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Dec 25, 2017, 12:01 AM
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localfiend's Avatar
Build Log

DTF Vought XF5U "Flying Flapjack"

Bit of a teaser. Finally got a prototype ready for flight on this project I started a couple years ago.

If it flies well tomorrow, I'll be building another, making a build log, and posting up plans.

************************************************** *******************

Now that the build is pretty much complete here's a consolidation of the relevant stuff.

XF5U "Flying Flapjack" Success 12.30.17 (4 min 27 sec)




Tiled A-Size Sheets

Tiled B-Size Sheets

Optional 3D Printable stuff:

The bulk of the 3D printable parts are here:

That link includes the nosecone, firewall pieces, landing gear mounts and skis.

The air intakes created by Dan can be found here:

And the steerable tailwheel assembly can be found here:
Last edited by localfiend; Jan 01, 2018 at 01:25 AM.
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Dec 25, 2017, 09:52 AM
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GermanTigger's Avatar
Very cool!

Dec 25, 2017, 11:00 AM
An itch?. Scratch build.
eflightray's Avatar
Looks like an ideal candidate for differential throttle mixed with the rudder.

Dec 25, 2017, 11:52 AM
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localfiend's Avatar
Originally Posted by eflightray
Looks like an ideal candidate for differential throttle mixed with the rudder.

Yup. I didn't even bother adding physical rudders for this first prototype. Got 30% rudder mixed into the throttle. We'll see if that's enough.

Got CG set at a bit more than 25% of the chord. Hopefully that's far enough. It's further forward than the full scale plane at least.
Dec 25, 2017, 01:49 PM
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localfiend's Avatar
Vought XF5U "Flying Pancake" First Test Taxi (0 min 31 sec)
Dec 25, 2017, 02:33 PM
An itch?. Scratch build.
eflightray's Avatar
Don't know if you looked for other threads, but there are some down below in the 'Similar Threads' list. They may have any pointers on CG, or things to watch out for.

Good luck with the first flight.

Re the video -- Now write your name in the snow

Dec 25, 2017, 02:48 PM
Registered User
I'm not 100% sure from the picture or video, but do you have the props set up to rotate in opposite directions? If so you would want the left prop (as viewed from the front) to go counter-clockwise and the right prop to go clockwise. It's not arbitrary; those rotations counteract the wing vortex, think about the swirl in the propwash helping to maintain low pressure above the body and high pressure below (when flying right way up at least...). In the grand scheme of things this is probably a minor effect but worth noting on a low aspect design.

Look forward to the first flight.
Dec 25, 2017, 02:59 PM
Kimbers Keeper.
BHOFM's Avatar
Very nice job, looks so good. Can't wait for plans and specs. Just my type of project!
Dec 25, 2017, 03:16 PM
Kimbers Keeper.
BHOFM's Avatar
Interesting reading, and looking.
Dec 26, 2017, 10:21 AM
Registered User
Very nice!My old dream to buid it...
Dec 26, 2017, 03:43 PM
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localfiend's Avatar
Originally Posted by FiftySlicks
I'm not 100% sure from the picture or video, but do you have the props set up to rotate in opposite directions? If so you would want the left prop (as viewed from the front) to go counter-clockwise and the right prop to go clockwise. It's not arbitrary; those rotations counteract the wing vortex, think about the swirl in the propwash helping to maintain low pressure above the body and high pressure below (when flying right way up at least...). In the grand scheme of things this is probably a minor effect but worth noting on a low aspect design.

Look forward to the first flight.
Yup, counter rotating props. I've built and flown quite a few twin planes, and have swapped prop directions on all of them without being able to tell any kind of difference. I think small RC planes have so much thrust that you're really not going to be able to notice, it's all just kinda lost in the mix. I swapped the Flapjack over after the test taxi. When I build the next one, I'll try both ways.

Originally Posted by BHOFM
Interesting reading, and looking.
Yeah, it's a pretty crazy plane with an interesting development plane. Lots of good ideas. Too bad jets came along and "spoiled" everything.

So, I got a chance to maiden it yesterday:

Flew quite well aside from being too nose heavy, and a bit touchy in the roll axis. Note to self. Land plane and adjust CG before attempting flat spins.

DTF Vought XF5U Maiden 12.25.17 (1 min 30 sec)

Dying an early death is all good. I need the parts to build the final version and only have 5 days to do it. There's a build competition over at the Flite Test Forums for Prototype WWII aircraft, and it requires a build log, with a deadline of December 31st.

Got all the parts cut out already and will spend a couple evenings building, making notes, and final plans tweaking. After flying it, I'm not concerned about any aerodynamic issues. Mostly I'll be making more battery room for CG adjustment, beefing up the motor pod attachment points and focusing on parts fitment for the best look.

