V2 vs. Vyse

[uwochris]

Hey guys,

Is V2 synonomous with Vyse? If you experience an engine failure while flying a large a/c, are you supposed to pitch for V2 or Vyse?

If these speeds are different, why would you not want to use Vyse, if this is the speed (AOA) that gives the best climb performance with one engine inop? I would imagine that if you experience an engine failure after takeoff, you would want to be gaining altitude as quickly, and safely, as possible by flying at Vyse, and NOT V2.

Thanks in advance,

Chris.

 

[Lead Sled]

Turbojet aircraft have a best angle of climb and best rate of climb speeds; but most pilots have no idea what they are - they're usually not published because they're not pertinent to any normal operation and when they are published, it is typically done by adding a certain speed to some other published speed such as V2, i.e. V2+15 knots. (Actually, it would be more correct to reference Vx and Vy to specific angles of attack, but this is a whole different topic.)

Remember, light, under 12,500 lb, aircraft are not certified to the same rules or criteria as the large (12,500 lb +) turbine-powered aircraft. Part 23 airplanes (light aircraft) have no guarantees when it comes to takeoff performance as large turbojet-powered aircraft have.

When you suffer an engine loss in a turbojet aircraft you follow a definate cleanup schedule. This is done to insure that you meet the required climb gradients. Further more, you are required to operate at a weight that will allow you to achieve the required performance with the loss of an engine. You are under no such obligation in a Part 23 airplane.

'Sled

 

[EagleRJ]

They are more or less equivalent speeds. V2 is charted for a transport-category aircraft certified under Part 25, and gives you the best single-engine performance on the second segment of your takeoff climb. Part 25 aircraft don't have Vx or Vy speeds.

Vyse is charted for smaller Part 23 normal category aircraft, and gives the best single-engine performance at any altitude (I know, I know, Vy does change with altitude- I'm talking general concept). It also gives you the minimum sink after an engine failure on takeoff, since you are not required to have positive SE climb performance under Part 23. Vyse gives you the best drift-down performance after an engine failure at altitude, too.

Part 25 certificated aircraft generally have enough power to cruise at normal speeds on one engine at low to mid altitudes. The only drift-down performance we have is an altitude we can expect to drift down to. The only time V2 is used is during the takeoff.

 

[Jeff Helgeson]

Simple put, it's about your weight....

....The above answers are good, but weight varies greatly on transport catagory aircraft. Vyse (or red radail and blue line) would vary with weight too greatly to paint lines on the A/S indicator. Hence the speed cards or other methods are used to display speeds for a given weight. It also may vary due to flap selection for T/O.

Most T/O limitations are:

1. Weight
2. climb limit
3. runway limit

The 4 segments of T/O were mentioned in a previous post. I find many of the performance limitations to come in to play deal with second stage climb (35' to 1000").

In addition, performance data is obtained from ATOG charts or based on a specific airport, runway, temperature, etc., and the T/O numbers are based on that and are very specific for the conditions. It takes in to account runway slope, elevation, and footnoted for engine anti-ice, standing water or slush, etc.

In short, there are more considerations and factors that make the speeds vary.

 

[avbug]

Chris,

All this sounds confusing, but it's really not. Yes, many large turbojet airplanes do have best single engine climb speeds published, and usually include a variety of performance charts to describe this. However, many factors affect what this speed may be; simply using one speed like most like twins do is overly simplistic.

V2 is usually a lesser speed that what the best rate of climb speed will be on one engine. It's sole purpose (V2) is to facilitate the early climb during a takeoff or go-around with one or more powerplants shut down. V2 is a speed used for "second segment" climb performance. Second segment begins with landing gear retraction, and usually continues to an altitude of 400' above the departure elevation. It isn't best angle speed, and it isn't best climb speed, either.

The purpose of V2 is to meet a specific climb gradient requirement, for a given weight and elevation. Beyond that, it has no relationship in comparison to a best angle, or best climb speed. It's the appropriate speed to meet a specific climb gradient. After completing the second segment climb, the airplane is usually given the final climb configuration (usually cleaned up), and accelerated to Vf, or the final climb speed to 1,500 (or higher, as appropriate) AGL, and from there to a cruise climb or best climb as may be required.