Answers to FAQs about Carplane®/BiPod

1). We welcome all positive contributions to roadable aviation.
2). We particularly welcome Burt Rutan to roadable aviation.
3). We thank Burt for validating our twin-hull roadable concept.
4). Main Similarities: Twin hulls, hybrid/electric drive, steering-wheel in road-mode/stick in air-mode.
5). Main Differences:

a). The Carplane®’s mode-conversion is push-button in 15 seconds. The BiPod’s mode-conversion involves detaching 4 stabilizers & 2 wings (+ 2 aileron linkages), then re-securing each stabilizer at one end and each wing & a canard at both ends. Burt Rutan states, this takes “1 person about 10 minutes” because “the wings have skateboard wheels on them”. 

b). Carplane® entry is via large side-doors. BiPod entry involves climbing over the cabin wall, then lowering down through the hatch.



c). The Carplane® is flown & driven from the same cockpit. BiPod drivers/pilots must change cabins to continue onward after mode-change.



d). In Road-Mode, the Carplane® generates road-hugging “downforce” (negative-lift) via its canard and via the wedge-like slant of its wings. Its tailplane veers downward to act like a spoiler. Burt Rutan states the BiPod’s mid-wing flap creates downforce in road-mode. However, the wings stored underneath would appear to prevent any Bernoulli-effect on the underside. And on the upper side, the flap appears to merely deflect - like an air-brake. [Its canard and fins over the rear wheels would appear to create downforce.]



e). The Carplane®’s wings are stored tips low/forward and shielded by the canard, thereby reducing drag. The BiPod’s wing-roots face perpendicular (flat) to the oncoming airflow,.        

f). The Carplane® conforms to road regulations in regard to wheel-base & overhang. The Bipod’s rear overhang exceeds 50% of its wheel base. A 50% limit prevents “weathercocking”. A large vertical stabilizer on a long moment-arm may increase crosswind-susceptibility in road-mode. Burt claims, in road-mode the Bipod has "driven 80mph in a 35mph" crosswind. He recently criticized another roadable aircraft for its crosswind-susceptability, although its side-panels are mid-wheel-base (and far smaller than the side-surface of a minivan).


g). Large flaps migrate the Carplane®’s Center of Lift (CL) aft, thereby preventing abrupt over-rotation. Its empennage extends rearward, thereby shifting weight aft and lengthening the moment-arm for improved elevator-leverage. Its elevator is large and its effectiveness is enhanced by its location directly in the prop-flow. Its canard augments nose-raising and is enhanced by ground effect.
The BiPod has battery & occupants fore of the Center of Lift. Its rotation is impeded by an unusually oblique angle between its Center of Lift & the rear axle (65°). Elevator area is reduced (to make room for motor-mounts), thereby reducing  pitch-force. Elevator effectiveness is reduced further due to limited prop-flow under the horizontal stabilizer (because its prop-arcs must remain clear of the wing-storage area below). Burt Rutan states that “a burst of wheel-power causes rotation”. He does not explain how sufficient traction is attained near maximum lift. [Note: The BiPod’s wheel-powered runway-hops (“wheelies”) were performed with only one occupant on board at low speed. Taxi tests are normal. We wouldn’t mention it if Burt hadn’t stated, “I never show an aircraft until it’s flown”.] 

h). The Carplane®’s conventional 26° CL/rear-axle angle enables normal flare and touchdown. The BiPod’s unusually oblique CL/rear-axle angle (65°) predisposes it to slap-down landings (accentuated further by elevator-size (small), elevator-moment (short) and nose-end weight).



i). The Carplane® has 15” block-section auto tires (block-section is required for road certification of a 4-wheeled vehicle). The BiPod has 10” (front) & 12” (rear) rounded-section motorcycle tires, thus reducing brake-effectiveness and hampering cornering (due to lack of tilt).



j). Architects design garages & parking spots to accommodate standard size cars, not big-rigs. [defined as 2.2mW/5.5mL/2mH  (7’2”W/18’L/6’5”)]. The Carplane® conforms to compact-car size. The BiPod exceeds it in both width & length.



k). The Carplane®’s seating dimensions are identical to a 3-series BMW. Elbow grooves enable normal armrest width. The BiPod has recumbent seating, no side elbow-space and occupants share the cabin with a wheel-well and a lithium battery.  



l). The Carplane® has a front bumper-bar, front wheels which deflect the cabin upward upon frontal impact over an oncoming obstacle, a rear shape which deflects the vehicle upward upon rear impact and a tubular-steel cocoon around each cabin. The BiPod cabin has a battery at chest height in front of each occupant and a motorcycle engine directly behind.

m). The Carplane® has medium aspect ratio and a high-wing configuration enabling wing-crab for a relatively high crosswind component. The BiPod has only slightly longer wings at mid-height, limiting crosswind capability.



n). The Carplane® is designed for roadable LSA certification (max. 650kg/1430lbs., 120kts./136mph). It has a non-laminar-flow  airfoil, low stall speed and high stability (laterally: due to twin-hulls, dihedral  & highwing/pendulum-effect; longitudinally: due to 3-surface configuration & centralized weight). It has high control-responsiveness throughout its envelope due to the long rudder & elevator moments enabled by empennage extension. It’s designed for low-experience owner-pilots. Scaled Composites has registered the BiPod with the FAA as a glider. Burt Rutan cites its high aspect ratio and claims it has LSA weight. Once motors are added, it will be a 40hp, 2-seat motor-glider, albeit one with 3 extra wheels, 2 extra batteries and the drag/wetted area of an extra hull. Citing its high aspect ratio and stating it has LSA-roadable weight (1.430 lbs./650kg), Burt claims it will do 197mph cruise (LSA max. is 136mph) at 12.000ft. (LSA-Max. is 10,000ft.)



o). The Carplane® has a single 2-blade prop. The airflow split by the wing increases noise. However, Carplane®’s prop location high & substantially between the fuselages yields a net reduction of the noise-footprint. The BiPod has two 4-blade props. Together, they cover less than half the area of Carplane®’s prop disk. [Prop efficiency decreases with radius whereas noise and RPM increase.]


p). The Carplane® has inter-hull joins at varying heights and cross-braces to counter divergent torsional forces which act separately on each hull due to road vibrations, uneven surfaces and potholes. The BiPod’s  hulls’ joins are all located at mid-fuselage although each hull is longer and farther apart, accentuating leverage.

q). The Carplane® employs a secondary spar to counter wing-torsion. The BiPod doesn’t.

r). The Carplane®’s thermal management places liquid-cooled electric hub-motors in the nose for road-mode and a partially liquid-cooled internal combustion engine wholly within the intra hull slipstream for air-mode. The Bipod has two motorcycle engines which are wholly enclosed within each hull behind each occupant. Neither air-intakes nor outlets are visible.
s). Carplane® development in its current form started Nov. 2007 and was disclosed via Int. Patent Application on July 28, 2008. BiPod development started Nov. 30, 2010 and was disclosed July 15, 2011.

t). The Carplane® can be flown with a single-engine rating. The Bipod requires a twin rating.

6). We encourage all roadable aircraft development as long as it doesn’t infringe on anyone’s IP or patents. We also welcome anyone proving a claim to have advanced the field of roadable aircraft and expanded the knowledge of the aviation community.

(All illustrations & current BiPod version based on photos & drawings released & statements made by Jeff & Burt Rutan/Scaled Composites. Sources: Aviation Week, G. Norris: Jul. 15; AOPA, T.Horne: Jul. 27, Airventure, S.Schapiro, Jul. 27; Scaled Composites Website; Toxology Website, Aug. 1; Pacific Flyer, Aug.1.)