Mountain Models EVA Sport Build Thread

[rockyboy]

A couple nights updates here - progress has been slow but steady around other activities.

First up was gluing down the edges of the canopy base, then trimming flat and sanding smooth.



Then it was time to attach the rear former on the canopy base, using the recommended method of protecting with wax paper and taping into place to get the angle of the former just right before dabbing with CA.



During a visit to the laser cutter for the Caudron C.460 project, I made up a batch of magnetic hold downs with a little twist from the first set I bought. As it proved super helpful to have a handle on the back of the 'finger' style clamps, I designed in a 90 degree brace as the handle. Two tools in one



Next was figuring out mounting for the front tricycle gear. Using scrap plywood from the kit, I cut two pieces - one just long enough to fit into the opening in the firewall, and the second longer to fit exactly between the bottom of the fuse and the brace on the back of the firewall.



I stuck them in place with some white gorilla glue and applied clamping pressure (using a small socket as a spacer so the clamp didn't crush the frame)



And presto - a very secure mounting point for the nose gear!



And last up here is gluing on some attachment blocks for the cowling to mount into. Never was crazy about putting screws into the side of the firewall or body for a cowling. If a landing goes rough, damage is likely to more difficult to fix structures of the plane. With a softer balsa mounting block as the cowling attachment point, I have an easy to repair breakaway mounting point that will absorb some energy but give way with some smacking around. And when the screws eventually strip out the balsa (which they will sooner or later) it's simple to glue in a new block.

 

[Joker 53150]

Good call on the balsa blocks for the cowl screws! I haven't attached mine yet, and will surely steal that idea.

 

[Turbojoe]

Good idea! I've used hardwood blocks on mine. Haven't had a problem but now you can bet something will happen next flight and I'll wish I had used balsa instead!

I really like your angle/handle on the hold down fingers. Another one of those "why didn't I think of that" ideas.

Joe

 

[rockyboy]

Thanks guys - I figured out the balsa trick after getting a rather battered eFlite L-4 Grasshopper at a swap meet than had some rather extensive repairs needed on the nose from the prior owner drilling more than a couple screw holes. The %!&^* little plane still likes to nose over on any landing that's not perfectly greased in, but now the post flying day repair time is less.

 

[rockyboy]

So here's my approach for moving the main gear back for the tricycle layout. I added an extra blind nut into the existing bottom bracing plate one former further back from the first two.



And then I fabbed up a plywood mounting plate that screws to the three blind nuts in the fuse, and has two blind nuts in it that connect to the main gear - spaced 55mm back from the original mounting location. If the spacing turns out to be problematic, it should be simple to put together a new plate - and if I decide to convert back to tail dragger all the original locations are accessible.



Next challenge - when I put on the 1/2A nose wheel and the larger sized main wheels I need for the rough field I fly in, there is a little height miss match problem. So I need to either get a longer nose gear, shorten main gear, or risk going back to the smaller sized wheels. I'll keep thinking on this and move on to other parts of the build.



Getting started on the flush servo mounting here - 1/16" plywood mounting hatch, 1/16" balsa sheeting and 1/16" plywood bracing so far. Next up is putting in the servo mounting blocks, and installing it all in the wing.

 

[Joker 53150]

For the gear, why not just widen the stance on the aluminum mount by rebending it? That would in turn lower the tail and even it out.

 

[Turbojoe]

The widened main gear would add stability too. Remember, I bent up a new nose gear for mine. I also went 1/8" and drilled the mount for it. I have a bender and put the coils in mine but if you stay with 3/32" wire I think you could get away with no coils and still have enough flex not to tear the nose gear out of the plane. You'd only have the one bend for the wheel and you'd have infinite up and down adjustment.

Joe

EDIT: This is the bender I used. LINK

 

[rockyboy]

Excellent ideas guys! I'm very happy I decided to set that part down and move on to something else for a moment. I'll definitely widen the stance on the gear, and I always welcome the excuse to buy another tool. Thanks for the recommendation on the bender!
Thank you!

