SkyDemon Plan Documentation: Aircraft Management and Calculations
The Aircraft Library
SkyDemon maintains a library of different aircraft profiles on your computer, so that if you have access to more than one aircraft (or you are just curious) you can plan flights using different aircraft to compare their performance. To access the Aircraft Library, press the Aircraft button on the toolbar.
The window displays a list of all aircraft profiles stored on your system. A green tick is shown next to the aircraft currently in use. To switch to a different aircraft for the current route, just click on it then press Use Aircraft. The window disappears, and your flight details are recalculated using the new aircraft.
Aircraft profiles are just files stored on your computer. To explore them, navigate to the SkyDemon folder within your personal Documents folder, then find the Aircraft folder within that. You can share these files with friends, and go to our online forum to look for aircraft profiles posted by other SkyDemon customers. If you find one, simply save it to this folder and restart SkyDemon, and you should see the new aircraft in your list.
To change the properties of an existing aircraft, select it then press Edit. To create a new aircraft, press Add. There are many variables that make up a full aircraft profile, and these are discussed in the remainder of this section.
Basic Properties and Fuel
These properties are contained on the General tab of the aircraft properties window. The first box is the name of the aircraft, which is usually just the manufacturer and model. Below this you can enter the registration of the aircraft. At the bottom of the page there are controls for setting the aircraft type and colour/markings, which map directly to the ICAO flightplan output if you should choose to use it.
This page also contains basic fuel information for the aircraft, such as what type of fuel it uses and whether fuel is referred to by volume or by weight. If fuel is specified by volume then the units are litres, US gallons or UK gallons. If fuel is specified by weight then the units are kilograms or pounds. These units are specified separately, in the Change Units tool under the Setup menu.
Take/Takeoff specifies how much fuel is required for the taxi and takeoff phase of the flight. Landing specifies how much fuel is likely to be required from arriving overhead your destination to shutting down the engine. Enter the maximum conceivable values in these fields to be safe; your aircraft POH or balance sheet may suggest appropriate values.
Holding Time specifies the time in minutes that should be allowed for holding at the destination airfield. This sometimes varies between aircraft but 45 minutes is a common value. When calculating the minimum required fuel, SkyDemon uses this value combined with the most fuel-efficient power setting (see later). Contingency is a percentage added to the enroute fuel calculations to add a safety margin and 5% is a common value.
Maximum Fuel is the total fuel that can be loaded on board.
Climb and Descent
SkyDemon models every stage of your flight including all climbs and descents needed to achieve your requested levels. This requires some knowledge by the software of the performance characteristics of your aircraft, and though the list of fields can be daunting it is reasonably easy to configure a very accurate model. Set the service ceiling according to the value given in your POH.
For the climb, you will need the rate of climb of your aircraft at sea level and at its service ceiling. The service ceiling of an aircraft is usually defined as that altitude at which climb performance decreases to 100 ft/min so this value is normally used. Indicated airspeed is the speed indicated during a climb. You will also need to enter the fuel burn at sea level and at the service ceiling. If you don't know the fuel burn in a climb at the service ceiling, just enter the same value as at sea level.
For the descent, you need to enter the descent rate in ft/min, the airspeed indicated and the fuel burn while descending.
Cruise Profiles
When specifying the speed for your journey or for a leg, you do not explicitly choose a speed but rather a known power setting for the aircraft, which will produce a given indicated airspeed and for which the fuel burn rate is known. These configurations are known as cruise profiles and you can set up as many for an aircraft as you like.
The cruise profiles for your aircraft are displayed in a list. To edit one, select it then change the values displayed in the boxes below the list. To create a new one, select an existing one and click Copy. To delete one, select it and press Del. You cannot delete the last profile in the list. The profile name is used later to select the profile, and is likely to be something like "2400 RPM". The indicated airspeed is the airspeed indicated by your aircraft while flying with this power configuration, and is converted to true airspeed automatically by the flight modelling engine. Fuel burn is the amount of fuel burned per hour while flying with this power configuration.
You should be able to refer to your POH for all the information required on this page.
Weight and Balance
Enter the empty weight and centre of gravity of your aircraft at the top of this page. The centre of gravity is usually either measured in inches or centimetres, but the units do not matter as long as you are consistent with the other inputs on the page.
Loading Points
SkyDemon calculates the weight and balance of your aircraft as you plan a route, and to do this it needs to know about all the loading points. These are usually provided in the POH or a balance sheet accompanying the aircraft. A default list of loading points will already be present, and you can edit the name or lever arm of any of them by double-clicking. The lever arm is a distance from a datum (the same datum as used in the empty centre of gravity) and is unitless, but ensure you use the same units as you used above.
There will normally be a loading point called Fuel. As long as there is such a loading point, SkyDemon will automatically enter the fuel weight while you are planning routes. If your aircraft has multiple tanks and they cannot share a loading point (i.e. they are not the same distance from the datum) then you will need to enter two separate fuel loading points, and SkyDemon will not know how to distribute fuel between them. You will need to specify this distribution manually when creating routes.
The actual weights for the loading points are entered later, when you create routes using the aircraft. You only need to configure the presence of the loading points once.
Acceptable Loading Envelope
In the POH there is usually a graph representing the acceptable loading envelope of the aircraft. The graph will usually have units from the datum along the bottom (x axis) and total weight of the loaded aircraft up the left (y axis). The graph is a polygon that will hopefully look something like the diagram on the right.
Describing the envelope to SkyDemon requires typing out the coordinates that make up the polygon one by one, starting at the bottom left corner and working around clockwise. Use a comma to separate the coordinates from each other and to separate each pair; looking at the data already in the box will give you an idea of the syntax required.
To reproduce the diagram on the right you would start at the bottom left corner and enter 83,500 because that point is 83 along the x axis and 500 along the y axis. Then enter a comma, then the values at the next vertex which are 83,880.
