5.3.1 Door Latches

This entry is part 9 of 16 in the series 05 - Doors / Windows

One of the things about the stock Velocity kit that I really don’t like is the door handle. Some people call them “Toilet flush” handles. Here’s why:

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That’s how you open the door from the outside.

The inside isn’t much better.


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After poking around on the internet, I found some door handles designed for experimental aircraft.

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Not only is it flush mounted, but it includes a lock. The handle is spring loaded and pops out to operate.

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Installing this is going to be easy compared to making it work with the four pins. The person that designed the handle made it for a Van’s RV airplane. They only have two pins (one going forward and the other going towards the rear). In this inside view you can see the center pivot screw and the forward and rear screws that the two links connect to.

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With the interior handle removed, you can see the hub (or what the manufacture call the “driver plate”.

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So how do you connect four links to a handle designed for two? Improvise!

The Velocity door has an upper front and rear pin like the RV’s. Which means I only needed to accommodate the two lower pins. So I made a “Cam Plate” that would tie in to the existing hub. In this picture, I haven’t drilled the two holes for the lower pins yet.

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Here it is on the hub.

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Once I was certain that I could design the interface between the handle and the pins, I was ready to install it in the door. First, I decided that I would use the hole for the existing handle for the lock of the new handle. Then I drew a level line on the outside of the door centered on that hole. I drilled a pair of holes on that line so I would know where the centerline was on the inside. Then I marked where the handle assembly would be and where the hub would be.

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Using Malcolm’s trick, I further identified the line with masking tape.

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Then I cut the inner skin and removed the foam leaving only the outer skin.

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Next I cut a template so I would know where the cut the outer skin.

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And marked the outer skin.

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And cut the opening.

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I had to recess the inner skin and foam to allow for the movement of the handle and lock.

Handle in place (closed).

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Handle in place (open)

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From the outside

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Besides the appearance, another bad thing about the handle is that it’s HARD to operate. Once I looked at it I discovered why.

There are four pins that engage the doorframe to keep the door closed. These pins are attached to shafts that tie in to a cam that the door handle operates. The reason it’s so hard to operate is that when the cam rotates, the shafts move laterally and bind in the sleeves at the door edge. Except for the upper/forward pin. That one uses an intermediate link.

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 Here’s an animated gif that shows what’s happening.


In a previous life, I was a repaired IBM Selectric Typewriters. They’re the typewriters with the golf-ball thing that bangs into the paper to make print. Something like over a thousand moving parts with almost 500 adjustments. It’s a wet dream for Rube Goldberg. So with that background, I was certain that I could build a better mechanism. The key was to keep the pins (and their attaches shaft) movement linear. That would require what I would call an intermediate link. So I make the shafts shorter, mounted a sleeve to maintain the alignment and built eight intermediate links.

 Here’s the end result.


Closed to open

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Over-center spring

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I located the holes in the cam so that the links would be over-center in the open and closed position. This is to keep the handle from opening (or closing) by itself. I also put a spring on one of the shafts to “load” the mechanism. This will apply pressure keeping the handle in the open or closed position.

Here’s a video (1 MB)

Then I had to remove the receiver sleeves in the door frame because they were set for the positioning of the old pins. Once I got them removed, I put the doors in just to give myself a pat on the back.

Right door.

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Left door.

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Uh-oh. Something doesn’t look right on the right door. So let’s play “Find Waldo” and see if you can tell what’s not… good.

I’ll wait.

Did you find it?

Here’s a close up.

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It’s not level! I put these marks on the outside but all the cutting is done on the inside. Somehow, I put the door handle in and didn’t check the outside alignment. I thought about for about 5 minutes before deciding to remove the handle to correct it. I know it’s only off by about 1/8″. But there’s the slippery slope. If you let this slide, it makes it easier to let the next thing go and pretty soon you’re flying something that’s held together with duct tape and bailing wire. Besides, what if I put a stripe down the side of the fuselage and it’s right next to the handle? Then it’s really stick out!

Removing the handle, enlarging the opening and epoxying the handle back in only took about two hours so it wasn’t a huge issue.

