Loss of rudder authority in PA38
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Loss of rudder authority in PA38
I'm a low hours PPL with experience on Katanas, Grobs, Cessnas and now Pipers.
I was taking off the other day and applied right-rudder. As the speed picked up, I found that I had to use more and more right-rudder until I was applying full right-rudder. At this point (around 40kts IAS) the nose of the A/C yawed left despite the fully deflected rudder controls. The speed was now ~55kts IAS so I elected to rotate (rather than brake - not enough space) before the A/C left the runway on the LHS.
The crosswind was 6kts from right to left and a jet (737) had recently taken off but I had waited about 2 minutes after it had cleared the runway. My subsequent landing was fine and went without incident.
I had just completed about an hour in the circuit doing touch&gos and nothing like this had happened during the previous take offs.
Would wake turbulence cause this problem?
Thanks for reading...
Loki.
I was taking off the other day and applied right-rudder. As the speed picked up, I found that I had to use more and more right-rudder until I was applying full right-rudder. At this point (around 40kts IAS) the nose of the A/C yawed left despite the fully deflected rudder controls. The speed was now ~55kts IAS so I elected to rotate (rather than brake - not enough space) before the A/C left the runway on the LHS.
The crosswind was 6kts from right to left and a jet (737) had recently taken off but I had waited about 2 minutes after it had cleared the runway. My subsequent landing was fine and went without incident.
I had just completed about an hour in the circuit doing touch&gos and nothing like this had happened during the previous take offs.
Would wake turbulence cause this problem?
Thanks for reading...
Loki.
Loki,you`ve answered your own question...a few observations,;the 73 probably started from the end of the runway,or an intermediate close to it,and he would/should be able to stop in the event of a failure from about 80-100kts,so I suspect you started from another intermediate,if as you say ,you couldn`t stop.Runway behind you is wasted if you had an engine failure ,or a tyre burst.
In a light x-wind,wake turbulence will take longer to dissipate across the runway,so you should give yourself about 4 mins,from the end of the runway.You should be airborne and above the turbulence before the area that the heavy rotated at. If you go from an intermediate position the vortices are probably still descending/dissipating..
Suggest you google `Wake turbulence and separation distances for take-off and landing aircraft`...Lots of info around...Safe flying,but make those considerations before you open the throttle...better to be a bit late `down here`,than early `up there`....
In a light x-wind,wake turbulence will take longer to dissipate across the runway,so you should give yourself about 4 mins,from the end of the runway.You should be airborne and above the turbulence before the area that the heavy rotated at. If you go from an intermediate position the vortices are probably still descending/dissipating..
Suggest you google `Wake turbulence and separation distances for take-off and landing aircraft`...Lots of info around...Safe flying,but make those considerations before you open the throttle...better to be a bit late `down here`,than early `up there`....
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I concur with sycamore's observation. I could be a combination of the torque (such as it is for an O-235) and latent disturbed air from the 737. Always consider the direction of any wind on the airfield, and where it might blow turbulence from another aircraft. After allowing adequate time for turbulence to dissipate, still fly toward the upwind area of possible turbulence whenever possible.
Though yaw is possible when encountering changing airflow, if full rudder applied and held will not control the plane at 40 knots, you encountered air which would have been much better avoided.
Though yaw is possible when encountering changing airflow, if full rudder applied and held will not control the plane at 40 knots, you encountered air which would have been much better avoided.
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Many thanks for the answers. I actually started my roll from the same point as the heavy a/c, not an intermediate point. Also, for clarity, the reason i was running out of tarmac was because I was heading left at about 30 degrees off the centreline. There was plently runway left in front of me. Just not so much to the side. Once i was airborne, there was no turbulence to remark about. Very strange and worrying at the time!
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I actually started my roll from the same point as the heavy a/c, not an intermediate point.
I had a wake encounter in a 150, behind another 150, and it was enough to sharply roll my plane, heavy to light is very much worse!
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Being unable to stop yourself veering off the LHS of the runway in a 172 could alternatively be because you've still got full flaps down after a T&G
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It's not just on take off and landing on the runway you have to worry about wake turbulence, if you're flying thru a terminal area where the big guys are manouverng in a clean and slow configuration it's important to visualise based on wind and time where in relation to your heading and altitude you estimate the turbulence may be. See linked accident report.
http://www.ntsb.gov/_layouts/ntsb.av...13FA438&akey=1
http://www.ntsb.gov/_layouts/ntsb.av...13FA438&akey=1
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Flaps affect lift and drag, and are symmetrically deployed. No yaw effect.
Realised what was going on, raised the flaps, and could steer again.
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flaps exacerbating the effects of the propwash, which isn't symmetrical
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I can admit to having a very similar experience to the thread starter, in a similarly lowly powered PA38, operating at that time from Liverpool with 2 POB. Lovely warm day, little if any breeze. Intersected take off after nothing heavier than a Shorts 360.
We were airborne by about 12 feet and then had almighty wing drop, one way then the other. How we never hit the deck again I can only imagine. My "passenger" was my instructor for the day and I was still a student.
Analysis of the near incident led me to believe that even the 2 minutes we had were inadequate, and that we were caught as much by residual prop wash as from the vortices generated upon the rotation of the previous aircraft.
You made the right decision to get into the air. That way you are flying in the parcel of air, despite what the air itself was doing.
We were airborne by about 12 feet and then had almighty wing drop, one way then the other. How we never hit the deck again I can only imagine. My "passenger" was my instructor for the day and I was still a student.
Analysis of the near incident led me to believe that even the 2 minutes we had were inadequate, and that we were caught as much by residual prop wash as from the vortices generated upon the rotation of the previous aircraft.
You made the right decision to get into the air. That way you are flying in the parcel of air, despite what the air itself was doing.
