VMCG less than VMCA
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Thank you all for your inputs
There comparison with each other is a myth and it’s BUSTED!
Like Airbus 310 (Vmcg less than Vmca)
Never mind Halfbaked boy thank you for your input. That’s why we are all here for
Vmcg and Vmca are separate demonstrated items. There is no underlying reason why either should be lesser or greater than the other
There comparison with each other is a myth and it’s BUSTED!
VMCG can be considered, generally, to be higher than VMCA.
.. except for those aircraft for which it is lower ..
.. except for those aircraft for which it is lower ..
Like Airbus 310 (Vmcg less than Vmca)
Never mind Halfbaked boy thank you for your input. That’s why we are all here for
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Hi JT, Sorry for the delay - but only just returned and have access to books.
All figures extracted for sea level conditions.
From FCOM A319 2.2.25 min V1 = 110 kts (this must be VMCG), Vr 113, V2 120
Min V2 VMU/VMCA from 35 to 50 tons = 119.
From 3.1.20 Min control speed VMCA = 108 kts.
So why can't I be airborne at VMCG?
There are two values quoted for VMCA in the FCOM:
V2 VMU/VMCA is for the take off case and VMCA is always above VMCG.
On approach; the VAPP minimum VMCA can be lower than VMCG.
Is this where the confusion comes from?
If I get airborne at VMCG with wings level ..
which might be foolish for most Types
which might be foolish for most Types
From FCOM A319 2.2.25 min V1 = 110 kts (this must be VMCG), Vr 113, V2 120
Min V2 VMU/VMCA from 35 to 50 tons = 119.
From 3.1.20 Min control speed VMCA = 108 kts.
So why can't I be airborne at VMCG?
There are two values quoted for VMCA in the FCOM:
V2 VMU/VMCA is for the take off case and VMCA is always above VMCG.
On approach; the VAPP minimum VMCA can be lower than VMCG.
Is this where the confusion comes from?
Last edited by rudderrudderrat; 16th Dec 2009 at 17:07. Reason: FCOM ref
rudderrudderrat,
It may be more usual for V1 to be greater than Vmcg because Vmcg is defined by Vef. Thence V1min is Vef plus any speed increase during the engine failure recognition period. ref CS 25.107.
In the example given an A319 might be accelerating relatively quickly, thus the 110 kts V1 quoted might equate to a Vmcg less than 108 kts, the Vmca comparison.
For the approach case, is it possible that the ‘Vmca’ quoted is in fact Vmcl - CS 25.149.
If so then in determining this speed a configuration different from takeoff might be relevant (Vmcl given for each landing config or the critical config), and a lower weight (MLW) would be used, hence a different, lower speed.
It may be more usual for V1 to be greater than Vmcg because Vmcg is defined by Vef. Thence V1min is Vef plus any speed increase during the engine failure recognition period. ref CS 25.107.
In the example given an A319 might be accelerating relatively quickly, thus the 110 kts V1 quoted might equate to a Vmcg less than 108 kts, the Vmca comparison.
For the approach case, is it possible that the ‘Vmca’ quoted is in fact Vmcl - CS 25.149.
If so then in determining this speed a configuration different from takeoff might be relevant (Vmcl given for each landing config or the critical config), and a lower weight (MLW) would be used, hence a different, lower speed.
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min V1 = 110 kts (this must be VMCG), Vr 113, V2 120. So why can't I be airborne at VMCG?
I'm presuming that the speed sequence above is that for min weight min speed ? .. in which case you really want to be airborne below Vr and V2 ?
On approach; the VAPP minimum VMCA can be lower than VMCG.
and the two are of no relevance to each other ?
Is this where the confusion comes from?
I think that the only confusion is wanting to come up with some correlation between Vmcg and Vmca when there is no valid reason to do so ? .. apples and oranges ..
I'm presuming that the speed sequence above is that for min weight min speed ? .. in which case you really want to be airborne below Vr and V2 ?
On approach; the VAPP minimum VMCA can be lower than VMCG.
and the two are of no relevance to each other ?
Is this where the confusion comes from?
I think that the only confusion is wanting to come up with some correlation between Vmcg and Vmca when there is no valid reason to do so ? .. apples and oranges ..
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Thanks for the replies Safetypee & J T.
JT - No I don't want to be airborne below VR & V2 on take off - but on the approach & GA (+ in the same configuration Flaps 3) I can fly 12 kts slower than V2.
