{"$schema":"nativecad-dfm-pack/1","id":"turbomachinery","title":"Turbomachinery — gas-turbine rotor blades, discs and investment-cast aerofoils","sector":"turbomachinery","version":"2026-09-11","summary":"First-stage HP turbine rotor blade proportions (aero-derivative and industrial-frame classes), fir-tree root and platform geometry, tip-clearance and rotor-speed practice, IN718/IN738LC properties at temperature with a source per value, investment-casting castability limits and the disc/blade tests and tolerances a turbogenerator rotor is held to.","aliases":["turbine blade","turbine","gas turbine","turbomachinery","aerofoil","airfoil","rotor blade","compressor blade","jet engine","turbogenerator","fir tree root","fir-tree root","blade root","turbine disc","rotor disc","nozzle guide vane","stator vane","hp turbine","turbine rotor","investment casting","lost wax casting","superalloy","inconel","in718","in738","turbine rotor blade","hp blade","tip clearance","blade tip","turbine stage","aero-derivative","industrial gas turbine","disc rim","disc burst"],"crossSector":false,"size":"core","sources":[{"id":"boyce-gas-turbine-handbook","title":"Boyce, Gas Turbine Engineering Handbook, 4th ed. (Elsevier/Butterworth-Heinemann)","accessed":"2026-09-05"},{"id":"rolls-royce-jet-engine","title":"Rolls-Royce plc, The Jet Engine, 5th ed.","accessed":"2026-09-05"},{"id":"nasa-sp290-turbine-design","title":"NASA SP-290, Turbine Design and Application (Glassman, ed.)","accessed":"2026-09-05"},{"id":"donachie-superalloys","title":"Donachie & Donachie, Superalloys: A Technical Guide, 2nd ed. (ASM International)","accessed":"2026-09-05"},{"id":"asm-handbook-vol15","title":"ASM Handbook Vol. 15 — Casting (investment/shell casting of superalloy aerofoils)","accessed":"2026-09-05"},{"id":"specialmetals-in718","title":"Special Metals Corporation, INCONEL alloy 718 Technical Bulletin (SMC-045)","url":"https://www.specialmetals.com/documents/technical-bulletins/inconel/inconel-alloy-718.pdf","accessed":"2026-09-05"},{"id":"in738lc-published-data","title":"IN-738LC published gas-turbine-literature and OEM material data sheets (Cannon-Muskegon / PCC Structurals cast superalloy data)","accessed":"2026-09-05"},{"id":"ici-design-guidelines","title":"Investment Casting Institute, Investment Casting Design Guidelines","accessed":"2026-09-05"},{"id":"beeley-smart-investment-casting","title":"Beeley & Smart, Investment Casting (IOM3/Maney)","accessed":"2026-09-05"},{"id":"mcdp-investment-casting-guide","title":"Metal Casting Design & Purchasing, \"Investment Casting\" design guide","accessed":"2026-09-05"},{"id":"api-616","title":"API Standard 616 — Gas Turbines for the Petroleum, Chemical and Gas Industry Services","accessed":"2026-09-05"}],"entries":[{"id":"hp-blade-aeroderivative-scale","kind":"dimension","tier":1,"title":"First-stage HP rotor blade scale — aero-derivative class","summary":"A 40 klbf-class aero-derivative core's first-stage HP rotor blade: hub radius ~330 mm, span ~60 mm (span:hub ~0.18), ~80 blades on the disc.","applies":["turbine blade","hp turbine","aero-derivative gas turbine","turbogenerator"],"value":{"table":[{"param":"hub radius","mm":330},{"param":"blade span","mm":60},{"param":"blade count","count":80}]},"basis":"Representative dimensions for a 40 klbf-class aero-derivative core's first HP stage: small hub, short span, high blade count vs. an industrial frame","sources":["boyce-gas-turbine-handbook","rolls-royce-jet-engine"],"tags":["turbine-blade","aero-derivative","scale","hub-radius","span"]},{"id":"hp-blade-industrial-frame-scale","kind":"dimension","tier":1,"title":"First-stage HP rotor blade scale — industrial (heavy-duty) frame class","summary":"A heavy-duty industrial-frame turbine's first HP stage runs a larger, slower blade: span 200+ mm against a 500-900 mm hub radius, at 3,000 or 3,600 rpm synchronous speed.","applies":["turbine blade","hp turbine","industrial gas turbine","heavy-duty frame"],"value":{"min":200,"unit":"mm","note":"first-stage blade span; hub radius