As my spare time is tending to zero (I’m typing with my sleepy 9 days old co-pilot in my arms now 🙂 ), I wanted to share another update of my MCD Generator. Originally the plan was including a Fuel consumption model to the MDC but I managed to finish only the calculation of GS (Ground Speed), TAS (True Air Speed) and Mach; necessary to obtain a close approximation of the time required to travel between each leg of the flightplan. Until this version, in fact, the ETA was calculated by means of a generic “Speed” value.
The speed reading usually used in-cockpit is the IAS, or Indicated Air Speed, but such number is not really applicable to ETA calculations: what we need is the Ground Speed. The problem is, as usual, that I wasn’t familiar at all with all these concepts and values and it took me a few days to create an IAS→GS/TAS/Mach model.
This is a very lengthy topic so, long story short, to get the TAS from IAS I used a JS algorithm I found online a while ago (unfortunately I didn’t save the source). I used a simplified NASA model (applicable for altitude < 36000) for the atmospheric temperature then Pythagoras to consider the Δ altitude between waypoints and again Pythagoras and trigonometry to add the wind. Unfortunately, not having access to DCS' actual implementation, I can only try to adjust different models and see which one gets closer to the in-game values.
I did some tests with the current model in the MDC and it's very close for default conditions (no wind, 29.92 QNH, 20°C). Unfortunately I do not have time to test specific conditions. If you want to tinker and play with my formulas go for it, if you find issues or solve bugs please let me know (NOTE: you can find different calculations and attempts in the hidden columns).
Keep in mind that ED is overhauling the weather system soon™, so I do not want to waste time on this matter at the moment.
Besides the Speed calculations, the biggest change is the Payload that now has a dedicated tab. The bottom part of such page is a placeholder for the future Fuel calculations: at the moment I plan to create a set of profiles based on in-game consumption and assign them to each leg to simulate a definite condition. Later on, the fuel consumption will be automatically approximated depending on the speed set in the Planner.
Another new feature is a more intuitive function to assign the payload to each station. It also shows the Weight of each ordnance and its Drag Index. I am still working on the DI: different sources freely googleable show different values. Ultimately my aim is to test payloads of similar Weight and different DI and viceversa and see the effect on the fuel consumption. I’m looking forward to doing these tests but unfortunately my time is now fully sucked by my co-pilot (on the other hand, I’m becoming a pro with the nappies 😀 ).
The Speed calculations in the Planner now calculate and show GS, TAS and Mach as functions of the IAS. Later on, I plan to add make the whole table dynamic so that other values can be used instead of the IAS.
The MDC page generated is much more complex now. There are a number of reasons for that. In primis the Airspeed Indicator shows an incorrect IAS depending on the altitude. At the same time, the Mach reading is quite accurate. If a more accurate speed value in needed, the ECMD shows the TAS and the GS so it was worth adding them to the MDC.
The new page also shows the ETA for each leg and the mission time, allowing a finer coordination with other assets. The latter also takes into account the time slots allocated for tasks such as CAP, AAR and so on.
This plethora of new information forced to me add a third page.
As already mentioned the bottom part of the page will be used by the Fuel model once it’s available so feel free to get rid of it in your copy of the MDC.
Fuel Consumption Model
The first results of the model (5000ft to 25000ft) are present in the Payload page in the form of an IAS vs Fuel Flow chart (the Flow value is for a single engine!) for an ordnance configuration close to a standard CAP mission (4xAIM-54, 2xAIM-7, 2xAIM-9, Fuel Tanks and Gun).
Intuitively, the lower the fuel flow, the more endurance the aircraft has. There are a couple surprises in the results, I will go into such details as soon as I find time to complete the Fuel model.