Flight Data System's Air-Data Fuel Performance Computer
In a quest to bring some glass-cockpit technology to their homebuilt, a couple of guys created an air-data computer with a very simple interface, small size, and low price, but with all the necessary features. Mike Corder, like many pilots they met, wanted one for himself and brings us this review.
A guy named Chuck flies 757s for a major airline, and builds and flies an RV-8. Flying the RV-8 is quite different from his day job: The 757 has a glass cockpit, side-by-side seating, and trainer wheel up front, and is designed for straight-and-level flight; RV-8 has steam gauges, fore and aft seating, is great for aerobatics, and the third wheel is at the rear. Problem is, the 757 had corrupted his mind; it doesn't take very long before he comes to a realization: "I need more information." Now if this were a normal story, Chuck would have taken some of his airplane-driver salary and bought some new toys for his panel. But Chuck had a deep, dark secret in his past that he seldom, if ever, mentioned to anyone: Before he became a pilot, he had been a computer programmer. And Chuck had a friend named Richard, who was a computer hardware designer.
So, not surprisingly, they quickly came up with the bright idea that it would be fun to build their own box to give Chuck just the information he wanted. Keep it simple, make it fit in the radio stack so it wouldn't require tearing into the dash ... piece of cake. Richard created the hardware and figured out how it would interact with the GPS, real-world sensors, etc., and Chuck created the software that would massage all the data and present it to the pilot.
Before long, other pilots see the box, like it because they've never seen anything quite like it, and want to buy one. And that's how Flight Data Systems of Aptos, Calif., came into being. Sometimes a good idea just wants to become a product and ends up spawning a complete company. Their new product is called the AFP-30. It's designed strictly for experimental aircraft and is an interesting combination of three devices:
- Air data computer
- Fuel flow computer
- Performance measuring computer
The product has been refined to the point where all the data is presented on a two-line LCD display -- which takes up minimal stack space -- and the only user-control device is a single knob with a built-in "press to select" push button. Whenever you see a data item with an asterisk next to it, you can change that data. Just push the knob to enter data-entry mode, rotate it until the correct number appears, and then push the knob again to exit data-entry mode. This is very easy to do, and the unit tries to help you by getting you close to the correct number automatically.
Since most of us are familiar with a fuel flow computer, it's easiest to start with a description of that functionality. In total, the unit can provide instantaneous fuel flow, total fuel used, fuel remaining, miles per gallon, range (miles till empty), endurance (time till empty) and arrival fuel (fuel remaining at next GPS waypoint). The user interface on the AFP-30 is very simple and consistent. Each screen lists up to four data values. To switch to the next screen, just rotate the knob left or right in the normal manner. The unit also has provision for a stick-mounted switch to advance pages.
This screen shows the basic fuel flow page. Shown are instantaneous fuel flow in gallons per hour, fuel used since the system has been powered up, endurance in hours and minutes based on current fuel flow and fuel remaining. This last figure is quite interesting. When you initially set up your unit, you indicate what your total fuel capacity is. Each time you refuel, you merely have to power up, press the knob and start twisting it to the right. It will automatically stop at the maximum. But what if you forget and don't reinitialize the unit until you've gotten up to altitude and leveled out ? No sweat. Just start twisting the knob until the indicator reaches maximum. The unit will then automatically recognize that you are a doofus and subtract the fuel that has been used since the last power-up. Pretty neat, eh?
The secondary fuel page shows fuel efficiency in miles per gallon (nautical or statute), range till empty and the amount of fuel that will be remaining at the next GPS waypoint.
Air Data Computer
The air data computer mode has three separate screens showing altitude, speed, temperature and wind data.
The altitude screen shows indicated altitude in feet, current barometric pressure in inches of mercury, pressure altitude and density altitude in feet. When you power the unit up, you naturally have to enter the local barometric pressure. The unit automatically starts at this page to make sure you do enter the correct pressure. When you go into data-entry mode, the unit automatically starts at 29.92 to make your data entry easy. Just entry the correct barometric pressure and then take a quick look at density altitude to see what your performance will be.
The speed screen shows Indicated Airspeed (knots or MPH), True Airspeed, Outside Air Temperature (Celsius or Fahrenheit) and Total Air Temperature, which is OAT plus the temperature rise due to air impact effects. (I told you he was an airline pilot!)
The wind page is a real winner and has lots of good information. The pilot must enter the current heading to allow the computer to do its stuff. When you enter data-entry mode for heading, the unit will automatically start at the current track based on the logical assumption that your heading isn't too far off the track. Just rotate the knob left or right until the correct heading is shown and then press the knob once to get out of heading entry mode. You will then see the correct headwind or tailwind component, the current wind direction and speed, and the crosswind component. All are in either knots or MPH.
This mode only has one page but it is very useful. When you order your unit, you specify your engine. The folks at FDS have translated those performance equations in your Pilot's Operating Handbook into equations that permanently reside in your unit and use that to generate the data on this page. This plus the relevant sensors allow you to display manifold pressure, RPM and percent horsepower. The last is quite unique and I think pilots will find it of great use once they get used to having it available.
But Wait, There's More
There is also one completely custom page that can hold up to four items. You can make this display anything you want from the possible data items shown on other pages.
As shown in this diagram, the AFP-30 requires the builder to provide connections to the static system, the pitot system, manifold pressure, the magneto P-lead or electronic ignition, the OAT sensor, fuel-flow sensor and the GPS; both panel-mount and handheld units are supported. The unit comes in a pretty complete package. Included are the display unit, a FloScan aircraft fuel flow transducer, an OAT probe, wiring harness and connectors, installation and operation manual and a one-year unconditional warranty.
Volume production has begun and the unit is offered at an introductory price of $799. Even though the design has been subjected to a pretty thorough shakedown, the company is interested in getting the first few units into the hands of active experimental pilots who will provide them with feedback, and they are giving these initial customers a good price as a way of encouraging owner feedback. In addition, the company is working on a round model for people who don't have room in their radio stack or just prefer that format. It will be available in the near future. Check with the company for details.
You probably won't be surprised to learn that the majority of the first units have gone to airline pilots!