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FTFC'18 WWII Focke-Wulf FW-42

rockyboy

Skill Collector
Mentor
Weird. Its throwing me a invalid attachment too now. And of course I already cleaned up the source image off my phone. *sigh*

Instead, lets try this preview of the skinned fuselage in progress. :)

20171106_233555-800x450.jpg
 

rockyboy

Skill Collector
Mentor
Thanks!

It was a real pain in the butt getting it aligned on the fuselage. The littlest angle compounds a lot at the other end of the long piece of foam - and 3M77 doesn't like to be repositioned.

But it turned out pretty OK so far :)
 

rockyboy

Skill Collector
Mentor
About 1/4 of the way through the build now... and taking lots of pictures for the build instructions. Since I'm doing the work jumping back and forth between parts, I'm not posting as I go here. There are a couple tricky things about the order of assembly so I want to write the instructions in a nice clean order to give anyone trying this a good build experience.

But for an update, let me share the link to the Easel online CAM software I'm using to run the cut jobs for the needle cutter. I'll post this up on the home page with the final plans links too.

http://easel.inventables.com/projects/KB1zU34DuBojtJqOJVP4EQ

It looks like this now, with all the parts coming out of 3 pieces of foam just like the full size printed plans.

Capture.PNG

I am having a couple challenges with the speed of the gcode this software puts out, but I've also got an idea to try to solve that. More info over on the Lowrider CNC thread if you're interested.
 

PsyBorg

Wake up! Time to fly!
Mentor
That looks great Rockboy! The camo really sets it off specially with insignia gfx.

When the time comes if you could get me the height and width dimensions on the big one from the windscreens most forward part to where it transitions back about 20 inches That would be where I am planning for the bomb sight and bomb bay assembly to be. Then just a to be determined angle to aim the cockpit camera out the bottom when it transitions to the bomb sight role where a clear plastic piece will allow us to see out the bottom of the craft to aim with.
 

rockyboy

Skill Collector
Mentor
Build Instructions

Cutting and Skinning

If you have access to a laser or needle cutter, that's great! You can probably use the gcode exported by the Easel tool here to get your 3 sheets of foam cut http://easel.inventables.com/projects/KB1zU34DuBojtJqOJVP4EQ

If not, and you don't mind spending a little scratch, use the full size PDF plans here. And if you're impatient and have a regular home or office printer, here are the tiled PDF plans for sticking together. Either way, get some print outs and use your favorite FT technique to cut some foam. Personally I like using stick pins on the lines to hold everything in place while I make the cuts with a straight edge.

If you want to use the skins, download them from here. You'll need a way to print out Arch D sized sheets - 24"x36" or larger. Personally I use Staples Engineering prints service https://www.staples.com/sbd/content/copyandprint/engineering-prints.html - about $5-$6 per page. Don't use their photo quality printing! Only the Color Engineering Prints!

To apply the skins, buy some 3M77 spray adhesive and check out this excellent tutorial by Rasterize. I had just enough overlap on the printed skins to cover the edges of the foam pieces for a nice clean look. Just make sure to use a stick pin or razor to make some holes where the important features of the parts are, like aileron lines and nacelle mounting holes, before putting the skin on the second side of the foam. Otherwise it can be tricky to figure out where things are supposed to go. I recommend starting with nacelle assembly if you're doing the printed skins - practice applying the skins on the small parts before trying the wings or fuselage. It can be a tricky process, but the end result looks great!

skin 2017-11-06 21.49.19.jpg
nacelle 2017-11-06 22.04.39.jpg
nacelle 2017-11-06 22.28.21.jpg

You'll notice the skins in the photos have some exposed black lines on the fuselage where the other parts are mounted. I've removed those the 'Pre Cut' version of the skins to address any alignment issues between pre-cut parts and the skins. There is a whole other methodology for doing skins where all the cutting / scoring marks are on the skin and it's meant to be applied to a full sheet of foam and then cut out - that's more of the idea behind the 'Post Cut' skins plan.

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Canard Assembly

The canard can be made operable in a couple different ways. Jpot1 and others have some posts showing how to make a fully operable canard surface with a bamboo skewer for a pivot point. Litterbug has shared out a 3d printed model for pivot points that will protect the foam and keep things moving nicely if you go this way, or you can glue on some washers or credit card material with a hole in it.

