Aeronautical Technologies for the Twenty-First Century (1992) / Chapter Skim
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7 Aerodynamics
7 Aerodynamics
Pages 109-148
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From page 109... ...
, advanced subsonic transports, and hypersonic vehicles of all types, as well as the need to maintain its facility capabilities through the Wind Tunnel Revitalization Program. In each of these areas, however, overall constraints have limited NASA's ability to establish the kind of aggressive research efforts newer to maintain U.S.
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From page 110... ...
Or. ~r In m~,~lram~.nt [Pie ~.ffr~l~ -~::::rnr: 1ltrnt::::~-,~.~h:::::::::::::::::::::~::::::::: :::::::: :: aerodynamics, structures, and controls were largely exercised sequentially in the design process.
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From page 111... ...
These NASA efforts are highly endorsed by the Committee and complement similar industry activities that will include manufac~nng considerations in the trade-off decision-making process. The impact of rapid design processes that allow time for examining the ~ade-offs between various disciplines was evident in He design of the folding wing tip of the Boeing 777.
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From page 112... ...
Low speed and high liquor supersonic configurations: Supersonic aircraft shapes are strongly influenced by the need for economical supersonic cruise performance Virtually all the design decisions to improve performance in this
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From page 113... ...
Aerodynamics of rotorcraft: Aerodynamics of rotorcraft and tiltwing aircraft are especially complex, because Key require investigations of exceptionally wide speed ranges and varying angles of airflow. Testfacilities: The numerous new or updated flight and ground test facilities Mat will be required to accomplish various technical goals set forth in the report are discussed in this section.
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From page 114... ...
Because of this, airframe companies do Heir development work in high Reynolds number wind tunnels-which, for the design of the new Boeing 777, meant extensive development work in European wind tunnels. The following developments in the technology for advanced high-lift system designs are needed: I .
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From page 115... ...
Ins pnncipally through their concerted efforts over several years to understarld the detailed flow physics associated with high lift. For the United States to compete in this area, greater investment is needed in the experimental capabilities and flow physics studies that lead to breakthroughs in high-lift capabilities.
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From page 116... ...
Other phenomena associated with high-lift systems are airframe noise and wake vortex prediction and alleviation. Continuing advances In engine noise reduction will mean that the airframe is responsible for a growing portion of the overall noise profile of an airplane.
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From page 117... ...
Comprehensive programs that address the issues and opportunities in noise research, wake vortices' and airplane separation requirements are needed. NASA is He appropriate organization to develop the technology and means for testing at the highest Reynolds numbers, which includes advanced flow diagnostic instrumentation development, innovative wind tunnel circuit components, the possible use of heavy gas, moderate cryogenics, and other options for high Reynolds numbers' half-model testing techniques, and wind tunnel wall interference · · · e m~mm~zahon.
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From page 118... ...
One is the development of wind tunnel test techniques and powered propulsion simulators to better represent installed power effects of the forthcoming generations of very high bypass ratio engines in wind tunnel testing. The other is He need to predict the installed characteristics of thrust reversers, both computationally and wig wind tunnel testing techniques.
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From page 119... ...
Engineering and op~mizabon tools have outpaced the state of the art in transition prediction theory.) Thus, the design of EFC, hybrid laminar flow control, and natural laminar flow systems depends on empirical bases to determine transition.
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From page 120... ...
Prediction and control have been hindered by the lack of reliable, efficient models of turbulence for complex geometries. Advanced Supercr~tical Airfoils Advanced supercritical airfoils, which reduce the shock strength on transonic airfoils, have contributed to drag reduction and have been used on all commercial transport aircraft developed since 1975.
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From page 121... ...
Cruise Mach Number Advanced airfad 757 Source': Boeing Commercial Airplane Group FIGURE 7-2 Improvements In transon~c wing technology. Status of Subsonic Technology As noted earlier, the past decade has seen large improvements in wing design technology, the successful demonstration of laminar flow control on a Boeing 757, the successful demonstration of nblets on a business jet, the successful demonstration of natural laminar flow on a business jet, and the use of supercntical airfoils and wingless on transports in everyday · ~ commercla .
