Turbine Nozzle to Thrust tube distance...really?!
10-07-2016, 10:10 AM
#1
Turbine Nozzle to Thrust tube distance...really?!
So, I've seen in the tube and read specs from 1/2" to 1.25" and everything in between.
So what is the "best practice" in the field? I have a Skymaster F-18c that I'm trying to polish up for a maiden and I'm stumped on this setting!!??
So what is the "best practice" in the field? I have a Skymaster F-18c that I'm trying to polish up for a maiden and I'm stumped on this setting!!??
10-07-2016, 11:35 AM
#3
I've usually heard that it should be around 3/4" to 1", which is right in the middle of what you've heard.
The main reason for the distance is to provide clearance for additional air from the fuselage to enter the pipe (due to the low pressure created by the turbine's exhaust). If you don't have enough clearance, in my experience, two things can happen. First, the engine/pipe will make a loud whistling sound that is quite annoying to say the least, and second, the engine may shutdown due to an overtemp reading.
I reality, in most planes moving the engine forward or aft 1/2" or so will not significantly change the CG. I'd start with the 1.25" of gap and go from there...
Bob
10-07-2016, 11:50 AM
#4
My Feedback: (57)
First, that distance is from the rear opening of the turbine exhaust to the front of the pipe where the beginning of the straight part is - the bell mouth is not included in this measurement - especially if its the large "CARF style bell mouth that is almost like a half-bypass.
I've usually heard that it should be around 3/4" to 1", which is right in the middle of what you've heard.
The main reason for the distance is to provide clearance for additional air from the fuselage to enter the pipe (due to the low pressure created by the turbine's exhaust). If you don't have enough clearance, in my experience, two things can happen. First, the engine/pipe will make a loud whistling sound that is quite annoying to say the least, and second, the engine may shutdown due to an overtemp reading.
I reality, in most planes moving the engine forward or aft 1/2" or so will not significantly change the CG. I'd start with the 1.25" of gap and go from there...
Bob
I've usually heard that it should be around 3/4" to 1", which is right in the middle of what you've heard.
The main reason for the distance is to provide clearance for additional air from the fuselage to enter the pipe (due to the low pressure created by the turbine's exhaust). If you don't have enough clearance, in my experience, two things can happen. First, the engine/pipe will make a loud whistling sound that is quite annoying to say the least, and second, the engine may shutdown due to an overtemp reading.
I reality, in most planes moving the engine forward or aft 1/2" or so will not significantly change the CG. I'd start with the 1.25" of gap and go from there...
Bob
