For Microsoft Windows
I wrote AirCalc as a desktop "what if" tool. I often find myself doodling the design of a new RC plane or reading a magazine article describing the flight performance of a full-scale aircraft. To calculate wing loadings, stall speeds, etc., or to see if quoted specs are really true I use AirCalc. Sure, you could probably put all of this into an Excel spreadsheet and do the same thing, but then you would have to load the hole Excel mess up and still wouldn't have the quick interaction that you have in a small purpose built program.
AirCalc will work for all sizes of aircraft from small models to large full-scale aircraft. I have used AirCalc many times to find inconsistencies in the published data for homebuilt planes and factory aircraft. When I use AirCalc in the RC model regime I can test or design a model for wing loading and stall performance. When designing RC planes I am a big believer in "adding" lightness. Low wing loadings (under 25ozs/sqft) for smaller RC planes (60 size and below) and maybe a little more for bigger ones make for nimble performance with good low speed performance.
AirCalc selectively calculates weight, wing Area, wing loading, stall speed, or lift
coefficient from the input of the others. It is not meant to be an exhaustive answer to
these complex parameters, but more of a designers rough ‘what if’ tool. AirCalc
also is useful for quick unit conversions and mixed unit calculations. A model airplane
designer may want wing loadings in oz/sqft while a full scale designer is more interested
in lbs/sqft.
AirCalc is based on a simple equation that consolidates standard pressure and temperature.
Weight = WingArea * LiftCoefficient * Speed**2 / 391
The most ambiguous number in the equation is Lift Coefficient (Cl). Because aircraft can
vary in speed and weight from small RC models weighing 5lbs to Giant 747s weighting
700,000lbs, the Cl can vary dramatically. A good rule of thumb is that small aircraft
operating at slower speeds (lower Reynolds numbers) have a lower Cl. Don’t count on
much over 1.0 for a model airplane. As the size and speed increase Cl will increase as
well. If the airplane has flaps, slats, etc. the lift coefficient can sometimes go over
3.0. One way to get a feel for the variation of this number is to input the performance
figures for some popular known aircraft and solve for Cl. You will probably notice that Cl
will hover around 2+ for aircraft with decent flaps and 2- for those without. If you plug
in the figures for XYZ homebuilt and you calculate a Cl of 4.2 for an aircraft with plain
flaps and a small wing you can probably assume they are pushing the truth. Another check
is one of consistency. If the manufacture publishes stall speeds for different weights,
then first calculate Cl at one weight and then hold Cl constant and solve for stall speed
at the other weight. There should be good agreement with the published figures. Once you
have a good idea of Cl you can tinker around with weights to see what the different stall
speeds would be.