what is the relationship between V1 Vr V2 ?

[cool_pilot]

Hi all,

I was looking through my training manuals to find a logical answer but unfortunately I didn't find any :ugh: plz help.......


cheers,

[WannaBeBiggles]

V1 - is the minimum speed to get airborn should you have a critical engine faliure during your takeoff run. Refered to as the critical engine failure recognition speed.

Vr - is the spee at which you rotate, in reference to the desired takeoff performance. (Always greater than or equal to V1)

V2 - is the minimum safe speed for the second segment of the climb.

[cool_pilot]

WannaBeBiggles,

Thank u. But,what if u increase V1 does that mean that VR and V2 increase as well ?:ugh:

[Ropey Pilot]

V1 VR V2

These will always be in that order.

There may be a gap between one or all - or they may all be the same, but they will never be out of order!

V1 is the speed from which you can reject a take off - above this speed then you must get airborne (even with an engine failure/fire); if you tried to reject you would be off the end of the runway! It is determined by aircraft weight and runway length/conditions primarily.

You wouldn't increase V1 above VR (Vr is a speed chosen by your performance manual; you will be lifting off the runway at that point so a V1 speed (rejected takeoff) which is faster is pointless - so although the runway length may not be the limiting factor for V1 in a light aircraft (eg 319) it is determined to be equal to Vr in this case. So basically you reduce V1 to be equal to Vr if it 'should' be faster

V2 is the 50 foot screen height with one engine inop (for a 2 engine ac)
There are other factors at work in the determination of these speeds such as the minimum control speeds on the ground/air. Eg the min control speed in the air is the speed above which the rudder is effective enough to counteract the yaw caused by losing an engine. For obvious reasons your Vr must be above this or an engine failure during rotation would be catastrophic as you couldn't keep it straight!

Clear as mud then:} Hope I haven't confused the issue!

[pugzi]

Not bad Ropey Pilot.

V2 is the take off safety speed, which is the target speed to attain before the screen height in the event of engine failure. BUT the screen height changes between 50ft for class B and 35 ft for class A.

It's called the safety speed because it has set safety limits from the unsafe speeds, i.e. stall speed (VSR) and min control speed (VMC). If you have V2 by the screen height, then your gonna be ok if something in the engine goes bang.

Pugs

Also be careful about VR. At VR you initiate rotation, but you don't actually lift off at that point, you simnply pull back on the control column. Just after VR the nose will start to come up and then just after that, perhaps 2/3 knots or more, the main wheels lift off. That lift off speed is called VLOF and it is faster that VR :8

[Keith.Williams.]

The answer to your question “if u increase V1 does that mean that VR and V2 increase as well?” is that it depends on the circumstances and why you increased V1.

Scenario 1.
Let’s assume that you are planning to take-off at a mass that is limited by your ASDA. This means that if you reject the take-off at V1 you will have just enough distance available to stop without over running the ASDA.

Now if you were arbitrarily to choose to increase V1 at the same mass, this will increase the distance required to reach V1 then stop. This will cause you to over run the ASDA in the event of a rejected take-off at V1. To prevent this you must decrease your take-off mass to compensate for your increased V1.

One of the factors that limit the minimum value of V2 is the stalling speed. This is proportional to the mass, so reducing mass will reduce the minimum V2.

So in this case by causing you to decrease mass, increasing V1 will allow you to reduce V2 provided it is not less than 1.1Vmc. The reduced mass will also allow you to reduce VR, provided it does not become less than V1.

Scenario 2.
Now let’s assume that you are nowhere close to the field limited mass. This means that you have excess distance available and have a range of values from which to select V1. The lowest value for V1 is the value at which you are just able to reach V2 within the TODA. The highest value of V1 is that at which you are just able to stop within the ASDA. In theory you can choose any value within this range, without needing to change your mass.

This means that you will not need to change VR or V2 provided VR is not less than V1.

Scenario 3.
Let’s again assume that you are nowhere close to the field limit, but that you need to improve your climb limited take-off mass. To do this you must increase V1, VR and V2, so that you climb away at a speed that is closer to Vx.

There are various other possible scenarios in which you might increase V1. Some will enable or require increases in VR and V2 and others will not.