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I note Loki's original post, so I make the follow observation as a generalization, not a specific comment on the OP.
I fly as a mentor pilot from time to time. I see pilots operate some controls through their full travel, yet other controls not. I'll see the throttle fully opened or closed appropriately, flaps fully extended or retracted, yet often when an aircraft is yawing undesirably, I'll press a pedal, and find that there is more rudder travel available. I'll roll the control wheel and find more aileron is available. The pilot has not applied full control.
Controls are there to be used. Their travel limits are carefully chosen, to provide enough control, without creating a risk of loss of or over control. Now you have to be sharp, and quick, to be applying full control, and maybe get it right back out, but that it what it's there for, and you're the qualified pilot.
If this seems un nerving, go up high, and fly some slips - well below Va, reduce power, point the plane down, and gently apply full pedal, countering with aileron as needed. Then check to assure you have full rudder applied. Can you apply full aileron? Maybe, maybe not, but experiment. When you're out on a very windy day, arrange to fly an approach to an out of the wind runway. Can you fly along the centerline perfectly? Even at 15 knots direct crosswind, you should be able to fly the centerline. You don't have to land, but you may realize that a landing might be possible in these conditions. It might take full control. I have many times applied full pedal, and held it in during a crosswind landing. If you can't hold the runway centerline, go around.
For those who fly tailwheel, the beginning of a groundloop (prevention of) is an opportunity to apply and hold full pedal, while hoping it's enough.
If you apply full control and it's not enough, speed up (usually by opening the throttle), and control will improve (engine torque effects not withstanding).
I fly as a mentor pilot from time to time. I see pilots operate some controls through their full travel, yet other controls not. I'll see the throttle fully opened or closed appropriately, flaps fully extended or retracted, yet often when an aircraft is yawing undesirably, I'll press a pedal, and find that there is more rudder travel available. I'll roll the control wheel and find more aileron is available. The pilot has not applied full control.
Controls are there to be used. Their travel limits are carefully chosen, to provide enough control, without creating a risk of loss of or over control. Now you have to be sharp, and quick, to be applying full control, and maybe get it right back out, but that it what it's there for, and you're the qualified pilot.
If this seems un nerving, go up high, and fly some slips - well below Va, reduce power, point the plane down, and gently apply full pedal, countering with aileron as needed. Then check to assure you have full rudder applied. Can you apply full aileron? Maybe, maybe not, but experiment. When you're out on a very windy day, arrange to fly an approach to an out of the wind runway. Can you fly along the centerline perfectly? Even at 15 knots direct crosswind, you should be able to fly the centerline. You don't have to land, but you may realize that a landing might be possible in these conditions. It might take full control. I have many times applied full pedal, and held it in during a crosswind landing. If you can't hold the runway centerline, go around.
For those who fly tailwheel, the beginning of a groundloop (prevention of) is an opportunity to apply and hold full pedal, while hoping it's enough.
If you apply full control and it's not enough, speed up (usually by opening the throttle), and control will improve (engine torque effects not withstanding).
We're you at the point where the aircraft wanted to fly, but you were trying to steer with the nosewheel, while all the wheels had less weight on them, and so little grip on the runway?
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The third wheel does not provide any effective directional control at speeds exceeding around 25MPH on most GA aircraft, The rudder is controlling direction. If you have managed to keep enough weight on the third wheel that it can affect direction, you're already having an exciting ride down the runway! I agree that the Tomahawk is a bit of a special case, as the elevator has little effect in lifting the nose early, compared to other types, but it's still the rudder doing the steering.
To demonstrate yourself in a 150/152/172, do the following: Load it toward an aft C of G (but within limits, of course). Extend the flaps to 15 degrees, Find a runway or taxiway to yourself, ideally into a 5 to 10 knots wind. Hold the controls full nose up and open the throttle until the nosewheel comes off, then no more. The aircraft may have only moved a few feet before the nosewheel comes off - be careful to not get the nose so high that the tail tiedown ring hits the ground, that's really bad for them! Now you're taxiing with around 1600 RPM, at 15 MPH or so, with about the same directional control by rudder steering, as you would have were the nosewheel to be in contact with the surface.
Similar the taildragger, Heels on the floor - so not accidentally applying the brakes, stick forward once on the roll, so the tail comes up, and you still have lots of steering with the rudder.
Note that in Cessnas and taildraggers, there are springs which allow the third wheel to track the runway, rather than to move with the rudder. The rudder is doing the steering at speed. Piper nosewheel aircraft have direct steering, so some nosewheel scrubbing could happen with lots of steering on the runway, but it's still primarily the rudder steering at speed.
To demonstrate yourself in a 150/152/172, do the following: Load it toward an aft C of G (but within limits, of course). Extend the flaps to 15 degrees, Find a runway or taxiway to yourself, ideally into a 5 to 10 knots wind. Hold the controls full nose up and open the throttle until the nosewheel comes off, then no more. The aircraft may have only moved a few feet before the nosewheel comes off - be careful to not get the nose so high that the tail tiedown ring hits the ground, that's really bad for them! Now you're taxiing with around 1600 RPM, at 15 MPH or so, with about the same directional control by rudder steering, as you would have were the nosewheel to be in contact with the surface.
Similar the taildragger, Heels on the floor - so not accidentally applying the brakes, stick forward once on the roll, so the tail comes up, and you still have lots of steering with the rudder.
Note that in Cessnas and taildraggers, there are springs which allow the third wheel to track the runway, rather than to move with the rudder. The rudder is doing the steering at speed. Piper nosewheel aircraft have direct steering, so some nosewheel scrubbing could happen with lots of steering on the runway, but it's still primarily the rudder steering at speed.
