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NASA/TM-2000-209024
Flying Quality Analysis of a JAS 39 Gripen
Ministick Controller in an F/A-18 Aircraft
John F. Carter and P. C. Stoliker NASA Dryden Flight Research Center Edwards, California August 2000 The NASA STI Program Office...in Profile CONFERENCE PUBLICATION.
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NASA/TM-2000-209024
Flying Quality Analysis of a JAS 39 Gripen
Ministick Controller in an F/A-18 Aircraft
John F. Carter and P. C. Stoliker NASA Dryden Flight Research Center Edwards, California National Aeronautics and Space Administration Dryden Flight Research Center Edwards, California 93523-0273 August 2000
NOTICE
Use of trade names or names of manufacturers in this document does not constitute an official endorsement of such products or manufacturers, either expressed or implied, by the National Aeronautics and Space Administration.
Available from the following: NASA Center for AeroSpace Information (CASI) National Technical Information Service (NTIS) 7121 Standard Drive 5285 Port Royal Road Hanover, MD 21076-1320 Springfield, VA 22161-2171 (301) 621-0390 (703) 487-4650 FLYING QUALITY ANALYSIS OF A JAS 39 GRIPEN MINISTICK CONTROLLER IN AN F/A-18 AIRCRAFT John F. Carter* and P. C. Stoliker ?
NASA Dryden Flight Research Center Edwards, California CHR Abstract Cooper-Harper rating CSA control stick assembly NASA Dryden conducted a handling qualities experiment using a small displacement centerstick KCAS knots calibrated air speed, mni/hr controller that Saab-Scania developed for the JAS 39 gain for compensation model, deg/deg Gripen aircraft. The centerstick, or ministick, was Kp gain for pitch rate transfer function, deg mounted in the rear cockpit of an F/A-18 aircraft. Kq Production support flight control computers (PSFCC) lift due to angle of attack change, 1/sec provided a pilot-selectable research control system. The Lc_ objectives for this experiment included determining LOES low order equivalent system whether the mechanical characteristics of the centerstick NOF number of frequency points controller had any significant effect on the handling qualities of the F/A-18, and determining the usefulness Nz load factor, g of the PSFCCs for this kind of experiment. Five pilots PSFCC production support flight control evaluated closed-loop tracking tasks, including echelon computers and column formation flight and target following.
Cooper-Harper ratings and pilot comments were Q pitch rate, deg/sec collected for each maneuver. This paper describes the s Laplace operator test system, including the PSFCCs, the Gripen centerstick, and the flight test experiment. The paper SRA Systems Research Aircraft presents results of longitudinal handling qualities compensator lag time constant, sec maneuvers, including low order equivalent systems, Tlag compensator lead time constant, sec Neal-Smith, and controls anticipation parameter Tlead analyses. The experiment showed that, while the VDC volts direct current centerstick controller provided a different aircraft feel, few handling qualities deficiencies resulted. It also ct angle of attack, deg demonstrated that the PSFCCs were useful for this kind difference in gain between actual and of investigation. Again LOES values, dB Nomenclature Aphase difference in phase between actual and LOES values, deg AC alternating current short period damping CAP controls anticipation parameter pitch attitude, deg equivalent system time delay, sec *Aerospace Engineel; Member AIAA.
compensator time delay, sec ?Aerospace Engineer. T'comp Copyright © 2000 by the American Institute of Aeronantics and short period frequency, rad/sec O)sp Astronautics, Inc. No copyright is asserted in the United States _mder Title 17, U.S. Code. The U.S. Government has a royalty free license to exercise all rights under the copyright clahned heroin for Govern mental proposes. All other rights are reserved by the copyright owner.
American Institute of Aeronautics and Astronautics Introduction target tracking were compared with selected handling qualities criteria.
Over the years, many types of pilot control sticks have Frequency responses of Gripen stick position to been used in fighter class aircraft. Each type has aircraft pitch rate were calculated from flight data and different mechanical properties, some of which have led then fit to a low order equivalent system (LOES) to problems with aircraft operation. Early development approximation. 4'5 This LOES analysis used a fixed lift of alternate controllers for fighter class aircraft due to angle of attack, Lc_, calculated from the NASA demonstrated some difficulties with fixed, force- command sidestick controllers. 1 Dryden nonlinear F-18 simulation. Estimated aircraft parameters from the LOES were used in controls anticipation parameter (CAP) 5 and Neai-Smith The aircraft company Saab-Scania (Link6ping, analyses. 6 These handling quality criteria were used to Sweden) designed a pilot control stick for the JAS 39 Gripen fighter/attack airplane. This stick is a small- estimate flying qualities levels (1, 2, and 3) for the aircraft independent of the Gripen stick. These displacement, position-command controller mounted in estimated ratings were compared with the actual pilot the center of the cockpit on a raised pedestal. This controller differs from the traditional F/A-18 control ratings. This paper discusses differences in the ratings in relation to pilot workload and the mechanical properties stick, which has large movement and pivots of the Gripen stick.
approximately at the floor of the cockpit. The center mounting of the Gripen control stick also ergonomicaily Use of trade names or names of manufacturers in this differs from the side-mounted force-command control document does not constitute an official endorsement of sticks found in aircraft such as the F-16 and F-22 such products or manufacturers, either expressed or fighters.
implied, by the National Aeronautics and Space Administration.
NASA Dryden Flight Research Center conducted an experiment to determine whether the mechanical Aircraft and System Description properties of the Gripen control stick would produce any change in handling qualities for an F/A-18 aircraft.
System Research Aircraft For the experiment, NASA Dryden mechanics mounted the Gripen stick in the rear cockpit of an F/A-18B The flight test used the F/A-18B aircraft known as the model. The Gripen stick interfaced with the F/A-18 Systems Research Aircraft (SRA) 7 (fig. 1). NASA aircraft with the use of the production support flight Dryden has used this two-seat aircraft for numerous control computers (PSFCC). 2 A quadruplex-redundant flight experiments of advanced systems such as flight control computer system controlled the F/A-18.
conformal load-bearing antennas, electric actuators, and The PSFCCs are F/A-18 flight control computers with a in-flight Schlieren photography. This aircraft has an research processor interfaced with all four channels.
extensive research instrumentation suite along with When selected, the research processors have full telemetering capability. Because the Gripen controller authority of all F/A-18 aircraft control surfaces. Each was mounted in the rear cockpit, the front seat pilot, research processor allowed for direct analog input from known as the safety pilot, performed all the engagement an external device. The Gripen stick connected directly and disengagement tasks of the research processors.
with the research processors via these analog inputs.
