Hall Bulldog Wing Shape Revisions - January 2023

Part of The Hall Bulldog Project — documenting Bob Hall's 1932 Thompson Trophy racer.

This engineering update from Kevin Kimball documents the revisions made to the Hall Bulldog CAD model to incorporate the refined surface model developed by Mirco Pecorari of Aircraft Studio Design. The updates ensure the structural design accurately matches the validated aircraft shape.

Wing Leading Edge Corrections

The most significant change involves the wing leading edge shape. Mirco’s photo analysis revealed that the original leading edge contour was different from initial assumptions, resulting in a much nicer look without the flat spot that appeared in earlier models.

Hall Bulldog wing planform differences — Old wing shape with new corrected shape shown in gray overlay

Hall Bulldog updated wing shape — Updated wing shape with improved leading edge contour

Structural Implications

The leading edge changes require updates to several components:

New Nose Ribs

The revised leading edge shape requires new nose rib profiles. These will be cut from plywood using a CNC router. The rest of the built-up truss ribs will work with minor contour adjustments.

Hall Bulldog thickness change detail — Thickness change requiring new nose ribs and front spar adjustments

Wing Fittings Optimization

The wing fittings and draw wire plates have been updated to reduce weight and size while ensuring proper clevis pin installation from either direction:

Hall Bulldog wing fitting detail — Updated wing fittings optimized for reduced weight

Hall Bulldog compression member and drag wire — Typical compression member and drag wire fitting

Strut Fitting Angle Change

The strut fitting angle has been changed from 33 degrees to 30 degrees to accommodate the revised wing geometry and lower wing attachment point:

Hall Bulldog updated strut fittings — Updated strut fittings with corrected 30-degree angle

Hall Bulldog front view strut angle — Front view showing new fitting angle, strut, and fairing

Wing Attachment and Dihedral

Several key parameters have been adjusted based on Mirco’s refined analysis:

Dihedral: Slightly different from the earlier Josh/Vern model - a bit more than previously estimated
Wing attach point: Lower than the Vern data indicated, now fitting inside Mirco’s skin model
Gull section tubes: Now properly positioned inside the Mirco gull skin model

Hall Bulldog lower wing attach point — New lower wing attach point positioned inside Mirco’s gull skin model

Hall Bulldog wing in skin shell — Top view of wing structure inside Mirco’s skin shell model, showing the old leading edge shape line

Summary of Changes

Parameter	Previous Value	Updated Value
Strut fitting angle	33 degrees	30 degrees
Wing dihedral	Josh/Vern estimate	Increased per Mirco
Wing attach height	Higher	Lowered to fit Mirco model
Leading edge shape	Flat spot present	Smooth contour

Collaborative Design Process

This update represents the ongoing collaboration between Aircraft Studio Design’s 3D modeling expertise and Kevin Kimball’s structural engineering experience. The iterative process of refining the surface model and updating the structural design ensures the replica will be both visually accurate and structurally sound.

About Kevin Kimball

Kevin Kimball of JKE Works continues to refine the Hall Bulldog structural design, incorporating feedback from the 3D modeling team while preparing deliverables including updated nose rib shapes, spar models, and tip bow shapes for builder Tony Horvath.