[DeTomaso] Rear Window
Stephen
steve at snclocks.com
Sat Mar 19 14:43:40 EDT 2016
Gads – thank you all for your input! I’m realizing I will have to put together a synopsis of all the great comments I am getting from the forum.
Last night’s tests were “impacted” by a roughly 20 mph wind coming down the Columbia river gorge. This morning the winds have died down, so will most likely get some more runs in tonight before the rains start again (this is the Pacific Northwest). None the less, it is pretty easy to see, from the attached plot, that there is a relationship between air flow through the condenser and how fast the car was going. I’ve corrected for wind speed (hence calling the X axis air speed – as cars speed relative to air with very rough correction).
I found that there was not sufficient air-flow through the a/c condenser to spin the computer cooling fan I have strapped to the inside of the condenser fan (see attached for my “southern engineered” setup). But, I knew that, standing still, the a/c fan spun the computer fan enough to generate around 1 volt across the computer fan. So, we made some runs with the a/c fan spinning, starting out with standing still. They showed the impact of speed pretty graphically. Caveats: I know the computer fan was not registering even with the car doing 80 unless the a/c fan was on. So, there is a threshold air flow required to get the computer fan spinning. But, given that blowing at the fan spins it, I’m surprised it didn’t spin when the a/c fan was shut down and car was going 80 mph. Will repeat but get the computer fan spinning with the a/c fan, then shut down the a/c and see if the computer fan keeps spinning when the car is moving.
I’ve attached my plot of a/c air flow vs car speed from last night’s runs. Realizing the data is “challenged” by the 20 mph ambient wind, which I am sure was quartering and wandering, heck, not a bad plot. Be interesting to see what I learn with calmer conditions.
I’ve also attached a shot of my instrument cluster. Interestingly, the temperature gauge on top of the swirl tank also shows up.
Of course, given the airs desire to flow backwards through the a/c condenser, it likely makes some sense to reverse the a/c fan direction. OK – will lose the benefits of a sucker fan in giving better coverage of the coils, and the fan will likely be a little less efficient spinning backwards (OK – fans are nearly flat, not much curvature – maybe not a lot less efficient) but I suspect a significant enhancement in air-flow would be beneficial. Will test this as well.
Stephen Nelson
From: jgkrenton at comcast.net [mailto:jgkrenton at comcast.net]
Sent: Saturday, March 19, 2016 7:58 AM
To: Stephen <steve at snclocks.com>
Cc: detomaso at poca.com
Subject: Re: [DeTomaso] Rear Window
Stephen:
It will be interesting to see what Tom Tjaarda has to say.
It's my recollection that the deck lid opening is in fact a big air exhaust duct, sort of based on the NACA duct principle. It was designed to help move high pressure air from under the car, up around the engine and out the back. This was intended to help with the cars stability and engine cooling at high speeds while reducing the overall aerodynamic drag of the car. Blocking the opening would impact these functions (as does removing the little side windows).
Somewhere around the industry is some information on wind tunnel tests that were done on the Pantera body back in the 70's. I just don't remember where now.
I did have the opportunity to be following a friends Pantera who was at 70 or 80 MPH when an air conditioning hose let go and filled the engine compartment with Freon mist (looked like smoke!). I can tell you from that experience that the deck lid opening is very efficient at moving large quantities of air from the engine compartment rapidly and smoothly.
Here is some information on NACA ducts which you might find interesting and useful in your explorations.
http://ntrs.nasa.gov/archive/nasa/ca...1993093623.pdf
http://ntrs.nasa.gov/archive/nasa/ca...1993091791.pdf
http://ntrs.nasa.gov/archive/nasa/ca...1993093645.pdf
I also seem to recall that the low pressure area behind the car, and the low pressure in the engine compartment are about equal in that 70 to 80 MPH zone. This means the stock Air Conditioning condenser has no airflow (the pressures are low enough the fan is ineffective) and the condenser can "freeze up" in certain conditions which causes over pressure and is why the hose broke on my friends Pantera.
FYI/Your experience may vary....
Jeff/2467
_____
From: "Stephen" <steve at snclocks.com <mailto:steve at snclocks.com> >
To: detomaso at poca.com <mailto:detomaso at poca.com>
Sent: Friday, March 18, 2016 8:35:52 AM
Subject: [DeTomaso] Rear Window
I've been pondering for quite a while now the idea of putting a piece of
glass in the "window" in the deck lid behind the engine in 5332. This would
keep the engine from getting wet every time it rains and would also keep
from sucking grit and water off the road when the car is running down the
road.
