The Aeroplane Spin Motion and an Investigation into Factors Affecting The Aeroplane Spin A thesis submitted for the degree of Doctor of Philosophy by Rein Inge Hoff Brunel Flight Safety Laboratory College of Engineering, Design and Physical Sciences Brunel University London ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! November 2014 ! 1 Abstract A review of aeroplane spin literature is presented, including early spin research history and lessons learned from spinning trials. Despite many years of experience in spinning evaluation, it is difficult to predict spin characteristics and problems have been encountered and several prototype aeroplanes have been lost. No currently published method will reliably predict an aeroplane’s spin recovery characteristics. Quantitative data is required to study the spin motion of the aeroplane in adequate detail. An alternative method, Vision Based State Estimation, has been used to capture the spin motion. This alternative method has produced unique illustrations of the spinning research aeroplane and data has been obtained that could possibly be very challenging to obtain using traditional methods. To investigate the aerodynamic flow of a spinning aeroplane, flights have been flown using wool tufts on wing, aft fuselage and empennage for flow visualization. To complement the tuft observations, the differential pressure between the upper and lower horizontal tail and wing surfaces have been measured at selected points. Tufts indicate that a large-scale Upper Surface Vortex forms on the outside wing. This USV has also been visualized using a smoke source. The flow structures on top of both wings, and on top of the horizontal tail surfaces, have also been studied on another aeroplane model. The development of these rotational flow effects has been related to the spin motion. It is hypothesized that the flow structure of the turbulent boundary layer on the outside upper wing surface is due to additional accelerations induced by the rotational motion of the aeroplane. The dynamic effects have been discussed and their importance for the development of the spin considered. In addition, it is suggested that another dynamic effect might exist due to the additional acceleration of the turbulent boundary layer due to the rotational motion of the aeroplane. It is recommended that future spin recovery prediction methods account for dynamic effects, in addition to aerodynamic control effectiveness and aeroplane inertia, since the spin entry phase is important for the subsequent development of the spin. Finally, suggestions for future research are given. 2 Disclaimer This report has been prepared at the Brunel Flight Safety Laboratory, Brunel University London, as part of a research degree and this report is prepared for research purposes only. Absolutely no information, and none of the instructions, contained in this report are for operational use. The spin characteristics depend on many variables and a slight change in configuration might alter the spin behaviour. Aeroplanes used in this research project, and aeroplanes discussed and referenced in the text, might be modified for research or test purposes, or might be experimental prototypes at an early development stage that might or might not have been certified at a later stage. Even if known aeroplane models are discussed in this report, the reader should be warned that the information might not be applicable or accurate. In some cases the aeroplanes have been modified for research or test purposes and are not representative of similar models even if the same name, type and model designation is used. Similar aeroplanes may have very different flight and spin characteristics. This report is not a guide or source of information on how to fly, do a flight test or how to perform spinning. The information in this report is not a substitute for formal flight training from a recognized source of hands-on stall, spin, aerobatic flight or flight test instruction. Pilots should never perform aerobatic flight, stalls, post-stall manoeuvres or intentional spinning without proper flight instruction from a qualified flight instructor. Always use appropriate safety equipment and always adhere to the information and instructions in the official documentation from the aeroplane manufacturer or operator. Aerobatic flight and spinning can be very dangerous and life threatening. 