What Is the Difference Between Vx and Vy, and When Would You Use Each?

Angle vs. Rate: Two Different Goals in the Climb

Before you can answer this question confidently on your checkride, you need to internalize what each speed is actually optimizing — because they are solving two completely different problems.

Vx is the best angle of climb speed. It gives you the greatest gain in altitude for every horizontal foot of ground you cover. Picture a steep ramp rising sharply over a short distance. That is what Vx buys you — maximum altitude packed into minimum horizontal distance. If there is a row of trees at the end of the runway, a power line, or any obstacle you need to clear immediately after liftoff, Vx is the speed that keeps you alive.

Vy is the best rate of climb speed. It gives you the greatest gain in altitude per unit of time. The airplane climbs faster in feet-per-minute, but it covers more ground doing it, so the climb angle is shallower than Vx. Once obstacles are behind you and below you, Vy gets you to cruise altitude as quickly and efficiently as possible.

The Pilot's Handbook of Aeronautical Knowledge (PHAK, FAA-H-8083-25) covers both speeds in the Performance chapter under V-Speeds, and the distinction is fundamental to understanding climb performance. Examiners expect you to know not just the definitions, but the reasoning behind each speed choice.

How and When to Use Each Speed on Departure

The practical application is straightforward once the concepts click. On a normal departure from a long runway with no obstacles, many pilots go straight to Vy after liftoff — it is the more efficient climb speed and puts less stress on the engine. But the moment there is any obstruction in your departure path, you rotate to Vx and hold it until you are clear.

Here is where a common mistake trips up student pilots: using Vy when obstacles are present. Because Vy produces a higher climb rate, it feels like the more aggressive option. But a higher climb rate does not help you if the airplane is also covering ground faster. You can still fly right into the trees at Vy when Vx would have cleared them. The steeper pitch attitude of Vx is what creates the obstacle-clearing geometry you need.

Once you are past the obstacles, transition to Vy without delay. This is not just about efficiency — it is about engine health. At Vx, the nose is pitched high and airspeed is relatively low, which reduces the cooling airflow through the cowling. Cylinder head temperatures can climb quickly in that attitude, especially on a warm day. Holding Vx longer than necessary puts unnecessary thermal stress on your engine. The correct procedure is Vx through the obstacle zone, then a smooth transition to Vy for the rest of the climb.

What Density Altitude Does to Both Speeds

A sharp examiner will not stop at the basic definitions. Expect a follow-up question about how these speeds change with altitude or atmospheric conditions, because the answer reveals whether you truly understand the underlying aerodynamics.

Both Vx and Vy are published for sea-level standard conditions, and both decrease as density altitude increases. Higher density altitude means thinner air, reduced engine power, and degraded aerodynamic efficiency — so your airplane simply cannot climb as well, and the speeds at which it climbs best shift downward in indicated airspeed.

The critical nuance is that Vy decreases more rapidly than Vx as density altitude rises. This means the two speeds gradually converge with altitude. At the airplane's absolute ceiling, they meet at a single airspeed — the only speed at which the airplane can maintain level flight, let alone climb. There is no longer a meaningful distinction between best angle and best rate because the airplane has no excess power left to work with. Practically speaking, this is why high-altitude takeoffs demand careful performance planning. Your published Vx and Vy numbers may not reflect reality on a hot summer day at a mountain airport.

Students often think of Vx and Vy as fixed numbers they simply memorize from the POH. They are a starting point, but understanding how density altitude compresses those two speeds together demonstrates the kind of aerodynamic reasoning your examiner is looking for.

One More Trap: What the Attitudes Actually Look Like

There is a persistent misconception worth correcting before your checkride. Many student pilots assume that because Vy produces a faster climb, it must look more aggressive — a steeper, nose-high attitude. The opposite is true. Vx results in a higher pitch attitude than Vy, which is part of why it reduces engine cooling airflow and increases drag. Vy actually produces a shallower pitch attitude with a higher airspeed, which is precisely why it is more sustainable for a long climb to cruise altitude.

If you find yourself holding a dramatically nose-high attitude during a long cross-country climb, you are probably flying closer to Vx than Vy — and you should check your airspeed and pitch down slightly to Vy to improve efficiency and protect your engine.

Mastering these concepts means you can answer the basic question, field the follow-ups, and demonstrate the kind of practical judgment that earns a passing grade. If you want to practice questions like this in a realistic oral exam format, try SimulatedCheckride.com.