Performance
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Performance
Please excuse me if this question has been asked before but -
How much allowance is given in the flight manual performance figures for "fudge factors" By that I mean the average pilot (me) flying a machine that maybe getting on in years and hours and the surprise factor when something goes cough splutter?
It is my understanding that 99% of aircraft testing is carried out in brand new machine with a graduate test pilot operating to a clearly defined plan. Are the profiles and charts the very best I can expect and should I apply my own "fudge factor"?
How much allowance is given in the flight manual performance figures for "fudge factors" By that I mean the average pilot (me) flying a machine that maybe getting on in years and hours and the surprise factor when something goes cough splutter?
It is my understanding that 99% of aircraft testing is carried out in brand new machine with a graduate test pilot operating to a clearly defined plan. Are the profiles and charts the very best I can expect and should I apply my own "fudge factor"?
I'm generalising here, for the simple reason that I'm a light fixed wing bod, and I'm sure somebody much more knowledgeable than I about rotaries can answer with specifics on helicopter performance (or airline ops for that matter, but your profile says that you are a helicopter pilot).
In general, the performance in the operators manual is the best available (by which I mean most accurate, not most impressive), produced by a company TP, but flying as near as possible to exactly the flight profile (speeds / heights / handling techniques) shown in the operators manual. This generally does not include any safety factors.
There are generally safety factors available, which are intended to account for variability in handling technique, through-life degredation in engine performance, through-life increase in profile drag (dents, surface finish, etc.) and so on. The should be included in any particular operating manual, company SOP, or in national information - the UK CAA have various AICs for example that are either advisory or mandatory depending upon type of flight. For fixed wing ops, these are primarily related to take-off and landing distances, but other factors do exist.
The precise nature of the factors will vary depending upon the nature of operation. For example, light GA ops do not generally include (in the UK anyhow) proverse factors in determining field performance, whilst heavy ops do, there's also a 1.3 safety factor on TODR which is mandatory for public transport ops, but only discretionary for non PT ops.
G
In general, the performance in the operators manual is the best available (by which I mean most accurate, not most impressive), produced by a company TP, but flying as near as possible to exactly the flight profile (speeds / heights / handling techniques) shown in the operators manual. This generally does not include any safety factors.
There are generally safety factors available, which are intended to account for variability in handling technique, through-life degredation in engine performance, through-life increase in profile drag (dents, surface finish, etc.) and so on. The should be included in any particular operating manual, company SOP, or in national information - the UK CAA have various AICs for example that are either advisory or mandatory depending upon type of flight. For fixed wing ops, these are primarily related to take-off and landing distances, but other factors do exist.
The precise nature of the factors will vary depending upon the nature of operation. For example, light GA ops do not generally include (in the UK anyhow) proverse factors in determining field performance, whilst heavy ops do, there's also a 1.3 safety factor on TODR which is mandatory for public transport ops, but only discretionary for non PT ops.
G
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Some comments on performance. From your 'handle' (semirigid rotor), I'll assume you're talking about helicopter perf.
There are two parts to this for turbine engine machines in the civil world- the first part is the engine power available, which is in the flight manual to make sure the engine is putting out at least minimum specified power.
The second part is less than clear, as it doesn't tell you (in most light helicopters) about power required to hover. In most civil manuals, it comes out as hover capability.
Yes this would be done with things like clean blades, and absolutely properly set torquemeters and the like.
In service, there should be some way to make sure that you do meet the performance thats in the flight manual - the UK CAA is pretty good about doing this. Other authorities are different.
If you're not getting the performance that the flight manual says you should be getting, and you're absolutely sure you've got everything covered from a maintenance point of view, then I'd think about contacting your airworthiness authority. Maybe submit a Service difficulty report (SDR), or write to them with the specifics. Enough reports ought to alert someone in the authority to check it out.
The certifying authority signs up to making sure the hover performance is correct, so if it's not, they should know about it.
There are two parts to this for turbine engine machines in the civil world- the first part is the engine power available, which is in the flight manual to make sure the engine is putting out at least minimum specified power.
The second part is less than clear, as it doesn't tell you (in most light helicopters) about power required to hover. In most civil manuals, it comes out as hover capability.
Yes this would be done with things like clean blades, and absolutely properly set torquemeters and the like.
In service, there should be some way to make sure that you do meet the performance thats in the flight manual - the UK CAA is pretty good about doing this. Other authorities are different.