3 Contents Page No. ! Abstract!................................................................................................................................!1! Disclaimer!............................................................................................................................!2! List!of!tables!........................................................................................................................!5! List!of!figures!......................................................................................................................!5! Abbreviations!.....................................................................................................................!9! Nomenclature!...................................................................................................................!10! Acknowledgements!........................................................................................................!12! List!of!Journal!Papers!.....................................................................................................!13! 1!Research!subject!introduction!................................................................................!14! 2!Review!of!literature!....................................................................................................!16! 2.1!Introduction!............................................................................................................................!16! 2.2!Prelude!to!spin:!Departure!from!controlled!flight!....................................................!17! 2.3!Aeroplane!spin!history!and!the!early!spin!investigations!......................................!20! 2.3.1!The!simplified!steady!state!spin!...............................................................................................!24! 2.3.2!Autorotation!explained!................................................................................................................!27! 2.3.3!The!existence!of!the!oscillatory!spin!......................................................................................!29! 2.4!The!worst!case:!The!flat!spin!.............................................................................................!30! 2.5!Successful!spin!recovery!defined!.....................................................................................!32! 2.5.1!The!spin!recovery!requirements!..............................................................................................!32! 2.5.2!Spinning!trial!conduct!...................................................................................................................!34! 2.5.3!NonCcompliance!...............................................................................................................................!37! 2.5.4!Aeroplanes!that!are!not!certified!.............................................................................................!38! 2.6!Spin!recovery!technique!.....................................................................................................!39! 2.7!Effect!of!controls!....................................................................................................................!41! 2.8!Problems!with!wind!tunnel!results!.................................................................................!42! 2.9!The!very!important!tail!.......................................................................................................!44! 2.9.1!The!Tail!Damping!Power!Factor!(TDPF)!..............................................................................!45! 2.10!Spin!problems!encountered!due!to!minor!modifications!.....................................!47! 2.11!Spin!resistant!aeroplanes!................................................................................................!48! 2.12!Nose!length!to!tail!length!ratio!and!scaling!effects!.................................................!49! 2.13!Moving!wall!and!accelerated!flow!effects!...................................................................!50! 2.14!Discussion!and!conclusions!............................................................................................!51! 3!Methodologies!for!evaluating!spinning!characteristics!.................................!53! 3.1!Introduction!............................................................................................................................!53! 3.2!The!research!aeroplanes!and!spin!entry!and!recovery!technique!.......................!54! 