It seems to me that V2 VMCA must assume wings level (else how did I get off the ground and be under control). However VAPP VMCA allows 5 degs bank.
Standing by for flame throwers.
JT - No I don't want to be airborne below VR & V2 on take off - but on the approach & GA (+ in the same configuration Flaps 3) I can fly 12 kts slower than V2.
It seems to me that V2 VMCA must assume wings level (else how did I get off the ground and be under control). However VAPP VMCA allows 5 degs bank.
Standing by for flame throwers.
Moderator
I have no specific background with the Airbus and am not able to offer any thoughts at the present .. but I will have a head scratch and see what I can come up with ... perhaps a revisit to the AC might give me a clue.
However, unless OEM data indicates explicitly that Vmca was done wings level, you probably would be better off presuming that the figure is for 5 deg into the operative engine - too much of a penalty otherwise as a general rule.
However, unless OEM data indicates explicitly that Vmca was done wings level, you probably would be better off presuming that the figure is for 5 deg into the operative engine - too much of a penalty otherwise as a general rule.
rudderrudderrat, JT, could the issue be associated with “the most adverse configuration”, which may not be the same configuration (wt, cg) for each speed, and/or involve the same defining parameter for the limit of control, e.g Vmca can be defined by the aircraft experiencing stall before a control limit.
A further thought is that for Vmcg there is some lateral force from ground contact, and although this is removed at liftoff, the transition to controlled flight with application of bank (Vmca) is a dynamic maneuver, perhaps not necessarily constrained to the test conditions which establish the speed, i.e. test conditions may not translate directly to practical operating conditions.
If Vmcg and Vmca do not refer to identical conditions, any attempt to compare these speeds or the aircraft’s ability to fly at one or other speed in identical conditions would be impossible.
A further thought is that for Vmcg there is some lateral force from ground contact, and although this is removed at liftoff, the transition to controlled flight with application of bank (Vmca) is a dynamic maneuver, perhaps not necessarily constrained to the test conditions which establish the speed, i.e. test conditions may not translate directly to practical operating conditions.
If Vmcg and Vmca do not refer to identical conditions, any attempt to compare these speeds or the aircraft’s ability to fly at one or other speed in identical conditions would be impossible.
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Hi JT & SP, I've copied and pasted some values below for A319 & A321.
It's interesting to note the minimum V2 compared with min VAPP.
On the GA from Flaps Full, the normal config. is Flaps 3.
So which VMCA do we refer to with Airbus figures; V2 VMCA or VAPP VMCL?
Hope these figures shed some light, sorry about the table spacing - but the extra spaces are stripped out when posted.
A321 MINIMUM CONTROL SPEEDS @ Sea level
VMCA (KT CAS) = 114
VMCG (KT IAS) Conf 1+F = 110, CONF 2 = 110, CONF 3 = 108.5
SPEEDS LIMITED BY VMC
Takeoff speeds all have a minimum value limited by control. These minimum values are given in the tables down below.
Minimum V1 CONF 1+F = 115, CONF 2 = 115, CONF 3 = 113
Minimum VR CONF 1+F = 121, CONF 2 = 121, CONF 3 = 119
Minimum V2 CONF 1+F = 126, CONF 2 = 125, CONF 3 = 125
V2 LIMITED BY VMU/VMCA
________________________________________
The following tables, one per configuration, provide the V2 limited by minimum unstick speed and minimum control speed in the air.
MINIMUM V2 LIMITED BY VMU/VMCA (KT IAS)
CONF 1+F
046 050 055 060 065 070 075 080 085 090 093 Take off Weight (tons)
125 125 127 133 138 143 148 152 156 161 164 Speed
MINIMUM V2 LIMITED BY VMU/VMCA (KT IAS)
CONF 2
046 050 055 060 065 070 075 080 085 090 093 Take off Weight (tons)
124 124 124 125 130 135 139 143 147 151 154 Speed
MINIMUM V2 LIMITED BY VMU/VMCA (KT IAS)
CONF 3
046 050 055 060 065 070 075 080 085 090 093 Take off Weight (tons)
124 124 124 124 124 129 133 137 140 145 147 Speed
A 321 V App QRH 4.00A
Weight inTons 052 056 060 064 068 072 076 080 084 088 092 094
VLS CONF Full 116 121 125 129 133 137 141 144 148 151 155 157
VLS CONF3 kt 121 125 130 134 138 142 146 150 154 157 161 163
A319 MINIMUM CONTROL SPEEDS @ sea level
VMCA (KT CAS) = 108
VMCG (KT IAS) Conf 1+F = 104.5, CONF 2 = 104.5, CONF 3 = 104.5
SPEEDS LIMITED BY VMC
Takeoff speeds all have a minimum value limited by control. These minimum values are given in the tables down below.
