Best-angle-of-climb speed is the airspeed that gains the most altitude over the shortest horizontal distance. Pilots call it Vx, and it is the go-to speed when something is in the way after takeoff.
How It Works#
Every aircraft climbs by trading engine power for altitude. At Vx, the aircraft produces the greatest excess thrust, meaning the difference between thrust available and drag is at its peak. That excess thrust is what drives the nose up and builds altitude quickly over the ground.
Vx produces a steep climb angle, but not the fastest climb in terms of feet per minute. A slower airspeed means the aircraft covers less ground per minute, so altitude stacks up quickly relative to distance traveled. The tradeoff is that engine cooling suffers at low airspeeds, so pilots limit the time spent at Vx.
Vx sits below Vy (best-rate-of-climb speed), which trades climb angle for climb rate. As altitude increases in a piston aircraft, Vx and Vy converge. They meet at the aircraft's absolute ceiling, where only one climb speed is possible.
Example in Aviation#
A student pilot departs from a short airfield with a stand of tall trees at the far end of the runway. The instructor calls for Vx immediately after liftoff. For that aircraft, Vx is 62 knots. The pilot holds 62 knots precisely, and the aircraft clears the trees with room to spare. Once past the obstacle, the pilot accelerates to Vy at 74 knots to continue the climb more efficiently.
Why It Matters#
Obstacle clearance is a real safety concern, especially at short fields, high-density-altitude airports, or after an engine failure in a multi-engine aircraft. Climbing at the wrong speed after takeoff can put an aircraft on a collision course with terrain or structures. Knowing Vx and trusting it removes the guesswork from that critical phase of flight.
Student pilots often confuse Vx with Vy because both are climb speeds. Understanding the difference matters on checkrides and in real operations. The FAA Private Pilot Airmen Certification Standards require applicants to demonstrate both speeds correctly.
Key Takeaways#
- Vx gives maximum altitude gained per unit of horizontal distance.
- Use Vx when an obstacle must be cleared after takeoff.
- Vx is always slower than Vy for piston-powered aircraft.
- In piston aircraft, Vx and Vy converge as altitude increases toward the service ceiling.
- Limit time at Vx to protect the engine from heat buildup at low airspeed.