N93-29717 45 PRELIMINARY DESIGN STUDIES OF AN ADVANCED GENERAL AVIATION AIRCRAFT /6o5%/ THE UNIVERSITY OF KANSAS Preliminary design studies are presented for an advanced general aviation aircraft. Advanced guidance and display concepts, laminar flow, smart structures, fuselage and wing structural design and manufacturing, and preliminary configuration design are topics to be discussed. This project was conducted as a graduate- leveI design class under the auspices of the KU/NASA/USRA Advanced Design Program in Aeronautics. This paper will present the results obtained during the fall semester of 1990 (P'nase I) and the spring semester of 1991 (Phase H). NOMENCIATtm]E Flight control systems of today's GA airplanes are still the same as those of 50 years ago: cables, pulleys, and bell-cranks: ACQ Acquisition this represents 2-3% of the design takeoffweight of the airplane. AEP Airplane estimated price In addition, tailoring mechanical control systems to today's APT Advanced Personal Transport handling quality requirements is fraught with problems, most ATC Air traffic control of these caused by friction and cable-tension problems associated C/A Coarse/acquisition with mechanical control systems. By switching to a fly-by-light CAT Category COM Communications or fly-by-wire system, much of this weight and all of the handling DEU Drive electronics unit quality problems can be eliminated. DISP Disposal Cockpit instrumentation has been improved since 1945 only DMU Digital memory units in the sense that the instruments are more capable and marginally EMI Electromagnetic interference FAA Federal Aviation Administration more reliable. The typical GA cockpit has anywhere from 150 FBL Fly-by-U#t to 300 clocks, bells, whistles, and switches. In terms of airplane FBW Fly-by-wire design takeoff weight, this amounts to 3-10%. Revolutionary GA General aviation cockpit design would start from scratch: with an empty panel. GPS Global positioning system HERF High-energy radio frequencies Through afunctionality analysis that gives priority to user friendly HSNLF High-speed natural laminar flow features, a new cockpit design should emerge with only very HUD Heads-up display few displays, bells, whistles, and switches. This should eliminate IFR Instrument flight rules a lot of weight and complexity. Heads-up displays should be IGG Integrated GPS/Glonass considered as a replacement of all existing displays. ILS Instrument landing system INS Inertial navigation system Navigation and communication with the FANs ATC system KU The University of Kaosas in today's GA airplanes is very cumbersome and extremely user LCC Life cycle cost unfriendly. Since 1945 the ATC environment has grown more LCD Liquid crystal display and more hostile toward GA airplanes. Most of these procedures MAC Mean aerodynamic chord MAN Manufacturing can and should be automated through the use of onboard micro- NAS National Airspace System processors. ATC coupling with GPS/GIonass should be con- NAV Navigation sidered. Optical disk storage of en-route and terminal guidance NLF Natural laminar flow should be considered. OPS Operations Airplane structural design and manufacturing is still done RDTE Research, development, testing, and evaluation RPM Rotations per minute mostly with conventional riveted aluminum materials. Recent SSSA Separate surface stability augmentation developments with .Mall (Aramid-aluminum), Glare, and other T-O Take-off types of composite materials opens the way to significantly lighter USRA Universities Space Research Association structures. The recently developed outside-in tooling approach VFR V'oaal flight rules makes it possible to design even aluminum structures with surface tolerances that allow for the attainment of laminar flow. 1. INTRODUCTION In addition, electrical signal and power paths should be inte- grated into the structure so that these paths also carry part Since 1945, when Beech Aircraft corporation came up with of the air loads. the Model 35 Bonanza, speed and range performance of GA The flight controls in GA airplanes are still so-called "rate airplanes have not improved to any significant extent. With few command control systems." The potential exists to change this exceptions, GA airplanes of today are still turbulent flow air- to attitude or decoupled response command systems. This is, planes. Laminar flow airplanes are now feasible. in fact, the logical way to proceed if FBL and/or FBW are used. 46 Proceedings of the NASA/USRA Advanced Design Program 7th Summer Conference This would lead to the complete elimination of many accidents 1200 nm that are fundamentally caused by the rate command nature of 5 today's flight controls. The purpose of this paper is to present the preliminary