The back of the vents is too big to allow much airflow if they were put in
from the back, assuming that you could get them in there. Furthermore, they
would not then cover the edges of the holes. This way, the square flange of
the vents serves as a bezel, and the assembly is moved far enough out that
there is plenty of room for air to get in from behind. Looking at the
Grimes louvers, I think the open surface area of these is only slightly less
than that of the Grimes, which have a multi-slotted shutoff valve behind the
louvers. The real test will be to see if we get adequate airflow. The only
other disadvantage of these is that they stick down about an inch farther
than the originals. We may find that the bow of our headsets hit them when
you lean forward. I don't think it will be a problem, but we'll see. Glad
that none of us is real tall.

We don't have a flapper valve on our plane ('74 Archer). There is a blower
switch, but no control for airflow other than the vent outlets themselves.
We screw a shaped plate over the opening on the vertical stabilizer leading
edge in the winter. This works very well to keep the cabin warm, although
you need to remember to do it before you take your first long trip in the
winter. We forgot when we went to Montreal for Thanksgiving and froze our
butts off on the trip up. Borrowed a stepladder and put it on at St Hubert
before we headed home. Much cozier coming back.

--
Bob (Chief Pilot, White Knuckle Airways)


"Jay Honeck" wrote in message
news:3kL0c.16390$PR3.415911@attbi_s03...
They look great, Bob!

Two questions:

1. Did you try inserting the vents from the BACK-side of the ductwork?
(The
eyeball vents look too thick and large for that, but it's hard to tell
from
the pix.)
2. What is this "plate" in the tail that you remove in the warmer weather?
Ours has a flapper valve, controllable from in the cabin.

Thanks,
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"