FT Explorer - SUV (Simplified Unibody V-Fold)

Greetings,

I admire pusher fixed wing foam board planes.   So I like the Bixler foam plane and love the FT Explorer kit build.   My passion is scratch building and experimentation so I set out to make an FT Explorer like plane that was easy to build from Dollar Tree foam board .   The principles I used for my modifications are simplicity, uni-body construction, and v-folds, hence I named my plane the FT Explorer - SUV.   Thank you Flite Test team for encouraging this type of modification, I hope you approve.

My FT Explorer built from a Flite Test kit.

Why I like the FT Explorer.

1. You have to want to crash this plane
2. Low stall speed
3. Great for cameras, and ability to lift any reasonable load.
4. Pusher planes don't break props

My FT Explorer - SUV   

Similarities of the FT Explorer to the SUV...

1. The vertical and horizontal stabilizers are identical.  The way they key together and then into the tail can not be beat.
2. The wing is fundamentally the same, it uses the same 6" cord, aileron size, and internal spar/formers.   

Differences of the SUV...

1. The boom connecting the tail to the body uses a V-fold rather than A/B folds.    It is strong, dimensionally stable, and simpler to construct from scratch if you don't have a laser cutter or special tools.
2. The body of the plane is just two pieces of foam board.   
3. The wing is glued to the body (uni-body).   It still fits easily into a small car like the Honda CR-V.   The wing adds to the strength without the extra weight of a stand alone body.   If you want to do stunts, this isn't the plane.  Try the Bloody Baron or any of the other great designs with a front mounted tractor propeller design and a short wing span.     You have to appreciate the modular approach the Flite Test team takes, but I find a bad crash usually requires a new plane and a minor crash can be repaired without taking the plane apart.   Finally, I try to build my planes not to crash, as if I was going to be flying in them myself.
4. The motor fuselage is glued to the wing.   The motor shaft is directly in line with the wing center so that the plane starts climbing directly after release without a tendency to nose over or loose altitude on take off.   This is part of the uni-body design, with the motor pushing the wing rather than the motor pushing the body pushing the wing.
5. The nose of the plane uses the same v-fold as the tail boom, but it is taller.  Raising the battery higher improves the center of gravity of the plane top to bottom.  This center of gravity improvement also reduces the tendency to nose over during full power take offs.

So lets start building the tail of the plane first...

I like using black colored board for the tail and body, and white for the elevator, rudder, and wings.

Use a 2" metal ruler and a 1.25" metal ruler.   Space the 2" from the edge using the 1.25.   Score both sides of the 2".   Move the 1.25 to the other side, and cut off the board.   Snap the score lines, and use your knife to put a bit greater than a 45 degree bevel on both sides of the score.   Make sure the sides will bend a bit more than 90 degrees.   Put a bead of glue down the grove and then use a wall to form a perfect 90" on both sides of the 2" center.   This method will give very precise dimensions and all of the strength you will require.   Don't worry how the ends come out as we will be cutting off 3" from both ends.   And if you nick the paper when cutting the 45 degree angles, that will be covered with tape in a later step.

Score each side of the 2" ruler

Use the 1.25" ruler to make the cut

45+ degree cuts shown above

Put glue in the grove and use the wall to form a good 90 degree angle

Add the stabilizers...

Build these exactly the same as the FT Explorer.   I like the way they did it.   Originally thought the BBQ skewers were not required, but after I cranked up the motor you could see the vertical stabilizer shaking.   The skewers create triangles, one of the best ways of building a strong structure.   

I create/use templates as shown above, made from heavy duty foam board from Hobby Lobby.

It is a good time to score and cut the rudder and elevator.   And to reinforce them with hot glue as shown in the Flite Test video for the FT Explorer.

I use my miter saw to cut 3" off each end of the tail boom, a bit overkill, but nice clean cuts

Glue the stabilizers into the tail boom.

View from the bottom

Finally add the BBQ skewers to strengthen the stabilizers.

Add the servos and control rods for the rudder and elevator...

This also is done much like Flite Test shows it.   

I put a small piece of foam board under the forward servo (toward the front of the plane) as the space is cramped and that helps it go over the top of the rearward servo.   One piece over the servo to insure it won't break free would probably be enough, but since these servos are almost under the CG, a bit more weight isn't a problem.   You can't get back to these servos and control rods once the plane is built, so build in resilience and test as you build.

Flite Test sells wood control arms, and they work as well as plastic, but my favorite are the plastic ones.   The wood does give it a cleaner appearance, if that is important to you.   You can see that I build almost entirely for service, reliability, and ease of build.

Use plenty of cocktail straws and the control rods don't need to be any bigger in diameter than will fit through the servo arms without reaming out the holes.   Oh, ACE Hardware sells piano wire in various sizes, thank you ACE Hardware.  And never will I ever (again) build a plane without accessible linkage stoppers at the rearward end.   Z bends are fine and best for the servo ends.   It seems like even though I use a small device to center the servos, the natural center of the radio is a bit different.    Note, you need to cut a bit of clearance in the tail boom for the control arms to swing toward the front of the plane (hard to see in the picture unless you look close).

Picture of linkage stopper and control horn mounted to the rudder.   Don't forget to use something to hold the linkage stopper nuts in place.   I use what used to be my wife's clear fingernail polish.  

