Performance Flashcards
How does temperature effect true altitude?
Temp increase, True Alt increase
What happens to M and Tas when climbing at constant CAS?
C/T/M - both increase
What is TAS?
True Air Speed - IAS (Cas corrected for instrument errors) but relative to the air mass.
What is M number a function of?
Temperature.
M = TAS / 39/(273+SATc)
What is the lift equation?
What does each stand for?
What about drag?
L = 1/2.p.S.V2.CL
P = air density
S = wing area
V = TAS
Cl / Cd = co-efficient of life / drag
What is VMO / MMO
350 / 0.82
What is VMCG
Minimum control speed on the ground.
the CAS at which after sudden failure of the critical engine it is possible to maintain positive control (without NWS) to enable T/O to be continued using normal pilot skills.
Maximum 30ft lateral deviation from centreline to back paralleling centreline.
What is VMCA?
- what criteria
- Significant numbers
- Ratio
Minimum control speed in the air.
The CAS at which, when critical engine suddenly fails, it’s possible to control a/c & maintain straight flight with MAX bank angle 5 degrees.
During recovery, a/c may not take up dangerous attitude or require exceptional pilot skill, alertness or strength to prevent heading change > 20 degrees
VMCA may not exceed 1.2 VS
Criteria:
- MAX TO PWR
- Worst C of G
- A/C trimmed for TO
- Max sea level TOW
- A/C most critical T/O config existing along flight path after a/c airborne EXCEPT the gear is UP
- A/C airborne and no ground effect
What is VMCL?
- Criteria
- Significant numbers
- Ratio
Minimum control speed in approach and landing configuration.
- The CAS at which, when critical engine suddenly fails, possible to maintain control and straight flight with bank angle
VMU?
Minimum Unstick Speed
- CAS at which a/c can safely lift off the ground and continue the take off
- During test demo at 80-100 knots pilot pulls stick to limit of aerodynamic efficiency. A/C accomplishes slow rotation to an AoA at which max lift co-efficient is reached (or tail strike).
- Pitch maintained until lift off with eng inop & 2 eng
Two speeds for all engines (N) and one engine (N-1)
- For one engine, must ensure a safe lateral control to prevent engine from striking the ground
Tell me about the stall speed
As AoA increases.
Air velocity over wing increases.
Air pressure DECREASES
Lift coefficient INCREASES
- Thus in level flight, lift coefficient increases (AoA increase) and required speed decreases.
Above certain angle, airflow starts to separate = max life co-ef and suddenly decreases when AoA increases beyond certain threshold.
Tell me about VSR, VS 1G and VS
VS 1G corresponds to max life coefficient (just before lift starts decreasing). At that moment, lift is still equal to one.
VS = corresponds to conventional stall (when lift suddenly disappears)
Tell me about max structural TOW and how it is defined
- Flight structure resistance criteria
- Resistance of L/G
- Structure criteria during landing impact with V/S of 1.83m/s or 360 ft / min (OVW)
Tell me about max landing weight and how defined
- Flight structure resistance criteria
- Resistance of L/G
- Structure criteria during landing impact with V/S of 3.05 m/s or 600fpm
Tell me about Max Structural Zero Fuel Weight (MZFW)
- Bending moments, which apply to wing root, are maximum when fuel in wing is minimum.
- Necessary to limit the weight when no fuel in tanks
Tell me about take off thrust
- How is thrust affected by temp?
- What are the limits for thrust reduction?
- For a given pressure altitude, temp has NO influence on engine t/o thrust below “reference temp - TREF” or “FLAT rating temp”.
- Temp above TREF, engine thrust is limited by EGT.
- For a given temp. Press alt up. Thrust down.
- Reduction in thrust must not exceed 25% full rated thrust. (TMAXFLEX).(TMAX=ISA+40)
- Thus: A319 ISA+60 (75) / A320 ISA+53 (68)
OAT/OR TREF lower limit: ISA+30 / ISA+29
What is VEF?