Minimum V1 CONF 1+F = 110, CONF 2 = 110, CONF 3 = 110
Minimum VR CONF 1+F = 113, CONF 2 = 113, CONF 3 = 113
Minimum V2 CONF 1+F = 120, CONF 2 = 119, CONF 3 = 120
V2 LIMITED BY VMU/VMCA
The following tables, one per configuration, provide the V2 limited by minimum unstick speed and minimum control speed in the air.
MINIMUM V2 LIMITED BY VMU/VMCA (KT IAS)
CONF 1+F
035 040 045 050 055 060 065 070 075 080 Takeoff Weight (tons)
119 119 119 119 122 128 133 138 142 147 Speed
MINIMUM V2 LIMITED BY VMU/VMCA (KT IAS)
CONF 2
035 040 045 050 055 060 065 070 075 080 Takeoff Weight (tons)
119 119 119 119 119 122 126 131 136 141 Speed
MINIMUM V2 LIMITED BY VMU/VMCA (KT IAS)
CONF 3
035 040 045 050 055 060 065 070 075 080 Takeoff Weight (tons)
119 119 119 119 119 119 123 128 133 137 Speed
A 319 V App QRH 4.00A
Weight in Ton 044 048 052 056 060 064 068 072 076
VLS CONF Full 108 113 117 122 126 130 134 138 142
VLS CONF3 kt 113 118 123 128 132 137 141 145 149
44 Tons Vref = 108 kts (**Vref is limited by VMCL)
VMCG : Minimum speed, on the ground during takeoff, at which the aircraft can be controlled by only using the primary flight controls, after a sudden failure of the critical engine, the other engine remaining at takeoff power.
VMCA : Minimum control speed in flight at which the aircraft can be controlled with a maximum bank of 5°, if one engine fails, the other engine remaining at takeoff power (takeoff flap setting, gear retracted).
VMCL : Minimum control speed in flight, at which the aircraft can be controlled with a maximum bank of 5°, if one engine fails, the other engine remaining at takeoff power (approach flap setting).
It's interesting to note the minimum V2 compared with min VAPP.
On the GA from Flaps Full, the normal config. is Flaps 3.
So which VMCA do we refer to with Airbus figures; V2 VMCA or VAPP VMCL?
Hope these figures shed some light, sorry about the table spacing - but the extra spaces are stripped out when posted.
A321 MINIMUM CONTROL SPEEDS @ Sea level
VMCA (KT CAS) = 114
VMCG (KT IAS) Conf 1+F = 110, CONF 2 = 110, CONF 3 = 108.5
SPEEDS LIMITED BY VMC
Takeoff speeds all have a minimum value limited by control. These minimum values are given in the tables down below.
Minimum V1 CONF 1+F = 115, CONF 2 = 115, CONF 3 = 113
Minimum VR CONF 1+F = 121, CONF 2 = 121, CONF 3 = 119
Minimum V2 CONF 1+F = 126, CONF 2 = 125, CONF 3 = 125
V2 LIMITED BY VMU/VMCA
________________________________________
The following tables, one per configuration, provide the V2 limited by minimum unstick speed and minimum control speed in the air.
MINIMUM V2 LIMITED BY VMU/VMCA (KT IAS)
CONF 1+F
046 050 055 060 065 070 075 080 085 090 093 Take off Weight (tons)
125 125 127 133 138 143 148 152 156 161 164 Speed
MINIMUM V2 LIMITED BY VMU/VMCA (KT IAS)
CONF 2
046 050 055 060 065 070 075 080 085 090 093 Take off Weight (tons)
124 124 124 125 130 135 139 143 147 151 154 Speed
MINIMUM V2 LIMITED BY VMU/VMCA (KT IAS)
CONF 3
046 050 055 060 065 070 075 080 085 090 093 Take off Weight (tons)
124 124 124 124 124 129 133 137 140 145 147 Speed
A 321 V App QRH 4.00A
Weight inTons 052 056 060 064 068 072 076 080 084 088 092 094
VLS CONF Full 116 121 125 129 133 137 141 144 148 151 155 157
VLS CONF3 kt 121 125 130 134 138 142 146 150 154 157 161 163
A319 MINIMUM CONTROL SPEEDS @ sea level
VMCA (KT CAS) = 108
VMCG (KT IAS) Conf 1+F = 104.5, CONF 2 = 104.5, CONF 3 = 104.5
SPEEDS LIMITED BY VMC
Takeoff speeds all have a minimum value limited by control. These minimum values are given in the tables down below.
