Air Vehicle Configuration Design
Air vehicle configuration design leverages the talents and requirements of many disciplines. Configuration designers need to be able to balance multiple conflicting quantitative and qualitative requirements in a way that:
- Informs critical trades while retaining options
- Differentiates appropriately between requirements and ‘desirements’ (the so-called ‘nice to have’)
- Tracks the myriad of changes that occur through even the shortest design process
- Maintains positive control and definition of the configuration selections and the criteria that lead to them
Recent advances in capability and applications for UAV configurations bring new opportunities and challenges to the configuration designer. The opportunity is to take advantage of both the direct capabilities inherent to this new technology and the indirect benefits from changes to existing requirements (for example, not providing a survivable environment for a human pilot). The challenges are to make sure the design space and criteria accurately capture the changes that come with these new, sometimes wildly different, technologies.
A key element for success is a robust process to identify critical criteria and to track their sources. A design limited by outdated criteria can be just as inefficient as one that does not leverage a new capability.
One of the traditional metrics for the capability of a configurator is the number of programs to which they have contributed. Sensible given that longer experience provides direct exposure to the design process. This includes the work involved, what worked with similar past programs, what didn’t work (actually the most important of the two), and the reasons why.
But, I think there is another metric now that new configuration possibilities are expanding to include radically different configurations. This is the breadth of different capabilities/missions/requirements your configuration team has seen. Working with many different vehicle types doesn’t just provide understanding of those specific types—the experience provides deeper insight into the meaning of the criteria and requirements that go into all of those types. That experience is invaluable when approaching any other configuration, including those that are different than ever seen before.
At TLG, our design team has experience with air and space vehicles ranging from sub-2-lb hand-launched observation platforms to the largest air vehicles in flight today, and everything in between. Plus, add space systems. Plus, add underwater and road vehicles, and even the occasional rail car. It’s what we do every day.
Our team understands not just what it does but also why it works and what the requirements are for it to be suitable for your needs. We have methods to track criteria, requirements, and configurations scalable to fit any configuration design effort.
Connect with the author:
TLG’s Director of Engineering, FAA Flight Analyst DER, and FAA Flutter DER, Robert Lind.
#TLGAerospace #EngineeringExcellence #AerospaceEngineering #AircraftDesign #AirVehicleConfiguration #SystemsEngineering #UAVDesign #AirVehicleConfigurationDesign
Interdisciplinary Foundations of Flutter: Insights from the Aeroelastic Triangle
Aeroelastic characteristics are defined by the interaction between structural dynamics and the incremental aerodynamics developed by the deformed surfaces. A standard depiction of this interaction is the aeroelasticity triangle. This one is from the classic text ‘Aeroelasticity’ by Bishplinghoff, Ashley, and Halfmann, universally called ‘BAH’:
A gratifying result for us Flutter enthusiasts is that Flutter appears front and center, involving all three elements. You can imagine flutter folks saying, ‘pity the poor analyst whose dominion only encompasses one or two of these disciplines!’ Of course the triangle puts the flutter engineer at the center—we made it! You could just as easily invent a diagram that puts us on the outside, and any other discipline you like in the middle.
But the diagram does indicate you need these three items working together for the dynamic instability of flutter:
- Elastic structure that deforms under load
- Aerodynamics that are affected by that deformation
- Weight to provide dynamics through mechanical vibrations
An interesting aside is that you don’t need weights to calculate static structural deformation under aerodynamic load, only stiffness and aerodynamics. Most aerostructure tools (including Nastran) take advantage of this simplification to formulate their static aeroelastic solutions.
You might be wondering: Which types of configurations are most likely to encounter flutter? Well, you need a structure that deforms under load in such a way that significant incremental aerodynamic forces result. For significant forces, you generally need a lifting surface, since fuselage and other non-lifting surfaces generally have low lift curve slopes by comparison. And you need the structure to deform in a way that develops this load. That leads to a few high-impact configurations:
Swept-back wings. Wings under load bend in the direction of their ‘elastic axis’, which is generally in a spanwise direction. For swept-back wings, this bending also results in an aerodynamic torsion load because of the difference between the bending direction and the airflow direction. This couples structures and aerodynamics in a significant way and is the most classic flutter example. Swept-forward wings are more stable in flutter for an equal and opposite reason.
Control surfaces. Maybe your bending-torsion coupling isn’t powerful enough to flutter? Add a trailing edge control surface like an elevator, rudder, or aileron. Tailor-made for the job, control surfaces convert physical rotation into aerodynamic force, and inertial coupling between the lifting surface (wing/stabilizer/whatever) does the rest. This should be the poster child for Flutter, probably 90% of a Flutter analyst’s work involves trailing-edge control surfaces.
