Flying Qualities Evaluation of a Commuter Aircraft With an Ice Contaminated Tailplane

NASA / TM--2000-210356 SAE 2000-01-1676

Flying Qualities Evaluation of a Commuter

Aircraft With an Ice Contaminated Tailplane

Richard J. Ranaudo Bombardier Aerospace, Wichita, Kansas Thomas P. Ratvasky Glenn Research Center, Cleveland, Ohio Judith Foss Van Zante Dynacs Engineering Company, Inc. Brook Park, Ohio C

September 2000

The NASA STI Program Office... in Profile CONFERENCE PUBLICATION. Collected Since its founding, NASA has been dedicated to papers from scientific and technical the advancement of aeronautics and space science. The NASA Scientific and Technical conferences, symposia, seminars, or other meetings sponsored or cosponsored by Information (STI) Program Office plays a key part NASA.

in helping NASA maintain this important role.

SPECIAL PUBLICATION. Scientific, The NASA STI Program Office is operated by technical, or historical information from Langley Research Center, the Lead Center for NASA's scientific and technical information. The NASA programs, projects, and missions, often concerned with subjects having NASA STI Program Office provides access to the substantial public interest.

NASA STI Database, the largest collection of aeronautical and space science STI in the world.

TECHNICAL TRANSLATION. English- The Program Office is also NASA's institutional language translations of foreign scientific mechanism for disseminating the results of its and technical material pertinent to NASA's research and development activities. These results mission.

are published by NASA in the NASA STI Report Series, which includes the following report types: Specialized services that complement the STI Program Office's diverse offerings include TECHNICAL PUBLICATION. Reports of creating custom thesauri, building customized completed research or a major significant data bases, organizing and publishing research phase of research that present the results of results.., even providing videos.

NASA programs and include extensive data or theoretical analysis. Includes compilations For more information about the NASA STI of significant scientific and technical data and Program Office, see the following: information deemed to be of continuing reference value. NASA's counterpart of peer- • Access the NASA STI Program Home Page reviewed formal professional papers but at http:/Iwww.sti.nasa.gov has less stringent limitations on manuscript length and extent of graphic presentations.

- E-mail your question via the Internet to TECI-INICAL MEMORANDUM. Scientific help@sti.nasa.gov and technical findings that are preliminary or • Fax your question to the NASA Access of specialized interest, e.g., quick release Help Desk at (301) 621-0134 reports, working papers, and bibliographies that contain minimal annotation. Does not • Telephone the NASA Access Help Desk at contain extensive analysis.

(301) 621-0390 CONTRACTOR REPORT. Scientific and Write to: technical findings by NASA-sponsored NASA Access Help Desk contractors and grantees.

NASA Center for AeroSpace Information 7121 Standard Drive Hanover, MD 21076

NASA/TM--2000-210356 SAE 2000-01-1676

Flying Qualities Evaluation of a Commuter

Aircraft With an Ice Contaminated Tailplane

Richard J. Ranaudo Bombardier Aerospace, Wichita, Kansas Thomas P. Ratvasky Glenn Research Center, Cleveland, Ohio Judith Foss Van Zante Dynacs Engineering Company, Inc. Brook Park, Ohio Prepared for the General Aviation Technology Conference and Exposition (GATC) sponsored by the Society of Automotive Engineers Wichita, Kansas, May 9-11, 2000 National Aeronautics and Space Administration Glenn Research Center

September 2000

Acknowledgments The authors wish to thank the participating organizations and guest pilots from the FAA, Transport Canada, Cessna, Raytheon, Bombardier-Learjet for pilot support and participation. We also would like to thank the sponsors of the NASA/FAA TIP: the NASA Aerospace Operations Systems base program and the FAA William J. Hughes Technical Center.

Trade names or manufacturers' names are used in this report for identification only. This usage does not constitute an official endorsement, either expressed or implied, by the National Aeronautics and Space Administration.

Available from National Technical Information Service NASA Center for Aerospace Information 5285 Port Royal Road 7121 Standard Drive Springfield, VA 22100 Hanover, MD 21076 Price Code: A03 Price Code: A03 Available electronically at ht_hJttttttt!12.2/: _g!trs.grc.nasa.gov/GLTRS

Flying Qualities Evaluation of a Commuter Aircraft

With an Ice Contaminated Tailplane

Richard J. Ranaudo Bombardier Aerospace Wichita, Kansas Thomas P. Ratvasky National Aeronautics and Space Administration Glenn Research Center Cleveland, Ohio 44135 Judith Foss Van Zante Dynacs Engineering Company, Inc.

