Mechanical Components

Hybrid Three-Axis Vibration Reducers

Hybrid (passive/active) devices have been developed to reduce the magnitudes of possibly threedimensional vibrations coupled from vibrating equipment on platforms to bases that support the platforms. These hybrid devices are three-axis generalizations of singleaxis hybrid vibration reducers developed and reported previously. Each hybrid device includes rubber passive vibration-isolator pads, piezoelectric actuators, optional piezoelectric force sensors, and accelerometers. Each device operates in conjunction with a computer and control-and-actuation circuitry, which process accelerometer readings using feedforward and/or feedback control laws to excite the piezoelectric actuators with signals having amplitudes and phases chosen to minimize acceleration of the base.

Posted in: Briefs, Mechanical Components, Vibration
Read More >>

Some Advances in Reducing Drag and Suppressing Convection

Theoretical and computational research has yielded some advances in the art of designing active feedforward and feedback controllers to suppress thermal convection and reduce drag (by suppressing turbulence) in boundary-layer flows. The advances include (1) improved means for designing reduced-order (and, hence, computationally more efficient) controllers and (2) discovery of a previously unknown phenomenon that could be exploited for feedforward control to reduce drag.

Posted in: Briefs, Mechanical Components, Electronic control systems, Drag
Read More >>

Simulations of Stall and Stall Control in Turbocompressors

Anumerical-simulation study of stall and stall control in radial and axial compressor stages of gas turbine engines has been performed. This and other similar studies are needed because even though the adverse consequences of stall are well known and rudimentary stall-warning and stall-control systems are in use, the scientific basis for predicting and mitigating stall is not yet established.

Posted in: Briefs, Mechanical Components, Simulation and modeling, Compressors, Gas turbines
Read More >>

Thrust-Augmented Nozzles for Rocket Engines

The thrust-augmented nozzle (TAN) has been invented as a means of obtaining high performance from a rocket engine both during liftoff at sea-level atmospheric pressure and later during flight under near-vacuum conditions. In effect, the TAN rocket engine amounts to a booster rocket engine contained entirely within a sustainer rocket engine, and very little weight is associated with the incorporation of the TAN portion. Heretofore, it has been difficult or impossible to design the same rocket engine to perform well at both extremes of ambient pressure.

Posted in: Briefs, Mechanical Components, Performance upgrades, Nozzles, Booster rocket engines, Reliability
Read More >>

Thermal Design and Analysis of a Rocket-Engine TAN Injector

A subscale thrust - augmented - nozzle (TAN) rocket engine was designed, built, and hot-fire tested to demonstrate the validity of the TAN concept. As described in more detail in the immediately preceding article, in a TAN, during operation at sea level, thrust is augmented through injection and burning of secondary propellants (a fuel and an oxidizer) within the nozzle, downstream of the nozzle throat. The secondary propellants can be the same as, or different from, the primary propellants (the fuel and oxidizer burned during operation, in a near vacuum, in the absence of thrust augmentation).

Posted in: Briefs, Mechanical Components, Propellants, Nozzles, Booster rocket engines, Fuel injection
Read More >>

Near-Precision Soft Landing Resupply Dispenser

AFRL munitions experts teamed with engineers from Systima Technologies, Inc., under a Small Business Innovation Research (SBIR) contract to develop a Covert Resupply (COVRES) dispenser. The team based its design on an existing Wind- Corrected Munitions Dispenser (WCMD™). The COVRES system, which will enable air delivery of critically needed supplies to troops who are under fire or otherwise isolated, uses the novel employment concept illustrated in Figure 1. As shown, the event sequence begins with (A) high-altitude release, and progresses as follows: (B) a WCMD tail unit provides nearprecision inertial guidance, (C) a drogue chute deploys 25 seconds prior to ground impact, (D) the drogue chute deploys the main parachute, (E) a crushable nose minimizes landing shock, and (F) quickrelease clamps enable easy access to the cargo.

Posted in: Briefs, Mechanical Components
Read More >>

Blended Wing Body Aircraft

Scientists from Boeing Phantom Works, the National Aeronautics and Space Administration (NASA), and AFRL are testing a new aircraft with the potential to realize up to 30% better fuel efficiency because of its unique "flying-wing" shape. The prototype blended wing body, or BWB, aircraft is a modified, triangular-shaped aircraft configuration with 20 control surfaces along its trailing edge. Researchers believe the BWB configuration will produce better fuel efficiency because a greater portion of the aircraft is involved in producing lift. The additional lift stems from the replacement of the conventional tube-shaped aircraft fuselage with the more aerodynamically efficient wing centerbody.

Posted in: Briefs, Mechanical Components
Read More >>

Improved Accuracy of Computational Fluid Dynamics Calculations

Understanding how air flows over the surfaces of an air vehicle can help AFRL designers maximize the vehicle's performance and minimize its cost. AFRL scientists recently developed a tool that improves the accuracy of airflow simulations that result from computational fluid dynamics (CFD) calculations. As part of a Small Business Innovation Research effort, AFRL collaborated with Combustion Research and Flow Technology (CRAFT), Inc., to develop the tool for use with unstructured CFD programs. The new tool uses the solver's initial solution to determine where grid points should be added or removed within the CFD mesh, a process which then improves the solver's solution in a second—and any subsequent—iteration. This enhanced accuracy improves AFRL's ability to support the warfighter with lower-cost, higher-value designs.

Posted in: Briefs, Mechanical Components
Read More >>

Remote-Controlled Aerial Vehicle for Application of Pesticides

AFRL demonstrated its Remotely Controlled Aerial Vehicle for Application of Pesticides (RCAVAP) at the Force Protection Equipment Demonstration (FPED) conducted at Quantico Marine Corps Base, Virginia. During times of war, disease has historically caused more deaths than bullets, far outnumbering any other cause. Consider, for example, the Mexican-American war. Over 1,000 soldiers were killed in action, 529 died of wounds sustained on the battlefield, 362 suffered accidental death, and 11,155 perished from disease— mostly yellow fever, a viral illness transmitted by the Aedes aegypti mosquito. During World War II, malaria ravaged the troops. Spread by the female anopheline mosquito, the disease affected thousands of American soldiers. More recently, a single 2-week period in Baqubah, Iraq, saw 250 cases of cutaneous leishmaniasis, a disfiguring parasitic disease spread by the female sandfly.

Posted in: Briefs, Mechanical Components
Read More >>

AFRL Proves Feasibility of Plasma Actuators

AFRL is laying the groundwork for the development of revolutionary hypersonic aerospace vehicles (see Figure 1). Accordingly, AFRL engineers are examining the feasibility of replacing an air vehicle's traditional, mechanically or electrically actuated flight control surfaces (e.g., wing flaps) with plasma actuators that require no moving parts and are therefore potentially less expensive and more reliable. As part of the laboratory's Boundary Layers and Hypersonics program, the engineers conducted a wind tunnel test to evaluate the feasibility of using plasma actuators for airframe flight control.

Posted in: Briefs, Mechanical Components
Read More >>