Saturday, August 08, 2009

Winds Aloft with PFMA

Internet search engines have quickly become something few of us can live without and it's because of an internet search that the developer of PFMA (an iPhone aviation calculator) contacted me. PFMA stands for Pocket Flight Management Assistant and after a test-drive, I found it to be a useful tool with a nice balance between simplicity and frequently-used features. Plus it has a user interface that resembles a Flight Management System - how cool is that?

One thing I've found missing from many iPhone E6B apps is the ability to calculate winds aloft, so that was the first thing I attempted with PFMA. I just located and tapped on the WIND item and just started entering the stuff one usually knows when trying to calculate winds aloft in flight - ground speed, true airspeed, heading and course (or track). You enter data into each of the fields by first typing in the value using the keypad (you'll see the value appear in the lower left side of the display) and then pressing the field you want to fill with that value. There's currently no user's guide (one should be available soon), but I was able to figure out how to calculate winds aloft in under 20 seconds. I find this to be a pretty good indicator of just how easy-to-use an interface is. PFMA passed my initial test with flying colors. (N.B.: Most of the enhancements I suggest in this post have been favorably received by the developer and should be addressed in an upcoming version.) You can use the WIND screen to determine landing crosswind components, too.

There's also an ALTITUDE-AIRSPEED screen that has the same simple design philosophy - fill in the fields you know and PFMA will calculate the fields you don't know. This prevents having a plethora of appropriately-name menu items for each function and really contributes to the ease-of-use. One design enhancement would be to have PFMA remember any field that was calculated in a previous screen and populate that field by default whenever it occurs in another screen. For example, if the ALTITUDE-AIRSPEED screen were used to calculate true airspeed, it would be cool to have that calculated value automatically appear by default in the WIND screen.

In the meantime, you can do a sort of cut-n-paste operation by tapping on a field displaying a value, which copies the value to the input field in the lower left side of the screen. Next, select the function screen where you want to enter that data and tap on the appropriate field - this will copy the value for, say, ground speed on one screen into the ground speed field on the next screen.

There's a dirt-simple SETUP screen that allows you to specify the units you plan to use most often for distance, altitude, speed, temperature weight, and volume.

The NAVIGATION screen is provided mostly for completeness, but I didn't find it terribly useful (maybe that's just me). Here I've entered the Origin Lat/Long for KAVL (Asheville, North Carolina) as N35:26.1/W82:32.5 and the Dest Lat/Long for KTRI (Tri-Cities Regional in Tennessee) as N36:28.5/W82:24.4. You can then solve either for time or for ground speed by supplying the appropriate field. PFMA will calculate the other field, providing the distance and bearing. I'm not a big fan of entering Lat/Long, but it works.

The FUEL screen is equally simple, allowing you to enter any two fields to obtain a solution for the third field. While the FUEL FLOW and FUEL QTY both indicate Gallons (since I selected that in the SETUP screen), you can really enter a value representing any volume or weight in your desired units and calculate the desired answer. In this example I entered a common Caravan fuel flow of 310 pounds/hour and a total fuel on board of 1300 pounds to obtain an endurance of just under four hours.

The CONVERSION screen lets you convert common values and has a nice, logical grouping. DISTANCE lets you convert a distance or speed from one unit to another. METEOROLOGICAL lets you convert barometric pressure to different values (this would have come in handy when I was flying in the Caribbean last summer) and Fahrenheit to Celcius. In the WEIGHT screen shown below, I've entered 600 pounds to determine the equivalent value in kilograms.

The VOLUME screen lets you convert a volume of your choosing into a weight (using a fuel density constant), but it's curious that the only weight you can solve for is KILOGRAMS. It would be nice if this screen defaulted to the weight unit you selected in the UNITS screen or, better yet, if pounds were just shown as another possible value along side kilograms.

In my example I've copied 272 kilograms (or 600 pounds) of Jet-A required from the WEIGHT screen to obtain a volume of 89 gallons since the guys and gals who do fueling usually dispense in gallons, not pounds. Of course you can calculate this conversion pretty easily in your head by dividing the desired weight of fuel in pounds by 10 and then multiply the result by 1.5 to get the approximate number of US gallons, but there can be times (say at the end of a very long duty day) when mental math becomes error prone and it's nice to have a way to verify your results.

The TIMER screen contains separate timers for block and air time as well as three elapsed timers for whatever use you might want. One suggestion here is a simple count-down timer: Let's say you enter a time value for one of the elapse timers and that would make it countdown rather than up and would also provide an vibrating alarm. Another idea would be a counter one could tap to count touch-and-go landings, but that's more of a gee whiz sort of feature.

In a nutshell, PFMA is a nice aviation calculator that works well and is easy to use. If you are new to aviation and need a product that will lead you by the hand with explicitly-named functions and features, then PFMA might not be for you. For experienced aviators who want a fast and simple-to-use app, PFMA is a good choice. And in a world of $400/year database subscriptions, US$4.00 for a full-featured calculator looks like a pretty good value to me.

1 comment:

Geoff said...

You might find this useful for using an iPhone in the cockpit: I just ordered one, so I can't tell you how well it works, but it looks like it'd work well.