Both seem like decent goals. Oh, and it would also make it more difficult
for someone to just reach in and remove 5332's dog-bone air cleaner. OK -
no one has taken it so far. But, hey, it would be all too easy to remove.
Looking at the opening - it sure looks like the original intent was to put
in a window.
I have sent an e-mail to Tom Tjaarda (attached) asking his thoughts.
Hopefully he will respond.
In the interim, I put together a set of sensors so I could see what I could
learn about conditions in the engine compartment just inches in front of the
opening, to the right side of the dog-bone. The attached photo shows the
instrument cluster shot from inside the car.
I'm measuring air velocity through the rear window (vane anemometer)
Vacuum just in front of the window
Rotation of the a/c condenser fan (volt meter connected across the motor,
which acts as a generator when the fan turns)
Two of the above are fairly straight forward. The vacuum - not so much.
When one talks about a vacuum, one is usually talking about a vacuum,
relative to ambient atmospheric pressure. So, if a vacuum gauge is hooked
up to your intake manifold, it reads the difference in pressure between the
atmosphere where the gauge is sitting, and the inside of your manifold,
where the hose from the gauge is connected.
So, what does one compare to in a moving car? The interior of the car?
That is what one would get if one puts a vacuum gauge in the cab and routes
the hose to the area in question. But, what does the pressure (or vacuum)
inside the car do with the car moving down the road. Open the windows, your
ears pop, and the pressure changes. Most of us don't have an external air
inlet (at least an intentional one) to the cab except for the windows.
My solution is to use a fairly sensitive pressure gauge (a sphygmomanometer
- gauge used to read blood pressure. It reads in inches of mercury. FYI,
there are roughly 50 inches of mercury per psi). I have connected the gauge
with small-diameter plastic tubing to a 200 ml stainless sample bomb. I
wrapped the bomb in towels and placed in a cooler to minimize temperature
changes. See, the pressure in the bomb will change by roughly .03 psi (1.5
mm Hg) for each 1 degree F change in temperature.
I then pressured up the bomb and let it sit overnight to stabilize. It
ended up at 280 mm. This is my "zero" at the then current barometric
pressure.
One has to view the pressure gauge as a delta-pressure device. It shows the
difference in pressure between the bomb (high pressure) and the atmosphere
around the gauge. So, if the reading on the gauge goes up, the differential
is increasing, which means the atmospheric pressure is going down. As in a
wee bit of a vacuum around the gauge. Flip side, if the reading on the
gauge goes down, well, there is less differential between the 280 mm Hg in
the bomb and the atmosphere around the gauge, so the pressure is going up.
OK - that is complex.
While a gauge that can be read down to around 1 mm hg (0.02 psi) is pretty
sensitive, I suspect we are talking pretty minimal vacuum levels.
Preliminary testing suggested a reading of 272 mm Hg at 80 mph. The
pressure around the gauge went up!
Huh. A lot to learn here.
I also noted that the volt meter did not show any rotation of the fan on the
a/c condenser. Need to make sure the wiring is ok. But, note, the meter
reads in mV, and, in my earlier testing, it showed voltage if the fan turned
at all.
The rubber for the new window shows up today, the window next Wednesday.
My plan is to get a decent video and stills of the test instruments at
several speeds. Then, when the new window is installed, rerun the test. I
suspect the anemometer will still be valuable, since I suspect there will be
a lot of turbulence in the air in the engine compartment even with the
window in place.
Needless to say, having the window in place will complicate putting the
deck-lid back in place.
Stephen Nelson
_______________________________________________
Detomaso Forum Managed by POCA
Posted emails must not exceed 1.5 Megabytes
DeTomaso mailing list
DeTomaso at poca.com <mailto:DeTomaso at poca.com>
http://poca.com/mailman/listinfo/detomaso_poca.com
To manage your subscription (change email address, unsubscribe, etc.) use the links above.
-------------- next part --------------
Gads - thank you all for your input! I'm realizing I will have to put
together a synopsis of all the great comments I am getting from the
forum.
Last night's tests were "impacted" by a roughly 20 mph wind coming down
the Columbia river gorge. This morning the winds have died down, so
will most likely get some more runs in tonight before the rains start
again (this is the Pacific Northwest). None the less, it is pretty
easy to see, from the attached plot, that there is a relationship
between air flow through the condenser and how fast the car was going.
I've corrected for wind speed (hence calling the X axis air speed - as
cars speed relative to air with very rough correction).
