Square Corners

[Bill Rusk]

To All

A while back I made a post and talked a little about Square Corners. Some folks suggested a thread on that topic so here we go.

First a little about the term "square corner". In the fighter world we talked about getting into a firing position on an opponent. You had to get within a certain cone at your adversaries 6 o'clock...BUT....you also had to be pointed in roughly the same direction as his flightpath in order to employ ordinance. You could not just fly to his six and be 90 degrees off his direction because the airplane can't make a square corner. Airplanes, even F-16's can't make square corners....thus the term. The term can be, and was, expanded to include just about any situation where you are asking the airplane to do something it just can't do, like make a square corner.

This was my first post on the topic.....

I lost a cohort recently and it turned on a light for me. He was a very experienced pilot, ex military fighter, current airliner, active in GA and in the CAF, in short he had the skills, knowledge, and probably a fair amount of judgement. He took off at an airshow, giving a ride in a 180hp Supercub, and did the max angle climb thing. I don't know if he stalled, or the engine hiccuped, but at that angle, altitude, and airspeed there is just not enough air under you to recover. The airplane is going to freefall for awhile because there is insufficient airflow over any of the control surfaces to make them work. About the time you can recover you hit the ground. It does not matter how quick you shove the stick forward at the first hint of a stall, it is too late.

The golden nugget for me is that every airplane has "Square corners" that if you get into you can't get out of.

I knew this, but it just got refreshed in a big way.

The F-16 didn't have many but it did have a couple, it also had an ejection seat that would get you out of a lot of those square corners (the airplane might not make it but you would). The 737 has a LOT of square corners. The Cub is so fun, honest, and good it is easy to overlook them. In fact, my initial response upon hearing of this accident was "How can you possibly kill yourself in a cub unless the wing falls off?" Bad mentality on my part. Answer....the Cub has square corners too. This is one. Don't go there.
So while I have enjoyed "spanking" a few Cubs on takeoff in the past I think I'll round off that corner in the future.

Thanks for listening.

Bill




Another Square Corner

Sink Rate

As you practice the steep slip, to a landing over the proverbial trees, remember that you can develop a sink rate that you may be unable to arrest before ground impact. Where this will bite you is.... you go out and practice an aggressive slip right to the flare, where you stop the sink rate, flare with no float and plop down. Perfect, except that you practice solo. When you increase the gross weight by adding your buddy and all your gear, you must increase the energy and altitude enough to stop the sink rate and greater mass on the vector. You will get wings level and may even get the nose pointed up but the plane (and its vector) will still be going down and you will hit the ground HARD. Generally sink rates in cubs are not a big problem, but they can happen, especially when you are heavy. In fighters, airliners and high performance aircraft, (Lancairs, Glassairs, the new VLJ's etc.) the issue of sink rates on final approach is critical and once you allow it to develop it becomes a square corner. No amount of pilot skill or thrust will get you out of this corner. You will crash. The airplane can't do a square corner. So.....be careful of developing a high sink rate close to the ground and don't get yourself into a square corner.

Thanks for listening

Bill

 

[Steve Pierce]

Where this will bite you is.... you go out and practice an aggressive slip right to the flare, where you stop the sink rate, flare with no float and plop down. Perfect, except that you practice solo. When you increase the gross weight by adding your buddy and all your gear, you must increase the energy and altitude enough to stop the sink rate and greater mass on the vector.

Been there, done that. Luckily I was in a Super Cub and it had new bungees. My buddy still tells the story of how I squared the @#$% out of him. Definite lesson learned.

 

[Bill Rusk]

Another one

There is a square corner with the tail up and no forward motion on the ground. If you are doing a full power run-up with the brakes set prior to take off and you get the tail too high.....well.....you can try anything you want and it will not help.....you are going to stand it on the nose. You have gotten into a square corner. No matter how good you think you are, and no matter what you do it is too late and you are screwed.
Same thing if you do a wheel landing and gently brake to a stop while keeping the tail up. ( a good exercise to practice ) If you let the tail get too high you go past the point of no return and she will go over on her nose. Release the brakes, go idle or full throttle, stick full aft etc, it will all be to no avail. Watch out for this square corner.

Thanks for listening

Bill

 

[Steve Pierce]

Tore down an O-540 with about 10 hrs. SMOH just before Christmas because a 40 hr pilot was "Flying the tail" as he called it. :evil:

 

[d.grimm]

When I was doing a lot of flight instruction a person I know had the engine
quit right after a short field takeoff demo with a student in a 152. He was at VX and pushed the nose over all the way to the stops. The airplane had just leveled off when it hit the runway and broke the tail off right behind the rear windows. Tail followed him down the remaining runway attached by cables.
On a VX climb at low altitude it may me impossible to recover from an engine failure. I include that in my discussion of short field takeoff and then demonstrate it at altitude.
Makes you think.

 

[CraigH]

Thanks for the post Bill. Good things to keep in mind. Sometimes in the process of building more and more accident free hours, these things tend to get shoved further and further back in the closet of your mind. It's good to take them out for a look-see every now and then.

 

[mvivion]

Bill,

Excellent points all. I discuss this, and demonstrate this with all my students in the Cub. Go to altitude, establish a true Vx climb (I emphasize a "true" one, because many don't use the 45 mph and full flap recommendationin in the book) and at some point, I fail the engine for them. At altitude, it seems like its not too bad, but they do realize that it is a VERY aggressive maneuver, and that you will lose some significant height in the process.

The point is, I teach that utilization of a Vx climb in a Cub is, for all intents and purposes, an emergency maneuver, to be used close to the ground only when you have trees/cliffs filling your windshield. Practice them at altitude, but only use them when you really have to.