5.5 Strake Extension Cutout

This entry is part 10 of 16 in the series 05 - Doors / Windows

One of the things Ann did at Oshkosh was look at every single Velocity interior she could find. Since she is designing the interior, she needed ideas. Unfortunately, she found some.

Here the scoop. The strake extends forward about halfway into the door. What most people do is make a triangular cutout in the door and use that space as a type of arm rest. My plan was to skip this step. Ann didn’t like that. She and Malcolm both strongly “suggested” that the cutout be made… and it was.

But there’s a catch. When I designed the door linkage, I didn’t think there would be a cutout. If I did, I would have accommodated it. As it was, it required a bit of a workaround.

First I had to remove the lower/rear pin and it’s linkage.

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Then it had to be relocated forward.

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Next I cut out the door panel where the strake extension was. That’s when I noticed that I would need a slight dogleg in that link.

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The strake is made of 1/2″ foam with a outer and inner fiberglass skin. That “sandwich” of foam and fiberglass is what gives the structure it’s strength. Now here’s a Hangar 18 special: Remove the inner fiberglass skin and foam. That way you pickup an additional inch of room. But it’s weak with just the outer skin. Carbon Fiber to the rescue. I hadn’t worked with CF before but afterwards, I think it’s easier to work with. If only it weren’t so EXPENSIVE. Here’s two layers of carbon fiber ready to be cut and laid in place.

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Opening before:

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Opening after:

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And it’s stronger.

5.2 Correcting Door Fit

This entry is part 11 of 16 in the series 05 - Doors / Windows

Now it’s time for the doors. Once again I didn’t get pictures but I’ll try and explain. The doors DON’T FIT. Well, they do, but not very well.

This is a picture where I’ve indicated the fit problems. It sticks up at the top rear. It sticks out at the bottom rear and it’s inset at the bottom front. Now one fix is filler. LOTS of filler. But there’s two problems with that: 1) You’ve got to try and fair in all that filler so it looks right and 2) that filler has weight. And every pound of filler is a pound of passenger or baggage or fuel that you can’t carry.

I had discovered this fit problem earlier but wasn’t sure how I was going to fix it. Malcolm to the rescue. 🙂

Here’s what we did. Where the hinge mounts at the top rear of the door, we added a two triax layup (the front got a 1 BID layup too). This moved the rear of the door down. The twist at the bottom will be taken care of by shimming the door so the bottom is flush and gently heating the door with halogen lights. After about 24 hours, the door will be “warped” into alignment.

Once the hinge pads were cured, we had to drill new holes for the hinges. This creates a bit of a challenge because if the holes are not in EXACTLY the right place, the door won’t fit properly. My solution was to use a VIXX bit. While I was at Home Depot looking for one (Which sucks because I’ve got a collection of them at home), Malcolm called with an idea. He had me buy 4 set screws with the same thread as the holes in the hinge (I think there were 10-32). When I got back, he drilled out the center of the set screws. So I climbed inside and the he held the door in position. I put two set screws in each hinge. When the door was in exactly the right position, I drilled through the center of the set screws into the fuselage. Then I removed the set screws, flipped the hinges out of the way and enlarged the holes to their final size.  I held the hinges in place and Malcolm screwed the hinges in place from the outside. Then I did the remaining two holes in each hinge. When we were done, the top of the door fit almost perfectly! 

Then is was time to do the other door. And that’s when I got a surprise. While we were working on the door, it’s sometimes necessary to bang on it to get the door in position. While I was inside and Malcolm was “encouraging” the door into position, I became weightless! Relative to the inside of the plane, that is. The main landing gear is held in the “down and locked” position with an over-center stop and latch. The nose gear has an overcenter stop and a gas strut. What I’ve always done is to put a wire tie around the nose gear arm and the over-center stop… Just in case. Well, in all the moving things around, that got over looked. While Malcolm was banging on the door, the nose gear actuator arm bounced and got… under-center. At which point the nose gear retracted. And the nose went down.