For this experiment, the aircraft was equipped with From February 23 to March 2, 1999, NASA Dryden PSFCCs. The PSFCC design uses a research processor conducted a brief flight-handling qualities test campaign in addition to the baseline quadraplex F/A-18 flight consisting of six flights. During these six flights, five control computers. If the aircraft were to exceed certain pilots evaluated both open- and closed-loop tasks. The performance limits or to suffer a system failure, the performance of open-loop tasks qualitatively measured PSFCC would automatically disengage the research aircraft response with the Gripen stick. Open-loop processor and revert to the baseline flight control maneuvers included doublets and frequency sweeps.
system. The safety pilot also has the ability to manually Closed-loop maneuvers included bank angle captures, disengage the research flight control system.
pitch attitude captures, echelon (wing) formation flight, For this flight experiment, the research flight control column formation flight, and target following. To acquire Cooper-Harper ratings 3 (CHR) and pilot laws replicated the F/A-18 baseline control laws using the Gripen stick pitch and roll commands in place of the comments, researchers developed adequate and desired standard F/A-18 control inputs. No other changes were criteria for each task. Data from the formation flight and American Institute of Aeronautics and Astronautics Figure 1. Systems Research Aircraft.
made to the baseline F/A-18 control laws, and the The control grip, or ministick, used position feedback baseline F/A-18 stick shaping and software breakouts as the control variable with the pivot point just below were used. Figure 2 shows the interface between the the handgrip in the pedestal. For roll control, the grip Gripen control stick and the PSFCCs in the SRA pivoted approximately 7 ° left and right. For pitch aircraft. The Gripen stick connects directly with the control, the ministick could be deflected 7 ° forward and research processors. Shared memory called a dual-port 15 ° aft, with an increase in force gradient at random access memory, between the research approximately 11°. For standard flight control processors and the baseline F/A-18 control law operations, the pitch and roll commands were processors, received all other necessary information. transmitted to the flight control computers as modulated This shared memory provided a separation between the high-frequency AC signals.
two control system processors for fault isolation of the The baseline roll stick software deadbands were research processor. Previous publications 2, 8 show 0.025 inches (in.) for the F/A-18 and 0.20 ° for the details on the operation of the PSFCCs.
Gripen. Software scaling matched full stick deflections of the ministick with full-scale deflections of the Gripen JAS 39 Control Stick Description standard F/A-18 control stick (_+7° of ministick equalled Saab-Scania developed the control stick assembly •+3 in. of standard F-18 stick). With the scaling (CSA) for the JAS 39 Gripen, a lightweight fighter described, the Gripen roll deadband equates to 0.086 in.
aircraft. The CSA consisted of a fixed pedestal that housed the triplex redundant electronics, with a fighter- Figure 4 compares the approximate gearing for the style handgrip mounted on top. Unlike other small roll stick as a percentage of full stick deflection. The displacement or force controllers typically mounted to baseline pitch stick software deadbands are 0.060 in. for the side of the pilot, the CSA was center-monnted the F/A-18 and 0.20 ° for the Gripen. With the scaling (fig. 3). This setup placed the hand controller in a described above for full-scale pitch deflections, the position between the pilot's legs similar to that of the Gripen pitch deadband equates to 0.071 in. The large displacement stick controllers nominally approximate gearing for the pitch stick was not associated with fighter aircraft. The software deadband compared, because the Gripen uses a normal acceleration command while the F/A-18 uses a and stick gearing were left unchanged from the standard F/A- 18 configuration. command of blended pitch rate and normal acceleration.
American Institute of Aeronautics and Astronautics Ministick Ministick pitch and roll commands pedestal assembly (analog input) Deft box Single channel of pitch and roll commands Aircraft Actuator commands flight control feedback switch Quad redundant flight control computers 000103 Figure 2. Engaged ministick system. Figure 3. Gripen stick installation.
JAS 39 Gripen m m F/A-18 -- f __ // __ // Roll rate 50 command, 0 deg/sec -50 -100 -150 J -200
I I I I
-250 -100 -50 0 50 100 Roll stick deflection, percent of full scale 000105 Figure 4. Comparison of stick gearing for roll commands for the Gripen and F/A- 18.
American Institute of Aeronautics and Astronautics For this experiment, researchers used a demodulator For the initial engagement flight, each pilot flew buildup activities such as engagement/disengagement box to read a single channel of the three high-frequency checks and gentle maneuvering. After flying an initial AC signals for pitch and roll commands and to convert it engagement, each pilot flew maneuvers (such as into a DC signal. This resulted in the roll command doublets, bank angle captures, and pitch angle captures) being scaled to -3.55 volts direct current (VDC) for full to become familiar with the characteristics of the stick.
left stick and +3.63 VDC for full right stick. In the pitch axis, full forward stick resulted in a signal -3.56 VDC.
Flight Test Execution Full aft stick resulted in a +7.78 VDC signal. Analog inputs sent these single-channel signals to all four The following information is from transcriptions of channels of the F/A-18 flight control system.
the pilot comments from the mission flight recordings for each maneuver. Some information was lost because Flight Test Procedure sections of the voice recordings were difficult to understand. Selected pilot comments provide The six flights performed between February 23 and comparisons and correlation between the CHRs and the March 2, 1999 used five pilots to conduct the evaluation.
handling qualities analyses. The pilots used the Telemetered data included aircraft surfaces, rates, questionnaire in table 1 to generate the handling accelerations, Euler angles, angle of attack, and health qualities ratings. CHRs 1, 2, and 3 indicate level 1 and status of the aircraft and PSFCC system. Strip handling qualities. This level is characterized by flying charts displayed parameters for aircraft dynamics, and qualities clearly adequate for the designed task, using computer display pages in the control room displayed only minimal compensation. CHRs 4, 5, and 6 indicate parameters for aircraft and PSFCC system status.