I found that there was not sufficient air-flow through the a/c
condenser to spin the computer cooling fan I have strapped to the
inside of the condenser fan (see attached for my "southern engineered"
setup). But, I knew that, standing still, the a/c fan spun the
computer fan enough to generate around 1 volt across the computer fan.
So, we made some runs with the a/c fan spinning, starting out with
standing still. They showed the impact of speed pretty graphically.
Caveats: I know the computer fan was not registering even with the car
doing 80 unless the a/c fan was on. So, there is a threshold air flow
required to get the computer fan spinning. But, given that blowing at
the fan spins it, I'm surprised it didn't spin when the a/c fan was
shut down and car was going 80 mph. Will repeat but get the computer
fan spinning with the a/c fan, then shut down the a/c and see if the
computer fan keeps spinning when the car is moving.
I've attached my plot of a/c air flow vs car speed from last night's
runs. Realizing the data is "challenged" by the 20 mph ambient wind,
which I am sure was quartering and wandering, heck, not a bad plot. Be
interesting to see what I learn with calmer conditions.
I've also attached a shot of my instrument cluster. Interestingly, the
temperature gauge on top of the swirl tank also shows up.
Of course, given the airs desire to flow backwards through the a/c
condenser, it likely makes some sense to reverse the a/c fan
direction. OK - will lose the benefits of a sucker fan in giving
better coverage of the coils, and the fan will likely be a little less
efficient spinning backwards (OK - fans are nearly flat, not much
curvature - maybe not a lot less efficient) but I suspect a significant
enhancement in air-flow would be beneficial. Will test this as well.
Stephen Nelson
From: jgkrenton at comcast.net [mailto:jgkrenton at comcast.net]
Sent: Saturday, March 19, 2016 7:58 AM
To: Stephen <steve at snclocks.com>
Cc: detomaso at poca.com
Subject: Re: [DeTomaso] Rear Window
Stephen:
It will be interesting to see what Tom Tjaarda has to say.
It's my recollection that the deck lid opening is in fact a big air
exhaust duct, sort of based on the NACA duct principle. It was
designed to help move high pressure air from under the car, up around
the engine and out the back. This was intended to help with the cars
stability and engine cooling at high speeds while reducing the overall
aerodynamic drag of the car. Blocking the opening would impact these
functions (as does removing the little side windows).
Somewhere around the industry is some information on wind tunnel tests
that were done on the Pantera body back in the 70's. I just don't
remember where now.
I did have the opportunity to be following a friends Pantera who was at
70 or 80 MPH when an air conditioning hose let go and filled the engine
compartment with Freon mist (looked like smoke!). I can tell you from
that experience that the deck lid opening is very efficient at moving
large quantities of air from the engine compartment rapidly and
smoothly.
Here is some information on NACA ducts which you might find
interesting and useful in your explorations.
[1]http://ntrs.nasa.gov/archive/nasa/ca...1993093623.pdf
[2]http://ntrs.nasa.gov/archive/nasa/ca...1993091791.pdf
[3]http://ntrs.nasa.gov/archive/nasa/ca...1993093645.pdf
I also seem to recall that the low pressure area behind the car, and
the low pressure in the engine compartment are about equal in that 70
to 80 MPH zone. This means the stock Air Conditioning condenser has no
airflow (the pressures are low enough the fan is ineffective) and the
condenser can "freeze up" in certain conditions which causes over
pressure and is why the hose broke on my friends Pantera.
FYI/Your experience may vary....
Jeff/2467
_______________________________________________________________________
From: "Stephen" <[4]steve at snclocks.com>
To: [5]detomaso at poca.com
Sent: Friday, March 18, 2016 8:35:52 AM
Subject: [DeTomaso] Rear Window
I've been pondering for quite a while now the idea of putting a piece
of
glass in the "window" in the deck lid behind the engine in 5332. This
would
keep the engine from getting wet every time it rains and would also
keep
from sucking grit and water off the road when the car is running down
the
road.
Both seem like decent goals. Oh, and it would also make it more
difficult
for someone to just reach in and remove 5332's dog-bone air cleaner.
OK -
no one has taken it so far. But, hey, it would be all too easy to
remove.
Looking at the opening - it sure looks like the original intent was to
put
in a window.
I have sent an e-mail to Tom Tjaarda (attached) asking his thoughts.
Hopefully he will respond.
In the interim, I put together a set of sensors so I could see what I
could
learn about conditions in the engine compartment just inches in front
of the
opening, to the right side of the dog-bone. The attached photo shows
the
instrument cluster shot from inside the car.