I climbed out, we lifted the nose off the ground and put a sawhorse under the nose and then looked at the damage.

During previous maneuvering, the nose wheel got rotated 180 degrees from it’s normal position. This turned out to be a good thing. When the nose gear came up, the tire hit the bottom of the fuselage and then broke through. This slowed the descent so that when the fuselage came in contact with the floor farther back, there was no damage. These cracks up here aren’t in a structural area and are easily fixed.

So from now on, either there will be a wire-tie on the nose gear arm and over-center stop or there’ll be a support under the nose.

Once the door hinges were finished, lights were placed on the inside warming the door while on the outside a heavy shot bag pushes the door into position.


5.2.3 Door Fit (Improving)

This entry is part 12 of 16 in the series 05 - Doors / Windows

At this point, the doors have been “encouraged” into the correct position as much as possible. They’re still not done. To get the rest of the way will require the sleeves around the door frame to be reinstalled so that the latching pins will engage more smoothly. When I modified the door latch mechanism, these had to be removed.

The first task is cutting new sleeves (4 for each door). Then with me inside, the door is closed and latched. Then Malcolm pushes on the door until it’s flush on the outside. While he’s holding it, I determine how much space exists between the door frame and the sleeve. Then it’s out of the plane and we temporarily glue a small wooden spacer (of the correct thickness to the sleeve.  Then back into the plane, the door is closed and the sleeve/spacer is glued to the door frame.

Here’s what it looks like.


This is temporary though. The sleeve can still move some. Now it gets potted in place with an epoxy/milled-fiber/cabo mix. Malcolm has a trick for making a nice end product for this assembly. Rather goop the epoxy around the sleeve and try to make it look nice, he had cover some thin cardboard with foil tape and cut to make a barrier.

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The first one needs to be open at the bottom for a micro switch. So a “cap” is put on the bottom of that sleeve. On the other sleeve, the bottom just gets covered over.

Then the epoxy mix is spread over the sleeve. Once it’s cured, we sand it smooth and cover with 2xBID.

The doors are officially “relaxed”. Into position, that is.

Here are some pictures of the doors after a lot of time under the lamps.



I can’t tell you how pleased I am with the results. Before this process, it was looking like large amounts of filler would be required to make the door fit look good. This is just one of the advantages of having access to one of the premier Velocity builders.

Thanks Malcolm!

5.2.2 Door openings

This entry is part 14 of 16 in the series 05 - Doors / Windows

After re-aligning the doors, there were some areas that didn’t have enough clearance. So those edges of the door opening got sanded down and in some places we went through the glass into foam. So those had to be filled and glassed.

Once that was done, then we had to make the space between the door and the fuselage a uniform width (and straight). This can be tricky and tedious. Since the doors are opening and closes all the time, a wider gap has to be created (unlike the wing-to-strake joint). And it’s not a straight line; it curves. So Malcolm obtained some conveyor belt material that was flexible and just the right thickness. We cut templates out of cardboard and then transferred those to the “spacer” material.

Here are some of the pieces ready to go.

The areas of the fuselage that are low have to be marked so we know where to add filler.

The following are pictures of the door with the spacer material inserted and the doors and fuselage marked.

Release wax is applied to the spacer material prior to being inserted into the gap between the door and fuselage. Then a thick cabo and Resin Research mixture is forced between the fuselage and spacer material. Since this will be an exposed edge, using just micro balloon would be too fragile. The cabo will provide a very hard edge that won’t crack when hit getting in and out of the plane.

Then regular micro balloon filler is used away from the edge to take care of the low spots on the fuselage.

And then it was sand, sand, sand.

Since the conveyer belt material was only smooth on one side, it was only possible to do one side at a time. So the procedure was repeated for the door side of the gap.

And then it’s sand, sand, sand.

I wish there was some way to illustrate the finished product. The lines are just awesome. When you run your hand over the surface from fuselage to door to fuselage, it feels perfectly smooth. But there’s no way to get a picture of that. So once we shoot it in white, shiny primer, you’ll see.

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.

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.


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.


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. 🙂