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ANY EXPERIENCE WITH THE IMPOSSIBLE TURN?

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09 Jul 2021 15:24 #1 by Jimmy Dulin
Replied by Jimmy Dulin on topic ANY EXPERIENCE WITH THE IMPOSSIBLE TURN?
I have never though of or used the upwind of centerline climb out to have greater ground speed in the return. That might be a good technique for those who climb at Vx or Vy as appropriate initially. Because of my crop dusting and engine failures doing that and pipeline patrol, I have always fallen off target downwind in any return to target. At my altitude 200' or less, that was never return to the field I had just left unless already pointed that way in the turn. Because we are slow, both crop dusters and pipeline pilots usually do the teardrop downwind in a crosswind component. We are just used to doing it that way. We slow in the zoom up, much less than 30 degrees off centerline downwind in a windy condition. Sometimes no offset because drift will cause the P or teardrop. Anyway, when the engine quit in the field several times with insufficient room to land there, I always zoomed up downwind in order to be pointed into the wind on the descent to a suitable landing site (never the field I left.) And I wanted slow ground speed into the LZ. Of course, when up a bit to see, I picked the LZ wherever in the near horizon. It was alway very obvious. It is a six second deal.

The impossible turn consideration is with much more altitude than I am used to. The zoom energy of staying in low ground effect until at cruise down long runways get us up to a hundred feet or so only without power. Startle/delay is not a problem when in six inch ground effect. Either we react quickly or we have already landed.

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09 Jul 2021 12:48 #2 by John Trowbridge
Replied by John Trowbridge on topic ANY EXPERIENCE WITH THE IMPOSSIBLE TURN?
GREAT TO SEE YOUR CONTRIBUTIONS -- YOU ARE ONE OF MY HEROES! How about ..... on takeoff, climb out at 30 degrees off the centerline (into the crosswind component, if any) rather than "on runway heading," so that an engine out could be handled by nose-drop turn into direction of the airport (now 30 fewer degrees to accomplish aiming there) and any tailwind component aids progress toward landing zone. Then glide as appropriate to the softest hard place within your hemisphere? JPT

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02 Jul 2021 04:49 #3 by Jimmy Dulin
Replied by Jimmy Dulin on topic ANY EXPERIENCE WITH THE IMPOSSIBLE TURN?
The 180 degree turn would be a racetrack pattern for the crop duster. We would leave the field, make a somewhat shallow banked turn, and reenter the field a quarter mile away going the other way. To return to target however, the crop row about 50' from where we left or the impossible turn, would require a greater than 180 degree P turn. Working the field crosswind from downwind border to upwind border, we first (in pull up) fall off target downwind at an angle. This angle is more in light crosswind and less in strong crosswind. Next we turn into the crosswind which slows our ground speed in the return to target. The slower we go, the faster we turn. The whole P turn is an energy management turn using the law of the roller coaster. Cruise airspeed in the crop field (or from acceleration in low ground effect to cruise on long runways) is traded for zoom up altitude (airspeed=altitude, Vx or Vy goes away quickly w/o power) in the downwind P part of the turn. That altitude is then traded for airspeed as we release back pressure to allow the nose to go down naturally in the return to the target (actually the second turn back into the wind.)

You might notice that crop dusters use most of the runway and then angle away from the centerline extended but do not climb rapidly. No need to climb up just to come back down and airspeed is more reliable altitude and/or maneuverability (happens with or without power) should the engine fail.

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01 Jul 2021 10:11 #4 by Jimmy Dulin
Replied by Jimmy Dulin on topic ANY EXPERIENCE WITH THE IMPOSSIBLE TURN?
While I have no actual experience with the impossible turn, I have considerable experience with engine failure (10) at very low altitude crop dusting and flying pipeline. The crop duster or patrol pilot has a tremendous low altitude advantage that is available to but rejected by normal airplanes in the pattern: airspeed. According to Wolfgang in Stick and Rudder, airspeed is altitude. So using Wolfgang's "law of the roller coaster," we simply use the cruise airspeed we normally fly at in the field or on the pipeline to zoom up (unless already up in the turn) and pick a landing zone in the near hemisphere. We have no problem with turning to that landing zone (no not the field behind us) because we have maneuvering airspeed, what Dan Gryder calls Designated Minimum Maneuvering Airspeed, and we allow the nose to go down naturally in turns (all turns) to prevent load factor. Someone is going to ask about climbing turns. Bank while releasing back pressure and resume climb after the turn.

The Ercoupe up elevator is safely limited so the cause of all stalls cannot happen: a pilot pulling back on the stick. At zero thrust and slow airspeed it will descend like a rock however. That little Continental engine makes the Ercoupe an excellent short field lander. Just pull the elevator back to the stop and use throttle to direct the glide angle to the numbers. Don't chop the throttle. Use it all the way down. Ok, that doesn't help with the impossible turn. Who needs it? We can land the Ercoupe slow enough to safely get down in the near hemisphere if we don't try to climb out too slowly.

What makes the impossible turn impossible, in most cases, is lack of maneuvering airspeed (DMMS) and not altitude. If we are at Vy in any airplane except Ercoupe, we statistically often stall in the three seconds average it takes a pilot to respond to engine failure. Don't try the impossible turn at Vy minus the speed reduction in three seconds at Vy pitch attitude without power. In the Cessna you may stall. In the Ercoupe you will descend like a rock until you shove the stick forward.

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23 Jun 2021 04:39 #5 by Michael Hainen
Replied by Michael Hainen on topic ANY EXPERIENCE WITH THE IMPOSSIBLE TURN?
Exactly, not done at altitude, AOPA is setting a bad example for readers and viewers. Go up stairs and find out what you can do without stalling and spinning your airplane. The follow on to doing that is, have yoy had spin training? Find out what your minimum maneuvering speed is, somewhere north of best glice speed most likely.
Is your aircraft approved for spins should you screw up at altitude? As Gryder notes, best glide speed goes out the window after 30-45 degrees of bank. And that is the speed you would be targeting at a minimum should your engine fail.
If you really want to do the impossible turn, get your glider rating at your next BFR, You'll practice the impossible turn in training and during one of your two check rides you will get the "rope break" at 200 agl and have to execure the "impossible turn" for real. Fun to do when your L/D is 20 to 1 or better.

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22 Jun 2021 06:27 #6 by George Polos
Replied by George Polos on topic ANY EXPERIENCE WITH THE IMPOSSIBLE TURN?
Here is what I have done in my 415-C with Continental A-75: I climb to 2.5 AGL over the airfield, fly the runway heading and simulate an engine out. I start my turn back to the runway with best glide and calculate the amount of altitude lost. I have been able to consistently turn 270 degrees without losing more than 750 feet. Of course wind direction and speed will affect this number. If you practice this enough you will have a good idea of what you can do in your coupe. 

What Dan Gryder is upset about is that the AOPA tests were not at altitude.


 

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