March 1, 2002
William K. Kershner
I've hit wake turbulence ( real wake turbulence) twice in my short career. I recovered from one encounter because of my aerobatic experience; the other time I crashed because there was nothing else to do.
The first was at what is now Memphis International Airport in the summer of 1950, when I was cleared to land on Runway 21. Unfortunately, so were five or six Curtiss C-46 Commandos, the fat, twin-engine World War II transports. Apparently the local reserve or National Guard squadrons were having a great time shooting touch and goes.
My Stinson Voyager was wormed into the group-grope with not a word about the hazards of existing "prop wash." (That's what we called it, since this was before jets and there was little discussion of the phenomenon between pilots or in aviation literature.)
On a rather long final I suddenly found that I was looking up at the ground and thought it was unusual for a final approach, even for me.
I pushed and rolled, fortunately having spent several months teaching aerobatics in a Meyers OTW-160, a biplane with a very heavy nose and a cambered airfoil requiring strong forward pressure when that airplane was inverted. I pushed while inverted and then pulled as I rolled upright, the Stinson turning slightly as I completed the roll.
As I recovered from this unusual display of exceptional piloting skill I thought I heard the tower ask if I "had a problem." I didn't give my desired answer, "No, I always do a roll on final when using Runway 21 here." I took it around.
I pointed out that while 21 was obviously the most exciting runway to use, I was going to land on 27. The Tower suggested that 21 was the duty runway. I said that I didn't want to delay the C-46 touch and goes. Self-preservation overrode even my anxiety about disobeying the "order" to use 21. (Note to low-time pilots: You are pilot in command; a fair number of those folks in the tower, approach control, and center are not pilots.)
I landed on Runway 27 and nothing was said. My legs shook for a while, though.
The fourth flight of the defensive flying course that I teach here in Sewanee, Tennessee, is the "recovery flight." The trainee is taught to "push and roll" if inverted and, as the airplane rolls upright, to pull to keep the nose up.
The question is — which way to roll? If the airplane is completely inverted at the time of the pilot's takeover it would probably be logical to continue the roll, letting the wake turbulence help get the airplane upright. It would also be hoped that during the recovery roll there would be a change of heading sufficient to turn out of the vortex. However, there are an infinite number of possibilities and combinations dictating the direction of roll. In turning out of the vortex it might be a good idea to head for the tower so those folks in there could get involved. (Just joking.)
Fortunately, I was by myself in the Stinson with no front seat passenger to grab the other control wheel and scream in my ear.
The problems with encountering wake turbulence are usually thus:
The opera soprano is the other type of person in the front seat with you when the event occurs. The sounds emitting from this individual are very disconcerting at a time when you'd rather have quiet.
The worst combination (a King Kong who now sounds like an opera soprano) assures that your recovery efforts will be interesting.
The problems just discussed concern control of the airplane and usually come into play when wake turbulence is encountered at an airport. Another wake turbulence problem, not so often mentioned, is that of imposing severe stress at cruise or higher airspeeds by crossing wake turbulence.
I was relaxed and complacent as I flew west about 25 miles south of Dayton on a winter day with an overcast of probably 15,000 feet or higher and perfectly smooth air. The Aztec was suddenly rocked by severe up and down jolts. It seemed that the wings creaked and the airplane reacted like a rat being shaken by a terrier.
After things were smooth again, I looked to the north and saw, about 15 miles away, the source of my trouble, a B-52 flying in a northerly direction. I had crossed the wake turbulence at a right angle at cruise airspeed. One analysis would be that in crossing the two wingtip vortices I would have gotten a sharp updraft, immediately followed by an equally strong downdraft at the first vortex. This could be followed by more downdrafts as the airplane continued across the wake in the downwash portion of the wingspan. The second vortex would give a strong downdraft, followed immediately by an equally strong updraft. (The aircraft structure would be taking forces and moments from different directions very quickly.) The Aztec suffered no damage but it would seem that if you prefer an "interesting" wake turbulence crossing, do it behind a B-52.
Surprise is still the big factor as I found out when making a carrier landing on the USS Philippine Sea on March 4, 1954.
In the straight-deck carrier days, approaches were made only a few knots above stall, and I encountered five of the six factors covered earlier associated with encountering wake turbulence. I was by myself in the F4U-5N Corsair (naturally) but was hit with:
As I got the "cut" from paddles (the landing signal officer) I closed the throttle and suddenly got a severe right wing drop (see photos on page 91). I reverted to previous civilian flying and instructing, diving for the deck (to catch a cable) but using top rudder before the ailerons to raise the wing. (It worked with Cubs and Champs so why not with an F4U?)
So, I wound up with the nose in the starboard catwalk, the center of all attention. I was told by the crash crew that I needed to get out quickly in case of fire, but knowing there would be an accident investigation board, my shaky answer was, "Not until all the switches are off."
We were operating carrier qualifications daily out of San Diego, so when we got in that afternoon I was assigned to return to Moffett Naval Air Station (near San Francisco) to get another F4U.
I found out in 1980 — 26 years later — from a fellow pilot who'd been on board the carrier at the time of the crash — that the commander of the air group made all the pilots look at the movie to see how I got the wing up enough to avoid cartwheeling and to be able to catch a wire. He said (I was told in 1980), "That was the best rudder flying I've seen in years. The guy must be a former Cub or Champ pilot." Which I was, having 900 hours of flying and instructing in lightplanes before reporting to Pensacola, Florida.
The accident report (I have a copy obtained in 1985) said the accident was the result of another Corsair making a too-low climbout after a wave-off just seconds before my "landing." It also suggested that in future situations like this in the F4U, rudder should be used to raise a wing before ailerons are involved.
I don't remember if I said anything during the wake turbulence encounter at Memphis but I distinctly remember, as the F4U rolled over, saying those time-honored, famous last words of pilots as a plane goes in. "Awww, [censored]."
William K. Kershner, AOPA 084904, a flight instructor and writer whose textbooks are published by Iowa State University Press, has flown for more than 50 years, has taught aerobatics to more than 500 students, and received the 1992 National Flight Instructor of the Year award.
Safety and Education,
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