Using some of the Flite Test water resistant foam for the outer parts to make painting easier.
Dec 27, 2017, 03:30 PM
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localfiend's Avatar
Here's the first section of the build log. I'll be adding more in successive posts as I get more work done on the plane. I'll probably also try and compile all of it into a single PDF just in case my image hosting source dies again.
Required Supplies:

Hot Glue
CA Glue
CA Activator (Optional I suppose)
Spray Adhesive
Clear Laminating Sheet, or other flexible thin plastic
6x Sheets Dollar Tree Foam or Equivalent
4x Paint Sticks
2x BBQ Skewers
4x Swappable Size Servo Horns
4x-7x 9g Servos (3x are optional for functional Rudders and Steerable Tail Wheel)
Appropriate Number of Servo Pushrods
2x Flite Test C Pack (2215/09) or Equivalent Motors - Bigger would allow for larger Props, smaller would work, but would look funny.
2x 9-10" Props
2x 30A ESC's
Battery bay has a decent amount of room. Should fly on a single 2200mah 3s, but has room for up to a 5000mah 4s.
2x FT Swappable Style Firewalls (Will Require Trimming)

The usual razor blades, bits of sandpaper, pliers, screwdrivers, ruler etc...

3D Printer is optional if you want some specific functional and cosmetic parts to enhance your aircraft.

Step 1, gather the shown internal structural parts and glue them together. The wing ribs pictured will actually be the same size. I decided to trim them down after I started building, so don't worry about any of that.

The 4 "Wing" spars shown go in the following order. Doubled up spar at the top of the picture is for the back of the plane.

All of the wing ribs simply slot into the spars. Don't glue anything together until you have all the wing ribs slotted into place.

Here they all are. The two smallest outer wing ribs can be put in place now, but it may be better to wait so you don't beat them up while skinning.

Just smear a bit of hot glue into the joints. It doesn't take much. Take your time and make sure that everything stays in it's proper slot as you glue. I like to work from the middle rib out.

Grab 3 of the top skin pieces. They will be going down like so.

Remove the paper from one side of each of the 3 pieces. You can see how it makes almost the perfect curve for most of the length.

Pre bend the curved sections to establish the proper curve for the tips. If you're using the Water Resistant foam, I've found this is quite easy to do by hand.

If you're not as practiced at bending foam, or are using the white stuff, a ruler can be a big help to slowly get the right curve.

Here's the first piece all pre-bent.

It will be glued in place like so. Split between wing ribs on the side, and over the top of one half of the doubled spar in the back.

For the first skin section, I prefer to only add glue under the red lines. Keeps the sides clean of glue globules, and you can go back from the underside and add more glue after the piece is in place. Go slow, the better you align things now, the better your plane will look at the end.

Here I'm adding glue from the underside, and using the table to hold the curves down. This isn't a complicated process, but you need to be patient, and wait until the glue cools fully before letting go of things.

Before finishing gluing down the first curve, now would be a good time to glue in the little step pieces. These will give the bottom skins something to rest on when you get to that point.

Here's the steps glued onto the back of the 1st spar.

Here's how you want the underside of your curve to line up. Once again, go slowly here, and hold down the parts until the glue dries.

Curve of the 1st skin section as it should look after being glued down.

View from the Top

Repeat all the steps for the next skin piece

Here's where I like to add glue for the first bit.

Try and get the skin sections pushed up as close to each other as possible.

Any gaps or unevenness can be filled with hot glue or tape, but the better job you do here will really make your plane look better. If something is just slightly misaligned, you can run your finger down the seam to even things out.

I'm not trying to scare anyone away from trying this build, it's more about patience than anything. I think your plane could have some really ugly seams and still fly just fine.

Front View after everything has been glued in the same manner as the first skin.

3rd skin section is mostly the same, but you'll want to trim the bulge of foam created after pre-bending. Use a razor blade or a sanding block.

Foam bulge trimmed off

Glue the flat area of the 3rd Section in place the same as the first two. Here's a shot of what glue joints on the underside should look like. Doesn't take much.

After the main portion of the skin is glued down, I like to do the curve in sections. Helps to get a clean bend all the way around the rib.

Here's what it can look like if you really take your time.

I like to get a good bit of glue on the outer section of this third skins curve. I usually apply it in layers, so you don't get too much and melt all the foam. The excess glue here is to make sure that the motor mount area is as strong as possible. This plane is very light, so this is a good place where some extra weight does more good than harm.

Here's all 3 of the first half of the upper skin sections all glued down.

Repeat all the previous skinning steps for the other side.
Dec 27, 2017, 09:29 PM
Ken's CAD Models
dz1sfb's Avatar
Really nice work! Your going to shame the the Flite Test community.

Dec 27, 2017, 10:14 PM
Registered User
localfiend's Avatar
Originally Posted by dz1sfb
Really nice work! Your going to shame the the Flite Test community.

Thanks, and we'll see. There's some nice builds coming along over there.

And here's the next set of build instructions.

Now the battery tray. Remove excess foam, and glue the sides up like so:


Flip it over and use your attachment method of choice. I like velcro, straps would work as well. Yep, it's crinkled. I stepped on it.


Slide into the battery area and glue in place. Think I'll alter the size of the tray a bit to make it easier to get into place.


Cut the paint stick to length. 8.75". I'll include a guide on the plans. You can also trim it to width if you have a super wide stick. These ones from the dollar store are 1" wide. The notches cut out of the front are to accommodate the long shaft that sticks out of the back of the C pack motor. You may not have to do this.


