Dead Calm Air...Good Flying?

[Michael Massey]

So the air at Eugene Airport was dead calm, save an occasional random “light gust” that came from where ever it felt like coming from.  So light it could not be a problem.  So fly where you want.  What could possibly go wrong?

Second flight, coming into the 3 consecutive outsides, step back about 2 feet at the exit of my first consecutive.  Second consecutive had a heart stopping turbulence experience.  But I stepped back a little further and entered the third consecutive.  The next experience I can only describe as surreal.  The plane seemed to literally stop flying.  The outboard wing pitched up 90 degrees and the plane seemed to “tumble” out of control.  The engine was running fine but the plane simply was not flying.  It was as if in a turbulent vacuum. (I know there is no such thing but that is the best I can describe it.)

So I broke into a 64 foot sprint to try to get line tension.  While running I lost sight of the airplane.  After all it was doing it’s own thing anyway.  When I got slight line tension, I saw the airplane headed straight down.  By the way, did I say that this is my contest Pathfinder and I fly on asphalt?  Anyhow, a quick up “yank” on the slightly tensioned lines and the plane “wallowed” out of the dive and floated away from the ground with a foot or so to spare.

I do not know this for sure, but I speculate that aside from the dead calm air, I may have experienced a small gust that blew the turbulence back into the flight path of the Path.  I was also flying a little slow for my plane.  I was at about 5.2 second laps. 

Hence forth, dead calm air as well as very windy will make me pick up the lap times a little more.

Bottom line; be very careful in dead calm air.  I have experienced turbulence before but what happened this time is not even in the same category.  Similar to the difference between a windy day and a hurricane I suppose.

[Matt Colan]

So the air at Eugene Airport was dead calm, save an occasional random “light gust” that came from where ever it felt like coming from.  So light it could not be a problem.  So fly where you want.  What could possibly go wrong?

Second flight, coming into the 3 consecutive outsides, step back about 2 feet at the exit of my first consecutive.  Second consecutive had a heart stopping turbulence experience.  But I stepped back a little further and entered the third consecutive.  The next experience I can only describe as surreal.  The plane seemed to literally stop flying.  The outboard wing pitched up 90 degrees and the plane seemed to “tumble” out of control.  The engine was running fine but the plane simply was not flying.  It was as if in a turbulent vacuum. (I know there is no such thing but that is the best I can describe it.)

So I broke into a 64 foot sprint to try to get line tension.  While running I lost sight of the airplane.  After all it was doing it’s own thing anyway.  When I got slight line tension, I saw the airplane headed straight down.  By the way, did I say that this is my contest Pathfinder and I fly on asphalt?  Anyhow, a quick up “yank” on the slightly tensioned lines and the plane “wallowed” out of the dive and floated away from the ground with a foot or so to spare.

I do not know this for sure, but I speculate that aside from the dead calm air, I may have experienced a small gust that blew the turbulence back into the flight path of the Path.  I was also flying a little slow for my plane.  I was at about 5.2 second laps. 

Hence forth, dead calm air as well as very windy will make me pick up the lap times a little more.

Bottom line; be very careful in dead calm air.  I have experienced turbulence before but what happened this time is not even in the same category.  Similar to the difference between a windy day and a hurricane I suppose.

It sounds to me like you hit your own wake. I'm no aero engineer, but the plane displaces air in the sky, just like a boat displacing water. When you pass over your own wake in a boat, what happens? you hit some waves, and go up and down and then keep going.  That's kind of like what happens in the sky with the airplane, except the effects can be catastrophic.

I'm guessing you didn't back up enough when that happened. When I fly in dead air, I tend to almost walk backwards sometimes so I know the plane won't get hit by wake turbulence.  I've had instances where I've backed up over 30ft and still gotten hit by my own air.

I haven't hit my own air so bad it stops flying and almost goes into the ground, but I've hit it to scare me sometimes.

