Models, pod and model interface

Models are 3D-printed. Each one is built around a standard pod that hides the balance, carries the pressure instrumentation and bolts to an aluminum puck on the balance.

Model interface

The puck (6061, Ø1.700 x 0.300 in, drawing WT-6C-002) bolts to the balance front face with 2x #10 screws and 2x 1/8 dowels. The printed pod slides over the balance and is held by 4 radial #8-32 screws through its wall into the puck, so models swap without touching the balance. A 3/16 in hole passes the pod-sensor wires.

Reference pod (2.25 in) with pressure instrumentation

Current 2.25 in pod (9.4 in long, 3D printed; STEP: pod_reference_2.25in_printed.step). Pod instrumentation: 4 base taps -> printed wall channels -> averaging ring in the nose -> sensor bay; separate cavity tap. Sections show the channels in the wall.

Base taps: 4x 1/16 in at 30°/150°/210°/330° (clear of the pod screws and the wing roots), 1.5 mm channels printed in the mid-wall, a manifold ring averages them.
Cavity tap near the aft fitting, own channel. Sensor bay in the nose for two barometric boards (base, cavity) and the attitude IMU.
Drag correction: forebody axial = measured axial + (p_base - p_∞) x A_base, A_base = 0.86 in². At 100 mph a base C_p of -0.1 is worth about ΔC_D 0.002 (20 counts).
Pod base 1.50 in, sting/pod diameter ratio 0.39 (≤ 0.5 per the NASA sting-interference report); ≥ 12 in of straight sting behind the pod.
Print standing on the base (nose up) so channels print as round vertical holes; leak-check every model.

Model guidelines

Topic	Guideline
Material	PC-CF preferred (low creep, low moisture). PA6-CF only if dried, sealed and stored dry. PETG for quick prototypes.
Stiffness	6 mm carbon tube spar in wings, or tips deflect noticeably at 100 mph.
Reference point	Wing quarter-chord at the BMC (x = 0). Moments are transferred to any other reference in software.
Size for rolling	Span ≤ 9 in for full ±90° roll; 12 in -> ±50°; 18 in -> ±25° (software-enforced).
Mass	Keep under ~1 lb; weight is removed by a wind-off tare at every attitude.
Surface	Smooth finish or trip strips: Re is only 1.9-2.7 x 10⁵.
Keep-outs	Do not drill or bolt into the pod wall at the tap-channel angles (30/150/210/330°).

The pod is 3D printed: the STEP file is the print file, and drawing WT-6C-004 gives the fit and inspection checks (puck bore, screw holes, tap layout, channel keep-outs, blow-through test) (export it to STL and print it; print it standing on its base, nose up, so the 0.060 in tap channels print as vertical round holes; no supports inside them). CAD: pod_reference_2.25in_printed.step, model_puck_6061.step.