Hi
I think it is a problem that cruise profiles are based on IAS instead of TAS. No propeller airplane can maintain the same IAS when altitude increases, and most POHs show TAS in their performance tables, not IAS.

Consider a standard profile which gives 100 kt at sea level. At most aircraft, the aircraft is still able to maintain 100 kt TAS at FL100, but when skydemon calculates TAS, 100 kt IAS will give about 116 kt TAS, which is not realistic for prop aircraft.

Consider changing this to TAS or let users choose between IAS or TAS when creating profiles.

Regards
Karsten

This is something we hear a request for from time to time, and will almost certainly happen.

It's a bit more complex because of turbos and turboprops, wouldn't the ideal thing be to have level-dependent performance (including fuel consumption), based on TAS as per the POHs? It will also make it very easy to pick up an optimal altitude given forecast winds.

We're gradually enhancing our flight modelling engine so that this can be supported, in fact we're nearly there. It remains to be seen how we're able to expose the functionality in the user interface, though. We want to keep the aircraft configuration stuff simple and unintimidating for those that don't have complex or powerful aircraft, but to be able to offer the powerful calculations for those that do.

Assuming we were to implement level-dependent configuration based on TAS, how would you envisage the user interface working to select the cruise configuration? Would you still want to select a given power level and have the software work out what TAS you could achieve at the selected level?

I think it could work like the climb performance. For each cruise profile (75% or 55% power for example) you enter the TAS and fuel consumption at ground level, and do the same at service ceiling; to keep things simple you could have that default at the ground values (wich won't be far from the truth for non turbos, which is why it's probably better to do this in TAS rather than IAS). Linear interp in between. It would be really useful for complex/ high performance aircrafts to be able to insert perf figures at additional levels, as many aircrafts start to see a loss of perfomance at a certain level.

It won't be more complicated than entering weight&balance stats I think, and by having a default for people who don't care about this it should keep things user friendly. The one issue is what can appear as the inconsistency of indicating IAS for climb and descent, but TAS for cruise; but this is what you have in POHs.

When creating a PLOG for such a route, should SkyDemon continue to have an IAS column or would this then become meaningless? It could be changed to TAS, for example, or could give the power setting.

That's a good question - traditional PLOGs have TAS, but maybe it' more useful to see the IAS so you can compare that to your instrument reading in-flight and evaluate how different the wind is from forecast. If I'm not mistaken just reading between the lines, Timothy Nathan's been doing some specifying for a project of yours, it may be worth asking him that question.

There are good arguments going both ways. I believe we're at the point where a "one size fits all" format of the PLOG actually won't do the job. Therefore I propose a setup option that allows me to choose which columns I want displayed on the PLOG.

Regarding cruise profiles in the aircraft model: I second the option of entering lines of data (altitude, rate of climb, IAS, fuel flow) for each altitude and power setting used. A simple aircraft only really needs one entry whereas a complex aircraft can use as many as required.

-- Chris.

Hello - just to confirm, being able to chose TAS or IAS in the profiles is great, and the fact that the plot adapts to that automatically is fantastic. Do you think we'll be able to see these improvements on the web version too? Thank you...