CUSTOM TUNNEL COVER

 

There is a small assembly in the plans called the "Tunnel Cover."  The elevator push/pull tube is slightly higher than the level of the seat floors so this part is designed to cover this tube.  The photo below left shows the cover after I made the individual pieces, drilled the appropriate holes, and cleco'd the assembly in place.  The fuselage is still upside down at this point.  The photo below right shows the assembly after I primed it and riveted it together.  At about this point I started to think that there may be room for a taller cover which I named the "Custom Tunnel Cover."

Tunnel cover cleco'd in place Tunnel cover assembled

In the next photo, I am taking some measurements to build a cover that will be the height of the forward spar carry through (F-704).  I made a drawing in AutoCAD  seen in the photo of my lap-top below right.

Taking some measurements Measurements turned into drawing

I printed the drawing and pasted the print to aluminum with some spray adhesive (below left).  I then cut the aluminum to the size of the drawing on a sheet-metal shear (below right).  A band saw would have worked just as well but this was quicker.  Any well equipped aircraft shop will have one of these.  This one is in our facility in Florida.  You will need a little help from a qualified aircraft sheet-metal man.  They can usually be "bribed" with beer.

Drawing glued to aluminum Part being cut on a shear

Below left is a picture of the cut-out part.  Now it needs two bends along the lines that you can see in the lay-out.  In the photo below right one side is bent and the other is ready.  This tool is called a sheet-metal brake.  Don't let the sheet-metal man drink the "bribe" until this step is completed.

Part is cut out..... .....and bent on a brake

The new cover is ready to be fit checked in the photo below left.  I made four attach angles out of aluminum in the photo below right.  Obviously I was kidding in my statement about "bribing" an aircraft sheet-metal man but if you can befriend someone who has access to a brake and a shear you can make some simple modifications to your plane that can be fun to do.  Plan carefully.  If you don't have AutoCAD, a pencil and a ruler will do nicely.  A dime store protractor also would come in handy.

Basic Shape of the "Custom Tunnel Cover" 4 sheet-metal angles

I made the cover from .040 2024 T3 aluminum.  I made the angles from .032.  The next step was to final trim the part to fit.  I didn't take any photos because the process is straight forward.  I drilled the holes to mount the angles off of the original tunnel cover (photos below).  The left photo shows the angles clamped to the new cover and the original is ready to be clamped for drilling.  As you can see by the photo at right which was taken after the angles were un-clamped from the new cover, my cover will be wider than the original.

Angles clamped to new cover, old cover on top After drilling holes

I then screwed these angles to the seat floors (below left).  I set the new cover in place and drilled two holes in each side through the angles (below right).

Angles in place Cover drilled and cleco'd to the angles

I placed a piece of masking tape along side the flange of the cover that runs up the slope of the seat floor to the top of the spar.  I removed the cover and the seat floor.  I laid one of the longer angles along side the tape and clamped it down.  I then transferred the three holes where the floor attaches to the seat rib to the angle.  (Photos below, left and right.)  I also trimmed the ends of the angle to clear the top of the new cover and the other angle that is attached to the base of the cover.  I repeated this procedure on the other angle.  By the way, your eyes are not deceiving you.  All of the holes in the seat floors are dimpled.  See "Finishing the Cabin" for details.

Angle clamped for drilling Angle attached with screws

The next parts to make were two "Z" angles to attach the aft end of the cover to the flap actuator housing.  These angles needed to be more precise so it took me two tries to make them.  I could have riveted two "L" angles back to back to get the same effect but that would not have been as much of a challenge.

Right "Z" angle Left "Z" angle

Now to etch, alodine, and prime.  Photo below left shows these parts along with the modified center cabin cover and its parts.  Below right is a photo of the "Z" angles riveted into place.

All of the "custom" parts after prime "Z" angles attached

The installation of the "Z" angles meant that the flap actuator housing needed to have a hole added (see arrow below left).  Below right is a photo of the F-766A actuator channel with the added hole dimpled for the extra nutplate. 

Added hole in flap actuator housing Added nutplate in the F-766A

Below left are the finished angles attached.  Below right is the finished assembly.  Building this part gives me some options.  I can paint it and leave it stand alone.  I can attach a console to the top of it.  I can attach an armrest to the top of it.  I am not sure what I will do yet as I write this.

Finished angles Finished tunnel cover

 

Above is a photo I took much later showing the Tunnel Cover installed with screws.  The tunnel cover is done for now.  The next section covers the center cabin cover which I also modified from the original.