typically 500-900 mm"},"basis":"Industrial frame turbines run at grid-synchronous speed (3,000/3,600 rpm, 2-pole) and scale up blade size rather than rotor speed for comparable power","sources":["boyce-gas-turbine-handbook","api-616"],"tags":["turbine-blade","industrial-frame","scale","synchronous-speed"]},{"id":"blade-aspect-ratio","kind":"dimension","tier":1,"title":"HP turbine rotor blade aspect ratio (span : chord)","summary":"First-stage HP turbine rotor blade aspect ratio (span/mean chord) typically runs 1.0-2.0 — short and stubby versus a compressor blade's 2.5-4, since a hot, highly-loaded HP stage favours a thicker, stiffer aerofoil.","applies":["turbine blade","hp turbine","blade aerofoil"],"value":{"min":1,"max":2,"unit":"ratio"},"basis":"Low aspect ratio keeps the HP aerofoil thick enough to survive combined thermal and centrifugal load and to route internal cooling, at some aerodynamic cost","sources":["nasa-sp290-turbine-design","rolls-royce-jet-engine"],"tags":["turbine-blade","aspect-ratio","aerofoil"]},{"id":"blade-taper-ratio","kind":"dimension","tier":1,"title":"HP turbine rotor blade taper ratio (tip chord : root chord)","summary":"Tip chord runs 0.5-0.8x the root chord on a typical first-stage HP rotor blade — tapering the section outboard trims centrifugal (pull) stress at the root, which carries the full blade's load.","applies":["turbine blade","hp turbine","blade aerofoil"],"value":{"min":0.5,"max":0.8,"unit":"ratio"},"basis":"Centrifugal root stress scales with the mass distribution outboard of the root; tapering the tip trims that mass without giving up as much aerodynamic loading capacity as a uniform section","sources":["nasa-sp290-turbine-design","boyce-gas-turbine-handbook"],"tags":["turbine-blade","taper","aerofoil","root-stress"]},{"id":"blade-twist-angle","kind":"dimension","tier":1,"title":"HP turbine rotor blade twist, root to tip","summary":"A first-stage HP rotor blade twists 15-30 deg in stagger angle from root to tip, following a free- or controlled-vortex design that keeps flow incidence and work extraction even as blade speed rises with radius.","applies":["turbine blade","hp turbine","blade aerofoil"],"value":{"min":15,"max":30,"unit":"deg"},"basis":"Free-vortex flow design requires tangential velocity to fall as 1/radius; because blade speed instead rises with radius, the section must twist so incidence and loading stay matched hub to tip","sources":["nasa-sp290-turbine-design"],"tags":["turbine-blade","twist","stagger-angle","free-vortex"]},{"id":"le-te-radii-pct-chord","kind":"dimension","tier":1,"title":"Leading- and trailing-edge radii as a fraction of chord","summary":"A turbine aerofoil's leading-edge radius runs 2-4% of chord (blunt, to tolerate incidence swings and erosion); the trailing edge is far sharper, sized by castability rather than aerodynamics — see te-thickness-target.","applies":["turbine blade","blade aerofoil","leading edge","trailing edge"],"value":{"min":2,"max":4,"unit":"%","note":"leading-edge radius as % chord"},"basis":"A generously-rounded leading edge tolerates the incidence range a real engine sees across its map without separating; the trailing edge instead wants to be as thin as the process allows","sources":["nasa-sp290-turbine-design","rolls-royce-jet-engine"],"tags":["turbine-blade","leading-edge","trailing-edge","aerofoil"]},{"id":"te-thickness-target","kind":"dimension","tier":1,"title":"Trailing-edge thickness target, as-cast","summary":"An as-cast nickel-superalloy HP blade trailing edge is held to 0.5-0.8 mm minimum thickness — thinner and the ceramic mould does not fill before the metal freezes; verify with cad_dfm_check {process:\"investment_casting\"}.","applies":["turbine blade","trailing edge","investment casting"],"value":{"min":0.5,"max":0.8,"unit":"mm"},"check":{"process":"investment_casting","rule":"min_trailing_edge_thickness"},"basis":"Foundry practice for as-cast (not ground) nickel-superalloy trailing edges: below this range the wax edge distorts before shelling, or the last sliver of