FAQ
Q1: Should one expect that higher taper ratio leads to lower aspect ratio and resulting with increased induced drag?
A: Up to 2-3 times lower CL with its square value and wide foldable wing tips that maintain a high aspect ratio result with
significant reduction of induced drag.
Q2. However, BDW with 4+ times higher wing area may lead to proportionally higher profile drag.
A. Between 2-3 times lower t/c and CL including higher Re Number are offsetting wing profile drag increase due to wing area
increase.
Q3. But, will such increased wing area introduce additional weight?
A: Please refer to the weight related savings under "Benefits" tab.
Q4. The shift of engines and fuel away from the wings that counterbalance lift loads on wings make wings more loaded
A1: Lift forces are split between wings while the removal of extra weight allows for streamlined & efficient wing structure.
A2: Streamlined and efficient wing structure is also made possible by removing many heavy flight control surfaces and leaving only pivotal trailing edge control surfaces with clean leading edge of both Front and Rear Wing.
A3: Also, clean leading edge of wings makes BDW aircraft a good candidate for application of laminar flow technologies
A4: Additionally, there is a much higher structural resistance of wings due to their high taper ratio.
Q5. However, highly tapered wings are suffering from poor stall characteristics and low roll damping.
A1: BDW aircraft fly at low attack angles due to high lift areas, hence no stall concerns.
A2: Also, BDW aircraft having tremendous stabilizing forces and momentums, thus highly minimizing stall risk.
A3: Additionally, wing span is wider than single-wing aircraft for the same payload capacity, hence no roll dumping concerns.
Q6. But Tandem-wing configurations suffer from longitudinal stability challenges.
A: BDW is not a tandem-wing aircraft as we know. Forward-camber airfoils move C.P. generally in aft direction with attack
angle change to decrease the destabilizing nature of Front Wing and increase the stabilizing nature of Rear Wing.
Q7. Forward-camber airfoils have worse aerodynamic characteristics than aft-camber airfoils.
A: True for thicker airfoils with t/c greater than 10%. However, t/c of BDW aircraft is close to 4%, which along with
2- 3 times lower CL and longer chords completely offsets such disadvantages including a higher wing area of 4+ times.
Q8. There would be higher cost to build two wings instead of one
A1: Rear wing is replacing the tailplane. Also, wing structure is simplified since no engines, slats, and flaps.
A2: However, it does require two sets of systems including deicing though no fuel tanks when using LH2.
Q9. Two wings may be complicating evacuation and ground handling.
A1: Evacuation would be no more complicated over Front Wing compared to single-wing aircraft. Same with aft exit.
A2: Handling on the ground would be somewhat more restricted but having enough room in the most recent design.
Q10. Rear wing on the top of the aft fuselage cabin require large support structures that restrict cabin cross section.
A: Addressed with full Wing-Fuselage integration due to simplified wing design, lower weight, and fuselage shape.
Q11. Landing gears may have to be placed in an unfavorable region of the Front Wing or even between both wings.
A: Very flexible flight mechanics allow for the optimal position of wings and disposal of landing gears.
Q12. Aerodynamic ground effect may be critical in terms of rotation and touchdown.
A: This should not be a problem at all for BDW aircraft due to much more powerful flight mechanics based on the new double wing flight model provided by multiple times larger Rear Wing area of BDW aircraft when compared to the tailplane