[Michael Massey]

You are absolutely right.  It was my own wake.  What's more, I believe that the wake vortex is likely what caused the outboard wing to pitch up as it did and give the appearance of the plane tumbling.  Just have never seen such an extreme case.

As for not taking large enough steps back, that is also probably true.  I am, however, leg length "challenged" so very large steps without throwing everything else out of sync is probably problematic.  I will, however, try for more than the easy 2 foot backward strides.

[minnesotamodeler]

you should fly in Oklahoma where there is never dead calm...

[David M Johnson]

Were you flying at the airport? and if so were there any full sized planes operating?  Could be wing vortexes (sp).
David Johnson

[Mark Scarborough]

Mike, another possibility is that when you stepped back, you actually followed the wake turbulance instead of walking away from it. If the wind was THAT light that you couldnt tell direction, its entirly possible that there was the slightest breeze moving the wake towards you.

good job on saving the plane by the way

[Dick Pacini]

Mike, PM sent to you.

[Michael Massey]

Hi David,

Even though our club flies at Eugene Airport, our flying site (a designated overflow parking area for customers) is a relatively long distance from large airplane traffic and still several hundred yards from the end of an alternate runway that has light use by mostly private pilots.  Thanks for the thought.

[Neville Legg]

C.A.T?  Clear air turbulence? Thermals from the tarmac? I know C.A.T has stopped airliners in the air, and made them tumble out of control? But I don't know at what height this starts? It was more than likely, like others have said, you flew through your own wake? Was there clear blue sky all around?

Cheers

[Steve Thomas]

Wingtip vortices can be very persistent; they tend to move around a bit, and also gradually descend. Given that we fly in a hemisphere, taking a couple of steps back might put you in just the right place to find a vortex which has descended a little.  Where I fly out of (the full-size stuff), some of the approach paths are over water, and if the conditions are right, the surface will just erupt about a minute after the jet has passed over. Almost like it's been hit by a little tornado (which I guess it has).  

I've got a lot of respect for wingtip vortices, as they caused the closest shave I've had in 25 years of flying.

Steve

[Randy Powell]

Yep, I lost a plane at that exact site in the dead calm while doing triangles. Hit my own wake turbulence coming out of the last corner and had an unscheduled landing resulting in deceleration trauma. Now I tend to back up 3 or 4 steps with each loop.

[David M Johnson]

Just a thought. I watched a Seagull try to cross a flight path after a plane went by at South Seatac the bird went poof nothing but feathers.
Glad you were able to recover.
David Johnson

[Steve Helmick]

Mike, another possibility is that when you stepped back, you actually followed the wake turbulence instead of walking away from it. If the wind was THAT light that you couldn't tell direction, its entirely possible that there was the slightest breeze moving the wake towards you.

good job on saving the plane by the way

I had this happen to me at NW Regionals this year in PA, at Mike's flying field. I was backing up into my own wake turbulence. The slight drift was changing direction about every 30 seconds. There's probably a Dr. Seuss poem about that, or should be. Something about "Crapped in the hat, I did, I did". Maybe Howard can come up with one, and put the JCT in there for good measure.    Steve

[Michael Massey]

Neville, the sky was blue, or at least would have been were it not for some smoke from a couple of forest fires.

Steve, somehow it seems sacrilegious to call you an Ensign when you have so much flying experience.  Welcome to the forums.

[john e. holliday]

At a stunt clinic one year in Topeka, Big Art told us to go up in  pitch on the prop in dead calm air.   Myself I don't move and have seen the top of the plane once.  In St Louis one year I was doing maneuvers with the wind in my face.  By the time I came back around it was behind me again.  I swear it was changing on every lap.   

[Peter Nevai]

This is really weird,
Back in the day I remember being thrilled when the leaves on the trees were motionless. That was when for certain we would go to flushing meadow park to fly. Or very early in the mornings when the air was still. Not once that I can remember having the trouble discussed in this thread. At worst it would be a couple of wiggles, but no more than that. Never had to take a step back, let alone run. When the lines went slack it was always near the top of the circle and that was because a light puff of wind came by at that altitude and the plane was heading directly into it.