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I like to make this canard with operable flaps instead of the whole thing moving. Just feels like the front end will hold up to my landing style better this way. I use a single long pushrod going to both flaps with bits of heat shrink tubing to keep things turning in the right place. To get a solid connection to the pushrod with a spare servo horn, rough up the pushrod at the connection with a file and use epoxy. I've tried this joint with CA glue, and had it fail after just a couple days of moving around the shop.

canard 2017-11-07 21.35.33.jpg
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canard 2017-11-08 16.44.32.jpg
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canard 2017-11-08 22.19.19.jpg

Fuselage Preparation

Before folding up the fuselage, glue in the two doublers that will hold the receiver & battery tray, and glue in a paint stirring stick or similar support across the transition between wide and narrow fuselage sections. Make sure to leave enough room for the canard up front.

fuse 2017-11-07 16.19.49.jpg
fuse 2017-11-07 16.21.36.jpg
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Use an A fold style for the sides of the fuselage, and insert the radio/battery try and wing saddle support blocks as shown.

fuse 2017-11-08 16.41.19.jpg
fuse 2017-11-08 17.02.46.jpg

Nacelle Assembly

You'll need these built before finishing the wing, so might as well do them now. Do NOT glue them to the wing until after the wing is inserted into the fuselage though - otherwise you'll need to either install the wing as two separate sections into the body, or cut the fuselage sides and top a bunch more so you can drop it in place. Much easier to just put the nacelles together now, and sit them to the side for a minute.

nacelle 2017-11-09 23.52.49.jpg
nacelle 2017-11-10 16.28.31.jpg


Wing Assembly

The wings need a spar to keep them from separating later in storage (like prototype v3 did) so I used a pair of chopsticks and a long bamboo piece from a busted window blind I saved. Look for whatever you have handy. This is also a place to modify the plans if you'd like a more stable flying experience, adding a touch of dihedral between the wing sections will have a very pleasant impact on the flight characteristics. See Nerdnic's bent aluminum spar technique from his SpeedWing for ideas on this. Run a BBQ skewer down the three score cuts on the inside of the wing tops and then a bead of hot glue down each. While the glue is hot, gently fold the wing over into it's final shape, and then open it back up once the glue is set. Repeat for all three cuts to build up some strength in the top of the wing.

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If you're using the skins, carefully hollow out the foam from the inside of the wing to fit your elevon servo. Otherwise you can just cut these in from the top. Either way, once you get the servo placed in the top of the wing, and before you glue it up, press it down into the bottom of the wing so you can see where it hits. Chances are the servo will be thick enough you'll need to remove/crush the foam on the bottom of the wing so it won't cause things to bulge up.

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Next dry fit the nacelle in place and cut an access hole down from inside the wing right in front of the spar and through the nacelle. Then set the nacelle back to the side and run a servo extension wire and a couple 12 or 14 gauge battery wires through the access hole and to the inside of the wing to the joint.

wing 2017-11-07 23.28.45.jpg

Cut a notch in the wing at the join to bring out all the wires. It will be easier to get the wings into the fuselage later if this notch is closer to the leading edge than shown in these pictures.

wing 2017-11-08 16.04.06.jpg

Now it's time to fold up the wing. I like to use White Gorilla Glue (WGG) on the spar and down the bevel cut at the front, and then hot glue on the last inch on both sides of the front and all along the trailing edge of the bottom of the wing. Fold the wing over for the final time and wait until the hot glue sets up. The WGG will foam up inside the wing and take a while to set, but the hot glue will hold everything in place while that happens.

wing 2017-11-07 23.35.34.jpg
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Later, rinse, and repeat on the other side of the wing.

wing 2017-11-08 16.24.58.jpg
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Wing Installation

For installation time here, the trick is getting the wires to slide through the fuselage slots at the same time as the wing. There is a little bit of front to back room for movement between the wing profile and the hole in the fuselage which enables the wires to pass through when pushing the wing in place. It's a little delicate, but go slow - I haven't torn one yet so it can be done :) Once the wing is in place push it to the front of the slot so it fits snugly along the leading edge and over the top of the wing. Fill in the little gap at the trailing edge fuselage joint with a small scrap of foam. Now make sure the wings are level out both sides of the fuselage and shim or trim as necessary.

fuse 2017-11-08 17.13.55.jpg

Seal up the outside of the wing joints at the fuselage sides with hot glue, and then put a good dose of WGG on the inside joints of the wing and fuselage so it will foam up for strength. Use long scrap of foam or those cotton swabs on a long stick to get the WGG down where it needs to go. By sealing the outside of the joint with hot glue it keeps things in place while the WGG cures, and also ensures none of the foamy comes out and ruins the finish. Try and keep the wires and connectors safely out of the way while the WGG is foaming away in there - I stick the exposed ends into a baggie and tape it out of the way.

fuse 2017-11-08 21.56.17.jpg
fuse 2017-11-08 22.09.42.jpg

Canard Installation

Dry-fit the canard - might need a little tweaking of the upper saddle shape depending on how close your final canard shape is to the fuse plan. Now the canard gets glued down to the bottom of the fuselage, and then the front fuselage sides get slid into place and glued down.

fuse 2017-11-08 23.05.45.jpg
fuse 2017-11-08 23.12.28.jpg

Closing up the Fuselage

Make sure all the servo wires reach into the receiver tray area - add extensions if necessary. Next cut the hatch lines free and glue the front and back fuselage tops in place.

