Hurel-Dubois HD.31 / HD.32 / HD.321 — Primary-Source Technical Documentation Collection

Maurice Hurel's ultra-high-aspect-ratio transport prototypes represent one of the most audacious aerodynamic experiments of the mid-twentieth century. This collection assembles the surviving primary-source documentation for the HD.31, HD.32, and HD.321 airframes — including official French STAé evaluation reports, manufacturer performance brochures, and the complete engine technical libraries for both powerplant families that defined the programme's evolution.

The HD.32 flew with the Pratt & Whitney R-1830-92 Twin Wasp. The HD.321 stepped up to the Wright Cyclone 982-C9-HE1. Both engine families are covered here in full depth — Parts Catalogs, Service Instruction Handbooks, and Overhaul Manuals — giving restorers, researchers, and serious collectors the complete technical picture in a single acquisition.

Document Manifest

Hurel-Dubois Airframe Documents (5 documents)

• HD.32 Performance Brochure — Manufacturer performance data sheet, aerodynamic coefficients, payload-range curves
• HD.321 Manuel — Ref. HD.321.01 — French-language technical manual covering the upgraded single-fin configuration
• HD.32 ALPA Evaluation Report, 1955 — Air Line Pilots Association independent flight evaluation; handling, stability, and crew workload assessment
• HD.32 Brochure — Commercial presentation brochure; route economics, passenger capacity, and airline suitability data
• HD.32 Description Brochure — Structural and systems description; wing geometry, strut configuration, empennage layout

Pratt & Whitney R-1830 Twin Wasp Engine Documents (3 documents)

• Parts Catalog — Models R-1830-43, -65, -90C, -90D, -92, -92A — (NAVY) AN 02A-10CD-4 / (USAF) T.O. 2R-R1830-4 — 1 January 1960, revised 1 October 1958 supersession. Joint USAF/Navy publication under authority of the Secretary of the Air Force and Chief of the Bureau of Aeronautics
• Handbook Service Instructions — Models R-1830-90C, -90D, -92, -92A — NAVWEPS 02A-10CD-2 — 1 December 1961. Published by direction of the Chief of the Bureau of Naval Weapons. Supersedes NAVAER 02A-10CD-2 dated 1 June 1945 and all subsequent revisions
• Handbook Overhaul Instructions — Navy Models R-1830-90C, -90D, -92, -92A / USAF Models R-1830-90C, -90D, -92 — (NAVY) NAVWEPS 02A-10CD-3 / (USAF) T.O. 2R-R1830-3 — 15 July 1960, revised 1 October 1965. Pratt & Whitney Aircraft, Division of United Aircraft Corporation, Contract NOw 64-0113-k

Wright Aeronautical Cyclone 9 GC Engine Documents (3 documents)

• Instruction Book — Wright Cyclone 9 Aircraft Engine, Series C9-GC — Installation, Operation, and Service Maintenance — Second Edition, September 1942. Wright Aeronautical Corporation (Division of Curtiss-Wright Corporation), Paterson, New Jersey. Provenance: original owner's copy, dated November 1942 in period hand
• Overhaul Manual — Wright Aircraft Engines Cyclone 9 GC — Third Edition, Part No. 114323-N3, October 1943. Wright Aeronautical Corporation, Paterson, New Jersey, U.S.A.
• Operation and Service Manual — Wright Cyclone 9, Series C9GA · C9GB · C9GC — Wright Aeronautical Corporation, U.S.A. Original blue softcover field edition

Aerodynamic Engineering Notes — The High-Aspect-Ratio Wing

Maurice Hurel's central thesis was that an aspect ratio exceeding 20:1 would radically reduce induced drag at cruise altitudes, yielding payload-range economics unattainable by conventional wing geometries of the era. The HD.32 and HD.321 validated this in flight:

• Induced Drag Reduction: Aspect ratio of 20.2:1 produced measurably lower induced drag across the cruise envelope
• Lifting Struts: Airfoil-section bracing struts contributed positive lift rather than parasitic drag
• Interference Drag: Wind tunnel data confirmed minimal aerodynamic interference at strut-to-wing junctions
• Stall Speed: Ultra-long wing chord reduced stall speed to approximately 120 km/h — exceptional for an 18,700 kg transport

Engine Variants by Airframe

HD.321 Performance Data

• Maximum Gross Weight: 18,700 kg (41,226 lb)
• Empty Equipped Weight: 11,112 kg (24,498 lb)
• Wing Area: 100.0 m² (1,076 sq ft)
• Aspect Ratio: 20.2:1
• Cruising Speed: 275 km/h (171 mph)
• Maximum Range: 2,200 km (1,400 mi)
• Rate of Climb: 4.8 m/s (940 ft/min)

Handling & Stability

• Roll Performance: Narrow-chord ailerons on the 45.3 m wingspan produced a surprisingly high roll rate
• Empennage Evolution: Initial twin-tail configuration caused stability tracking issues under high power; engineers retrofitted a prominent single fin with auxiliary finlets to counter asymmetric engine-out torque
• Legacy: Air France provisionally ordered 24 units before cancelling in favour of the Caravelle. The design lineage continued in the HD.34 cartographic survey aircraft. Hurel's lifting-strut principles are studied today in contemporary green-aviation research including the Boeing SUGAR Volt concept

⚠️ Regulatory Notice: Under FAA 14 CFR § 43.13 and EASA Part-M, any mechanic performing maintenance on an active aircraft must use current, manufacturer-approved revision-controlled data. This archival document does not satisfy that requirement.

This is an archival, static-copy edition fixed at its original publication date. Intended for historical reference, flight simulation, museum restoration, and educational use only. Not approved for active airworthiness maintenance under FAA 14 CFR § 43.13, EASA Part-M, or equivalent international regulations. Operators of active aircraft must use current, revision-controlled publications from the Type Certificate holder or an authorized distributor.
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