By Matthew Neumann • Originally published in Stunt News, March/April 2009
Editor’s note: This article was originally published in Stunt News and has been reformatted for digital readability. Original terminology, measurements, and technical details have been preserved where possible.
On some cowls, the head of the engine sticks out just a bit like on my Mustang. The design did not allow for the engine to be completely enclosed in the cowl. On this setup it is really easy to get to the glow plug for attachment of the glow plug clip and replacement of the glow plug itself.
You also do not have to worry about scratching or chewing up anything when you hastily remove the clip when the engine starts.
Matthew Neumann’s Mustang is finished as “Big Beautiful Doll.”
However, for my taste, I like a “clean look” airplane the best if at all possible. What this means to me is that you completely enclose the engine in the cowl, such as I did on my Stuka. But how do you get to the glow plug? The neatest and cleanest way would be to install a remote plug that has wires, one of which attaches to the top of the plug and one that goes to ground.
But you have to draw a line somewhere and I did not really want to add a remote plug and put it in an inconspicuous spot. So I do what many people do and made a hole in the bottom of the cowl that is slightly larger than the glow plug clip. However, this hole has a nasty habit of getting chewed up with use.
This happens when the clip is pulled out quickly when the engine is running because I am more worried about my fingers getting clipped by the prop than dinging the sides of the balsa access hole in the cowl. This is also an area which can get oil soaked very easily. Hey, it is right next to the engine! I had resigned myself to the fact that no matter how well I keep up with the scratches and gouges, this area will eventually just look lousy. Take my 2005 plane’s cowl. Yuk! But it does have over 2000 flights on it so I can forgive it.
The wear on this Stuka cowl after thousands of flights inspired Matthew Neumann to find a better solution.
One day, when I was shortening a carbon pipe, I took a look at the “waste” piece and got a brain storm. It looked to be about the same diameter as the hole in the bottom of the cowl for the glow plug clip. After a quick check of the dimensions, sure enough, it was. I now had a solution to the “chewing up” problem. I could use this piece to line the hole. I did this on my 2007 Stuka and after over a 1000 flights this area looks as good as new. I did get a couple of scratches over time but because the carbon is fuel proof, it was just a matter of getting out a fine paint brush and touching up that area.
To install the tube it is a simple matter of cutting off a slightly longer section than needed, making an appropriate size hole in the cowl, and then gluing in the tube.
The bare wood cowl with a hole cut for the carbon tube.
Now, on my Stukas I have a slightly unique situation because I install a baffle in the cowl to help air flow. I angle the baffle so the intake area at the front of the engine is smaller than the back. This helps to create a low pressure area behind the engine helping airflow. At least that is the theory/hope.
To construct this baffle, I use a piece of 1/16-inch sheet balsa that is installed cross-grain inside the cowl. I have to install some sort of tube in my cowl or I will get lots of oil in between the baffle and the bottom of the cowl with no way to clean it out.
The carbon tube installed in the cowl and sanded smooth. Note the similar treatment around the venturi opening.
To solve this problem, I originally installed a molded balsa tube but then came up with the carbon tube that I am writing about in this column. Here are some pictures of my current cowl being constructed.
This is a unique situation and most people will just be able to cut off a much shorter piece of carbon tubing to install in the bottom of their cowl without having to worry about the baffle. I am just showing this as an extreme case and how easily it can be installed.
Until next time remember: It is in the details!
The cowl as seen from the inside.
This article first appeared in the March/April 2009 issue of Stunt News and has been preserved as part of the PAMPA digital archive project.
