Bill_H
Well Known Member
That manometer pressure reading is not that simple. Take a one inch piece of the
existing blast tube and blow through it as hard as you can. Now do the same with a
2 foot piece. You won't detect a difference. R may equal Rho D V over mu and all that (I'm a M.E.)
but for the low flows we are talking about I do not think that the friction losses in the corrugated
tube are the governing factor.
Actually the pressure at the "start end" of the tube doesn't tell the whole tale. If delta-p
is the only thing driving air through the tube, then you need to look at the other end - the
ambient pressure at ground idle next to the exit point of the voltage regulator radiator fins.
That could be higher than might be thought because of the air blowing in from the prop through
the starboard inlet, as well as the air exiting the coolant radiator. That has the effect of pressurizing
The entire compartment.
I think the currently-as-designed tangential connection to the shroud is a much bigger
factor and (as you pointed out) the poor generation of airflow from the root of the prop
for a non-moving plane. Think of it - why would that air going into the shroud want to
make a right angle turn into the blast tube? Shoot, there could even be a vacuum effect there!
I was thinking about modifying the existing setup by sticking the blast tube INTO the
shroud rather than the current flush mount - either at an angle or with a 90 degree
turn so it is facing the prop. But that seemed a poorer idea than what I am showing.
If a goodly amount of air is blowing through the duct at ground idle- and I think it certainly is because
it is certainly blowing through considerable resistance of the oil cooler, then it would also
have "no choice" but to go through the scoop I show.
Thoughts?
existing blast tube and blow through it as hard as you can. Now do the same with a
2 foot piece. You won't detect a difference. R may equal Rho D V over mu and all that (I'm a M.E.)
but for the low flows we are talking about I do not think that the friction losses in the corrugated
tube are the governing factor.
Actually the pressure at the "start end" of the tube doesn't tell the whole tale. If delta-p
is the only thing driving air through the tube, then you need to look at the other end - the
ambient pressure at ground idle next to the exit point of the voltage regulator radiator fins.
That could be higher than might be thought because of the air blowing in from the prop through
the starboard inlet, as well as the air exiting the coolant radiator. That has the effect of pressurizing
The entire compartment.
I think the currently-as-designed tangential connection to the shroud is a much bigger
factor and (as you pointed out) the poor generation of airflow from the root of the prop
for a non-moving plane. Think of it - why would that air going into the shroud want to
make a right angle turn into the blast tube? Shoot, there could even be a vacuum effect there!
I was thinking about modifying the existing setup by sticking the blast tube INTO the
shroud rather than the current flush mount - either at an angle or with a 90 degree
turn so it is facing the prop. But that seemed a poorer idea than what I am showing.
If a goodly amount of air is blowing through the duct at ground idle- and I think it certainly is because
it is certainly blowing through considerable resistance of the oil cooler, then it would also
have "no choice" but to go through the scoop I show.
Thoughts?
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