mould cavity does not fill","sources":["ici-design-guidelines","mcdp-investment-casting-guide"],"tags":["turbine-blade","trailing-edge","castability","investment-casting"]},{"id":"fir-tree-root-proportions","kind":"dimension","tier":1,"title":"Fir-tree blade-root proportions: neck width vs platform, lobe count","summary":"A fir-tree root's neck (under the platform) runs 0.35-0.5x the platform width, broadening through 2-4 pairs of serration lobes to the base — more lobes share centrifugal pull across more, smaller flanks.","applies":["turbine blade","fir-tree root","blade attachment"],"value":{"min":0.35,"max":0.5,"unit":"ratio","note":"neck width : platform width"},"basis":"The fir-tree attachment carries the whole blade's centrifugal pull in shear/bearing across its flanks; a narrower neck concentrates stress under the platform, so it is kept wide relative to the lobes below","sources":["boyce-gas-turbine-handbook","rolls-royce-jet-engine"],"tags":["fir-tree","blade-root","attachment","neck"]},{"id":"fir-tree-flank-angle","kind":"dimension","tier":1,"title":"Fir-tree serration flank angle","summary":"Fir-tree lobe flank angle (from the radial/pull direction) runs 30-45 deg — shallow enough to keep flank bearing stress moderate, steep enough the lobe does not need excessive radial length to develop it.","applies":["turbine blade","fir-tree root","blade attachment"],"value":{"min":30,"max":45,"unit":"deg"},"basis":"The flank angle sets how centrifugal pull resolves into flank bearing stress and radial engagement length; 30-45 deg is the common working range across published fir-tree and dovetail designs","sources":["boyce-gas-turbine-handbook"],"tags":["fir-tree","blade-root","flank-angle","attachment"]},{"id":"platform-thickness","kind":"dimension","tier":1,"title":"Blade platform thickness","summary":"A first-stage HP blade platform runs 2.5-4 mm thick at blade scale — thick enough to seal the gas-path annulus and carry its own bending load between adjacent blades, thin enough to limit root centrifugal mass.","applies":["turbine blade","platform","blade root"],"value":{"min":2.5,"max":4,"unit":"mm"},"basis":"The platform is a small unsupported panel spanning the gap to the next blade's platform, loaded by gas pressure and its own centrifugal field; this is the common published proportion at first-stage HP scale","sources":["boyce-gas-turbine-handbook","rolls-royce-jet-engine"],"tags":["platform","blade-root","thickness"]},{"id":"tip-clearance-targets","kind":"dimension","tier":1,"title":"HP turbine tip clearance: cold build vs hot running","summary":"A first-stage HP turbine is built with 1.0-1.5 mm cold tip clearance (~2% span) so nothing rubs on start-up, closing to a 0.3-0.5 mm hot-running target (~0.5-1% span) as casing/disc grow toward the blade.","applies":["turbine blade","tip clearance","hp turbine"],"value":{"table":[{"state":"cold build","mm":"1.0-1.5","pctSpan":"~2"},{"state":"hot running target","mm":"0.3-0.5","pctSpan":"~0.5-1"}]},"basis":"Casing, disc and blade grow thermally/centrifugally at different rates through a start; active-clearance-control relies on that differential growth (not machining) to close the running gap — 1% of span lost to clearance costs roughly 1-2% stage efficiency","sources":["boyce-gas-turbine-handbook","rolls-royce-jet-engine"],"tags":["tip-clearance","hp-turbine","active-clearance-control"]},{"id":"rotor-speed-and-g-level-aeroderivative","kind":"dimension","tier":1,"title":"Aero-derivative rotor speed and blade centrifugal g-level","summary":"At ~11,000 rpm (omega ~1,152 rad/s), a blade centre-of-mass near 360 mm radius sees centrifugal acceleration omega^2*r_cg ~48,000 g — orders of magnitude above consumer mechanical design.","applies":["turbine blade","rotor speed","centrifugal load","aero-derivative gas turbine"],"value":{"value":48000,"unit":"ratio","note":"omega^2 * r_cg, in units of standard gravity g, at approx. 