Flying (or Handling) Qualities. Aircraft Flying Qualities Robert Stengel, Aircraft Flight Dynamics MAE 331, Flight Testing Instrumentation: Then

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1 Aircraft Flyin Qualities Robert Stenel, Aircraft Fliht Dynamics MAE 331, 2008 Fliht test instrumentation Flyin qualities requirements Flyin qualities specifications Pilot opinion ratins CAP, C*, and other lonitudinal criteria Pilot-induced oscillations Copyriht 2008 by Robert Stenel. All rihts reserved. For educational use only. Flyin or Handlin Qualities Stability and controllability perceived by the pilot 1919 fliht tests of Curtiss JN-4H Jenny at NACA Lanley Laboratory by Warner, Norton, and Allen Elevator anle and stick force for equilibrium fliht Correlation of elevator anle and airspeed with stability Correlation of elevator anle and airspeed with wind tunnel tests of pitch moment Fliht Testin Instrumentation: Then Fliht Testin Instrumentation: Now Fliht recordin instruments: drum/strip charts, inked needles, film, alvanometers connected to air vanes, pressure sensors, clocks

2 Nose Boom and Calibration Quadrants First Flyin Qualities Specification First flyin qualities specification: 1935, Edward Warner for Doulas DC-4 transport Interviews with pilots and enineers Flyin Qualities Research at NACA Hartley Soulé and Floyd Thompson late 1930s Lon- and short-period motions Time to reach specified bank anle Period and dampin of oscillations Correlation with pilot opinion Robert Gilruth Parametric reions and boundaries Multi-aircraft criteria Control deflection, stick force, and normal load factor Roll helix anle Lateral control power Modern Fliht Research and Development Application of control theory Variable-stability research aircraft, e.., TIFS, AFTI F-16, NT-33A, and VRA The Princeton Connection [Fliht Research Laboratory] USAF/Calspan TIFS USAF/Calspan NT-33A USAF AFTI F-16 Princeton VRA

3 Gilruth Roll-Rate Criterion [pb/2v] Helix anle formed by rotatin win tips, pb/2v Roll rate, p, rad/s Win semi-span, b/2, m Velocity, V, m/s Robert Gilruth criterion pb/2v > 0.07 rad Simplified Roll-Rate Response Tradeoff between hih pb/2v and hih lateral stick forces prior to powered controls: p t = [C lp pt + C l!a!at]q Sb/ I xx = a pt + c!at q = 1 2 "V 2, dynamic pressure, N / m 2 Initial-condition response!a = 0 pt = p0e at Step response [p0 = 0] pt = c a eat "1#A * Steady state response p* =! C l "A C l p "A * FockeWulf 190 Supermarine Spitfire Cooper-Harper Handlin Qualities Ratin Scale Effect of Equivalent Time Delay on Cooper-Harper Ratin

4 Inverse Problem of Lateral Control Given a fliht path, what is the control history that enerates it? Necessary pilotin actions Control-law desin Aileron-rudder interconnect ARI simplifies pilot input Yaw Anle Anle of attack " = 10 de; ARI off " = 30 de; ARI off Roll Anle Lateral-Stick Command Difficult flyin task Hih potential for PIO Alternative desins Riid boom USAF Probe and droue USN Aerial Refuelin Doulas KC-10 McDonnell-Doulas F/A-18 McDonnell-Doulas F/A-18 Doulas KC-10 Grumman F-14 " = 30 de; ARI on Doulas A4D Grumman F-14 Tomcat Formation Flyin Coordination and precision Potential aerodynamic interference US Navy Blue Anels F/A-18 Carrier Approach on Back Side of the Power/Thrust Curve Precise path and airspeed control while on the back side of the power curve Slower speed requires hiher thrust Lihtly damped phuoid mode requires coordination of pitch and thrust control Reference fliht path enerated by optical device, which projects a meatball relative to a datum line