I'm measuring air velocity through the rear window (vane anemometer)
Vacuum just in front of the window
Rotation of the a/c condenser fan (volt meter connected across the
motor,
which acts as a generator when the fan turns)
Two of the above are fairly straight forward. The vacuum - not so
much.
When one talks about a vacuum, one is usually talking about a vacuum,
relative to ambient atmospheric pressure. So, if a vacuum gauge is
hooked
up to your intake manifold, it reads the difference in pressure between
the
atmosphere where the gauge is sitting, and the inside of your manifold,
where the hose from the gauge is connected.
So, what does one compare to in a moving car? The interior of the car?
That is what one would get if one puts a vacuum gauge in the cab and
routes
the hose to the area in question. But, what does the pressure (or
vacuum)
inside the car do with the car moving down the road. Open the windows,
your
ears pop, and the pressure changes. Most of us don't have an external
air
inlet (at least an intentional one) to the cab except for the windows.
My solution is to use a fairly sensitive pressure gauge (a
sphygmomanometer
- gauge used to read blood pressure. It reads in inches of mercury.
FYI,
there are roughly 50 inches of mercury per psi). I have connected the
gauge
with small-diameter plastic tubing to a 200 ml stainless sample bomb.
I
wrapped the bomb in towels and placed in a cooler to minimize
temperature
changes. See, the pressure in the bomb will change by roughly .03 psi
(1.5
mm Hg) for each 1 degree F change in temperature.
I then pressured up the bomb and let it sit overnight to stabilize. It
ended up at 280 mm. This is my "zero" at the then current barometric
pressure.
One has to view the pressure gauge as a delta-pressure device. It
shows the
difference in pressure between the bomb (high pressure) and the
atmosphere
around the gauge. So, if the reading on the gauge goes up, the
differential
is increasing, which means the atmospheric pressure is going down. As
in a
wee bit of a vacuum around the gauge. Flip side, if the reading on the
gauge goes down, well, there is less differential between the 280 mm Hg
in
the bomb and the atmosphere around the gauge, so the pressure is going
up.
OK - that is complex.
While a gauge that can be read down to around 1 mm hg (0.02 psi) is
pretty
sensitive, I suspect we are talking pretty minimal vacuum levels.
Preliminary testing suggested a reading of 272 mm Hg at 80 mph. The
pressure around the gauge went up!
Huh. A lot to learn here.
I also noted that the volt meter did not show any rotation of the fan
on the
a/c condenser. Need to make sure the wiring is ok. But, note, the
meter
reads in mV, and, in my earlier testing, it showed voltage if the fan
turned
at all.
The rubber for the new window shows up today, the window next
Wednesday.
My plan is to get a decent video and stills of the test instruments at
several speeds. Then, when the new window is installed, rerun the
test. I
suspect the anemometer will still be valuable, since I suspect there
will be
a lot of turbulence in the air in the engine compartment even with the
window in place.
Needless to say, having the window in place will complicate putting the
deck-lid back in place.
Stephen Nelson
_______________________________________________
Detomaso Forum Managed by POCA
Posted emails must not exceed 1.5 Megabytes
DeTomaso mailing list
[6]DeTomaso at poca.com
[7]http://poca.com/mailman/listinfo/detomaso_poca.com
To manage your subscription (change email address, unsubscribe, etc.)
use the links above.
References
1. http://ntrs.nasa.gov/archive/nasa/ca...1993093623.pdf
2. http://ntrs.nasa.gov/archive/nasa/ca...1993091791.pdf
3. http://ntrs.nasa.gov/archive/nasa/ca...1993093645.pdf
4. mailto:steve at snclocks.com
5. mailto:detomaso at poca.com
6. mailto:DeTomaso at poca.com
7. http://poca.com/mailman/listinfo/detomaso_poca.com
-------------- next part --------------
A non-text attachment was scrubbed...
Name: A-C Condenser Air Flow.xls
Type: application/vnd.ms-excel
Size: 36352 bytes
Desc: not available
URL: <http://server.detomasolist.com/pipermail/detomaso/attachments/20160319/4d48af41/attachment.xls>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Fans small.jpg
Type: image/jpeg
Size: 461170 bytes
Desc: not available
URL: <http://server.detomasolist.com/pipermail/detomaso/attachments/20160319/4d48af41/attachment.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Test Rig Small.jpg
Type: image/jpeg
Size: 256930 bytes
Desc: not available
URL: <http://server.detomasolist.com/pipermail/detomaso/attachments/20160319/4d48af41/attachment-0001.jpg>
More information about the DeTomaso
mailing list