Need help with Rotax 912 radiator installation!

The title pretty much says it all.

My good friend and neighbor, Leo, is having some cooling problems
on his Zodiac.

The first taxi tests proved the airplane handles well on the ground,
accellerates like a banshee, but the coolant and CHT temps peg in
only a few minutes.

The radiator is mounted near the firewall with an enclosure around it
to direct cooling air through the rad.

The inlets are NACA vents on the side of the cowl, 4" Scat tube to the
radiator enclosure, and a lip on the bottom at the exit from the
radiator.

We tufted the cowl, with special emphisis around the inlets and exit.
The results are about as expected.

The inlet tufts do (eventually) go down the Scat tubes, but there is
a noticible amount of 'bulge' in the strings along the ramp.
One that overlapped past the back edge of the inlet simply stuck to
the surface of the cowling (Man, I hate when that happens!)

The outlet tufts do show a little bit of down angle coming out of
the radiator enclosure. But it's pretty mild, with hardly any
turbulence behind the lip.

We also plumbed up a spare altimeter to several places - inside the
cowl about 1/2 way up the firewall, about 1/2 way down the Scat tube,
in front of the radiator lip, and one behind the lip.

The numbers show the correct pressure differences where they ought
to be, but the total difference was only 10 or 15 feet of altitude.
That's not much pressure differential!

We are going to let her cool off and try clamping an extension to
the exit lip for the next performance. See if that will make any
difference.

If any of you guys have been down this path with a 912 installation,
would you mind sharing what you did, How yours works and how its
built?

Could really use some help figgering thisone out...


Thanks

Richard

NACA vents are some what difficult to get to flow. Radiuses and lip height
are critical I've been told. For details go to page 187 of Tony Bingelas'
book "The Sportplane Builder" Quote --- These indent vents must be buuilt
to a precise shape AND installed in a suitable location or air may not
enter. When that happens, a small barrier has attached over the opening.
For all practical purposes, it then becomes a conventional air scoop with
all its inherent drag..."

If the addition of a lip barrier solves the cooling problem then you know
you have to rebuild or just use what you have to preserve your engine.

Cy Galley - Chair, Emergency Aircraft Repair
Safety Programs Editor - TC
EAA Sport Pilot

----- Original Message -----
From: "Richard Lamb"
Newsgroups: rec.aviation.homebuilt
Sent: Wednesday, June 30, 2004 2:49 PM
Subject: Need help with Rotax 912 radiator installation!


The title pretty much says it all.

My good friend and neighbor, Leo, is having some cooling problems
on his Zodiac.

The first taxi tests proved the airplane handles well on the ground,
accellerates like a banshee, but the coolant and CHT temps peg in
only a few minutes.

The radiator is mounted near the firewall with an enclosure around it
to direct cooling air through the rad.

The inlets are NACA vents on the side of the cowl, 4" Scat tube to the
radiator enclosure, and a lip on the bottom at the exit from the
radiator.

We tufted the cowl, with special emphisis around the inlets and exit.
The results are about as expected.

The inlet tufts do (eventually) go down the Scat tubes, but there is
a noticible amount of 'bulge' in the strings along the ramp.
One that overlapped past the back edge of the inlet simply stuck to
the surface of the cowling (Man, I hate when that happens!)

The outlet tufts do show a little bit of down angle coming out of
the radiator enclosure. But it's pretty mild, with hardly any
turbulence behind the lip.

We also plumbed up a spare altimeter to several places - inside the
cowl about 1/2 way up the firewall, about 1/2 way down the Scat tube,
in front of the radiator lip, and one behind the lip.

The numbers show the correct pressure differences where they ought
to be, but the total difference was only 10 or 15 feet of altitude.
That's not much pressure differential!

We are going to let her cool off and try clamping an extension to
the exit lip for the next performance. See if that will make any
difference.

If any of you guys have been down this path with a 912 installation,
would you mind sharing what you did, How yours works and how its
built?

Could really use some help figgering thisone out...


Thanks

Richard
"Richard Lamb" wrote in message
...
The title pretty much says it all.

My good friend and neighbor, Leo, is having some cooling problems
on his Zodiac.

The first taxi tests proved the airplane handles well on the ground,
accellerates like a banshee, but the coolant and CHT temps peg in
only a few minutes.

The radiator is mounted near the firewall with an enclosure around it
to direct cooling air through the rad.

The inlets are NACA vents on the side of the cowl, 4" Scat tube to the
radiator enclosure, and a lip on the bottom at the exit from the
radiator.

We tufted the cowl, with special emphisis around the inlets and exit.
The results are about as expected.

The inlet tufts do (eventually) go down the Scat tubes, but there is
a noticible amount of 'bulge' in the strings along the ramp.
One that overlapped past the back edge of the inlet simply stuck to
the surface of the cowling (Man, I hate when that happens!)

The outlet tufts do show a little bit of down angle coming out of
the radiator enclosure. But it's pretty mild, with hardly any
turbulence behind the lip.

We also plumbed up a spare altimeter to several places - inside the
cowl about 1/2 way up the firewall, about 1/2 way down the Scat tube,
in front of the radiator lip, and one behind the lip.

The numbers show the correct pressure differences where they ought
to be, but the total difference was only 10 or 15 feet of altitude.
That's not much pressure differential!

We are going to let her cool off and try clamping an extension to
the exit lip for the next performance. See if that will make any
difference.

If any of you guys have been down this path with a 912 installation,
would you mind sharing what you did, How yours works and how its
built?

Could really use some help figgering thisone out...


Thanks

Richard

"Cy Galley" wrote in message
newsiFEc.5861$Oq2.2704@attbi_s52...
NACA vents are some what difficult to get to flow.

I had read somewhere, that NACA ducts are poor at pushing air through
something as restrictive as a radiator. Add to that, the side of a cowl is
not a high pressure area, (lower than the front of the cowl, as a matter of
fact)

Push comes to shove, your friend may have to do a total rethink on the
setup.
--
Jim in NC


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Morgans wrote:

"Cy Galley" wrote in message
newsiFEc.5861$Oq2.2704@attbi_s52...
NACA vents are some what difficult to get to flow.

I had read somewhere, that NACA ducts are poor at pushing air through
something as restrictive as a radiator. Add to that, the side of a cowl is
not a high pressure area, (lower than the front of the cowl, as a matter of
fact)

Push comes to shove, your friend may have to do a total rethink on the
setup.
--
Jim in NC

---


Way back when he started doing the NACA inlets, I made the same
comments, refering to Bingelas and Jim Clement.

But hey, when somebody wants to do something, they gonna do it.

We clamped a 3" extension to the outlit lip and re-ran the test.
No change in altimeter readings and no noticible difference in the
tufts.

Does sound like the inlets are not in-letting, doesn't it.

Refering back to the photos (ain't digital cameras wonderful!) there
is also some indication that the big opening in the cowling is not
letting much air in. I'll add some shorter hair deeper in the opening
and take another look.

Next (easy) step is probably remove the Scat tubes and see if the
cowling internal pressure is any better at letting air into the
radiator enclosure.

After that, only thing I can think to do is remove the enclosure
and ReDo (the true meaning of R&D).

So far as our (net) research indicates, there are few other Zodiacs
with an internal radiator setup. All the earlier ones have the rad
hanging below the cowl.

Thanks guys.

Richard