level 2 handling qualities. These handling qualities are adequate to accomplish the designed task, but with an Formation flying criteria used visual features of the increase in pilot workload, or decrease in task lead aircraft, such as maintaining the formation flying effectiveness, or both. CHRs 7, 8, and 9 indicate level 3 light of the lead aircraft within the blue stripe on the handling qualities, with excessive pilot workload or fuselage of the lead aircraft. For the tracking tasks, a inadequate task effectiveness, or both. 5 transparency attached to the inside center of the front cockpit canopy of the test aircraft, was just above the Pilot E made the following comment about the helmet of the front pilot. This transparency had two installation of the Gripen stick as related to a standard concentric ovals that, when mounted at an angle on the F/A- 18 stick: front canopy, appeared circular. Figure 1 shows the "Okay, stick installation, for me, is about six position of this simulated gunsight. The pilots flew these inches farther forward than normal and looks like maneuvers with feet on the floor in an attempt to assess it has about 5 to 7 degrees of excessive forward tilt only the control stick characteristics.
for perfect position for me. My arms are a little bit overextended. And also, I'm having to raise my This evaluation used five pilots who were very ejection seat up higher than I would to get an experienced in F/A-18 aircraft. They also had adequate arm rest. The shape of the stick experience flying the F-16 aircraft, which is equipped conforms naturally to the hand. It's a modern with a sidestick controller. All five had extensive shape, different from a normal F-18, with support experience with handling qualities flight test, including for the base of the thumb and l find that to be an CHRs. All pilots had extensive experience tracking enhancing characteristic."
targets from the rear cockpit of an F/A-18. Two pilots had flown direct duplicates of the maneuvers in this Echelon Formation Flight program from the rear cockpit of standard F/A-18 aircraft. One pilot had flown the JAS 39 Gripen aircraft. Maneuver Description After the pilots conducted some familiarization Because the research flight control system maneuvers and flying qualities tasks, they performed software was not designed to meet flight-critical echelon tracking. The maneuvers were made in loose reliability standards, the flight test could only be parade position (the approximate position of a #3 performed at relatively low dynamic pressure aircraft). The test pilot visually lined up the wingtip and conditions. All study maneuvers were planned for 0.60 fuselage of the lead aircraft to complete the tasks. The Mach at 27,500 feet (ft).
American Institute of Aeronautics and Astronautics Table 1. Cooper-Harper rating scale.
Aircraft Demands on the pilot in selected Pilot I characteristics task or required operation* rating Excellent Pilot compensation not a factor Adequacy for selected Highly desirable for desired performance task or required operation* Good Pilot compensation not a factor Negligible deficiencies for desired performance Fair -- some mildly Minimal pilot compensation unpleasant deficiencies required for desired performance Minor but annoying Desired performance requires deficiencies moderate pilot compensation Deficiencies No Moderately objectionable Adequate performance requires warrant deficiencies considerable pilot compensation improvement Very objectionable but Adequate performance requires tolerable deficiencies extensive pilot compensation Adequate performance not Major deficiencies attainable with maximum tolerable pilot compensation, Controllability not in question Deficiencies require Major deficiencies Considerable pilot compensation improvement is required to control Major deficiencies Intense pilot compensation is required to retain control Improvement Control will be lost during some mandatory H Major deficiencies portion of required operation * Definition of required operation involves designation of flight phase and/or subphases with accompanying conditions, I Pilot decisions I 960377 vertical reference was the wingtip formation light 2. Tracking aircraft starts from straight and level, vertically centered within the blue fuselage striping offset 10 fl downwards, then aggressively captures (fig. 1). The horizontal references were to align the the formation position.
forward tip of the missile rail with the tip of the lead 3. Lead aircraft starts from straight and level and aircraft radome and the aft tip of the lead aircraft missile continues with maneuvering up to 90 ° bank angle rail with the aft red ejection seat warning decal. This and _+30 ° pitch angle.
results in approximately 15 ft of separation. Altitude was maintained between 15,000 and 32,000 ft, and Adequate and desired criteria were as follows: airspeed was maintained between 160 and 250 knots calibrated airspeed (KCAS). The three maneuvering • Desired: Maintain the formation light within blue phases for echelon formation flight are as follows: stripe for 5 sec.
• Adequate: Maintain the formation light within 1. Lead aircraft starts from straight and level and vertical fuselage limits for 5 sec.
continues with gentle maneuvering of up to 30 ° bank and __.30° pitch.
Table 2 tabulates CHRs for each pilot using the criteria above in conjunction with the questionnaire from table 1.
American Institute of Aeronautics and Astronautics overshoots and exceeded the limit, the fuselage.
Table 2. Echelon formation CHRs.
But now I've got it steady within desired criteria.
I'll move back down .... Just putting the missile Pilot A B C D E rail just above the canopy .... trying to be very Echelon aggressive with it, I had one overshoot. Got formation adequate criteria and now easily, pretty easy to phase 1 4 2 2 3 3 capture and fly standard desired .... I got adequate criteria there, but that was pretty aggressive. I'd Echelon give that a 6for the extensive compensation."
formation phase 2 6 3 3 5 4 Pilot C stated: Echelon formation "... The airplane pitches rather abruptly, then phase 3 4 to 7 4 2 5 5 moves up and needs to have the nose pushed back over. However, on the third attempt, there was Comments dramatic learning between the first, second, and Apparently the pilots could perform the phase 1 tasks third attempt. And the third attempt, I was able to maintain desired criteria with essentially no without difficulty. One pilot commented on roll sensitivity, giving a CHR of 4. None of the pilots overshoot. The final attempt was a very aggressive maneuver, and I was able to bring it up and stay in reported any pitch and roll cross axis coupling of the aircraft for this task.
desired criteria. There is a little tendency to bobble. Very similar to most of the other formation Pilot B was very satisfied with the ergonomics of the airplanes we have out here. Certainly reminiscent stick, and the ability to control the airplane for this task: of both F/A-18s, the F-15B, and the F-16. I think it's certainly satisfactory. Control forces are "... You really lose track of the stick in the sense of acceptably low. And I like the little bit of you just think the airplane around and I have no, movement to give you feedback on how much pitch no comments on the stick in the negative sense. So input you've made. Overall, I think the stick, I couM smoothly fly the airplane and achieve, ergonomically, is pretty well put together."