design "results of an advanced aircraft design project at the University 4 of Kansas. The goal of the project was to take a revolutionary look into the design of ageneral aviation aircraft including those items mentioned above. This project was conducted as a 7 graduate-level design class under the auspices of the KU/NASA/ ¢ USRA Advanced Design Program in Aeronautics. The class is open to aerospace and electrical engineering seniors and first- 1. Engine Start and Warm-up 5. Cruise level graduate students. This paper will present the results 2. Taxi 6. Descent 3. Takeoff 7. Land, Taxi, and Shutdown obtained during the fall semester of 1990 (Phase I) and the 4. ClimbtoCruiseAltitude spring semester of 1991 (Phase II). References 1 through 17 are reports documenting the work completed in Phase I and Fig.1. Mission Profile. references 18 through 25 document the work completed in Phase II. 2. PRELIMINARY SIZING twin turboprop powerplant; 8000-ft cabin at 45,000 ft; FAR 23 certification; and 45,000-ft service ceiling. A market survey was conducted to create a database of The mission profile is shown in Fig. I. information that could be used as a reference in preliminary design work It was also used to identify and compare current 3. CONFIGURATION DESC_ON AND CABIN LAYOUT. and potential designs that would offer competition for the i planned design, provide _cific aircraft information character- Two configurations, a tractor and a pusher, were designed istics to aid inconligttration design and development, and identify to meet the mission specifications. A twin-boom three-surface potential voids in the current market. The market survey included configuration was selected for the APT pushcr layout. This con- 16 aircraft that were considered to be potential competitors figuration provides a=_gh degree of structural synergism by for the planned design in the 4-10 passenger range. The two allowing the aft pressure bulkhead, wing carry-through mounL main competitors in the survey were considered to be the Piaggio and main landing gear mount to form one integral fail-safe unit. P-180 Avanti and the Socata/Mooney TBM-700. Performance Recent research (26'27) has shown that, for the same basic data for the 16 aircraft were collected. These data included geometry, three-surface configurations typically have a higher range, number of pa.ssengers, maximum cruise speed, rate of trimmed lift-to-drag ratio than either conventional or canard climb, and service ceiling. By plotting the range vs. number configurations. The research has also shown that three- surface of passengers for the 16 aircraft, voids in the general aviation layouts can have lower trim drag over a wider center of gravity market were located. The Advanced Personal Trmxslx)rt (APT) range than do two-surface layouts. Flap-induced pitching was selected to be a 6-passenger aircraft capable of a 1200- moments can be automatically trimmed by incorporating a flap n.m. range. The average values of selected performance para- on the canard that is "geared" to _ deflecti0n. meters for the 16 aircraft are listed in Table 1. Athree-view and table of geometry of the final design isshown The mission specifications were _ected to make the APT in Fig. 2. One of the p_ _-:afures of this layout is that it competitive with those aircraft studied in the market survey. was designed to attain a high extent of NLE. All flying surfaces The mission specifications _6 passengers, 175 lb each, with use NLF airfoils, and the fuselage features a pusher propeller 30 lb of baggage each; range of 1200 n.m. with reserves of and smooth NLF forward fuselage. The wing is swept forward 10% mission fuel; 420-kt cruise speed; takeoff field length of 15° (measured at the leading edge), and features a midwing 2000 fi at sea level conditions; landing field length of 2500 ft location to decrease fuse|age interference _. Astrake is incor- at sea level conditions; maximum rate of climb of 4000 ft/min; porated at the wing root to stiffen the wing root against the high torsional loads inherent with forward swept wings. The strake also provides local strengthening for tail boom support and increases the avaUabie voiume=for fuel. TABLE1. Average values ofperformance parameters. The horizontal tail was located at the top of the vertical tails 7575 lb Empty weight to place it above the propeller slipstream, which reduces struc- 13244 lb Maximum takeoff weight tural noise and fatigue and should allow attainment of natural 55.2psg Maximum wing loading laminar flow on the tail _e. Ventral fins mounted on the 2.73 Ib/lb Maximum power loading underside of the tail booms _ agahxst prop strikes if the 2730 fi Takeofffield length 3797 ft/min Maximum rate of climb airplane is