Aerodynamics

Wing Loading

A key element of the Goomie concept is to simultaneously reduce wing-loading and size over other aircraft. The goal for Goomie is an effective wing loading of 45 kg/m², while keeping wing span under 6.5m. To achieve this without encountering excessive induced drag penalties is possible because of two key features:

1. Very high power-to-weight ratio engines and advanced structures, resulting in low empty weights.
2. The inherent span-efficiency of the delta wing / tipsail and canard wing arrangement.

Airfoil Sections

A NACA 23112 section is chosen for the main wing and NACA 4418 for the canard. This provides a low pitch moment on the main wing and an efficient high lift for the canard.

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The airfoil sections were chosen with consideration for avaialble thrust, L/D and stall requirements. Structural considerations encourage the use of a relatively thick airfoil— 18% for the canard and 12% t/c ratio for the main wing. The use of a thick airfoil also offers the best aerodynamic tradeoffs.

The main wing has a slightly reflexed wing (NACA 23112) which is responsible for the very low pitch moment at all angles of attack.

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Wing Aerodynamics

The BVH Goomie uses a delta wing with winglets and canard. None of the wings has any twist or dihedral and both wing and canard are rigged at zero incidence. The airplane’s aerodynamic characteristics are tailored through airfoils and planforms alone.

Planform

The delta main wing is swept by 30 degrees and combined with a fairly convensional high aspect ratio canard. This planform arrangement provides several advantages:

• A highly spin resistant configuration.
• Induced drag is minimized, since lift distribution is near optimum, and because the span efficiency of a planar wing is optimized when maximum span is at the trailing edge.
• Aileron power is maximized. This wing planform allows the greatest aileron span and area relative to wing area.
• The pitch up tendency of high trust line engines is effectively eliminated.

Note that the effective (aerodynamic) sweep will be less than the wing geometric sweep, due to the winglet's contribution to the lift vortex.

A further virtue of this planform is the visual order created by the straight trailing edges of all flying surfaces.

Winglets

Relatively small winglets are utilized, they improve lateral as well as increased directional stability and effectively increase pressures on the outboard aileron thus improving roll rate. The winglets have a secondary role to reduce induced drag, which translates into reduced energy losses during high-G maneuvers. The winglets use the same airfoil section as the main wing. They are rigged at zero incidence and are highly swept to cope with the widely varying flow conditions at the wing tip.

The winglets contribute a large part to increasing the roll rate, while simultaneously reducing adverse yaw and induced drag.

Stall characteristics

The stall characteristics are very docile. Since the canard always stalls before the main wing it is not possible to stall the main wing under normal flight conditions. The aircraft remains controllable and with very little loss of aileron authority throughout the canard stall.

There is no post stall break or wing drop. With full aft stick, the canard stalls, the nose drops, the canard resumes flying and the nose rises again. Througout this process the main wing remained flying.

Given the stall characteristics the Goomie can be described as a highly spin resistant design. It would not be possible to induce the aircraft into a spin from anywhere in the normal flight envelope.