120% FT 3D Swappable with Dowloadable Plans

by clough42 | November 30, 2013 | (26) Posted in How To

Here are my plans for a 120% size FT3D.  I think it hits the sweet spot of size, weight and power, and it flies easily on common 3s-2200 batteries.

This plane is 20% larger than the original, giving it 44% more wing area, enabling it to loft a heavier motor and battery while still maintaining a very light wing loading.  Unlike other scaled up FT3D models, this one keeps the height and width of the fuselage the same, which maintains the foam geometry and allows it to use a standard swappable power pod.

I have lots of 3s2200 batteries, so this plane is sized and equipped to use these batteries.  I recommend a 3530-size 1100KV motor with an 11x7 prop.  This combo pulls a peak of about 30A and generates about 1750g of thrust.  The plane weighs only 850g, with the battery, giving it a thrust-to-weight ratio over 2:1.  Since most flying (even hovering) requires 50% throttle or less, flight times are very respectable.  Depending on how you fly, you will get six to ten minutes on a battery.

This 120% version goes together just like the original FT 3D.  You can reference the original scratch build videos for instructions.  The spar is different, so see the detailed instructions below.

The thing you will notice first when building this plane is that the fuselage is longer than a standard 30 inch sheet of foam.  Just join another ten inches or so of foam to the end of a sheet to make a sheet large enough.  Make a clean, straight cut on each piece of foam so they fit together neatly.  Put a piece of Extreme packing tape on one side, then open up the joint and apply a bead of hot glue.  Close the joint, hold the foam flat on your building board and squeegee the excess glue to seal the side without the tape.  This is the same technique used to glue the tail on the Bloody Wonder.  There is no need for tape on the glue side of the foam.  Just cut the pieces so the tape will be on the inside of the fuselage and you will be all set.  Because the joint wraps around the fuselage, the geometry makes it very strong.

This plane needs a carbon fiber spar.  I built the first version with a balsa spar, but it snapped in flight when I loaded up the wing, so something stronger was needed.  This spar is a carbon fiber arrow shaft, purchased at Wal-Mart for $4.  To make a pocket in the wing, glue down a regular spar strip to each side of the wing, just like the original FT3D, and then add two narrow strips to each wing half, leaving a pocket for the spar.  When the wing folds over, it leaves a hollow foam spar with a channel in it just the right size for the arrow shaft.

Be sure to trim the foam portions of the spar short so they fit into the hole in the fuselage, but do not extend into the interior of the fuselage.  This allows the power pod to sit lower, giving the plane a zero degree thrust angle.  The original FT3D has significant down-thrust built in—apparently due to interference with the foam spar.  If you want down-thrust in this model, you can easily move the skewer holding the back of the power pod up to get whatever angle you desire.  When the pod is all the way down against the spar, as marked in the drawings, the motor angle is at zero degrees.

I recommend 1.8mm carbon fiber rods for all of the servo linkages.  These fit easily into the standard HobbyKing linkage stoppers.  They are light, easily adjustable, and they completely eliminate pushrod flexing.

Reinforce the landing gear attachment points with carbon fiber strips.  Wood will also work, but will crack more easily.  Glue 1.5x5mm carbon fiber strips to the inside and outside of the fuselage bottom and attach the landing gear with zip ties that punch through the foam and go around both the inside and outside carbon strips.  This is very durable and easily keeps the landing gear from tearing through the foam on hard landings.

To keep the paper hinges from tearing or separating, reinforce all of the hinge joints with Extreme packing tape.  Just place a 1 inch wide strip across the joint on the paper side.  Then, fold the control surface back on itself and wrap a second piece of tape around the open foam edges.  Make sure it adheres well to the foam.  When you fold the surface back down, it will be virtually indestructible.  Do this at each end of each hinge, and you won’t have any trouble with tearing.

You can easily add a tail wheel for taxiing.  A standard .40 size tail wheel is about the right size.  Just glue a piece of popsicle stick to the bottom of the tail and screw the wheel bracket on.  I also use a little hot glue to make it stronger.  Bend the rudder rod back and capture it between a couple of small sticks or carbon strips embedded in the bottom edge of the rudder.  Do not glue it to the rudder.  Since the hinge point of the rudder is offset slightly from the steering axis, it needs to be able to move a bit where it contacts the rudder.