over-rotated. A standard retractable tricycle landing 389 kt High-speedcruise gear arrangement was selected, with the nose gear retracting 1858 n.m. Maximum range forward into the nose and the fuselage:mounted main gear 38OOOft Service ceiling retracting aft into the area underneath the wing. Crosswind $4million Cost landing gear is used to allow the APT to land in a crabbed University of Kansas 47 Table of Geometry of the Pusher APT Configuration Wing,..._. Horiz Tail Canard Area (f12) 130 31.7 38.6 8.0 Span (ft) 36.0 I1.9 6.5 7.8 Aspect Ratio 9.97 4.5 1.1 3.8 Sweep Angle -15°(@L.E.) 0° 40°(@L.E.) 0°(@0.10c) M.A.C. (fl) 3.28 2.6 4.2 1.00 Taper Ratio 0.35 1.0 0.4 0.70 Dihedral Angle 3° 0° 90° _5° Incidence Angle I° 0° 0o 3o Twist Angle 0° 0° 0o 0o Airfoil Custom NLF Section " ° Thickness Ratio 0.13 0.09 0.09 0.11 Control Surf. Chord Ratio 0.25 0.30 0.32 N/A Control Surf. Span Ratio 0.72-1.00 0-0.98 0.20-0.85 N/A Flap Chord Ratio 0.25 NIA N/A 0.35 Flap Span Ratio 0.19-0.72 NIA NIA 0.21-1.00 Cabin Overall Length (fl) 11.17 29.33 34.75 Max. Height (ft) 4.67 5.42 9.92 Max. Width (II) 4.58 4.92 43.40 _c) ©__ Fig. 2. Three-view of the APTpusher configuration. conliguration. Cabin access is provided by an air-stalr door on isalso used for the tractor configuration. Cabin access is achieved the left fuselage, which is a convenient feature usually found by first stepping up onto the wing and then entering a side- only on larger turboprops and business jets. hinged door located on the left side of the fuselage. A conventional configtwation was selected for the APT tractor Unlike the pusher configuration, there was no practical place layout. This layout provides good balance and flexible wing in the fuselage of the tractor configuration to mount the weather placement. It should also reduce development costs due to the radar. Consequently, the radar was mounted in a pod on the extensive database of similar airplanes. A three-view and table left wing, similar in arrangement to that of the Cessna P-210 of geometry of the tractor layout are shown in Fig. 3. As can Centurion. be seen, the layout is rather conventional and is similar to many The cabin layout of the APT was sized by comparison with popular GA airplanes. similar current GA airplanes, and the final layout is shown in To allow a fair comparison with the pusher configuration, Fig. 4. The cabin dimensions selected for the APT are relatively the tractor configtmation uses the same cabin layout (Fig. 4) large compared to similar airplanes because current small GA and wing geometry. However, the pusher design was iterated airplanes are not known for cabin comfort. To improve market- to meet the mission specifications, resulting in a smaller wing ability, the cabin of the APT was designed to ease this problem than the tractor configuration, the design of which was not as much as practical, without causing undue weight or drag iterated. A low wing arrangement was selected to allow the penalties. The fuselage cross section of the APT is shown in wing carry-through structure to pass under the cabin and to Fig. 5, and features a circular upper and a rounded square lower allow simple wing mounted landing gear. A T-tail arrangement cross section. This arrangement was selected as a compromise was used to remove the horizontal taft from the turbulence between the structural efiiciency of a fully circular cross section of the fuselage and propwash, which can allow a small reduction and the low wetted area and volume penalties of a fully square in tail area and should allow attainment of NLF on the tail surface. cross section. An illustration of a proposed APT cockpit layout A standard retractable tricycle landing gear arrangement was is shown in Fig. 6. The layout features two sidestick controllers, selected, with the nose gear retracting underneath the engine one on each side of the cabin, and a center console containing and the main gear retracting into the wing. Crosswind gear the speed control handle. Due to the high degree of automation 48 Proceedings of the NASA/USRAAdvanced Design Program 7th Summer Conference Table of Geometry of the Tractor APT Configuration Wing.