Raised Threshold, Gull Wing Doors & Piano Hinges

I've never been a fan of the Bearhawk's swing out door that conflicts with the wing strut.  When the lower portion of the door swings out, it hits the strut.  The workaround has always been what some call a "mouse door" at the bottom of the swing out to allow more door travel.  Personally, I think it just looks bad...  And functionally, it's just something you always have to be mindful of.  Passengers will always want to put their weight on the swing out when climbing in.  Who needs it?  I'm going to eliminate the swing out door completely.

Here's an example of a Bearhawk with a "mouse door" on the bottom of the swing out door:

I am a big fan of the Gull Wing style door.  I like how it flips up and is totally out of the way.  If built right, the airplane can be flown with the doors open.  When on the ground and walking around the plane, there is no bumping into doors or having the wind take one off its hinges.  

In order to have the Gull Wing style doors on the Bearhawk, a fairly involved modification is required.  First, the door thresholds must be raised for the door bottoms to clear the strut.  

 Before the Mod.  Existing door openings.

 Aluminum formers from the factory.

The factory door frames come in two pieces.  Upper and Lower.  My plan was to marry these two together.  

Mock up with zip ties.  The bottom portion will be shortened and the mouse door cut out removed.  I set them aside now that I have an image of what the door will look like and will finish modifying these doors later. 

I thought long and hard about how I would raise the threshold.  I was really thinking this would be a major cut and weld job.  But I was not interested in cutting into the airframe. 

So I came up with the idea of using wood.  Not just any wood.  Cedar.  It's light and rot resistant.  And, it is important to note that I am not using this wood structurally, only as a former.  But regardless, I wanted to make sure I was compliant so I consulted my AC 43.13-1B and found Table 1-1 Selection and Properties of Aircraft Wood. 

White cedar does comply...

It took a lot of compound cutting and shaping, but I think it came out great!  Once the airplane is covered the wood will never be seen.  The cedar is attached from the bottom tabs using stainless steel wood deck screws.

Trimmed the factory aluminum formers and they fit perfectly!

I welded the top and bottom portions of the doors together and placed them untrimmed in the new door openings.  I will use this as a guide to determine how much tube I will need to remove from the bottom of each door.

Cut the bottom tube for the fit.

Will use the cut-off as a guide to make the fit.

Running both pieces together through the band saw.

Using an insert with a plug weld to make a solid connection.

Trimmed bottom piece has been installed and now its time to remove the mouse door opening.

Same as before, cut both pieces together and use a smaller diameter piece to join the pieces together.

Corners and new bottom tubes installed.  Also working on the spring loaded pivot latch system. 

Newly fitted door and spring loaded pivot latch system

Two sets of small tube/pin hinges are included from the factory.  The door hangs on these.  I decided it needed a third tube/pin hinge in the center for support and stability.  

The spring loaded pivot latch works perfectly!

Zinc Chromate primer

Almost finished...  But wait!  I've decided that I do not like the tube/pin hinges.  Too rinky dink for me.  Since I've gone this far, I think I will do it right...  I will remove the tube/pin hinges and install a continuous aluminum piano hinge instead.  This will make for a nicer finish and better sealing.

Piano hinges fitted and installed.  I also installed gas shock door lifts.

I would have preferred to have installed the hinges inside the openings to hide all but the hinge pins like a normal door, but I could not come up with fasteners that would be 1.) flush, and 2.) allowed for occasional quick removal of the doors.

The only thing left to do now is cover both doors with Lexan.