SkyDemon Plan Documentation: Aircraft Management and Calculations
Aircraft Management
SkyDemon allows you to maintain a library of aircraft to use while planning routes. When the software is installed a default aircraft is created, called simply "Default Aircraft" with some typical attributes of VFR light aircraft. To add and remove aircraft from the library and to change their properties, open the Data menu and select Aircraft Library.
The list of aircraft displayed will initially contain just one item. Press Add to add a new aircraft to the database, or you may choose simply to edit the default aircraft (you can change its name).
Aircraft Properties
Many of the properties of the aircraft should be self-explanatory. The name is what appears in the dropdown list on the main window, so that you can select which aircraft to use for a route you're planning. The default TAS is the normal cruising true airspeed of the aircraft as you usually fly it.
The Fuel tab contains all the properties dealing with fuel type and consumption. Firstly you must define what type of fuel the aircraft uses and whether normal operating figures are specified by quantity (in litres or gallons) or weight (pounds or kilograms). The operating figures then need to be defined for the various stages of flight (taxi/takeoff, cruise, holding, landing) and also the maximum fuel holdable. These figures should be available in your POH and are used when calculating the fuel plan for a route.
The controls under the Weight & Balance tab require a little more explanation and they are very important to get right. You will need to refer to your POH. The centre of gravity (CoG) does not have units associated with it: some aircraft give this in inches and some in cm. It doesn't matter which you use, as long as you are consistent between this figure and the rest on the page.
An aircraft has a series of loading points associated with it, which are combined with the empty weight automatically to arrive at the final weight and balance calculation. For many aircraft the default list of loading points will suffice: Fuel, Pilot, Front Passenger and two rear passengers. If your aircraft does not have any of these loading points, simply select it and press Del. To add a new loading point press the Add button and give it a name. To edit the name or lever arm for any loading point, double-click the value and it will become editable. Remember that lever arm has no units; it just requires consistency across the page. SkyDemon looks for a loading point called "fuel" to automatically enter fuel weight during fuel planning. If it cannot find one, you will need to enter fuel weight manually.
Lastly the acceptable loading envelope for the aircraft must be defined. This will be found in the POH as a graph with centre of gravity on the X axis and weight on the Y axis. These values are imported in to SkyDemon by starting at the lower-left of the graph and entering the coordinates as X,Y pairs going clockwise around the graph edges. The pairs of coordinates are also separated by commas (or semicolons depending upon your locale settings). A minimum of four pairs of coordinates must be entered. The values for the default aircraft are as follows:
83.00,544, 83.00,885, 87.00,1055, 93.00,1055, 93.00,544
And they describe the acceptable loading graph shown on the right.
Importing and Exporting Aircraft
We encourage SkyDemon users to share their aircraft definitions so that others using the same type of aircraft do not have to locate and enter all the same information. A hyperlink in the aircraft manager will take you to our public forums, where you can look for your aircraft. If you find it, press the Import button to import the file and you will then see it in the list.
If you have configured your aircraft yourself, please consider sharing the file so that others can benefit from it. To export it, select the aircraft in the list and hit the Export button. Give the file a name, then you can upload it to our forum along with some photos of the plane (if you wish).
Fuel Planning
The Flight Details window is at the bottom-right of the main window and contains the fuel plan. You will see that it shows the minimum fuel required for the trip, the amount of fuel you have actually planned to take, and the absolute endurance of the aircraft given that amount of fuel. You can expand the required fuel to reveal its six component calculations. These are updated in real time as you plan your route and switch between aircraft.
The fuel calculation components are as follows: Taxi/Takeoff is a fixed amount of fuel defined in the aircraft properties. Cruise (including Diversion) and Holding fuel consumption rates are set per hour in aircraft properties and multiplied according to your route. Landing is a fixed amount also defined in the properties for the aircraft. Contingency is a multiplier set at 5% by default but this can be changed in the Preferences window accessible from the Tools menu.
Calculations are performed as you plan your route, with the required fuel figure updated in real time. To set the planned fuel for the trip click on the hyperlink, and a slider will appear which can be dragged to any amount between with minimum required and the maximum loadable. The amount of fuel you are planning to take is saved alongside your route and is entered in to the weight and balance calculation.
Weight and Balance Calculations
The Weight & Balance window is next to the NOTAMs window. It consists of a list of aircraft loading points in the upper half, and a graph of the loading envelope below, with the results of current calculations plotted on it. The loading points are defined once in aircraft properties, and are simply filled in, in this window, when you plan a route. The value for fuel is automatically filled in as a result of the fuel calculations done in the Flight Details window.
Each loading point has a weight value. This is a hyperlink and can be clicked to change it. For instance, you will see an entry for the Pilot; click where it says 0 kg and enter the actual weight of the pilot. Press enter to confirm and you will see the graph update. All the values apart from Fuel need to be entered manually. The Fuel value can also be adjusted manually if you wish, but it will be overwritten when the fuel plan is next updated.
On the graph is drawn a thick orange line, with a solid green bar at one end denoting the full fuel weight and an empty red bar at the other denoting the empty fuel weight. On this line are plotted a black X which reflects your takeoff weight and a gray X which reflects your landing weight. It is of course important to ensure that both takeoff and landing weight are within limits on the graph. The graph will turn red if this is not so.
Planning Warnings
If any part of your planned route or aircraft configuration is considered unsafe or worthy of attention, a red box will appear in the Flight Details window telling you about it. This includes the following items:
- If your route passes through class A airspace
- If your route passes through a danger, restricted or prohibited area
- If you have not planned enough fuel or your journey requires more fuel than the aircraft can carry
- If a leg of your journey is planned at a level below the MSA for that leg
- If your route passes through a TRA promulgated by NOTAM