__ Horiz. Tail Verl. Tail Area (It2) 151.7 36.4 27.3 Span fit) 42.7 12.8 5.6 Aspect Ratio 12.0 4.5 1.2 Sweep Angle -15°(@L.E) 9°(@L.E.) 40°(@I..E.) M.A.C. (ft) 3.89 2.87 5.7 Taper Ratio 0.35 0.7 0.4 Dihedral Angle 3° 0° 90° Incidence Angle 1° 0° 0° Twist Angle 0° 0° 0° Airfoil Custom NLF Section Thickness Ratio 0.13 0.09 0.09 Control Surf. Chord Ratio 0.25 0.30 0_32 Control Surf.Span Ratio 0.72-1.00 0-0.98 0.20-0.85 Flap Chord Ratio 0.25 N/A NIA Flap Span Ratio 0.19-0.72 N/A N/A Cabin Fuselage Overall Length (ft) 11.17 29.33 34.75 Max. Height (It) 4.67 5.42 9.92 Max. Width (f0 4.58 4.92 43.40 Fig.3- Three-view ofthe APTtractor configuration. J 7111 in the flight control system, neither rudder pedals, brake pedals, fly and communicate at the same time. Reductions are also flap handles, or landing gear handles are required(t2). The layout expected since the pilot isno longer monitoring multiple instru- features a HUD projected directly onto the windshield and a ments. Another objective was to be able to navigate vertically single LCD touch screen. The LCD will display all required as well as horizontally with great accuracy using only onboard systems information and will also be used for data entry; there- computers and positioning satellites. In this way, the onboard fore, no other instruments or separate data entry devices are computer could build an approach into any airport even if no required in the cockpit. One interesting feature of this cockpit instrument approaches were established. arrangement is that it allows incorporation of a sliding table The GPS is a method of navigation using a constellation of or tray, which can be slid out from under the control panel satellites with known positions to calculate current position. to hold aeronautical chartS_ maps, or even drinks. Both the U.S.and the Soviet Union have been working individually on establishing a network of satellites. The NAVSTAR satellite 4. ADVANCED GUID_CE AND DISPLAY system is the name #yen to the U.S. effort in global positioning. The system consists of 24 satellites, only 85% of which are pre. The overall objective of the navigation system was to reduce sently in orbit. The constellation is expected to be completed pilot workload. If possible, the pilot should not have to do by 1993. The satellites are grouped in six orbital planes with anything except fly the airplane. A pilot workload study was four satellites in each plane. Each satellite has aone-day ground conducted (x)to determine the workload apilot must complete track repeat, meaning that it will pass over the same spot once to make typical flights under two scenarios: the 1990 ATC system aday. and the-proposed IGG system. Each scenario included pro- Each satellite contains almanac information about its orbit cedures for both VFR and IFIL From this study, it was estimated and position, and transmits it to the onboard receiver. Tune that at ieast a 30% reduction in pilot workload would be delays measured in the signal are then used to caIcuIate the experienced due to the time saved from the capability of the distance from the satellite to the receiver. By tracking multiple IGG to monitor the nm,-igation instruments. Additional work- satellites, the position of the airplane is triangulated from the lo-ad reduction is possible i_cause the pilot does not have to known positions of the satellites. The satellites transmit two University of Kansas 49 SIDESTIC K 1.5 FOLDING REST CONTROLLER_RM _-_0 BENCH SEAT SPEED CONTROL-_ [J: HANDLE .... ALL DIMENSIONS IN INCHES SCALE: I150 ,.S-l, AFT PRESSURE BULKHEAD FORWARD BPURLEKSHSEUARDE_ I 6J /BAGGAGE AREA BAGGAGE AREA (18.4 CU, FT.) (7.7 CU. FT.) Fig.4. Cabin layout ofthe APT. codes. The P code has high accuracy and is encrypted and presently restricted to use bythe military. AC/A code is available for civilian use, but its accuracy is limited to 50 m. The C/A code is simply a degraded form of the P code. The NAVSTAR system results in the ability to know longitude, latitude, and altitude at any given time. Glonass represents the Soviet effort in global positioning. The main difference between the U.S. and Soviet systems is that Glonass is in a slightly lower orbit with an eight-day ground track repeat. The satellites are grouped into three orbital planes with eight satellites in each plane. This results in less consistent coverage over a given area. With NAVSTAR, there is a 10-hour period for which these eight satellites are in reception range for a given area. Satellite coverage can be expected over that area at the same time of day, every day, using only eight satellites. Even with 10 satellites, Glonass only repeats every eight days, resulting in inconsistent times of area coverage. GPS can be used to update an INS to reduce the time- cumulative errors. GPS has the problem that the time delays used to calculate position result in a time lag. This means that the indicated position of the airplane is actually a few seconds behind the actual position. INS, however, can reduce this 12- second lag to instantaneous update rates resulting in higher Fig.5. APTcabin cross section. position accuracy. 