V-SPEEDS Flashcards
Go through the V-speeds from start to finish and place them in the correct order?
Vmcg Vef V1 Vmbe Vmca Vr Vs Vmu Vlo V2
Define “Vmcg”
Lowest speed that provides directional control on the ground with the critical engine inoperative
What factors affect Vmcg
Density. Thrust varies with density therefore the assymetric moment is higher when density is higher. That is at low altitudes and low temperatures
Describe the certification rules for Vmcg
Steering can’t be used Max 30 ft lateral excursion from the centerline is permitted
What is Vmcg:s relationship with V1?
Vmcg has to be equal or lower than V1
When might V1 be lower than Vmcg?
At low weights and altitudes At low weights V1 can be reduced At low altitudes Vmcg might be higher than V1 due the increased turning moment
Define Vef?
The speed at which an engine failiure occurs, to be recognised at V1.
1 second reaction time is used
Upon recognition at V1, 2 seconds are given to react to close the throttles
Definition of V1?
Min speed to accept an engine failure and continue T/O and make V2 by 35 ft within TODA
and
Max speed to reject T/O and stop with in ASDA
How do you get your Field limited take-off mass?
Merge the Vstop and Vgo graphs
Vstop: V on vertical axis, T/O mass on horizontal axis.
As mass increases the speed at which we need to stop decreases
Vgo: As T/O mass increases the speed at which we to go increases.
Limitaions on V1?
- Can’t be greater than Vr but equal
- Can’t exceed Vmbe
- V1 must be faster than Vmcg
Why is a high V1 speed choosen, if possible?
As to delay the “must-go” descision as it is safer to be on the ground.
If an a/c is T/O mass is climb- or obstacle limited an as high as possible V1 is choosen to get good climb performance
What does an increase in V1 means in terms of ASD and TOD?
ASD increases, higher abort speed that eats more runway
TOD decreases
What happens to V1 when density is reduced?
We’ll have less thrust which, on a limiting T/O, the reduced acceleration means we won’t make V2 by 35 ft within TODA.
We must then increase V1. On a balanced field the increased V1 would lead to a decrease in mass
What are the correction made for V1 with regards to:
- Slope
- Wind
- Altitude
- Temperature
- Weight
- Slope: Upslope increases V1, down slope decreases V1
- Wind: Headwind increases V1, tailwind decreases V1
- Altitude: Altitude increases V1
- Temperature: Temp increase increases V1
- Weight: More weight increases V1
Reduced stopping capability calls for lower V1
Reduced acceleration capability calls for a higher V1
How does slippery runways, with no roll resistance affect V1?
Reduced stopping action reduces V1
Since there’s no reduced acceleration there’s no correction for that.
What happens is that V1 reduces
How does a slippery runway, with roll resistance, affect V1?
Runway has snow, slush or more than 3 mm standing water
Reduced stopping action lowers V1
Reduced acceleration action increases V1
What’s happening is that V1 doesn’t change
Definition of Vmbe?
It’s the lowest CAS at which the brakes can absorb all the energy from a rejected T/O at V1
For a mass travelling at a True GS, the kinetic energy is 1/2 MV2
When braking, this energy goes into the brakes as heat
V = a True GS, so the corresponding IAS varies with
- Alt, temp, wind and slope
What is Vmbe:s relationship to V1?
Vmbe has to be equal or greater than V1
When is Vmbe slowest and most likely to be limited by V1?
Vmbe is slowest and most likely to be limited by V1, when the aircraft is:
- Heavy
- High pressure alt, for same IAS/CAS the true GS will be higher which leads to more brake energy needed
- High temp, same reason as above
- Tailwind, slow CAS due to less air into pitot tube means that for the same CAS the true GS will be higher
What are the corrections made for Vmbe with regards to:
- Slope
- Wind
- Altitude
- Weight
- Temperature
- Slope: Vmbe decreases with downslope due to more potential energy, which is harder to stop
- Wind: Tailwind decreses Vmbe. True GS will be higher for the same CAS in no wind cause less air goes into the pitot tube
- Altitude: Higher alt will decrease Vmbe cause CAS will be the same but the true GS will be higher
- Weight: Decresing weight will increase Vmbe
- Temperature: Lower temp will increase Vmbe
What’s the definition of Vmca?
Vmca is the lowest CAS at which the critical engine is suddenly made inoperative where, it’s possible to maintain directional control and stright forward flight with an angle of bank not exceeding 5 degrees
How does Vmca change with density?