certainly achieve desired performance. I was happy with the ergonomics of the stick in the sense Pilot E commented: of where it is in the cockpit and so on. So I can, as "... Aggressiveness effects, definitely if you were I said before, lose myse_andfly ..."
more aggressive, there's no question that that During phase 2, pilot ratings reflected some level 2 would potentially force you into an overshoot. But handling qualities with CHRs of 4 through 6. Extensive definitely, if you're more aggressive than you compensation was required for the task in the pitch axis.
would under normal instrument formation Some pilots noticed an abruptness in roll as well.
position conditions, that's going to cause overshoots, probably driving you to adequate The pilot comments indicated that it was possible to rather than desired performance."
improve performance to desired levels based on learning from repeated maneuvering and extensive Although this task was designed to evaluate pitch axis compensation. The pilots noted that aggressiveness performance, there was a significant comment regarding affected performance. One pilot made a comparison of abruptness and initial acceleration in the roll axis.
formation flight with other aircraft. The pilot comments Figure 4 shows that the baseline F/A-18 stick gearing results in a steeper slope for roll rate command versus also noted an appreciation for the position displacement stick deflection than the slope for the Gripen. Because and feedback from this controller, as opposed to fixed, this flight experiment was an evaluation of the force-sensing control sticks.
mechanical characteristics of the ministick, software Pilot A stated: deadband and gearing were not changed. A slight adjustment to the roll stick gearing might have corrected "... Okay that was pretty aggressive, I was the noted abruptness without significantly affecting the probably 15 to 20 feet low and I had two performance.
Amelican/nsfimte of Aeronautics and Astronautics Pilot B stated: 3. Lead aircraft flies straight and level. Test aircraft offsets laterally to align with aileron/flap junction "... The one thing that I do notice is just the initial of the lead aircraft. Test aircraft aggressively acceleration in roll. It's quite high and so you captures a lateral position aligned with the center notice that abruptness. You see it every once in of the opposite aileron.
while when you're doing even the pitch things .... " Adequate and desired criteria for phases 1 and 2 were as follows: Phase 3 pilot comments ranged from level 1 to level 3, with the majority of the ratings being level 2. This • Desired: Maintain lateral position within the limits maneuver required control in both the pitch and roll of the fuselage for 5 sec.
axes. The one level 3 rating was for the pitch portion of the task. Again, the pilots commented on the initial and • Adequate: Maintain lateral position within the undesirable acceleration in roll. The spatial positioning limits of the wingspan for 10 sec.
of the aircraft also affected the ability to perform the Adequate and desired criteria for phase 3 were as task. As the lead aircraft was maneuvering, the chase follows: aircraft had to roll and vertically translate the aircraft to maintain proper spacing, because of the relative lever • Desired: Maintain lateral position within the limits arm between the aircraft.
of the aileron-flap junction with one overshoot.
PilotAsaid: • Adequate: Maintain lateral position with no more than one overshoot, or any displacement greater "... we are out here on a long lever arm so if he's than one aileron span beyond the wingtip or rolling with that much time in between, we can't aileron-flap junction.
really achieve even adequate criteria. If l had 5 or Comments 10 seconds in there of constant rate or near constant angle of bank, it's easy to get in there Pilots gave level 1 and level 2 CHRS for all phases of and get desired performance. You're still working the column maneuvering, which table 3 shows. For reasonably to do it. So .... I'd still keep the 4 these tasks, the pilots were more emphatic in the rating. And for verticals it's up to 7, but simply comments on roll ratcheting and abruptness in roll.
kind of due to the nature of the task .... " Some abruptness in roll can be attributable to the difference between the baseline software deadband Pilot B noted: (0.025 in.) and the rescaled Gripen deadband (0.086 in.). A better matching of these values probably "... I can be very smooth with the exception of the sense that there's this initial acceleration lurking would have reduced the abruptness noted by the pilots.
there in the roll .... " One pilot did notice cross axis coupling. The pilot comments also reflected the ability to learn from Column Formation Flight repeated maneuvers and apply compensation and change piloting techniques to improve performance.
Maneuver Description Column formation flight maneuvers were performed Table 3. Column formation flight CHRs.
aligned with the longitudinal axis of the lead aircraft, with 10 ft of vertical separation and 15 ft nose-to-tall Pilot A B C D E separation. Altitude was between 15,000 and 32,000 ft, Column and airspeed was between 160 and 250 KCAS. The three phases of column formation flight were as follows: formation phase 1 4 2 4 3 4 1. Lead aircraft starts from straight and level and Column continues with gentle maneuvering of up to formation 30 ° bank and _+30° pitch.
phase 2 3 2 4 3 5 2. Lead aircraft increases maneuvering to include up Column to 45 ° bank angle. Random roll input steps are formation permissible with greater than 15 sec between phase 3 3 to 4 5 4 5 4 inputs.
American Institute of Aeronautics and Astronautics Pilot E stated: of maneuvering. Altitude was maintained between 15,000 and 32,000 ft, and airspeed was maintained "...the only thing that I really noticed was that the between 160 and 250 KCAS. Criteria for gross if 1 failed to pay any attention, I got a little bit of acquisition and fine tracking provided a reference for roll ratcheting in there, or roll bobble. Very pilot comments and ratings.
sensitive there, in terms of roll acceleration ....
And the compensation was for hand position. And As discussed earlier, the tracking task was performed an awareness as you initiated maneuvers, or did using concentric ovals on a transparency attached to the initiated reversals that the airplane is abrupt in front cockpit as a gunsight. The oval placement in the roll and you couM easily cause a little bit of aircraft resulted in a positive depression angle for the acceleration. So you have to work to be smooth gunsight, possibly resulting in a slight "pendulum but you can do it."
effect." Because the ovals were at an angle to the flightpath angle of the aircraft, they moved in a conical Pilot A said: motion as the aircraft rolled, resulting in more lateral "... All in all, this seems like an easier task than movement than a gunsight reticle would exhibit for the the echelon, because when you roll, it's a lot same maneuver. When interviewed, however, the pilots easier for me to roll quickly .... During the felt that this movement was not significant for this flight phase 2, it seems obviously more abrupt than front program.
seat maneuvering."
