Submersible Engineering And Design
This statement describes the engineering tasks in the form of design, modeling, simulation, and analysis processes to be used prior to and during the construction of the Whisper submersible.
The goal will be to provide engineering design drawings and computer simulations of sufficiently high fidelity so that construction and use of this experimental vehicle may proceed as intended, thus minimizing the developmental and safety risks associated with the fabrication and use of the submersible during production of the film “Whisper of the Blue.”
This statement must also clarify the intended use of the submersible resulting from the engineering development described below. By its very nature, the submersible is considered to be highly experimental and is designed for very limited use anticipated during the filming of Whisper. As such it will require operation by trained personnel and is not intended for production as a commercial or consumer grade recreational craft. Design issues such as structural integrity and vehicle controllability, and consequently pilot safety under adverse maneuvering conditions, are not addressed herein.
The overall work will be broken into four major sub-tasks associated with vehicle design, feasibility testing, and construction. The four major engineering tasks consist of (1) Hydrodynamic Computer Simulation, (2) Propulsion System Design and Integration, (3) Preparation of Pre-Construction Design Drawings, and (4) Vehicle Fabrication. These topics are developed further below.
Hydrodynamic Computer Simulation
One of the most crucial and essential aspects of the submersible’s design will be to obtain a viable description of the vehicle hydrodynamics and response to pilot input. It is quite likely that the original design will have undesirable handling characteristics which must be altered by design modifications. The early development of a dynamic simulation of the vehicle will be crucial in developing a submersible design which will perform as intended and minimize the development risk before fabrication begins.
Hydrodynamic Coefficient Estimation
The hydrodynamic stability and control coefficients of the submersible will be estimated using proprietary software. This will be an iterative process, since the design will be modified until sufficient control authority and stability has been attained. For example, it is likely that the submersible’s vertical stabilizers will require modifications since they possibly offer too much lateral stability and resistance to rolling motion. Possible changes to the external configurations will be made based on these hydrodynamic estimates and the results of six degree-of-freedom computer simulations described below.
Flight Control System Design
A simplified flight control system will be necessary for the evaluation of the submersible dynamics and response characteristics. It would be desirable that prior to filming, we have some expectation as to the submersible’s response characteristics in pitch, yaw, and roll at various flight speeds. The flight control system design will be based upon conventional aircraft multi-axis control formulations and will include vehicle response to stick and rudder pedal input. This will also be required to determine the size and location of canard and elevon control surfaces. Inboard locations are desirable from structural integrity considerations, while outboard locations are preferable from the standpoint of control authority. Issues such as these will be solved in an iterative fashion using the hydrodynamic computer simulation and hydrodynamic estimation methods.
Weight & Balance Estimation
Estimates of the submersible’s weight and inertial characteristics will also require computer simulation to ensure that the final design meets balance and buoyancy specifications. Using a detailed component weight breakdown, vehicle dry weight, center of gravity, center of buoyancy (flotation), and moments of inertia will be calculated with and without human pilot occupancy. From these calculations, fore/aft, port/starboard ballast volumes will be calculated such that neutral buoyancy and vehicle balance can be achieved. During vehicle design and fabrication, sufficient internal volume must be dedicated to these ballast volumes such that each vehicle may be balanced with flotation devices (mono-cell foam) or high pressure gas bottle pressurizing sealed ventable ballast cavities. It is anticipated that gross overall buoyancy and balance may be achieved during the fabrication and assembly process and fine tuning left for onsite location preparation prior to filming. Sufficient latitude must be designed into the configurations such that unforeseen payloads may be accommodated during filming.
Six Degree-Of-Freedom Computer Simulation
Vehicle weight and balance data, center of gravity, center of flotation data, and hydrodynamic coefficient estimates will be combined into existing six degree-of-freedom computer simulations for the submersible. Using previously designed attitude control systems, the dynamic response of the submersible to pilot input will be simulated. Conditions as straight and level flight, banked turns, wing rocks, and barrel rolls will be simulated at various flight speeds. Stick and pedal input to achieve the various maneuvers will also be recorded. This information will be useful in designing the mechanical controls and gearing required for human control of the full scale vehicles.
Propulsion System Design And Integration
The selection of a powerful, yet safe and reliable propulsion system is critical for the success of the project. In order to minimize the risk of this aspect of the design, power calculations will be performed for the submersible using computer simulation. Vehicle drag estimates provided by the proprietary software will be confirmed through the use of existing experimental hydrodynamic data. Using these data, the power required to sustain submerged flight at selected flight speeds will be calculated via computer simulation. At the present time, there appear to be two distinct possible candidates offering the potential of satisfying propulsion requirements. They are hybrid electrical propulsion and standard electrical propulsion.
The hybrid electrical propulsion will come from recently declassified military hardware which is available to the production. The system is very likely to provide more than adequate power for the vehicle and meet our specifications for weight and volume, as well as endurance. The hybrid electrical propulsion will provide an efficient and reliable source of power for the submersible.
Standard electrical propulsion represents a more conservative approach in meeting the propulsion requirements for the submersible. However, it probably will be less desirable from the perspective of providing the required vehicle speeds, weight, endurance, and the logistics of energy storage. Electrical propulsion will require a relatively large and heavy array of submersible batteries with limited storage capability and also the design of an internal turbine or fan assembly.
Submersible Pre-Construction Design
Based upon the results of computer simulations and hydrodynamic design iterations, the submersible airframe will be finalized. Detailed design drawings will be prepared both in composite and component form. Individual drawings will be prepared for the fuselage, wings, and vertical stabilizers. The submersible design represents a very conservative approach from the perspective of structural integrity due to its low aspect ratio wing geometry. There is some concern regarding the vertical stabilizer root bending stresses; however, it is anticipated that the span and area of the vertical stabilizers will be reduced considerably during the design process described above.
Construction Of The Submersible
At present time, we anticipate using standard molded fiberglass, uni-body construction. If possible, the fuselage should be molded as an integral unit with provisions for canopy attachments, engine compartment, ducting, and ballast compartments. Particular attention should be given to all airframe appendages which might incur damage in handling, assembly, and filming. We will fabricate additional units of vulnerable airframe components during the initial fabrication, in anticipation of damage likely to be incurred during filming.