This is how it will glue up. Make sure it's straight. If the back end of your stick is square, you're probably pretty safe just butting it up against the spar. I'll include lines on the plans for that last rib to aid in alignment.

You're looking for the paint stick to be exactly inline with the body of the plane. If you're off a bit, no big deal, just try and make sure that both sides are the same.


Here's both sticks glued in place.


Next split off a section from another paint stick. This is actually quite easy to do by just running a razor blade down the length. I cut my stick here in half, but it would probably have been better to go with a little less. Check out reference pictures 52 & 53 to see why. You can leave it wide, but it may interfere with the final wing rib, which will then require modification.


You're going to want to cut that split section into a couple pieces.


I didn't really measure, just cut off enough to do something like this. I used CA to glue these pieces together. Be careful if you have aerosol activator. One bit of mispray bubbled my foamboard. Fortunately, that spot will be covered up by the motor pod skin.


And the other side. As you can see, I cut a bit of the foam away so I could slide the piece in further. No clue if that's necessary, It's quite likely strong enough even if you don't fit it in. I suppose if you decided to put giant motors on your plane, that a stronger arrangement might be in order. Maybe make some tabs and slots for the paint stick pieces.


Squirted some hot glue into the cracks on both sides for good measure.


Next, the bottom skin pieces. I'll include battery doors on both middle sections in the plans so you can choose which side you want to use. Or both. I'd make a hot glue hinge on that door to strengthen it up.

Glue it on the same way you did with the upper skin pieces. Remove paper from the back side.

All of the bottom skin pieces are just slightly over length. So butt them up against the folded over front skin pieces. The back can be trimmed afterwards if needed.


Glue in the next piece. This piece is curved a bit on either side. I didn't really have a good way to mark it, but you'll be able to tell when you do a test fit. One direction will be flush, the other will leave a gap. Use whatever orientation gives the best fit.


And, that's about as far as you'll want to go before adding some electronics. I chose to use a splitter power cable as I had one handy, but you could run two batteries if you wanted.


There is a ton of room inside this plane, so you can route stuff wherever you want. If you want to solder on longer motor wires, you could run the ESC wires through the pod. I chose to come cut a hole instead as it's faster, and very easy to swap motor direction this way. If you're concerned about cooling for your setup, you could place the ESC behind the actual engine air ducts if you wanted. I'm not going to run any cooling for this build. There's lots of room inside the plane, and the 30A esc's have lots of headroom for C pack motors.


Next, glue in a servo like so. It won't be in exactly this position on the plans, but it'l be close. Changed it after I installed mine. Also make note of the bevel I put on the skin piece circled in red. I cut that bevel a little deep. Stuff will fit better later on if you leave half of the foam thickness for the bevel.


Do both sides.


Once your ESC's, wires, and servos are in place, we can put on the 3rd bottom skin piece. It is also beveled. Ignore the other servo hole. Wasn't sure when I cut the parts if I wanted stuff on the top or bottom.


Glue the skin piece down like normal, except for the red areas. I find it's easier to add glue here after the piece has already been fastened in place.


And here's why I like to wait. You want to make sure the skins don't curl up or down on the ends. You want them to be straight and inline with each other when all of the bottom pieces are on.


After all the bottom skin pieces are in place, you can add the final wing rib. I had to modify mine a bit with the tip of my hot glue gun to clearance the paint stick parts that I left a bit wide.


Here it is glued in place. Do both sides.


Bevel and clearance like so. You may have to do more or less depending on the size of your paint stick.



Glue into place.


You can add a bit more glue to the underside if needed. Also note that I beveled the edge.


Flip the plane over and do the bottom. Here it is all beveled up.


Do both sides.


Next up are the tail section skin pieces.


Bevel the hinge, and smear in a small amount of hot glue to reinforce it.


Remove the paper from the back side like so.


Glue in place.



You can add addition glue from the bottom side if needed. Also note the bevels I've added to the foam.


Install servos like so. I just dropped the wires together through the holes in the spars up to my receiver.


Once the servos are in place, it's time for the bottom tail skin sections. They are beveled just like the top.


If needed, you can trim away the excess left from the other bottom skin sections. Depending on how much glue you used on the rear spar, fitting the blade between those two pieces makes a nice guide so you get straight cuts.

Last edited by localfiend; Jan 24, 2018 at 03:46 PM.
Dec 27, 2017, 10:15 PM
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localfiend's Avatar
And a bit more, cause there's a 40 image per post limit.

It's easiest to glue this in place in two steps. Red first, then green.


Glue on both sides.


Next, grab the taileron thingy. Remove paper, bevel and reinforce hinge with glue, then bevel all the show areas. I may have gone overboard with the red lines. That's where I add glue and fold over.


Once you've glued the pieces together you can start fitting them to the main body. I like to use BBQ skewers here to add additional strength.


Two short pieces is probably enough. Do a bunch of test fitting to ensure stuff slides together well, then glue together. You want the side tail pieces to stick straight out from the body. If you mess up and one side droops a bit, just make sure the other matches. Don't worry about a perfect fitup either. On the real plane there is a decent gap in the skin between the main plane and these sections.


Do both sides.


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