Flight Testing in CoD

[Viper2000]

Looking at the threads in this forum, it appears to me that a concerted and organised flight test effort will be required to work out exactly what is going on.

It isn't just a matter of posting (for example) a figure showing TAS vs altitude for a Spitfire I and then comparing it with the performance attained during a flight test in the sim.

The fact is that at the moment, we don't know what atmosphere model is used in the sim, we don't know what airframe and engine mod state is being simulated, we don't know whether the aircraft instruments read IAS, CAS or EAS, and we therefore don't know what corrections to apply. Therefore, we could have:

• Perfect simulation of the "wrong" aircraft
• Imperfect simulation of the "right" aircraft
• Non-standard ambient conditions
• Some combination of the above, across all components affecting kinematic performance

Because this simulation is considerably more complex than the original IL2, it follows that we're going to need to do an awful lot of work in order to properly understand what is going on so that we can make sensible comments to 1c. For example, the very fact that altimeters now have variable pressure settings implies that barometric pressure is a variable, and may well be a function of both geographical location and time.

I am therefore looking for volunteers to form a team to help me conduct some serious flight testing work.

Effort may usefully be divided into several strands across two departments:

History department
This half of the effort comprises the collection of historical data and its conversion into SI for comparison with data collected from the sim. Conversion work is particularly important because different flight testing organisations used different standards, and therefore it is not necessarily possible to immediately compare their data.

1. Data reduction standards (historical)
   • Atmosphere model
   • Constants & conversion factors
   • Other corrections
2. Aircraft performance data collection
   • Airframe drag estimation
   • Airframe lift estimation
   • Handling information
   • Airframe limits
   • Transonic behaviour
   • Failure modes
3. Engine performance data collection
   • Engine brake power map
   • Engine brake SFC map
   • Exhaust thrust map
   • Propeller map
   • Reliability data & failure modes
4. Conversion of the above to SI under a single set of data reduction assumptions for subsequent comparison with the simulation.

Simulation Department
This half of the effort comprises collecting data from the sim for comparison with the converted historical data collected by the History Department.

1. Atmosphere/weather testing
   • Temperature vs Altitude
   • Pressure vs Altitude
   • Density vs Altitude
   • Acceleration due to gravity
2. Aircraft & engine mod state derivation (in conjunction with history department)
3. Flight testing
   • Level speed
   • Rate of Climb
   • Turn performance
   • Cruise performance
   • Dive performance (including transonic behaviour)
   • Handling
   • Exceedances & failure modes
4. Data reduction & correction

It would obviously be extremely helpful to get authoritative information from 1c about modelling assumptions; as may be seen from the above, a substantial proportion of the effort envisaged at present is associated with deriving those assumptions rather than with testing the aeroplanes themselves.

N.B. The intention of this thread is to assemble a test team and discuss flight test methods & standards, not to get into a flamewar about the performance of aircraft A vs aircraft B.

[Stealth_Eagle]

I'll join the team if needed but I am in North America so I have to wait some.

[Sven]

Big thumbs up for this plan!

[Viper2000]

Originally Posted by Stealth_Eagle

I'll join the team if needed but I am in North America so I have to wait some.

Given the scale of the effort likely to be required it's pretty unlikely that you'll miss the party!

[Stealth_Eagle]

Originally Posted by Viper2000

Given the scale of the effort likely to be required it's pretty unlikely that you'll miss the party!

I personally want to test bombers and the G. 50. In IL-2 online play, I can dominate late war fighters with it so I'll put that in my comparison. However I don't have TrackIR since it is too expensive.

[Viper2000]

Perhaps it would be a good idea for those people who are interested in this work but cannot yet access the sim to concentrate on collecting historical data?

In order to avoid possible accusations of bias, I suggest that we work exclusively from verifiable historical documents (which may be translated to *.pdf or *.jpeg files for transmission, provided that it's obvious that they are derived from original sources).

At this stage, I would like to point out that a lot of the historical work is going to come down to interpretation, especially as regards handling. Unfortunately, interpretation is emotive.

My intention is to try to keep this thread objective. Past experience strongly suggest to me that this will be almost impossible if we discuss individual aircraft types, because there will always be partisans both "for" and "against" any given type's performance characteristics*.

Therefore, I suggest that we split our work as follows:

1. This thread should be the "general purpose" flight testing thread
2. Individual aircraft types should each have 3 threads:
   • An historical thread, detailing reference material
   • A flight test thread detailing what the simulation does
   • A comparison thread detailing what (if anything) we think needs to be changed

This arrangement should act as a sort of fire-break, such that we only get flamewars in a relatively small percentage of our threads.

I hope that in the fullness of time we might get our own sub-forum, possibly with limited posting rights in order to reduce the risk of trolling; naturally any such hope does not constitute an expectation.

*I've never really understood this; if you think that "your" airforce's aeroplanes were "better" then you're naturally implying that its pilots were "worse" and vice versa, since the historical record is essentially fixed...

[Kianoni]

Originally Posted by Viper2000

...

The fact is that at the moment, we don't know what atmosphere model is used in the sim, we don't know what airframe and engine mod state is being simulated, we don't know whether the aircraft instruments read IAS, CAS or EAS, and we therefore don't know what corrections to apply.
...

well, this is one of the features that should be looked into in the future. would be nice to get viable information about the planes/weather.

[JG14_Jagr]

You really need to determine what resources you will have to actually measure the data.. using the GUI is not a good idea. Also, certain maps often create issues.. standardize the testng on a particular map..maybe one of the simple online maps...

[Viper2000]

I think that the first thing we need to do is to try to find standard day conditions.

There are quite a lot of possibilities available.

One option would be to use a relatively modern standard like the ISO standard atmosphere or the 1976 US standard atmosphere. This would facilitate compatibility with modern data. However, the ISO standard atmosphere is not directly available for free.

Alternatively, we could attempt to use older NACA standards; doing so would lend an historical flavour to our work, but might complicate comparison with more modern sources. A few possible standards may be found by following the links below. This list is not exhaustive.

1926 NACA standard
1930 simplification
1952 NACA/ICAO standard
1976 US Standard Atmosphere

I suggest that we use the 1976 standard for comparison purposes because this allows us to avoid some otherwise potentially nasty conversions (eg changes to Temperature scales over time...).

Obviously the next thing that we need to do is to find some way of measuring the atmosphere properties on a variety of available maps so that we can pick the best one for testing.

Does anybody have any suggestions as to how we might best go about this?

[TUCKIE_JG52]

Viper, that's a really nice effort, seriously focused... some time ago I was discussing in other forums about real charts of the planes, that were not corrected to the same atmosfere models...

I fly a Cessna 152 and from my early stages of training, I can see the big influence that ambient contitions have in performances like climb rate.

As ambient conditions I mean specially pressure and temperature. For example, before each takeoff I check the forecast for exact data and I get the exact calculation for the Pressure Altitude. If the pressure altitude of my airfield is below the real altitude of the field, that day the Cessna climbs a lot. It's the most common case in winter, with temperatures below ISA (15º) and sometimes pressures over ISA (1013Mb).

The inverse case is a higher pressure altitude when ambient is very hot and low pressures are registered... to the point that if pressure altitude is a lot higher than real altitude of the airfield, it can be a factor that can lead to an accident.

I see that your initial point of view takes this into account, so I'll follow your results with very interest.

I would collaborate with you if I were not so busy with video editing...