When initial fuel estimations change enroute (headwinds, whatever) we sometime find ourselves doing on-the-fly in-the-head calculations of reasonable range remaining, including , for ecample "how much more range will I have if I slow down from 110 knot to 70 knots?"
Yeah I know the fuel per hour for my aircraft at 110 knot and 70 knots and can do that part pretty well and the basic rule is the slower the more hours of fuel I have. What complicates it is with different headwinds there's a point where slowing down has diminishing or even negative results in how many more miles of fuel I have.
Here's where iFly could be very helpful. It always knows my ground speed. It also knows what I've told it about my gallons per hour at my stated standard cruise speed. So if I stayed at my standard cruise speed it could at any moment read out my miles per gallon (and it's miles, not hours, that I need to know in deciding if I need to deviate for an extra fuel stop.)
So even without any other user aircraft performance factors input that we already give it, it should be simple to have from instantanious (or five minute sample) an optional instrument readout of my current miles per gallon (assuming I stay at standard cruise. Now, although that doesn't fully deal with the issue I raised about "how much would my range increase if I reduced speed 40 knots" it is giving me a dynamic readout of what the headwind is doing to my range. And can immeadiatly show me that when I climbed up 3000 feet and got into higher headwinds just now it's just cost me bigtime knocking my miles per gallon significantly down.
So the simplest item of my wish list would be this optional instrument that just reports miles per gallon dynamically based only on the stated cruise gallons per hour and, say, the last three minutes of ground speed. Should be very easy to implement.
A more slightly more sophisticated version would require that into iFly's aircraft performance screens I enter three different cruise true air speed estimated (call them "high" "medium" and "low" ... or better yet user entered as, for example "120", "100", "70". In that case this optional instrument would at any given moment have a dynamic changing readout something like this:
120->20mpg
100->25mpg
70-> 35mpg
This would allow me to instantly get a pretty decent read on whether the 12 gallons I can reasonably trust being reported on my fuel gauges would give me decent margin to my prefered landing, and if it would be worth slowing down to 70 for more safety factor.
Alex