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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.

42 news items

AVweb

AVweb
Mon, 28 Dec 2015 03:17:11 -0800

Then with the ground approaching quickly and perhaps even after a bounce, he pulls back and magnifies the oscillation even more. This is a classic example of pilot-induced oscillation (PIO), with control inputs out of synch with the motion of the airplane.

ScienceAlert

ScienceAlert
Fri, 27 Nov 2015 06:48:45 -0800

First off, if you want to learn how to hover a helicopter, you're going to have to overcome your urge to commit pilot induced oscillation, which basically means constantly freaking out and over-controlling the vehicle to make the whole thing wobble ...

BGR

BGR
Mon, 27 Jul 2015 07:21:17 -0700

If you thought turbulence can be a scary during flights, then you probably haven't experienced a windstorm landing. The pilots of a commercial Boeing 777 airplane skillfully landed the aircraft a few days ago in the Netherlands in the middle of these ...

AVweb

AVweb
Mon, 14 Dec 2015 00:51:37 -0800

The pilot gets precisely 180 degrees out of phase with the airplane, leading to pilot-induced oscillation (PIO), which can quickly generate a bent airplane and worse. Some airplanes cannot be wheel-landed because they do not have enough propeller ...
 
Cycleworld
Wed, 11 Mar 2015 06:41:35 -0700

Each street-riding priority moves to the front of the list as your circumstances change, but this single priority should always be first: mastering your bike-control skills. When the worst happens and you need to get your bike stopped, or change your ...

Breaking Defense

Breaking Defense
Mon, 02 Feb 2015 15:11:08 -0800

PENTAGON: The Navy 2016 budget yields to Congress's strong opposition to the service's previous efforts to cut the active fleet to save money. It funds nuclear refueling and overhaul of the aircraft carrier USS George Washington –that it had tried to ...

Air & Space Magazine

Air & Space Magazine
Fri, 31 Jan 2014 09:04:14 -0800

The resulting pilot-induced oscillation generated over 12 Gs. Both engines were ripped from the airframe and Felsman was killed. (A later attempt succeeded.) Single Page Previous Page 1 of 6 Next 1 2 3 4 5 6. Like this article? SIGN UP for our newsletter.

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 ...
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