If you're not getting the performance that the flight manual says you should be getting, and you're absolutely sure you've got everything covered from a maintenance point of view, then I'd think about contacting your airworthiness authority. Maybe submit a Service difficulty report (SDR), or write to them with the specifics. Enough reports ought to alert someone in the authority to check it out.
The certifying authority signs up to making sure the hover performance is correct, so if it's not, they should know about it.
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Apologies for taking time to reply, computer problems
Shawn, some of the performance figures can be checked on a regular basis, ie. single engine rate of climb (CAA air test), engine performance figures, but some are a bit more "intangible"
For example, rejected take off distance, these involve pilot performance as well as aircraft performance. When I flew in the US, various pilots who were far more experienced than me repeatedly told me - the flight manual figures are the very best you can expect, always add your own safety factor depending on individual circumstances. I have always flown with that in mind, so far without mishap
But am I adding safety factor on top of safety factor?
Shawn, some of the performance figures can be checked on a regular basis, ie. single engine rate of climb (CAA air test), engine performance figures, but some are a bit more "intangible"
For example, rejected take off distance, these involve pilot performance as well as aircraft performance. When I flew in the US, various pilots who were far more experienced than me repeatedly told me - the flight manual figures are the very best you can expect, always add your own safety factor depending on individual circumstances. I have always flown with that in mind, so far without mishap
But am I adding safety factor on top of safety factor?
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sorry for the delay in this reply.
The performance figures in the flight manual are based on not requiring favorable conditions, or exceptional pilot alertness or skill.
For takeoff and landing stuff, there is testing done to ensure that 5 knots faster or slower, or maybe 10 feet higher or lower don't have negative effects. And they are tested by other than the factory pilots.
They certainly do not include the use of any transients in limitations of the engine or transmission.
So you may be adding a safety factor on top of a safety factor- but is that a bad thing?
The performance figures in the flight manual are based on not requiring favorable conditions, or exceptional pilot alertness or skill.
For takeoff and landing stuff, there is testing done to ensure that 5 knots faster or slower, or maybe 10 feet higher or lower don't have negative effects. And they are tested by other than the factory pilots.
They certainly do not include the use of any transients in limitations of the engine or transmission.
So you may be adding a safety factor on top of a safety factor- but is that a bad thing?
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Performance
During flight testing, the aircraft's engine(s) power is calculated. However, this power is usually not used for FM calculations, instead a lower power level is assumed (for example a "minimum" engine), corresponding to the least powerful NEW engine that may be accepted be the aircraft manufacturer. The ratio between these levels is something of an educated guess, but usually one ends up with the right numbers (no guarantee, however). This adds some safety margin as well.
Engine degradation due to flight hours is usually not taken into account, AFAIK. But manufacturers may be able to provide you with the numbers to expect.
Engine degradation due to flight hours is usually not taken into account, AFAIK. But manufacturers may be able to provide you with the numbers to expect.
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Sirius:
The engine power available is based on a minimum specfication engine - the power that the engine should always be capable of producing, even 1 minute before reaching TBO.
In flight testing, the airframe manufacturer will know this value from the engine 'deck' provided by the engine manufacturer, corrected for any installation losses due to the airframe. Since the engine provided is probably above this specification, a way to correct the data is made.
For some Digital Fuel Control engines, this is a simple process of adjusting the maximum power via the flight test computer to that which would be provided by the spec engine. For hydro-mechanical fuel controls, things are a bit more complicated...
It's not a 'new' engine that is used, but the minimum specification one.
The engine power available is based on a minimum specfication engine - the power that the engine should always be capable of producing, even 1 minute before reaching TBO.
In flight testing, the airframe manufacturer will know this value from the engine 'deck' provided by the engine manufacturer, corrected for any installation losses due to the airframe. Since the engine provided is probably above this specification, a way to correct the data is made.
For some Digital Fuel Control engines, this is a simple process of adjusting the maximum power via the flight test computer to that which would be provided by the spec engine. For hydro-mechanical fuel controls, things are a bit more complicated...
It's not a 'new' engine that is used, but the minimum specification one.
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SC. Thanks for the explanation, 5000Hrs on, I will just keep on doing what I have always done - add my own safety factor depending on circumstances, it's worked well so far. Because one thing you do not test for, and that is when the pilot is just having a bad day