50 Proceedings of the NASA/USRAAdvanced Destgn Program 7th Summer Conference Heads Up Display LCD/Touch Screen Optical Disk Drives (2) Avionics Access Panels Turn Hold Switch Climb Hold Sidestick Controllers Switch (both sides) Speed Control Sliding Table Handle (both sides) Master Start W/Key Fig.6. Proposed cockpit layout of theAPT. The use of differential multichannel GPS receivers will increase The complete navigation package will allow complete auton- the accuracy of the navigation system. By continuously tracking omous flight planning and management, with the exception of multiple satellites with multiple receivers, the efficiency of the some communication requirements for traffic avoidance. It will updates is increased, and the noise _in the signal and the power allow point-to-point navigation with continuous flight infor- required to maintain lock on a satellite are reduced compared mation available to the pilot and will also allow CAT Happroaches to a single receiver cycling through several satellites. The result even into undeveloped fields where no approaches are estab- of this when coupled with INS yields horizontal accuracies that lashed. The cost of the navigation system isestimated at $400,000. will- allow for zero visibility g_m_cl navigation and approach The overall objective of the display system was to take arevo- accuracies to satisfy CAT II approach criterkt lutionary look into possible improvements in cockpit instru- By the year 2000, advances in the NAS should allow for a mentation with an eye toward automation and user friendly G_equipped airplane to navi_te point tO pointl Itis doubtful, operation. Ideally, the _rumentation and the display formats however, that they will allow an airplane without communi- used in this cockpit should enable any pilot to fly this airplane cations to enter controlled airspace. This depends on the under any weather conditions. advances made in the Data-IAnk system currently in use. Data- The advanced display system is composed of amap computer, Link allows ATC to talk directly to onboard computers and to DMUs, the DEU, aHUT),and amultifunction touch-screen display. issue departure clearances. In the next 10 years, the system The map computer is an optical disk-based system that handles should be able to handle all traffic and routing information alloperating system functions, input processing, and the control autonomously. of both the DEU and the multifunction display. The DEU provides The only foreseen problem in the NAS is that automatic the power, information, and control to the HUD. computer-generated approaches with CAT II criteria will not The HUD, with the combiner integrated into the windscreen, be allowed. To account for this by the certification date, an performs two functions. It incorporates all ff_ght-crucial infor- ILSsystem _ have to l_elncorp0mted. Itisbelieved, however, mation into the pilot's heads-up field of view. In this way, the that GPS-based navigation will reach certification for en-route, pilot will never have to take his eyes off where he is flying DME, ADF, and VOI_ _fiohs-. "I'he=only unwanted addition to tryand find an important piece of information from acluttered to the _ _tmmentation is a dual King KX-155 e_ent instrument panel. By providing the pilot with a wide field-of- NAV/COM. This will not _crease panel complexity. It can be view display that can use pictorial representations of the outside worked in as an extra module and therefore does not increase world, the influences of spatial disorientation can be greatly pilot workload, only system complexity. reduced. University of Kansas 51 inlet ducts with gradual bends were used. Both engines are supported by one very rigid support truss to minimize gearing mismatch at the engine power takeoff shaft. For maximum accessibility, it was determined that the truss should have hinged members that would swing up and out when a certain engine accessory needs to be replaced or receive maintenance. An oil / cooler is incorporated to improve reliability and lower main- tenance. Firewalis and a fire suppression system have been included for safety, and chip count sensors were included for prognostics/diagnostics. Torque, RPM, and fuel flow instruments are integrated into the onboard computer for system monitoring. Fig.7. Head-ups display inflight mode. / The multifunction/touch-screen display is used to display all ; I { _/z_ ' _x___,I{C// ' _.,ki-._-- _:_ non-flight-crucial information and for pilot interfacing. The multifunction display would be used for things such as flight planning/changes, monitoring of airplane systems and flight status, display of low priority Data-Link communications, etc. An example of what the HUD would display during flight is shown in Fig. 7. The price of the display system is estimated to be $600,000. 