Use the longest servo arm you can get on the elevator.  I cut the short side off the asymmetrical horn that came with the servo, because it was the longest.  This plane likes lots of elevator throw for harriers.  Also, make sure you have the elevator connected to the upper servo.  The shaft of the top servo is aligned with the hinge of the elevator to optimize the geometry and give the largest, most consistent throw possible.

A couple of bonus tips:  You can cut a hole in the bottom of the power pod and make an intake duct from a plastic spoon to get airflow over the ESC.  Dental floss picks make great servo horns.  Just clip off the floss and the handles and drill some holes for the push rods.

And here it is in flight.  My flying skills are limited, but this plane will hover, harrier and knife edge with very little effort.

 

Downloadable plans:

FT3D-120 Downloadable Plans

 

For electronics, I recommend the following:

Motor: RCTimer BC-3530/14 1100KV or Turnigy D3530/14 1100KV

Propeller:  11x7 Electric (RCTimer 11x7E)

ESC:  HobbyKing 40A BlueSeries Brushless Speed Controller

Servos:  (4) Hextronic HXT900 Micro Servo

Tail Wheel:  Du-Bro #375 Tailwheel Bracket (.40 size)

COMMENTS

scratchbuilder101 on December 11, 2013
Very nice.... Good job...
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clough42 on December 11, 2013
Thanks. I'm really enjoying it. Now, if the weather would warm up...just a little.
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sailorJohn on December 11, 2013
Well thought out and beautifully executed.
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themajik1 on December 11, 2013
Very nice. I would not harp on your piloting skills at all. You flew this plane very well, and look like you are doing fine. Great build, she looks like she flys very well.
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clough42 on December 11, 2013
Thanks. I've never really filmed my flights before. Watching (and editing) the footage, I can see things I'm doing that I hadn't noticed. It gives me something to work on. :)
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thejosh108 on December 13, 2013
Respect for your tail wheel set up, I built something similar but, yours is how i should have done it.
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rogerjiangcf on December 13, 2013
Would like to see a flight video of that. Also, what's the size of the carbon fibre spar?
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clough42 on December 14, 2013
The spar is a carbon fiber arrow shaft, available at Wal-Mart in the US. It's 0.3" (7.55mm) in diameter, and 30" (76cm) long. There's a flight video at the end of the article, above. Is it not working for you?
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CUFC on December 17, 2013
What's the wingspan?
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clough42 on December 17, 2013
Wingspan is 39 inches.
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iwan_canobi on December 19, 2013
This looks great, ordered all the bits to build it now, was interested in the FT3D but wanted something bigger so this is perfect!

Printed the plans off on the plotter at work so just need some foam and that's my Christmas build sorted!

Thanks a lot for plans and the guide!
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dan106 on December 29, 2013
Thanks for the awesome plans, I only have 2200mA batteries so this was perfect for me. Plane is half done and ready for paint! Just waiting on electronics and landing gear. Should be flying by next weekend. Do you know how to post a Tiled version of your plans? May help out other builders who can't print large scale... took a while to figure it out on mac but theres an app called "tiled" if anyone out there is having the same trouble
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Thoskins202 on December 30, 2013
what size paper do you need to put in the plotter for it to come out the correct dimensions?
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clough42 on December 30, 2013
The pages in the PDF are ANSI D. (22x34 inches). This will print horizontally on a standard 36 inch roll.
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Implicit on January 8, 2014
I also broke the balsa spar on mine during a high-G maneuver and are currently building a hybrid FT/Cassutt. This time I'm using 2 5mm carbon tubes glued together instead of the balsa spar.
I'm also using de-papered $Tree foamboard, which gives a very significant weight saving. (~22%) and hope to keep the AUW below 450grams.
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dan106 on April 12, 2014
Just built and flew mine with the motor you recommended and an 11x7 prop. Flew great with 3c 2200mAh, when I tried one of my 4c 2200mAh it burnt the motor up. Forgot to go down a prop size... what do you think would be the best Diameter and Pitch for a FT3D 120% running a 4c 2200 40c Battery, 40A Esc and the Trunigy D3530 1100kv would be? I have more 4c battery's wanna see if i can get it flying with them. Not that much more weight than the 3c, Will it have more torque with a 8x4 or a higher top end running on 4c than 11x7 running on 3c?????
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vicwhit on August 29, 2014
I have built two FT 3Ds in the past and then I found this one. I built it with removable wings for easier transportation. I also added magnetic catches for the cockpit cover and another added hatch just forward of the cockpit. I think it makes it easier to fit in the battery.

