Q0: What is the difference between the FMX-4 and the FMX-5 Facetmobiles?
A0: The FMX-4 is our single-place prototype airplane, which has flown over 130 hours. The FMX-5 is the 2-place version we hope to build .
For more details, see the Facetmobile Web Page.
Q1: Are plans available?
A1: There are no plans for sale, and we cannot offer plans for sale in the future. There are several reasons for this. First, plans would require a lot of time and effort to draw and we are still working at our day jobs. Drawing the plans would not be worthwhile for us because in today's market, selling plans is a money-losing proposition. You can't charge very much per plan set, and many builders expect the same level of support as if they had baught a full kit. The phone bill alone is enough to more than you can charge for the plans. Second, many designers have had their designs "borrowed" by unscrupulous people, who either copy the plans for their own use, or make slight modifications and sell them as their own. Barnaby has already had this happen to him on another project. Finally, it would be too easy for people to make modifications which might lower the margins of safety we have designed in. There is a definite possibility that we will offer kits of FMX-5, if the test program convinces us that the airplane performs well, and if enough people express interest. Drop us a line if you would like to vote for a kit version of the FMX-5.
Q2: Is the Facetmobile legal to Part 103 standards?
A2: No. We considered making the FMX-4 Part 103-legal, but decided against it. Instead we opted for a design that is faster and heavier than the standards allow. A Part 103 Facetmobile is possible, but we have no plans to work in that direction. The FMX-5 is intended as a sport and cross-country airplane and not as a Part 103 machine.
Q3: Why do you use a tractor prop instead of a pusher prop or a ducted fan engine?
A3: A pusher prop would necessitate much longer landing gear, to avoid prop strikes on landing. To get the center of gravity correct, it would have required an extension shaft, which adds weight and complexity. We believe in the philosophy of "test 1 radical idea at a time". Given that vehicle shape was aready a dramatic departure from what had been done in the past, we decided to keep the rest of it as conventional as possible to minimize the number of potential problems. We also concluded early in the design of the Facetmobile that a pusher propeller configuration offered no performance advantage over a tractor. Since it was likely to be heavier and more complex than a tractor, the idea was dropped. Ducted fans do not appear to offer any performance advantage over propellers for the speed range of the Facetmobile. Although a ducted fan propulsion system would certainly add to the jet-like look of the airplane, this was not enough incentive for us to aboandon the tried-and-true propeller.
Q4: Could you use composites?
A4: It might be possible in the future to build using composite components, or covering. The current design aimed at simplicity, low cost, light weight. The skin weight is an issue, because there is so much of it. We have looked at very light honeycomb material for future covering material, but for now we're sticking with fabric covering. So far, none of our design studies have concluded that composites would be lighter or lower cost than the current metal structure with fabric covering. We will continue to look at new materials and concepts as the project progresses.
Q5: What engine will you be using for the FMX-5?
A5: The baseline engine is the Lycoming 0-235 (116horsepower). Other installations are possible with a minimum 100 hp requirement.
Q6: What is the FMX-5 schedule for completion?
A6: It will fly on Tuesday. (Which Tuesday is the question)
Q7: How much will an FMX-5 kit cost?
A7: It's really too early to start pricing the kit. We are still quite a ways from completing the prototype. Upon completion of our flight test program, we will start costing out the components and develop a total price.
Q8: Do you get flow separation over the facets?
A8: The flow over the facets stays attached. We have verified this by wind tunnel tests, where some lovely tuft photos show attached flow up to the highest angle of attack we could get in that particular facility. During early RC model work to come up with the break angles, we used a "poor man's flow visualization tool" of liquid tempra paint applied just before the model took off. The smears seen after the model landed showed us on one model that the break angle over the canopy was too large and we had some separated flow. From these experiments, wind tunnel tests, and flight tests, we have determined the maximum break angles that should be used, and have stayed well within them. If you think about an elevator's break angle relative to a horizontal tail, you would probably never think of the flow detaching, and essentially what we have in the Facetmobile geometry is similar. The performance of the airplane in flight also verifies that the flow is remaining essentially attached. The airplane could not perform as well as it does if there were significant areas of separated flow on the body.
Q9: Why didn't you paint it black?
A9: With all the window area, and no air conditioning, we considered planting geraniums in the Facetmobile. As our test pilot, Peter Lert observed, "if you painted the Facetmobile black, you could measure the appropriate flight times by waiting for a turkey timer inside the pilot's navel to pop out"
Q10: Were you inspired by Lockheed's F-117 stealth fighter?
A11: Actually, we prefer to think that they copied us. It turns out that we had already started construction of the Facetmobile when the stealth fighter configuration was announced to the public. Their facets, of course, were present to deflect radar. Our facets were for a different reason. Straight sticks are easier to build than curved sticks. As far as its stealthiness, the Facetmobile is picked up clearly on radar, due to the engine installation. However, our photographs of the wind tunnel model all turned out blurry, as the infrared auto-focus device in the camera was either deflected, or it focused on the back of the wind tunnel. As far as us copying Lockheed, Peter Lert says we did, "of course we copied Lockheed. The Facetmobile is actually a nose wheel chock for a C-5"