Brook Park, Ohio 44142 ABSTRACT respectively. By comparison, the same task conducted at the 30 -0flap setting, resulted in Level II flying qualities for During the NASA/FAA Tailplane Icing Program, pilot the approach portion, and Level III for the go-around evaluations of aircraft flying qualities were conducted portion.

with various ice shapes attached to the horizontal tailplane of the NASA Twin Otter Icing Research Aircraft. The results of this program indicate that safe and Initially, only NASA pilots conducted these evaluations, acceptable flying qualities with an ICT condition, can be assessing the differences in longitudinal flight effectively assessed by task-oriented pilot maneuvers. In characteristics between the baseline or clean aircraft, addition, other maneuvers such as repeat elevator and the aircraft configured with an Ice Contaminated doublets provide good qualitative and quantitative Tailplane (ICT). Longitudinal tests included Constant assessments of pitch damping and elevator effectiveness, which are characteristics that correlate Airspeed Flap Transitions. Constant Airspeed Thrust Transitions, zero-G Pushovers, Repeat Elevator well with pilot task ratings. The results of this testing Doublets, and, Simulated Approach and Go-Around indicate that the FAR 25 zero-G pushover maneuver, tasks. Later in the program, guest pilots from which requires no CFR during its execution, may be an government and industry were invited to fly the NASA overly conservative pass/fail criteria for aircraft certification.

Twin Otter configured with a single full-span artificial ice shape attached to the leading edge of the horizontal INTRODUCTION tailplane. This shape represented ice formed due to a "Failed Boot" condit,on and was generated from tests in the Glenn Icing Research Tunnel on a full-scale tailplane Aircraft accident analyses have revealed ice model. Guest pilots performed longitudinal handling contamination on horizontal tailplanes as the primary tests, similar to those conducted by the NASA pilots, to cause of 16 accidents resulting in 139 fatalities'. Ice can lead to a premature tail stall that causes the aircraft to evaluate the ICT condst,on In general, all pilots agreed that longitudinal flying quaht,es were degraded as flaps pitch nose-down, which at low altitude may not be were lowered, and further degraded at high thrust recoverable prior to impact with the ground. Three settings. Repeat elevator doublets demonstrated International Tailplane Icing Workshops were convened reduced pitch damping effects due to ICT, which is a to appraise the collective experience on ice- characteristic that results in degraded flying qualities. contaminated tailplane stall (ICTS) from airframe Pilots identified elevator control force reversals (CFR) in manufacturers, operators, aviation regulators, and other zero-G pushovers at a 20 Q flap setting, a characteristic interested parties. Workshop attendees provided recommendations to reduce the number of accidents that fails the FAR 25 no CFR certification requirement.

However, when the same pilots used the Cooper-Harper attributed to ICTSo In response to some of these rating scale to perform a simulated approach and go- recommendations, the Federal Aviation Administration around task at the 202 flap setting, they rated the (FAA) requested the National Aeronautics and Space airplane as having Level I and Level II flying qualities Administration (NASA) to conduct research into the characteristics of ice-contaminated tailplane stall and to NASA/TM---2000-210356 1 Flow visualization on the tailplane was accomplished by develop techniques and methodologies to minimize the mounting a video camera to the bottom aft section of the hazard.

fuselage with a field-of-view of the lower left-hand horizontal tail. Yarn tufts were attached in a matrix of NASA developed the NASA/FAA Tailplane Icing Program spanwise and chordwise positions to visualize the flow (TIP), a four-year research effort utilizing a combination separation and reattachment in various zones on the of icing experts and test facilities. These included the tailplane.

NASA Glenn (formerly NASA Lewis) Icing Research Tunnel (IRT), The Ohio State University (OSU) Low Another unique video system was installed to record the Speed Wind Tunnel, and the NASA Glenn DeHavilland pilot actions during the maneuvers and also record the DHC-6 Twin Otter Icing Research Aircraft 2. The TIP view through the windscreen to obtain the pilots succeeded in: 1) improving the state of knowledge of perspective. These two views were merged onto a single iced tailplane aeroperformance and aircraft aero- screen format by using a screen splitter so that the upper dynamics 3.,. 2.6., 7, 2) developing analytical tools to help part of the screen showed the view through the discriminate tailplane sensitivity to icing s. ,, and 3) windscreen, while the lower part of the screen presented producing training aids to expand the awareness of the an over-the-shoulder look at the pilot controlling the ICTS aviation hazard 1°'" aircraft. This single screen presentation was annotated with engineering unit data to indicate the aircraft pitch and Although much of the TIP data has been reported, the roll angles, pilot forces, thrust coefficient and elevator flying qualities aspect of an ice-contaminated tailplane angle. This video signal was then recorded in SVHS (ICT) has not been fully discussed. Therefore, the format with an audio record of the intercom comments purpose of this report is to present NASA's findings on made by the pilots and engineers.

the longitudinal flying qualities of an ICT. The report is organized in the following sections: description of the research aircraft, instrumentation systems, ice shape used, flight test procedures, results of the evaluation, and conclusions drawn from the effort.

RESEARCH AIRCRAFT The NASA Icing Research Aircraft - N607NA (Figure 1) is a modified DeHavilland DHC-6 Twin Otter. It is powered by two 550 SHP Pratt and Whitney PT6A-20A turbine engines driving three-bladed Hartzell constant speed propellers. The flight controls are mechanically operated through a system of cables and pulleys. Control surfaces consist of elevator, ailerons, rudder, and wing flaps. The horizontal tailplane has a fixed stabilizer with an elevator and trim tab.

