Why Does It Look That Way?            General Specifications               Performance            The future Airplane

But Why Does it Look That Way?

Take another look at the aircraft.  Why does it look the way it does?  Well, the resulting shape is directly driven by the various Design Goals.  The Phoenix geometry is the integrated aircraft layout that provides an opportunity to meet all the stringent major Design Goals related to (1) performance, (2) handling qualities, (3) room, (4) cockpit noise, (5) visibility and (6) ease of entry and exit.  The process of integrating the shape to meet all these goals was complex, indeed, but let’s see if we can give you at least an abbreviated feel for why it looks the way it does.

Look, all the other Design Goals aside, performance is a big factor; “speed sells”, as the old saying goes.  And, as a matter of fact, so does good looks.  So, how to get a significant improvement in performance while, at the same time maintaining good looks while at the same time meeting the other Design Goals.  That’s the question that had to be answered.  It’s accurate to say that, from the very beginning, the approach that we took was to go to the “Pusher” configuration (we did look at the tractor but only briefly). Why?  Because, from a performance standpoint, airframe drag is obviously an important factor and one way to reduce drag is to get the fuselage out of the propeller slipstream.  Moving the propeller to the rear of the aircraft not only reduces skin friction drag by removing the fuselage from the propeller slipstream, it also permits the forward section of the fuselage to be shaped so as to maintain laminar flow for a significant distance back from the nose, even further reducing drag (performance Design Goal) and it also permits the fuselage to be shaped so as to maximize cockpit room (room Design Goal) while maintaining fuselage esthetics.  Combine this with current technology Natural Laminar Flow airfoil sections and minimize interference drag (additional drag that occurs where surfaces intersect each other) and you’ve got a good shot at a low drag airplane.

With the engine/propeller out of the way, it becomes possible to introduce a canopy area that results in excellent visibility in all directions (visibility Design Goal).  With the propeller at the rear of the aircraft and the engine aft of the cockpit, it becomes much easier to meet the noise Design Goal (as an aside, laminar flow produces less slipstream noise than turbulent flow; consequently, even though the primary reason for going to a clean fuselage is to reduce drag, there is an added benefit with respect to cockpit noise).

OK, so the airplane is going to be a Pusher.  All well and good; but, where are we going to put the engine?  One of the design problems with locating the propeller “Aft” is that the engine has got to go “Aft” as well; but where “Aft”?  For two very good reasons, the engine can not be located at the very rear of the fuselage.  First, placing the engine at the very rear of the fuselage would result in both empty and loaded Center of Gravity locations that would severely impact on the handling qualities Design Goal.  Second, placing the engine at the very rear of the fuselage would cause severe problems in streamlining the fuselage rear end, thereby causing an increase in fuselage drag that would impact the performance Design Goal.  So, what to do?

Enter the carbon shaft (first conceptual innovation).  Driveshaft technology has come a long way in the past twenty years and very light, very strong carbon composite shafts are now readily available.  Utilizing a short length, large diameter carbon composite shaft would make it possible to locate the engine amidships and the propeller at the rear of the fuselage, thus satisfying both the performance and handling qualities Design Goals.  So, we did our homework and looked into the carbon composite shaft.  Turns out that a carbon shaft with associated hardware comes in at about 15 pounds.  Not bad.  It also turns out that shaft life can be designed for infinite life (no overhauls) and that the overhaul periods on the shaft hardware can be designed to correspond to the engine overhaul periods.  We also knew that the Bell P-39 Air Cobra fighter very successfully used a shaft during World War II and that helicopters routinely use shafts to drive the tail rotor as a matter of necessity.  The carbon composite shaft was the solution to our design problem.  We think that when you evaluate what the use of this concept means to over-all Phoenix capabilities, you’ll agree that we made a good move.

A note on the engine-  Fundamental decision.  The engine that powers Phoenix had to be a certified engine.  Very important.  Also, the engine had to be able to hold the Take-off Power/Maximum Continuous Power ratings up to a Density Altitude of at least 8,000 feet (Denver on a Hot Day), important for Flight Safety reasons (Hot Day/High Altitude Take-off and climb performance) and relatively high altitude cruise performance.  Further, it would be very advantageous if the engine Maximum RPM Rating permitted us to use it without installing a gearbox to match the engine RPM with the design propeller RPM.  Our all around first engine choice was the Mistral Engines (http://www.mistral-engines.com) G-230-TS twin rotor, turbo-charged, liquid cooled, 230 Brake Horsepower Rotary (Wankel) engine.  First choice because of its small size and because of its low vibration characteristics (on the down side, the engine burns about 10% more fuel than comparable piston engines).  However, Mistral is still busy developing and certifying this engine and you can’t launch an aircraft program not knowing when or whether the design engine will be available.  So, we turned to Continental.  The engine that’s going to go into the Phoenix prototype is the 225 Brake Horsepower, turbocharged Continental TSIO-360-BD because it meets the power and “no gearbox” requirements that we’ve discussed above.  Our intention is to monitor Mistral progress and to leave open the option of installing that engine should it become available down the road.