 

[Joker 53150]

I keep forgetting to buy a coil bender...

 

[rockyboy]

So I bought a coil bender. Now I need to learn how to use it.



But back to the flush mount servos for a bit. Below are a series of pictures that probably combine both the left and right side builds in an out of sequence fashion, but attempt to illustrate the process I used. Also, I missed taking a couple pictures in the early part of this process, but will attempt to explain in words what I missed.

First I messed around with a piece of foam board making a template for the plywood panel. Cutting a hole for the servo arm and cutting the foam out in a healthy square that left plenty of room around the servo to add mounting blocks, but didn't take up too much room. That foam template is in the picture above. In hindsight, I made the servo arm slot a lot wider than it needed to be.

I cut a piece of sheet balsa that fit snugly between the two ribs where I wanted to put the servo, grain parallel to the leading edge of the wing. Then I cut out the plywood square on the right side of the picture to match my foam template.

Placing the plywood square in the middle of the balsa, I carefully cut around the edges with the xacto knife. Before I got my sides flipped around too much, I marked one edge of the plywood and the balsa so I knew which way it fit in.

Then I cut two plywood braces wide enough to overlap the edge of the balsa hole and hold a screw hole - these are the darker strips on the left and right sides of the opening parallel to the ribs and crossing the balsa grain. Then I cut two balsa braces to make a fully framed in opening, and glued in the side braces on the hole edges parallel to the leading edge.



Next I put the plywood panel in the balsa and from the outside (the pretty face side) pre-drilled the screw holes in the corners. Very close to the corners - better view of this in pictures below, although you can sort of make out the holes in this shot from the back side too.

Then using my foam template I drew on the outline for the servo control arm slot, drilled a hole in the middle of it, and used a scroll saw to finish cutting out the slot.

Then it's time to glue in the balsa sheet to the ribs. Working carefully to keep the wing flat to the building surface so the servo panel will be flush to the covering, and putting a little side pressure on the ribs to keep a good fit, I added a little CA to tack it in place.

Then I added a couple thin balsa scraps up against the ribs and the box spar to add some strength at the glue joints, and did a final round with CA glue to lock it in place.



Next is a test fit of the servo and mounting blocks. I used 1/4" bass wood for the mounting blocks. One one wing the balsa side braces were a little too tight and had to be notched so the mounting block would fit in. Once that was dry fit and the servo still in place, I did a little drop of CA to hold the mounting block to the balsa side brace.



Then I removed the servo and did a solid bead of CA around the mounting block to the plywood.



Then it was time for a little bit of cutting on the balsa side brace to release the servo mounting block and let the servo panel slide out. Also shaved a little off the balsa side brace so the servo panel would easily fit back in.



With the servo panel lifted out of the wing, I did a dry fit of the servo, marked and drilled the mounting holes. I ran a screw into the holes with the servo in place to make sure it fit well, then removed the screws and servo to drip thin CA into the screw holes for reinforcement.



Here's the fully assembled flush mount servo from the back...



And the pretty shot from the front side. I mounted the plywood panel with servo mounting screws that came with cheap plastic 9 gram servos (that were hot glued into DTFB planes). Never throw away spare hardware from a project. It'll always come in handy later.



Next is canopy time - per instructions I drew a thin marker line around where the canopy edge should end and did a first pass cut leaving a healthy 1/4" extra plastic in place.



Then came the final cut to get the right shape. Afterwards the marker came off the edge with a quick thumb and finger rubbing. And if permanent marker slides off this material, I am sure most glues are going to be a problem too. Time to order or pick up some specifically made clear canopy glue for the final attachment.



And for inspiration I dry fit the whole plane together at this point. Looks pretty good sitting there.



