Corkscrewing Motion

MuseChaser

MuseChaser

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MuseChaser
On a recent Delta flight from DTW to SAT, during the majority of the time the plane was slowly corkscrewing, with one oscillation about every two seconds... very steady rhythm and motion. For those of you who sail, it felt quite similar to sailing just slightly off direct downwind. Sort of like the plane was in an endless cycle trying to find coordinated flight. It wasn't bad in the air, but once I got on ground, the aftereffects were noticeable for a few days..every once in a while, when I stood still, the ground felt like it was moving. FWIW, that happens after a long sail, too. Not bothersome, just interesting.

Never felt that motion in the air before, commercial or otherwise. Any ideas what was going on with the plane?
 
MuseChaser said:
On a recent Delta flight from DTW to SAT, during the majority of the time the plane was slowly corkscrewing, with one oscillation about every two seconds... very steady rhythm and motion. For those of you who sail, it felt quite similar to sailing just slightly off direct downwind. Sort of like the plane was in an endless cycle trying to find coordinated flight. It wasn't bad in the air, but once I got on ground, the aftereffects were noticeable for a few days..every once in a while, when I stood still, the ground felt like it was moving. FWIW, that happens after a long sail, too. Not bothersome, just interesting.

Never felt that motion in the air before, commercial or otherwise. Any ideas what was going on with the plane?
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Noticeable for a few days afterwards? Like you felt dizzy?
 
No. Hard to describe unless you've sailed and experienced it. If your body is subjected to a subtle periodic rhythmic motion over a long period of time, it seems to adapt to that motion as "normal." Once the motion stops (you get off the boat, or plane in this case), that lack of motion doesn't feel normal whenyou hold still. Very common... sort of the inverse of "getting your sea legs." Not a question of balance, lightheadedness, or other symptoms of dizziness.
 
luvflyin said:
Noticeable for a few days afterwards? Like you felt dizzy?
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Sailors call it land sickness. Makes you walk funny when you first step off a boat after a long passage. Feels like the bed is moving in your house when it obviously can't be.

I wouldn't call it dizzy, it just feels like you legs aren't meeting the ground like you're used to.
 
MuseChaser said:
No. Hard to describe unless you've sailed and experienced it. If your body is subjected to a subtle periodic rhythmic motion over a long period of time, it seems to adapt to that motion as "normal." Once the motion stops (you get off the boat, or plane in this case), that lack of motion doesn't feel normal whenyou hold still. Very common... sort of the inverse of "getting your sea legs." Not a question of balance, lightheadedness, or other symptoms of dizziness.
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I’ve experienced that. Not for a couple days though. But I’ve never had a long time doing the thing that led to it. Anyway, thinking back I’m pretty sure I’ve felt that corkscrewing thing in an airliner before. The big iron guys should be around soon to explain it.
 
When I was serving aboard a sub we didn’t have seasickness kind of problems, but rather weird vision effects. After weeks of a maximum horizon of 50 feet and then going ashore to a horizon of miles really messes with the eyes and brain.
 
luvflyin said:
I’ve experienced that. Not for a couple days though. But I’ve never had a long time doing the thing that led to it. Anyway, thinking back I’m pretty sure I’ve felt that corkscrewing thing in an airliner before. The big iron guys should be around soon to explain it.
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On some of our longer passages, 13 days from Chesapeake Bay to St Maarten for example, it lasted a while afterwards. Usually it is short lived.
 
It sounds like Dutch roll, and the only time I seem to consistently experience it on airliners are on Delta md-90 fleet.. I used to like a booking on those since they are very smooth and quiet when sitting up front, but I avoid them now after a few flights and all experiencing that motion. Actually made a small video of it looking out the window it was that apparent
 
Dutch ro
GRG55 said:
Sounds like Dutch roll.
..
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Exactly. Video says it's caused by strong lateral stability and weak directional stability. Never experienced it in an airliner before, but my CFI, years ago, told me it's a good idea to practice what he called Dutch Rolls as a good way to maintain coordinated flight and proper rudder use...I still do a couple every flight. Still unsure why an airliner on autopilot would do it uncoordinated.
 
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^I read somewhere that the Soviets designed their jets with anhedral wings as a way to combat the tendency for their jets to Dutch roll.. I think it's most apparent for some reason with tail engined jets, especially with lots of sweep, which the TU-154 had both.. tons of sweep, tail engined, and fairly aggressive anhedral

there is something *SO* cool about Russian jets
upload_2019-8-2_10-59-23.png
 
Dutch rolls and rolls about a point are two different things, but this does sound like the true definition of Dutch Roll.
 