5 Military Flyin Qualities Specifications, MIL-F-8785C Specifications established durin WWII US Air Force and Navy coordinated efforts beinnin in 1945 First version appeared in 1948, last in 1980 Distinctions by fliht phase, mission, and aircraft type MIL-F-8785C Identifies Satisfactory, Acceptable, and Unacceptable Response Characteristics Dampin Ratio Short-period anle-of-attack response to elevator input Frequency Response Step Response MIL-F-8785C Aircraft Types Northrop YF-23 MIL-F-8785C Fliht Phase I. Small, liht airplanes, e.., utility aircraft and primary trainers II. Medium-weiht, low-to-medium maneuverability airplanes, e.., small transports or tactical bombers III. Lare, heavy, low-to-medium maneuverability airplanes, e.., heavy transports, tankers, or bombers IV. Hihly maneuverable aircraft, e.., fihter and attack airplanes A. Non-terminal fliht requirin rapid maneuverin precise trackin, or precise fliht path control air-to-air combat round attack in-fliht refuelin receiver close reconnaissance terrain followin close formation flyin B. Non-terminal fliht requirin radual maneuverin climb, cruise in-fliht refuelin tanker descent C. Terminal fliht takeoff normal and catapult approach wave-off/o-around landin

6 MIL-F-8785C Levels of Performance 1. Flyin qualities clearly adequate for the mission fliht phase 2. Flyin qualities adequate to accomplish the mission fliht phase, with some increase in pilot workload or deradation of mission effectiveness 3. Flyin qualities such that the aircraft can be controlled safely, but pilot workload is excessive or mission effectiveness is inadequate Convair F-106 Lonitudinal flyin qualities static speed stability phuoid stability fliht path stability short period frequency and its relationship to command acceleration sensitivity short period dampin control-force radients Principal MIL-F-8785C Metrics Lateral-directional flyin qualities natural frequency and dampin of the Dutch roll mode time constants of the roll and spiral modes rollin response to commands and Dutch roll oscillation sideslip excursions maximum stick and pedal forces turn coordination Lon-Period Flyin Qualities Criteria MIL-F-8785C Fliht Phase A. Non-terminal fliht requirin rapid maneuverin B. Non-terminal fliht requirin radual maneuverin C. Terminal fliht Level of Performance 1. Clearly adequate for the mission 2. Adequate to accomplish the mission, with some increase in workload 3. Aircraft can be controlled safely, but workload is excessive Static speed stability No tendency for aperiodic diverence Stable control stick radient Increasin pull force with decreasin speed Fliht path stability [Phase C] 1.!"/!V SS < 0.06 de/kt 2.!"/!V SS < 0.15 de/kt 3.!"/!V SS < 0.24 de/kt Lon-Period Flyin Qualities Criteria MIL-F-8785C Phuoid stability 1.Dampin ratio! Dampin ratio! 0 3. Time to double, T 2! 55 sec T 2Ph = "0.693/# Ph $ nph Grumman XF5F

7 Short Period Criteria Northrop XB-35 Short-Period Bullseye or Thumbprint Important parameters Short-period natural frequency Dampin ratio Lift slope Step response Initial la Rise time Over-/under-shoot Settlin time Pure time delay Pitch anle response Normal load factor response Fliht path anle response landin " nsp vs.# SP Nichols Chart: Gain vs. Phase Anle Bode Plot Two plots Open-Loop Gain db vs. lo 10 # Open-Loop Phase Anle vs. lo 10 # Nichols Chart Sinle crossplot; input frequency not shown Open-Loop Gain db vs. Open- Loop Phase Anle Gain and Phase Marins Gain Marin: At the input frequency, #, for which $j# is 180,the difference between 0 db and the transfer function manitude, 20 lo 10 ARj# Phase Marin: At the input frequency, #, for which 20 lo 10 ARj# is 0 db, the difference between the phase anle $j#, and 180 Axis intercepts on the Nichols Chart identify GM and PM

8 Examples of Gain and Phase Marins # 10 &# & H blue j" = % % $ j" +10 ' $ % j" j" ' # 10 2 &# 100 & H reen j" = % % $ % j" j" ' $ j" +100 ' Bode Plot Nichols Chart Sinificance of Gain and Phase Marins Assume Pilot tracks a sinle output usin the elevator Plant has 3rd-order transfer function Gain/phase-chanin element, Ke j$, in the forward loop Gain marin = value of K that causes unstable control e.., root loci at riht Crossover frequency predicted by open-loop Bode plot Phase marin = value of $ that causes unstable control Short-Period Approximation Transfer Functions Elevator to pitch rate "qs k "#Es = k q s $ z q q s $ 1, + s % SP & nsp s + & ' * T. 2 - nsp s % SP & nsp s + & nsp Short-Period Approximation Transfer Functions Elevator to pitch anle "#s "$Es = k q s % z q s s & SP ' nsp s + ' nsp Pure ain or phase chane in feedback control cannot produce instability Pure ain or phase chane in feedback control cannot produce instability