Minimum V1 CONF 1+F = 110, CONF 2 = 110, CONF 3 = 110
Minimum VR CONF 1+F = 113, CONF 2 = 113, CONF 3 = 113
Minimum V2 CONF 1+F = 120, CONF 2 = 119, CONF 3 = 120
V2 LIMITED BY VMU/VMCA
The following tables, one per configuration, provide the V2 limited by minimum unstick speed and minimum control speed in the air.
MINIMUM V2 LIMITED BY VMU/VMCA (KT IAS)
CONF 1+F
035 040 045 050 055 060 065 070 075 080 Takeoff Weight (tons)
119 119 119 119 122 128 133 138 142 147 Speed
MINIMUM V2 LIMITED BY VMU/VMCA (KT IAS)
CONF 2
035 040 045 050 055 060 065 070 075 080 Takeoff Weight (tons)
119 119 119 119 119 122 126 131 136 141 Speed
MINIMUM V2 LIMITED BY VMU/VMCA (KT IAS)
CONF 3
035 040 045 050 055 060 065 070 075 080 Takeoff Weight (tons)
119 119 119 119 119 119 123 128 133 137 Speed
A 319 V App QRH 4.00A
Weight in Ton 044 048 052 056 060 064 068 072 076
VLS CONF Full 108 113 117 122 126 130 134 138 142
VLS CONF3 kt 113 118 123 128 132 137 141 145 149
44 Tons Vref = 108 kts (**Vref is limited by VMCL)
VMCG : Minimum speed, on the ground during takeoff, at which the aircraft can be controlled by only using the primary flight controls, after a sudden failure of the critical engine, the other engine remaining at takeoff power.
VMCA : Minimum control speed in flight at which the aircraft can be controlled with a maximum bank of 5°, if one engine fails, the other engine remaining at takeoff power (takeoff flap setting, gear retracted).
VMCL : Minimum control speed in flight, at which the aircraft can be controlled with a maximum bank of 5°, if one engine fails, the other engine remaining at takeoff power (approach flap setting).
Last edited by rudderrudderrat; 20th Dec 2009 at 22:54. Reason: spelling & definitions & tables & Landing VApp
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However, unless OEM data indicates explicitly that Vmca was done wings level, you probably would be better off presuming that the figure is for 5 deg into the operative engine - too much of a penalty otherwise as a general rule.
Maintain speed at V2. Use sufficient rudder to hold a constant heading whilst maintaining the control wheel at about neutral. If a change of heading is required, aileron application should be limited to avoid an increase in drag due to roll spoiler deployment.
I am sorry if this post is irrelevant at this point of discussion.
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Maintain speed at V2. Use sufficient rudder to hold ..
Not at all irrelevant. However, the words relate to "normal" OEI technique. In routine operations, for most aircraft, we are not often down near/at Vmca.
Once you are somewhat above Vmca there is no need to apply the bank .. it is a specific near/at Vmca thing ... and only because the "real" Vmca is VERY bank dependent. For routine OEI, the preferred bank is around 2-3 degrees to get rid of sideslip .. however, for a small performance penalty, it is a lot easier and generally recommended to fly wings level.
If you search for sideslip and Concorde, you will see a snazzy little sideslip gauge used for OEI on Concorde.
Not at all irrelevant. However, the words relate to "normal" OEI technique. In routine operations, for most aircraft, we are not often down near/at Vmca.
Once you are somewhat above Vmca there is no need to apply the bank .. it is a specific near/at Vmca thing ... and only because the "real" Vmca is VERY bank dependent. For routine OEI, the preferred bank is around 2-3 degrees to get rid of sideslip .. however, for a small performance penalty, it is a lot easier and generally recommended to fly wings level.
If you search for sideslip and Concorde, you will see a snazzy little sideslip gauge used for OEI on Concorde.
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Hi JT, you are correct.