3.3!The!creation!of!a!Firefly!CAD!model!...............................................................................!59! 3.4!Obtaining!high!quality!video!imagery!of!the!2Uturn!Firefly!spin!..........................!60! 3.5!Vision!Based!State!Estimation:!Capturing!the!spin!motion!....................................!64! 3.6!Video!imagery!of!tufts!on!wings!and!tail!surfaces!.....................................................!70! 3.7!The!MTiUG!Flight!Data!Recorder!......................................................................................!73! 3.8!The!PSSU8!Pressure!Sensor!System!.................................................................................!74! 3.9!The!Multi!Purpose!Boom!....................................................................................................!77! 3.10!Data!accuracy,!synchronisation!problems!and!integrity!of!measured!data!...!79! 3.10.1!VBSE!accuracy!considerations!................................................................................................!83! 4 4!The!spin!motion!...........................................................................................................!84! 4.1!Introduction!............................................................................................................................!84! 4.2!Qualitative!descriptions!of!the!spin!motion!as!perceived!by!the!pilot!...............!85! 4.2.1!Norman!Aeroplane!Co.!Firecracker!.........................................................................................!86! 4.2.2!Aermacchi!Impala!...........................................................................................................................!89! 4.2.3!Slingsby!Firefly!.................................................................................................................................!91! 4.2.4!Saab!Safir!............................................................................................................................................!91! 4.2.4!Summary!of!qualitative!descriptions!of!the!spin!motion!..............................................!93! 4.3!Additional!data!from!the!Tucano!and!the!Jet!Provost!spinning!trials!.................!94! 4.4!Gyroscopic!effects!.................................................................................................................!95! 4.4.1!Historical!note:!‘The!cornfield!bomber’!.............................................................................!102! 4.5!The!variation!in!spin!motion!...........................................................................................!102! 4.6!Data!obtained!from!the!Vision!Based!State!Estimation!of!the!spinning!Firefly !..........................................................................................................................................................!107! 5!Aerodynamic!flow!over!wings!and!empennage!..............................................!116! 5.1!Introduction!..........................................................................................................................!116! 5.2!Flow!over!the!wings!of!the!spinning!aeroplane!........................................................!117! 5.2.1!Spin!entry!and!first!turn!............................................................................................................!117! 5.2.2!Second!turn!and!recovery!........................................................................................................!119! 5.3!Flow!across!the!vertical!tail!and!aft!fuselage!.............................................................!123! 5.4!Upper!Surface!Vortex!smoke!visualization!................................................................!126! 5.5!Saab!Safir:!A!special!case!of!rudder!control!limiting!..............................................!130! 5.5.1!Saab!Safir:!Outside!wing!in!a!right!2Cturn!spin!...............................................................!132! 5.5.2!Saab!Safir:!Inside!wing!in!a!left!2Cturn!spin!(spiral!mode)!........................................!134! 5.5.3!Saab!Safir:!Outside!wing!in!a!left!2Cturn!spin!(spiral!mode)!.....................................!135! 5.5.3!Saab!Safir:!Description!of!observed!flow!on!the!horizontal!tail!surfaces!............!135! 6!Point!measurements!of!differential!pressure!between!upper!and!lower! horizontal!tail!and!wing!surfaces!...........................................................................!138! 