INSTRUMENTATION SYSTEMS The research data acquisition systems enabled measurements of the 1) aircraft dynamics, 2) tailplane aeroperformance, and 3) tailplane flow visualization and pilot visual and tactile cues. The aircraft dynamics data set included: inertial data, air data, control surface deflection data, pilot forces, and engine parameter data.

The tailplane aeroperformance data set consisted of three 5-hole flow probes to measure tail inflow angles and velocities and a pressure belt wrapped chordwise around the stabilizer and elevator to measure surface pressures (Figure 2).

Figure 1. NASA Glenn Icing Research Aircraft NAS A/TM--2000- 210356 2 FLIGHT TEST PROCEDURES The flight test maneuvers selected for this program were developed to acquire tailplane aerodynamic data for the TIP program, and to provide pilot evaluation scenarios for assessing the effects of the ICT condition on airplane flying qualities. Quasi-steady maneuvers, which included Flap Transitions, and Thrust Transitions, were used to isolate configuration and power effects on longitudinal stability and control. Dynamic maneuvers included; a.)

the zero-G pushover, to demonstrate a CFR condition and the effects of pilot technique on CFR tactile cues; and, b.) repeat elevator doublets, to demonstrate ICT effects on longitudinal pitch damping and elevator effectiveness. Lastly, an approach and go-around pilot evaluation task was flown with a 20 g and a 30 Q flap setting. The Cooper-Harper 12 pilot rating scale was used to rate the approach and go-around tasks for each flap Figure 2. Flow probe and pressure belt layout setting. This test allowed pilots to evaluate the effects of increasing flap angles on longitudinal flying qualities in a ICE CONTAMINATION structured manner. During the course of this particular exercise, pilots were also asked to associate their ratings Within the context of this report, the NASA Twin Otter for the 20 o flap cases with the observations they made was tested with an ice shape that represented a Failed while conducting the zero-G pushover maneuver in the Boot ice accretion (Figure 3). The Failed Boot shape same configuration. This provided an opportunity to resulted from a NASA Icing Research Tunnel (IRT) test compare results from a closed loop task (approach and on a full-scale Twin Otter tailplane model using FAR 25 go-around), and an open loop task (zero-G pushover) in Appendix C conditions. A mold of the IRT ice accretion assessing acceptable flying qualities. A description of was made; from which urethane casts were formed.

each of the flight test maneuvers follows: These casts retained the overall shape and rough texture of the actual ice accretion. Multiple casts of the Failed Flap Transitions (Figure 4-Figure 5) were flown to Boot Ice were made to cover the entire span of the evaluate the effect of flap position on longitudinal trim horizontal stabilizer's leading edge. No other surfaces and control characteristics. The aircraft was initially were contaminated.

trimmed at 85 KIAS with the flaps up, and a thrust setting equivalent to a CT=0.10. Flaps were then lowered from 0Q to 40L Trim speed was maintained without changing engine thrust setting or longitudinal trim setting, while noting the effect of increasing flap angle on stick force characteristics. The results reported herein are from NASA in house testing, and illustrate a comparison between the clean and contaminated tail for the same maneuver.

Constant airspeed thrust transitions (Figure 6) were flown to evaluate the effect of thrust on longitudinal trim and elevator control force characteristics. The example provided in this report shows a thrust transition that eventually resulted in a tail stall. Here, the aircraft was configured with the Failed Boot ice shape, and initially trimmed at 85 KIAS with the flaps set at 40L Power Failed Boot IRT Shape ° levers were gradually advanced and pitch attitude _ • V=135 kts, alpha=2.9 adjusted to maintain speed. Elevator control force and _,. • LWC=O.5g/m 3, MVD=20pl_ " ___ • "1"0=-4 ° C, time=22 min pitch characteristics were evaluated throughout the maneuver.

"..,-..__.

Figure 3. Failed Boot Ice Shape NASA/TM--2000-210356 3 Thrust Transitions, and Repeat Elevator Doublets were Pushover maneuvers (Figure 7-Figure 8) described in from NASA tests only. The results of the zero-G this report were flown with the Failed Boot ice shape, and Pushovers and Approach and Go-Around were from flaps set at 200 . Pilots were asked to perform the tests with both NASA and guest pilot as participants. The maneuvers from an initial level flight trimmed condition at following discussions are comments and perspectives 75 KIAS. A shallow dive was then entered to from the pilots who participated in each respective test.

approximately 100 KIAS at which point the pilot would initiate a 1.5G pull-up. At approximately 15 knots above Flap Transitions: Referring to Figure 4, the flap transition trim speed, the pilot would begin the pushover, using flown with a baseline (un-iced) tail demonstrates typical either a slow constant push on the elevator, or a step longitudinal statically stable characteristics. As flap angle input technique. The objective of the task was to achieve increased, elevator push force (Yoke Force in chart) a zero-G condition as the aircraft passed through the increased to about 30 Ibs. as the flaps moved from 5F=0- level flight attitude at trim speed. Control Force Reversal 10Q. As the flaps moved dF=10-40 _, the elevator push (CFR) was then qualitatively assessed by tactile force decreased to about 10 Ibs., but always remained a feedback in the elevator control column. Post flight data push force. However, with the failed boot ice shape, analysis of elevator deflection angle (3E) and stick force Figure 5, the elevator force reversed from a peak push (FYE) provided verification to the pilot comments.

