FLEDERMAUSER (ger) means "Bats" or "of Bats" and is a registered trademark. The aircraft is inspired by the agile flight characteristics, purposeful appearance and diverse roles of mammals of the order 'Chiroptera'.

  • The Fledermauser is an optionally crewed VTOL aircraft designed to provide multirole organic airpower for austere operations.
  • Primary features include a turbine-electric powerplant, a patented fixed ducted wing VTOL system, an open central payload bay, dual sensor stations and robust quad landing gear. 
  • The unique Fledermauser configuration potentially provides a higher degree of speed, safety, resilience and variable sound mitigation compared to open rotor systems of similar weight and technology level.
  • Utility and Design Patents Pending
  • The Fledermauser aircraft is currently under development by Sierra Technical Services, Inc. in Tehachapi, California.

Primary System Description

Technical Approach

Mature Commercial Enablers

Development risk is reduced by utilizing commercially available enabling components, including:

  • Optional Pilot Flight Control Architecture
  • Turbine Electric Power Generation
  • Distributed Electric Propulsion and Lift
  • Aviation lithium-polymer batteries
  • Electric Ducted Fans

Patented VTOL System

Operational Advantages of the fixed ducted box wing and trailing edge flaperons include:

  • Reduced low frequency structure vibration
  • No Vortex Ring State Hazard
  • Shrouded Fan Debris Safety
  • Quiet Forward Flight
  • Low-Drag VTOL transitions

Modular Component Efficiency

Grouping identical parts to achieve combined aero effects also creates lifecycle advantages:

  • Low-cost fabrication for prototype and test
  • Full scale testing in smaller wind tunnels
  • Reduced discrete part numbers to sustain
  • Increased flight safety through redundancy
  • Lightweight, plug-and-play components to repair and replace

Positive, Timely, Confirmed Feedback

Integrated Concept Design is a process that integrates multiple technologies and systems into a complete concept vehicle, for the purpose of performing specified capabilities. The main utility of an integrated concept design is twofold. First, it facilitates a better understanding of the hard limits of new technology, and the trade space between different systems as priorities evolve during its development – especially when multiple new technologies are being integrated for combined effects.  Second, it provides a firm foundation for explaining the technology to potential users, for the purpose of generating equally clear formative feedback. It is not intended the be  perfect solution at first. But the resulting understanding and prioritization of the trade space, informed by specific positive and negative feedback, minimizes the risks of guesswork and timid design on the road to successful innovation. 

Fledermauser FM1

FM1, scaled to 6 inch diameter Electric Ducted Fans, is the smallest concept design.  The size is driven by the intersection turbine electric generator efficiency, available payload and achievable forward airspeed, compared to other UAS of similar size and expense.

At this scale, it is depicted conducting missions similar to the U.S. Navy MQ-8B, because it provides the closest operational analogy for refining it’s mission potential.  However it would be just as capable for ship-to-shore missions and as a land based asset.

Fledermauser FM2

FM2, scaled to 9 inch diameter Electric Ducted Fans, is the medium concept design.

This size is driven by the minimum space needed to perform unattended CASEVAC missions.  The size also the derives greater efficiency from current hybrid technology, which can be utilized to integrate a broader range of mission systems such as a vertical payload winch. FM2 is depicted performing land-based missions, providing organic airpower to manpower-intensive units that would otherwise have very little. 

Fledermauser FM3

FM3, scaled to 12 inch diameter Electric Ducted Fans is the largest concept design. The size is driven by the size of commercially mature Electric Ducted Fan technology, and the size of turbine electrical generators currently planned by industry leaders for commercial UAM markets.  The payload and internal volume of FM3 makes missions with up to three people possible; expanding it’s utility to civil and commercial applications where safety, speed and resilience are high priorities. 

Development Progress

Sierra Technical Services

Sierra Technical Services, Inc. (STS) designs, engineers, and manufactures composite aircraft and components using next generation materials and processes for government and commercial customers. 

STS Core capabilities:

  • Digital Engineering
  • Low-cost Manufacturing
  • Test & Evaluation

STS Key prior performance includes: 

  • Prime contractor to design, build and support flight test of the 5th Generation Aerial Target (5GAT)
  • Multiple Department of Defense, NASA and Commercial contracts to support the development of systems and components including electric and VTOL aircraft

Trusted Technical Partners

STS is the licensed Fledermauser developer.

As an experienced small business near the innovation-rich Mojave Air and Space Port, STS thrives on building teams of expert technical partners – from small start-ups to traditional aerospace giants – to create solutions for our customers.

STS continually integrates feedback from experienced commercial and military users to improve the utility and flexibility of Fledermauser technology.

Similarly, as specific opportunities to develop Fledermauser emerge, STS is confident in our ability to build a team and implement a system will be scalable, affordable and deliver mission advantages for a specific end user.

Next Steps

Step 1:  Physical prototyping and bench testing of wing components, Computational Fluid Dynamics (CFD) analysis and digital structural analysis were successful.

Step 2: Planned wind tunnel testing on a full-scale wing segment; to improve 1) digital models 2) performance estimates 3) dynamics of the structure and moving parts.   

Step 3: Build three subscale flying prototypes to characterize and mature the control and transition dynamics.

Step 4: With cost, schedule and estimated outcomes for steps 2 and 3 in hand – we are seeking technical, developmental and resource partners who are interested and capable of seeing a Fledermauser threshold prototype through to first flight.