6.1!Introduction!..........................................................................................................................!138! 6.2!Differential!pressure!between!upper!and!lower!horizontal!tail!surfaces!during! spins!in!the!Safir!.........................................................................................................................!139! 6.3!Slingsby!Firefly!stalls!.........................................................................................................!141! 6.4!PostUstall!Large!Amplitude!Wing!Rock!(LAWR)!mode!............................................!144! 6.5!Differential!pressure!measurements!between!upper!and!lower!wing!surfaces! during!spins!in!the!Firefly!.......................................................................................................!147! 7!Discussions!and!Conclusions!................................................................................!150! 7.1!Vision!Based!State!Estimation!(VBSE)!..........................................................................!150! 7.2!Qualitative!assessment!of!the!aerodynamic!flow!.....................................................!150! 7.3!Initialisation!of!the!Upper!Surface!Vortex!(USV)!......................................................!151! 7.4!Rotational!aerodynamic!flow!effects!............................................................................!152! 7.5!The!change!in!flow!condition!over!the!horizontal!tail!...........................................!155! 7.6!Autorotation!of!the!wings!.................................................................................................!156! 7.7!The!importance!of!the!dynamic!effects!for!the!development!of!the!spin!.........!156! 7.8!Conclusions!...........................................................................................................................!158! 8!Suggestions!for!future!research!...........................................................................!159! References!......................................................................................................................!160! Appendix!1! 5 List of tables TABLE!1.!A!SUMMARY!OF!QUANTITATIVE!SPIN!REQUIREMENTS!FOR!AEROPLANES!AND!SAILPLANES!......!36! TABLE!2.!EFFECT!OF!CONTROLS!ON!THE!RECOVERY!FROM!THE!SPIN.!.............................................................!41! TABLE!3.!EXAMPLES!OF!DISCREPANCIES!OBSERVED!WHEN!FLIGHT!TESTING!5!PROTOTYPE!AEROPLANE! MODELS.!............................................................................................................................................................!43! TABLE!4.!SLINGSBY!T67M200![67]!AND!SAAB!SB91B2![69]!GENERAL!DATA.!........................................!57! TABLE!5.!GENERAL!DATA!FOR!4!MILITARY!TRAINING!AIRCRAFT!.....................................................................!85! TABLE!6.!SUMMARY!OF!SPIN!CHARACTERISTICS!AS!OBSERVED!FROM!THE!COCKPIT.!...................................!93! TABLE!7.!COMPARISON!OF!LEFT!HAND!6CTURN!SPINS!IN!THE!JET!PROVOST!AND!THE!TUCANO.!..............!95! TABLE!8.!EFFECTS!OF!THE!POSSIBLE!IMPOSED!MOMENTS!ON!THE!ANGULAR!MOMENTUMS!FOR!THE! SPINNING!AEROPLANE.!...................................................................................................................................!97! TABLE!9.!THE!CORRELATION!COEFFICIENTS!FOR!THE!LEFT!6CTURN!SPIN!OMEGA!HISTORIES.!...............!104! TABLE!10.!DATA!OBTAINED!FROM!9!SPINS!SHOWING!THE!VARIATION!IN!TIME!AND!ALTITUDE!LOSS!PER! TURN!FOR!THREE!GROUPS!OF!SPIN!(ALL!6CTURN,!RIGHT,!LEFT!AND!LEFT!WITH!MPB!INSTALLED). !.........................................................................................................................................................................!105! TABLE!11.!SUMMARY!OF!TUFT!OBSERVATIONS!ON!OUTSIDE!WING!FROM!THE!SAFIR!2CTURN!RIGHT!SPIN. !.........................................................................................................................................................................!134! ! ! List of figures FIGURE!1.!TYPICAL!VARIATIONS!OF!THE!AERODYNAMIC!PARAMETERS!SHOWING!THE!LOSS!OF!STABILITY! AT!THE!STALL!(FIGURE!FROM!REF.![18]).!..................................................................................................!18! FIGURE!2.!THE!CESSNA!TC37!TWIN!ENGINE!USAF!JET!TRAINER!(COURTESY!OF!USAF).!..........................!20! FIGURE!3.!A!RESULT!FROM!THE!SPIN!ANALYSIS!PUBLISHED!IN!1918,!THE!VARIATION!OF!ANGLE!OF! ATTACK!(TERMED!