Although there is no clue about that in FCOM “Use rudder to prevent yaw. Shortly after lift-off, ß target will appear. Adjust rudder position to zero the ß target. Control heading conventionally with bank, keeping the ß target at zero with rudder.”
But from the FCTM “When the beta target is centred, total drag is minimized even though there is a small amount of sideslip. The calculation of the beta target is a compromise between drag produced by deflection of control surfaces and airframe drag produced by a slight sideslip. Centering the beta target produces less total drag than centering a conventional ball, as rudder deflection, aileron deflection, spoiler deployment and aircraft body angle are all taken into account. The crew will keep in mind that the yaw damper reacts to a detected side slip. This means that, with hands off the stick and no rudder input, the aircraft will bank at about 5 ° maximum and then, will remain stabilized."
But I'm still puzzled by what Airbus actually refers to as "VMCA". Their A319 V2 "VMCA" CONF3 is 119 kts - but their "VMCA" VMCL CONF3 on the GA is 108 kts. I think the 108kts is what I would understand to need full rudder and 5 degs bank to hold heading. I think their V2 VMCA is controllable with wings level so I can transition from ground to flight.
Thanks Haroon for a great thread.
Although there is no clue about that in FCOM “Use rudder to prevent yaw. Shortly after lift-off, ß target will appear. Adjust rudder position to zero the ß target. Control heading conventionally with bank, keeping the ß target at zero with rudder.”
But from the FCTM “When the beta target is centred, total drag is minimized even though there is a small amount of sideslip. The calculation of the beta target is a compromise between drag produced by deflection of control surfaces and airframe drag produced by a slight sideslip. Centering the beta target produces less total drag than centering a conventional ball, as rudder deflection, aileron deflection, spoiler deployment and aircraft body angle are all taken into account. The crew will keep in mind that the yaw damper reacts to a detected side slip. This means that, with hands off the stick and no rudder input, the aircraft will bank at about 5 ° maximum and then, will remain stabilized."
But I'm still puzzled by what Airbus actually refers to as "VMCA". Their A319 V2 "VMCA" CONF3 is 119 kts - but their "VMCA" VMCL CONF3 on the GA is 108 kts. I think the 108kts is what I would understand to need full rudder and 5 degs bank to hold heading. I think their V2 VMCA is controllable with wings level so I can transition from ground to flight.
Thanks Haroon for a great thread.
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Do not forget the fuselage effect
Dear all
As far as I know the path of an object is defined by adding up all the forces at the CG. Its rotation by putting all the moments with ref to the same point, does not have to be the CG.
On the ground the reaction forces of the gear do not have a horizontal component so there is no shifting from gear towards CG as mentioned before.
When airborne there will be slip and the forces created by fuselage will play an important role.
It is therefore impossible to reason with rudder forces only when comparing VMCG and VMCA. That's what certification flights are all about. Don't worry be happy.
As far as I know the path of an object is defined by adding up all the forces at the CG. Its rotation by putting all the moments with ref to the same point, does not have to be the CG.
On the ground the reaction forces of the gear do not have a horizontal component so there is no shifting from gear towards CG as mentioned before.
When airborne there will be slip and the forces created by fuselage will play an important role.
It is therefore impossible to reason with rudder forces only when comparing VMCG and VMCA. That's what certification flights are all about. Don't worry be happy.
Last edited by Pitch Up Authority; 22nd Dec 2009 at 20:59.
but on the approach & GA (+ in the same configuration Flaps 3) I can fly 12 kts slower than V2.
J_T Isn't V1 (min) 1.05 x Vmcg by FAR 25? It certainly seems so based on the numbers posted above. I know the spread is about that in our planes.
GF (A Vmcg thread junkie)
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I might be missing something,
Until someone comes up with a plausible story we're all a tad confused at the moment, methinks.
Isn't V1 (min) 1.05 x Vmcg by FAR 25
Present (and recently preceding) §25.107 infers something along that sort of path. [You may possibly be thinking, explicitly, of 25.107.(e).(1).(ii) ?]
A Vmcg thread junkie
We're a bunch of sad cases, I think ...
Until someone comes up with a plausible story we're all a tad confused at the moment, methinks.
Isn't V1 (min) 1.05 x Vmcg by FAR 25
Present (and recently preceding) §25.107 infers something along that sort of path. [You may possibly be thinking, explicitly, of 25.107.(e).(1).(ii) ?]
A Vmcg thread junkie
We're a bunch of sad cases, I think ...
