Abstract
Wake vortices are an inevitable result of lift generation and can pose a threat to any aircraft, which accidentally encounters the wake of another aircraft. However, wake vortices can also be used in a beneficial way. Due to its rotational direction, the air flows upwards outside of the vortex pair, giving additional energy to any aircraft located in these regions. This method of saving energy is used by migratory birds, resulting in these birds flying in typical V-formations. This study deals with the question, whether it is possible with a standard autopilot (without a dedicated formation flight mode) to keep the aircraft’s position accurately at a desired position in the wake flow field without accidentally encountering those areas of the wake where steady-state flight is impossible, even in the presence of atmospheric disturbances (e.g. turbulence) and fluctuating vortex core positions. For this purpose, simulations were performed applying three-dimensional flowfields generated with large eddy simulations. Here, even with young vortices, the target sweet spot position varies in the lateral and vertical directions with a magnitude of a few metres at a constant distance behind the generator aircraft. Hence, also the vortex-induced forces and moments change continuously while flying at the same relative position to the leading aircraft. Preliminary simulations with an A320 flying in the wake of an A340, utilizing the regular autopilot of the comprehensive DLR A320 flight simulation model without a dedicated formation-keeping mode, show that the autopilot does not accidentally encounter hazardous regions within the wake. This indicates that it could be sufficient for a formation-keeping autopilot for civil transport aircraft to be designed as the outer loop of the regular autopilot.
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Abbreviations
- AIM:
-
Aerodynamic interaction model
- ATRA:
-
Advanced Technologies Research Aircraft
- AVES:
-
Air vehicle simulator
- DLR:
-
German Aerospace Center
- DME:
-
Distance measuring equipment
- FL:
-
Flight level
- IAE:
-
International Aero Engines
- ICAO:
-
International Civil Aviation Organisation
- ILS:
-
Instrument landing system
- LES:
-
Large eddy simulation
- NASA:
-
National Aeronautics and Space Administration
- NDB:
-
Non-directional beacon
- P2P:
-
Probabilistic two-phase model
- RCR:
-
Roll control ratio
- VOR:
-
Very-high-frequency omnidirectional radio range
- Γ :
-
Circulation (m2/s)
- Γ 0 :
-
Initial circulation (m2/s)
- Γ 5–15 :
-
Circulation averaged over radii between 5 and 15 m (m2/s)
- b 0 :
-
Initial vortex spacing (m)
- b :
-
Wing span (m)
- \({C_{{\text{l,ind}}}}\) :
-
Induced rolling moment (−)
- \({C_{{\text{l}},{\xi _{{\text{max}}}}}}\) :
-
Maximum control rolling moment (−)
- ε*:
-
Normalised eddy dissipation rate (−)
- Φ :
-
Bank angle (°)
- g :
-
Earth’s gravitational constant (m/s2)
- ρ :
-
Air density (kg/m3)
- r :
-
Distance from vortex core (m)
- r c :
-
Core radius (m)
- m :
-
Aircraft mass (kg)
- N*:
-
Normalised Brunt–Väisalää frequency (−)
- V T :
-
Tangential velocity (m/s)
- V TAS :
-
True airspeed (m/s)
- u, v, w :
-
Velocity components (m/s)
- \(\xi\) :
-
Aileron deflection angle (°)
- x, y, z :
-
Cartesian co-ordinates (m)
References
N. N.: Procedures for air navigation services, air traffic Management. ICAO Doc 4444, 15th edn (2007)
Hummel, D.: Aerodynamic aspects of formation flight in birds. J. Theor. Biol. 104, 321–347 (1983)
Cutts, C.J., Speakman, J.R.: Energy savings in formation flight of pink-footed geese. J. Exp. Biol. 189, 251–261 (1994)
Lissamann, P.B.S., Shollenberger, C.A.: Formation flight of birds. Science 168(3934), 1003 (1970)
Hummel, D.: Die Leistungsersparnis beim Ver-bandsflug (english: the power saving during formation flight). J. Orn. 114, 259–282 (1973)
Beukenberg, M., Hummel, D.: Aerodynamics, performance and control of airplanes in for-mation flight. In: 17th Congress of the International Council of Aeronautical Sciences (ICAS). Stockholm, Sweden (1990)
Blake, W., Multhopp, D.: Design, performance and modeling considerations for close formation flight. In: AIAA Atmospheric Flight Mechanics Conference and Exhibit, AIAA 1998–4343, pp. 476–486 (1998)
Wagner, M.G., et al.: Flight test results of close formation flight for fuel savings. In: AIAA Atmospheric Flight Mechanics Conference and Exhibit, AIAA 2002–4490 (2002)
