SAWE Technical Papers

@inproceedings{3840,

title = {3840. The Learjet 85: Historical Evolution, Critical Challenges and Lessons from a Misguided Program},

author = {Darrin McCloud},

url = {https://www.sawe.org/product/3840-the-learjet85-historical-evolution-critical-challenges-and-lessons-from-a-misguided-program/},

year  = {2026},

date = {2026-05-21},

urldate = {2026-05-21},

booktitle = {85th SAWE International Conference on Mass Properties Engineering},

publisher = {Society of Allied Weight Engineers, Inc.},

abstract = {The story of the Learjet 85 (LJ85) starts with the Learjet 60 (LJ60). In 2004 the LJ60 was the largest Learjet in production, however it suffered from many problems that were causing it to lose valuable market share. Foremost was that the LJ60 used the same basic wing and main landing gear (MLG) design that traced its lineage all the way back to the Learjet 23 in the early 1960’s. Based off the original Swiss fighter jet wing design, this design was thin, very strong, high speed optimized and originally came equipped with tip tanks for additional fuel storage. It was now being used on a plane that weighed twice as much, had winglets instead of tip tanks and was limited to the same small size wheels. The following issues were the result:

1. Poor landing performance due to high landing speeds and undersized brakes

2. Large fuselage tank required due to small wing fuel volume

3. CG issues due to short MAC length and large fuel moment change



By the Summer of 2005, Learjet was ready for an internal launch of our new project. It was a design that would have instantly been recognized as a Learjet in both the performance and the external lines. Heritage aluminum structure and classic manual flight control systems would be used in line with all previous models. Newer LJ45 style systems and wing aerodynamics would be combined with a lengthened LJ60 fuselage to create a low-cost successor to the long in the tooth LJ60. It was called various official program names over the next year, but many of the employees liked to call it the Learjet 65.},

keywords = {Aircraft - Commercial},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{3855,

title = {3855. Double-Shell and Sandwich Fuselages for Future Aircraft},

author = {Hans-Peter Dahm},

url = {https://www.sawe.org/product/3855-double-shell-and-sandwich-fuselages-for-future-aircraft/},

year  = {2026},

date = {2026-05-21},

urldate = {2026-05-21},

booktitle = {85th SAWE International Conference on Mass Properties Engineering},

publisher = {Society of Allied Weight Engineers, Inc.},

abstract = {There are several fuselage concepts which show alternatives in comparison to the classical cylindrical fuselage concept. Double-shell fuselages include classic double-bubble cabins, double-D variants, and multi-shell arrangements in which one or more near-cylindrical pressure lobes are enclosed by an outer aerodynamic shell. This paper restructures the topic and describes basic structural-mechanical behavior of double-shell sandwich fuselages. The objective is to determine when shell duplication in a sandwich creates a real mass benefit and when it redistributes mass among pressure skins, outer shells, webs, floors, and reinforcement details. A literature review is combined with a mechanics-based preliminary sizing method and a worked A220-like derived sample calculation. The paper then develops a separate aircraft-level estimate for a concentric circular double-shell sandwich concept manufactured as pre-equipped major shell modules. The approach combines a bottom-up structural mass build-up for the circular double-shell fuselage concept with a top-down aircraft-level fuselage-group allocation for the broader savings assessment. These two approaches serve different purposes and therefore produce different mass values. A future aircraft must integrate cryogenic hydrogen tanks, insulation, battery systems, cable runs, thermal management hardware, and larger secondary systems volumes than conventional kerosene aircraft. The architecture-only estimate yields a net installed mass saving of about 1.28 t. When a conservative transition from a public A220-like mixed-material fuselage baseline to a full thermoplastic-resin CFRP fuselage is added, with overlap correction to avoid double counting, the holistic aircraft-level rises to about 2.01 t. On a 39.0 t class level operating-empty-weight baseline this corresponds to about 5.16% of OEW, while remaining a concept-level result rather than a validated OEM design value. Public thermoplastic fuselage demonstrator results are treated conservatively as weight-positive but recurring-cost neutral relative to a metallic barrel, so the recurring production benefit remains dominated by modular preinstallation and reduced detail count at about €0.30 million per aircraft.},

keywords = {Aircraft - Commercial},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{3844,

title = {3844. Unintentional Lateral Imbalance Calculation Methodology for Freighter Aircrafts},

author = {Alejandro Fiestras Corcho},

url = {https://www.sawe.org/product/3844-unintentional-lateral-imbalance-calculation-methodology-for-freighter-aircrafts/},

year  = {2026},

date = {2026-05-21},

urldate = {2026-05-21},

booktitle = {85th SAWE International Conference on Mass Properties Engineering},

publisher = {Society of Allied Weight Engineers, Inc.},

abstract = {In heavy-cargo operations, lateral imbalance is a silent threat to flight efficiency. This methodology introduces a proactive simulation framework designed to identify and prevent "non-viable" loading states before the process even begins. It specifically targets the complexity of empty positions, leading to scenarios where asymmetrical cargo locking or mechanical failures prevent balanced loading across the aircraft’s roll axis.



