Density Altitude
If you have ever flown into a small strip in early morning and found, after a few hours, that the temperature increased to a point where the calculation of takeoff distance was necessary before takeoff?
I can remember several such instances at Dawn Patrols I attended in the Summer.
You have to take humidity into your calculations. Water vapor can reduce the percentage of oxygen in the atmosphere. Neglecting density altitude with small, not too powerful planes can lead you to a much closer look at the trees below, upon takeoff, than you may have desired
The problem with humidity is that water vapor does not combine with aviation gas to produce ignition. Here's the important point. If water vapor partial pressure is five(5) percent of the total airpressure the available power to the plane is reduced by five(5) percent. this means your takeoff distance will be increased. Maybe too much!
At high temperatures and dew points the problem of high density altitude is compounded by a possible six(6) percent or more power penalty due to humidity. This factor is not accounted for in the Operators Manual of many antique aircraft.
If your manual allows you graphs to determine distance for takeoff, increase that distance by the humidity factor. If that seems like too much trouble, just add six(6) percent for all conditions below 90 degrees F or seven(7) percent for all conditions up to 100 degrees F.
If you have ever flown into a small strip in early morning and found, after a few hours, that the temperature increased to a point where the calculation of takeoff distance was necessary before takeoff?
I can remember several such instances at Dawn Patrols I attended in the Summer.
You have to take humidity into your calculations. Water vapor can reduce the percentage of oxygen in the atmosphere. Neglecting density altitude with small, not too powerful planes can lead you to a much closer look at the trees below, upon takeoff, than you may have desired
The problem with humidity is that water vapor does not combine with aviation gas to produce ignition. Here's the important point. If water vapor partial pressure is five(5) percent of the total airpressure the available power to the plane is reduced by five(5) percent. this means your takeoff distance will be increased. Maybe too much!
At high temperatures and dew points the problem of high density altitude is compounded by a possible six(6) percent or more power penalty due to humidity. This factor is not accounted for in the Operators Manual of many antique aircraft.
If your manual allows you graphs to determine distance for takeoff, increase that distance by the humidity factor. If that seems like too much trouble, just add six(6) percent for all conditions below 90 degrees F or seven(7) percent for all conditions up to 100 degrees F.
