Cooling and the VW

The subject of cooling came up recently (and thanks for the input Dave!). Here are a few picts of the things done to keep the little VW that powers Skye Racer cool.

Back when the plane was still flying in primer I installed a ground adjustable cowl flap to determine the optimal cooling outlet size. After I found the opening size at which speed went down and cooling stayed the same I made a fixed outlet of the same area.

The VW comes with what are typically referred to as "cool tins". In airplane speak they are referred to as inter cylinder baffles or shell baffles. Cool tins pretty much suck (in a bad way) letting massive amounts of air to get by the cooling fins without picking up any heat. I had found an article about a KR builder that had used fiberglass to make form fitted versions.

Here is a picture of my original set of "cool glasses" from the top. The bottom looks much the same. They were ultimately discarded since the engine would not cool properly. However, I have learned a lot since then and my most recent set look much the same but with "lips" on the inlet and outlet to reduce turbulence.

Oddly enough he concluded that they did not work... I have consistently seen head temps in the 350 degree F range @ WOT when measured under the spark plug for the past 6 years.

In 2006 I removed the 1850cc engine and built a 2110cc engine VW for the plane. Here is a quick pictorial guide to how I made the new "Cool Glasses" which have been in place since 2007.

Fast forward... One of this winter's mods was to add a 2"longer prop extension and a 2" smaller diameter spinner. The purpose of these changes is twofold. First, allow enough room to install a properly designed diffuser. Secondly, reduce frontal drag.

One of the pains that we VW airplane guys face is the annoyance of the exhaust pipes exiting the front and back of the heads rather than the bottom. Usually this forces our front two pipes to pass through the cooling plenum. The longer extension and smaller spinner allow for a lower drag cowl shape and a properly proportioned diffuser into the top cooling plenum without the exhaust pipes interfering. Below is a preliminary visualization of the new nosebowl shape.

Stay cool! (pun intended)