Document
102741
NASA Technical Memorandum
CONTROL
F-106B AIRPLANE ACTIVE
LANDING GEAR DROP TEST
PERFORMANCE
McGehee, Willian E. Howell, John R.
Robert H. Daugherty, and
William A. Vogler
November 1990 (NASA-T_-lO_741) F-IO "_o,_ AIRPLANE ACTIVE N91-13445 CONTR,qL LANDING GEAR DROP TEST PERFORMANCE (NASA) I2 p CSCL OIC G3/OS National Aeronautics and Space Administration Langley Reseamh Centre" Hampton, Virginia 23665 F-106B AIRPLANE ACTIVE CONTROL LANDING GEAR DROP _ST PERFORMANCE William E. ttowell, John R. McGchce, and Robert It. Daughcrty NASA-Langley Research Center, Mail Stop 497 ttampton, VA 23665 and William A. Vogler, Staff Engineer Lockheed Engineering and Sciences Company NASA-Langley Research Center, Mail Stop 497 Hampton, VA 23665 SUMMARY Aircraft dynamic loads and vibrations resulting from landing impact and from runway and taxiway unevenness are recognized as significant factors in causing fatigue damage, dynamic stress on the airframe, crew and passenger discomfort, and reduction of the pilot's ability to control the aircraft during ground operations. One potential method for improving operational characteristics of aircraft on the ground is the application of active-control technology to the landing gears to reduce ground loads applied to the airframe.
An experimental investigation was conductcd on series-hydraulic active control nose gear. The experiments involved testing the gear in both passive and active control modes. Results of this investigation show that a series- hydraulic active-control gear is feasible and that such a gear is effective in reducing the loads transmitted by the gear to the airframe during ground operations.
INTRODUCTION Aircraft dynamic loads and vibrations resulting from landing impact and from runway and taxiway unevenness are recognized as significant factors in causing fatigue damage, dynamic stress on tile airframe, crew and passenger discomfort, and reduction of tile pilot's ability to control the aircraft during ground operations. The ground-induced structural vibrations on large, flexible airplanes can reduce the pilot's capability to control the airplane during high-speed ground operations. These ground-induced
dynamic loads and vibrations are magnified for supersonic-cruise aircraft
because of the increased structural flexibility inherent in these slender-body, thin-wing designs. Such operational problems with supersonic-cruise airplanes have occurred at high take-off and landing speeds on some runways which are only marginally acceptable for most subsonic commercial airplanes. One potential method for improving operational characteristics of such airplanes on the ground is the application of active-control technology to the landing gears to reduce the ground loads applied to the airframe.
Previous analytical studies (references I and 2) have been conducted to determine the feasibility and potential benefits of applying active load control to the airplane main landing gear to limit the ground loads applied to the airframe. The results reported in reference 2 indicate that a shock strut incorporating a hydraulically controlled actuator in series with the passive elements of a conventional shock strut have acceptable properties and would be quite feasible to implement. Based on the results of reference 2, a modified version of the series-hydraulic active gear which eliminated the actuator and effected control by using a servovalve to remove or add hydraulic fluid to the shock-strut piston (lower cylinder) was analytically and experimentally investigated in references 3 through 6. Based on the results described in these references, the gear from a F-106B was modified for drop tests. The purpose of this paper is to present the results of passive and active drop tests of the F-106B nose gear.
SERIES-HYDRAULIC ACTIVE-CONTROL GEAR Control Concept The series-hydraulic control concept limits the gear force applied to the airfiame by regulating the damping force (hydraulic pressure) in the piston of the oleo-pneumatic shock strut. To incorporate this active control concept into a conventional gear requires a modification to the gear to control the flow of fluid in or out of the shock-strut with a servovalve. A schematic drawing of a series-hydraulic landing gear that has been fabricated to permit experimental verification of the concept is shown in figure 1. The gear represented is a simple generic oleo-pneumatic shock strut without a metering pin. The control concept is designated series-hydraulic because the control
servovalve is in series with the shock-strut piston and hydraulic fluid is
removed from or added to the piston to provide force regulation.
The actual gear selectedfor inclusion of the active control concept was
the nose gear of the F-106B with no meteringpin. The gear was modified to
accommodatethe control by adding a three-tube arrangementto the orifice as
shown in figure 2. A collection chamber at the top of the 3 tubes connects the
fluid in the shock-strut piston to one side of the secondary piston. The other side of the secondary piston is connected to the servovaive. The purpose of the secondary piston is to mechanically limit the amount of fluid that can be taken out or added to the shock strut for flight safety.
The control hardware required for the active gear test program included a 200 GPM (0.76 m3/min) servovalve, a low-pressure (atmospheric) reservoir, a 9 GPM (0.04 m3/min) hydraulic pump, a high-pressure (3000 psi (20.7 MPa)) accumulator, an electronic controller, and feedback transducers.
The isolation valve allowed isolation of the gear from the control hardware to permit passive gear testing.