Vmca is fastest at cold and low airports because the yawing moment is greatest when the air is more dense
What is the configuration criteria when deciding Vmca?
MTOW
Most rearward CG
Max 5 deg bank
Full rudder
Critical engine failed
Max contious power on live engine
What is the speed limitaion on Vmca?
Vmca may not exceed 1,2 Vs
Does Vmca increase or decrease with:
- Weight increase
- Fwd CG
- Altitude increase
- Incresed bank angle
- Increasing flap setting
- Weight increase: Vmca decreases. W adds stability
- Fwd CG: Vmca decrease
- Alt increase: Vmca decreases due to lower density
- Bank angle: Vmca decreases with more bank
- Flaps: Vmca increases because flaps increase lift and therefore drag
What does Vr ensure?
Vr ensures that, in case of engine failure, lift-off is possible and V2 is reached at 35 ft
With no engine failure V2 speed is usually higher at 35 ft and is sometimes called V3
What is VR:s relationship with Vmu and Vmca?
VR must be such that Vlof is greater than Vmu by 1,10 if all engines are operating or by 1,05 OEI
If the a/c is geometrically limited (A318 is not limited) the margins are 1,08 Vmu AEO and 1,04 Vmu OEI
VR may not be less than 1,05 Vmca
What kind of speed is VR and does it change with density and if so why?
VR is a CAS and shouldn’t change with density. However, because VR may not be less than the specified percentages above Vmu and Vmca it is affected by density
Vmca increases with higher density (low,cold wx) so to maintain 1,05 Vmca VR must be increased
Vmu decreases at low alt, high density airfields
At cold, low alt, high density Vmca limits VR
At warm, high alt, low density Vmu limits VR
Define Vmu?
Is the lowest CAS at which an aeroplane can safely lift off the ground and continue without undue hazard
Vmu is related to stall speed out of ground effect
Does Vmu vary with density?
Yes it does, unlike a normal stall speed
Vmu reduces as air density increases
In cold temp and at low alt the density is higher and thrust and it’s vertical component is also higher which means that lift required can be achived at a slower CAS
Why can an aircraft lift off at Vmu ?
Due to a vertical component of thrust which reduces the actual lift required
What may limit Vmu?
Geometry and elevator power capacity
Define VLOF ?
The CAS when the aircraft first gets airborne
Define V2?
V2 is the minimum speed that should be achieved at 35 ft having suffered a critical engine failure @ V1
It provides the required climb gradient
What must V2 not be less than i terms of speeds?
V2 must not be less than:
- 1,2 VS and
- 1,1 Vmca
Why does V2 vary with density?
Draw the VS vs Vmca diagram
V2 varies with density
It’s not Vs that varies but it’s Vmca
What effect does extending flaps or reducing weight have on V2min?
Extending flaps or reducing weight decreases Vs
Decreasing Vs leads to a decrease in V2min at airfields with low density (hot, high). This leads to Vmca determining V2min in more situations
When are both V2min and VR likely to be limited by Vmca?
When:
- Temperature is cold
- Airport is at low altitude
- Flaps are at a high setting
- Aircraft is lighter
To what speed should V2 ideally be as close to as possible and why?
V2 should be as close as possible to Vmd to get max climb gradient in the 2nd segment
V2 in itself is usually slower than Vx
If the rwy is long enough, increasing VR and V2 speeds could be an option.
What the limiting factor for “Tyre speed limitations”?
Limit is a True Ground speed
So the limiting IAS and mass will vary with
- Altitude
- Wind
- Flap setting
Slope has no effect
How does wind affect the Tyre Speed limit?
Tailwind pushes the VLOF to a slower CAS for the same GS
CAS in no wind will be the same for V1/VR in a tailwind but the true GS will be higher with a tailwind due to less air going into the pitot tube which leads to that we have to speed up t get same CAS
How does less flaps affect Tyre Speed limit?
Lift off will be at a higher speed with less flaps so therefore the True GS will be higher
How does Altitude affect Tyre Speed limits?
CAS for V1 at MSL and 5’000 ft are the same
True GS at 5’000 will be higher due to decreased density
If Vmcg is limiting, how would you increase aircraft weight?
reduce takeoff thrust, as it is the single engine takeoff asymmetric thrust which dictates Vmcg, along with rudder size.