Gross acquisition adequate and desired criteria were Additionally, one pilot compensation technique was as follows: to change the hold on the handgrip. By relaxing grip on the stick and flying with fingertips, the pilot could • Desired: Maintain lateral position within large oval with one or no overshoots.
compensate for some of the undesirable characteristics that had been noticed.
• Adequate: Maintain lateral position within large oval with two or fewer overshoots.
Pilot E noted: Tracking adequate and desired criteria were as "... There was some awareness of control motion follows: in there, especially if I tried to be abrupt. I tended to grip the stick more and I could sense when I • Desired: Maintain the target aircraft within inner was moving it. I don't like that. And abo there was oval for 5 sec.
some cross axis coupling as I attempted to be • Adequate: Maintain the target aircraft within outer smooth in roll. When you put in a little bit of a oval for 5 sec.
pitch change on top of that sometimes that excited a little bit of a smooth but perceptible pitch Table 4 contains all the CHRs taken during the gross bobble.., both in terms of hand position, the grip acquisition and fine tracking maneuvers.
on the stick, and the technique that was used in the requirement to back off the performance to compensate for the superimposed small bank angles..."
Table 4. Tracking CHRs.
Target Tracking Pilot A B C D E Gross Maneuver Description acquisition n/r 2 2 6 to 7 4 The final target-tracking task used the F/A-18 chase Longitudinal aircraft as a target. The initial setup placed the two fine tracking n/r 2 2 3 3 aircraft at the abeam position at 220 KCAS and an Lateral fine altitude greater than 20,000 ft mean sea level. At tracking n/r 2 3 4 6 "cleared to maneuver" call, the target aircraft began a military power 2 to 3 g normal acceleration turn away Comments from the test aircraft. The test aircraft pilot would aggressively maneuver to perform a gross acquisition Pilot A did not fly the target tracking maneuvers. For and tracking task. After the test aircraft called the most part, pilots rated this task level 1. Pilots B and "tracking," the target was cleared to increase the severity American Institute of Aeronautics and Astronautics C could perform the tasks very easily. The only issue Pilot E gave a CHR of 6 for the lateral fine tracking, mentioned was some difficulty in tracking laterally.
resulting from adverse yaw developed during fine lateral Abruptness in roll acceleration was once again reported inputs. The pilots flew these maneuvers with feet on the to be undesirable and a degrading factor in the ability of floor in an attempt to assess only the control stick the pilots to perform the tasks. characteristics. Pilot E said: Pilot C noted: "... Once you go out to the wingtip, and then go from one wing to the other especially, if there's "So,for gross acquisition we were able to meet all any aggressiveness whatsoever, you tend to get the desired criteria with ease. The target comes up into a lateral oscillation with superimposed and stops. Primarily a pitch maneuver and there adverse yaw on top of it .... " were no overshoots apparent, stopping inside the oval with ease. Fine tracking both in pitch and ...
Handling Qualities Analysis well starting with pitch, we were able to move the pipper from canopy to the rail pipes with ease.
To analytically assess the potential impacts of the There was no tendency to PIO [pilot induced mechanical characteristics of the ministick on the oscillation] or to overshoot.., a little bit of longitudinal dynamics of the F/A- 18, an evaluation was difficulty with the abruptness of the roll conducted using criteria from the military specification acceleration that gave you a little bit, little bit of MIL-STD-1797. 5 This military specification provides difficulty in predicting where the pipper was going handling qualities guidelines for piloted vehicles and laterally..."
addresses the CAP and Neal-Smith criteria used in this report. The evaluations below used the transfer function Pilot D gave CHRs of 6 and 7 for the gross acquisition evaluated from pitch stick to pitch response from the task because of poor predictability with aggressive flight data, providing an analytical assessment of the maneuvering and some coupling of the pitch and roll handling qualities of the F/A-18. The correlation and axes. Poor control in the yaw axis was also described.
analysis of the pilot comments and ratings in Pilot Dsaid: conjunction with this assessment were helpful in understanding any variations that might be attributed to "...The difficulty with the gross acquisition is the the Gripen stick.
more aggressive you are with the acquisition, the harder it is to stop the pipper at the point that you The primary consequence of the low cost nature of want to stop it....What you have to do is back off this project was that the Gripen stick position and the on your aggressiveness...Okay, on the lateral axis, flight control system pitch rate were only recorded at ... you put your inputs in and it would seem like 20 samples per second. Frequency analysis of the the nose would, like the airplane would develop a Gripen longitudinal stick position to pitch rate was used little yaw or something like that, because you to estimate the stick position to pitch angle transfer would roll back the other way. But the nose lags, function used with handling qualities techniques would lag the inputs relatively significantly.
presented in MIL-STD- 1797.
Generally, laterally, you'd get much larger overshoots. And it's harder to get back over to The frequency response of Gripen stick to pitch rate where you want it because of this adverse yaw (Q) was fit into a LOES model. 5'9'10 Fast Fourier tendency. So the undesirable motion was the Transform analysis was performed on each of the adverse yaw, plus it's kind of an abrupt response maneuvers to extract the frequency response data. These on the airplane. So the airplane's kind of models were used to calculate the following parameters wallowing around almost like you couM force it into a dutch roll type of motion. The predictability for the handling qualities analysis: aircraft short period was, I think, poor on that. The difficulty was frequency (t.0) and damping (_), and time delay (-x), primarily not so much the lateral axis as it had to and static gain (Kq) of the system, using a fixed value do with this kind of coupling into the directional for lift due to angle of attack, Lce The LOES technique axis. Compensation techniques, you could back off uses an optimization program to fit a frequency response the gains and improve the situation a little bit.
of pitch rate to stick position to a simplified linear Sensitivity was, in the lateral axis, I think it's too model: sensitive. It needs to be, it needs to be reduced somewhat."
