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FT 3D depron profile


Active member
Hello everybody. This is my first build thread over here, so please be reasonable with your comments :)

The background:
1. Light = cheap.
2. I live in a country where 1,2m x 0,8m depron sheet costs less than 10$. EPP foam is almost twice that, and DTFB/FTFB is not available by any means.
3. Carbon rods of reasonable size are $0,5-$1 per 1m.
4. I've recently build some light planes (deporn Baby Blender, Twin Twirl from the original plans) and loved the idea.
5. I've already build FT 3D following the original plans (modified for 6mm depron) and loved the plane. Unfortunatelly it's not flyable anymore (car's inside on a warm, sunny day is not the best place to store planes put together with hot glue).

It was my plan to build light aerobatic plane for some time; but I wasn't able to find anything that would catch my attention. Currently, most planes are designed for EPP; which is not bad, but I just happen to not like it at all. The choice of KIT/ARF plaes available on the market is the same. I was almost ready to buy one anyway; when the idea came to me to use original FT 3D plans to build my own profile plane. The research was quickly re-oriented from "what" to "how"; but that wasn't any easier. I didn't find any good build tips/videos for depron planes yet (everybody seems to forget this wonderful material ever existed); but I did found a great example of exactly what I had in mind:


It may not be the most popular 3D profile in the world; but it's build beautifully with all the materials I have readily available and using building techniques I'd love to learn. That's how FT 3D "Pro(file)" was born.

After examining everything I've found both on RC Groups and the original Product Page, I started to redesign and cut out parts. I have to admit, it wasn't as easy as I thought. First I taped one half of the fuselage plans with the vertical fin/rudder together. Then decided to make it a bit longer, to move the elevator cutout from the rudder to the stabilizer without moving the horizontal surfaces forward. I also reshaped the nose part to have the motor fit nicely "inside". Then I had to properly rearrange wings, reshape ailerons and design brand new horizontal fuselage, along with all the doubler plates on the nose. Here are all the parts cut out:


And here's how all the horizontal parts come together (roughly):


Now, I'm glueing carbon stiffeners along the fuselage and the wing. Here's how it looks like:


Next will be glueing the carbon to elevator/rudder/ailerons, cutting out all the holes in both parts of the fuselage, and putting all of this together. I'm really excited and curious how all this will turn out.
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Active member
Thank you very much :)

Right now all the "integral" stiffeners are glued in/on. Here's how the front of the fuselage looks like before covering it with the doublers:


After that, I cut out all the mounting holes in the vertical fuselage. Only then the fuselage was covered with the doublers, the holes were repeated in the doublers after each of then was in place:


Horizontal part of the fuselage have only the "engine bay" cut out at this point. All other holes (for vertical fuse alignment tabs) will be cut out when it will be ready for attachment. Right now both parts of the fuselage look like this:


And here are the close-up photos of engine mount stiffeners - that's all what will be visible after the final assembly:




Active member
The work is moving forward better than I thought. Right now, the plane looks like this:


It's not glued together yet; from this point on, I'm going to try to stick to the original plane's Assembly Manual :D Unfortunatelly, it's getting late over here; I'm not sure I'll be able to maiden her tomorrow morning...


Active member
Thank you; I certainly will.

It's 4 AM here, I can't keep working anymore. The fuselage is all glued together; but no external bracing have been mounted yet - those will need to wait for the servo holes being cut out. The engine mounting plate is in place. ESC's battery conector is soldered, reciever is binded to the radio, servos are centered and servo arms have been installed, basic radio setup programmed. Lots of small tasks have been done; but actually not much to show on the pictures.

Too bad I coundn't make her ready for the morning. The weather is going bad again; I don't believe I will be able to maiden her on the afternoon; even if she would be ready.


Active member
Progress report:

- Motor cables soldered to the ESC; motor, ESC and reciever installed on the plane.
- Servo holes cut out, servos installed and glued in. Location of those holes was determined after the previous step to achieve correct CoG; but that wasn't completely successful. It turned out that CoG was exactly where it's supposed to be for the flight; so I had to move evarything I could as forward as possible. That's why servos location is quite different from the original one. I'm still not happy with that - a lot of carbon is gong to be installed aft of the CoG.
- Control horns have been installed acc to the final servo location

Gosh, I'm always surprised how long it takes to do all those small things... No photos this time, I need to go out very soon. I'll update the thread in the evening.

P.S. bare fuselage weighted approx 70g. Right now, it weights approx. 120g. The goal of 200g AUW is getting uncomfortably close...
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Active member
Here are the pictures:

1. The weight of "empty shell" airframe (bare depron + "integral" carbon stiffeners)


2. Electronics


3. Total weight with all the electronics onboard; no battery, no "external" carbon bracing


4. + 5. Electronics layout (black tape on the antenna will be removed - it's just to hold it in place untill the glue dries)



6. Tail feathers control horns and hinges close-up



Gravity Tester
Awesome! Reminds me of my adventures trying to build the RCPowers Extra 300 with a very similar electronics setup. It was just DTFB and not very reinforced so it quickly disintegrated itself, but felt pretty good for the time it was one piece. I tried making a 60% version to fly in my backyard, but it was very hard to control. Looking forward to seeing the maiden!


Active member
The only thing more I've managed to do today is to cut, bend, assembly and install push rods.



Last thing to do to make her airworthy is to measure, cut and glue in external carbon braces. I have five evenings to do that, so don't expect to see updates as often as they were posted till now :) After few successful flights (and I don't expect any to be unsuccessful...) I'll add landing gear; and only after that I'll think about a make-up :D
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Hostage Taker of Quads
Staff member
4. + 5. Electronics layout (black tape on the antenna will be removed - it's just to hold it in place untill the glue dries)

View attachment 45500
Beautiful build so far, but . . .

