hi mike,
believe me i do agree with you this is why i have been trying to figure out how to find the DA on the whizz wheel (which i think i found out last night at work)
the bob tait book said "for light aircraft, CAS and IAS can be concidered the same."
but when you do the math in the book (one of the practical examples, airspeed modified for slower u/light speed)
cruise altitude of 5000 ft (pressure altitude) , OAT +22, CAS 55 kts , which is CAS of 55 kts and TAS of 56.5 kts,
1.5 kts over 80 Nm is.... well 55 kts CAS over 80 Nm is 87 mins
56.5 kts over 80 Nm is 85 mins,
so you will plan an 87 minute trip and you will be looking for an airfield which is actually 2 minutes in front of you, actually i will re phrase that you will overshoot the waypoint by 2 minutes..... and be looking for a waypoint 2 minutes behind you...
but if you where in a faster aircraft like a jabiru you will be a few more minutes off course..
now, my next question to get off my chest is, when you are doing pre flight and you set your alt to 1013 qnh which is about 1430 ft AMSL at ballarat, is this the pressure height ? if so am i correct in saying that when you make these calculations you use the Pressure altitude displayed on your altimeter ? IE: circuit height at ballarat is 2430 Ft which is also the Pressure height ?
does pressure altitude ever change ? like one day it will be 1013 QNH and tomorrow it will be 1020 ?
can i set my altimeter to the QNH for a x country flight and have the correct height for all airfields i will visit ? for arguments sake from ballarat to narromine ?
ah too manny more questions but need to understand these first.