American Institute of Aeronautics and Astronautics Figure 6 plots the CAP versus equivalent short period -- _ _ "_ s Q Kq (s + Lc_ ) e damping ratio. CAP analysis relates the aircraft short (1) period natural frequency to the acceleration sensitivity.
stick s 2 + 2_O3sp s + 6Osp The approximation for CAP is calculated from the following expression: To increase the fidelity of the LOES fit, the Lc_ was calculated from the NASA Dryden nonlinear simulation for each flight condition and fixed in the LOES model.
CAP = 6Osp/(Nz/ct ) (3) Figure 5 shows a typical fit of the LOES to a where co is the short period natural frequency, Nz is sp frequency response. The LOES program calculates a the normal load factor, and c_is the angle of attack.
cost function to indicate the quality of the flight data match to the LOES model by comparing the differences 10.00 in gain and phase between the LOES transfer function and the transfer function derived from flight data. The Level 2 expression for the cost function is as follows: 1.00 20 -- . 2 CAP, Cost - N--_)__(Agatn + O.O175Aphase2), (2) 1/g'see 2 0.10
where NOF is the number of frequency points, Again is ,_ "eve'___2
the variation between the original and approximated transfer functions, and Aphase is the variation between 0.01 0.1 1.0 5.0 the original and approximated transfer functions.
Damping ratio 000107 Figure 6. CAP analysis.
-- Input ------ LOES 25 "'" - .... Bound The CAP criterion originated for unaugmented 20 "'''-" Gain, aircraft, and analyzes only the dynamics of the aircraft dB 10 ---- without taking into account the time delay of the aircraft flight control system. This aircraft was evaluated for category A flight phase for class IV aircraft, high- Kq = 21.7705 L(_ = 1.7 maneuverability fighters. Category A is defined as "c = 0.13 nonterminal flight phases that require rapid (0=2.8 maneuvering, precision tracking, or precise flight path = 0.65425 Cost function = 13.1897 control. The circles on this figure represent the echelon, column, and tracking maneuvers performed during this flight test. The results indicate that the aircraft should Phase 50 ._...
have level 1 handling qualities in pitch for all of the angle, -50 deg -100 maneuvers included in the analysis.
-150 -200 MIL-STD-1797 also establishes a criterion for 0.1 1.0 10.0 Frequency, rad/sec equivalent time delay. The specification requires a time 000106 delay less than 100 milliseconds (msec) for level 1 and Figure 5. Typical LOES data fit of equation (1).
less than 200 msec for level 2 handling qualities. From table 5, most of the calculated time delays range between 110 and 130 msec, which are borderline Table 5 shows the parameters for all of the LOES fits level 1/level 2 values. Five cases meet the level 1 for the handling qualities data taken. The cost numbers criterion. Two cases have values of 180 msec ranged from 12 to 972. The fits were examined, and corresponding with level 2. The comparison of the those that did not reflect a realistic LOES model for the LOES equivalent time delay values correlates with the aircraft were not included in analysis.
pilot ratings and comments.
Amelican Institute of Aeronautics and Astronautics Table 5.LOES fitsofmaneuver data.
m x Neal Smith Neal Smith
L a (rad/sec) _ (sec) Cost Kq CAP lead (deg) peak (dB) Echelon 1 Pilot A 1.80 3.1 0.65 0.12 17 23.6 0.92 51.2 1.6 Pilot B 1.89 2.6 0.78 0.11 81 18.7 0.78 66.0 1.9 Pilot C 1.73 3.0 0.70 0.11 36 26.6 0.90 53.5 1A Pilot D 1.72 2.8 0.65 0.13 12 21.8 0.72 57.7 4.5 Pilot E 1.97 3.3 0.66 0.12 35 24.7 1.09 50.3 2.6 Echelon 2 Pilot A 2.07 3.3 0.44 0.13 72 21.8 1.31 39.2 1.9 Pilot B 1.63 2.9 0.51 0.10 49 21.6 0.77 45.0 3.3 Pilot C 1.62 2.9 0.70 0.11 35 26.7 0.76 53.8 5.5 Pilot D 1.84 3.1 0.37 0.18 189 20.3 0.96 37.4 12.9 Pilot E 1.64 3.0 0.59 0.10 23 20.7 0.83 46.5 8.1 Echelon 3 Pilot A 2.18 2.7 0.59 0.12 45 17.6 0.95 63.1 2.4 Pilot B 1.66 3.0 0.51 0.10 136 18.8 0.90 42.7 1.5 Pilot C 2.23 3.0 0.56 0.07 60 21.0 1.17 51.3 5.2 Pilot D 1.84 3.0 0.56 0.10 77 18.7 0.90 48.5 3.7 Pilot E 1.84 3.1 0.69 0.11 42 23.9 0.96 52.8 4.7 Cohnnn 1 Pilot A 1.88 3.0 0.63 0.11 25 23.1 0.92 52.7 2.4 Pilot B 1.77 3.3 0.65 0.11 43 17.6 1.11 45.9 1.9 Pilot C 1.62 2.9 0.69 0.12 53 22.0 0.76 54.4 1.8 Pilot D 1.82 3.2 0.70 0.12 45 22.4 1.04 51.4 1.7 Pilot E 1.96 3.3 0.59 0.09 32 18.8 1.18 44.1 2.7 Cohnnn 2 Pilot A 1.76 2.9 0.64 0.11 25 23.3 0.79 54.1 2.4 Pilot B 1.74 2.7 0.69 0.11 55 17.8 0.78 59.8 1.7 Pilot C 1.62 2.9 0.69 0.12 53 22.0 0.76 54.4 2.4 Pilot D 1.80 3.1 0.69 0.11 34 22.2 0.91 51.8 3.4 Pilot E 1.68 2.6 0.64 0.11 55 18.8 0.60 60.0 2.7 Cohnnn 3 Pilot A 2.14 3.1 0.62 0.11 25 22.7 1.20 54.3 3.6 Pilot B 1.67 3.0 0.76 0.11 32 22.3 0.94 54.4 2.6 Pilot C 1.54 2.8 0.64 0.12 54 20.4 0.71 53.1 0.9 Pilot D 2.22 3.4 0.48 0.15 130 22.4 1.58 44.3 6.9 Pilot E 2.22 3.5 0.53 0.10 52 18.3 1.59 41.3 2.4 Tracking Pilot B 1.84 2.8 0.80 0.13 31 22.9 0.92 63.0 2.6 Pilot C 1.69 3.1 0.65 0.12 63 24.3 0.94 49.5 1.9 Pilot D 1.93 2.5 0.84 0.18 56 20.9 0.72 73.7 2.5 Pilot E 1.79 3.3 0.65 0.11 972 13.1 1.03 45.5 5.6 American Institute of Aeronautics and Astronautics The Neal-Smith criterion 6 assumes a simple closed- pilot might use to perform certain flying tasks. Analysis loop pitch attitude tracking task; in the task a is conducted to relate the measured pilot stick activity with the results of the carpet plot.
