First Principle Performance Data
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First Principle Performance Data
I am looking for an academic definition of first principle performance data and the difference between it and AFM data (AFM DPI). I have looked through FAR25 and JAR25 but have not found a definition. I would be very grateful if anyone can offer pointers as to where to find the answer.
Thank you
EM
Thank you
EM
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AFM Data should indicate the source, be it flight test, extrapolation of flight test, first principles, etc.
First principle performance data will be based on physical laws and a number of assumptions. The accuracy will be in question, but some spot checks of the data may have been completed in flight test to confirm reasonable accuracy.
Flight test data in the AFM may have a line drawn through or beyond data points that is based on the first principles, so in some cases the "academic" difference between the two is minimal.
Matthew.
First principle performance data will be based on physical laws and a number of assumptions. The accuracy will be in question, but some spot checks of the data may have been completed in flight test to confirm reasonable accuracy.
Flight test data in the AFM may have a line drawn through or beyond data points that is based on the first principles, so in some cases the "academic" difference between the two is minimal.
Matthew.
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I'm curious to know why you want to know the difference - performance data for the approved sections of the flight manual has to come from flight testing, and then be corrected for specification engines and non-standard atmospheric conditions.
I can't imagine any certification agency accepting 'first principles' data for inclusion in a flight manual or any computer program for predicting performance.
I can't imagine any certification agency accepting 'first principles' data for inclusion in a flight manual or any computer program for predicting performance.
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Shaun,
Many manufacturers and service companies that offer computer performance programmes will calculate performance data using either AFM(DPI) or 1st Principle data. As I understand it 1st principle is the data that is used during the certification program for FAR or JAR 25, however there is a difference between the two SCAP modules and I am trying to find out exactly what the difference is. Is there an ICAO answer to this or does it vary from one manufacturer to the other?
EM
Many manufacturers and service companies that offer computer performance programmes will calculate performance data using either AFM(DPI) or 1st Principle data. As I understand it 1st principle is the data that is used during the certification program for FAR or JAR 25, however there is a difference between the two SCAP modules and I am trying to find out exactly what the difference is. Is there an ICAO answer to this or does it vary from one manufacturer to the other?
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Shaun,
Sorry but you are wrong, the B777-200 only comes with "1st Principle" calculations, be they from AFP-DPI or SCAP. 1st Principles are also used by Embraer, Airbus and possibly Bombardier if they have finished writing the program.
Epsilon minus
AFM-DPI is based on first principles, for the B777-200 it replaces Chapter 4 of the AFM. You do not get a "2nd Principle" look up option. Are you trying to compare weights between AFM-DPI and a SCAP takeoff chart program? If so, the differences that you find are usually caused by the calculation methodology rather than the actual data, the methodology is manufacturer dependant. For example, Embraer offer 2 different calculation methodologies for 1st principles in the ECAFM, the 2nd option has a 40% faster calculation time for a small decrease in calculated weight. They do not offer 2nd principles.
Matthew
Not so, when Boeing offered us AFM-DPI for the B747-400, they showed an 8000 kgs weight improvement from J'burg. Its all from the same flight test data 
Mutt
I can't imagine any certification agency accepting 'first principles' data for inclusion in a flight manual or any computer program for predicting performance.
Epsilon minus
AFM-DPI is based on first principles, for the B777-200 it replaces Chapter 4 of the AFM. You do not get a "2nd Principle" look up option. Are you trying to compare weights between AFM-DPI and a SCAP takeoff chart program? If so, the differences that you find are usually caused by the calculation methodology rather than the actual data, the methodology is manufacturer dependant. For example, Embraer offer 2 different calculation methodologies for 1st principles in the ECAFM, the 2nd option has a 40% faster calculation time for a small decrease in calculated weight. They do not offer 2nd principles.
Matthew
Flight test data in the AFM may have a line drawn through or beyond data points that is based on the first principles, so in some cases the "academic" difference between the two is minimal.
Mutt
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Mutt
Thank you I am aware of the use of 1st priciple data in current performance calculation tools, espicially Embraer which offers an AFM or FP option. However my question is what is the difference?
I assume the AFM data has a safety margin factored into the 1st principle data to allow for differing reaction times from line pilots compared to test pilots. Is this correct and if it is what are the safety margins? There must be a written definative somewhere, can you point me to it please?
EM
Thank you I am aware of the use of 1st priciple data in current performance calculation tools, espicially Embraer which offers an AFM or FP option. However my question is what is the difference?
I assume the AFM data has a safety margin factored into the 1st principle data to allow for differing reaction times from line pilots compared to test pilots. Is this correct and if it is what are the safety margins? There must be a written definative somewhere, can you point me to it please?
EM
Use of safety factors is variable, but where there is a requirement to include one, it's likely to be in subpart B of the relevant airworthiness standard (or if not there, in the section corresponding to operating data requirements). In the UK, if you can get hold of it, the old BCAR Section K is still CAA's preferred guidance for sub-25 aeroplanes.
In general however, my experience is that the use of theoretical derived data in the AFM (or related documentation) is only done after modification and/or validation using real-world flight test data. I'm not aware of any published data, except that for initial flight testing (where it's inevitable) being based upon analysis alone.
G
In general however, my experience is that the use of theoretical derived data in the AFM (or related documentation) is only done after modification and/or validation using real-world flight test data. I'm not aware of any published data, except that for initial flight testing (where it's inevitable) being based upon analysis alone.
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I assume the AFM data has a safety margin factored into the 1st principle data to allow for differing reaction times from line pilots compared to test pilots.
Look at appendix 1 of http://www.airweb.faa.gov/Regulatory...7?OpenDocument AC25.1581 shows the requirements for an AFM regardless of if its a paper version or electronic version.
You have said that Embraer supply an AFM or FP option, I presume that you are talking about the E135/145 aircraft as there is only one option available for the E170-195 series of aircraft based upon 1st Principle.
If you are finding differences, it because of the calculation methodology, we had the same problem running B744 analysis on a mainframe, 2nd Principle and 1st Principle, its all based upon the same certification requirements and data, but the answers are slightly different.
None of the manufacturers will tell you the exact methodolgy that they use as its considered a trade secret, but considering that Embraer (E-series) have managed to cut 40% off the calculation time by changing the methodology, it demonstrates that there are various metholdogies available.
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First Principle vs 2nd principle
My understanding was:
1st principle: Performance data derived directly from a physics-based simulation of the aircraft. ("Octopus" program on airbus)
2nd principle: Performance data derived from lookup tables, diagrams, electronically stored tables etc., generally what is called "tabulated" data. Performance for one certain point (Weight, alti, temp...) is derived from interpolation in this data.
Historically, 2nd principle was used for perfo calculations, until computers became fast enough to do a 1st principle calculation within a reasonable time.
Certified performance can be either 1st or 2nd principle.
I have no idea, however, why they are called 1st and 2nd principle.
1st principle: Performance data derived directly from a physics-based simulation of the aircraft. ("Octopus" program on airbus)
2nd principle: Performance data derived from lookup tables, diagrams, electronically stored tables etc., generally what is called "tabulated" data. Performance for one certain point (Weight, alti, temp...) is derived from interpolation in this data.
Historically, 2nd principle was used for perfo calculations, until computers became fast enough to do a 1st principle calculation within a reasonable time.
Certified performance can be either 1st or 2nd principle.
I have no idea, however, why they are called 1st and 2nd principle.
