Post by Andrew Godden on Jan 13, 2012 0:37:22 GMT -5
In the interests of participants maybe undertaking better or more detailed flight planning for each Flight Leg, the following detailed explanantion is provided on how the "Target Time" is calculated.
Unlike previous events, the extreme altitude variations present administrative challenges before the flying even begins. Consequently, whereas in previous events an average cruise altitude was used for the calculation, this approach could not be applied without disadvantaging participants.
The basic principles of the original calculation have been retained. Based on the "Test Flight" time, the cruise speed is derived and used to allocate aircraft into one of four performance categories. These categories group aircraft by approximate performance characteristics across the flight profile with parameters for rate of climb, speed during climb to cruise, and speed during the circuit and approach phases.
The derived cruise speed, and the performance characteristics from the associated category are then used to calculate the "Target Time", with elements factored in for the various stages of flight, Climb, Cruise, Descent and Circuit. The Climb component factors in a reduced speed and distance covered against the total Flight Leg distance, as does the Circuit component, which is based on a combined Downwind, Base and Final Leg of approximately 12 nm. Where a Flight Leg involves a "touch and go", the additional Circuit and subsequent Climb components are included further.
The following variations have been added to the calculation process:
- the maximum terrain height has been determined for each Flight Leg using Plan-G and the digital elevation model (DEM) feature;
- using the principles for calculating a Maximum Elevation Figure (MEF), an MEF has been calculated for the flight path. This involves adding 100 feet for vertical error, then adding the height of the highest obstacle in the quadrangle or 200 feet, whichever is higher, then rounding up to the next hundred feet. (This would normally be done on a quadrangle basis, each spanning half a degree of latitude and half a degree of longitude, however, due to the obvious base data limitations, the logic has been applied to the flight path);
- a minimum height AGL of 1,500' has been added to the MEF, representing the minimum cruise altitude for a Flight Leg;
- using the Semicircular / Hemispheric Rule for VFR flights, the appropriate cruise altitude has been determined for each Flight Leg; and
- the altitude of the departure airport is subtracted from the calculated cruise altitude and the result is used in the Climb component of the "Target Time" calculation.
Two last important points:
- the "Target Time" is calculated without reference to weather for
the Flight Leg; and
- your flight planning has to consider the weather, as presented "on the day".
This process ensures a more realistic and accurate calculation of the "Target Time" relative to the aircraft being flown. Of course, it is not perfect, but then, I cannot aim for it to be. The weather variables and individual flying and planning abilities provide that additional "X factor", and that is what the event is about - your ability to plan and fly to get as close as possible to the "Target Time".
There, simple enough, and my MS Excel spreadsheet does it automatically for me. All I do is enter the registered "Test Flight Time". Hopefully this will be of benefit to some.
Cheers
Andrew
Unlike previous events, the extreme altitude variations present administrative challenges before the flying even begins. Consequently, whereas in previous events an average cruise altitude was used for the calculation, this approach could not be applied without disadvantaging participants.
The basic principles of the original calculation have been retained. Based on the "Test Flight" time, the cruise speed is derived and used to allocate aircraft into one of four performance categories. These categories group aircraft by approximate performance characteristics across the flight profile with parameters for rate of climb, speed during climb to cruise, and speed during the circuit and approach phases.
The derived cruise speed, and the performance characteristics from the associated category are then used to calculate the "Target Time", with elements factored in for the various stages of flight, Climb, Cruise, Descent and Circuit. The Climb component factors in a reduced speed and distance covered against the total Flight Leg distance, as does the Circuit component, which is based on a combined Downwind, Base and Final Leg of approximately 12 nm. Where a Flight Leg involves a "touch and go", the additional Circuit and subsequent Climb components are included further.
The following variations have been added to the calculation process:
- the maximum terrain height has been determined for each Flight Leg using Plan-G and the digital elevation model (DEM) feature;
- using the principles for calculating a Maximum Elevation Figure (MEF), an MEF has been calculated for the flight path. This involves adding 100 feet for vertical error, then adding the height of the highest obstacle in the quadrangle or 200 feet, whichever is higher, then rounding up to the next hundred feet. (This would normally be done on a quadrangle basis, each spanning half a degree of latitude and half a degree of longitude, however, due to the obvious base data limitations, the logic has been applied to the flight path);
- a minimum height AGL of 1,500' has been added to the MEF, representing the minimum cruise altitude for a Flight Leg;
- using the Semicircular / Hemispheric Rule for VFR flights, the appropriate cruise altitude has been determined for each Flight Leg; and
- the altitude of the departure airport is subtracted from the calculated cruise altitude and the result is used in the Climb component of the "Target Time" calculation.
Two last important points:
- the "Target Time" is calculated without reference to weather for
the Flight Leg; and
- your flight planning has to consider the weather, as presented "on the day".
This process ensures a more realistic and accurate calculation of the "Target Time" relative to the aircraft being flown. Of course, it is not perfect, but then, I cannot aim for it to be. The weather variables and individual flying and planning abilities provide that additional "X factor", and that is what the event is about - your ability to plan and fly to get as close as possible to the "Target Time".
There, simple enough, and my MS Excel spreadsheet does it automatically for me. All I do is enter the registered "Test Flight Time". Hopefully this will be of benefit to some.
Cheers
Andrew