> This is Dave's current system. He is not entirely happy
> with the water cooling.
> Air flows through the inter cooler on the left side and the oil
> cooler on the right side and then through the 2 inch thick rad
> mounted below the engine and out the exit below the cowl.
> The air is also heated by passing over the turbo charger
> and exhaust manifold before it flows through the rad.
>
> Does anybody have any suggestions what Dave could to to improve
> the water cooling?
>
> Oil cooling and inter cooling are fine.
Leave the oil cooler and intercooler ducted & positioned as-is. Leave
the radiator positioned as-is, but add a chin scoop and duct to the
current backside of the radiator. Let the airflow through the radiator
be reversed from the current pathway. Add vents on the top of the cowl
slightly ahead of the firewall. If the windscreen is near the firewall,
that area of the cowl should be a lower pressure area (compared to the
rest of the cowl; it's still high relative to the static port).
Russell Kent
Russel,
I like that Idea best so far, as it would be the easiest to implement
and would leave the cleanest looking cowl..
There is little doubt that the other suggestions could be made to work
as well. Some would be impossible because of limited space.
However, I would like to now throw out some other points for consideration:
1) The point of improving my cooling system is all about going faster.
After all, it works perfectly fine (em... recent incident excluded) to
get average performance for an RV.
2) up above 200 mph. (the speed I now travel at) reduction in drag
becomes more important than increases in power
3) Cooling drag is 10% of overall drag - give or take.
4) Therefore, maintaining low cooling drag, or decreasing it, should
take priority in any planned improvements - for reasons of both speed
and economy. After all, we want to disprove the rotary's reputation as
a gas gussler.
So given the 'minimize cooling drag' premise, I submit that:
1) All air used for cooling must be heated to the maximum extent -
otherwise it is waisted cooling drag.
And I know from measuring temperatures in my cowl that:
1) The intercooler and oil cooler add very little temperature rise to
the incoming air, about 10-20 deg. There is plenty more cooling to be
had from it (as is proved by the relative success of my current system).
So, until convinced otherwise, I am more or less committed to the
minimization of cooling drag and the re-use of my intercooler and oil
cooler air for at least some of the water cooling.
That being said, improvement is needed. Clearly, more air is part of
that solution. The other part of the solution appears to be more
radiator volume - used to obtain more cooling from each bit of air.
Weight penalty yes, but still more efficient IMHO.
Paul is a big proponent of a cowl flap, and I agree. As soon as things
are cooling so well that I need to warm things up in cruise, it will be
a simple matter to add a cowl flap to close down the air outlet.
A spray system is still an excellent addition for augmenting climb
cooling without adding drag. Used mostly for bragging rights etc. but I
have not ruled that out yet.
And that's all I know. (well, pretty sure of anyway :-)
BTW, I have also come to accept the wisdom that the rotary does not
tolerate temperatures above 180 very well. My previous red-line was
230 and I would not start reducing power until it hit 210. In the
future, my "reduce power" limit will be 190 and redline (dramatically
reduce power) will be 210. The goal is to not get there very often.
Unfortunately, that is the big problem with the turbo. I can always make
more power. And BHP is like money: not matter how much I have, I
always would like a little more.
--
Dave Leonard
Turbo Rotary RV-6 N4VY
http://members.aol.com/_ht_a/rotaryroster/index.html
http://members.aol.com/_ht_a/vp4skydoc/index.html
One rule of thumb that seems to apply here is every decrease
in air temp going through the rad increases the cooling by 1%.
This is because of the temp difference between air and rad.
Assuming 100 degree air going in and a 200 degree rad temp.
Another rule of thumb is the first half of the rad (thickness) does
3/4 of the cooling.
Lets review a few cooling principles. We need x amount of airflow
given in cubic feet per minute raised to temperature x to carry
away the necessary heat.
If we had a hole in the front of the airplane with enough area
to take in the requires CFM of air at the speed of the airplane in
question and that hole was connected to the back of the airplane
with a duct and there was no heat exchanger in the duct the "cooling"
drag would be the skin friction of the air in the duct alone. This
is a lower limit on the "cooling" drag. As we install a heat
exchanger in the duct the friction or drag on the air and the airplane
increases.
The drag added depends on how easy it is for the air to flow
through the heat exchanger. A highly porous heat exchanger
is very little drag. The thicker the heat exchanger the harder it is
for the air to flow through it. In other words it becomes less
porous.
Now a few years back it was discovered that the drag in the heat
exchanger was proportional to the square of the speed of the air
flowing through the heat exchanger. If we increase the frontal area
of the heat exchanger somehow keeping the air volume flow the same and slow
the air going through it we can decrease the drag on the heat exchanger
and the airplane. That was done by a diverging area duct called a diffuser.
What we also need to do however is speed the air back up before we let
it exit the duct.
If we slow the air we must also increase the frontal area of the heat
exchanger to keep the CFM the same. If we want to keep the volume flow the
same we must make it thinner. It just so happens that that makes the heat
exchanger more efficient in the bargain. Now here is a quote from Kays &
London on the subject.
"highly compact surface geometries [read optimum heat transfer for a given
HE core volume] is that the resulting core shapes are characterized by large
flow frontal area and short flow lengths for the gas-flow path."
Now if we do nothing other than make the heat exchanger thicker with
out greatly adding to the transfer of heat from the heat exchanger to the
air stream all we have really done is greatly increase the drag along with
a slight increase in the cooling.
All this is assuming of course one has a converging duct on the out let
side of the heat exchanger. That is where the cowl flaps come in. They ARE the
converging duct.
Dave is attempting to increase the cooling keeping the drag the same
without making the hole in the front of the airplane larger in area and
without using cowl flaps and at the same time increasing the temp of
the air flowing through the water rad.
Good luck Dave :)
For the new guys read
http://www.rotaryeng.net/how-to-cool12.html
Paul Lamar ...No rotor no motor.
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