“ANGLE'OF'INCIDENCE”)!OVER!THE!WINGSPAN!OF!A!SPINNING!AEROPLANE! (FIGURE!FROM!REF.![27]).!............................................................................................................................!22! FIGURE!4.!ILLUSTRATION!OF!“THE'PROTOTYPE'SPIN”,!SHOWING!THE!RESULTANT!AERODYNAMIC!FORCE! AND!ITS!COMPONENTS,!LIFT!BALANCED!BY!CENTRIFUGAL!FORCE!AND!DRAG!BALANCED!BY!WEIGHT! (FIGURE!FROM!REF.![30]).!............................................................................................................................!25! FIGURE!5.!THE!COMPONENTS!OF!THE!ANGULAR!VELOCITY!VECTOR!IN!AN!ERECT!SPIN!TO!THE!RIGHT.!....!26! FIGURE!6.!ILLUSTRATION!(FROM!REF.![30])!SHOWING!THE!DIFFERENCE!IN!ANGLE!OF!ATTACK!FOR!THE! UPC!AND!DOWNCGOING!WING.!.......................................................................................................................!28! FIGURE!7.!ILLUSTRATION!(FROM!REF.![30])!SHOWING!BOTH!THE!SPONTANEOUS!AUTOROTATION!(ACB)! AND!THE!LATENT!AUTOROTATION!(BCC)!REGIONS.!.................................................................................!29! FIGURE!8.!THE!SHORT!TUCANO!T!MK.1!RAF!TURBOPROP!TRAINER!(COURTESY!OF!G.!GRATTON).!.......!37! FIGURE!9.!SKETCH!OF!THE!BAC!JET!PROVOST!T!MK.!5!RAF!JET!TRAINER.!NOTE!THE!NOSE!STRAKES!AND! CAMREX!PAINT!APPLIED!TO!THE!OUTER!WING!LEADING!EDGE!(ILLUSTRATION!FROM!REF.![43]).!38! FIGURE!10.!A!3CVIEW!OF!THE!SLINGSBY!T67MX!FIREFLY.!THE!POSITION!OF!THE!MULTI!PURPOSE!BOOM! WITH!THE!AIR!DATA!PROBE!ATTACHED!IS!SHOWN!TOGETHER!WITH!THE!POSITION!OF!THE!STATIC! PORTS!USED!FOR!DIFFERENTIAL!PRESSURE!MEASUREMENTS!(DP1!AND!DP2).!..................................!55! FIGURE!11.!A!3CVIEW!OF!THE!SAAB!SAFIR!(MODEL!SB91B2)!USED!IN!THE!BFSL!SPIN!RESEARCH! PROGRAMME.!...................................................................................................................................................!56! FIGURE!12.!THE!COLOURED!POINTCCLOUD!OF!THE!FIREFLY.!NOTE!THE!LASER!SCAN!TARGETS!ON!THE! WALLS.!...............................................................................................................................................................!59! FIGURE!13.!THE!POINTCCLOUD!BEFORE!THE!CLEANING!AND!MESHING!PROCEDURE.!..................................!60! FIGURE!14.!THE!FIREFLY!AFTER!THE!MESHING!PROCEDURE.!..........................................................................!60! FIGURE!15.!THE!CAMERA!INSTALLATION!IN!THE!HELICOPTER.!.......................................................................!61! FIGURE!16.!THE!FLIGHT!POSITION!OF!THE!CAMERA!OPERATOR.!.....................................................................!62! FIGURE!17.!LEFT!SPIN!ENTRY!(JUST!OVER!½!TURN)!‘SHOT’!FROM!THE!HELICOPTER.!.................................!63! FIGURE!18.!AEROPLANE!ABOUT!TO!COMPLETE!1CTURN!IN!THE!SPIN.!............................................................!64! 6 FIGURE!19.!SPIN!MOTION!FROZEN!IN!3D!SPACE!AND!VIEW!ROTATED.!...........................................................!65! FIGURE!20.!A!SCREENSHOT!FROM!SYNTHEYES![79]!SHOWING!POINTS!ON!AEROPLANE!WITH!GEOMETRY! OVERLAY!FROM!THE!CAD!MODEL!AND!POINTS!IN!THE!BACKGROUND.!.................................................!66! FIGURE!21.!THE!SMOOTHING!OF!THE!AEROPLANE!CG!TRACKLINE.!THE!RED!LINE!IS!THE!ORIGINAL! TRACKLINE!AND!THE!YELLOW!DOTS!ARE!THE!POINTS!THAT!WERE!OUTSIDE!THE!STANDARD! DEVIATION!TUBE!AND!WERE!THEREFORE!REMOVED.!...............................................................................!67! FIGURE!22.!ESTIMATED!ANGLE!OF!ATTACK!(Α)!AND!SIDESLIP!(ß)!WERE!MEASURED!EVERY!5TH!FRAME.!68! FIGURE!23.!AN!ILLUSTRATION!SHOWING!THREE!SPIN!POSITIONS!FROZEN!ON!THE!TRACKLINE.!THE! SECOND!POSITION!IS!THE!SAME!AS!SHOWN!IN!FIGURE!18!AND!FIGURE!19.!........................................!69! FIGURE!24.!THE!FIREFLY!RESEARCH!AEROPLANE!WITH!THE!SYMMETRIC!AND!STRUCTURED!TUFT!GRIDS! ON!WINGS!AND!HORIZONTAL!TAIL!SURFACES.!...........................................................................................!71! FIGURE!25.!FOUR!MOVIES!SYNCHRONISED!AND!SHOWN!TOGETHER!IN!THE!SAME!IMAGE.!THE!FIREFLY! HAS!COMPLETED!1CTURN!IN!THE!SPIN!AT!4!SECONDS!AND!10!FRAMES!(THE!SPIN!ENTRY!WAS!AT!0! SECOND!20!FRAMES).!.....................................................................................................................................!72! FIGURE!26.!SAAB!SAFIR!YAW!RATE!FOR!A!RIGHT!HAND!6CTURN!SPIN.!THE!TURN!COMPLETIONS!ARE! SHOWN!AS!VERTICAL!LINES!