It flies very well and is a less twitchier than the regular size version. However, I also equipped it with a Lemon receiver with stabilizer and WOW does it fly nice now. Very steady and predictable. Holds high alpha and harriers with ease and does knife edges that I always find tough. I also fly a Visionaire and it is my #1 favorite. The FT-3D 120% is my #2.

I highly recommend this project especially when combined with the Lemon receiver Lemon DSMX 7-Channel Stabilizer + Lemon DSMX Satellite (DSM2 backward compatible)

http://www.lemon-rx.com/shop/index.php?route=product/product&path=76&product_id=107

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clough42 on August 29, 2014
Thank you. I'm currently flying it without stabilization, and have been very happy. When trimmed right, it shoots a straight line wherever you point it. I do get a little rocking side to side as air spills off the wings in a harrier. I played around with a multiwii controller at one point, and it was uncanny. It almost felt like cheating, it was so stable.

Thanks for the tip on the Lemon receiver. I'll check it out.
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revoman on January 14, 2015
Thank you for posting the plans for these. I did notice that the wing spars could be another 1" long to match the final FT-3D plans. The other thing I wish I'd known was the standard power pod fits, but this build would benefit from a power pod an additional 2" long.
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clough42 on January 14, 2015
The spar is shorter to allow a zero degree thrust angle on the power pod, as described above. The power pod is standard size, in order to make it swappable.
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revoman on January 16, 2015
Thanks clough42. I totally missed the details about the motor pod and thrust angle change. I'll have to go back and modify that before my maiden.

Nice thought about the swappable pod too. I scratch built the pod, with no plans of swapping it, so an extra 2" would have been nice, and allowed me to drop the battery into the pod.

Once again, thank you for this article, its awesome! I think I'm going to love your 120% build once its finished. My electronics were too heavy for the 100% 3D, which died a horrible death (actually 4 deaths) due to crashes.
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FliteGreg on February 18, 2015
Thank you for posting this 120% FT3D, you've hit the right size and you found smart improvements that will apply to many other builds. Good work! When my visionaire dies, I will build this one as a successor and recycle the electronics.
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clough42 on February 18, 2015
Thank you. That will be a seriously powerful plane. The Visionaire has a huge power system, if I recall. Let us knew how it goes.
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planebreaker2000 on January 28, 2016
Thanks for posting the 120% plans. I built it from your plans, and it flies much better than the 100%size.
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Illusion on April 14, 2016

hello :) , can I use ntm 2826 1200KV motor and 3s 1800 Turnigy lipo?
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clough42 on April 14, 2016
I think that motor is going to be too small for the plane to be 3D-capable. It also weighs less than half what the recommended 3530 does, so you'll likely have trouble getting the CG far enough forward for it to fly well--especially with the lighter 1800 battery.
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Illusion on April 15, 2016
Thanks for the reply :) , I had these doubts , especially for CG :/
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Illusion on April 14, 2016
Thanks for the reply , I had these doubts , especially on gc :/
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Illusion on September 20, 2016
If I use an ntm 3530 1100kv my lipos 1800 3s 20-30c will work or are small? :/
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clough42 on September 20, 2016
The current draw will depend on the prop. You should measure to be sure, but I think a 3s1800 should be okay.
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mightybubble on June 25, 2018
Thank you for publishing these plans. Plane went together easily. Flies like a dream. Ive got a 400kv motor swinging a 13x6x3 prop and pulls 16amps on 4s. Flies inverted no problem at all and knife edges all day long. Has become one of my favourite planes to fly.
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120% FT 3D Swappable with Dowloadable Plans