Convair Model 61 — The Twin-Jet That Could Have Challenged the DC-9

A Lost Convair Airliner Reconstructed Through CAD (2026)

The Convair Model 61 was a proposed twin-engine narrow-body jet airliner, developed internally during the late Convair era and conceptually continued under General Dynamics. Designed as a smaller, more efficient derivative of the Convair 880/990 family, the Model 61 represents a rare and largely undocumented paper study — one that could have positioned Convair as a direct competitor to the Douglas DC-9, had the company survived in commercial aviation.

Unlike well-documented commercial aircraft programs, the Model 61 survives only through fragmentary three-view drawings, internal references, and limited archival material, much of it sourced from historically obscure aviation research communities such as The Secret Projects Forum. This CAD reconstruction is an effort to preserve, analyze, and technically revive one of Convair’s most intriguing unrealized airliner concepts.

Concept Overview — A Twin-Jet Convair Successor

The Model 61 was envisioned as a twin-engine turbofan airliner using the CJ805 turbofan series, derived from the Convair 990’s powerplant lineage. In contrast to the four-engine Convair 880 and 990, the Model 61 sought to achieve:

  • Lower fuel burn
  • Reduced maintenance cost
  • Improved dispatch reliability
  • Competitive economics against emerging short- to medium-haul aircraft such as the DC-9

This design direction mirrors what Douglas later achieved with the DC-9 family, and later McDonnell Douglas with the MD-80 series — a scaled, efficient derivative built on proven aerodynamic and structural foundations.

Airframe Geometry — Shortened Convair 880 Lineage

Based on available three-view references and CAD interpretation:

  • The fuselage is shortened to ~87.5% of the Convair 880’s length
  • Approximate fuselage length: ~34.5 m
    (down from ~39 m on the Convair 880)
  • The reduction lowers structural weight but also reduces passenger capacity
  • The aircraft retains a T-tail configuration, requiring careful CG and pitch-stability balancing

Despite the shorter fuselage, the Model 61 appears longer than the Convair Model 60, due to operational dimensional differences associated with a higher and more aft horizontal stabilizer placement, characteristic of a T-tail architecture.

Wing & Aerodynamics — Proven 880M Platform with Modifications

A key design philosophy was reuse of the Convair 880M wing and wingbox, minimizing development risk while preserving high-speed cruise efficiency.

Wing Data (Inherited & Modified)

  • Span: 36.58 m
  • Root Airfoil: NACA 64-0012
  • Tip Airfoil: NACA 64-0008

Aerodynamic Adjustments

  • Wing sweep and wingtip geometry modified to compensate for:
    • T-tail moment-arm changes
    • Modified CG envelope
    • Shortened fuselage mass distribution

Unlike the Convair 880M and 990A, the Model 61 relocates engines to the rear fuselage, similar to the Sud Aviation Caravelle, introducing different yaw inertia, pitch coupling, and structural load paths.

By retaining the 880M aerodynamic platform, the Model 61 would likely match Convair 880 cruise performance, while benefiting from lower drag and reduced structural mass.

Powerplant — CJ805-23B and the Hypothetical CJ805-41C

The baseline engine assumption is the CJ805-23B, producing approximately:

  • 71 kN thrust per engine

A later conceptual upgrade suggests a fictionalized or proposed CJ805-41C, estimated at:

  • ~74.73 kN thrust per engine

Performance Gains

This modest thrust increase improves:

  • Takeoff performance
  • Hot-and-high airport capability
  • Payload margin
  • Overall thrust-to-weight ratio

Estimated Thrust-to-Weight Ratio

Using CJ805-23B engines:

  • T/W ≈ 0.24

A strong value for a 1960s–1970s twin-jet, aligning closely with DC-9-class performance.

Weight & Fuel Capacity — Downsized but Efficient

Estimated Maximum Takeoff Weight (MTOW)

  • Metric: ~60,312.61 kg
  • Imperial: ~133,000 lb

Due to fuselage shortening and reduced internal fuel volume, total fuel capacity is lower than the Convair 880 — reinforcing the Model 61’s intended role as a medium-range, high-frequency trunk-route or regional aircraft.

Cabin Layout & Passenger Capacity Estimation

The Model 61 retains Convair’s 5-abreast (2+3) seating layout, preserving a comfort advantage over 6-abreast competitors.

Seating Assumptions

  • Seat pitch: 33 inches
  • Cabin layout: 2+3
  • Fuselage reduction: ~5 m shorter than Convair 880

This results in a noticeable reduction in seat rows, trading capacity for:

  • Improved operating economics
  • Lower empty weight
  • Faster turnaround times

Estimated Passenger Capacity

  • ~85–110 passengers, depending on:
    • Galley placement
    • Lavatory count
    • Exit layout
    • Airline density configuration

Operational & Engineering Challenges

Despite its promise, the Model 61 would have faced real-world challenges:

Market Competition

  • DC-9 already established airline trust
  • Boeing 737 emerging as a strong competitor
  • Convair lacked long-term commercial production continuity

Engine Efficiency Limits

  • CJ805 turbofans were early-generation, less efficient than later high-bypass turbofans

Structural & Flight Dynamics Complexity

  • T-tail deep-stall risk
  • Pitch-authority and trim sensitivity
  • Wing torsion changes due to CG relocation
  • Maintenance complexity inherited from Convair’s high-performance design philosophy

Why Rebuild the Convair Model 61 in CAD — Even 50+ Years Later?

Reconstructing the Model 61 in 2026 serves multiple technical and historical purposes:

1. Preserving Lost Aerospace Engineering Knowledge

This aircraft exists only on paper — CAD transforms it into an analyzable digital artifact.

2. Testing “What-If” Design Pathways

It enables comparative analysis against DC-9, 737, and A320 evolutionary trajectories.

3. Studying Legacy Aerodynamics

The NACA 64-series wing remains valuable for:

  • CFD benchmarking
  • Retro-modern optimization
  • Turbofan integration studies

4. Educational & Research Value

A digitally revived paper aircraft becomes:

  • A CFD test platform
  • A structural FEA case study
  • A propulsion-matching research model
  • A historical engineering reference

5. Proving Convair’s Missed Potential

The Model 61 demonstrates that Convair was not technologically behind — but rather constrained by corporate and market realities.

Conclusion — The Twin-Jet That Never Flew

The Convair Model 61 stands as a symbol of a lost lineage — a credible, technically sound DC-9 rival that could have reshaped Convair’s future in commercial aviation.

By reconstructing it in modern CAD, we transform a near-forgotten paper concept into a living engineering case study, ensuring that Convair’s unrealized innovation is not lost to time.