Next up is spreading the main landing gear out and getting the nose gear height issue resolved, and then final sanding in preparation for covering. :applause:

 

[Turbojoe]

Nice clean work on the servo mounting. I just build 'em in place and slap sections of sheeting in. If I tried to make the hole in just one piece I'd miss the mark every time. Something I really suck at as I always seem to blow one measurement. Kinda like what I did with the EVA twin nacelles.

Don't try CA on the canopy. It'll fog it. HERE is the only canopy specific glue I know of. In the old days it was called RC56. Most LHS's carry it. It has very low tack and takes forever to cure so make sure the fit is perfect and tape or weight it in position until it cures. It does dry clear though.

For the wire bender it does take a little practice to get the hang of it. I trashed a few feet of wire before I finally made a good result.

Joe

 

[jsknockoff]

I agree on the canopy glue. RC56 works well but it's thinner than you'd expect and takes at least 24 hours to cure. Just did mine with it and it took 2 days for a clear cure, and it had to be taped in place. Dries crystal clear.

 

[Joker 53150]

Canopy glue for the win!

The servo plates look good, and it's a much cleaner look than stock. I've made plates like this for a few different planes - they're an annoyance to build, but are always worth it in the end.

 

[SlingShot]

Yeah. This definitely was a good choice. You guys are gonna do a great job showing these things off to advantage.

You've already sold me. I expect to go with one of their P-51's myself

 

[rockyboy]

Thanks guys!

Canopy glue on order.

 

[rockyboy]

Quick update. Distracted by fixing a bunch of indoor models and some Taranis programming for my Caudron, but this is back on the bench.

I gently spread out the main landing gear to a nice wide stance to bring the height down for the 1/2A nose gear. Then I snapped off a good 1-1/2" of the front nose gear wire trying to make the axle bend. And that just makes it too short. So I'm practicing slower bends with the remaining nose gear wire, making ugly pretzel shapes with my new wire bender, and getting ready to just order in a new set of 1/2A sized nose gear. :black_eyed:

 

[rockyboy]

New nose gear bent to appropriate size and mounted. Need to take a picture of that.

Time to finish up the tail pieces. First, a couple clamps hold the horizontal stabilizer down while I line up the elevator pieces and lay the connecting dowl across them for measuring.


After cutting the dowel to length, all the pieces can be clamped down leaving just a sliver of space between all the pieces for covering and movement clearance.


Adding good old Titebond wood glue for superior gap filling around the dowel. Added some filler on a couple rough joints to prepare for final sanding.


And final sanding and beveling of the edges where they need to move. The recommended bevels are on the rudder and the horizontal stabilizer - not the elevator. With the big dowel connecting the two elevator segments, it's not going to be easy to get that to bevel smoothly. Also added the bevel on the ailerons - following the instructions to make one right and one left ailerons, rather than two identical ones.


And getting ready for covering. Here's the work area and most of the parts stretched out. The wooden working surface is a cheap hollow core door, with a piece of glass over about half of it. Glass is sharp, so I taped over all the edges with painters tape - leaving it loose over the edge - to prevent leaking blood all over the balsa. On the left are the heat gun, covering iron, trim iron, and heat glove. On the ledge are trim, pinstripes, and my dwindling box of 100 single edge razor blades.


The covering idea I have is something like this scheme, done in black and cream, with a curve or two thrown in just to try and up my covering game a bit. Probably do the underside of the wing primarily black, with a little cream color thrown in - maybe a star burst effect to try another technique.

 

[jsknockoff]

I like the 2 tone in the fuse. If you're trying some curves I'd say a good spot to put one is up in the cowl area to avoid the straight edge where the color meets the edge of the cowl.

 

[Joker 53150]

I love those magnetic building jigs, and now that I have a 3D printer I'm going to start making some different styles.

 

[rockyboy]

I like the 2 tone in the fuse. If you're trying some curves I'd say a good spot to put one is up in the cowl area to avoid the straight edge where the color meets the edge of the cowl.

Exactly the one I've been thinking of first