Perhaps it is because back then most everyone was flying 35 sized planes and not the monsters common today. I suppose one solution would be to move the leadouts back a notch on those calm days to add more line tension.

[Mark Scarborough]

Peter,
a lot has been written about this issue actually,
moving the leadouts forward in a lot of cases actually makes for better line tension, ( at least overhead)

it seems that the magnitude of wake turbulence is dependent upon the airframe design more than size.  Flap configuration being one thing I seem to get from the discussions. also the overall weight of the airframe seems to play into the equation.
I have experienced wake turbulence, my Avenger can be kind of painful in calm air on the repetitive maneuvers. My skills at backing up while flying maneuvers is somewhat lacking so I have scared myself several times. I was there when Randy had an issue with his Novi, it just dropped like it went through a vacuum,,

[Steve Helmick]

The thing is that when you're sport flying and just zigging all over the sky flying "solo combat" kind of maneuvers, you won't likely have wake turbulence problems. Maybe a little wiggle here and there as you go through your wake by accident. When you start doing the actual patterns (to include OTS), you will run into serious wake problems, and it will make you clench your hindquarters bigtime. The OTS program should be worse, with 5 loops and 3 of the other tricks. It isn't such a problem, because the maneuvers (properly done) are much larger, so the amount of required lift is less, so less wake generated. Also, seldom are flaps used, which should create much more wake.

My first experience with wake turbulence was flying a Sneaker/ST .35 at 116 mph. When flying in still air, if I did a tight inside loop, when it was back at the bottom, the outboard wing would flip up to about 45 degrees. I think this was partly due to the low A/R and wingtip design, as I never had another design do that. I tried trim changes (engine offset and tipweight), with no improvement on the Sneaker, so it wasn't my favorite combat design.    Steve

[GGeezer]

Micheal is luckier than me, he was able to save his plane. Last Monday I was flying in warm calm conditions with thermal fill-in air randomly and momentarily coming in from all directions. I'm new to C/L and for the first time really noticed the self generated turbulence which can be serious and scary. I was doing a tight inside close to the ground when a puff of thermal air caused the lines to slacken. Before I had time to react, the plane hit the ground doing some serious hurt to my "Monty Special". Fortunately the damage is almost repaired so I will be in the air again soon. Maybe I won't be complaining so much in the future about the windy weather!

Orv.

[Ted Fancher]

Over my many years of flying and watching stunt airplanes I've seen at least four airplanes crash in wake turbulence.  I've, of course, suffered many a "buffet" myself although haven't yet lost an airplane to wake turbulence.

I don't think engine size has all that much to do with it because one of the most memorable wrecks I've seen was David Fitzgerald's dad, Bill, flying a Veco .19 powered Dolphin while doing the last corner of a set of triangles.  Everything looked fine until the last corner when the outboard wing came up dramatically, the ship rolled in and "whacked" itself inverted.

I'm of the opinion, based on my years of exposure to this stuff, that most of the turbulence we fret about is the result of flap deflection and the vortices they produce.  Not certain how they'd differ from tip vortices off of an unflapped wing, but...

I've never...while understanding my "old-timer's infected memory banks"...experienced a significant wake turbulence event when flying an unflapped airplane.  As a kid I flew dozens of Ringmasters and Circus Kings hundreds of flights in very calm conditions and can't remember even thinking about such things.  Later years flying OTS ships like deBolt All Americans and Stuntwagons as well as the original and few other Doctors and Medics I've had the same experience.

Just curious.  Does anyone on this thread have a solid memory of losing (or almost losing) an unflapped ship clearly due to wake turbulence in dead air?

