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Relieving turbine disc thermal stress with cooling air

Aviation Mechanic Powerplant (AMP) practice question 7 of 9 on Turbine Engine Air Systems. ACS element AM.III.K.K3 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONWhat is one method used to partially relieve the thermal stresses in a gas turbine engine turbine disc?

  1. Aspray lubricating oil across the disc rim face
  2. Bbleed cooling air onto the face of the disc
  3. Cwrap the disc rim in a foil heat blanket
Show the answer and explanation

Correct answer: B. bleed cooling air onto the face of the disc

  • A — incorrect Oil spray nozzles lubricate the main bearings; oil is kept out of the hot gas path, not sprayed on the turbine disc.
  • B — correct Bleeding cooling air back onto the face of the disc is named as one method of partially relieving the disc's thermal stresses.
  • C — incorrect Foil-and-fiberglass insulation blankets are installed around the tailpipe area, not around a rotating turbine disc.

BACKGROUND

The rim of a turbine disc is washed by hot gases and also picks up heat conducted from the turbine blades, so rim temperatures run well above those of the inner portion of the disc. The resulting temperature gradient adds thermal stress on top of the rotational stress already present. One way to relieve part of that stress is to bleed cooling air back onto the face of the disc. Another relief comes from the way blades are installed: the broached grooves in the rim leave clearance for thermal expansion, so the blade root is loose in its notch when the disc is cold. Turbine blades themselves are also cooled, many being cast with internal air passages and cooling holes and coated with a ceramic heat barrier.

STUDY TIP

Group the internal cooling methods together: cooling air on the disc face, air holes in the blades, and ceramic heat barrier coatings.

KEY POINTS

  • Disc rim temperature is much higher than the inner disc, adding thermal stress to rotational stress.
  • One relief method is bleeding cooling air back onto the face of the disc.
  • Blade cooling holes and ceramic coatings let the engine run a higher exhaust temperature.

SOURCES

  • amp-powerplant ch01 "Turbine Section" (turbine disc thermal stresses; turbine blade cooling holes)
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MORE ON TURBINE ENGINE AIR SYSTEMS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-32B Aviation Maintenance Technician Handbook – Powerplant, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.