Engine Fail Speed
- CAS at which critical engine issued to fail
- Must be great or equal to VMCG
What is V1?
Take off decision speed
- Max speed at which crew can decide to reject T/O and is ensured to stop within limits of RWY
- VMCG ≤ VEF ≤ V1
- Time from engine fail at VEF to pilot recog & action is 1 second with acceleration with OEI.
What is Vr?
Rotation speed
- Speed at which pilot initiates rotation at rate of approx 3° / second
- Speed that allows V2 to be reached before reaching 35ft above T.O surface
VR must be GREATER than: 1.05 VMCA and V1
What is VLOF?
Lift Off Speed
- CAS at which a/c first becomes airborne
- Speed at which lift overcomes weight
- VLOF ≥ 1.04 VMU N-1
- VLOG ≥ 1.08 N (2 eng)
What is V2?
Take off climb speed
- V2 minimum climb speed that must be reached at height of 35ft above T.O surface OEI.
V2 ≥ 1.13 VS1G
V2 ≥ 1.10 VMCA
GREATER OF:
- V2 Min
- VR + Speed attained before 35ft reached
What is VMBE?
Max break energy speed
- When T/O aborted, brakes must absorb and dissipate the heat corresponding to the kinetic energy and the decision point.
- Tested with no more than 10% brake remaining
- V1 ≤ VMBE
What is Vtire?
Max tire speed
- Max ground speed (195kts) that can be reached in order to limit centrifugal forces and the heat elevation that damages the tire structure.
VLOF ≤ Vtire
What was amendment 25 - 42? Why significant?
Change in calculation.
- Now Accel Stop Distance includes “distance margin equal to 2 second at v1 speed”
Talk me through TOD for dry and wet
TOD = Take Off Distance
DRY: greater of
1) TOD-N-1 Dry = B.R.P to point 35ft above T.O.S, assuming crib engine fails at VEF and recog at V1
2) 1.15 TOD-N Dry = 115% distance from BRP to 35ft with both engines
WET: Greater of:
- TOD dry
- TOD-N-1 WET = BRP to 15ft above T.O.S ensuring V2 reached before 35ft above T.O.S and crit eng failed
Difference between TOR and TOD?
TOD = Take Off Distance
DRY: greater of:
1) TOD-N-1 Dry = B.R.P to point 35ft above T.O.S, assuming crib engine fails at VEF and recog at V1
2) 1.15 TOD-N Dry = 115% distance from BRP to 35ft with both engines
WET: Greater of:
- TOD dry
- TOD-N-1 WET = BRP to 15ft above T.O.S ensuring V2 reached before 35ft above T.O.S and crit eng failed
Difference between TOR and TOD?
For wet runways, the take off run (one engine) is always equal to the TOD with one engine inop (to 15ft). Therefore a clearway does not give any performance benefit on a wet runway, as the TOR is always more limiting.
(TORA less than TODA)
When there is no clearway - TOR = TOD
Tell me about TOR for Dry and WET=
Take Off Run
- DRY: Greater Of:
1) TOR-N-1 Dry = B.R.P to equidistant point between VLOF and 35ft above T.O.S assuming crib engine and V1 recog.
2) 1.15 TOR-N Dry = 115% of distance from BRP to equidistant point between VLOF and 35ft above T.O.S with all engines - WET: Greater of:
1) TOR-N-1 Wet = B.R.P to point 15ft above T.O.S ensuring V2 achieved before airplane is 35ft above T.O.S.