(WHICH!ARE!NUMBERED!1ST,!2ND!ETC.).!....................................................!74! FIGURE!27.!THE!MODIFIED!PITOTCSTATIC!SYSTEM!CIRCUIT!BOARD!WAS!INSTALLED!IN!THE!AFT!SAAB! SAFIR!FUSELAGE!AND!THE!PLASTIC!TUBES!WERE!ROUTED!ON!UPPER!AND!LOWER!SURFACE!TO!THE! DESIRED!POINTS!USED!FOR!MEASUREMENT.!..............................................................................................!76! FIGURE!28.!THE!MODIFIED!PITOTCSTATIC!SYSTEM!CIRCUIT!BOARD!WITH!TWO!DIFFERENTIAL!PRESSURE! SENSORS!IS!SHOWN!TO!THE!LEFT!AND!THE!STATIC!SINK!PORT!IS!SHOWN!IN!THE!IMAGE!TO!THE! RIGHT.!................................................................................................................................................................!77! FIGURE!29.!THE!STATIC!SINK!PORTS!ON!THE!RIGHT!FIREFLY!WING.!THE!SMALL!ELECTRONIC!CIRCUIT! BOARD!CAN!ALSO!BE!SEEN!JUST!IN!FRONT!OF!(TOWARDS!THE!FUSELAGE)!THE!DP2!PORT!ON!THE! UPPER!SIDE!OF!THE!WING.!.............................................................................................................................!77! FIGURE!30.!THE!‘SMOKE!BOOM’!ATTACHED!TO!THE!RIGHT!WING!OF!THE!FIREFLY!RESEARCH!AEROPLANE. !............................................................................................................................................................................!78! FIGURE!31.!THE!ADP!ATTACHED!TO!THE!RIGHT!WING!OF!THE!FIREFLY!RESEARCH!AEROPLANE.!NOTE! THE!NEGATIVE!INCIDENCE!OF!THE!ADP!RELATIVE!TO!THE!WING!CHORD.!...........................................!79! FIGURE!32.!TIME!HISTORY!OF!THE!PULLCUP!MANEUVER!USED!FOR!SENSOR!TIME!SYNCHRONIZATION.!...!81! FIGURE!33.!THE!NDNC1!FIRECRACKER!PROTOTYPE!AEROPLANE.!.................................................................!86! FIGURE!34.!LEFT,!3CTURN!FIRECRACKER!SPIN!1)!ENTRY!2)!½CTURN!POINT!WITH!HORIZON!VISIBLE!IN! THE!LOWER!RIGHT!CORNER!3)!1CTURN!POINT!4)!2CTURN!5)!3CTURN!AND!FINALLY!6)!RECOVERY !............................................................................................................................................................................!88! FIGURE!35.!THE!AERMACCHI!MBC326M!IMPALA!USED!AT!THE!NATIONAL!TEST!PILOT!SCHOOL!(PHOTO! FROM!NTPS).!..................................................................................................................................................!89! FIGURE!36.!LEFT!HAND!IMPALA!SPIN!1)!ENTRY!2)!½CTURN!POINT!3)!1CTURN!POINT!4)!RECOVERY!...!90! FIGURE!37.!LEFT,!2CTURN!FIREFLY!SPIN!1)!JUST!PASSED!½CTURN!POINT!2)!BEFORE!1CTURN!POINT!3)! 1½!CTURN!POINT!4)!BEFORE!2CTURN!5)!½CTURN!IN!RECOVERY!6)!RECOVERY!CONTINUED!........!92! FIGURE!38.!ESTIMATED!ANGULAR!MOMENTUM!COMPONENTS!(H ,!H !AND!H )!WERE!PLOTTED!USING! X Y Z ESTIMATED!MOI!AND!ANGULAR!RATES!FROM!A!FIREFLY!6CTURN!LEFT!SPIN!(CG!AT!21%!MAC,! TAKEOFF!MASS!WAS!900!KG!AND!SPIN!ENTRY!WAS!AT!APPROX.!5900!FEET!DENSITY!ALTITUDE).!96! FIGURE!39.!COMPARISON!OF!Ω!FOR!THREE!6CTURN!LEFT!SPINS!IN!THE!FIREFLY!WHERE!TWO!OF!THESE! SPINS!WERE!MISHANDLED!CONTROL!CASES.!...........................................................................................!100! FIGURE!40.!COMPARISON!OF!ROLL,!PITCH!AND!YAW!RATES!FOR!THE!SAME!SPINS!AS!SHOWN!ABOVE!IN! FIGURE!39.!....................................................................................................................................................!101! FIGURE!41.!OMEGA!(Ω)!TIME!HISTORY!FOR!4!RIGHT!6CTURN!SPINS.!..........................................................!103! FIGURE!42.!OMEGA!(Ω)!TIME!HISTORY!FOR!5!LEFT!6CTURN!SPINS,!TWO!OF!THEM!WITH!THE!MPB! INSTALLED.!....................................................................................................................................................!103! FIGURE!43.!AVERAGE!VERTICAL!VELOCITY!FOR!THE!THREE!GROUPS!OF!SPINS!(6CTURN!LEFT,!RIGHT!AND! LEFT!WITH!MPB!INSTALLED)!SHOWN!IN!TABLE!10.!............................................................................!107! FIGURE!44.!ESTIMATED!BETA!(Β)!ANGLE!AT!THE!AEROPLANE!CG!FOR!A!LEFT!2CTURN!SPIN!IN!THE! FIREFLY.!.........................................................................................................................................................!109! 7 FIGURE!45.!COMPARISONS!OF!TWO!LEFT!2CTURN!SPINS!IN!THE!SLINGSBY!FIREFLY.!1)!¼CTURN!POINT!2)! ½CTURN!POINT!3)!BEFORE!1CTURN!POINT!4)!AFTER!1CTURN!POINT!5)!AT!RECOVERY!