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From page 122... ...
This work, although seemingly basic in nature, must be actively pursued and must include companion theoretical, computational, and experimental efforts conducted under careful, well-documented conditions. A better understanding of flow physics will also afford the opportunity for effective use of flow control.
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From page 123... ...
Large-scale, low-disturbance, supersonic wind tunnels are needed to support a~rc~ft development. The existing infrastructure of government facilities and capabilities that support the U.S.
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From page 124... ...
The biggest challenge is to achieve good overall cruise economics with acceptable community noise and emissions levels. The challenges for L/D enhancement include EFC, turbulent drag reduction, reduction of drag due to lift, volume wave drag reduction, and the development of design optimization methods.
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From page 125... ...
; · application of conventional takeoff and landing aircraft vortex drag due to lift reduction approaches (other than aspect ratio) ; and · engine exhaust flow tailoring for panial shock reflection/favorable Interference wave drag reduction.
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From page 126... ...
In addition, high-lift devices must work in harmony with other advanced concepts such as supersonic 1aTninar flow control that are beneficial to supersonic cruise efficiency. These requirements result in ample opportunity for innovative and aggressive aerodynamic development TAKEOFF AND CLIMR Point 3 (Approach)
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From page 127... ...
Because supersonic laminar flow control may play art important part in the supersonic cruise efficiency of high-speed vehicles, careful attention must be paid to the interrelationships of the high-lift system and the suction system used for laminar flow control. SUPERSONIC AIRCRAFT PROPULSION/AIR~AME INTEGRATION With increasing cruise flight speeds, the achievement of close aerodynamic coupling between the propulsion system and the a~rfrmne becomes more and more important .
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From page 128... ...
Engines for supersonic aircraft should also be designed with variable geometry inlets to reduce sensitivity to flight conditions and, in particular, to enable efficient operation at takeoff and landing, as well as in cruise flight. Such inlets will require sophisticated boundary-layer control systems.
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From page 129... ...
Prediction of aerodynamic dumping for conventional subsonic aircraft, for example, has not progressed much beyond He work done by the National Advisory Committee on Aeronautics In the 1950s. Also, He possible role of dynamic wind tunnel testing for commercial transports has not been explored.
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From page 130... ...
NASA should undertake a systematic, in-depth review of current practice in the dynamics and control of aircraft, initiate a program to extend the applications of CFD methods to a prion analysis, and include an extension of mode! wind tunnel testing to dynamic derivatives.
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From page 131... ...
This becomes particularly cndcal for tiltrotors. An extensive wind tunnel test on this problem as experienced by conventional helicopters has just been completed using a Bell 412 rotor in the 40' x 80' wind tunnel, and some experimental work has been done on the rotor wing
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From page 132... ...
Wind tunnels adequate for lO-foot model rotors are generally available for the achievable envelope of modern helicopters, including tunnels with moving ground planes to enhance their low-speed-in-ground-effect fidelity, and the Ames facility extends this capability to full-scale helicopters up to the 10? 000to 20,000-pound class.
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From page 133... ...
These critena should probably be defined in terms of noise footprint for terminal operations. Because noise footprint is the critical factor in community heliport acceptance, condom developments to allow steeper-gradient landings arid takeoffs can play a major role in reducing the external noise problem.
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From page 134... ...
Aerodynamic Interaction As discussed above, developing the analytical tools to address the aerodynamic interaction of rotor and airframe requires attention to complement wind tunnel test programs recently undertaken. A special subset of this problem is the development of better concepts for rotor head drag reduction on conventional helicopters at high speeds and for rotor/empennage interaction improvement In low-speed flight.
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From page 135... ...
; technology to allow steep-gradient and vanable-speed approach envelope expansion to midsize noise tootpnnt; active control for whir} flutter prevention with less wing weight penalty and by allowing a more flexible, thinner wing raising the Mach divergence limits and hence the cruise speed; active control for nde quality optimization, by recognizing that civil tiltrotors will spend more time at lower altitudes than will {ong-range jets (a flight dynamicsJelectronic control problem) ; and active control to allow smaller empennages, perhaps even canards, that wit!