5. PROPULSION SYSTEM INTEGRATION AND PERFORM&NCE EVALUATION For reasons of ef_ciency throughout the flight envelope, a tudx_rop powerplant and propeller were selected as the propulsion system of the APT. Two Garrett TPE331-15 engines Fig. 8. Front view of the propulsion sTstem integration for the APT are connected to asingle shaft through aSoloy twin-pac gearbox. pusher. These engines power aHartzell HC-E5N-3L/L8218 propeller. Asurvey of several manufacturers was conducted to determine a pool of propeller candidates that may be used on the APT. The five-bladed Hartzell HC-E5N-3L/L8218 was selected fix_m this pool as the propeller for the APT. Due to the large power plant, the Hartzell HC-E5N-3L/L8218 was not able to accept all the power available at its original diameter. To keep the propeller tip Mach number at an acceptable level, the rotational speed had to be decreased from 1885 to 1687 RPM, and the diameter was increased from 85 to 95 in. The designers of the HC-E5N-3L/IB218 specifically designed the blades to operate e._e in a range where tip Mach numbers reached 1.0. The tips of firewall the HC-E5N-3L/L8218 use the most advanced transonic airfoil cross-sections. Three-dimensional effects are taken into account for precise tailoring of blade twist. As aresult, the manufacturer claims that the tips are lightly loaded and fly at less than 2° angle of attack at this flight condition. Therefore, the transonic losses are 75% to 90% lower than atraditionally designed blade. 77 in The power plant and propeller installation for the pusher IO0in configuration is shown in Figs. 8 and 9. Asmall shaft extension, which does not appear on the tractor configuration, was added to the gearbox of the pusher configuration to allow better faring of the aft end of the aircraft. To reduce ducting losses, short Fig.9. Sideview ofthe propulsion system integration oftheAPTpusher. 52 Proceedings of the NASA/USRA Advanced Design Program 7tb Summer Conference 6. AIRFOIL DESIGN 8. STABILITY AND CONTROL "i_e airfoil, designated as HSNLF-30I 2, isdesigned for a cruise The stability and control derivatives for both APT configu- Mach number of 0.73 at a Reynolds number of 5 × 106. The rations were estimated for three flight conditions (power HSNLF denotes "High Speed Natural laminar Flow" and the approach, climb, and cruise) (3°). Both configurations were 3012 denotes a cruise lift coe_cient of 0.30 and thickness ratio determined to be trimmable in all three flight conditions of 12% chord, At these conditions, approximately 60-70% investigated. i laminar flow boundary layers are expected on the upper and It is important to the pilot that certain modes of motion lower surfaces. In addition, a maximum lift coefficient of 1.4 of the airplane are well behaved. The longitudinal and lateral- at a Mach number of 0.1 and Reynolds number of 2 million directional mode shape characteristics of both configurations is a design condition. were calculated (3°) for the same three flight conditions used The HSNLF( 1)-0213 airfoil was used as abasis for the design. in calculating the stability and control derivatives. The tractor Because the HSNLF(I)-0213 airfoil drag-rise Mach number is configuration satisfies level 1flight requirements in the phugoid too low for the APT design cruise speed conditions, some mode in all three flight conditions. The pusher, however, has modifications had to be made. The drag rise Mach number was slightly low damping ratios in both cruise conditions. Both increased by decreasing the thickness ratio of the airfoil and configurations satisfy level 1 short-period flight requirements by giving the wing sweep. After scaling down the HSNLF( 1)- for all three flight conditions. The spiral mode requirements 0213 and reshaping the airfoil afterbody, the desired conditions for level 1 flight are satisfied for both configurations, but the were met. The airfoil maintains natural laminar flow on 58% spiral mode is too stable in all three conditions for the tractor and 70% of the upper and lower surfaces respectively. and in power approach for the pusher. Decreasing the wing dihedral will alleviate this. Both configurations satisfy the re- 7. WEIGHT AND BALANCE quirements for level 1 dutch roll flying qualities except for the pusher configuration in both cruise conditions. "this can also The component weights and the aircraft balance were be corrected by changing the wing dihedral or the size of the determined (28).Table 2 lists the results of the weight estimations. vertical tail. Both configurations satisfy the roll requirements The weights for the pusher configuration are higher because for level 1flying qualities in all three flight conditions. it was resized in Phase II design to meet the mission specifications. 