5 bladed props on a King Air 90
- Thread starter JDP
- Start date
spbrian
Well-Known Member
Depends upon who you talk to about spinning the garrets.
To pax your winding the rubber band for the next start.
For maintenance purposes, depends on who you talk to. I have heard it doesn't nothing on the newer engines except gives you something to do for a minute.
The most common two are to help keep "shaft bow" to a minimum and to help cool the engine's cumbustion chamber down by injecting cool air inside.
Shaft bow is when during cool down the drive shaft for the engine will park in one spot and with the shaft being very warm from operation it will bend downwards from the force of gravity in between the bearings inside the engine (think telephone wire). By spinning the prop you are pulling cooling air inside the engine to take the residual heat out of the engine and also helping to keep the shaft straight.
You do not have to do this on a Pratt or Walter because the engines on those have 2 shafts inside that are not connected together, because of this there are more supporting bearings for the shaft to rest on.
The way the two shafts are connected inside the engine is through a "fluid coupling". No there is no oil or water inside the engine think of a fluid coupling as air, air moving a high enough pressures is a fluid. The PT6 depending on the model has 2 different turbines, the first turbine that the hot gas comes into contact with provides the power to spin the compressors and all of the accessory's on the engine at the front of it. The second turbine only spins the propeller, these 2 turbine's are not connected and the fluidic coupling is between those.
On the older versions of the Garrett's spinning the propeller after shut down also on top of doing the 2 above mentioned things would help to prevent coking of the fuel nozzles which can disrupt the spray pattern of the fuel nozzles and lead to poor performance and also lower engine life due to damage to the lining of the combustion chamber.
(All above correct to my knowledge, which is limited)
-Brian
To pax your winding the rubber band for the next start.
For maintenance purposes, depends on who you talk to. I have heard it doesn't nothing on the newer engines except gives you something to do for a minute.
The most common two are to help keep "shaft bow" to a minimum and to help cool the engine's cumbustion chamber down by injecting cool air inside.
Shaft bow is when during cool down the drive shaft for the engine will park in one spot and with the shaft being very warm from operation it will bend downwards from the force of gravity in between the bearings inside the engine (think telephone wire). By spinning the prop you are pulling cooling air inside the engine to take the residual heat out of the engine and also helping to keep the shaft straight.
You do not have to do this on a Pratt or Walter because the engines on those have 2 shafts inside that are not connected together, because of this there are more supporting bearings for the shaft to rest on.
The way the two shafts are connected inside the engine is through a "fluid coupling". No there is no oil or water inside the engine think of a fluid coupling as air, air moving a high enough pressures is a fluid. The PT6 depending on the model has 2 different turbines, the first turbine that the hot gas comes into contact with provides the power to spin the compressors and all of the accessory's on the engine at the front of it. The second turbine only spins the propeller, these 2 turbine's are not connected and the fluidic coupling is between those.
On the older versions of the Garrett's spinning the propeller after shut down also on top of doing the 2 above mentioned things would help to prevent coking of the fuel nozzles which can disrupt the spray pattern of the fuel nozzles and lead to poor performance and also lower engine life due to damage to the lining of the combustion chamber.
(All above correct to my knowledge, which is limited)
-Brian
febtober29
Well-Known Member
KLB
Well-Known Member
You're on!