fuse 2017-11-08 23.21.13.jpg
fuse 2017-11-08 23.25.47.jpg
fuse 2017-11-08 23.36.40.jpg

Nacelle & Power Pod Installation

Now it's time to pull the wires through the access hole in the top of the nacelles and glue the nacelle bodies up to the wing. I like hot glue for this as the WGG could foam out onto the finish of the plane, or up through the access hole preventing excess length in the wires from being stuffed back up inside.

fuse 2017-11-08 23.40.21.jpg

Solder up the battery leads to the ESC, motor to the ESC, and connect it up to the previously installed servo extension wire. It's good to check your motor rotation at this point too. The motors should turn in opposite directions from each other - doesn't really matter if they come inward or outward at the top - just so they go different directions. If you are confident you'll never need to repair the ESC, feel free to glue the power pod into the nacelle. Personally, I use the classic bamboo skewers to hold it in place.

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Final Assembly

I like to wait until the motors are all connected before gluing the rudder in place - just easier to work on that way as the airplane can sit upside down on the workbench.

fuse 2017-11-10 22.46.19.jpg

Cut the ailerons free and install the servo control rods. Hook up the reciever and glue it to the side of the fuselage so it's out of the way of the battery.

Now it's time to start thinking about balance. Put a pencil under the fuselage at the CG marks and then set the battery in place. See how far you have to slide the battery around to get the plane to balance out. Leave yourself enough room on the battery leads to have an inch or more of battery movement forwards or backwards. Hot glue in some battery straps for the maiden flight - I also like to glue in little foam bumpers to keep the battery in the right place once I find a good CG over several flights.

I use differential throttle in place of a rudder control and mix in about 50% canard in with the elevator control for the maiden flight. With canard designs, when the elevator stick is pulled back, the elevons point up and the canard flaps or trailing edge points down. Don't forget to set the failsafe for zero throttle, about 1/2 up elevons & down canard, and a very gentle right turn for best odds of a smooth recovery.

Now go fly!
 

rockyboy

Skill Collector
Mentor
With some better weather this weekend, I got out to fly and put prototype #3 (the white one) up for a maiden. Figured I wanted some experience with it before putting the pretty one up in the air. And I'm glad I did :) No video, but I did have some flight behavior I wasn't happy with, and want to share my experience and how I'm trying to resolve it.

Takeoff is still super nice and stable. But I was having to hold almost full back elevator to keep it level. And it was not very responsive to roll control at all. I was able to get it around the field a couple times and down safely, but it certainly didn't fly like I wanted. No porpoising or weird stalls, but it pretty much wanted to do into a dive when I let off the stick. I didn't run into the side stall when I turned into a tail wind this time, but I also kept the speed a lot higher and made sure to turn into a headwind when I came in for the final turn into landing.

So I'm doing a couple things in the workshop tonight to address these issues. First, I'm increasing the amount of downward deflection on the canard control surface when the elevator stick is neutral. This should in turn provide upward pressure on the nose of the craft in flight, and reduce (or hopefully eliminate) the need for heavy back on the elevator stick to keep level flight without adding additional drag at the rear from reflex on the elevons, or the surgery of changing the canards incidence angle.

Second, I'm increasing the throw rates on the elevons by two holes at the servo horn. This is a lot easier than going to a double sized elevon - but honestly that's what I'd recommend for anyone building this. I know jpot1 had good luck going with much larger elevon, and I should have listened better :black_eyed: My quick and dirty solution of more throw on the control surface will add a lot more drag along with the up or down pressure, but might start introducing some yaw coupling effects.

And the third thing I did was cut 8cm of under camber at each wing tip. This should help with preventing stalls on slow speed turns when I'm banked over a bit, which was what killed v2. I was planning to do this before the maiden this weekend, but I forgot about it until after the flight when I was tossing my FT Spitfire into the air and thought about what was causing it to fly so well.

So hopefully I'll be able to get this back in the air in the next week or two and see if the changes worked the way I think it will.
 

SlingShot

Maneuvering With Purpose
We have flight!! :applause:

And she's a sweet heart too - very stable and easy flier, just like I was hoping for!

3s1800 battery, a pair of 2206 2000kv motors w/ 20 amp esc and 6030 props


I had very low throws and coupling between the elevator and the canard control surface - worked perfect out of the gate!

Was already overdue to get home when I did this flight, so I didn't get a chance to go back up and test out higher throws and aerobatic abilities this trip. I'll get to that next time :)

So with this success in the bag I think we are ready to make the final updates to the plans from jpot1's and my build notes, and get a set of decals worked up too.

In the home stretch for the Mighty Mini FW-42!
Wow Rockyboy! I am way behind on my "reading". That thing flew right out of your hand! Nicely done :D