THE RETURN OF THE COMET ONE TEST PILOT’S APPROACH TO ‘FIRST FLIGHT’ IN A ‘ONE - OFF’
IT STARTED WITH THE ANNOUNCEMENT OF THE ‘GREAT AIR RACE’ LONDON-MILDENHALL TO MELBOURNE - 1934
TYPICAL 1930’s BRITISH AIRLINERS
TYPICAL DE-HAVILLAND AIRCRAFT - BC (BC = Before Comet)
THE ‘GREAT AIR RACE’ OF 1934 MILDENHALL TO MELBOURNE - 11323 MILES
THE HANDICAP RACE FORMULA 0.2𝑀 𝑄 1 3 𝑊 = 140. {1 − 𝐵 } (𝑋−𝑀) }.{ Where, for Comet; L Load Payload (lb) 400 P Power Max Continuous (BHP) 450 W Weight Loaded aircraft (lb) 5320 A Area Wing area (square feet) 188.5 80 450 1 3 𝑊 = 140. {1 − 188.5 } 4920 }.{ 1 3 = 140. {1 − 0.0162 }.{ 2.387} = 140. {0.9838 }.{ 1.3364} = 184 𝑛𝑞ℎ (𝑚𝑏𝑢𝑓𝑠 176 𝑏𝑢 𝑋5550, 𝐵212. 𝑀360)
THE AIRCRAFT THE DESIGNER Arthur Hagg
ONE TEST PILOT’S APPROACH TO ‘FIRST FLIGHT’ IN A ‘ONE - OFF’
FLIGHT TEST RISK ASSESSMENT METHOD RISK ASSESSMENT METHODOLOGY WITH ACKNOWLEDGEMENTS TO DONALD RUMSFELD There are known knowns. These are things we know that we know. Research Reports, Books, Periodicals There are known unknowns. That is to say, there are things that we know we don't know. Investigate/Plan/Test/Analyse But there are also unknown unknowns. There are things we don't know we don't know. Minimise these by maximising the above!
The KNOWN KNOWNS (What we know we know) George Ellis - 1988
The KNOWN KNOWNS (What we know we know) 1934 - Karachi
The KNOWN KNOWNS (What we know we know) 1936 - Martlesham Heath 1936 - Martlesham Heath 1934 - Karachi
The KNOWN KNOWNS (What we know we know) 1936 - Martlesham Heath 1934 - Karachi 1938 - Cyprus
The KNOWN KNOWNS (What we know we know) 1936 - Martlesham Heath 1934 - Karachi 1938 - Cyprus 1987 - Hatfield
The KNOWN KNOWNS (What we know we know) 2002 – Old Warden 1987 - Hatfield 1936 - Martlesham Heath 1938 - Cyprus THEREFORE WE KNOW THAT THERE WAS A TENDENCY FOR THE UNDERCARRIAGE TO COLLAPSE! 1934 - Karachi
‘MITIGATION MEASURE’ LANDING GEAR – ANALYSIS &RE-DESIGN Cranfield MSc thesis by Fabien Horbin led to a revised undercarriage system
LANDING GEAR RETRACTION
LANDING GEAR EXTENSION
MORE KNOWN KNOWNS
MORE KNOWN KNOWNS THEREFORE WE KNOW THAT THERE WAS MARKED TENDENCY FOR TIP STALL/WING DROP!
WHY THE WINGDROP AT THE STALL? NO WASHOUT WING TAPER
MODERN INSIGHTS Cranfield MSc student thesis CFD Analysis
CLOUSTON’S CLUES
CLOUSTON’S CLUES
CLOUSTON’S CLUES
SOME KNOWN UNKNOWNS 1. HOW TO AVOID THE TIP STALL/WING-DROP? BY NEVER PERMITTING THE ANGLE OF ATTACK TO APPROACH THE STALLING ANGLE - EVEN DURING A BOUNCE OR SKIP 2. LENGTH OF RUNWAY REQUIRED WOULD THE LANDING DISTANCE AVAILABLE AT OLD WARDEN BE SUFFICIENT? 3. FIELD OF VIEW - WOULD THIS BE SUFFICIENT TO:- • JUDGE HEIGHT/HEIGHT RATE TO ACHIEVE A ‘SMOOTH’ TOUCH DOWN? • LAND AT OLD WARDEN IN THE REQUIRED TOUCHDOWN ZONE? HOW TO MITIGATE THE RISKS ASSOCIATED WITH ABOVE?