force of about 30 Ibs. at 6F=7 _, to a pull of about 30 Ibs.

at 8F=40 -°.This force feedback to the pilot is indicative of Repeat Elevator Doublet maneuvers (Figure 9-Figure 10) a large change in hinge moment, due to the change in were flown with the Failed Boot ice shape with flaps at pressure distribution on the underside of the elevator. As 200 and 30 g. The aircraft was initially trimmed for level the wing flaps reached 35 Q,the elevator began a pulsing flight at 75 KIAS. A sharp series of repeat elevator motion, which the pilot could not arrest. Pilot elevator doublets, each held for approximately one second, were forces were also oscillatory. Videos of tufts on the input by the pilot. Pitch response and damping underside of the tailplane confirmed the presence of an characteristics were observed throughout the maneuver, unsteady separation bubble that covered approximately along with tactile feedback in the control column.

25% of the chord from the leading edge. Level flight in Damped or divergent response was assessed as the this configuration was maintainable, but the pulsation in criteria for acceptable flying qualities.

the control column made precise attitude control very difficult, and longitudinal trim was not possible. In Simulated approach and go-around maneuvers (Figure addition, there was a strong non-linear elevator control l l-Figure 14) were flown to assess the effects of force gradient, which resulted in high pull forces when taiiplane contamination on the performance of this task.

The task was flown "heads down", at altitude, with the making nose-up corrections and a strong negative pitch- over tendency when correcting towards nose-down. With Failed Boot ice shape and flaps set to both _;F = 20 ° and full flaps (_F=40g), longitudinal handling qualities for 30 °. During the maneuver, the Flight Test Engineer maintaining a level flight task were not acceptable.

commanded course and glide slope corrections, forcing the pilot to change both rate of descent (ROD) and heading every 20 seconds, while maintaining a constant 1.3 Vs velocity. Heading changes of +5° off a reference heading, and RODs of 0, 500, or 1000 ft/min were commanded. Pilots were required to maintain ROD's within +100 ft/min of target. The idealized flight paths are represented by the dashed lines in Figure 11 through Figure 14. The 20 sec intervals required the pilot to make fairly aggressive control and thrust inputs. At the conclusion of the simulated approach, a go-around was , ] 4O commanded requiring takeoff thrust while raising the nose to maintain airspeed. After the pilot established a

" !2o

positive rate of climb, the flaps were raised. Upon completion of the maneuver, the pilot rated both the /- - .

approach and go-around task, using the Cooper-Harper .Io _ handling qualities rating scale (Figure 15).

EIdeg) ! 20 RESULTS AND DISCUSSION 5 _0 15 20 25 30 35 40 Ttme (=) The results and discussions that follow are referenced to specific test points conducted during the course of the Figure 4. Flap transition - baseline, V=85KIAS program. Figures of Flap Transitions, Constant Airspeed NASA/TM--2000- 210356 4 4O 3O ' ' ' ' 75 _ 0,05 > 65 { ' 55 ' 0 5 ................ --delF(deg) 4t .

4 _ n

t

200 . . . ; . , .

5 10 15 20 25 30 35 40 Tirol (e) 100 - -' ....... - - -,- - , , Figure 5. Flap transition - Failed Boot Ice, V=95KIAS o t Constant Airspeed Thrust Transition: The constant I 2s2 _i 0S airspeed thrust transition provided one of the more 0 t I I _ I I l • --T_,: -0.5 * surprising results of the test program. Referring to Figure ...... ii 6, pilot elevator force (FYE in chart) increased as thrust was applied. Throughout the thrust application, the Flight -20 Test Engineer reported a growth in the separation bubble -30 -40 as seen from the video of the tufts on the underside of the tailplane. Elevator pulsing became severe, and pitch 720O control became increasingly more difficult to maintain.

. _ . . . . . . . . _ 1 _ _ L r _ 4 0 Approaching moderate thrust, elevator force rapidly built 6500 to approximately 100 Ibs., followed by a hard negative 0 5 10 15 28 25 30 35 40 45 time 50 pitch rate as the horizontal tail stalled. Aft control column was immediately applied, and elevator force reached Figure 6. Thrust transition - Failed Boot ice, 8F=40 g about 170 Ibs. Thrust was simultaneously reduced to idle, and the flaps raised to break the stall. The aircraft different control techniques; and 2.) Test pilots could was recovered from an approximate 40 Q nose-down compare the zero-G pass/fail criteria against a task- attitude, and returned to level flight. This maneuver oriented flying qualities evaluation in the same demonstrated the effects of thrust on tailplane lift configuration. The following discussion will focus on characteristics. Since the thrust line of this aircraft is results obtained in the first case. The second case will be above the center of gravity, increased thrust caused a discussed with the results of the task-oriented maneuver.

nose-down pitching moment, which further increased the For some tests, the CFR or no CFR assessment can be trimmed lift requirements of the horizontal tailplane. The strictly a judgement call on the part of the test pilot.