Ted

[Randy Powell]

Ted, I'm pretty sure wake turbulence had to do with the loss of my Coyote. No flaps. But I was flying it in dead calm and very hot weather. Came out of square loops and it dropped like a rock and bounced off the pavement. But that was awhile back and could have been something else.

[Peter Nevai]

The thing is that when you're sport flying and just zigging all over the sky flying "solo combat" kind of maneuvers, you won't likely have wake turbulence problems. Maybe a little wiggle here and there as you go through your wake by accident. When you start doing the actual patterns (to include OTS), you will run into serious wake problems, and it will make you clench your hindquarters bigtime. The OTS program should be worse, with 5 loops and 3 of the other tricks. It isn't such a problem, because the maneuvers (properly done) are much larger, so the amount of required lift is less, so less wake generated. Also, seldom are flaps used, which should create much more wake.

My first experience with wake turbulence was flying a Sneaker/ST .35 at 116 mph. When flying in still air, if I did a tight inside loop, when it was back at the bottom, the outboard wing would flip up to about 45 degrees. I think this was partly due to the low A/R and wingtip design, as I never had another design do that. I tried trim changes (engine offset and tipweight), with no improvement on the Sneaker, so it wasn't my favorite combat design.    Steve

I suppose that all those times when I was showing off. Running out an entire tank while sitting or lying down in the middle of the circle doing eights, inside and out side loops, overheads and wingovers I was lucky that the turbulence was not an issue. During those dumb animal tricks the plane never did a whole lap between anything. Never was brave enough to try squares or other fancy stuff from that position though. 

[Ted Fancher]

Ted, I'm pretty sure wake turbulence had to do with the loss of my Coyote. No flaps. But I was flying it in dead calm and very hot weather. Came out of square loops and it dropped like a rock and bounced off the pavement. But that was awhile back and could have been something else.

Interesting Randy,

The Coyote had one design issue that could contribute to such an event, a particularly sharp leading edge.  As I recall it was a 1/8 X 1/2 inch balsa strip installed horizontally which made the bluntest possible radius 1/16".  Could be a memory issue here as I no longer have plans handy but I built two of them and that's my memory.  A sharp leading edge is subject to stalling at a lower angle of attack and, in hot moist weather, it would be additive to the resulting increased density altitude. 

Was there any evidence of roll or loss of line tension before impact?

Thinking ahead of your answer.  I have experienced something similar to what you describe landing a DC8-62 on a muggy dead calm day at Dulles or JFK a hundred or so years ago.  We were making a long straight-in approach following a DC-10 and we could see the vortices off the wing tips sort of hanging in the air.  Made a modest attempt to stay a bit high but as we approached the threshold the bottom fell out and we ended up touching down only a short ways past the threshold with the engines pretty much firewalled and full up elevator.  The touchdown was still pretty "firm".  Nowadays spacing would have been greater and we would have had the experience and "literature" on the subject to have paid more attention.

There was essentially no "warning" in the form of turbulence or rolling, simply the drop out of the bottom.  I've always subscribed that to getting caught right in the middle of the vortices off the wing tips where the cyclonic and anticyclonic (I think those are the right terms) met and ther result is a lowering air mass.

Could have been something like that with the Coyote?

Ted

[Steve Helmick]

If you ask PW about wake turbulence (I did), he'll relate his story of testing one of his .40VF powered Impacts with a 9-4 prop (pretty sure), howling away. He said there was no wake turbulence, but also no line tension above 45 degrees.

So, while I know I don't like wake turbulence, I'm really confused. It does seem to me that a heavy airplane would create more turbulence than a light one, and a flapped one would create more than a non-flapped design. We also know that there is not a complete vacuum in that turbulence, so the problem pretty much has to be either airspeed (not it!) or getting the air to reattach to the wing. This is where turbulators should help, as they do in FF. Anybody want to test their plane with turbulators specifically in wake turbulence? Anybody? C'mon, your superb piloting skill will save it!  Steve