1. HOW TO AVOID THE TIP STALL/WING-DROP? • BY NEVER PERMITTING THE ANGLE OF ATTACK TO APPROACH THE STALL EVEN DURING A BOUNCE OR SKIP – BUT HOW? • STOP THE AIRCRAFT FROM ‘FLYING OFF’ BUMPS AT LOW SPEED/HIGH ANGLE OF ATTACK BY PUTTING THE AIRCRAFT AT ZERO LIFT AoA ( a 0 ) ON THE GROUND. • HOW TO DETERMINE THE ZERO LIFT AoA? • ESTABLISH ZERO LIFT AoA FROM CONTEMPORARY AEROFOIL WIND TUNNEL TEST RESULTS – BUT WHICH AEROFOIL? • WHAT WOULD THIS ZERO LIFT AoA LOOK LIKE FROM THE COCKPIT? • SIT IN THE COCKPIT AT ZERO LIFT AoA AND NOTE THE ATTITUDE. • WHICH AEROFOIL?
WHICH AEROFOIL? RAF 34 SECTION Wind Tunnel Test N.P.L. 1934 Reynolds No = 6,470,000 FULL SCALE REYNOLDS No At Stall (85 mph) = 4,350,000 At Climb (125 mph) = 6,406,000 At Cruise (210 mph) = 10,763,000 THESE WIND TUNNEL RESULTS SHOULD BE BROADLY APPLICABLE
AEROFOIL CHARACTERISTICS AERODYNAMIC DATA FOR RAF 34 AEROFOIL SECTION Data obtained from Handbook of Aeronautics Volume 1, Part 1 - Pitman 1938 a C L Lift Curve Slope - RAF 34 -1.7 -0.066 -0.6 0.017 1.6 0.185 Maximum Lift Coefficient 1.4 3.8 0.352 6.1 0.520 (C L MAX ) = 1.3 1.2 8.3 0.698 10.4 0.848 1.0 12.6 0.998 Lift Coefficient - C L 14.7 1.150 Pre Stall 0.8 16.9 1.286 19.0 1.306 Post Stall 0.6 21.0 1.240 Linear (Pre Stall) 23.0 1.090 25.2 0.962 0.4 27.3 0.826 29.3 0.760 0.2 C L = 0.0735 a + 0.0691 0.0 -5 0 5 10 15 20 25 30 Angle of Attack - a - (deg) Lift Curve Slope ( a 1 ) a0 equals -0.0691/0.0735 -0.94 deg = 4.2 per Radian Angle of Attack for Zero Lift ( a 0 ) = -1 deg
KNOWN UNKNOWNS – AVOIDING WING DROP Aircraft attitude with wing at a 0 N.B. WING IS RIGGED AT PLUS 1 DEG TO LFD N.B. ADEQUATE PROP CLEARANCE IN ZERO LIFT ATTITUDE
KNOWN UNKNOWNS – AVOIDING WING DROP Establishing the cockpit picture when wing at a 0 N.B. CHT GAUGES ON THE HORIZON N.B. RUNWAY EDGES IN VIEW
2. FIELD LENGTH REQUIRED WHAT TAKE-OFF AND LANDING DISTANCES WERE REQUIRED AND, WOULD THE LANDING DISTANCE AVAILABLE AT OLD WARDEN BE SUFFICIENT? CLOUSTON “NORMALLY I MUST HAVE 1,000 YARDS FOR SAFETY….”
FIELD LENGTH HATFIELD 1990’s = 1000 METRES = 700 METRES
FIELD LENGTHS = 1000 METRES = 700 METRES GRANSDEN LODGE HENLOW OLD WARDEN
3. KNOWN UNKNOWNS – FIELD OF VIEW – 3 PT
KNOWN UNKNOWNS – FIELD OF VIEW Forward Field of View - DH88 80 60 Vertical Angular FOV (deg) 40 Runway edges 20 0 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 -20 -40 Horizontal Angular FOV (deg)
KNOWN UNKNOWNS – FIELD OF VIEW – a 0 N.B. RUNWAY EDGES IN VIEW PRACTICE APPROACHES AT GRANSDEN LODGE INDICATED THAT THERE WAS ADEQUATE VIEW TO FLY CURVED APPROACHES AT OLD WARDEN BUT STRAIGHT-IN APPROACHES ARE NOT PRACTICABLE.