compensator of predetermined form is used to close the loop around the airframe plus flight control system Figure 8 shows a Neai-Smith "carpet" plot based on a transfer function for pitch attitude from the control stick representative case from figure 7. This plot is (0/stick). The compensator is assumed to be of the form: constructed by varying bandwidth for the criterion between 2.5 and 4.0 rad/sec, while simultaneously allowing the low frequency droop to vary by K p* e "tc°mps* ( T lead* S -I" 1) (4) (Tlag*S + 1) _+0.5 decibels (dB). This carpet shows an area of pilot ratings that can be obtained by assuming that variations where Kp is the gain for compensation model, Tlead is in compensator bandwidth can be correlated with pilot the compensator lead time constant, Tlag is the stick activity. The predicted CHRs for the representative compensator model with a bandwidth of 3 tad and a compensator lag time constant, and "Ccomp is the time delay of 0.3 sec would be in the lower portion of compensator time delay.
level 2 bordering the level 1 region, suggesting a CHR The parameters in the model are adjusted to meet the of 4. As the modeled compensator bandwidth increases, desired closed loop solution of having 90 ° of rolloff in the handling quality predictions move from level 1 to the phase angle at the desired bandwidth of level 2 to level 3. If the compensation has a bandwidth 3.0 rad/sec. 6'9 The relationship between the required or activity greater than the baseline value, the CHR will phase compensation and resultant resonant peak of the move along the solid line on the carpet plot toward level 3.
closed loop transfer function can be related to level 1, level 2, and level 3 handling qualities (fig. 7). Figure 7 also shows circles for handling quality maneuvers flown DROOP in this program. The compensator model for this (dB) 2.5 analysis used a time delay (Xcomp) of 0.3 sec. Note that 3.0 the results of this analysis would predict the CHRs to be .... 3.5 in the level 2 area with some of the data on the border of 12 -- Leve, 3 ;// the level 1 region. These results demonstrate that the
analysis corresponds substantially with the pilot CHRs. ,o
8 -- Iw_ Resonance Band 12 -_- 6 -- Level 23.5 rad Jil" l dB peak, *= ..... ///Increasing 10 -- .__ Level 3 4 Bandwidth " " - -- / " stick , 8 -- 2 i/B Nominal
andwidth
Resonance 6 -- o 1 I I _/" I i Level 2 "" -..
peak, dB --20 0 20 40 60 80 o o Lead compensation, deg 4 -- 000109 o°o o -- -- oO Figure 8. Neai-Smith carpet plot of representative case.
,-/ Leve,, "'< i °
I I °
-20 0 20 40 60 80 For the echelon phase 3 task, Pilot A gave a CHR of 7 Lead compensation, deg 000108 (level 3) to the vertical position capture task, (refer to echelon phase 3 comments and table 2). Pilots B, C, D, Figure 7. Neal-Smith analysis.
and E gave ratings of 4, 2, 5, and 5 (level 1/level 2 ratings), respectively, for the same task. Figure 9 shows By varying the bandwidth and allowed droop for the a power spectral density of the pitch stick activity for the closed-loop frequency response in the Neai-Smith gross acquisition and tracking task. Pilot A had criterion, an assessment can be made on the robustness significantly more high-frequency stick activity than of a predicted handling qualities level. Steep slopes tend pilots B, C, D, and E had. This higher frequency activity to show sensitivity to the pilot technique, or bandwidth a is indicative of a pilot with a bandwidth greater than the American Institute of Aeronautics and Astronautics compensator used for the Neal-Smith analysis. As the short-period damping, time delay, and transfer function Neal-Smith carpet indicates, this greater bandwidth gain using fixed Lce These values were used with control anticipation parameter and Neal-Smith analyses could cause the pilot to be well into handling quality to determine the handling qualities of the airframe levels 2 or 3, and possibly a CHR of 7.
independent of the Gripen control stick. The control anticipation parameter analysis indicated that the aircraft should have level 1 handling qualities, while the 10- \ Pilot Symbol CHR 9 -- _ A -- 7 Neal-Smith analysis indicated that the aircraft should 8 __ \ B o 5 have borderline level 1/level 2 or level 2 handling 7 -- D .... 5 qualities, which corresponded with the majority of pilot comments and ratings.
Power 6 -- E • 5 density, 5 C ----- 2 The LOES data show good comparison with the dB 4 criterion for equivalent time delay of 100 msec for level 1 and 200 msec for level 2. Most of the cases have equivalent time delays between 110 and 130 msec; this finding is consistent with borderline level 1 and level 2 handling qualities.
0.1 1.0 10.0 Frequency, rad/sec 000110 Overall, the pilot ratings and comments correlated well with the Neal-Smith analysis with a bandwidth of Figure 9. Power spectral density of echelon phase 3.
3.0 rad/sec. Most ratings for a wide range of tasks were level 2. A few borderline level 1 and level 2 CHRs were given. One noticeable exception was a CHR of 7 Summary (level 3) given by one pilot for vertical motion during the echelon phase 3. Power spectral density analysis A six-flight program evaluated whether the showed that this pilot had significantly more stick mechanical characteristics of the Gripen small activity than the other pilots, which is correlated with displacement control stick affected the handling performing the closed-loop task at a higher bandwidth.
qualities of an F/A- 18 aircraft. Production support flight The Neal-Smith carpet plot correlated with the control computers (PSFCC) supported this effort.
comments and rating given by this pilot. This analysis NASA Dryden installed the Gripen hardware in the aft shows that a higher bandwidth for the closed-loop task cockpit of a two-place F/A-18. The analog inputs of the would result in degraded handling qualities.