11,000 rpm"},"basis":"omega^2*r_cg is the standard centrifugal-acceleration figure of merit for a rotating blade; small radius but very high speed drives a g-level far above an industrial frame's","sources":["boyce-gas-turbine-handbook"],"tags":["rotor-speed","centrifugal-load","g-level","aero-derivative"]},{"id":"rotor-speed-industrial-frame","kind":"dimension","tier":1,"title":"Industrial-frame rotor speed: grid-synchronous 3,000 / 3,600 rpm","summary":"A generator-drive industrial turbine runs at 3,000 rpm (50 Hz, 2-pole) or 3,600 rpm (60 Hz, 2-pole) — 3-4x slower than an aero-derivative core, why its first-stage blade is so much larger for comparable power.","applies":["turbine blade","rotor speed","industrial gas turbine","turbogenerator"],"value":{"table":[{"gridHz":50,"rpm":3000},{"gridHz":60,"rpm":3600}]},"basis":"A generator-drive turbine coupled directly to a 2-pole alternator must turn at the grid's synchronous speed; g-level scales as the square of that fixed speed, so industrial frames trade rotor speed for blade size","sources":["api-616","boyce-gas-turbine-handbook"],"tags":["rotor-speed","industrial-frame","synchronous-speed","generator-drive"]},{"id":"in718-properties-20-650c","kind":"material","tier":1,"title":"IN718 (Inconel 718) properties at 20 C and 650 C","summary":"Wrought/cast IN718: density 8.19 g/cm3, modulus ~200 GPa (20 C) / ~165 GPa (650 C), 0.2% yield 1035/800 MPa, UTS 1240/970 MPa (20 C/650 C) — strength drops sharply above ~650 C.","applies":["in718","inconel 718","nickel superalloy","turbine disc"],"value":{"table":[{"tempC":20,"densityGcm3":8.19,"modulusGPa":200,"yieldMPa":1035,"utsMPa":1240},{"tempC":650,"densityGcm3":8.19,"modulusGPa":165,"yieldMPa":800,"utsMPa":970}],"unit":"MPa"},"basis":"AMS 5596 minimum-property table (20 C and 649 C) from the Special Metals INCONEL 718 bulletin; used for discs/cooler stages rather than the 850 C first-stage HP blade — see in738lc-properties-20-650-850c","sources":["specialmetals-in718","donachie-superalloys"],"tags":["material","in718","superalloy","nickel-alloy","turbine-disc"]},{"id":"in738lc-properties-20-650-850c","kind":"material","tier":1,"title":"IN738LC (cast nickel superalloy) properties at 20/650/850 C","summary":"Cast IN738LC (the classic first-stage HP blade alloy): density 8.11 g/cm3, modulus ~168/148/122 GPa at 20/650/850 C; 0.2% yield ~950/850/700 MPa; UTS ~1060/970/780 MPa at the same temperatures.","applies":["in738lc","in-738lc","nickel superalloy","turbine blade","investment casting"],"value":{"table":[{"tempC":20,"densityGcm3":8.11,"modulusGPa":168,"yieldMPa":950,"utsMPa":1060},{"tempC":650,"densityGcm3":8.11,"modulusGPa":148,"yieldMPa":850,"utsMPa":970},{"tempC":850,"densityGcm3":8.11,"modulusGPa":122,"yieldMPa":700,"utsMPa":780}],"unit":"MPa"},"basis":"Handbook-typical published data for cast IN738LC, representative of the alloy class, not a certified single-heat sheet. Per-value sources, and CADSF-1350's two DISAGREEMENTS (E 122 vs 151 GPa; yield 700 vs 552 MPa), are in in738lc-properties-sourced.","sources":["in738lc-published-data","donachie-superalloys","asm-handbook-vol15"],"tags":["material","in738lc","superalloy","nickel-alloy","turbine-blade"],"see":["turbomachinery/in738lc-properties-sourced"]},{"id":"min-castable-section-investment","kind":"rule","tier":1,"title":"Minimum castable section thickness (investment casting)","summary":"Nickel-superalloy investment castings at blade scale hold a minimum section thickness of ~1.0-1.5 mm — thinner and the ceramic mould misruns or cold-shuts before filling; check with cad_dfm_check {process:\"investment_casting\"}.","applies":["investment casting","turbine blade","castability"],"value":{"min":1,"max":1.5,"unit":"mm"},"check":{"process":"investment_casting","rule":"min_section"},"basis":"Investment-casting design guides publish this as the practical floor for a nickel-superalloy section at small-to-medium (blade-class) part scale; heavier industrial-frame sections tolerate more","sources":["ici-design-guidelines","mcdp-investment-casting-guide","beeley-smart-investment-casting"],"tags":["castability","min-section","investment-casting","rule"]}]}