Structural Analysis and Loads Prediction Facilities

Test facilities have an important role in verifying and improving anal­ysis methods. A few test facilities that had a lot to do with the devel­opment and validation of structural analysis methods are described below. In addition to those described, other "landmark” test facilities include large-scale launch vehicle structural test facilities at Johnson and Marshall Space Centers, and the crash dynamics test facility at Langley Research Center.

Structural Dynamics Laboratory (Ames Research Center, 1965)

During the 1960s, Ames and Langley collaborated on some of the struc­tural dynamics and buffet problems of spacecraft during ascent. (This collaboration occurred through some of the same meetings at NASA Headquarters that led to the development of NASTRAN.) To help assess the structural dynamic characteristics of boosters, and to build confi­dence in predictive methods, a large structural dynamics test facility was built at Ames (completed in 1965). This facility was large enough to hold a full-size Atlas or Titan II, had provisions for exciting the struc­tural modes of the test article, and could be evacuated to test the struc­tural damping characteristics in zero or reduced ambient air density.[1005] The facility was also used for research on buffet during reentry and land­ing impacts.[1006] Much of the structural dynamics research at Ames was discontinued or relocated during the early 1970s. The laboratory is long since deactivated, but the large, pentagonal tower still stands, housing a machine shop and a wind tunnel that can simulate Mars’s atmosphere by evacuating the chamber and then filling to low pressure with CO2.[1007]

Thermal Loads Laboratory (Dryden Flight Research Center, 1960s)

A 1973 accounting of NASA research facilities listed only one major ground laboratory at Dryden: the High Temperature Loads Calibration Laboratory.[1008] High supersonic and hypersonic flight research created a need (1) to test airframes on the ground under simultaneous thermal and structural loading conditions and (2) to calibrate loads instrumen-

tation at elevated temperatures, so that the data obtained in flight could be reliably interpreted. These needs " . . . led to the construction of a laboratory for calibrating strain-gage installations to measure loads in an elevated temperature environment. The problems involved in mea­suring loads with strain gages. . . require the capability to heat and load aircraft under simulated flight conditions. . . . The laboratory has the capability of testing structural components and complete vehicles under the combined effects of loads and temperatures, and calibrating and evaluating flight loads instrumentation under [thermal] conditions expected in flight.”[1009]

The laboratory is housed in a hangarlike building with attached shop, offices, and control room. Capabilities included:

• Hangar-door opening 40 feet high by 136 feet wide.

• Unobstructed test area 150 by 120 by 40 feet allowed the testing of aircraft up to and including, for example, a YF-12 or SR-71.

• Ten megawatts of electrical heating power via quartz lamps and reflectors.

• Temperatures up to 3,000 °F.

• Hydraulic power of 4.5 gallons/minute at 3,000 pounds per square inch (psi) to apply loads.

• Fourteen channels closed-loop load or position control of up to 34 separate actuators.

• Sensors including strain gages, thermocouples, load cells, and position transducers.

Slots in the floor provided flexible locations for tiedown points, as well as routing for hydraulic and electrical power, instrumentation wir­ing, compressed air, or water (presumably for cooling). Closed-loop ana­log control of both mechanical load and heating was provided, to any desired preprogrammed time history.

The facility was used in the YF-12 thermal loads project (discussed elsewhere in this paper), in Space Shuttle structural verification at high

temperatures, and for a variety of other studies.[1010] The loads laboratory made contributions to the validation of computational methods by pro­viding the opportunity to compare computational predictions with test data obtained under known, controlled, thermal and structural load­ing conditions, applied together or independently as required. At time of this writing, the facility is still in use.[1011]