Page 21 - Volume 13 Number 8

power section stays behind. The hot section components, along with fuel nozzles, are sent to the engine shop for inspection, repair and/or replacement. The power section (male) and the hot section (female) fit together like a hand in a glove. Great care is taken at reassembly.
Segments and T-Wheels
Segments, which surround the T­wheel (turbine wheel), should always be changed at the HSI because the T­wheel is removed and trued (brought back to its original shape). If the old segments are left in, the clearances between them and the newly trued wheel are increased; this, in turn, causes the engine to run hotter and possibly not make performance specs.
Pratt had an issue a while back with warping segments rubbing against the T­wheel and reducing the outside diameter of the T­wheel too much. The T­wheels had to be re­bladed.
There are 58 CT blades on each wheel and they are expensive. These days they can run as high as $1,900 per blade. I’ll let you do the math on that one.
Sulfidation is a type of corrosion on the T­wheel blades found in engines that operate regularly in heavily polluted or salt­laden air. Turbine compressor washes help keep sulfidation to a minimum. Heavy sulfidation (Stage 3) will condemn the T­wheel blades.
Burner Cans
Burner cans (aka, combustion liners) always seem to crack, especially the newer two­piece construction. Some cracks are perfectly acceptable, but others need welding or new pieces installed (such as cooling rings). Burner cans are typically sent out for repairs which are always expensive and take extra time; but to exchange a burner can in the interest of saving downtime is an expensive proposition.
CT Guide Vanes
Compressor turbine (CT) guide vanes are subjected to the highest temperatures inside the engine. They are assaulted by flame pattern and corrosive particulate matter such as smog or salt­laden air. This abusive environment results in cracks, erosion and warping. Guide vanes have had lots of improvements in material and design over the years so they are better now than
AUGUST 2019
Half of the newer two-piece style burner cans (aka combustion liner).
KING AIR MAGAZINE • 19