5.5.1 Install Door Lift Gas Struts

This entry is part 1 of 16 in the series 05 - Doors / Windows

Once again, I’ve deviating from the manual. I picked up a pair of Hangar 18 designed door gas strut brackets. These are supposed to cause less deformation in the door, operate smoother and be less obtrusive.

First task is to create hardpoints in the D-tubes that make up the door frame. For hardpoints, I’m going to use a 2″ x 1-1/2″ x 1/2″ block of aluminum. First I drilled and tapped the holes in the hardpoint. Then I located the position of the bracket.

Next I marked where I would open up the D-tube to slide the hardpoint in.

I then sanded the inside of the door frame and the aluminum hardpoint. Masking tape is applied to the outside of the door frame and bracket to keep adhesive from sticking to it.

Then I mixed up some structural adhesive with some cabo to thicken it. The adhesive is applied to the door frame and the hardpoint.The hardpoint is then inserted and the bracket is attached until the adhesive sets.

Once it set, I patched the d-tube and moved on to the hardpoint on the b-pillar.

11.1 Engine Cowl Mod

This entry is part 4 of 17 in the series 11 - Fairings

You may remember all the work that has been done to get the engine to fit: two of the intake tubes were replaced with custom built tubes to clear the cowling and then a hole was cut in the cowling for the main air intake.

Now it’s time to, sadly, modify the cowling so the air intake will fit.

Here’s a side, top and inside view:


I drew a shape to provide a symmetrical guide and rounded it out.  Then I made the cut and sanded the surrounding area.

To prevent an “bubble” where the hole was, I made relief cuts around the opening. Then I cut a piece of foam that was a little smaller than the relief cuts to go under the cowling. I large piece of aluminum sheet went under that. Then I made a “plug” out of triax that I covered with duct tape.

Then the area was covered with two progressively larger layers of BID.

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.


11.1 Engine Cowl Mod

This entry is part 5 of 17 in the series 11 - Fairings

Once the epoxy cured, I removed the cowling and flipped it over. A new triax “plug” was cut and epoxied into the hole which was then covered with 2 layers of BID and one layer of carbon fiber BID.


5.5.1 Door Lift Gas Struts

This entry is part 3 of 16 in the series 05 - Doors / Windows

Turns out that I was using the wrong length gas struts. Once Malcolm saw my pictures, he noticed that my strut was longer than he was used to seeing. So I picked up a 12″ (extended length) strut from McMaster-Carr, moved the hardpoint and voila! Door stays up when open and doesn’t distort when closed.

Here’s a picture looking forward from the back of the plane with the door closed.

Notice how the direction the strut is pushing is inboard of the hinge. Before the direction of force was outboard of the hinge.

Outside view.

Now I’ve just got to make the hardpoint permanent (it’s only temporary now), patch the holes in the B-pillar and repeat the whole install process on the pilot side door.

5.5.1 Door lift gas struts

This entry is part 4 of 16 in the series 05 - Doors / Windows

Now that I’ve got the door lift situation figured out, it’s time to work on the pilot side door. I did the initial work on the co-pilot door since that door won’t get as much use as the pilot side.

Now that I know how the system works, I’m going do the pilot door a little differently. As in stronger. The first thing to do is create a large backing plate/hardpoint out of 1/8″ aluminum.

Then I cut an opening in the top of the D-tube that will accept the plate. I drilled and tapped holes in the plate that will align with the mounting bracket and also drilled holes for rivets. Then I formed the plate so that it matched the contour on the D-tube.

Finally, I spread structural adhesive on the inside of the D-tube and the back of the plate and slid the plate into the D-tube and riveted the plate into position. Once the adhesive set, I inserted a piece of soft foam into the space and left a cavity about 1/2″ deep that a little longer than the opening I made to get the plate in. Then I mixed a flox/cabo paste and filled the area behind the plate. This will strengthen the D-tube where the bracket is.

Once cured, the area gets sanded down and I’ll cover it with a layer of carbon Uni and BID.


11.1 Engine Cowl Mod

This entry is part 6 of 17 in the series 11 - Fairings

Once the inside work was completed, I put the cowling back on to see how much room I’ve got.

It’s hard to tell from the picture, but there’s about 1/2″ clearance between the top of the intake and the inside of the cowling. It’s tight, but it should be enough.

The top needed a bit of work though. It was a bit bumpy with a couple low spots. So after consulting with Malcom, I filled the low spots with micro and covered the whole thing with  one layer of fine BID.

A little bit (hopefully, very little) of filler and it should be ready to move on to the next step.

5.5.1 Install Door Lift Gas Struts

This entry is part 5 of 16 in the series 05 - Doors / Windows

Once the pilot side door was done, I covered the area with a couple layers of carbon BID then filled and sanded the area. I then installed the hard point in the B-pillar and mounted the door.

Both doors open. But there’s a slight problem. Because of the geometry, a variation of 1/8″ in the hard point location translates to a difference of about 2″ in the door open position. You’ll notice the pilot door is just a bit lower than the copilot door. Without the horizontal lines of the door behind it, this would be almost impossible to see. Of course, if I weren’t 6’5″ tall, I would worry about it at all. But as it is now, that lost 2″ makes it just low enough to bump my head. Malcolm said that there are adjustable struts that provide about an inch of adjustment. I’m looking, but I haven’t found any yet.

To keep the motion of the strut smooth, I angled the hardpoint in the B-pillar. This made for an unsightly appearance. So I took some 1/2″ aluminum, drilled it, turned it down and then cut a wedge. I call this a wedge washer. 🙂

5.2.4 Door Hinge Installation (Modification)

This entry is part 6 of 16 in the series 05 - Doors / Windows

One of the common complaints about the door design is that it can leak. This is due to the hinge cutouts.

Here’s the top of the pilot side door opening with the door removed. You can see where the two hinges mount.

And here’s a closeup. Notice how you can see though? That’s how rainwater ends up in your lap.

Malcolm suggested covering this opening. So I got a piece of scrap fiberglass and cut it to the correct shape. Then I bonded it up place with an epoxy/cabo mix.

Once it cured, I covered the inside with a layer of BID and then filled the outside and sanded it smooth.

It won’t look perfect, but I think it will not be at all noticeable and any rainwater that come in around the hinge will have no place to go but out around the door.

11.1 Engine Cowl Mod

This entry is part 7 of 17 in the series 11 - Fairings

After the two outer layers of BID had cured, I filled the low spots with micro and covered the whole area with one layer of fine BID. Looks like a Turtle. I was tempted to put a head and legs on it and leave it. 🙂

Then it was time (once again) to fill. This is after the first layer of fill has been sanded and then another layer put down and guide coat and sanding.

Now it’s getting close. I had the shape worked out and all I’m doing at this point is fixing voids and a couple minor low spots.

I REALLY hate the spotted dog. But hopefully by next week I’ll be cutting the oil access door.