ice shape reduced the tail lift capability to the point where Figure 7 & Figure 8 show the results of two widely a stall ensued as elevator was applied to trim off the different techniques in performing the zero-G pushover effect of increased engine thrust.

maneuver. Figure 7 is the result of a slow smooth pushover, while Figure 8 is the result of an aggressive Pushover Maneuvers: Zero-G pushover maneuvers are step function input. The target speed at the zero-G flown to identify elevator Control Force Reversal (CFR) condition in both cases was 75 KIAS. It is apparent that characteristics with an ice-contaminated tailplane. The CFR occurred in both cases, i.e., the control force (Stick certification criteria at zero-G requires that no CFR Force in chart) crossed the trim point before the elevator occur, and that the aircraft return to trimmed flight upon was deflected trailing edge up. Moreover, the onset of release of the elevator during the maneuver. This is an CFR occurred at approximately the same G-level, important test, which if failed, can result in the imposition regardless of technique. Pilots flying the maneuvers, of reduced flap angles for approach and landing, however, indicated that they could do a better job in decreasing landing performance. Zero-G maneuvers detecting the onset of CFR approaching the zero-G were therefore flown in the TIP Guest Pilot Program for condition using the slower, more gradual entry, than the two purposes: 1.) They offered test pilots the opportunity more aggressive step function. Pilots indicated that to compare their subjective evaluation of CFR against tactile feedback assessments over the relatively short NAS A/TM--2000- 210356 5 10-second interval. In the clean case, note that the two-second interval experienced during the step inputs aircraft response was damped within approximately 0.5 were harder to accurately sense than the feedback second of the initial input for each interval flown.

experienced over the slower, 5 sec entry. This result may However, in the ICT case, the response remained be indicative of the need to ensure that qualitative divergent until the pilot applied an opposite elevator assessments of CFR require a consistent technique on input• With ICT, aircraft was dynamically unstable, but the part of test pilots performing the evaluation. Where controllable. In this condition, the aircraft could be safely data systems are used to record the required flown, providing that control inputs were very small, and parameters, pilot technique is of lesser importance.

resulted in relatively low vertical acceleration rates. The data shown here resulted in vertical acceleration rates on g754po27 dF = 20 Pilot #C4 l _,'_ ................................................................................................................................ I_-_,o,L_jc__.. r ,o the order of +/-0.5G.

I This test technique was also applied to cases where the tail was configured with the Failed Boot condition. In Figure 10, repeat doublets for the 30 g flap setting show that the pitch response was undamped, but damped with flaps at 20L From a flying qualities standpoint, the aircraft was stable and controllable with flaps set at 30L lc ..................................................................................................................... I, ................................................. _o at low thrust settings, providing that pitch rates did not introduce vertical accelerations exceeding +/-0.25G. On the other hand, with flaps at 200 , the aircraft was stable Figure 7. Zero-G pushover- Failed Boot ice, slow and controllable at all thrust settings provided that pitch input, 6F=20 g rates did not introduce vertical accelerations exceeding +/-0.5G. Therefore, the elevator doublet maneuver is an 9753po05 dF=20 Pilot#C1 effective means of assessing stability and controllability, and correlates with pilot handling assessments of the approach task described in the next section of this o report.

o" Baseline, dF = 30, V = 1.6 Vs 4_ s_ _z _3 54 55 5s _1 se 5g so _o ii_e (s) Figure 8. Zero-G pushover - Failed Boot ice, step input, 6F=20 ° Elevator Doublets: Elevator doublets provided a means o -,,- i i -- !!i for comparing pitch response characteristics of the Twin Otter between a clean and an ice-contaminated tailplane OCT). A damped response indicated dynamic 0 5 10 t5 longitudinal stability, and an undamped response time (s) indicated divergence. In the undamped case, controllability was apparent if the aircraft responded in S & C,dF=30, V=1.6Vs the proper sense to elevator input. Poor or no pitch damping makes the aircraft difficult to control precisely.

When performing a pitching maneuver, pitch damping 15 lends a measure of predictability to the piloting task, and in turn, has a large bearing on the pilot's impression of the aircraft's flying qualities. To illustrate, Figure 9 compares pitch response characteristics between a clean and ICT condition with flaps set at 30L Note: The -5 ICT condition in this particular example was a special -10 artificial shape (S&C ice) that provided a more degraded -15 stability and control characteristic than the Failed Boot 0 5 10 15 case. The purpose for introducing this configuration here time (s) is to clearly illustrate the difference between damped and undamped characteristics. In both the clean and S&C ice Figure 9. Elevator doublet comparison - S&C Ice cases, a repeat pitch doublet was applied within a NASA[I'M--2000-210356 responding to commands. Figure 11 and Figure 12 Failed Boot, dF:20, V: 1.3Va = 75kts display results from the 20 o flap cases. Handling quality (9746ED11 ) ratings (HQR) from each pilot are summarized in Figure 16 for the given portion of the task flown. With flaps set at 200, descent and heading tracking was readily accomplished during the approach phase, and all pilots rated the airplane Level I, meaning that the task could be performed with minimal pilot compensation. This rating correlated with the results of the repeat elevator doublets (Figure 10-upper), which showed that in this configuration, the airplane was stable, controllable, and that response to elevator input was well damped. Note -10 5 tO lS that during the elevator doublets, G-levels were time (e) approximately +/- 0.5G, and thrust was set at CT=0.11, which was approximately the same CT used for the level Failed Boot, dF=30, V= 1 +4V$ = 75k15 flight portion of the simulated approach task. The go- (9746E D15) around task, however required thrust settings of approximately C,=0.24. This configuration and thrust setting induced power effects that reduced flying qualities to Level I1. In summary, three pilots rated the go-around task as having mildly unpleasant deficiencies, one rated it as having minor but annoying deficiencies, and one rated it as having very objectionable deficiencies. Here pilot ratings indicated that minimal to extensive