Body effects. For most historical airplanes, fuselage effects were considered unimportant. So much so that an airplane’s wing and tail flutter effects were often calculated independently. But even then, this wasn’t quite true. Aft fuselage torsion and side bending contribute to vertical fin/rudder flutter for even those classic configurations. And from there we have more esoteric effects:
- Slender fuselages that allow coupling between wing and tail modes
- Short stubby fuselages that allow coupling between wing bending and the airplane’s short-period mode, so-called ‘body freedom flutter’
- Unique configurations like twin-boom airplanes. These fuselage modes are coupled with wing torsion and bring a new dimension to flutter characteristics
Gyroscopic precession. In the 1930s, mathematicians and aeronautical engineers found a unique issue. Propeller/engine/mount installations are subject to precession, just like a spinning top. I loved watching my toy tops in precession when I was a kid, it was such an interesting motion. If a propeller is spinning at the end of the ‘top’, the resulting unsteady aerodynamics are destabilizing. In the 1930s, this was a mathematical special case and not a practical issue. That was because the rotating inertia of the current engines was nowhere near enough to make the coupling dangerous. It took until the 1960s for turbopropeller installations to provide enough inertia to cause actual flutter in airplane flight envelopes. And so ‘whirl flutter’ was born.
Next up in our Flutter series, we’ll look at some specific examples of these different types of Flutter.
Connect with TLG’s Director of Engineering, FAA Flight Analyst DER, and FAA Flutter DER, Robert Lind.
Check out our last article on Flutter: Understanding Flutter: The Feedback Loop Behind Aerodynamic Stability in Aircraft
#TLGAerospace #TLGFlutterSeries #Aeroelasticity #FlutterAnalysis #AircraftStructures
Meet TLG’s Aerodynamics Team
TLG’s Aerodynamics group is at the forefront of innovation, applying state-of-the-art capabilities across various flight sciences disciplines. Stay tuned in the coming weeks for a deep dive into each of our capabilities, including:
- New Aircraft Design: Systems Engineering, Aerodynamic Configuration
- Shape Design: Wings, Airfoils, Highlift Systems, Bodies, Nacelles, Pylons, Auxiliary Cooling Systems, …
- Computational Fluid Dynamics (CFD): Multi-fidelity, Aero Database, Forensic Analysis, Steady, Unsteady, Multiphase, Aeroelastic
- Performance, Handling Qualities, Stability, and Control
- Flight Dynamics Simulation, Store Separation
- Decompression Analysis
- Component Icing Analysis
- Wind Tunnel Testing
- Flight Testing
- Laser Scan (Aerodynamicist-Led Metrology Surveys)
From new aircraft design and shape optimization to performance analysis, wind tunnel testing, and flight dynamics simulations, our team’s expertise is informed by practical experience and understanding of the product life cycle from concept inception to certification.
Our team excels at tailoring the right level of precision to each project, making our small but skilled team a trusted partner for clients ranging from innovative start-ups to established organizations.
Meet our Team:
Andrew McComas
Andrew is TLG’s Chief Aerodynamicist and has led the design of numerous flight-proven systems, including new aircraft configurations, special missions, and performance-enhancing modifications. The speed range of flight-proven designs spans Mach 0 to 5 and includes experimental aircraft, GA, transport, UAS, after-market STCs, and OEM factory hardware.
Reid McCaul
Reid is TLG’s Flight Sciences Lead and FAA Flight Analyst DER, and is an expert in aircraft performance, handling qualities, flight operations, test planning, certification, and flight safety management. Reid has over 1,200 on-aircraft experience as a test director or data analyst, contributing to numerous STCs, and brings that criteria-focused approach to his design and analysis projects.
Dr. Peter Burns
Peter is TLG’s CFD Lead and was the Aerospace Global Technical Specialist for Siemens PLM Software covering the STAR-CCM+ CFD software segment before joining TLG. Peter’s deep expertise combined with TLG’s methodical approach to best practices and quality assurance means that TLG CFD is fast, robust, high-quality, traceable, and appropriately documented. CFD analysis at TLG is informed by TLG’s extensive applied and experimental aerodynamics expertise.
Connect with TLG’s Chief Aerodynamicist, Andrew McComas, to learn how we can support your program’s success.
Understanding Flutter: The Feedback Loop Behind Aerodynamic Stability in Aircraft
Flutter is the engineering study of potentially unstable interactions between the aerodynamic forces on an air vehicle and the deformation due to those forces. The formal name for these studies acknowledges interaction in ‘aeroelastic stability’ by combining the terms ‘aerodynamic’ and ‘elasticity’.