9. STRUCTURAL CONSIDERATIONS The center of gravity travel is 9 in (20 % of the wing MAC) for the tractor configuration and 7 in (15% of the wing MAC) The wing and fuselage structural layouts and manufacturing for the pusher configuration. Typical c.g. ranges for similar aircraft processes were determined for the pusher configuration. The are 8-16 inches and 10- 21% of the wing MAC(29). This indicates fuselage skin is to be made of Glare 3, the upper wing skin that the results for the APT are reasonable. of 7075 aluminum, and the lower wing skin of 2024 aluminum. TABLE2. Comparison of theAPT with the competition. APT APT Socata/Mooney Beech Piaggio Pusher Tractor TBM-700 Starship P-180 Weights 7,264 6,247 6,510 14,400 10,510 i Maximum Takeoff weight (lb) Standard empty weight (lb) 4,3!1 3,661 3,637 10,320 6,700 _- Maximum useful load (lb) 2,800 2,800 2,646 4,280 3,810 Maximum wing loading (psO 55.9 412 32.2 51.3 61.95 -- Performance 1,961 2,050 1,936 3,280 2,4i5 "_ ! TO. Fieldlength (if) [sLs,Lsa] ! Maximum climb rate (fpm) 4,000 4,650 2,380 3,100 3,650 Best climb rate speed (kt) 260 243 123 180 160 Clean stall speed (kt) 76 77 75 99 105 i Landing stall speed (kt) 60 63 61 84 82 Service ceiling (fi) 45,000 44,000 30,000 41,000 41,000 Normal cruise speed (kt) 310 300 282 270 320 ataltitude of (it) 40,000 44,000 30,000 35,000 41,000 | High speed cruise (kt) 415 350 300 335 400 ; ataltitude of (ft) 20,000 25,000 26,000 22,000 27,000 323 330 312 --- 460 i NO_ cruise (lb/hr) [ High speed cruise (Ib/hr) 708 700 320 984 860 -_ Maximum range (nm) 1,300 930 1,000 1,450 1,800 University of Kansas 53 ALUlvllNUM ALLOY GLASS/EPOXY PREPREG .... l I GROUND(-) NEUTRAL GROUND( -) Fig. lO. Smart structure power bus and tapconfiguration, The supporting structures of both components will be made The possibility of using aluminum alloy strips, integrated into of conventional aluminum alloys. Both the wing and the pres- one or more of the aluminum layers of the Glare laminate, as surLzed section of the fuselage were analyzed with a finite power busses was also investigated. This would allow the structural element program to size the structural members. electrical bus to be used as a structural member and could Outside-in tooling methods will be used to improve surface lead to asubstantial weight savings. Aschematic of this concept smoothness of the components to allow for the attainment of is shown in Fig. 10. The feasibility of this concept is yet to natural laminar flow. Skin splices and surface waviness and gaps be verified and warrants further research. A major concern is will be within required levels (31) to maintain natural laminar the repairability and redundancy requirements of such asystem. flow. The imbedded strips would make it difficult to repair. The The APT will incorporate the use of smart structures. The solution accepted at this time is to have triply redundant busses. use of embedded sensors in a laminate material can play four If an area is damaged, it would be repaired only structurally. key functions: monitoring of the manufactttring process, allowing The damaged power bus would be "turned off" and the system nondestructive evaluation of each individual structure at any would simply tap into one of the backup strips. point in the manufacturing or assembly process, vehicle health monitoring, and complementing the flight control system. 10. SYSTEMS Optical fibers will be used for data transmission to take ad- vantage of their immunity from electromagnetic interference The layout of the major systems of the APT was designed and also to take advantage of the savings in weight (about 4%) for both configurations. These systems include the pressxu'iza- and volume over conventional copper wire bundles. Optical tion, pneumatic, air conditioning, oxygen, fuel, de-ice, escape, fiber sensors will be incorporated into the aircraft using the avionics, electrical, and primary flight control systems. A spec- smart-skin approach primarily for vehicle health monitoring. ialized electro-impulse de-icing system was designed to accom- Power transmission by optical fiber will only be considered modate maintenance concerns without depreciating the amount an option for low power (3 W or less) applications such as of obtainable laminar flow. Detailed analyses were also con- simple electronic circuits and active sensors. Optical fibers ducted on the electrical and primary flight control systems. All intended for sensing applications will be standard fiberoptic system conflicts that have been identified have been corrected. #ass. Optical fibers intended for data transmission will be of Trade studies were conducted on rate command, attitude the polycarbonate type because of the simpler connection sys- command, and decoupled response command flight control tems