.i

compensation was required to achieve the desired performance, although stability and controllability were never in question.

The same approach and go-around tasks were then Figure 10. Elevator doublet comparison - Failed Boot flown with flaps set to 30L Figure 13 and Figure 14 display pilot performance in the 300 flap cases. Four Handling Assessment of an Approach and Go-Around pilots rated the airplane Level II, i.e. HQR's from 3 Task: through 6, while one rated it a Level III with a HQR of 8.

Pilots who felt that the airplane fell within Level II criteria Five pilots representing industry and NASA were asked seemed to agree that control buffet was quite evident, to evaluate the approach and go-around landing tasks precise tracking was difficult, and required pilot for flap settings of 20 o and 30 Q with the Failed Boot ice compensation was moderate to extensive. The pilot who shape. The Cooper-Harper (C-H) rating scale (Figure 15) provided an HQR of 8 (Level III) appeared to have was used as the rating criteria. Handling Quality Ratings reached task saturation while performing the maneuver.

(HQR) were assessed to determine flying qualities for Comparing these results to the elevator doublets in the both the approach and go around tasks. Based on these 30 _ flap configuration, (Figure 10-bottom), we note that ratings, the configuration tested was assessed as having the aircraft displayed weak or no damping in response to either Level I (minor deficiencies and no improvements elevator inputs. In this case, it is evident that HQR's do reflect the poor stability and control characteristics required), Level II (deficiencies require improvement), or Level III (deficiencies require mandatory improvement) shown in the doublet maneuvers. Again, G levels reached in the doublet maneuvers were +/- 0.5G. All flying qualities.

pilots rated the airplane a Level III while performing the The performance and tracking accuracy for two go-around maneuver with flaps set to 30 _. Here, the representative pilots are shown relative to the flap addition of maximum thrust severely degraded elevator configuration and task segment in Figure 11- Figure 14. authority as pilots struggled to execute a precise pitch The dashed line in these figures represents the tracking task. Pilot comments indicated that the maneuver was very difficult to perform, elevator buffet commanded change in either descent rate or heading, was excessive, intense compensation was required, and and provides no adjustment for pilot reaction time, Pilots were asked to be as aggressive as possible in one pilot felt he could not control the airplane at all.

NASA/TM--2000-,. 10356 7 , --hdot (fpm) i hd0f (Ip_]-- i i Ideal (fpm) Rate of Decent i I IIdeal(fpm) Rate of Decent i .... Go Around 1500 7-- .................................................................................. _'-i .... Go Around I _ Simulated r_ 1000i'_I_I Approach _ 11_ /_ 1 500 t ' "q " " -soo I '

- oo 7." ]

ii .1ooo L_ _ _I !

-1000 I _ ..,:.".'.'.'.'.'.'.'.'_ - I-. _W_ GO Around Go Around .i5oo ............................................................................ : ......................... i ........................ .... .19oo J .............................................................................. I o 15 3o ,5 ,o ,5 , IO, 0 20 40 :60 80 t00 120 140 160 i Velocity (kte) Velocity (kte) ] 9o, I l

.o°° ........ ]

70 _ I 70 ; i 60 _- ; i ] 60 "' "} 0 15 30 45 60 75 90 105 0 20 40 60 80 100 120 140 160 !

__Rel Psi (deg) Heading i _ _ Ideal (deg) 15 _- ................................... "-_ .... Go Around L 94 I ot ---i -5 4 !

-io 4 . 1 -15 J -1° 1 . i -15 1 .................................................................. • ................

-20 • ................................................

0 20 40 60 80 100 120 140 160 0 15 30 time (e) J Figure 11. Approach & Go-around, 8F=20 _, pilot I Figure 13. Approach & Go-around, 5F=309, pilot I I 1 _hdot (fpm) Rate of Decent i _hdot (fpm) __ i Ideal (fpm) Rate of Decent ! -- __ ideal (fpm) I ..... Go Around I . . .Go Around l ,,oo T .................................. S,mu,ated ..................... ] .......... IV _ I 1000 ] _ Approach

,oooi -- .o,o.. /

= L 5oo f_ : , 1500 ............................. S Im u laleo:: ...... _ I' 1 I_ _ o _ _ +- -_ i ', o_ , ;- ! :--, 9oo /_ "1_" -1000 L. _ _l L.__ Go Around

! 1

-1500 -" = i -1500 . . . . . . . . . . . . . . . . . . . . .

