5.5.1 Install Door Lift Gas Struts

This entry is part 2 of 16 in the series 05 - Doors / Windows

 

For the B-pillar hardpoint, I decided that since the mount would be in shear, I would use steel instead of aluminum. It only added about 5oz of weight and seemed the best approach. I had some steel from a trailer hitch mount that I cut a piece off of. Drilled and tapped for the stud.

Then I cut a slot into the B-pillar and inserted the hardpoint with some structural adhesive and let it cure overnight.

The next morning, I mounted the gas strut and…

 

From the inside with the door closed:

So far so good at this point. But after a few operations, I made a discovery.

Where I cut the slot to insert the hardpoint weakened the d-tube so that the stress of the 90lb gas strut cracked the fiberglass. When Malcolm builds the doors, he inserts a large piece of aluminum and secures it with structural adhesive and fiberglass. Since my doors are already together, I had to use a plan-B.

I drilled a hole near the hardpoint and injected an epoxy/cabo/flox mixture into the cavity behind the hardpoint. This creates a solid mass that distributes the load over a larger area.

The next morning I put everything back together and it worked.

But then I noticed a new problem. One that almost every builder has fought.

This is a view of top rear of the closed door.

The right, which is higher is the door. The left, which is lower is the fuselage. Now this is before latching the door. Once the latching pins are engaged it’s not as noticeable.  But here’s the problem.

The blue arrows are the hinges for the door. The single red arrow is the gas strut and the direction of the 90lbs of force that reduces the amount of effort required to open the door and hold it open. Since that force is pushing up at the rear, the front hinge becomes the pivot for the whole door. And what is about 3/4″ to the rear of the top hinge becomes about 1.5″ of deflection at the bottom of the door (black arrow).  The end result is that the door can’t be closed easily. I have to push the door forward to get it to close all the way before I can latch the door closed. And throwing the latch isn’t very easy either.

The current factory approach is to reverse the gas strut so it point down when the door is closed. But that just reverses the deflection pushing the door forward.

So I’m currently working on a solution. I’ve got it narrowed down to two candidates.

A) Reinforce the hell out of the top of the door. I determined that the area of the door where the hinges attach is flexing. If I can eliminate the flex, then I will have reduced the amount of deflection.

B) Use two opposing gas struts. When closed, one strut will be applying force upward and the other downward. They should cancel each other out resulting in zero deflection. I think two struts is going to look downright weird, So I’m going with Plan A first.

I’ve ground off the rear hinge pad. Then built up the area with 4 layers of Carbon Fiber BID. Since carbon doesn’t have the flexibility that glass has, I’m hoping this will reduce the flexing. If it does, problem solved. If it doesn’t… Plan B.

 

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