1. Duringthe early 1970% asmallhypersonicwind tunnel designedto performaerodynamicandflutter testing at Mach 10 in air and designated as the Hypersonic Flow Apparatus (HFA) was relocated within Langley. First operated in 1959 in what is referredto asthe eastarea ofthe LangleyResearch Center, thisfacilitywas movedto thewest areaand housedinthe building containing the Unitary Plan WindTunnelandthe 31-InchMach 10Tunne 116-i7i8 (formerlythe Continuous Flow HypersonicTunnel). Theprimaryreasonforthismovewasforthe HFAto augment the 31-Inch Mach 10Tunnel by providing complementary flow visualization capability, principallyviaschlierenorshadowgraph. The 31-Inch tunnelemploysaside-mountedinjectionsystemand has limited optical access, thereby precluding the utilization of conventional-type schlierenlshadowgraph systems. The HFAwas essentially inactive fromthelate 1970'stothe mid-1980's.
2. When the National Aero-Space Plane (NASP) TechnologyMaturationPlanwasinitiated inthe midto-late 19803, it was realized that all four basic simulationparametersprovidedby hypersonicwind tunnels (Le. M, as an indicator of compressibility effects, R, for viscous effects, y to simulate this aspectof arealgas,andTdaWasanindicatorofthe thermal driver potential) were needed to develop NASPtechnology. Ideally, experimentalists would likethecapabilitytovaryMachnumber,while holding the otherthreeparametersnearlyconstant. Testing inthe 20-Inch Mach 6 Tunnel (which had become schedulesaturated)andthe 31-InchMach 10Tunnel providessuchavariationinM, for agivenR, andy, but TWIT, variesby afactorof 2. Becauseof the inability to maintain a constant value of TWITa, betweenMach 6 and 10without coolingor heating
3. Thetestgasisheatedtoamaximumtemperatux^'dof approximately 1460"Rbya 1.25MWACelectrical resis!ance heater. The test gas flows through 216 'J electricaliy 3ieated Inconel tubes, each having an insidediameterof 037inchandanoutsidediameter of 0.44inch The heater ismeunted vertically to accommodate thermal expansionf thswbes and locatedoutsidethe buildingas seeninfigurerT h e I flow rate through the heater ranges from approximately 3 to 16 Ibmlsec for typical run concliiions. Theheater,settlingchamberandnozzle aredesjgnedfcr 2maximumtemperatureof 2060W. Figure 4. ElectricalResiiiam?Heater