Vachon, M.J., et al.: F/A-18 aircraft performance benefits measured during the autono-mous formation flight project. AIAA Atmospheric Flight Mechanics Conference and Exhibit, AIAA 2002–4491 (2002)
Bieniawski, S.R., et al.: Summary of flight testing and results for the formation flight for aerodynamic benefit program. In: AIAA 2014–1457, AIAA SciTech, 52nd Aerospace Sciences Meeting, national Harbor, Maryland, USA, 13–17 January (2014)
Slotnick, J.P., et al.: Computational aerodynamic analysis for the formation flight for aerodynamic benefit program. In: AIAA 2014–1458, AIAA SciTech, 52nd Aerospace Sciences Meeting, national Harbor, Maryland, USA, 13–17 January (2014)
Kaden, A., Luckner, R.: Modeling wake vortex roll-up and vortex-induced forces and moments for tight formation flight. In: AIAA Modeling and Simulation Technologies Conference, AIAA 2013–5076 (2013)
Raab, C.: Flugdynamisches Simulationsmodell A320-ATRA—Validierungsversuche und Bewertung der Modellgüte (english: Flight Dynamics Simulation Model A320-ATRA—Validation Tests and Rating of the Model Accuracy), DLR Internal Report IB 111–2012/43, Braunschweig, Germany (2012)
N.N.: Manual of criteria for the qualification of flight simulation training devices. ICAO Doc-9625, (3) (2009)
N.N.: A320 flight crew operating manual, part I, system description, Issue 01-Dec-2008
N.N.: A320/A321 aircraft maintenance manual AMM, reference DG. AMM AEF, Issue 01-May-2009
Gerz, T., Schwarz, C.W.: The DLR project wetter und fliegen. DLR Research Report 2012-02, ISSN 1434–8454, Oberpfaffenhofen, Germany (2012)
Fischenberg, D.: Bestimmung der Wirbelschlep-pencharakteristik aus Flugmessdaten (english: Determination of Wake Vortex Characteristics from Flight Test Data), German Aerospace Congress, Stuttgart, Germany (2002)
Burnham, D., Hallock, J.: Chicago monostatic acoustic vortex sensing system 4, wake vortex decay. National Information Service, Springfield (1982)
Rosenhead, L.: The formation of vortices from a surface of discontinuity. Proc. R. Soc. Lond. Ser. A. 134, 170–192 (1932)
Holzäpfel, F.: Probabilistic two-phase wake vortex decay and transport model. J. Aircr. 40(2), 323–331 (2003)
Vechtel, D.: Simulation study of wake encounters with straight and deformed vortices. Aeronaut, J., 120, 1226 (2016)
Barrows, T.M.: Simplified methods of predicting aircraft rolling moments due to vortex encounters. In: AIAA Paper 76-61, AIAA 14th Aerospace Sciences Meeting, Washington DC, USA (1976)
de Bruin, A.: WAVENC—wake vortex evolution and wake vortex encounter. Publishable Synthesis Report, National Aerospace Lab., NLR-TR-2000-079, Amsterdam, The Netherlands (2000)
Jategaonkar, R., Fischenberg, D., Gruenhagen, W.V.: Aerodynamic modelling and system identification from flight data—recent applications at DLR. J. Aircr. 41(4), 687 (2004)
Vechtel, D.: Inflight simulation of wake encounters using deformed vortices. Aeronaut. J. 117, 1196 (2013)
Vechtel, D.: Flight simulator study on the influence of vortex curvature on wake encounter hazard using LES wind fields. Aeronaut. J. 116, 1177 (2012)
Fischenberg, D.: A method to validate wake vortex encounter models from flight test data. In: ICAS 2010, 27th International Congress of the Aeronautical Sciences, Nice, France (2010)
Schwarz, C.W., Hahn, K.-U.: Full-flight simulator study for wake vortex hazard area investigation. Aerosp. Sci. Technol. 10(2), 136–143 (2006)
Hahn, K.-U., Schwarz, C.W.: Safe limits for wake vortex penetration. In: AIAA Paper 2007–6871, AIAA Guidance, Navigation and Control Conference and Exhibit, Hilton Head, South Carolina, USA (2007)
Schwarz, C.W., Vechtel, D.: Wake vortex encounter severity criteria for RECAT. DLR Internal Report IB 111–2012/44. Braunschweig, Germany (2012)
Crow, S.C.: Panel discussion, symposium on aircraft wake turbulence. Seattle, Washington, US, 1–3 September (1970)
Duda, H., et al.: Design of the DLR AVES research flight simulator. In: AIAA Modeling and Simulation Technologies Conference, AIAA 2013–4737 (2013)
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Vechtel, D., Fischenberg, D. & Schwithal, J. Flight dynamics simulation of formation flight for energy saving using LES-generated wake flow fields. CEAS Aeronaut J 9, 735–746 (2018). https://doi.org/10.1007/s13272-018-0318-z
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DOI: https://doi.org/10.1007/s13272-018-0318-z