(ROTATION! STOPPED)!.......................................................................................................................................................!110! FIGURE!46.!LEFT!AND!RIGHT!2CTURN!SPIN!DATA!OBTAINED!FROM!THE!VBSE.!........................................!112! FIGURE!47.!4!DIFFERENT!VIEW!ANGLES!OF!THE!AEROPLANE!SHOWING!THE!CG!(BLACK)!AND!THE!WING! POINT!(RED)!TRACKLINES!AT!THE!1CTURN!POINT!IN!THE!SPIN!(FRAME!157).!...............................!113! FIGURE!48.!COMPARISONS!OF!ESTIMATED!Α!FOR!THE!AEROPLANE!CG!AND!THE!TWO!WING!POINTS!(WP)! PLACED!2.6!M!FROM!THE!AEROPLANE!CENTRE!ON!THE!OUTSIDE!AND!INSIDE!WING!RESPECTIVELY.! ERROR!BARS!WERE!ADDED!FOR!AN!ESTIMATED!ANGLE!ERROR!OF!+/C!2.5!DEG!(SEE!SECTION! 3.10.1).!.........................................................................................................................................................!114! FIGURE!49.!THE!TRACKLINE!OF!A!POINT!PLACED!AT!THE!AEROPLANE!TAIL!AND!ITS!PATH!IN!THE!3D! SPACE.!.............................................................................................................................................................!115! FIGURE!50.!A!LARGE!VORTEX!FORMS!ON!THE!OUTSIDE!WING!AS!INDICATED!BY!THE!WOOL!TUFTS.!THE! BLUE!LINES!ARE!DRAWN!TO!ILLUSTRATE!HOW!THE!SHAPE!OF!THE!VORTEX!MIGHT!BE!AND!ARROWS! INDICATE!FLOW!DIRECTION.!......................................................................................................................!118! FIGURE!51.!TUFTS!ON!THE!WING!AT!JUST!PAST!THE!¾!TURN!IN!A!LEFT!HAND!SPIN.!THE!VORTEX!ON!THE! OUTSIDE!(RIGHT)!WING!IS!CLEARLY!SEEN!WHERE!THE!FLAP!MEETS!THE!AILERON.!.......................!118! FIGURE!52.!AT!THE!2CTURN!POINT,!SPANWISE!OUTBOARD!FLOW!IS!CLEARLY!APPARENT!ON!THE!OUTSIDE! WING.!ONLY!THE!OUTER!ROW!OF!TUFTS!ARE!STREAMLINE.!IRREGULAR!FLOW!CAN!BE!SEEN!ON!THE! INSIDE!WING.!.................................................................................................................................................!120! FIGURE!53.!THE!AEROPLANE!JUST!BEFORE!COMPLETING!ONE!TURN!WITH!RECOVERY!CONTROLS!SET!(THE! THIRD!TURN!FROM!SPIN!ENTRY,!LEFT!HAND!SPIN).!ALL!OF!THE!OUTSIDE!WING!TUFTS!INDICATE! STREAMLINE!FLOW.!FLOW!ON!INSIDE!WING!IS!STILL!IRREGULAR!AT!THIS!POINT.!..........................!121! FIGURE!54.!ESTIMATED!Α!AT!THE!AEROPLANE!CG!FROM!THE!VBSE!OF!A!LEFT!2CTURN!SPIN!IN!THE! FIREFLY.!THE!NUMBERS!MARKED!ON!THE!ALPHA!GRAPH!CORRESPOND!TO!THE!SLIDES!IN!FIGURE! 55.!...................................................................................................................................................................!122! FIGURE!55.!THE!VORTEX!ON!THE!OUTSIDE!WING,!SHOWN!TOGETHER!WITH!THE!SPIN!POSITION!AND! ESTIMATED!Α!AT!THE!AEROPLANE!CG.!THE!ARROWS!ON!THE!WING!SHOW!THE!DIRECTION!OF! AIRFLOW!AS!INDICATED!BY!THE!TUFTS.!THE!LARGE!ARROW!BEHIND!THE!WING!INDICATES!THE! DIRECTION!OF!VORTEX!MOVEMENT!ON!THE!WING.!................................................................................!123! FIGURE!56.!THE!TUFTS!ON!TOP!OF!THE!STABILISATOR!INDICATE!THE!PRESENCE!OF!A!LEADING!EDGE! VORTEX.!..........................................................................................................................................................!125! FIGURE!57.!MEASUREMENT!OF!PRESSURES!ON!HORIZONTAL!TAIL!SURFACES!FROM!NASA!WIND!TUNNEL! SPIN!RESEARCH.!ILLUSTRATION!IS!FROM!NASA![55].!.........................................................................!125! FIGURE!58.!SMOKE!IS!PULLED!INWARDS!BY!THE!USV!AS!IT!MOVES!TOWARDS!THE!WING!TIP!DURING!THE! SPIN!ENTRY!(FROM!THE!½CTURN!POINT).!THE!TOP!AND!BOTTOM!IMAGES,!FROM!THE!HELICOPTER! CHASE!AND!THE!COCKPIT!CAMERA!RESPECTIVELY,!ARE!SYNCHRONISED.!..........................................!127! FIGURE!59.!SMOKE!VISUALIZATION!BEFORE!THE!1CTURN!POINT!IN!THE!LEFT!SPIN.!................................!128! FIGURE!60.!BEFORE!THE!2CTURN!POINT!(LEFT!IMAGE)!IN!THE!SPIN,!AND!AFTER!FULL!RIGHT!RUDDER! WAS!APPLIED!FOR!THE!RECOVERY!AT!THE!2CTURN!POINT!(RIGHT!IMAGE),!SMOKE!WAS!VISIBLE! TOWARDS!THE!WING!TIP.!............................................................................................................................!129! FIGURE!61.!AEROPLANE!RECOVERS!FROM!THE!SPIN.!......................................................................................!129! FIGURE!62.!PICTURES!OF!THE!SAFIR!RUDDER!SHOWING!FULL!LEFT,!NEUTRAL!AND!FULL!RIGHT! POSITIONS.!NOTE!THE!TWISTED!RUDDER!AND!THE!DIFFERENCE!IN!RUDDER!ANGLE!WHEN! DISPLACED!FULL!LEFT!AND!FULL!RIGHT.!.................................................................................................!131! FIGURE!63.!MEASURED!YAW!RATES!FOR!THREE!2CTURN!LEFT!