83 100 120 t40 160 20 40 60 80 100 120 _40 160 0 20 4C [ ¥1_¢_1 lill) Velocity {kls) g0 .

80 ..... ............ --_ _ 80 -- i 60 , ,,,,,,i 60 !

0 20 40 60 80 100 120 140 160 0 20 4C" t 8C: I00 120 140 !

i --psi - rel (dog) Heedmg I --psl - rel (deg) Heading Ideal (deg) i i I Ideal (deg) I .... Go Arodnd i .... Go Around lO .................................................... ; ............... I -5 -I0 -15 -20 -10 ± 0 20 40 60 80 I00 120 140 0 20 40 60 80 100 120 140 160 Figure 14. Approach & Go-around, 6F=30 °, pilot 3 Figure 12. Approach & Go-around, 5F=20 °, pilot 3 NASA/TM--2000-210356 unstable dynamic responses. These responses were relatively easy to control. They provided a good means for assessing acceptable flying characteristics, based on pitch damping and control effectiveness. The zero-G maneuvers, however, were more difficult to perform consistently. Pilot comments supported the fact that tactile cues for CFR could be masked to a degree by pilot technique, however the data showed that pilot technique was not a factor on a CFR. Using a properly structured task-oriented methodology, which in this case was an approach and go-around task, an accurate assessment of adequate flying qualities was made. In the 20 _ flap cases where pitch response was well damped, pilot task ratings showed that the aircraft met Level 1 flying qualities criteria. When performing the more severe Figure 15. Cooper-Harper HQ Rating Flow Chart go-around maneuver, the aircraft still met Level II criteria.

However, the same configuration did not pass the no- CFR requirement when a zero-G pushover was HQR for Tracking Task performed. Although the zero-G pushover maneuver may provide a rather conservative screening test for ICTS, the potential restrictions it imposes on the aircraft flight envelope can be excessive.

4, m > REFERENCES _== =1 [] I. Dow, J.P. Sr., FAA Small Airplane Directorate, private communication 2. NASA/FAA Tailplane Icing Program Overview, T.P.

Ratvasky, J.F. Van Zante, J.T. Riley, NASA TM-1999- 208901, AIAA-99-0370, Jan, 1999 Sirn Appr Go Around Sim Appr Go Around 3. DHC-6 Twin Otter Tailplane Airfoil Section Testing in the 2 3 3 7 • 1 Ohio State University 7'X10' Wind Tunnel. D.W. Hiltner, 2 3 6 8 • 2 M. McKee, K.B. La No_, G. Gregorek, NASA CR-209921 3 6 8 10 Vol. 1, publishing pending 2 3 6 8 O 4 4. Additional Testing of the DHC-6 Twin Otter Iced Airfoil 2 4 4 8 [] 5 Section at the Ohio State University 7'X10' Low Speed 2.2 3.8 5.4 8.2 Wind Tunnel. G. Gregorek, J. Dreese, K.B. La No_, NASA _F = 20 ° 8F = 300 CR-209921 Vol. 2, publishing pending 5. NASA/FAA Tailplane Icing Program: Flight Test Report.

T.P. Ratvasky, J.F. Van Zante, A. Sim, NASA TP-209908, Figure 16. HQR for Approach and Go-Around Tasks DOT/FAA/AR-99/85, March, 2000 6. Investigation of Dynamic Flight Maneuvers With an Iced CONCLUSION Tailplane, J.F. Van Zante, T.P. Ratvasky, NASA TM- 208849, AIAA-99-0371, Jan. 1999 "7. In-Flight Aerodynamic Measurements of an Iced The NASA Twin Otter Icing Research Aircraft provided Horizontal Tailplane, T.P. Ratvasky, J.F. Van Zante, an excellent test vehicle for investigating the effects of NASA TM-208902, AIAA-99-0638, Jan. 1999 tailplane icing on longitudinal flying qualities. Artificial ice 8. A Nonlinear Aircraft Simulation of Ice Contaminated shapes used on the tailplane caused a progressive Tailplane Stall. D.W. Hiltner, Ph.D. Dissertation, 1998 reduction in longitudinal static stability as wing flaps were 9. An Evaluation of an Analytical Simulation of an Airplane with Tailplane Icing by Comparison to Flight Data. D.W.

lowered, a characteristic which was manifested by Hiltner, NASA CR, publishing pending.

inability to trim, and a tendency to diverge from a desired 10. Tailplane Icing. NASA Glenn Research Center, video flight path following an elevator input. The condition was tape, 1998. http://icebox.lerc.nasa.gov/Education._./Vjde_ also accompanied by a pulsing of the control column, 1]. Icing for Regional and Corporate Pilots. NASA Glenn which was the result of a highly unsteady separation Research Center, video tape, 1999.

bubble on the underside of the tail that grew as a http://icebox.lerc.nasa..qov/Education/Videos/ 12. Learjet Syllabus and Background Material for the U.S. Air function of increasing flap angle. Aggressive pilot Force/U.S. Navy Test Pilot School Programs. J. Ball, C.

