I can sit with other normal people in my plane and we don't even touch. Mine is almost 3" wider than the plans call for, and that width is at the shoulders, rather than at the kness.
My aileron control system works fine, but one thing I'd do differently is make sure that I had a .75" diameter aluminum tube conduit for the cables to slip through between the sticks and outer wing. I used fiberglass arrow shaft, which works fine for the cable, but traps the cable assembly so that it is a permanent part of the plane, and it also adds another connection to the system.
Right now my stub wing gap is covered with a "vertical blind panel" duct taped into place. I'll glass over this and make a lighter fiberglass gap seal, but I wish I'd simply stuck a 2" piece of urethane foam on the end of the stub wing and made the wing skin extend far enough to make the gap seal an integral part of the stub wing.
My canopy works fine, but it would be stronger, easier to build, and would leave room for a forward baggage compartment (or header tank) if the hinges were located at the longerons, rather than out in the middle. Also, I'd make the front of the canopy assembly squared off vertically, rather than rounded, because it would move the sealing surface from a high pressure area to a low pressure area.
If I were to do it again, I'd hinge both flaps and ailerons with piano hinges, rather than the fancy (and draggy) aluminum hinges that I made. Pull one pin and the surface is removed!
Third flight (second for me), May 28, 2005 -
Today I tried out the new airspeed indicator. Markings are for an RV, but at least the flap range is correct. First I did a few taxi tests, and was temporarily amazed to see it reading almost 70 mph when I got up to my usual high speed taxi test speed. That was my second clue that it was probably going to be reading high. The first clue was the night before, when I calibrated the new airspeed indicator and it showed a 7% error in the 60 mph range. The vertical speed indicator read zero or slightly less at high speed taxi, so I was hopeful that I'd fixed the static port problem too.
I'd really decided I wasn't going to fly it, because the weather wasn't absolutely perfect, but Larry Flesner called to give me a pep talk, and I was standing right next to the plane, and decided "why not?"
So I took off (that's the easy part), climbed to about 4000', and did a few power off stalls to see what my landing speed was going to be. It stalled at about 60 mph indicated without flaps, and 55 with flaps (56 mph clean, 51.5 mph with flaps, after correction), but I'm pretty sure that's still higher than reality. I did about three of each, just to make sure. The thing really just mushed, but there was some nose down break, and once or twice the right wing dropped a little, but I probably didn't have the ball centered, knowing me. I also determined that the VSI was reading a few hundred feet of descent while maintaining altitude, so the static system is less than optimal. I'd wondered if the location I chose would be in a negative pressure area, but that's where Troy's are located, and they work fine for him. Mine don't though. I think I can fix it by adding a "bump" behind each static port hole, and I'll do that tomorrow with some .060 welding rod and clear packing tape. That way I can move them around until indications are more accurate. This also means that my stall speeds are lower than measured, but I can't say how much yet. I also proved that the flaps work fine up to 100 mph, so I used them for the landing this time around. They definitely slow you down, and make a big difference in pitch attitude, for improved visibility over the nose.
Armed with my new airspeed numbers, I thought I'd try a few runway runs, but was going too fast each time to land it. On the last attempt, I was probably still going 75 (indicated, probably closer to 70) when I touched down, which is apparently still too fast. And I'm pretty sure I was overcontrolling it, so I was doing the porpoise thing (the only time I do that is during landings!). I'm going to have to chill out a little and start "thinking" about attitude changes, rather than actually moving my hand to effect them. Anyway, I did the big bounce, another balloon affair, but still maintained directional control. I'm just glad the landing gear can take that kind of stuff. The medflight pilot told me I needed to let some air out of my tires, and I'll do that (28 psi now), but the biggie is to simply slow it down and concentrate on that last few inches of altitude, as Jim Faughn mentions in his Perfect landing - in a KR? article. Unfortunately, control in terms of inches is a pipe dream for me at this point. I'd be happy with feet instead of yards! But I'm going to try to memorize this before my next flight (maybe next weekend, weather permitting). Maybe meditation will help! I think this is really the key to a decent landing...speed control. And Larry gave me an exercise or two to do at altitude before I try another landing, so I'll do that too.
Other than pilot problems, the plane flies great. But it's a world apart from the Champ and C-172 that I'm more familiar with. At the risk of fulfilling Larry's prophecy, I'm beginning to get a little "freaked out" at this landing thing. One slightly different turn of events on either of them could have trashed the plane. The guys who do their "best landings ever" the first time around in their taildragger KRs have my respect. I'm certainly hoping Bill Clapp makes it by here this weekend for some dual...
Contact Mark Langford (if you must) at N56ML "at" hiwaay.net (replace the "at" with @)
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