View Full Version : Cessna FR172H Exhaust question
I was recently asked why the exhaust stack on the Cessna FR172H is inclined forward (yes it is!) anyone know the reason why?.
Rainboe
8th Nov 2008, 04:52
Is there any reason you know why it shouldn't?
Piper19
8th Nov 2008, 12:31
Not all H models have this. I found a picture of what you mean I think: Photo Private Reims-Cessna FR172H Rocket CS-AHX (http://www.planepictures.net/netshow.php?id=744029)
Doesn't the whole cowling look a bit strange for a 172? Maybe these models have a non standard engine, thus a somewhat different exhaust.
Cant think of any reason why it should not point point forward, but like all things aviation I imagine there is a reason why this design is adopted on this model,
Piper19, thanks-thats pic illustrates exactly what i mean
Some of these airplanes have been modified with what is called a 'power flow exhaust' an aftermarket certified product that has proven to be quite a good performer.
IE: slightly more BHP delivered due to less exhaust back pressure.
I think his point is that it is difficult to get lower backpressure with an exhaust that has a component of the airflow blowing up the pipe!
RJ Kanary
9th Nov 2008, 12:28
It could well be that the aerodynamics result in a low pressure area developing at the end of the stack, increasing scavenging efficiency. :)
RJ
It could well be that the aerodynamics result in a low pressure area developing at the end of the stack, increasing scavenging efficiency.
Yup...:ok:
RJ Kanary
9th Nov 2008, 18:49
The only clue that I had as to the reason is the way the stack is cut. "Bologna Style" instead of straight across.Commonly seen in some automotive and over the road truck (Lorry for you subjects Of The Crown.) exhaust pipes.
Airflow over the enlongated opening [in the correct direction.] should induce a depression.
RJ
MOLWillie
9th Nov 2008, 20:03
The 'scarf' cut on some 172s parallels the profile of the cowl as mine does..........go figgir?
"Airflow over the enlongated opening [in the correct direction.] should induce a depression."
Yeah that would make sense, if the exhaust duct were inclined aft to achieve the same elongation it would be obstructed by the fire wall, OK I'll buy that.
Ta guys