And, of course, if you'd planned a bit better to start with, you wouldn't have got into the situation where you HAD to use a Vx climb.

Tom Wardleigh used to say that the Super Cub is such a gentle little airplane that it can just barely kill you.

It's true that it has few vices, but as you've noted, Bill, there are some corners.

Another is high AOA circling, and introduction of a bit of skid to see around a wing. That one requires just the wrong set of circumstances to come loose on you, but the result is sometimes what is referred to as a "moose stall".

Thanks for starting the thread.

MTV

 

[Steve Pierce]

d.grimm, Lost a friend like that. He was hauling jumpers in a C182, lost the engine on climb out, it spun and appeared he was getting it under control but not enough altitude to fully recover.

 

[SuperUrsus]

Great thread!

Thanks.

 

[cubflier]

Interesting thread. I talk to myself a lot about my flying and how I balance the risks and rewards of the sport. For me there are corners where I go because I like it there. It's not for the thrill of it or ego it's just they are such fantastic places to be. I hunt there, I explore, I take pictures, and sometimes I just sit there like I'm the only person on this earth.

Most of the places I'm refereing to are various one way in strips that I've grown fond of over time. Every one of these one way in strip has a square corner off the end of it just waiting for you. Miss your landing - smack into the corner. Your landing is in effect the ejector seat of the F16 as Bill put it. Landing simply serves to terminate flying prior to reaching the end of the corner.

Striking a balance between the reward I find in some of these corners and the risks that I take getting there is something that I try to reevaluate often.

Jerry

 

[Gordon Misch]

One red-faced day I discovered a 'corner' was descending spiral with low power, full flaps, and empty in the back (fwd CG). All it cost me was a lightly scraped wingtip and bent gear tube, but boy did I ever feel stupid! A cub pilot & ex P51 pilot friend in Juneau, Det Robinson, had warned me about diving spirals in a cub and I really learned what he was talking about that day! A rollout from the bank is imperitive to lift the nose. I became VERY cautious about landings in a turn!

 

[Jon B.]

Many, if not most, of us here use the old 'behind the power curve' method to shorten our landings. Nose in the air, gobs of power, airspeed in the 40s. It's quite effective. For those of us flying behind puny engines - a C-90 in my case - there is, I imagine, a point at which there's no longer enough power to climb, or to increase the airspeed. It may be true for you guys with big motors if you get heavy enough.

If you find out soon enough, and you're a ways off the ground, you can lower the nose, add any power you may have left in the bank, and then, having picked up a knot or three, pitch for climbout. With little power, too low an airspeed, and no more vertical room remaining, I have painted myself into Bill's 'Square Corner'. I may not yet have stalled and the Kick-Ass Champ is still under control but, there's no way that I can do more than hope to reduce my descnt rate to a value that the gear can survive.

I haven't arrived at that corner, yet , but, given time and enough testosterone, I may, unfortunately get close to it, if not into it.

Thanks, Bill, for the "heads up".

Jon B.

 

[bob turner]

A friend directed me to this thread. Before I came here I reminded him that I had tried the Vx full flap climb just exactly once, and decided: (1) that it might not be survivable if the engine quit, and, (2) it was plainly and simply an emergency procedure. Same with the C-180 at flaps 20 and Vx. Deck angles in these two birds are impressive!

All of which leads me right back to my usual statement: If you need to climb, you need excess power, and flaps subtract from that excess power. I always recommend climbing with flaps up, and at 50 mph in a Super Cub or 70 mph in the C-180 the deck angle looks survivable if the engine quit. Just shove the nose over. In either aircraft, flap extension on takeoff is not effective unless you need to shorten the takeoff roll or you are on a rough field, wet grass, or water. That's my opinion.

 

[mvivion]

Bob,

That is certainly a safer way to climb.

However, Piper did flight test the airplane, and Vx does occur with full flaps, 45 mph and full power.

I have played with it a bit at altitude, which may or may not be a totally fair comparison, and the full flap, 45 mph Vx does seem to provide better climb rate compared to forward movement. Remember, this isn't best RATE of climb we're talking about here, it's the highest you can get for a given distance over the ground.

I have students practice it at altitude, never close to the ground, and admonish them that this is what you do if the alternative is flying into rocks/trees/etc because you misjudged your takeoff and climb. It is purely, in my opinion, a get out of trouble (maybe) device and borders on an emergency maneuver in my opinion.

I see WAY too many people doing these radical climbs close to the ground, and I always cringe.

MTV

 

[bob turner]

Hi Mike - your comments were noted, and I was actually surprised that my advice to my friend was the same as your comments a few posts ago. We agree completely on this one.

My addition was triggered by the many lightplane pilots that I encounter that maintain that climb is assisted by flaps! More lift means "go up faster"! I have a buddy who extends flaps 20 on his C-180, then lifts the tail to accelerate to 60, and climbs to pattern altitude at 80, all with the flaps out. Says he got that from the 180 experts.

On this forum some time ago I found out about the full-flap best-angle that Piper recommends, and tried it. Exhilarating, and scary, all at the same time! I also tried the flaps 20 Vx climb in the 180, and found it to be roughly the same - you are pointed at the sky!

It was my Boeing training that alerted me to the fact that flaps do not make airplanes go up faster. And one can find any number of well-known experts who can explain that with math and vectors. But not so long ago I saw a letter in the AOPA magazine bemoaning a fatal Bonanza crash - it was a high, hot, heavy crash; the aircraft got airborne but couldn't climb. The writer said that, had the pilot used more flaps, he would have made it! And AOPA never corrected the comment. Once a jet transport passes a given takeoff weight, the only way to go out heavier is with lower flap settings. Same, in my opinion, with any other aircraft.