Finally, use your 2" metal ruler to cut a bottom for the tail boom and glue it on.   Then two pieces of 2" tape will cover the bottom and the lower sides of the foam board, which will keep the foam board dry during a wet landing.   If you are going to paint your plane, the waterproof foam board that Flite Test sells is great, but with some tape and hot melt gluing of the exposed foam board ends you can make a very serviceable plane that will likely last longer than the itch to build a new one.   At some point, you have to set a limit to how many planes you own, unless you ARE Flite Test :-)

Build the nose section and cut and attach the plane body to the nose and tail boom...

I created a template for the body of the plane using heavy duty foam board from Hobby Lobby.  You will use the template to cut the two two sides of the body from black foam board.   You can see how the tail boom comes in 6" and the nose is 10.75" long.  

The nose is cut just like the tail boom including a cover that is glued on, except that you use a 2" metal ruler on the top, bottom and both sides.  I used the miter saw to cut the 45 degree angle on the nose and the overall length of the nose at 10.75", but that is optional

Glue the nose and tail boom to one side of the body.  Notice I cut the nose upside down so the cap is on top rather than the bottom as the tail boom was done.   Actually I didn't cut it upside down, I built one long nose section and then used it to build two planes.    I should have not tapped the tail where it will be glued to the body, which will weaken the hot melt glue bond.   It may not matter but do as I say not as I do.  On a positive note, notice that the wires from the rudder and elevator servos come out in the gap between the nose and tail, no cutting or extensions required; and you can push the excess wires into the empty nose but be sure they can't tangle into the tail boom servos.

Insert the radio receiver and some of the control wiring...

Do this before you glue the other half of the body on; making it easy to work.   Once the other half of the body is on it get doubly difficult to work in the small space between the two body halves.  And once the wing is attached it gets almost impossible to work in the small space.

Build the wing...

Although the wing I build is the same 6" cord as the FT Explorer, I do take a bit different approach.   Watch the FT Explorer build video, make your own choice.

Biggest difference is that I don't put any dihedral / polyhedral in the wing.   You will see later that I like using the Eagle Tree Guardian stabilization.   The two together would be overkill.   For passive leveling, dihedral / polyhedral is great.   But on the other hand, with a 5' wingspan, if you can't keep the plane level manually, you should think about active stabilization, which you can turn off and on using the radio transmitter in mid-flight.   

The above dimensions and notes tell the story of how I build the wing.   Another more significant difference in my modification is that I leave the ailerons attached to the bottom of the wing, not the top as Flite Test does it.   Their method looks prettier, mine may be better aerodynamically, but certainly I would never argue aerodynamics with Josh, Josh, and the team of experts at Flite Test.

Her are the four pieces required to create the former/spars.   No A/B folds, just glue four into two.

End of the former/spars glued together; top view and edge view.

In this view I have used my ball point pen to score each side of the spar and cut the leading edge double bevel.

I really like the way Flite Test attached the two 30" pieces together, this is the maximum strength you can build in.  Strength, especially in the center of the wing is important because you are not using any carbon fiber rods or wooden dowels to build in strength.

Former/spars attached in the above.   Watch how Flite Test does it from here.

You are looking at the top of the wing.  I have put a bevel on the trailing edge of the top curved wing portion and glued it down as tight as possible to the bottom of the wing, just forward of the ailerons.

Cut 10.5" out of the ailerons on the center of the plane.   This plane was designed for a 9" prop, but it will just handle a 10" prop.   The bigger the prop, the better the plane will fly (within reasonable specifications for the motor).   I use a 10x4.5 prop (always letter on the prop facing the direction of the flight, not that I ever forgot this rule :-).  Formally I used slow fly props, but the regular ones seem quieter and you can always throttle down to go slower (my favorite speed).   This plane isn't built for speed, but the 10" prop on a 1000KV motor will make the plane scoot along very well.

To improve the air passage over the top of the wing, I add a piece of white tape across the hinge seam.

And I use my 1.5" ruler to draw a CG line from the leading edge on the bottom of the plane.   I will put a small peg of BBQ skewer on either side of the body on this line so that I can easily balance the plane by feel.   Flite Test put their balance point 2.25" back.    The general rule is 25 to 33% of the cord back from the leading edge.   These guys are wicked smart, but my plane flies great at 1.5".   

I find it is easier to put the aileron servos close to the hinge line.   Just cut out some of the bottom of the wing.  Use the piece you cut out to hold the servo up a bit  so that the control arm easily clears the bottom of the wing and put a piece of gift card over the servo to insure it stays in place and is protected.   You can see I tape the servo wires to the bottom of the wing and not run them through the center of the wing.   Very simple to do and makes no difference in how the plane flies.

Insert electronics and ESC...

Add the other half of the body...

Put glue on both parts of the nose and tail plus some on the sides of the pieces holding down the radio and stabalizer.   The radio and stabalizer hold downs become part of the structure and strength of the body.

Attach the wing...

Create the cutout for the motor

Use glue on the top of the body naturally but also add some glue to where the cut out for the motor meets the body also.   The wing adds rigidity to the body.

Build motor firewall and install...

I build the firewall using two plastic gift cards glued to foam board.   Then I cut to size using my miter saw.   Use bolts & nuts to connect the motor to the firwall, not screws.   

Glue the firewall of the motor to the wing AND to the body both.   Every part is performing dual functions in the structure.

Finishing touches...

A small piece of foam board in front of the wing, glued to the body and the wing gives both a bit more strength.

I cover the nose with a piece of foam board and tape the bottom surface of the body/nose.   It improves the look and waterproofs the landing surface.

Install the battery and use the pegs in the wings to balance the plane.

I built a cutter to create notches in scrap foam to spread the glue you put on all exposed ends of the foam board.

Hopefully you enjoyed this article.   It was a pleasure to share my ideas with you.   Happy flights    Mike