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From page 136... ...
The most readily achievable solution appears to be the addidon of acoustic treatment for the 40' x 80' full-scale wind tunnel. Funding for this facility has been the top-pnonty request for construction of facilities from the Ames Center, but it has not survived the cut at higher levels.
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From page 137... ...
A discussion of flight testing and the use of CFD in vehicle design is also included. Existing Facilities Wind Tunnels Over the range from low to high supersonic speeds there are some 90 major wind tunnels in the Undo States and another 70 in foreign countries, including Canada, France, Germany, Japan, He Netherlands, and the United Kingdom.
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From page 138... ...
sizes relative to test section dimensions can be tested at supersonic speeds, the Reynolds numbers noted are significantly higher Can for subsonic and tran sonic wind tunnels;~3 however, the Reynolds numbers for complete supersonic aircraft configurations are at least twice as mgh as those noted above, which are based on root chord. A comparison of the Reynolds number capabilities of major subsonic, tran sonic, and supersonic wind tunnels is shown in Figures 7-5 Trough 7-7.
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From page 139... ...
Air-breathing Propulsion Facilities 139 Major a~r-breathing propulsion facilities can be divided into three categones: propulsion wind tunnels, altitude engine test facilities, and engine/propulsion component facilities.~4 The Wind tunnels are large facilities in which engine burn tests and propuision/a~rframe integration tests can be non. A drawback of wind tunnels for engine testing is their inability to provide true temperature simulation over wide operating conditions.
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From page 140... ...
20 24 28 Of some 60 altitude engine test facilities in the world, the one with the greatest capability by far is the AEDC Aeropropulsion Systems Test Facility with two 28-foot diameter cells, 85 feet long, mass flows exceeding 2,000 pounds per second, a broad temperature range, and speeds up to Mach 3.8. There are 46 engine/propulsion component facilities in the United States for testing turbines, compressors, and combustors; the only foreign ones are in Japan and Belgium.
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From page 141... ...
Flight Test Facilities The national flight research assets include the flight testing range and related ground facilities and the aircraft in NASA's research fleets stationed at Ames-Dryden Flight Research Facility, Ames-Moffett, Langley, and Lewis Research Centers. Current research aircraft are listed In Table 7-2.
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From page 142... ...
~ 7-2 blent Rese~cb ~rcr~ Il1~111~1111<~1111~1111~Il~I~l! lIllll ~1~1!
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From page 143... ...
It is currently being upgraded. A major facility expect to become operational in the mid-199Os is the European Transonic/Cryogenic Wind Tunnel near Cologne, Germany It win have a test section of 2.4 m x 2.4 m and cover the speed range from Mach number 0.15 to I.2, with Reynolds numbers based on effective chord length up to 50 million, which is adequate to meet most future test requirements.
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From page 144... ...
None of these facilities reach the full-scale Reynolds numbers needed for a HSCT or supersonic military systems. In terms of low-disturbance supersonic wind tunnels to study laminar flow control and boundary layer transition, NASA presently has in operation a Mach 3.5 tunnel and is developing a new facility with Mach 3.5 and Mach 6 nozzles.
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From page 145... ...
The future ability of the United States to remain competitive in aeronautics is directly dependent on He quality of its experimental and computational facilities, which, along with flight testing, are the design tools for new aircraft. Economic and technical compromises must be made to determine where each of these tools kits into the design process.
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From page 146... ...
· To proceed with all haste ~ flitting its Ames' 40' x 80' wind tunnel with an acoustic lining essential for noise testing on fud-scale vehicles. To develop a low-speed, low-dish~rbance test capability that can operate at fun- scale Reynolds number (based on chord length of at I~t 50 minions In the range from Mach number 0.l to 0.5.
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From page 147... ...
aeronautical flight experimental capabilities, NASA should (~) vitalize capability and ~n-fliaht technology validation efforts In aU speed regimes, , A, Regarding the flight research and develop advanced measurement technologies for flight research.
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From page 148... ...
148 AERONAUTICAL TECHNOLOGIES Guenette, G.R., A.H. Epstein, M.B.
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