Professionally built?

In a previous article, Orval Fairbairn said:
What we found (and corrected):

1. The oil cooler had insufficient airflow (both in and out). Remember
-- any cooling MUST provide an exit path for the air, as well as an
entry path. This installaltion had neither.

2. There was no blockage of cooling air in the nose bowl behind the
spinner, allowing air to exit behind the spinner. We installed the
appropriate baffles and seals there.

[etc]

Ok, this is where I get confused. I'm not a builder (yet). Don't the
plans or kit instructions tell you how to do all this? Do people diverge
that much from the plans, and if so, why?


--
Paul Tomblin http://blog.xcski.com/
Microsoft: bringing the world to your desktop -- and your desktop to
the world.
-- Peter Gutmann

Paul Tomblin wrote:


Ok, this is where I get confused. I'm not a builder (yet). Don't the
plans or kit instructions tell you how to do all this? Do people
diverge that much from the plans, and if so, why?

On many if not most kits the FWF instructions is not as nearly as complete
as the airframe instructions/plans. One reason for this is simple, The kit
maker also has little to do with the engine used in a lot of planes. For
example in the Zenith 601XL there are people that have installed multiple
flavors of Conts & Lycs, and Rotaxs, Jabirus, Subaru's, Corvairs, Suzukis,
and even Harley Davidsons.

In article ,
(Paul Tomblin) wrote:

In a previous article, Orval Fairbairn said:
What we found (and corrected):

1. The oil cooler had insufficient airflow (both in and out). Remember
-- any cooling MUST provide an exit path for the air, as well as an
entry path. This installaltion had neither.

2. There was no blockage of cooling air in the nose bowl behind the
spinner, allowing air to exit behind the spinner. We installed the
appropriate baffles and seals there.

[etc]

Ok, this is where I get confused. I'm not a builder (yet). Don't the
plans or kit instructions tell you how to do all this? Do people diverge
that much from the plans, and if so, why?

As "gig601builder" pointed out, a lot of plans are sketchy, at best, FWF.

That said, there are some decent books out there on FWF installations,
plus the exercise of common sense.

The biggest mistakes relate to airflow management, as on my friend's
plane.

A few basic principles:

1. Air must have a path out, as well as in. I have seen oil coolers
mounted with only 1/2 inch clearance between firewall and the aft face
of the cooler. No matter how much air you blow at the front side, it
cannot escape the back.

2. Use all of the air that comes in for cooling. Make sure that baffles
and their seals fit tight and that there are no gaps on their periphery.

3. You need blast tubes on the mags and alternator, as well as the oil
cooler.

4. Air inside the cowl will seek the lowest pressure areas to exit. A
common place is the front of the cowl, behind the spinner. That air
creates unnecessary drag and doe no cooling work. Baffle that area and
force the air past the cylinders, oil cooler, etc.

5. Exhaust pipes are an excellent heat source inside the bottom of the
cowl. You need some airflow there.

6. The more eyes that see your plane before it flies, the better. It is
far better to discover your errors (remember -- everybody makes some) on
the ground than to have them discover YOU in flight!

7. Get active with your local EAA Chapter and get to know the wise ones
-- they can save you a lot of grief!