PILOT PREPARATION AIRCRAFT TAKEOFF START & TOUCHDOWN TECHNIQUE MILES GEMINI PERCIVAL MEW GULL SIMILAR APPROACH SPEED SENSITIVE PITCH HANDLING POOR FIELD OF VIEW
SOME KNOWN UNKNOWNS 1. HOW TO AVOID THE TIP STALL/WING-DROP? BY NEVER PERMITTING THE ANGLE OF ATTACK TO APPROACH THE STALLING ANGLE - EVEN DURING A BOUNCE OR SKIP 2. LENGTH OF RUNWAY REQUIRED WOULD THE LANDING DISTANCE AVAILABLE AT OLD WARDEN BE SUFFICIENT? 3. FIELD OF VIEW - WOULD THIS BE SUFFICIENT TO:- • JUDGE HEIGHT/HEIGHT RATE TO ACHIEVE A ‘SMOOTH’ TOUCH DOWN? • LAND AT OLD WARDEN IN THE REQUIRED TOUCHDOWN ZONE? HOW TO MITIGATE THE RISKS ASSOCIATED WITH ABOVE? 1. BY MAKING ‘ZERO LIFT ATTITUDE’ TAKEOFFS & LANDINGS, 2. WITH INITIAL LANDING ATTEMPTS ON LONGER RUNWAYS, 3. AT AIRFIELDS WITH CLEARER APPROACH AREAS
SOME MORE KNOWN UNKNOWNS POSSIBLE AIRSPEED INDICATOR IN-OP? Low static margin (i.e. poor or absent longitudinal static stability – controls fixed and free) meaning that there will be little or no stick force cue to AoA/Airspeed change, and absence of stall warning – inadvertent stall/wing drop on approach/landing. Mitigations for first flight:- • Carry a ‘heads - up’ GPS groundspeed indicator • Have a chase aircraft available
OTHER CONCERNS – HUMAN FACTORS ON FIRST AND EARLY FLIGHTS PILOT WORKLOAD CAN BE HIGH DUE UNFAMILIARITY WITH THE AIRCRAFT AND POTENTIAL FOR DISTRACTION, ERROR, OMISSION, IS THEREFORE HIGH 1. THE CANOPY IS HINGED ON THE SIDE. IF NOT SECURE BEFORE TAKE-OFF IT WILL OPEN DURING THE TAKE-OFF ROLL OR AT LIFT OFF. SHOULD THIS HAPPEN THE EFFECT ON THE PILOT AND AIRCRAFT COULD RESULT IN A LOSS OF CONTROL. 2. THE TAIL SKID CASTORS FOR TAXYING AND CAN BE LOCKED FOR TAKEOFF AND LANDING. ON THE GROUND IN THE THREE POINT ATTITUDE THE DIRECTIONAL STABILITY AND CONTROL RELIES HEAVILY ON THE TAILSKID BEING LOCKED. IF THE TAKEOFF IS ATTEMPTED WITH THE SKID UNLOCKED (OR A LANDING IS ATTEMPTED WITH THE SKID UNLOCKED) THIS COULD RESULT IN A LOSS OF DIRECTIONAL CONTROL. MITIGATION: HAVE GROUNDCREW HOLD UP CHECK CARDS BEFORE TAKE0FF AS A REMINDER TO CHECK CANOPY SECURE AND TAILSKID LOCKED.
ANOTHER CONCERN IT HAD BEEN REPORTED THAT NON-LINEARITY IN THE ELEVATOR TO STICK GEARING WOULD LIKELY CAUSE PILOT INDUCED OSCILLATIONS OR OVER-CONTROLLING ON LANDING. WAS THIS REPORT SIGNIFICANT? Known low static stability characteristic means very small elevator movements are required to change angle of attack/lift coefficient/airspeed. Therefore most flying will likely be made in the linear section near neutral - ACCEPTABLE
WEIGHT & BALANCE & FUEL DISTRIBUTION DESIRABLE CONDITIONS WEIGHT – AS LOW AS POSSIBLE TO MINIMISE STALL SPEED TO MAXIMISE ONE-ENG IN-OP PERFORMANCE C OF G – AS FORWARD AS POSSIBLE TO MINIMISE LONGITUDINAL INSTABILITY TO MINIMISE SPEED REQUIRED TO HOLD AIRCRAFT IN TAIL-UP ATTITUDE FUEL DISTRIBUTION TO PROVIDE COMFORTABLE ENDURANCE - > 2 HOURS TO MAINTAIN CG IN FORWARD PART OF ENVELOPE AS FUEL CONSUMED TO REMOVE THE NEED TO ‘CROSS - FEED’ FUEL ON EARLY FLIGHTS
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