System Operation System operation is briefly described as follows. The electronic controller determines the operational mode (take-off or landing), and implements the control laws. The control laws programmed into the controller are based on the following logic. At touchdown, the controller receives a signal from a transducer to measure the instantaneous sink rate. Assuming a constant mass, the present energy is then calculated. An integration of the acceleration is also begun at this time so that the gear upper mass velocity is known at all subsequent limes. As the gear compresses, the relnaining work capability of the shock strut is calculated using the instantaneous values of acceleration (or force) and stroke remaining. This remaining work capability is then compared with the present energy of the upper mass calculated using the instantaneous upper mass velocity. When the remaining work capability equals or exceeds the present energy of the upper mass the controller stores in memory the instantaneous value of the scaled acceleration (wing-gear interface force) for use as the impact limit force and activates the servovalve control loop. The controller attempts to maintain Ibis force by removal or addition of hydraulic fluid from or to the oleo-pneumatic shock strut lower
chamber. Feedback from the accelerometerprovides the controller with a
means of determining the difference between the present and the desired
force. The slope of the accelerometer output is also used for rate feedbackin
the control laws, so that if the force is not at the proper level but is tending to
return to it on its own, the magnitudeof the servo commandwould be reduced
by some amount. Likewise, force trends away from the desired level provoke
servo commandslarger than would be generatedif using force difference
alone in the control laws. When the upper mass energy has been dissipated
and the sink velocity is nearly zero, the controller linearly transitions the
impact limit force to a value of zero for roliout control. During rollout and taxi
the controller maintains the wing-gear interface force within a designed
tolerance (deadbandof +1750 lbf (+7.8 kN) for these tests) about the static
normal force. After control initiation at touchdown, the controller continuously operates with a long-time constant (5 seconds) control to return the gear stroke to the designed static equilibrium position.
EXPERIMENTAL INVESTIGATION Landing simulation tests (passive and active) with the nose gear from a F-106B fighter interceptor airplane (fig. 3) were conducted at the NASA Langley Research Center to demonstrate the feasibility and the potential of the active gear for reducing ground loads transmitted to the airframe. The vertical drop tests simulated touchdown impact with and without lift.
Drop Tests A photograph of the test apparatus for conducting the vertical drop tests of the nose gear is shown in figure 4. Additional details of the gear and apparalus are shown in figure 5. Using the drop test apparatus, the nose gear was dropped vertically with simulated lift at 4.5 fps (1.37 m/s) in both tile passive and active modes. A l-g lift simulation was obtained by using crushable aluminum honeycomb to stop the drop carriage (upper mass) vertical acceleration. The chosen test condition is representative of the airplane being derotated at a high pitch rate. A second test of the gear was also conducted at a vertical speed of 2.5 fps (0.76 m/s) without lift. Without lift applied, vertical speeds higher than about 2.5 fps (0.76 m/s) would cause the
gear to bottom out. Such a drop test is representative of losing pitch control
during derotation.
A comparison of the measured upper mass acceleration for the active versus passive gear without lift is shown in figure 6. Significant events such as drop carriage release, free fall, tire impact, and control activation are indicated in the figure. A 47% decrease in upper mass acceleration was obtained with the active control gear. The decrease in acceleration translates to a 47% decrease in the amplitude of forces transmitted to the airframe. For the 2.5 fps (0.76 m/s) vertical drop without lift, the passive gear stroke shown in figure 7 nearly bottomed out; consequently, the active gear stroke was essentially the same as for the passive gear case. Upper mass acceleration data for a 4.5 fps (1.37 m/s) drop with lift are shown in figure 8. A 36% decrease in the transmitted force was obtained with the active gear. As shown in figure 9, there was a 10% increase in the strut stroke associated with the active control.
CONCLUDING REMARKS A potential method for improving the operational characteristics of aircraft on the ground by the application of active-control technology to the landing gears to reduce ground loads applied to the airframe has been investigated. An experimental program was conducted on a series-hydraulic active-control nose landing gear from a F-106B fighter interceptor aircraft involving both passive and active control modes. Results of the investigation show: (a) That such a concept can be achieved through modificalion of existing hardware, and (b) that the concept is effcclive in significantly reducing the loads transmitted by the gear to the airframe during landing and ground operations.
REFERENCES
1. Wignot, JackE.; Durup,Paul C.; andGamon,Max A.: Design
Formulation and Analysis ot" an Active Landing Gear. Volume I, Analysis.
AFFDL-TR 71-80, Vol. I, U.S. Air Force, August 1971. (Available from DDC as AD 887 127L.)
2. Bender E. K.; Berkman, E. F.; and Bicber, M.: A Feasibility Study of Active Landing Gear. AFFDL-TR-70-I26, Air Force, July 1971. (Available from DDC as AD 887 451L.)
3. McGehee, John R.; and Dreher, Robert C.: Experimen!al Investigation of Active Loads Control for Aircraft Landing Gear. NASA TP-2042, 1982.
