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# Vx vs. Vy

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Let’s imagine for a moment the following hypothetical situation: Two airplanes are taking off at exactly the same moment from parallel runways. Airplane A accelerates to and climbs out at Vx while Airplane B accelerates to and climbs at Vy.

What will happen in each case?

Of course, we already know that Vx is the speed for best angle of climb while Vy is the speed for best rate of climb. (If you sometimes have a hard time remembering which is which, think of an X as having lots of angles.) The rule of thumb for which speed to fly is easy: We use Vx immediately after takeoff to clear obstacles, followed by Vy to reach our cruising altitude quickly.

But wait a second. If Vy gives us the best reading on our VSI, why would we ever use a lower rate of climb initially?

The answer has to do with distance vs. time – namely the fact that clearing obstacles is a distance problem (i.e. gaining the maximum altitude in the shortest space possible by flying at best-angle speed) while climbing to cruise altitude is a time problem (because every second at Vy puts the maximum space between the ground and our airplane).

The benefit in climbing at Vx initially is that it allows us to reach a sufficient altitude in the available horizontal distance between the start of our takeoff roll and those tall trees off the departure end of the runway. Once clear of obstacles, the next challenge lies in reaching our cruise altitude as soon as possible, hence the transition to Vy.

So let’s return to our hypothetical dual takeoffs. After passing the runway departure-end threshold, Airplane A climbing at Vx will be higher than Airplane B climbing at Vy. But after, say, 10 minutes, Airplane B climbing at Vy will be higher, and also farther from the departure airport.

For safety’s sake, the FAA Flying Handbook says a blend of Vx and Vy is the best choice at airports with obstacles. And yet many pilots on takeoff will shove the throttle forward, rotate and then immediately allow the airplane to accelerate to a speed much faster than Vx. For some, this undoubtedly has to do with the fact that they’re intimidated flying at such a slow speed so near to the ground. If you fall into this group, ask an instructor to demonstrate a proper Vx climbout with you. The next time you must fly at Vx to safely clear obstacles, you’ll be glad you did.

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I think your statement that "After passing the runway departure-end threshold, Airplane A climbing at Vx will be higher than Airplane B climbing at Vy. " is a correct but a bit confusing.

If you have two identical airplanes taking off simulanesouly from parrallel runways Airplane A climbing at Vx will be lower than Airplane B when Airplane B crosses over the threshold... but Airplane A hasn't made it to the threshold yet. So... a few seconds later, when Airplane A does pass over the the threshold it will be at a higher altitude than when Airplane B passed over it.... but Airplane B will still be above it but much further on course.

Vx is great after takeoff but now lets combine Vx and takeoff roll to find out the best way to get over the trees at the end of the runway? Vx does not mention flaps. My takeoff roll is 1600 feet without flaps, 1200 feet with 25 degrees of flaps. I can be off 400 feet sooner and start my (possibly weaker) climb earlier with the flaps down. I can only assume that my climb is weaker with flaps down (or Vx would include flaps) so should I retract the flaps as soon as the wheels are up and get that sinking feeling or keep them down? Where can I find a published climb gradient like Vx or Vy with flaps at 10 or 25 degrees?

SteveW: This article was written based on FAA-recommended short-field procedures and is really meant more as Vx and Vy 101. Sounds like you're ready to go flying with a bush pilot for the "rest of the story" on short-field takeoffs. Now that's information you won't find in any POH. :-) SP

One major concern that makes me hesitate to climb out at Vx unless there is a good reason (obstacles) is that the engine is rarely at full operating temperature during initial take-off and I cannot help but feel this loading of the engine before it is fully warmed up will be harmful. Thoughts?

Good Point about engine temp and loading. May be good to see this as it's own topic.

This article seems primarily intended for students and new pilots. Here's my two cents about Vx, Vy and cruise climb.

If obstacle clearance is what you require, check the POH to confirm that the airplane can climb above the obstacle before you think about taking off! Before establishing Vx you need to think about rotating right at Vr, to get the plane up and climbing ASAP. The value of Vr for your airplane can be found in the "Limitations" section of the POH (pilot's operating handbook). Accelerate to Vr and then do a brisk pull back on the stick but don't pitch beyond about 15 degrees up on your attitude indicator. Then quickly stabilize then airplane at Vr and leave the throttle and prop levers alone until the obstacle is cleared. At such a slow speed you'll need plenty of right rudder to keep the ball in the middle. If there is any significant headwind on takeoff the angle you achieve will be a bit more steeper, and the opposite applies as well. Pilots should not fear climbing at a steep angle as long as their airspeed is controlled at, or slightly above, Vx. That is what the airplane was built to do. If you cannot control airspeed that accurately you need to seriously consider getting more instruction.

Once all obstacles are cleared you'll want to reduce power to climb setting and change the propeller pitch setting as you accelerate to Vy for maximum climb rate. But that is not the end of the story.

Many light aircraft climb nearly as well as Vy as higher indicated airspeeds. Experiment with your airplane and see what the tradeoffs are. Use the cruise climb technique when you want to maximize groundspeed in exchange for a bit less climb rate.

Whether you get to your destination faster by climbing at Vy or cruise climb is a subject for another day.

Happy landings!

Douglas M
Surrey, BC Canada

I'm occasionally asked by my CE172P students why the initial 50 ft obstacle clearance airspeed is 56KIAS when Vx is 60KIAS. Good question, I always respond. There's no elaboration in the POH to provide guidance, so I point out that Vx and Vy intersect at the service ceiling of the airplane. So, presumably the 56KIAS obstacle clearance airspeed is actually the Vx speed (as defined) but it's too slow to provide adequate engine cooling all the way up to the airplane's service ceiling.

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