+x

Pete - 10/14/2017 11:34:04 AM

" I find it strange that you have defined your cruise performance in terms of a power setting and a TAS.  A given power setting will produce a giver Indicated Airspeed, but the TAS will vary with atmospheric conditions."

H‌ave to disagree on this, a given power setting tends to give a constant TAS at any altitude(that we fly) , however the IAS decreases with altitude for a given power setting‌. This is supported by my POH, hence I use TAS with my power settings in SD

Which DA40 have you got?! I fly both the petrol -180 and the turbo-diesel -NG, and both show that TAS increases as altitude and/or temperature increases.

Thanks everyone for the useful replies.

I am hoping to get skydemon to a‌t least nearly replicate what i get with my wizz wheel. I do appreciate that TAS varies slightly with temp and altitude, but notwithstanding that i am getting very odd things on my skydemon plog.

C‌heck this image out for example (i screenshot it when planning a flight this morning). The first and final legs are flown in pretty much exactly the same place, at the same altitude, less than 20 mins apart. Yet Skydemon says the TAS on the first leg is 101, and on the second leg is 113.  Presumably the reason for this is that skydemon is adding in some kind of correction because it thinks im taking off from Brighton marina. But in fact im taking off at shoreham and flying to brighton marina where i start my nav.

W‌hat would be really useful would be if i could just override all of skydemons cleverness and tell it what TAS i want to use for the leg, or even better the entire flight.

‌‌

+x

macs86 - 10/17/2017 1:21:37 PM

Thanks everyone for the useful replies.

I am hoping to get skydemon to a‌t least nearly replicate what i get with my wizz wheel. I do appreciate that TAS varies slightly with temp and altitude, but notwithstanding that i am getting very odd things on my skydemon plog.

C‌heck this image out for example (i screenshot it when planning a flight this morning). The first and final legs are flown in pretty much exactly the same place, at the same altitude, less than 20 mins apart. Yet Skydemon says the TAS on the first leg is 101, and on the second leg is 113.  Presumably the reason for this is that skydemon is adding in some kind of correction because it thinks im taking off from Brighton marina. But in fact im taking off at shoreham and flying to brighton marina where i start my nav.

W‌hat would be really useful would be if i could just override all of skydemons cleverness and tell it what TAS i want to use for the leg, or even better the entire flight.

‌‌

I suspect the climb and descent phases are exactly what is causing that difference since the other two legs are showing exactly 120ktas. 

I‌‌ am intrigued as to why you would want to "turn off" the features that Tim and the team have worked on so hard which make the SkyDemon PLog the most accurate paper PLog I have ever flown with. I can even use heading hold mode on the auto-pilot (rather than programming the route into the aircraft GPS) and fly the plan perfectly in "my" DA40. In fact, I prefer to do it that way as the built-in GPS flies a great circle route rather than a rhumb line and thus deviates from the SkyDemon line by a mile or so on long legs.