All flight vehicles experience forces due to traveling through the air. This is a requirement for aircraft because it generates the lift that keeps the airplane in the sky (as well as the drag that must be overcome by engine thrust).
But there’s more going on outside that airliner cabin window. The airplane deforms under those loads like bending and twisting a stick or a straw. Thinner wings generally deform more than thicker ones, and fuselages usually deform the least, but they all deform under load. That change in shape affects the aerodynamic forces. But those forces were causing the deformation in the first place, so now the deformed shape is different. And the aerodynamic forces are different again, and so on. We call this a ‘feedback loop’. Flutter is the study of whether this feedback loop is stable or unstable. A stable response converges to a final static state. An unstable response, once started, will grow on its own until the structure breaks.
Every airliner trip you have taken has been on a flutter-free airplane. Have you looked out the window and seen the wing shaking in turbulence? This is the airplane’s dynamic response to the unsteady gusts of air. When the turbulence stops, the wing stops shaking. That is a stable response to the gust input.
Here are two examples. In the first clip, this NASA experimental airplane is intentionally flown close to a flutter boundary speed. You can see the tail starting to deform. In the second clip, you can see the wings of a glider bending and twisting at high speed.
Lighter-weight structures may flutter more easily, but lightweight is not a requirement. The most famous flutter example is the Tacoma Narrows Bridge across Puget Sound. The bridge shape allowed for unstable coupling with the wind, and the bridge tore itself apart not even a year after it was finished:
Flutter engineers analyze the airplane using mathematical models of the structure and the aerodynamics. Airliners must be free from flutter throughout the ‘flight envelope’ – all speeds and altitudes at which the airplane is designed to operate – including a ‘dive’ margin for accidental overspeeds, and a 15% additional margin on top of that. All possible loads of passengers/cargo/fuel must be considered in addition to a laundry list of ‘non-normal’ conditions, including equipment or structural failures. Ground and flight test campaigns validate the analysis data and provide the final demonstration of safety.
Next time you ride through turbulence, you can watch the wing flex and know that motion has been thoroughly evaluated by flutter engineers.
TLG Aerospace specializes in aircraft flutter analysis and certification. We help ensure aircraft are free from flutter across all configurations and conditions for flight safety and compliance with airworthiness standards.
Our services include ground and flight testing, as well as advanced modeling techniques like Finite Element Models (FEM) and Computational Fluid Dynamics (CFD) to validate structural and aerodynamic data. TLG also conducts Ground Vibration Tests (GVT) to assess structural vibration modes and simulate failure scenarios.
Our series on Flutter will be expanded in the coming weeks with discussions on various types of Flutter.
Connect with TLG’s Director of Engineering, FAA Flight Analyst DER, and FAA Flutter DER, Robert Lind.
Structural Analysis at TLG
Aircraft Internal Loads Model and Bird Strike Simulation
Structural analysis is essential to achieving mission success in the aerospace industry, where precision and reliability are non-negotiable. Founded in 2008, TLG Aerospace’s addition of stress and design in 2014 enabled us to support the entire iterative aircraft design cycle, from initial concept development to final certification.
Our solutions empower innovators to design confidently, tackle complex challenges, and achieve breakthroughs in an industry that reaches for the sky and beyond.
We conduct aircraft structural analysis using a combination of classical methods and numerical simulation tools to evaluate and optimize the sizing of structural components.
TLG uses several of the latest industry-leading simulation applications. We can run a comprehensive range of simulations, including linear static, modal, buckling, frequency response, thermal, implicit, and explicit nonlinear.
TLG’s Structural Analysis Services also include:
- Metallic and Composite Analysis and Formal Reports
- Composite Material Property Development
- Static, Fatigue, and Damage Tolerance Analysis
- Continued Airworthiness Documentation
- Support in-service Major Repairs and Alterations
- Ground Test Planning, Support, and Analysis
Benefits for Aero and Space Sector Applications:
- Design Optimization: Develop stress distributions in critical components like fuselages, wings, or spacecraft structures, helping to ensure maximum performance in extreme conditions.
- Cost Savings: Optimize material usage in lightweight designs that still stand up to the immense pressures of flight and space environments.
- Enhanced Safety: Deliver spacecraft, aircraft, and satellites that meet rigorous safety standards, minimizing the risks associated with high-stakes missions.
- Innovation Support: Push the boundaries of aerospace technology—whether it’s reusable rockets, next-gen satellites, or supersonic aircraft—knowing your designs are fortified by advanced analysis.
