Take-off speed schedule

[bronlund]

Hi everyboby !

I'm trying to figure out the complete speed schedule from Brake release point up to V2 with a "class A" aircraft, and i could really need some help on it..

I'm not sure about it, but the order i have figured out sounds like this:

- Brake release point
- Vmcg
- Vmc
- Vef
- V1
- Vr
- Vmu
- Vlof
- V2min
- V2
- V4

As i said, i'm not sure about if this is in the correct order, so quote me if im wrong, and if you think of any other speeds there are missing in this schedule please come with your suggestion on the correct schedule..

thanks.. :ok:

[Stratocaster]

Vmca comes before Vmcg because you can't get a few degrees of bank to stay on track when you're on the ground.
;)

So you need those extra knots to be able to keep the centreline (Vmcg).

Vmu is definitely below V1, possibly lower than Vmca. That's the first speed where your flight controls have some degree of authority on the aircraft. Have you ever seen those test flights with the B777 or the A340's tail dragging on the runway and making lots of sparks ? That's roughly Vmu.


Now where did I throw all my books ? I should get a more precise answer...

[bronlund]

I don't get it.. Vmca before Vmcg.. :confused: .. How can that be.
As i see it, Vmcg (Minimum control speed on or near the ground) can only come before Vmca (Minimum control speed, take off climb).. maybe i'm wrong.. :confused: .

And V1 (Decision speed) before Vmu (Minimum unstick speed).. :confused: ..
That too i don't understand.. because how can it be possible to begin the Rotate before decision speed.. :confused:

If it is possible for you to find a more precise answer, i would really appreciate it..

[redsnail]

From Aircraft Performance Theory for pilots by Swatton.
Brake release point.
Vmcg
Vmca
Vef (engine failure!)
V1
Vr
Vmu (min "safe"unstick)
Vlof (lift off or aka Vus - unstick)
[end of TOR]
screen height 35' = V2.
[end of TOD]

Vmcg. This is the minimum control speed on the ground and is the CAS (speed) , at which, when the critical engine is suddenly made inoperative during the take off run and with its propeller, if applicable, in the position it automatically takes, it is possible to maintain control with the use of the primary aerodynamic controls alone (ie No nosewheel steering) to enable the take off to be safely continued using normal piloting skill. (can't deviate more than 30' from the centre line)

Vmca. Similar speil but control in the air and maintain straight flight with an angle of bank no greater than 5° Angle of Bank without a heading change of greater than 20°. It may not exceed 1.2Vs.

I thought Vmca was slower than Vmcg but I guess the action of friction on the tyres and so forth resists the tendency to swing.

[Mad (Flt) Scientist]

redsnail

there's nothing forcing Vmca and Vmcg to take any particular relationship - things such as undercarraige geometry, side force characteristics and control system design can all have an effect. All that can be said usually is that the two speeds are often (but by no means always) similar. You are neither right nor wrong...

Also, Vmc may not exceed 1.2Vs for MTOW - which allows it to be considerably higher than 1.2Vs at lighter weights.

[Stratocaster]

I finally found the book !
:p

Here it says Vmcg is higher than Vmca because with the wheels firmly on the ground there's no way you can get 5° of bank to help you stay on the centreline (I'm tempted to agree on this one).
:D

So you need the extra knots on the rudder to keep the aircraft under control. They don't seem to care about friction and they don't say how close the two speeds can be.

The restrictions on controllability (to make sure you stay on the runway in case of engine failure and can keep the aircraft under control after rotation) should be applied on Vlof, but since nobody ever calculates that speed, the restriction is applied to the speed just below Vlof: Vr.

For a multi-engine aircraft, Vr must not be less than 1,05.Vmc.

Vmc is only affected by the amount of asymmetric thrust and the aerodynamics of the aircraft. It is not affected by the TOW. Vmca and Vmcg increase when the air density goes up, and are the highest at...
- low pressure altitudes
- low temperatures
- low humidities
because that's where asymmetric thrust is the greatest.


Vmu is the lowest possible speed at which you can leave the ground with all engines running. It means you have the highest nose-up angle and you're limited either by the length of your aircraft (tail-strike) or by the elevator power. For class A aircraft, Vr must be equal or greater than 1,1.Vmu.

Now if your books say something different we might have a problem somewhere...
:)

[bronlund]

Hmm..

Redsnail.

Seems like the list you have made agrees with the schedule i started out with.. :D

But still, it may not be all correct..
From Stratocaster and Mr. scientist's point of view, Vmca could be lower than Vmcg.

I've tried to put some speeds in my previous list, taken from my books, and it sounds like they don't quite agree with Stratocaster's books, but here they are..
and as stated earlier, i could be wrong.. :hmm:

BRP
Brake release point

Vmcg
Minimum control speed Ground

Vmc
Minimum control speed with critical engine inoperative
Must not exceed 1.2 Vs

Vef
Engine failure speed

V1
Decision speed
May not be less than Vef
Must not exceed Vr
Must not exceed Vmbe

Vr
Rotate speed
May not be less than V1
May not be less than 1.05 Vmc
May not be less than 1.05 Vmu ( One engine)
A speed such that V2 can be attained before 35ft

Vmu
Minimum unstick speed

Vlof
Lift off speed
May not be less than 1.1 Vmu (All engines) or 1.08 Vmu if limited by elevator power
May not be less than 1.05 Vmu (One engine) or 1.04 Vmu if limited by elevator power

V2min
Minimum take off safety speed
May not be less than 1.2 Vs ( 2 and 3 engine turboprop and turbojet )
May not be less than 1.15 Vs ( more than 3 engines turboprop and turbojet )
May not be less than 1.1 Vmca

V2
Take off safety speed
35’ screen height speed
May not be less than V2min
May not be less than Vr + the speed increment up to 35ft ( Same as V2, but thats what the book is teeling)