Types of Climb
Aircraft Climb Speeds
Most aircraft accidents occur during the take-off or landing phase of the flight. Collisions with obstacles during climb out, runway overruns on landing do occur every now and then. In this section of the site we will take a look at the various factors contributing to the performance of the aircraft in this part of the flight.
There are a number of speeds defined for aircraft where it has a certain predictable performance. These are: best rate of climb speed (Vx) and best angle of climb speed (Vy). Both are used by the pilot to reach an altitude in the minimum amount of time or distance traveled.
Aircraft normally climb at a steady speed and rate of climb. But we can also perform a so called zoom climb in which speed is converted to altitude (kinetic to potential energy) without changing the power settings. If overdone, raising the nose too high, speed will decrease until the aircraft stalls. Done correctly the aircraft will level at a higher altitude but with a lower airspeed. This technique is usually done during enroute flying to correct for small altitude changes, think plus or minus 100 to 200 ft or so.
A more powerful engine enables the aircraft to climb better. As the aircraft has to overcome drag and the rearward component of weight while pitching up to and in the climb attitude. The more excess power it has the steeper the climb angle can be, like some fighter jets are able to climb vertically solely by virtue of their massive engine power.
Power Required vs Available at different altitudes
This can be expressed in speed, rate of climb and the angle of climb and is defined as follows:
- Speed, determined with the nose attitude set by the pilot. The higher the nose the lower the speed.
- Rate of Climb (VY), is the altitude gain in feet per minute as seen on the VSI.
- Angle of Climb (VX), the angle the aircraft climbs with as seen over the ground.
Rate of Climb, RoC
This is determined by the amount of excess power available over power required to overcome drag at that speed. During climbing to a higher altitude the power required will go up and the power available will go down (both due to air density). So that maximum excess power and climb performance will both reduce.
At a certain altitude aircraft climb performance will reach 100 ft/min on the VSI, the aircraft is then said to have reached its service ceiling. Absolute ceiling will be reached when the RoC is 0 ft/min, which will take a bit longer too attain.
Maximum Rate of Climb, VY
Also known as: Maximum Power Available or Minimum Power required Airspeed.
This occurs at that speed where we have the greatest excess of power available for maximum MAP/RPM. This is determined by the engine and propeller combination compared to airframe drag.
If you need to determine that speed just go about that as follows: execute a number of timed full power climbs between two altitudes at different airspeeds and plot that data in a rate of climb (time to climb between the two altitudes in feet/minute) vs airspeed curve. Be sure to record the flap configuration too.
The result will be a curve that peaks at the point and speed where your aircraft has its maximum rate of climb, VY.
Maximum Angle of Climb, VX
Also known as: Maximum Thrust Available or Minimum Thrust required Airspeed.
Occurs where the amount of excess thrust is at its maximum available over the amount of drag, which is not necessarily the point where airframe drag is at its minimum.
In short: angle of climb depends on maximum thrust and rate of climb depends on maximum power. But as power and thrust are not the same we need some explanation.
Power Required vs Airspeed
Thrust is a force
Thrust is generated by the propeller and is at its maximum when the aircraft sits still and starts to reduce the moment airspeed increases until the speed is reached where the propeller can no longer accelerate the air backwards. Thrust and drag are then equal and the aircraft flies at a steady speed.
Power is the rate of doing work
In our case it is the result of the combined force (work, propeller thrust) applied and the velocity as a result of that (work over time). The power required curve combines the thrust needed and the resulting TAS, all for level flight.
So, thrust is the force produced by the propeller and power is how effectively the propeller force is put to work over time. Resulting in a straight and level flight or climb when there is enough excess power.
Concluding: the maximum angle of climb is lower than the maximum rate of climb speed and occurs on the power required vs airspeed curve where this is the lowest. Maximum rate of climb occurs at the point of the power required curve where a line is draw from the origin tangential to the curve
Cruise or normal climb speed is higher than the best rate / angle of climbs speeds as this is a trade off between speed and rate of climb. In small piston powered aircraft climbing is normally done at maximum power. Climbing with higher cruise climb speeds sets a lower nose angle permitting better visibility and sufficient engine cooling during long climbs.