elevator inputs, such as those used in performing repeat Berthe, S. Buethe, L. Knotts, M. Parrag, Feb 1994 elevator doublets, would further aggravate the unsteadiness of the condition, and result in longitudinally NASA/TM--2000-210356 9 REPORT DOCUMENTATION PAGE Form Approved OMB No, 0704-0188 m Public reporting burden for this collection of information is estimated to average t hour per response, including the time for reviewing instructions, searching existing data sources, gathering and malntainlng the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Fleports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED September 2000 Technical Memorandum i 4. TITLE AND SUBTITLE S. FUNDING NUMBERS Flying Qualities Evaluation of a Commuter Aircraft With an Ice Contaminated Tailplane WU-548-21-23-00 6. AUTHOR(S) Richard J. Ranaudo, Thomas P. Ratvasky, and Judith Fuss Van Zante 8. PERFORMING ORGANIZATION 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) REPORT NUMBER National Aeronautics and Space Administration John H. Glenn Research Center at Lewis Field E-12405 Cleveland, Ohio 44135-3191 10. SPONSORING/MONITORING 9. SPONSORING/MONITORING ,&GENCY NAME(S) AND ADDRESS(ES) AGENCY REPORT NUMBER National Aeronautics and Space Administration NASA TM--2000-210356 Washington, DC 20546-0001 SAE 2000-01-1676 11. SUPPLEMENTARY NOTES Prepared for the General Aviation Technology Conference and Exposition (GATC) sponsored by the Society of Automotive Engineers, Wichita, Kansas, May 9-11, 2000. Richard J. Ranaudo, Bombardier Aerospace, 1 Learjet Way, Wichita, Kansas 67277; Thomas P. Ratvasky, NASA Glenn Research Center; Judith Fuss Van Zante, Dynacs Engineering Company, Inc., 2001 Aerospace Parkway, Brook Park, Ohio 44142. Responsible person, Thomas P. Ratvasky, organization code 5840, 12a. _'I_II_I_I_P_,,&ILABILITYSTATEMENT 12b. DISTRIBUTION CODE Unclassified - Unlimited Subject Categories: 08, 05 and 02 Distribution: Nonstandard This publication is available from the NASA Center for AeroSpace Information, (301) 621-0390.

13. ABSTRACT (Maximum 200 words) During the NASAfFAA Tallplane Icing Program, pilot evaluations of aircraft flying qualities were conducted with various ice shapes attached to the hori- zontal tailplane of the NASA Twin Otter Icing Research Aircraft, Initially, only NASA pilots conducted these evaluations, assessing the differences in longitudinal flight characteristics between the baseline or clean aircraft, and the aircraft configured with an Ice Contaminated Tailplane (ICT). Longitudinal tests included Constant Airspeed Flap Transitions, Constant Airspeed Thrust Transitions, zero-G Pushovers, Repeat Elevator Doublets, and, Simulated Approach and Go-Around tasks. Later in the program, guest pilots from government and industry were invited to fly the NASA Twin Otter configured with a single full-span artificial ice shape attached to the leading edge of the horizontal tailplane. This shape represented ice formed due to a "Failed Boot" con- dition, and was generated from tests in the Glenn Icing Research Tunnel on a full-scale tailplane model. Guest pilots performed longitudinal handling tests, similar to those conducted by the NASA pilots, to evaluate the ICT condition. In general, all pilots agreed that longitudinal flying qualities were degraded as flaps were lowered, and further degraded at high thrust settings. Repeat elevator doublets demonstrated reduced pitch damping effects due to ICT, which is a characteristic that results in degraded flying qualities. Pilots identified elevator control force reversals (CFR) in zero-G pushovers at a 20 ° flap setting, a characteristic that fails the FAR 25 no CFR certification requirement. However, when the same pilots used the Cooper-Harper rating scale to perform a simulated approach and go-around task at the 20 ° flap setting, they rated the airplane as having Level I and Level II flying qualities respectively. By com- parison, the same task conducted at the 30 ° flap setting, resulted in Level II flying qualities for the approach portion, and Level III for the go-around portion.The results of this program indicate that safe and acceptable flying qualifies with an ICT condition, can be effectively assessed by task-oriented pilot maneuvers. In addition, other maneuvers such as repeat elevator doublets provide good qualitative and quantitative assessments of pitch damping and eleva- tor effectiveness, which are characteristics that correlate well with pilot task ratings. The results of this testing indicate that the FAR 25 zero-G pushover ma- neuver, which requires no CFR during its execution, may be an overly conservative pass/fail criteria for aircraft certification.

15. NUMBER OF PAGES 14. SUBJECT TERMS 16. PRICE CODE Aircraft icing; Tailplane icing; Stability and control; Flying qualities A03 20. LIMITATION OF ABSTRACT 19, SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 17. SECURITY CLASSIFICATION OF ABSTRACT OF THIS PAGE OF REPORT Unclassified Unclassified Unclassified Standard Form 298 (Rev. 2-89) NSN 7540-01-280-5500 Prescribed by ANSI Std. Z39-18 :298-102