User manual

Aerosoft Aspen Extended 1.00
Page 11
APPENDIX A; HIGH DENSITY ALTITUDE
If there is one thing that makes this product special it is the high altitude of the airports. It is our experience
that many sim pilots do not fully understand the effects of the resulting lower air pressure, so a full chapter on
flying in these conditions is in order.
HIGH DENSITY ALTITUDE
In this chapter we are going to use the Cessna 182RG as our base model, for all other aircraft the principle is
the same, only the figures change. There is one complete factor that should be used when dealing with Density
Altitude that we will not mention humidity. It is not a major factor and in FS it is not used. In case you’re
interested: high humidity will RAISE the Density Altitude.
IMPORTANT: The ACTUAL altitude of an airport is of little or no consequence, the
only aspect that matters is the DENSITY ALTITUDE of the airport. The only thing
that is of relevance is the AMOUNT of air molecules!
Air is needed for many things (we will use the word ‘air’ to describe the mixture of gasses we experience);
 to create lift
 to create a forward pushing force for jets or pulling force for propeller planes (props)
 to assist the combustion of the fuel
 to cool the propulsion system
 and of course, the pilot also needs something to breathe.
If there is less air all of these aspects will not be as efficient as under optimal conditions. So what is the effect
on the performance of the aircraft? And in particular on takeoff and landing? Well how does a takeoff run of
1,800 ft. sound to you? For a Cessna that is not loaded very heavy? Is that impressive or not? Look at the
following table that shows the relation between altitude, temperature and pressure. The data for takeoff and
landing are for a moderately loaded Cessna 182 RG.
Altitude
in ft.
Temperature
in degrees F
Altimeter
Setting
in Inch Hg
Resulting
Density
Altitude
Required
Runway
Takeoff
Required
Runway Landing
0
59
29.291
0 ft.
640 ft.
600 ft.
4,000
59
29.291
4,924 ft.
950 ft.
720 ft.
8,000
59
29.291
9,816 ft.
1,350 ft.
900 ft.
8,000
100
29.00
13,255 ft
1,850 ft. ?
1,200 ft. ?
Where there are question marks they are there because the Cessna manual does not supply these numbers
and they have been extrapolated from the other numbers. Keep in mind that a turbo-charged aircraft like the
182 is built to operate at higher altitudes and that it will perform much better than a non turbo-charged
aircraft. If you try to take off with a Piper Cub meant for a Density Altitude of 1,300’ you’ll probably never
reach takeoff speed before running out of runway and landings will have to be done at speeds ABOVE cruise
speed. In the last row of the example the aircraft is located at 8,000’ feet but for all logical and practical
purposes it is 5,000’ higher.
Density Altitude is the altitude that the aircraft THINKS it is at.
Also it is not only performance that suffers; your engine will also overheat MUCH faster because there is less
air to cool the engine. And when winter comes and Density Altitude becomes less of an issue you run into