Are you sure you want to mount your antenna as the highest point on your skid plate? I know the HK RX's are cheap, but I just see bad things happening to it, followed by a long wait for the slowboat to deliver.


Active member
No I'm not, especially since it looks awfull. But when you are in the mddle of "build rush" at 4 AM, what else would you expect? I will most likely move some things around and hide the antenna closer to the fuselage joint.

I have bigger problem right now. It seems that I messed up some measurements or something (that's what I will say whenever asked), and the CoG turned out to be much more forward than expected. The plans for the Extra 260 I'm trying to follow state that it's supposed to be at approx. 1/3 of the wing root chord including ailerons. With current layout, I can't move it back more than... 1/3 of the choord EXCLUDING ailerons :) Now the big question is: how much I'm ......?

And seriously: does anyone know what's the acceptable range of CoG (especially the forward end of it) for light 3D plane (preferably depron profiles)? Any answer will be highly appreciated.


Active member
The CoG issue is partially resolved. Here's how:





The change visible above moved the CoG back for about... 1cm (less than 1/2"). It's still not enough; but better than nothing. I might try to further improve it by relocating other components (RX for sure, ESC maybe). Additionally, tail feathers' control rods are shorter and thus do not flex as much; I believe I wouldn't need to brace them in any way anymore.

For those wondering if the big hole in the middle will not make the fuselage weaker: the answer is "no". This part of the fuselage is completely surrounded by five carbon rods (two on the leading and trailing edges of a wing, two on the sides of the fuselage, one at the bottom). Also, the original Extra has a very similar hole in the exact same location. This hole makes wonderful spot for the battery - exactly at the CoG. Looks like it's the perfect win-win solution.

Unless there's a catch I don't see yet, that will reveal itself in the worst possible situation... :D


Active member
Despite of having a very busy day, I've managed to carve out a couple of hours to work on the plane. The last major thing to do was to measure, cut and install external carbon bracing, including a support lattice from the tail surfaces to the wings and four carbon struts, two under each wing. Here's how the process looks like using professional depron perforating tool (brass tube):


The bracing revealed that in this type of construction, it is very important where exactly both of the tail push rods go. I routed one of them too far from the horizontal fuselage (control horn installed too low). As a result, the push rod touches the bracing rods (two of them).


And here's how it looks like when everything is in the right place.


Wing supporting struts were installed using the same professional tool, equipped with ultra high-end extension device (another brass tube with smaller diameter, fitted inside).


With everything in place, the plane looks roughly like this (when diving to the ground inverted - I hope I will not see her this way on the maiden flight).


I don't know what's the total weight right now, I'm stil waiting for the glue to set completely. There are still some minor tasks to complete before the flight (relocate RX and the antenna, install velcro strip for the battery, secure all the wires etc.), and even more to consider the building process complete (landing gear, painting... anything else?); but at this point nothing can stop me from taking her out for a spin tomorrow evening - the plane is officially AIRWORTHY.


I weighted the plane; but the result does not make me happy:


I was hoping for 160g total without battery. Now, it looks like 180 or even 190 (I still need to add landing gear), resulting in 220-240g AUW. I wonder where this additional weight is coming from. Between 120g few posts ago and now, I added:
- approx. 5g of carbon,
- two servo extension leads (7g),
- 3.5g propeller
That leaves 25g for... glue? I don't think so; the whole tube of glue is 30g and I didn't use any noticeable part of it. What a mistery...
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Active member
I DID IT. (and the plane is still in one piece).

It's just a short clip from the last flight today. As you can see, it's already very late; I'm too tired to edit all the material I have. I'll try to come up with something in the next day or two. Stay tuned.


Active member
With this type of construction you definitely need a lot of reinforcements. Without them, the plane is very floppy and does flex a lot at even the slightest control input. My previous experience with very light planes tells me that it would be flyable; but I would not dare to perform any aerobatics.

I don't have plans yet; but I'm planning to prepare something as soon as all the issues will be found and resolved :) And seriously: yes, the very minimum I'm going to share is the detailed description of how to transform FT's own FT 3D plans into profile plane. Only the time will tell if I will be able to create the actual, useable plans. I hope so; but I never did that before.

I'm sorry guys, but it's almost midnight here, I'm still too excited to go to bed and too tired to do anything else. I'll try to write more and maybe share some photos/video closer to/on the weekend.


Biplane Guy
Very cool! Nice flying as well. I've been watching some 3D vids soo I make myself pull the trigger and order the electronics for my 3DHS Slick. $50 is a little steep for a motor, so I'll be hunting around for something cheaper.


Active member
As I said in my first post, I built the "almost original" FT 3D some time ago. It's not flyable anymore, but it still exists. Thanks to that, I could shoot some comparison photos:




As you can see, the changes aren't big. Basically, the plane is a touch longer and an inch or two wider. The motor is installed slightly lower to hide it completely inside the fuselage. The most important change is actually the hardest to notice - the location (in vertical plain) and inclination angles for both the horizontal surfaces were adjusted (very slightly) to put them in one plain and to have this plain cross the motor mount. I will try to describe all those changes in greater detail when the plans/design process description will be ready for release; but if anyone wants to ask more specific questions, I'll be more than glad to answer. Oh, and the specs will be described with the next video - I still need to figure out the battery/prop combo I would prefer to use on this plane.