| 11. |
- Tomac, Maximilian, et al.
(författare)
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Comparing & benchmarking engineering methods on the prediction of X-31 aerodynamics
- 2010
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Ingår i: 28th AIAA Applied Aerodynamics Conference. - Reston, Virigina : American Institute of Aeronautics and Astronautics. - 9781617389269 ; , s. 2010-4694-
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Konferensbidrag (refereegranskat)abstract
- NATO RTO-AVT-161 is an assessment of Stability and Control Prediction Methods for NATO Air and Sea Vehicles. Though the assessment includes the use of advanced CFD methods, a number of useful engineering methods are available for fast and economic estimates of the aerodynamic characteristics of complex flight vehicles. The objective of this paper is to investigate the use of three specific engineering methods on the X-31 fighter configuration for which CFD, wind tunnel, and flight test data are available for comparison and evaluation purposes. The emphasis is on static longitudinal stability aspects up to high angles of attack; however, selected asymmetric and unsteady effects are considered. Results from the engineering methods are in good agreement with experiment and CFD for angles of attack up to 15 degrees for most cases and higher angles for some cases. Results for pitching moment are in good agreement with CFD, but many of the nonlinear characteristics of the airplane are not predicted by the engineering methods. The quality of the longitudinal stability results is discussed in terms of the prediction of the center of pressure on the vehicle. The results provide improved understanding of the continued usefulness of engineering methods as an analysis tool during the design phase and into the flight test diagnostic phase of a new aircraft.
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| 12. |
- Tomac, Maximillian, et al.
(författare)
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Engineering methods applied to an unmanned combat air vehicle configuration
- 2012
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Ingår i: Journal of Aircraft. - 0021-8669 .- 1533-3868. ; 49:6, s. 1610-1618
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Tidskriftsartikel (refereegranskat)abstract
- Engineering methods provide fast and economic predictions of the aerodynamic characteristics of complex flight vehicles. This paper investigates the application of three specific engineering methods to a unmanned combat air vehicle (UCAV) configuration, termed the Stability and Control Configuration (SACCON), that is still under investigation and that is the subject of an intensive computational and experimental study by the NATO Research and Technology Organization task group AVT-161 for better understanding of its stability and control characteristics. Computational fluid dynamics (CFD) data are computed for theSACCONat wind-tunnel conditions and are compared and evaluated against the measured values, especially in terms of their implications for low-speed longitudinal flight characteristics. Because of their reduced-order modeling compared with Reynolds-averaged Navier-Stokes CFD, predictions by the engineering methods are restricted to the flight-condition range governed by linear flow physics, which, for the SACCON in low speed is 0 α 10 deg. Despite the limited range in angle of attack, it was discovered that, due to the large sweep angle of theSACCONwing and its tip section of zero taper ratio, peak suction levels at the tip were so high that the boundary layer separated there instead. This viscous effect caused a discrepancy between the predicted and measured values of the pitching moment. The remedy taken was to increase the washout for theSACCONwing by modifying its twist and camber, and predictions made for this shape confirmed that linear flow physics prevailed then and that the static stability margin was increased. Furthermore, a series of predictions were made at high speed to establish the drag-divergence Mach numberMdd. The investigations carried out here demonstrate the continued usefulness of engineering methods not only as an analysis tool during the initial aircraft design phase but also as a design tool to improve the shape definition of the vehicle to achieve better performance.
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| 13. |
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| 14. |
- Tomac, Maximilian, et al.
(författare)
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Stability and control assessment of a generic UCAV design using the edge flow solver
- 2014
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Ingår i: 32nd AIAA Applied Aerodynamics Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics (AIAA).
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Konferensbidrag (refereegranskat)abstract
- Accurate estimations of control effectiveness are crucial for flight mechanical model development to assess controllability. Any deficiency in the design should be corrected at an early stage. An increased interest in Unmanned Combat Aerial Vehicles (UCAV) has put focus on the controllability of low observable platforms with highly sweep delta wings without the traditional fin. The NATO STO task group AVT-201 was formed to meet this stability and control challenge and build on previous knowledge gained on complex vortical flow of rounded leading-edge delta wings. This paper presents the numerical results, using the FOI developed flow solver Edge, of the common cases for the DLR-F19 model. The effect of trailing-edge ap deections was investigated using steady RANS or time-accurate hybrid RANS-LES methods. Both static and dynamic pitch cases at low speed and high angle of attack were evaluated and compared to experimental data.
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| 15. |
- Tomac, S., et al.
(författare)
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Ionic effects on the stability and conformation of peptide nucleic acid complexes
- 1996
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 118:24, s. 5544-5552
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Tidskriftsartikel (refereegranskat)abstract
- Peptide nucleic acid (PNA) is a DNA analogue in which the negatively charged sugar phosphate backbone has been substituted by uncharged N-(2-aminoethyl)glycine units. The study of a PNA-DNA duplex and the corresponding DNA-DNA duplex gives a unique opportunity to compare two polyelectrolytes with virtually identical geometry but greatly different linear charge density. The results provide a basis for a study of the applicability of the Poisson-Boltzmann (PB) and counterion condensation (CC) theories. UV and circular dichroism spectroscopy as well as isothermal titration calorimetry (ITC) have been used to study the effect of different ions on the stability and conformation of PNA-DNA, PNA-PNA, and DNA-DNA duplexes having the same base sequences. Cations in general destabilize both antiparallel (N/3') and parallel (N/5') PNA-DNA duplexes whereas they stabilize the DNA-DNA duplex. Studies on the effect of monovalent salt such as NaCl on T-m were carried out over a wide range of salt concentrations (0.01 to 5 M). The decrease in the T-m of the N/3' PNA-DNA duplex with increasing ionic strength in the range of concentrations of 0.01 to 0.5 M, where electrostatic effects predominate, is explained in terms of counterion release upon duplex formation in contrast to the counterion association accompanying the formation of a DNA duplex. The uncharged PNA-PNA duplex shows no significant destabilization in this concentration range. The higher stability of the N/3' PNA-DNA compared to the DNA-DNA duplex (Delta Delta G similar to-7 kcal/mol) is ascribed to more favorable entropic contributions consistent with the counterion release that accompanies the PNA-DNA duplex formation. At high salt concentration (>1 M), where electrostatic contributions saturate, similar trends in the decrease in T-m, were observed for the three types of duplexes irrespective of their backbone charges. The destabilizing effects of a series of Na salts with various monovalent anions on N/3' PNA-DNA and PNA-PNA duplexes were found to follow the Hofmeister series, emphasizing the importance of the hydrophobic interaction between nucleobases for the stability of the PNA complexes in high salt concentration.
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