Fiveslide you need a faster boat...Just did STT to NYC (Liberty Landing) in 8 days in a Lagoon 50...I am one of those who gets a heavy dose of land sickness and the effects can last 4-5 days. I just deal with it but my symptoms include waking up with the bed rolling through 20-30 degrees almost a bad case of vertigo...takes me a while and do not fly until I settle back down. I have experience the same results since I was young and have just dealt with it...I do a couple of multiday passages a year and my wife laughs at me every time I exhibit symptoms of bracing walls and jumping out of bed to stop the rolling. Interestingly enough I have never been seasick in my life and had plenty of times when the whole crew is grabbing rails.
 
If you sit far away from the CG (esp way in back) you will feel yaw motions more. The worst flight I ever experienced was in a Dash 8 in the rear bench seat flying over mountains during a frontal passage. It was like a roller coaster ride, but not in a good way. If you sit near the wings the amplitude of these yaw motions is minimized.
 
It's a natural tendency of swept wing aircraft, that's why they have yaw dampener and modal suppression systems.
 
Warlock said:
Fiveslide you need a faster boat...Just did STT to NYC (Liberty Landing) in 8 days in a Lagoon 50...I am one of those who gets a heavy dose of land sickness and the effects can last 4-5 days. I just deal with it but my symptoms include waking up with the bed rolling through 20-30 degrees almost a bad case of vertigo...takes me a while and do not fly until I settle back down. I have experience the same results since I was young and have just dealt with it...I do a couple of multiday passages a year and my wife laughs at me every time I exhibit symptoms of bracing walls and jumping out of bed to stop the rolling. Interestingly enough I have never been seasick in my life and had plenty of times when the whole crew is grabbing rails.
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That sounds like a great trip. We were on a Lavezzi. Wind was either light and on the nose or calm, uneventful trip for sure. Burnt up nearly all our fuel to do it in 13. That's with an extra 40 gallon tank installed and 25 in jerry cans on the deck. The trade winds had us coming into SXM fast on the last day, made us look good, screaming by Anguilla at 11 knots.
 
Thanks for the replies and info. I looked it up; the plane was a Boeing 717-200 and we were seated at the leading edge of the left wing. @Tantalum guessed right ... MD95.
 
A DC or MD anything called a Boeing is just wrong IMO.

Dutch roll sounds about right. I wonder if that airplane had a yaw damper issue. That would be my uneducated guess.
 
Greg Bockelman said:
A DC or MD anything called a Boeing is just wrong IMO.

Dutch roll sounds about right. I wonder if that airplane had a yaw damper issue. That would be my uneducated guess.
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Can the yaw damper be MEL'ed?
 
Greg Bockelman said:
A DC or MD anything called a Boeing is just wrong IMO.

Dutch roll sounds about right. I wonder if that airplane had a yaw damper issue. That would be my uneducated guess.
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To your point the Airbus a220 also sounds kind of odd. It's the stepchild
 
Sure sounds like dutch roll. Swept wings do it by nature, and it takes a yaw damper to fix it. I saw it when I hired on to a 135 job. The company was the launch customer for the then new Sikorsky S-76. I think the buy was about 16 initially. The type was designed to have autopilts and air conditioning. The hicks that did the order spec'ed them without that stuff. Not even a yaw damper. In Texas/LA. In July.

Although not checked out in the type, I got stuck in the C/P seat for a while and found out what real dutch roll is. The PIC also showed me how to cope with it. Its all in your feet. Its a yaw thing that if allowed, will quickly progress to a roll couple. It increases alarmingly fast and the roll increases to 40 deg. or more. It wants to keep going if you don't jump in and fix it. After a year, I checked out in the type. We flew them single pilot as a rule. We had an FAA exemption to the rule that limited single pilot turbine A/C to nine passengers and carried a full house of twelve pax. Things were busy and we usually timed out with eight hours most days. Dealing with the dutch roll became automatic. Then they said two pilots are now required.

The fleet increased, the stripped A/C were retrofitted with Sperry APs, Some had Ham Standard Stability augmentation systems. New guys were now not familiar with dutch roll. By the mid nineties, Sikorsky felt they should deal with dutch roll and put a requirement in the EMERG section of the Flight Manual to reduce speed to 125KTS if you lose one or both APs. I checked my CPs out to deal with Dutch roll up to 150KTS.
 
Was there a sign on cockpit
“If this cockpit’s a rockin’ Don’t come a knockin’”
Or a sock on the door?
 
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