June 15, 2005 - deadstick landing!
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 you just proved it", and I guess I did, so I'm still in the game...
Contact Mark Langford (if you must) at N56ML "at" hiwaay.net (replace the "at" with @)
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