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I've been watching this thread with considerable interest. And all
the concerns seem valid. There seem to be three ways to deal with
the problem:
1. No A/C. Not a great answer.
2. Detailed structural analysis. Problematic due to cost, and
variability in individual builds.
3. Flight testing with a competent test pilot.
I think #3 is best since it deals with the variabilities of the
installation and creates a hard VNE number. Also, there are a lot of
A/C installations flying. This implies a degree of safety.
Ted Noel
N540TF
On 5/8/2012 7:51 AM, Colyn Case wrote:
Hi Bob,
That would appear to be a huge improvement in that the area
of penetration through the fuselage is greatly reduced.
Congrats on getting your 8 knots back b.t.w.
However, given all previous discussion (e.g. read the
"flutter" article on the main lml page) I personally wouldn't be
comfortable pronouncing it "safe" especially to others, unless I
had had the engineering analysis done on the resulting entire
fuselage structure.
Colyn
On May 7, 2012, at 7:51 AM, Bob Rickard wrote:
Charlie K /
Colyn
I just did
the opposite this winter, and removed the Airflow
systems scoop from my IV-P and engineered a low drag
plenum out back. I saw an 8 knot gain in TAS at
FL180. My original system was installed in 2001
time frame (1st flight in
’02), so I don’t know if it was the “reduced drag”
version. I’m very aware of the topic of cutting
holes in the fuselage and took great care to
overdesign the modification and have a carbon expert
build and install it. There are bids of reinforcing
carbon both inside and outside the fuselage that are
cut well beyond the scoops, which are also made of
carbon and hysol’d in. A couple of pics attached,
I’m planning a LOBO paper on it sometime soon. It
works very well, looks fantastic, is light (except
for the fan), and is strong and safe.
Bob R
Yes-it worked out fine. By that- I
mean- it was the best you can do.
In the beginning, The pressurized IVs
had the cabin intercooler located on the side of
the left lower cowling- with louvers. The intake
air was taken from the engine air cleaner box.
Even after moving the intercooler to the
front/left side the air (thanks Don) into the
cabin was measured at 105°on the 70° day.
What I didn't say in the post yesterday
was that selecting 11,000 feet on the controller
put an electrical signal to the outflow valve to
open it wide open. You also could use the "dump"
switch to open the valve. That helps a lot. But
the big Issue is to shut off that 105° air from
entering the cabin.
I liked the idea of the Airflow
design--but I heard stories of airspeed
penalties with the P51 scoop. I asked Bill
Genevro if he had ever considered doing wind
tunnel testing.Then they did-- at Ohio
University. They tucked the condenser up closer
to the fuselage and drag reduced drastically. I
bought his system. At that time there was no
choice. I did testing later and saw less than
three knot change--. The only holes cut in the
fuselage was a pair of 1 inch holes for freon in
and out of the condenser. The beautiful part of
it, is that --it works. Very well! In all
regimes.
Charlie, how did
that work out? You eventually added the
airflow systems unit right?
Does that require
a hole through the fuselage floor?
On May 3,
2012, at 1:20 PM, Charlie Kohler
wrote:
In
the years before AC was
available, I developed a plan
for Summer (hot) flying. On take
off I set the controller to
11,000 feet with the Pressurized
air to the cabin OFF. I opened
the air valve from the fresh air
from the vertical stabilizer.
I
took off and climbed to 11,000
feet . At 10,000 feet I closed
the fresh aHim himir from the
vertical stabilizer and
gradually selected the
pressurized air to the cabin to
the ON position. Then as I
continued to climb I selected
the cruise altitude on the
pressurization controller and
adjusted the rate knob to 200
feet a minute descent. The cabin
would then descend and level off
1000 feet above selected
altitude.
On
the descent into the landing
airport-- I set the controller
to 1000 feet above field
elevation.
Complicated
maybe--but it kept the hot
turbocharged air out of the
cabin until it was necessary.
It can
be really warn even at
17,000 feet without
A/C in an IV-PT. Why?
The bleed air is super
warm. Absolutely
necessary? Not IMHO.
But a few letdowns
from 20k+ and a drip
drip drip off the end
of your nose will tell
you it’s nice. Or in
summer heat in
Houston, Phoenix or
some other sauna, it
is even better than
nice.
Wouldn’t
it be good to use that
air to air heat
exchanger in line with
the bleed air to the
cabin?HEAVY.
With
all the discussion of
structural integrity
compromises of the
IV-P fuselage by
cutting air
conditioning holes, I
have a question for
you seasoned IV-P
drivers… How
necessary is air
conditioning in this
aircraft?
I have
been flying my 320 for
almost 9 years now and
certainly would love
to have had it during
ground operations on
hot summer days with
the green house
canopy. However, once
moving and at
altitude, there is no
need. I realize that
the IV-P is going to
have warmer air
because of the
pressurization but it
is also typically
flying much higher
(colder ambient) and
it doesn’t have the
bubble canopy.
So, in
normal cross country
cruise operations
above FL180, do any of
you that don’t have
A/C *really*
wish that you had it?
I’m
early in the building
of my IV-P and don’t
want to put it in for
several reasons:
· Potential structural
issues
· One more thing to
break down the road
I live
in Colorado and will
be using this plane as
a cross country
traveler with my wife,
so comfort is
certainly a factor but
not at all costs. One
thought is to get one
of those
cooler-with-ice-and-a-fan
systems to toss in the
back seat for those
few days that are very
hot.
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