PSFCCs connected the pitch and roll commands from the Gripen control stick to the baseline F/A-18 control Pilots with F-16 flying experience used F-16 flying laws in the research processor. The flight program techniques such as loosening their grip on the control demonstrated the suitability of the PSFCCs for this type stick in higher gain maneuvers. Many pilots used very of flight research.
loose grips while controlling with the Gripen stick, some using only three fingers to hold the top of the Five pilots evaluated both open-loop maneuvers such control stick while maneuvering.
as doublets, and closed-loop maneuvers such as bank angle and pitch angle captures, echelon formation flight, The pilots did notice an abruptness in initial roll column formation flight, and target tracking. Cooper- response for small amplitude inputs. The software Harper ratings (CHR) and pilot comments were deadbands and stick shaping used with the Gripen stick were not modified from the standard F/A-18 software.
collected. The ratings and comments from the closed- Tuning of the deadband and the stick gearing more loop tasks were used for the handling qualities evaluation. closely to the mechanization of the Gripen stick could lead to better pilot ratings for the gross acquisition task.
Pilot comments indicate that no serious handling These software changes could also have addressed the quality deficiencies resulted from the installation or pilot comments on abruptness and roll acceleration mechanical characteristics of the Gripen stick. Handling sensitivity. Pilots also commented on poor yaw control.
quality analysis was performed using the flight data. Allowing the use of the rudder pedals during Low order equivalent system (LOES) model fits maneuvering flight could have controlled this provided estimated values for short-period frequency, deficiency.
American Institute of Aeronautics and Astronautics Pilot comments demonstrated an ability to easily 5U.S. Air Force, Flying Qualities of Piloted Vehicles, control the airplane. The pilot comments were favorable MIL-STD-1797, Mar. 31, 1987.
with respect to the motion feedback provided by the 6Bailey, Randall E. and Rogers E. Smith, "Analysis of Gripen controller as opposed to the lack of feedback in Augmented Aircraft Flying Qualities Through force-command sidestick controllers.
Application of the Neal-Smith Criterion," AIAA-81- References 1776, Aug. 1981.
7Sitz, Joel, F-18 Systems Research Aircraft Facility, 1Hall, G. Warren and Rogers E. Smith, Flight NASA TM-92-4433, 1992.
Im'estigation of Fighter Side-Stick Force-Deflection Characteristics, AFFDL-TR-75-39, May 1975.
8Carter, John E and Mark Stephenson, Initial Flight Test of the Production Support Flight Control 2Carter, John F., Production Support Flight Control Computers at NASA Dryden Flight Research Center, Computers: Research Capability for F/A-18 Aircraft at NASA TM-1999-206581, 1999.
Dryden Flight Research Center, NASA TM-97-206233, 1997.
9Stoliker, P. C., High-Angle-of-Attack Handling Qualities Predictions and Criteria Evaluation for the 3Cooper, George E. and Robert P. Harper, Jr., The Use X-31A, NASA TM-4758, 1997.
of Pilot Rating in the Evaluation of Aircraft Handling Qualities, NASA TN D-5153, 1969.
l°Hodgkinson, John, "Equivalent Systems Criteria for Handling Qualities of Military Aircraft," AGARD 4Mitchell, David G. and Roger H. Hoh, "Low-Order Conference Proceedings No. 333, June 1982.
Approaches to High-Order Systems: Problems and Promises," AIAA-81-1774, Aug. 1981.
Amelican Institute of Aeronautics and Astronautics
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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORTTYPE AND DATES COVERED August 2000 Technical Memorandum 4.TITLE AND SUBTITLE 5. FUNDING NUMBERS Flying Quality Analysis of a JAS 39 Gripen Ministick Controller in an F/A- 18 Aircraft WU 529 61 14 M1 00 14 0 00 S 000 6. AUTHOR(S) John E Carter and R C. Stoliker 8. PERFORMING ORGANIZATION 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) REPORT NUMBER NASA Dryden Flight Research Center RO. Box 273 H-2418 Edwards, California 93523-0273 10. SPONSORING/MONITORING 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) AGENCY REPORT NUMBER National Aeronautics and Space Administration NASA/TM-2000-209024 Washington, DC 20546-0001 11. SUPPLEMENTARY NOTES Presented at AIAA Guidance Navigation and Control Conference, Denver, Colorado, August 14-17, 2000, AIAA-2000-4444.
12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Unclassified--Unlimited Subject Category 08 This report is available at http://www.dfrc.nasa.gov/DTRS/ 13. ABSTRACT (Maximum 200 words) NASA Dryden conducted a handling qualities experiment using a small displacement centerstick controller that Saab-Scania developed for the JAS 39 Gripen aircraft. The centerstick, or ministick, was mounted in the rear cockpit of an F/A-18 aircraft. Production support flight control computers (PSFCC) provided a pilot- selectable research control system. The objectives for this experiment included determining whether the mechanical characteristics of the centerstick controller had any significant effect on the handling qualities of the F/A-18, and determining the usefulness of the PSFCCs for this kind of experiment. Five pilots evaluated closed-loop tracking tasks, including echelon and column formation flight and target following. Cooper-Harper ratings and pilot comments were collected for each maneuver. This paper describes the test system, including the PSFCCs, the Gripen centerstick, and the flight test experiment. The paper presents results of longitudinal handling qualities maneuvers, including low order equivalent systems, Neal-Smith, and controls anticipation parameter analyses. The experiment showed that, while the centerstick controller provided a different aircraft feel, few handling qualities deficiencies resulted. It also demonstrated that the PSFCCs were useful for this kind of investigation.
14. SUBJECTTERMS 15. NUMBER OF PAGES Aircraft control, Flight control, Handling qualities, JAS 39 Gripen, Piloting 16. PRICE CODE A03 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT OF REPORT OFTHIS PAGE OF ABSTRACT Unclassified Unclassified Unclassified Unlimited NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) Prescribed by ANSI Std. Z39-18 298-102