4. Morris, David L.: Active Landing Gear Response Testing. ADWAL-TM- 82-177-FIEM, U.S. Air Force, April 1982.
5. McGehee, John R.; and Morris, David L.: active Control Landing Gear for Ground Load Alleviation. AGARD-CP-384, pp. 18-1 through 18-12, March 1985.
6. Morris, David 1.: F-4 Active Control Landing Gear Dynamic Response Testing. AFWAL-TR-85-3005, Air Force, August 1985. (Available from DDC as AD-B096481L.)
Isolation valve Secondary piston
' t
I 1 i I I Linear potentiometer
r e vova
Electronic controller !
I pressure !
transducer Pump _" J Low-pressure High-pressure reservoir acc umulator Figure 1.- Schematic of series-hydraulic active control landing gear.
O_GINA[ PAGE BLACK AND WHITE PHOTOGRAPM Figure 2.- Disassembled, modified F-106B nose gear.
Figure 3.- F-106B fighter interceptor airplane.
?
OR1GINAE PAGE' BLACK AND WHITE PHOTOGRAPI_ Figure 4.- Nose gear drop test apparatus.
Figure 5.- Nose gear mounted on drop carriage.
1.0 I" .,,.__- Passive / 47% decrease ..,,/" _"
/
|lDropcarriage .,,_'T \ - - Upper mass 0 _'_ release J/" [ _Active _" accelerati°n' _ __/t______g-units Passive stroke ____- Control initiated "1"01 I' - _ (b°thtests) I I-_:rl?-_ _--- Tire impact I I I ! I 0 0.1 0.2 0.3 0.4 0.5 Time, sec Figure 6.- Comparison of passive and active control accelerations for vertical drop of nose gear at 2.5 ft/sec (0.76 m/sec) without lift.
E Active No change _/...F"__ Stroke, in. 5
v' I i i =
0 0.1 0.2 0.3 0.4 0.5 Time, sec Figure 7.- Comparison of passive and active control strut stroke for vertical drop of nose gear at 2.5 ft/sec (0.76 m/see) without llft.
J_./1= 1.0 - 36% decrease te.,J _ Pass,ve Drop carriage __ I release _ • " / Active _'_=,, ...
011 [ _- Control initiated Upper mass U J J acceleration, I_ I_ g-units i[_ lil-: .............
-1.0 H;, ._..,__,_';1 rnpac I _--- ;r_! e ----_--, g wing lift initiated I I I I ! I 0 0.1 0.2 0.3 0.4 0,5 Time, sec Figure 8.- Comparison of passive and active control accelerations for vertical drop of nose gear at 4.5 It/see (1.37 m/see) with lift.
8 Active
'F
7 r 10% increase ---__ __'__ Stru_troke, ,, 0 0.1 0.2 0.3 0.4 0.5 Time, sec Figure 9.- Comparison of passive and active control strut stroke for vertical drop of nose gear at 4.5 It/see (1.37 m/see) sith lift.
//
Report Documentation Page .¢>C,_('e/'_,_SIr 3,1K)n 2. Government Accession I_1o. "" 3. Recipient's Catalog No.
1. Report N_o. '- NASA TM-I02741 5. Report Date 4. Title and Subtitle F-IO6B Airplane Active Control Landing Gear November 1990 Drop Test Performance 6. Performing Organization Code 8. Performing Organization Report No.
7. Author(s) William E. Howell, John R. McGehee, Robert H. Daugherty, and William A. Vogler 10. Work Unit No.
505-63-]0-02 9. Performing Organization Name and Address 11. Contract or Grant No.
NASA Langley Research Center Hampton, VA 23665-5225 13. Type of Report and Period Covered 12. Sponsoring Agency Name and Address Technical Memorandum National Aeronautics and Space Administration 14. Sponsoring Agency Code Washington, DC 20546-0001 15. Supplementaw Notes William E. Howell, John R. McGehee, and Robert H. Daugherty: Langley Research Center, Hampton, Virginia.
William A. Vogler: Lockheed Engineering & Sciences Company, Hampton, Virginia.
16. Abstract Aircraft dynamic l_ds and vibrations resulting from landing impact and from runway and taxiway unevenness are recognized as significant factors in causing fatigue damage, dynamic stress on the airframe, crew and passenger discomfort, and reduction of the pilot's ability to control the aircraft during ground operations. One potential method for improving operational characteristics of aircraft on the ground is the application of active_control technology to the landing gears to reduce ground loads applied to the airframe.
An experimental investigation was conducted on series-hydraulic activ control nose gear. The experiments involved testing the gear in both passive and active control mode_. Results of this investigation show that a series-hydraulic activeXcontrol gear is feasible and that such a gear is effective in reducing the loads transmitted by the gear to the airframe during ground operations.
18. Distribution State_nt 17. Key Words (Suggest_ by Author(s)) Unlimited - unclassified Aircraft landing gear Active controls Subject category: 05 Landing loads 22. Price 21. No. of pages 20. SecuriWClassif.(ofthispage) 19, SecuriW Cla_if. (of this report) ]l A0 3 Unclassified Unclassified NASA FORM lg26 OCT