(SPIRAL!MODE)!AND!THREE!2CTURN!RIGHT! SPINS!IN!THE!SAFIR.!.....................................................................................................................................!131! FIGURE!64.!ILLUSTRATION!BASED!ON!THE!FLOW!DIRECTION!INDICATED!BY!TUFTS,!SHOWING!THE! DIPOLAR!VORTEX!STRUCTURE!TEMPORARILY!OBSERVED!ON!THE!OUTSIDE!WING!OF!THE!SPINNING! SAFIR!AFTER!THE!1CTURN!POINT!IN!THE!RIGHT!SPIN.!..........................................................................!133! FIGURE!65.!TUFTS!INDICATING!UNSTEADY!STREAMLINE!FLOW!ON!LEFT!HORIZONTAL!TAIL!SURFACE!IN!A! LEFT,!2CTURN!SPIN,!JUST!BEFORE!THE!ELEVATOR!MOVES!DOWN!FOR!THE!RECOVERY!TO!THE!LEFT,! AND!ELEVATOR!IN!NEUTRAL!POSITION!ON!THE!RIGHT.!.........................................................................!136! 8 FIGURE!66.!TUFTS!INDICATING!SPANWISE!FLOW!ON!THE!LEFT!HORIZONTAL!TAIL!SURFACE!IN!A!RIGHT! HAND!2CTURN!SPIN!(AT!APPROX.!THE!¾CTURN!POSITION!IN!THE!SPIN).!..........................................!137! FIGURE!67.!DIFFERENCE!IN!PRESSURE!MEASURED!AT!POINT!DP1!DURING!A!6CTURN!RIGHT!SPIN!IN!THE! SAFIR!(CG!AT!11%!MAC,!WEIGHT!WAS!980!KG!AND!SPIN!ENTRY!WAS!AT!APPROX.!4800!FEET! DENSITY!ALTITUDE).!A!10CPOINT!MOVING!AVERAGE!TREND!IS!SHOWN!AS!A!BLACK!SOLID!LINE.!140! FIGURE!68.!DIFFERENCE!IN!PRESSURE!MEASURED!AT!POINT!DP2!DURING!A!6CTURN!RIGHT!SPIN!IN!THE! SAFIR!(EXACTLY!SAME!SPIN!AS!ABOVE!FOR!THE!DP1!MEASUREMENT).!A!10CPOINT!MOVING! AVERAGE!TREND!IS!SHOWN!AS!A!BLACK!SOLID!LINE.!.............................................................................!141! FIGURE!69.!STALL!FLOWN!IN!THE!FIREFLY!T67MX!WITH!THE!FAA!METHOD!USED!FOR!STALL! RECOVERY.!.....................................................................................................................................................!142! FIGURE!70.!TIME!HISTORY!FOR!A!PITCH!DELAYED!STALL!RECOVERY,!WHICH!RESULTED!IN!AN!EVEN! HIGHER!Α!(AOA).!.........................................................................................................................................!143! FIGURE!71.!THE!HIGHC!AND!LOWCWING!POSITIONS!DURING!THE!POSTCSTALL!LAWR!MOTION.!...........!145! FIGURE!72.!POINT!DIFFERENTIAL!PRESSURE!MEASUREMENTS!FOR!THE!LAWR!MODE!IN!THE!FIREFLY! RESEARCH!AEROPLANE.!THE!DP1!AND!DP2!POINTS!WHERE!PLACED!ON!THE!RIGHT!HAND!SIDE! WING!AS!SHOWN!IN!FIGURE!29.!THE!SMALL!ARROWS!POINT!TO!THE!MINIMUM!DP!VALUES!AS!THE! FLOW!SEPARATES!ON!THE!UPCGOING!WING.!............................................................................................!146! FIGURE!73.!POINT!DIFFERENTIAL!PRESSURE!MEASUREMENTS!FOR!THE!6CTURN!LEFT!SPIN!IN!THE! FIREFLY!RESEARCH!AEROPLANE.!THE!VERTICAL!LINES!REPRESENT!THE!TURN!COMPLETIONS!IN!THE! SPIN.!................................................................................................................................................................!148! FIGURE!74.!POINT!DIFFERENTIAL!PRESSURE!MEASUREMENTS!FOR!THE!6CTURN!RIGHT!SPIN!IN!THE! FIREFLY!RESEARCH!AEROPLANE.!..............................................................................................................!149! FIGURE!75.!SLIDES!SHOWING!THE!INITIALISATION!OF!THE!USV.!TIME!INCBETWEEN!THE!SLIDES!WAS! 20/300!SECONDS!(FRAME!RATE!WAS!300!HZ).!...................................................................................!152! ! 9 Abbreviations AAIB Air Accidents Investigation Branch ADP Air Data Probe AHRS Attitude and Heading Reference System AI Aileron In (Aileron set with the spin direction) BCAR British Civil Airworthiness Requirements BFSL Brunel Flight Safety Laboratory CAA Civil Aviation Authority CAD Computer Aided Design CAS Calibrated Air Speed CCD Charge-coupled Device (camera image sensor) CEP Circular Error Probable CFD Computational Fuid Dynamics CG Centre of Gravity CS Certification Specifications DEF-STAN Defence Standard EASA European Aviation Safety Agency FAA US Federal Aviation Administration FAR Federal Aviation Regulation FDR Flight Data Recorder GPS Global Positioning System IAS Indicated Air Speed IMU Inertial Measurement Unit LAWR Large Amplitude Wing Rock LEV Leading Edge Vortex MAC Mean Aerodynamic Chord MATLAB Matrix Laboratory MEMS Micro Electro Mechanical System MPB Multi Purpose Boom MoI Moment of Inertia NACA US National Advisory Committee for Aeronautics NASA National Aeronautics and Space Administration NPL National Physics Laboratory NRC National Research Council NTPS National Test Pilot School OS Operating System