Trent's RV14 Build: Cabin Arm Rest / Storage Box / Seat Foams / Throttle 42-02: Flap Cover

I finally recieved the seat foams from Lemke in Germany, and have been working on my panel. Part of that planning was to work out where i wanted the throttle to be located. Since i can't order the throttle cable until i get the engine hung, my dad 3D printed a throttle mockup for me to use. I was able to sit in the cockpit and make sure that the throttle posistion felt good.

However, when i first sat in the cockpit i felt that a centre arm rest would be a good addition, plus would add some storage. There is one commercial option available for this, but it is expensive and to be honest i didn't like the look of it that much - so i decided to come up with my own.

Initial Mockup

I began by making up a cardboard mockup, to work out the best height and location for the armrest. I wanted it to have an opening lid (for storage) and have an integrated place to include a USB-C ipad charging plug. I used some timer battens to make sure the top of the arm rest was parallel with the longitudinal axis of the aeroplene, by aligning it with the existing side armrest. I was then able to drop some measurements and draw up the required side profile. From here, i cut out a couple of iterations of cardboard before i had one i was happy with.

The battens on the side allowed me to align the top of the mockup with the longitudinal axis of the aeroplane - also to offset the armrest a little higher (as the side armrests are very low).

The original design was stright up and down at the front, so it did not cover the location of the power adapter port i the centre tunnel, however i hated the look of this. So ended up angling the front faces, and including a location for the power port, integral to the armrest.

I didn't really like the look of this.

Looks like it's from a Volvo.

This is a lot better IMHO!

Modelling in 3D

Once happy with the mockup, I drew up a basic box in On Shape, which represented the outer dimensions of what i was going for. This was thin enough in width, so i had room to add flanges to bolt the armrest to the existing #8 screw holes in the centre tunnel cover, with the appropriate edge distance.

The OnShape file can be viewed / downloaded here.

From here, i was able to use the excellent 'sheet metal' tools in onshape to create sheet metal parts from each of the faces. The parts were made such that the outer dimensions did not exceed the original box size. Rivet holes were added through the parts, and screw holes were laid out on the lower flanges. Space was left to allow a standard hinge (left over from the kit) to be used to hinge the top lid. I chose to make it out of 1.5mm sheet metal, as this will be getting sent to China for cutting (and that is a standard metric size there).

OnShape is an awesome tool for this - it has all sorts of tools to make professional looking sheet metal parts, including reliefs at flange bends etc. I stuck to standard bends - like 15, 30, 45, 60 degrees etc - as this keeps the manufacturing cost down (least that's what i read).

Once complete, the parts are exported as 3D .STEP files, and they were sent off to JLC CNC in China to be manufactured. I chose 1.5mm 5052 Aluminium.

The files were uploaded on the 29th of August, and after a couple of days where they wanted me to adjust a couple of flanges etc, they had been manufactured and were sent to me on the 31st August. Unbelieveably fast - the total cost, including shipping was $70 USD! (This is about 20% of the cost of a commercially purchased console).

Parts in Real Life

The parts arrived on the 12th of Sep - that was 2 weeks from file upload to parts on my doorstep. I think that is unbelieveable. I immediately cracked on to cleaning up all the edges, as well as drilling the hinge to the top and lid. I had to modify the lower flange of the front face a little bit - they needed to have this flange this way for their benders to work.

This flange corner needed to be this way for their bending machines to work - it wasn't a big deal to trim this off.

I was a shocked as anyone that the screw holes all aligned to the floor. Afterall, these were just measured with a ruler!

I match drilled some left over hinge to for the lid.

The hinge pin is bent 90 degrees, and is held in place by tucking it in against the armrest sides. The hinge is modified slightly to allow the pin bend radius to nest into position.

The hinge pin won't vibrate out of place like this, but this lid can still easily be removed.

The aft side holes of the armrest, get match drilled to the flap cover sides. These will be updilled and the armrest will eventually screw in with #6 panhead screws.

The aft side holes will be matched drilled to the flap cover, and screwed on with #6 screws.

The wires for this power plug will come up through the original hole location. I will probably 3D print a little cover for this which will just friction fit into place.

The height worked out really nice - once i include a pad on top of the armrest, it should be perfect.

The angled face of the lower panel allows for easy viewing when plugging in an ipad or phone charging cable.

It was cool to take something from a computer screen and into real life so easily - what a world we live in!

Finishing it off

All the rivet holes were countersunk for flish rivets, and the whole thing was deburred. The aft #40 holes on the sides overlap the flap cover, so these were match drilled then i enlarged the holes for #6 screws and drilled the flap cover for nutplates. The sides of the armrest were drilled to accept some standard cabinet magentic closures, and these will be held on with #6 screws and nuts. The lid was drilled to accept the steel catch plates - these will be double flush riveted on.

A little drill template was made up - the small #40 holes are to accept the non-rotation dimples on the steel plate. The plate iself will be double flush riveted using a single AD4 rivet.

All the parts were cleaned, etched and primed. I was then able to rivet the nutplates to the flap cover using the squeezer, and rivet the flap cover together. I used the gun and a bar - it's been a while was but good to know i still had the skills!

These nutplates are not as per plans - they are added so the armrest can be screwed to the flap cover.

A gross error check to make sure the holes all lined up!

I was then able to rivet the armrest together also - this was done with flush rivets.

I squeezed the rivets for the hinge. The 5052 is pretty soft, so you have to be careful not to oversqueeze.

As designed, the hinge in can be inserted with the lid open - the pin is then rotated so it is flush with the sides of the armrest, and won't vibrate out.

The completed unit!

The magnetic catch plates were riveted on, then the magnetic catches were installed using #6 screws.

The top side is double flush riveted using AD4 rivets. I really could have used a -3 length but didn't have any, and my cutter doesn't go that low. These are -4 but i think they are ok - you won't feel them with your elbow once the pad is on.

I thought i better test the catches holding power - they release at 5.32 Kgs (11.7 lbs). I think this is ok.

The only small issue which i did not forsee, was a little bit of interference with the top plate and the rivets of the flap cover. I could have dimpled these and used flush rivets had i known, or adjsuted the design of the top plate. However, it was minor so i just relieved the top plate with a file.

It's in!

The only thing left was to screw it in, and see how it works! I am very happy with this - it is very sturdy and it can easily take my body weight when lifting myslef up and out of the cockpit. When sitting in the cockpit, it can easily be opened to access the contents inside. I may add a 3D printed Ipad storage sleeve on the side one day.

Heaps of storage! I will likely add a thin bit of carpet on the bottom eventually.

I think the deisgn looks ok. The from panel angle was designd to roughly match the seat back angle.

It can easily take my body weight.

The top will ultimately have a little 1" thick pad and be covered in leather, so i mocked up a little pad to see how it felt. I think the height is perfect.

I will do better than this when the seats are upholstered, but this gave an idea of height needed.

Such high level upholstery skills! :)

Like the look of this and want one?

If you would like this for your own aircaft, a link to the .STEP files are below. Keep in mind that these are 1.5mm sheet metal - if you are sending to the US, you may need to access the OnShape file and adjust the settings for 0.062" sheet metal - althrough i think SendCutSend can do this for you.