The method, based on a published patent (ref [1]), allows the user to explore specific cargo layouts with stochastic weight distributions. The system executes multiple simulations to project the accumulated lateral moment. This allows the method to assess flight feasibility against given limit conditions, even when exact individual weights are unknown a priori.



Key Technical Advantages:



- Preventive Risk Mitigation: It establishes a clear "Viable/Non-Viable" binary before any physical loading occurs, preventing potentially inconvenient roll-axis

moments.

- Stochastic Modeling: Uses input probability functions to account for weight uncertainty, ensuring efficiency in real-world conditions where load data is often

uncertain.

- Asymmetrical Failure Analysis: Specifically models the impact of "locked" or disabled cargo locations, turning a complex mechanical limitation into a predictable data point.



This method transforms aircraft loading from a manual estimation task into a data-driven protocol, ensuring that no freighter departs with a lateral moment profile that is not convenient for the airline.},

keywords = {Aircraft - Commercial},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{3827,

title = {3827. Dynamic Mass-Aware Trajectory Tracking of Airships Using Multi-Actors Proximal Policy Optimization},

author = {Rongwei Liang and Duc Thien An Nguyen and Samuel Maimako},

url = {https://www.sawe.org/product/3827-dynamic-mass-aware-trajectory-tracking-of-airships/},

year  = {2025},

date = {2025-05-22},

urldate = {2025-05-22},

booktitle = {84th SAWE International Conference on Mass Properties Engineering},

publisher = {Society of Allied Weight Engineers, Inc.},

abstract = {Dynamic mass variations significantly influence the attitude and trajectory tracking performance of stratospheric airships. To address this challenge, this paper proposes a dynamic

mass-aware control algorithm for airships using Multi-Actors Proximal Policy Optimization (PPO), a deep reinforcement learning framework. We first establish a comprehensive airship dynamics model that explicitly accounts for varying mass characteristics, formulating the state space, action space, and reward function to capture the impact of payload shifts or fuel consumption on flight stability. Multi-Actors PPO, leveraging a clipped probability ratio objective, enhances policy update stability and data efficiency in the presence of mass disturbances.  Neural networks are employed to approximate the policy and value functions, while Generalized Advantage Estimation (GAE) further boosts optimization performance. Preliminary analyses under diverse flight conditions and dynamic mass scenarios suggest that the proposed approach can significantly outperform traditional controllers such as PID and LQR in terms of trajectory tracking accuracy and robustness. Consequently, it offers an effective and stable solution for dynamic mass-aware intelligent control in unmanned airship systems.},

keywords = {Aircraft - Commercial},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{3791,

title = {3791. Reverse Engineering the Mass Properties of a Civil Aviation Aircraft},

author = {Darrin McCloud},

url = {https://www.sawe.org/product/paper-3791},

year  = {2023},

date = {2023-05-20},

urldate = {2023-05-20},

booktitle = {82nd Annual Conference, Cocoa Beach, Florida},

pages = {22},

publisher = {Society of Allied Weight Engineers, Inc.},

address = {Cocoa Beach, Florida},

abstract = {In Mid-2017 I started my first project taking a certified civilian aircraft and turning it into a special mission aircraft while working in a small consultant company. This was not a small project, it involved numerous airframes and significant aerodynamic and secondary structural modifications in addition to a completely new cabin layout with equipment installed throughout the cabin. This project was being run and integrated by a large, well known US company, but they subcontracted out the aircraft portion, including structural modifications and certification to a smaller Modification Center company. Due to contract issues, the Original Manufacturer (OEM) would not be supporting any of the modification efforts. My company, which specializes in static and dynamic loads certification, was subcontracted for Loads certification and would need to have complete aerodynamic and mass properties data for both the standard and modified aircraft to be able to show compliance with all the applicable Federal Airworthiness Regulations (FARs). As the sole mass properties engineer on the program, I would be entirely responsible for creating detailed mass properties for an aircraft while only using the paperwork that comes with a customer aircraft and any public information available on the internet or in print. This paper will document the system that was devised, and has continued to be used on numerous other projects, where detailed mass properties data is needed for customer certification issues without the benefit of any OEM engineering reports.},

keywords = {Aircraft - Commercial},

pubstate = {published},

tppubtype = {inproceedings}

}