2) 1.15 TOR N-WET = 115% of distance from BRP to equidistant point between VLOF and 35ft all eng
Tell me about ASD
Accelerate Stop Distance (*established with fully worn brakes)
- DRY: Greater Of
- ASD N-1 DRY: Sum of:
1) Accelerate the a/c with all engines to VEF
2) Accelerate from VEF to V1 assuming crib eng (1 sec)
3) Come to a full stop
4) Plus distance equiv to 2 seconds at constant V1 speed
or
ASD N DRY: Sum of:
1) Accelerate a/c with all engines to V1
2) All engines, come to full stop
3) Plus distance equiv to 2 seconds at constant v1
WET: Greater of:
- ASD Dry
- ASD N-1 Wet (same def as dry but wet)
- ASD N wet (same def as dry but wet
Influence on V1 on accel-go / stop distances
- Given weight.
V1 UP. TOD&TOR N-1. DOWN
(all engine acel longer thus in case of eng fail occurring at VEF, same V2 can be achieved at 35ft in shorter distance)
- TOD N and TOR N independent of V1 as no engine fail and thus no consequence on acel and necessary distance to V1
- V1 UP. ASD N-1 AND ASD N UP.
- B.R to V1 range longer and decal longer
- 2 second segment longer
- Thus minimum distance achieved at particular V1 speed called “Balanced V1” and corresponding distance called “balanced field”
(When not ASD limited, V1 > VR. But V1 brought back to VR (restriction) hence V1 = VR
Define: TORA
- Take Off Runway Available
- Length of runway which is declared available by the appropriate authority and suitable for the ground of a airplane taking off
TORA = RWY (or RWY from intersection
Define TODA:
Take off distance available:
The length of takeoff run available plus length of clearway available.
TODA = TORA + CWY
What are the regulations regarding clearway?
- Centrally located about the extended centreline of the runway and under airport control
- Be expressed in terms of a clearway plane, extending from the end of the runway with an upward slope not exceeding 1.25%
- Have a minimum width not less than 152m (500ft)
- Have no protruding objects or terrain. Threshold lights may protrude above the plane, if their height above end of runway is
Define ASDA?
Accelerate Stop Distance Available
- the length of the take off run available plus the length of stopway, if such stopway declared available by airport and is capable of bearing mass of a/c under prevailing operating conditions
Regulations regarding a stopway?
- At least as wide as runway
- Centered upon the extended centreline of runway
- Able to support a/c during an abortive T/O without causing structural damage to a/c
- Designated by airport for use n decelerating the airplane during abortive t/o
Tell me about alignment to the runway?
Either 90m line up or 180m line up is catered for. For the 320 / 319 it is approx 12m to TODA and 24m to ASDA with a 90 degree line up.
Tell me about the influence of V1 on RWY limited TOW?
- A MTOW can be obtained for each runway limitation
- E.G When for given TOW the TOD is equal to TODA, the TOW is max regarding the TOD limitation
- For given TOW, increase V1 leads to a decrease TOD/TORN-1, no effect on TOD/TOR N and increase in ASD.
Therefore, for given RWY (given TORA, TODA, ASDA) any increase in V1 leads to an increase in MTOW-TODn-1 and MTOW-TOR-n1 but has no influence on MTOW-TOD-N and MTOW-TOR-N.
The point where TODN-1 (MTOW increasing with V1) and TODN intersect is MIN V1. Where ASD MtOW (decreasing with increasing V1) intersect TODN equals max V1.
Tell me about the Take Off Path
- Starts from standing start to point where:
1) 1500ft above TOS OR
2) Point at which transition from T/O to En-Route config (clean , MCT) is completed and final take off speed (green dot - but min 1.25VS) reached,
whichever higher.
Tell me about the take off FLIGHT path
- Begins at 35ft above the take off surface at the end of the TOD
What is the regulatory assumptions of TOP and TOFP
- Aircraft accelerated o the ground to VEF
- Critical engine inop and remains so
- V2 speed reached before 35ft above TOS
- A/C continues at a speed no less than V2 until 400ft
Minimum climb gradients for first, second, third and final segents
0%.