After a whole bunch of analytical “tweaking”, we froze the configuration in preparation for the wind tunnel tests.  The model that was tested in the wind tunnel is shown in a CAD drawing in Figure 4.  As pointed out under the Wind Tunnel tab, following the wind tunnel tests, we made a number of changes to the bird and it’s interesting to see the two configurations side by side. Figure 5 shows the final, present configuration of the aircraft.

A Note on the Wing Shape and Location-  The wing platform, incorporating moderate forward sweep coupled with the wide-chord center section, is important in several respects.  First, it promotes stall inboard on the wing, an important handling qualities consideration.  Second, because it permits the wing/fuselage junction to remain well aft (while maintaining longitudinal aerodynamic balance), the exposed boom lengths carrying the vertical stabilizers can be shortened, an important structural and esthetic consideration.  Third, the wing vertical location, in the “shoulder” position, high on the fuselage, promotes lateral (roll) stability, an important handling qualities consideration.  Finally, look closely at one of the side views of the airplane and you’ll see that the wing is located at the pilot’s eye level, enabling visibility both under and over it.  Interesting how it fit together.    

A Note on the Canard Shape and Location - With the wing located aft, the relationship between the wing aerodynamic center and the airplane Center of Gravity required that a canard be used to tailor longitudinal stability characteristics and to provide trim.  The canard employs moderate aft sweep.  The aft sweep contributes to lateral (roll) stability and helps offset the negative wing contribution.  The canard utilizes a trailing edge flap that is programmed to move with wing flap deflection so as to minimize pitching trim changes when the flaps are deflected.  So, both the wing and canard would be flapped (unlike the Varieze style pure canard).  The result would be high lift and the ability to fly slower as well as fast, not possible with the pure canard/aft wing configuration.

A Note on the Vertical Stabilizers - The vertical stabilizers are conventional in function.  They have been sized to provide a high level of directional stability.  The outboard cant contributes to lateral/directional stability (and looks pretty good).

A Note on the Ventral Fins - Two small, fixed ventral fins, mounted on the aft fuselage, are there for two reasons.  First, to maintain directional stability at high angles of attack (where the main vertical fins would be partially blocked by the fuselage/wing) and, second, to act as propeller protection in the event of very high angle landings (although we have indications that it’s going to be impossible to get the bird up high enough to get the ventrals/prop in any landing; flight test will give us the final answers).

A Note on Entry and Exit - As we noted under the Design Goals tab, one of the major goals was to make this airplane easy to get in and out of (Orangutan agility not required).  To do this, we’ve gone to two upward swinging, centrally hinged clamshell doors, opening down to floor level.  Combined with this feature, the height of the seats above the ground (and one other feature that we’re not going to tell you about here, heh, heh) makes it possible to enter and sit in one motion directly from a standing position with the reverse being true upon egress.

Some Random Notes on Other Noteworthy Features - Yes, we’re thinking about crashworthiness (we’ll be using the requirements of FAR 23 and FAR 27 as guidelines for crashworthiness).  An overturn structure will be incorporated and, in accordance with the Military Specifications (U.S. Army), automatic fuel shut-off valves will be used to prevent fuel leakage from starting a fire in the event of a severe crash (Numerous studies by the U.S. Army and the U.S. National Transportation Safety Board have shown that the major causal factor in aircraft fires was not rupture of the fuel tank but rupture of the fuel lines leading to and from the tank, allowing fuel to escape.) 

Cockpit sun protection - We’ve come up with a neat way to keep the sun from cooking the cockpit on those hot, sunny days.

Microprocessor/Instrument Display - The kit will be equipped with an onboard computer and an advanced instrument/annunciator display. The computer will be used to monitor various aircraft systems and make life easy for the pilot in such areas as weight and balance computations, checklist display, navigation, etc, etc.

That’s all we’ve got to tell you about the airplane at the moment. We hope you’ve enjoyed it and found it informative.