| How about you fill in a field with the values you have, but allow the user to change it. I will measure my Dt and would be able to use that.
No doubt it could stand improvements for sure,
Jeff.
There are four DT's I employ in the cooling
equations. Change in air temperature across the radiator, change in
air temperature across the oil cooler and change in fluid temperature of
the coolant and oil as they flow through their heat exchanger.
I have heard of Air DT across
the radiator ranging from 50-100F, I am currently using a DT of 70F , but I know that Tracy has
reported a
DT of 100F. I am also using DT of 70F for the oil cooler and that is
probably too high. For both fluid DTs, I am using 16F.
IF anyone has reference material or sources that could
help me refine those figures - it would undoubtedly improve the cooling
section.
As Jeff pointed out for the cooling section there is no
input for OAT although there is for the power section. My initial thoughts
would be to pick
some OAT and I'm thinking of 59F (SL standard
day temp) as a nominal mid point of
DT. Then if OAT is above that DT, then to simply subtract the difference
between OAT and 59F and reduce the air DT across the radiator by that amount.
Conversely if OAT is below 59F then to add that DT to the 70F I am currently
using.
By increasing the DT factor more heat is transferred (better cooling)
by reducing the DT factor less
heat is transferred (worst cooling)
IF anyone has reference material or sources that could
help me refine those figures - it would undoubtedly improve the cooling
section.
Ed
Sent: Friday, August 24, 2012 11:49 AM
Subject: [FlyRotary] Re: [flyRotary] Spreadsheet Cooling
Section
Ed, you did say he cooling chart is not quite where it should
be
Plugging some numbers in there is very interesting; however,
not to be too critical but I think the constants used to calculate HP Vs OAT Vs
Cooling Capacity are a bit fuzzy.
For example, at any RPM, AF, HP, simply increasing the
OAT value in the spreadsheet results in improved cooling capacity
My
installations capacity to cool was much more influenced by OAT than the
resulting change in HP due to OAT . I had no cooling problems at 50F but
had big problems at 100F
The spreadsheet indicates opposite.
Jeff
|
From: |
Ernest
Christley |
|
Subject: |
Re:
[FlyRotary] Spreadsheet Cooling Section |
|
Date: |
Fri,
24 Aug 2012 10:41:30 -0400 |
|
To: |
Rotary
motors in aircraft
| |
| |
|
Ed Anderson
wrote:
> But, as stated
before the cooling section is on less solid ground due to
> the fact that
installation variables play such a large role in cooling
> and they are not
taken into consideration. But, you can play with it to
> see the effects
of changing several variables on cooling.
>
> Ed
>
Just been playing with
this, pulling data out of my data logs. I don't have all my numbers
exact yet, but I think this
will be useful for
making a SWAG at determining if the system will stay within safety margins
during various phases of
flight.
Would it be to much to
ask those with flying machines if they can go out and determine where
their system starts to warm
up, which would be a
rough indication of where the cooling capacity is exceeded? I
thinking of doing a steep climbout
and slowly dropping
the nose until the temps start coming down, noting the temp, MAP, airspeed
and AFR at that point. I
don't think it is
necessary to tell grown people that built their own airplane that they
need to be careful about
airspeed while doing
something like this. If we can get a variety of samples, we
can put error bars around the
numbers that the
spreadsheet gives. |
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