2.4%
- 2%
When does each take off segment start
1) VLOF reached
2) When gear fully retracted
3) Acceleration altitude (400 minimum)
4) En route config achieved
What is the minimum height for track changes following an engine failure?
What are the maximum limits according regs?
- Should not be allowed up to point at which net take off flight path has achieved a height equal to one half the wingspans but not less than 50ft above elev.
- For us: 56ft
Max limits standard:
- 15 degrees until 400ft.
- 25 degrees above 400ft
Special approval:
- 15 degrees until 200ft
- 20 from 200 - 400
- 30 degrees above 400ft
Gross / Net take off flight pats - explain
A margin between the aircraft and each obstacle needs to be considered and the margin, based on climb gradient leads to the definitions of gross and net flight path:
- The gross flight path is the path actually flown by the aircraft
- Net flight path = Gross - Mandatory reduction
(0. 8% for us)
Net starts from 35ft above the TOS.
Tell me about obstacle clearance during a straight take off?
And clearance during a turn?
- Net take off flight path must clear all obstacles by 35ft
(This may see increase of 2.4 / 1.2% climb gradients if obstacle restricted which may reduce MTOW)
- Any part of the net take off flight path in which a/c is banked by more than 15 degrees must clear all obstacles by a vertical distance of 50ft
- The net acceleration segment is longer than the gross one, as the end of both segments is assumed to be reached after the same flight time.
Tell me about the take off funnel.
- Represents area surrounding take off flight path, within which all obstacles must be cleared, assuming they are projected on the intended track.
- Normally 90m + (0.125 X D) where D is horitzonal distance the a/c has travelled from the end of TODA or end of TOD if a turn is scheduled before end of the TODA.
- But for A/C with wingspan 15 degrees,
- 600m
or - 900m
Tell me about outside elements and their effect:
Wind: 50% HW, 150% TW
ALT: Given weight:
ALT ↑ TODs ↑ TCG ↓ = MTOW ↓
Temp: (air density / thrust > TREF)
TEMP ↑ TODs ↑ TCG ↓ = MTOW ↓
Slope: +/-2% - Sometimes improve MTOW / sometimes lower depending on the limitation
UP SLOPE = TODs ↑ ASD ↓
DOWN SLOPE = TODs ↓ ASD ↑
What is aqua planing?
Where there is an intervening film of water between and tire and runway leading to reduction of dry area.
More critical at higher speeds, where water can not be squeezed out from between the tire and runway
Aquaplaning is a situation where tires of the aircraft are, to a large extent, separated from the runway surface by a thin fluid film.
Under these conditions tire traction drops to almost negligible values along the aircraft wheels braking and wheel steering for directional control is therefore virtually ineffective.
Aquaplaning speed depends on tired pressure and specific gravity of the contaminant.
What is a consequence of contaminated runway calculations with regards to the TO flight path?
On a wet or contaminated runway the screen height (height at end of the TOD) is 15ft. The net take off flight path starts at 35ft at the end of the TOD. So gross flight path starts at 15ft whereas et is 35ft. Thus if an engine failure occurs at V1, a/c can initially be as much as 20ft below the net takeoff fight path, and therefore may clear close in obstacles by only 15ft.
WET / CONTAM and TOW?
What is the risk? How is it corrected?
- Possible to obtained shorter TOD / ASDs on wet / contemn runways due to the power screen height and ability to use reverse to stop.
- Therefore possible to obtain higher TOWs on surface covered with water / slush or snow than on dry runways
- Regulation says for Wet / Contam the TOW must not exceed that allowed for a dry runway of same conditions.
“Dry Check”
Flexible take off: why do we do it?
- Aircraft weight is often lower than the max reg. TOW
- Possible to perform take off with thrust less than maximum take off thrust
- Increases engine life and reliability
- Decreases maintenance and operating costs
Possible to determine the temperature at which the needed thrust would be maximum for the take off thrust for this temp. This temperature is called the FLEX temp or “assumed temp”