9 Normal Load Factor "n z = V N "# $ "q = $V N & L # "# + L %E "%E+ ' V N V N * Therefore, with neliible L!E aft tail/canard effect positive down "#n z s "#$Es = 1 & L "#%s % "#$Es + L & $E +, L % + "#%s ' * ' *"#$Es Elevator to anle of attack L!E = 0 "#s "$Es % k # s 2 + 2& SP ' nsp s + ' nsp 2 positive up Control Anticipation Parameter, CAP Inner ear senses anular acceleration Inner ear cue should aid pilot in anticipatin commanded normal acceleration & M " q 0 = M #E $ % L #E + "#E SS ' V N + L % * & "n SS = V N "q = $ & V M L % #E $ M L #E VN % + N ' VN * SS + "#E ' * & M L % SS q + M ' VN % + * CAP = " q 0 = "n SS & M # M $E # % L $E ' V N + L % * + & M L % + M + ' q VN % * L % M $E # L $E M % with L!E = 0 " $ & M L % # + M ' q CAP = VN # * + 2 n SP n z /# L # " nsp vs. n z # Control Anticipation Parameter vs. Short-Period Dampin Ratio MIL-F-8785C, Cateory A MIL-F-8785C Short-Period Flyin Qualities Criterion Level of Performance 1. Clearly adequate for the mission 2. Adequate to accomplish the mission, with some increase in workload 3. Aircraft can be controlled safely, but workload is excessive Fliht Phase A. Non-terminal fliht requirin rapid maneuverin B. Non-terminal fliht requirin radual maneuverin C. Terminal fliht Level of Performance 1. Clearly adequate for the mission 2. Adequate to accomplish the mission, with some increase in workload 3. Aircraft can be controlled safely, but workload is excessive " nsp = CAP n z # n z " # L "

10 Gibson Dropback Criterion for Pitch Anle Control Step response of pitch rate should have overshoot for satisfactory pitch and fliht path anle response When criterion is satisfied, "qs "#Es = k q s $ z q s % SP & nsp s + & nsp ' k q s + & n SP * %, SP + = s % SP & nsp s + & nsp C* Criterion C* = "n pilot + V crossover "q = l pilot " q + "n cm + V crossover "q = l pilot " q + V N V crossover "125 m /s "q # " $ + V crossover Hypothesis C* blends normal load factor and pitch rate Step response of C* should lie within acceptable envelope Below V crossover,!q is pilot"s primary control objective Above V crossover,!n pilot is the primary control objective Pilot opinion does not always support the hypothesis "q Lare Aircraft Flyin Qualities Hih win loadin, W/S Distance from pilot to rotational center Slosh susceptibility of lare tanks Hih win span -> short relative tail lenth Hiher trim dra Increased yaw due to roll, need for rudder coordination Reduced rudder effect Altitude response durin approach Increased non-minimum-phase delay in response to elevator Potential improvement from canard Lonitudinal dynamics Phuoid/short-period resonance Rollin response e.., time to bank Reduced static stability Off-axis passener comfort in BWB turns Control Desin for Satisfactory Flyin Qualities Satisfy procurement requirement e.., Mil Standard Satisfy test pilots e.., Cooper- Harper ratins Avoid pilot-induced oscillations PIO Minimize time-delay effects Frequency domain criteria Crossover model Neal-Smith criterion Bandwidth-phase delay criteria Smith-Geddes PIO criterion Elevator-to-pitch anle Nichols chart ain vs. phase anle Northrop YF-17A

11 Pilot-Induced Oscillations MIL-F-8785C specifies no tendency for pilot-induced oscillations PIO Uncommanded aircraft is stable but pilotin actions couple with aircraft dynamics to produce instability Pilot-Induced Oscillations Cateory I: Linear pilot-vehicle system oscillations Cateory II: Quasilinear events with nonlinear contributions Cateory III: Nonlinear oscillations with transients Hodkinson, Neal, Smith, Geddes, Gibson et al YF-16 Test Fliht Zero Hih-speed taxi test; no fliht intended Pilot-induced oscillations induced by overly sensitive roll control Tail strike Pilot elected to o around rather than eject Next Time: Fourth-Order Lonitudinal Dynamics