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PostPosted: Fri Mar 20, 2009 4:46 pm
by uscgairdale
I don't consider myself an "aviation expert", but I like to think that I know a fair bit about flying. Up until a few months ago I couldn't have told you what "Vmca' was, but I got a first hand lesson. The story......

Last October I was flying solo at sunset. It was darn near perfect weather with not the slightest bit of movement in the air. I stayed in the local pattern and was still getting used to my engines. At the time my max rpm was still only 4500 on an engine designed for a max smoke of 6300. My airport has a 4000' paved runway with a parallel taxiway and some of us on occasion will use the grass in between for takeoffs and landings. I hadn't used it for some time so on my last approach headed for the grass. As I entered my flare near the deck I noticed that the grass was much longer that I had thought so I added full power, started a climb, and banked left to sidestep to the runway. At about 30' in the left turn I suddenly heard a high pitch sound and had severe vibrations from the left engine. I immediately leveled the wings, cut it's power, and added full power to the right engine. I could just keep level flight and there was a tree line on the opposite side of the runway that I thought I would impact so I made the split second descision to deadstick the Lazair. Near stall speed all I could do was dive (a little bit) for the deck and then set a level landing attitude. The aircraft landed FIRMLY and then slide directly to the left in the grass! I bent up some tubing on the nose axle, but that was about it. Other than that there was zero damage to the plane (or me)....thank God! What helped me safely get on deck is my practice with deadstick landings and the training that I do at work with engine out helo landings. I highly encourage the practice of single engine landings and deadstick landings.

Any guesses on what happened and why you should care about Vmca?

More to come....

Dave A.

PostPosted: Fri Mar 20, 2009 6:09 pm
by Shannon
You definitely made the right call to "deadstick" the plane immediately and straight ahead. At 30' feet AGL your options are very limited. This is especially true with the two-seater. You could probably fly a good distance from that height OEI straight ahead and decending slightly, say 300 yds maybe, I'm not sure ? Any attempt to initiate a hard turn however would put you behind the power curve and stalled. Of course bank angle in the turn raises the stall speed. I've watched this very thing with a single seater when a guy tried to make a 270 degree turn from 30'. In that case the plane landed drifting sideways and did a 180 upon contact.

I gather from the term "deadstick" you cut the power to both engines before you made the shallow dive. Had you tried to continue on with full power to the right engine and with the left engine idling asymmetric drag would have overcome rudder authority. It's actually better if a sick engine quits all together or you shut it down before attempting single engine. The thing to remember (of course I don't have to tell you this) is that an idling engine produces "disk" or "plate" drag that is greater than that of a stopped engine.

If I had to take a guess I'd say you had a fuel related problem of some sort. I'm not familiar with the KFM's and the particular problems they can have.

PostPosted: Fri Mar 20, 2009 6:49 pm
by uscgairdale
Here's what happened!

Dave A.

PostPosted: Fri Mar 20, 2009 7:36 pm
by Shannon
HOLY MACKEREL ! MAN ! You were very lucky not to have had a major crack-up !

Prop failure is no joke ! Were there any visible signs of delamination ? Were those the original props that came with the engines ? If so then they must have sat exposed to the weather for a prolonged period.

PostPosted: Sat Mar 21, 2009 10:29 pm
by uscgairdale
There were absolutely no signs of delamination. The original props on this plane were so punky that I just tossed them out. These were the original 34x20 props that came from Ultraflight witht the KFMs.

You may recall that I never could get more than 4700 rpm static rpms out of them. At that rpm, the KFMs are actually only putting out 50% power! After this incident I bought some 34x20 props from Arrowprop and the workmanship was so bad that after one short flight the polyurethane was oozing off of the tips! After months of trying to get my money back I finally did. Now I have outstanding propellers made by Culver Props. For a single place I would never stray from p-tips or biprops, but if you are ever looking for a good company they are awesome. The owner worked with me on my application and came up with a narrow tip 34x16 prop hich almost give me 6000 static and my two-seater is awesome! Temps are even better and the engines now sound sweet. According to the past owner of KFM, Ultraflight overproped the heck out of the engine to the point that at full power the idle jet is still working.

As for Vmca here's the definition and exactly the situation that I was in last fall...

"Minimum control speed in the air – the minimum airspeed at which the aircraft is directionally controllable in flight with one engine inoperative and takeoff power on the operative engine(s). Aircraft certification standards specify the most critical engine becoming inoperative and its propeller windmilling (propeller unfeathered), not more than a 5 degree bank towards the operative engine, takeoff power on the operative engine(s), landing gear up, flaps in the takeoff position, and center of gravity in the most unfavorable position. In the USA Vmca is defined at FAR Part 23.149 for normal category and commuter category airplanes; and Part 25.149 for transport category airplanes."

Dave

PostPosted: Sat Mar 21, 2009 10:33 pm
by uscgairdale
Another view....

Oh, by the way, all of the video that I've taken of my Lazair has been with the old props. I'll try and get some new footage so you can see the difference.

Dave A.

PostPosted: Tue Mar 24, 2009 6:00 pm
by Shannon
I always thought it was odd that Lazair used the same props for both the JPX's and KFM's. I do recall Chappy saying something about the KFM's scorching the tips on some props during testing. Was the reason for "over proping" the engines to keep the revs lower ?

Anyway now you may have proof that a more suitable prop will yeild much better results. I guess the next question is if the new 34x16 props hold up to 6,000 rpms.

Any of you guys with tons of heavy twin time have a comment on Vmca with a 2-Seat, Tyler ?

PostPosted: Wed Mar 25, 2009 1:47 am
by JPXman
I have had several engine outs (unplanned) in a 2-seater with JPX's but they were all in a "landing configuration" (read: I was landing anyway) - except one.

For the outlier, the engine quit on turn to crosswind at about 100'. I was able to fly a teardrop pattern (180 degrees) to a "base leg" for a downwind landing. the turn I feared was the turn into the dead engine for the turn onto final.

With the good engine (right) screaming, I started my turn and lined up OK. Once I was lined up on the runway, I killed the 2nd engine and coasted in for a good downwind landing.

I would have to say, like dave, the most important thing was keeping flying speed. Vmca, whatever you want to call it - the speed where you can control the thing you're flying is the most important thing to remember when manoevering at low altitude. Attempting turns or unco-ordinated flight at low airspeed is a recipe for disaster and shows lack of want for self preservation.

I have had many more single engine landings (unplanned) in my series III JPX lazair and all i recall is keeping airspeed, and selecting the field with the least number of fences and/or cows. I have since solved the JPX engine.

Tyler
Edmonton, AB

PostPosted: Wed Mar 25, 2009 5:42 pm
by uscgairdale
I brought up the Vmca thing because you can still be flying, but not have control authority for single engine operations. The small rudervators (for a two-place) don't help either!

Dave

PostPosted: Tue Mar 31, 2009 9:57 pm
by Shannon
I suppose that flying the 2 seat calls for someone to be a bit more reserved in how and where they fly the plane. Probably a good idea to fly the plane in a more "conventional" manner where you operate higher than in a single seat.

I discovered way back there that a Lazair actually has good single engine performance and range. If you have any altitude at all you can fly one hell of a long way. I think I was in my 10th hour of Lazair flying when I had engine failure. It was no big deal really as I had started playing with simulated single engine just as soon as I was comfortable flying the plane. Flying over open safe areas (like the one in the pic below) I would pull one engine back to idle and practice what I could do. I quickly realized that engine failure at altitude gave you plenty of time to figure your options.