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Pilot-induced oscillation rating scale, start position at bottom left

Pilot-induced oscillations, as defined by MIL-HDBK-1797A,[1] are sustained or uncontrollable oscillations resulting from efforts of the pilot to control the aircraft and occurs when the pilot of an aircraft inadvertently commands an often increasing series of corrections in opposite directions, each an attempt to cover the aircraft's reaction to the previous input with an overcorrection in the opposite direction. An aircraft in such a condition can appear to be "porpoising" switching between upward and downward directions. As such it is a coupling of the frequency of the pilot's inputs and the aircraft's own frequency. During flight test, pilot-induced oscillation is one of the handling qualities factors that is analyzed, with the aircraft being graded by an established scale (chart at right). In order to avoid any assumption that oscillation is necessarily the fault of the pilot, new terms have been suggested to replace pilot-induced oscillation. These include aircraft-pilot coupling, pilot–in-the-loop oscillations and pilot-assisted (or augmented) oscillations.[2]

In a controls sense, the oscillation is the result of reduced phase margin induced by the lag of the pilot's response. The problem has been mitigated in some cases by adding lead to the instruments - for example, cause the climb rate indication to not only reflect the current climb rate, but also be sensitive to the rate of change of the climb rate.

The physics of flight make such oscillations more probable for pilots than for automobile drivers. An attempt to cause the aircraft to climb, say, by applying up-elevator, will also result in a reduction in airspeed.

Another factor is the response rate of flight instruments in comparison to the response rate of the aircraft itself. An increase in power will not result in an immediate increase in airspeed. An increase in climb rate will not show up immediately on the vertical speed indicator.

A pilot aiming for a 500 foot per minute descent, for example, may find himself descending too rapidly. He begins to apply up elevator until the vertical speed indicator shows 500 feet per minute. However, because the vertical speed indicator lags the actual vertical speed, the pilot is actually descending at much less than 500 feet per minute. The pilot then begins applying down elevator until the vertical speed indicator reads 500 feet per minute, starting the cycle over. It's harder than it might seem to stabilize the vertical speed because the airspeed also constantly changes.

Pilot-induced oscillations may be the fault of the aircraft, the pilot, or both. It is a common problem for inexperienced pilots, and especially student pilots, although it was also a problem for the top research test pilots on the NASA lifting body program. The problem is most acute when the wing and tail section are close together in so called "short coupled" aircraft.

The most dangerous pilot-induced oscillations can occur during landing. Too much up elevator during the flare can result in the plane getting dangerously slow and threatening to stall. A natural reaction to this is to push the nose down harder than one pulled it up, but then the pilot ends up staring at the ground. An even larger amount of up elevator starts the cycle over again.

While Pilot-Induced oscillations often start with fairly low amplitudes, which can adequately be treated with small perturbation linear theory, several PIO's will by definition become very large.[3]

In February 1989 a JAS 39 Gripen prototype crashed when landing in Linköping, Sweden. Pilot-induced oscillation as a result of an over-sensitive, yet slow-response steering system was determined to be the cause. Subsequently, the steering system was redesigned.

Pilot-induced oscillation was blamed for the 1992 crash of the prototype F-22 Raptor, landing at Edwards Air Force Base in California. This crash was linked to actuator rate limiting, causing the pilot, Tom Morgenfeld, to overcompensate for pitch fluctuations.

See also[edit]

References[edit]

  1. ^ DEPARTMENT OF DEFENSE INTERFACE STANDARD, Flying qualities of piloted airplanes, Washington, D.C.
  2. ^ Witte, Joel B, An Investigation Relating Longitudinal Pilot-Induced Oscillation Tendency Rating To Describing Function Predictions For Rate-Limited Actuators https://research.maxwell.af.mil/papers/ay2004/afit/AFIT-GAE-ENY-04-M16.pdf
  3. ^ McRuer, Duane T. "Pilot-Induced Oscillations and Human Dynamic Behavior". NASA. Dryden Space Flight Research Center. Retrieved 16 September 2011. 

External links[edit]


Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Pilot-induced_oscillation — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.

28 news items

Athens NEWS

Athens NEWS
Sun, 26 Apr 2015 19:10:45 -0700

For many years the gyro pilot's greatest fear was of something called pilot-induced oscillation. Overly simply put, this was an issue involving the aircraft's center of gravity; even more overly simply put it meant that you could maneuver such that the ...
 
Cycleworld
Wed, 11 Mar 2015 06:41:35 -0700

In addition to the pilot-induced oscillation, the bar moving back and forth opened and closed the throttle in my hand. Luckily, it was a 1/6 turn throttle on a CBR1000RR in 3rd gear, so small angular changes didn't make a big difference, right? Of ...

The Indian Express

The Indian Express
Mon, 29 Dec 2014 06:15:05 -0800

... Flight Data Recorder (SSFDR) on Mig-27 by HAL, modification of flying helmets on a fast track basis as the existing helmets flew off during ejection by pilots and to introduce the mechanism of pilot induced oscillation (PIO) as part of ground ...
 
Nelson Star
Sun, 31 Aug 2014 12:08:05 -0700

“We heard later it was porpoising,” she said, referring to pilot-induced oscillation, which is when a pilot inadvertently corrects in opposite directions, causing the plane to violently switch between upward and downward directions. The plane ...

Edwards Air Force Base

Edwards Air Force Base
Wed, 18 Jun 2014 13:26:15 -0700

TPS designed a flight test technique to replicate pilot induced oscillation in a safe and controlled environment called switch-induced simulated PIO. This project tested SISPIO to determine if it was a viable way of reproducing actual PIOs. HAVE POSIT ...

Space.com

Space.com
Mon, 18 Nov 2013 07:21:42 -0800

The fifth approach and landing test, with the Enterprise landing on the Edwards Air Force Base concrete runway, revealed a problem with the Space Shuttle flight control system that made it susceptible to Pilot-Induced Oscillation (PIO), a potentially ...
 
The Economist (blog)
Tue, 10 Jun 2014 04:36:05 -0700

FINANCIAL MARKETS have been celebrating since June 5th when the European Central Bank (ECB) announced a new battery of measures to counter low inflation in the euro area. Stockmarkets around the world have been hitting new highs. In Frankfurt the ...

AVweb

AVweb
Thu, 05 Jun 2014 18:49:59 -0700

One potential handling trouble spot is PIO (pilot-induced oscillation) during landings. Although not unique to Champions, the spring-steel main gear can bounce the airplane if the pilot dumps it too hard or if he or she fails to go around. More bounces ...
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