Our expertise in stress analysis empowers your projects to withstand the demands of atmospheric reentry, microgravity environments, and everything in between. TLG is your trusted partner to build stronger, smarter, and safer aerospace solutions.
Contact our Business Development Director, Tommy Gantz, or Engineering Manager, Ian Draycott, to discuss how TLG can help your project goals.
Let’s collaborate. Contact Tommy Gantz, our Business Development Director, or Ian Draycott, our Engineering Manager, to discuss your project.
Design Engineering at TLG
TLG’s Design Engineering Team leverages our extensive industry experience to deliver robust and certifiable products for all aerospace applications. Our dedicated design team supports your product development at every stage, from conceptual design through final design and into production.
We enable a seamless transition from concept to reality. At TLG, our design team has experience supporting new vehicle concepts, major/minor modifications, and Supplemental Type Certificates (STCs) for Part 23 and 25 aircraft and various spacecraft.
We have successfully delivered engineering support to our customers on over 50 projects worldwide.
Types of Projects include:
- Aerial Firefighter Tanker Conversions
- Passenger-to-Freighter Conversions
- Radome and Antenna Modifications
- Aerial Dispersant Conversion
- Spacecraft & Launch Vehicle Primary and Secondary Structures
- Spacecraft & Launch Vehicle Systems Design and Systems Routing
- Float Plane Development
- Wind Tunnel Model Design and Testing Support
- Material Trade Studies
- Production Support & Liaison
- BOM/EAMR Preparation
- Repair Design
- STC Modifications
- Submarine Systems
- Design & Drawing Reviews
- Technical Publication Creation & Revision
- Supplemental Technical Publications/Instructions for Continued Airworthiness
- Weight Reduction / Manufacturing Improvement
- Special Misson Modifications
Our Design Team Makes Your Team Stronger! Our team has:
- An average of 15 years of industry experience
- Level 2-4 Designers with 5-25 years of specialized knowledge
- Extensive aircraft expertise from Tier 1 suppliers, MROs, and OEMs including Boeing, Airbus, and Lockheed Martin
- Capabilities spanning Widebody & Narrowbody Commercial, Military, Regional Jet, General Aviation, and Special Missions
- Work permits for countries within the European Union
- Diverse backgrounds in structural design
Proficiencies include:
- Catia V5 and V6/ 3DExperience
- ENOVIA LCA & ENOVIA SmartTeam
- On-Premise 3DX PLM/PDM (Enables Secure Customer Data Management)
- CREO/Windchill
- SolidWorks
- Siemens NX / Teamcenter
- Boeing Drawing System (MyFleet, etc.)
- Jira
- MS Project Suite
- Aircraft Conceptual & Preliminary Design
- Certification Test Article Design
- NDI Methods Development
- Ergonomic Design Practices
- Lightning Protection
- Seal Application Requirements
- Aerodynamic Surface Modeling and Lofting Methodology
- Reverse Engineering (3D Scan to CAD Conversion)
- Composites Design & Manufacturing (including 2D, 3D MBD, Manual Ply, Zone-to-Ply, Grid Design)
- Metallic Design & Manufacturing (Sheetmetal & Machining)
- 3D Functional Annotation and Tolerancing (FT&A)
- Spacecraft, Military, and Commercial Vehicle Primary/Secondary Structure Development
- Reverse Engineering/Digital Twin
- Weight/Cost Reduction Savings Trade Studies
- 2D Drafting to ASME or Customer Specifications
- Design Review and Drawing Redlining by TLG Senior Engineers
Contact us by emailing Tommy Gantz to discuss your design engineering project goals.
Connect with TLG’s Design Engineering Manager Jeff Barnes.
TLG’s Designated Engineering Representatives (DERs)
TLG Aerospace provides aerospace engineering services from concept development through certification. We are distinguished by our FAA certification experience, notably featuring five Designated Engineering Representatives (DERs).
Our DERs, authorized by the FAA, provide specialized technical reviews and approvals across key engineering disciplines including loads, flight analysis, flutter, and structures.
Our in-house certification expertise significantly streamlines the design-build-certification process for clients. With these experts embedded within our engineering team, TLG offers clients efficient and direct access to critical certification approvals, facilitating a smoother and more predictable path to FAA compliance.
Contact TLG today through Tommy Gantz to further discuss how TLG’s experience can best support your project’s certification requirements.