and the ease of repair associated with this type of liber. systems. Adecoupled response control system was selected for Optical fibers to be used for data transmission will be too thick the APT because it offers advantages over the rate and attitude to be embedded in the Glare laminate regardless of the type command systems. A decoupled response control system sig- of fiber used, and will therefore be attached to the inner surface nificantly reduces pilot workload and improves the handling of the Glare panels. qualities over conventional rate command systems, esp_iaUy Coatings for the fiberoptic cables were selected to ensure during low-visibility IFR flight conditions. It has the potential protection from the heat generated during the manufacturing to make flying an airplane as easy and safe as driving a car. of the laminate and the strain from dynamic ioadings during The system is particularly well suited for operation by novice flight. Itwas determined that optical fibers used for data trans- and infrequent pilots, though it is also easily adapted to by mission will be coated with acrylate to protect and insulate experienced pilots. Each primary response variable of the them from shock and stress, and optical fibers intended for airplane is afunction of only one cockpit control position, which sensing applications will be coated with Polyaimide B,athermo- provides intuitive and easy-to-learn operation. The system auto- set material. matically compensates for speed and trim changes due to flap 54 Proceedings of tbe NASA/USI_4 Advanced Design Program 7th Summer Conference Elevator Surfaces Servotab (Typ.) Rudders Actuator (Typ.) Fiber Optic Signal Paths (Typ.) Accelerometers Gyros To Throttle Speed Control // Wing Flaps // Air Data Surfaces Sidestick Controllers Flight Control Computers Air Data Pressure Sensors Slotted Canard Flaps Fig.11. Preliminaryflightcontrol systemlayout. deflection, landing gear extension, and steep turns. This con- for the flight control system of the APT. Considering recent siderably decreases pilot workload, especially during approach technological advances in areas such as microprocessors, andba]ked ianding flight conditions. The _em makes the type fiberoptics, and electr0mechanical actuators, itseems likely that and sign ofthe steady-state airplane responses the same asthose by the time of certification of the APT in 1_ these problems of the initial response, again providing intuitive operation. The can be practically overcome (32).As a result, an irreversible FBL system automatically damps out the annoying phugoid control system was selected for the APT (Fig. 11). oscillation. Several control surface/actuator arrangements were investi- Trade studies were also conducted for several flight control gated for the APT flight control system. A multiple-segment system arrangements: reversible mechanical, reversible control surface arrangement was selected toprovide redundancy mechanical with SSSA,and irreversible fly-by-wire/fly-by-light in the case of actuator failure, using the following segment (FBW/]VBL).Due to the impo_ce ofproviding enhanced flying numbers: seven aileron segments (per aileron), five elevator qualities to the APT project, the mechanical reversible system segments, and two rudder _ents (one on each vertical tail). was immediately eliminated from consideration since itdid not One of the primary advantages of this muidple surface arrange- allow practical stability augmentation. In general, the results ment is that it _ designed to provide a constant actuation showed thatthe SSSAsystem should be lessexpensive todevelop, force for all control surfaces. Hence, one common actuator can build, and certify, more reIiabledue tothe mechanical p_ be _ for allcontrol surfaces, which should provide significant controls, and easier to certify due to the extensive database cost and maintenance advantages Servotab actuation of the of similar airplanes and the relative simplicity of the _em. control_ surfaces _ selected to allow use ofa smaller actuator The irreversible _ Syste_ was,=in genePai, the higher _r_ (for the same control power), which provides the advantage fo_/:e system since it _ mtich Defter handling qualities, that the actuators shouldbe lighter, less expensive, and have allows the safetyoffllght envelope protection, pofent_ weighs smaller power requirem_ts. less, and reduces pilot workload and training requirements, it An iron bird has been built and tested. The iron bird involved was apparent that if the cost, reliability, and certification a simulation of an aileron-tab configuration for lateral control, problems of FBL could be overcome, it was the best choice an investigation to see if a servotab can be used to control