No abstract

Preliminary design studies indicate that a cruise-efficient short takeoff and landing aircraft has enhanced takeoff performance at competitive direct operating costs when using high-speed propellers in combination with internally blown flaps. The original tractor configuration is compared to an over-the-wing propeller, which allows for noise shielding. An additional geometry with partially embedded rotor similar to a channel wing is considered to increase the beneficial interaction. This paper shows the aerodynamic integration effects with a focus on climb performance and provides an assessment of the three aforementioned configurations for a simplified wing segment at takeoff conditions. Steady Reynolds-averaged Navier-Stokes simulations have been conducted using an actuator disk model and were evaluated based on the overall design. Interacting with the blown flap, the conventional tractor propeller induces large lift and drag increments due to the vectored sliptream. Although this effect is much smaller for an overthe-wing configuration, by halving the lift augmentation, the lift-to-drag ratio and the propulsive efficiency are considerably improved. Besides a moderate lift gain, the main advantage of a channel wing design is the location of the thrust vector close to the center of gravity resulting in a smaller nosedown pitching moment due to thrust. A disadvantage of over-the-wing propellers is the inhomogeneous inflow at higher velocity, which leads to oscillating blade loads and reduced efficiency.lift coefficient of aircraft C M;y = M y ∕q ∞ · S ref · MAC, pitching moment coefficient of aircraft C P;s = shaft power coefficient C T = 2 · T∕q ∞ · S ref , thrust coefficient of aircraft c = chord length of rectangular wing segment c d = section drag coefficient c l = section lift coefficient c m = section pitching moment coefficient c p = p − p ∞ ∕q ∞ , pressure coefficient D P = propeller diameter p = static pressure q ∞ = dynamic pressure of freestream S ref = wing area of reference aircraft s = semispan of rectangular wing segment T = thrust of one engine T inst = T − ΔD, installed thrust t∕t max = relative blade element thrust V ∞ = freestream velocity α = angle of attack α e = effective angle of attack at blade element β 75= propeller blade pitch angle (at 75% radius) η P = propeller efficiency η Pro = propulsive efficiency ρ ∞ = density of freestream Subscripts x,y,z = Cartesian coordinates

No abstract

No abstract

Today, main hub airports are already at their capacity limit and hence, smaller airports have become more interesting for providing point-to-point connections. Unfortunately, the use of regional airports induces an increased environmental footprint for the population living around it. In an attempt to solve the related problems, the research project Coordinated Research Centre 880 aims to examine the fundamentals of a single-aisle aircraft with active high-lift configuration powered by two geared ultra-high bypass turbofan engines mounted over the wing. Low direct operating costs, noise shielding due to the over-wing configuration, and short runway lengths are the main advantages. Highlighting the performance, economical and noise benefits of a geared ultra-high bypass engine is the key aim of this paper. This assessment includes a correspondingly adjusted aircraft. Open literature values are applied to design the two investigated bypass ratios; a reference engine with a bypass ratio of 5 and 17 respectively. This study shows that a careful selection of engine mass flow, turbine entry temperature and overall pressure ratio determines the desirable bypass ratio. The aircraft direct operating costs drop by 5.7% when comparing the designed conventional with a future ultra-high bypass ratio engine. Furthermore, the sound at source for a selected mission and operating condition can be reduced by 7 dB. A variable bypass nozzle area for the ultra-high bypass ratio engine is analysed in terms of performance and operability. An increase of safety margin is shown for the turbofan engine with a variable bypass nozzle. It is concluded that this unconventional aircraft configuration with ultra-high bypass ratio engines mounted over the wing has the potential to relieve main hub airports and reduce the environmental impact.

System noise has been integrated as an additional design objective within conceptual aircraft design. The DLR system noise prediction tool PANAM accounts for individual noise sources depending on their geometry and operating conditions. PANAM is integrated into the existing aircraft design framework PrADO from the Technical University of Braunschweig in order to realize a design-to-noise simulation process. In addition, a ray-tracing tool from DLR, SHADOW, is incorporated into the simulation framework in order to account for structural engine noise shielding. The overall simulation process is then applied to identify promising low-noise aircraft concepts. The presented application aims at fan noise reduction through shielding. For the selected reference aircraft, the fan is a major noise source during both landing and takeoff. It is demonstrated, that the aircraft designers influence on the environmental vehicle characteristics is significant at the conceptual design phase. Usually, a trade-off between extensive engine noise shielding and economical flight performance is inevitable. The new design-to-noise process is well suitable to assess all four measures of ICAOs balanced approach.

No abstract

A methodology for improving the quality of high-lift-system performance prediction within a multidisciplinary conceptual design process is presented. The high-lift-system geometry is explicitly modeled and a multiple-lifting-line method is used to compute its aerodynamic characteristics. Computation times are acceptable for use in a conceptual design process. The results for several test cases show good agreement with wind-tunnel and/or high-fidelity numerical data. In addition, the method allows for further enhancement by using nonlinear airfoil polars for interpolation, improving drag prediction, and introducing some degree of nonlinear aerodynamic behavior.