Connect with TLG DERs: Steve Muenzberg | Robert Lind | Ian Draycott | Josh Sementi | Reid McCaul
TLG presented at AIAA SciTech 2025
Peter Burns presented a paper “Automated Method for Rapid Estimation of Aeroelastic Wing Shapes – TLG StarBeam” at AIAA SciTech on January 7, 2025. which he co-authored with Andrew McComas and Andy Magstadt. The topic was TLG Aerospace’s internally developed code ‘StarBeam’ which brings aeroelastic capability within our workhorse CFD code Star-CCM+.
StarBeam couples a structural solver and a mapping algorithm using a STAR-CCM+ macro capability. The structural solver calculates deformations under load and the mapping algorithm transfers those deformations to the CFD grid in a physically realistic way. The CFD solution provides results for the deformed structure and the solution iterates to convergence.
The tool was developed by and for our TLG industry aerodynamicists and structural dynamics experts and contains useful features often unavailable in other tools and codes. These capabilities help TLG efficiently and accurately drive our analysis and engineering evaluations for customer programs:
- Ideal for early stages of a project
- Elastic wing shape is needed to enable structural design and inform CFD and wind tunnel models
- Calibrated aeroelastic model may not exist yet
- Beam properties or stiffness matrix from higher-order FEM
- Loads Reference Axis (LRA), approximate rib plane locations and orientations, incremental fuel load
- Splining is fully automatic and robust
- Appendages rigidly translate and rotate about their attachments
- Performs fully non-linear large deflections process in a single execution
- Classical methods require manual iteration of the model to address large deformations
It’s terrific we spoke on this particular effort and highlighted some of the great work TLG brings to the engineering world. Thank you to Peter for presenting, to Andrew, Peter, and Andy for writing the paper, and to everyone who helped put this process together and use it—and our other tools—every day.
The paper was well received at the conference and we look forward to continuing discussions.
Please connect with our authors: Andrew McComas, Dr. Peter Burns, and Andy Magstadt.
Robert Lind
Director of Engineering
#TLGAerospace | #EngineeringExcellence | #AIAASciTech | #Aerodynamics | #Aeroelasticity | #CFD
TLG Aerospace is Your Trusted Partner for CFD Services
From designing cutting-edge aircraft to predicting aerodynamic performance, computational fluid dynamics (CFD) plays a pivotal role at all stages of the product lifecycle.
Since we were just in the wind tunnel last month (see our post here), we thought it would be fun to discuss how CFD can be used as a virtual wind tunnel. We’re big fans of real-world testing, but we think you get more value when you combine it with CFD-based predictions.
Below are a few of the advantages CFD has over a wind tunnel which make it a complementary tool.
◾ Upfront costs and schedule – Wind tunnel models are expensive and take time to build. These costs pay off once you are in the tunnel, but CFD has a much lower cost and lead time to seeing the first actionable results. Further, CFD allows teams to refine their early-stage concepts quickly, which means a design is much more mature by the time you enter the tunnel.
◾ Maximizing value – During a wind tunnel test campaign, time is a limited resource, and you want to extract the most value you can. Having a good set of CFD-based predictions allows the test engineers to focus on key strategic objectives or to troubleshoot unexpected results. One example is simulating full-scale Reynolds numbers in a low-speed (non-pressurized) tunnel. Full and model-scale CFD results can help the test crew employ techniques to approximate full-scale results.
While software and cloud computing have come a long way, you still need a team that knows how to interpret and deliver actionable results. TLG offers our customers world-class CFD services led by our in-house expert Dr. Peter Burns. Before joining TLG, Peter was the global aerospace technical specialist for Siemens PLM Software supporting their STAR-CCM+ software. Check out Peter and the rest of our leadership team, as well as a complete look at our engineering service offering, at https://lnkd.in/g9i2jwQ7.
To learn more about the CFD capabilities at TLG, check out the links below.
◾ AWS webinar in partnership with Siemens – https://lnkd.in/g5rj2veX
◾ TLG was one of the earliest AWS HPC partners, just check out this case study from 2016! Quite a bit has changed since then, but it is an interesting look back – https://lnkd.in/gvmvhk6Z
Extreme Offset Hinge Line on the DC-3 Rudder
TLG had a great time at #NBAABACE 2023 meeting with our customers and friends, and forming new relationships. We look forward to following up.
One of the highlights of the annual show is visiting the flight line with Robert Lind as there are so many exciting parts and functions of aircraft to learn with an expert at your side. Tommy Gantz and Christy Fields were thankful to share Robert’s excitement and learn more great facts from him during our last day at the show.
Below, Robert summarizes his mission to document some control surface aerodynamic balance concepts at the aircraft display. The DC-3 rudder is an example of an extreme ‘offset hinge line.’ Read on for more from Robert . . .
