Cowl Surgery Continues

Since my last post, I have gotten the cowl flanges jigged to the airplane, and started to build the form for the new cowl. I previously had made a template that will define the outlet of the air exit, and that was bolted to the prop extension. The next step was to add some guides to the areas over the cylinders to define the shape.

I did this by adding thin, flexible pieces of of wood between the air exit template and the top of the spar in front of the cylinders. I am extending the cylinder bump forward over the spar for two reasons. One is to make the curve more gradual to prevent flow separation. The second reason is to add clearance on the engine mount bolts where the mount attaches to the airplane.

You can see what will eventually be the shape of the cylinder bumps defined by the splines.
You can see what will eventually be the shape of the cylinder bumps defined by the splines.

These splines are pieces of 1×2 that were ripped to 1/8 inch. In hind sight, it would have been much easier to use round dowels, but I didn’t have any on hand. The length of the wood spline is what changes the curvature of the cylinder bump. NOTE: These splines were how I proceeded. They were too bulky, giving excessive clearance on the cylinders creating a balloon like shape thus being higher drag and ugly. I have to remove them and lower the profile, and have a new method of gauging engine clearance.

Next was a marathon session of creating dams and mixing pour foam to cover over the engine and give me something to work with. It took almost a gallon of pour foam to do this, now I wasn’t as good with my dams and a lot spilled out and into areas that were not useful. Take your time plugging holes and areas where the pour foam will go that you don’t want it.

All pour foamed and ready for shaping.
All pour foamed and ready for shaping.

I started by sawing away that which looked like it didn’t belong, taking little bits at a time and trying not to take off too much. Eventually, I switched to the surfoam file and then sanding blocks, both round and flat. It is a tedious, slow process since you don’t want to take off too much. The aft template and the splines act as guides for the shaping. This is what I ended up with after 3 sanding sessions representing a few hours.

While I am to the spline references, I am not happy with the shape.
While I am to the spline references, I am not happy with the shape.
The back end looks reasonable, but not there yet. The aft slope of the cowl bumps have too steep an angle.
The back end looks reasonable, but not there yet. The aft slope of the cowl bumps have too steep an angle.
The back end looks reasonable, but not there yet. The center hump has a huge discontinuity that needs to be addressed.
The back end looks reasonable, but not there yet. The center hump has a huge discontinuity that needs to be addressed.

 

 

 

 

 

 

 

By this point, I was disappointed with the cowl shape that was emerging. Luckily, I have some friends who are very experienced, educated, generous with their time, and extremely patient with a person who sometimes needs to be led along the path by baby step. So now I have a clearer plan to correct these problems and inch towards something better. Lets see  how that goes.

In other news, over the last few work sessions, from time to time I needed a break from working on the cowl (scratching my head). Plus it keeps me more motivated and happier with the project if I feel like I am getting something done. So I try to keep small projects going so that by the end of a work session, I can “check” something off “the list.”

A few of these things have included getting the front seat intercom jacks and 12V receptacle mounted. They are mounted in a recess in the left console that will have a spring loaded door. There will be a finger sized, semi-circular hole in the top of the door for opening the door as well as for coords to pass thru. This idea was shamelessly stolen from Nick Ugolini. The door is yet to be hinged and finished.

Other things were closing out the elevator root ribs and mounting the rudder pedal hard points for the adjustable pedals in the front cockpit. I also had to make the slip tubes that connect the pedals to the master cylinders. These will need further work to rig them for the proper rudder/brake actuation. The pedals also need the cable attachment installed.

The rudder pedal hard points were glassed in and the slip tubes connecting the pedal to the master cylinder were fabricated.
The rudder pedal hard points were glassed in and the slip tubes connecting the pedal to the master cylinder were fabricated.
The elevators were trimmed for the root fairings, and the root ribs were added with flox corners.
The elevators were trimmed for the root fairings, and the root ribs were added with flox corners.
The recess will have a spring loaded door on it. Inside are the intercom and 12V receptacle.
The recess will have a spring loaded door on it. Inside are the intercom and 12V receptacle.

 

 

 

 

 

 

 

 

I have a few hours tomorrow to work on the airplane, lets see if I can get a start on streamlining the cylinder blisters.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s