UPDATED 5/14/2014 (See below.)
Designed in 3D in Sketchup after the Multiplex FunCub, the Swappable FoamCub is a versatile airplane. It flies slow or fast, has STOL capabilites, climbs vertically, has plenty of aerobatic capability and prefers a rough landing surface to a smooth one. It's one fun airplane.
If you build one, please tell us how it went! (The forum thread is a good place to do that.)
Share your photos, tips, build experiences, mods, etc. on the FoamCub Swappable forum thread. I'd love to see them and I suspect others would too!
All-up weight with 2200mah 3S lipo: 53 oz. (using Elmer's foam board which is heavier than others)
Fuselage Version 2
Small Foam Board Parts
Plywood and Poster Board Parts
Power Pod Thrust Angle Modification
Standard FliteTest Swappable Power Pod
All of these PDF files are a single page, so you'll need your PDF reader and printer to do the tiling - I think most printers can do this. Here's what I recommend:
- Get Adobe Reader
- Download all of the files (right-click > Save link as... or Save target as...)
- Opening the PDF file in Adobe Reader
- When you print, in the print dialog, choose "actual size" or turn off all "fit to page" options.
What you want is to print at 100% without any shrinking or auto-sizing and let the PDF reader and printer do the rest. Printers and PDF readers are different so you might have to do some figuring out.
- Elmer's foam board 30"x20", about 4-5 sheets - I find Elmer's to be much higher quality and strength than Dollar Tree. I find it at Walmart for around $1.50 a sheet. However, Elmer's weighs twice as much as Dollar Tree - you would knock 1lb off the AUW by using Dollar Tree. If anyone tries Dollar Tree, let us know how it goes!
- poster board
- 9-gram servos (6) - I used HobbyKing HXT900's
- 5-channel receiver
- 0.047" x 36" music wire (1-2)
- 3/32" x 36" music wire (1)
- Firepower Sport 3542-10 brushless motor (550W) from headsuphobby.com (for a Dollar Tree build, a smaller motor could be used - see Motor Choice below)
- Turnigy Trust 45A ESC from HobbyKing
- APC 12x6 Composite Propeller
- Du-Bro 2" Diameter Spinner
- 50cm servo extensions (4)
- servo Y (2)
- Du-Bro E/Z or Mini E/Z connectors(6)
- plywood 1/32" one small sheet
- Sullivan Tailwheel Bracket 10-22lbs
- BBQ skewers, medium diameter and small
- rubber bands - I use the blue size 125 rubber bands from rubberbandguns.com - they're great!
- Dave Brown Treaded Lite Flite Wheels 5" (2)
- Du-Bro 1 3/4" Super Lite Wheels (1)
- Du-Bro 3/32" Plated Brass Dura-Collars (3)
- 2200mah 3S lipo
Ailerons: 0.75-1" up and down, 35% expo
Elevator: 1.25" up and down, 35% expo
Rudder: 1" both directions
Flaps: 1.5" down and program some down elevator to prevent ballooning
Of course, customize these as desired.
Also, most Cubs (of any type) produce significant adverse yaw, which means you'll want to coordinate turns to turn smoothly. This means using the rudder along with ailerons in a turn, and if you're not accustomed to using your rudder, you can often program your transmitter to do it for you. But, I would encourage you to learn how to use your rudder in turns - it's a very helpful skill.
(Sorry they're so long - I figure too much info is better than not enough...)
Design - As I mentioned above, I designed this in 3D in SketchUp. I highly recommend the program - the only real downside is that printing designs well is a little tricky.
Foam Board Choice - I used Elmer's foam board, which is very different from Dollar Tree. It has much heavier paper backing and as a result is stronger, looks better (IMHO) but also weighs *twice* as much. A 30"x20" Elmer's foamboard weighs about 8.4 oz whereas Dollar Tree is about 4.1 oz. Building this plane out of Dollar Tree foamboard would reduce the AUW by around 1lb, which would be awesome. But, Dollar Tree might not be strong enough, especially where the wing halves join. The strength of that joint relies on the crush strength of the top surface of the wing - so be careful. If anyone tries this build with Dollar Tree, please let us know how it works out.
Spar Design - This design has no real wing-to-wing spar, relying on only glue and foamboard structure for strength. I tested the strength by setting the center of the inverted wing on a scale and placing books along the length of each wing. The wing happily supported 120 oz, about 2.5x the weight of the plane. I have also performed some emergency "pull up quick!" maneuvers which I'm guessing has put the plane through more than 2.5 Gs without trouble.
Flight Characteristics - I've had a FunCub owner fly this plane and he said it flew just like a FunCub, which it should since they are so similar. This plane is a blast to fly - the motor in the specs has plenty of power, and the flaps allow it to float along beautifully. The gigantic tires allow it to land almost anywhere. The plane will fly inverted, but the airfoil shape and weight require a fair amount of speed and down elevator to do so.
Motor Choice, Flight Time - The above motor (550W) works well for an 53oz plane (the weight when building with Elmer's foam board) and allows for 4.5 minutes of hard flying on a 2200mAh 3S lipo. If you build with Dollar Tree, your weight will be around 37oz which is about 70% of 53oz, and I would scale the motor power accordingly. For a Dollar Tree buld, I would suggest getting a motor that produces at least 350W. Remember, a FoamCub is WAY more fun with plenty of power. It will fly with much less, but it won't be nearly as fun.
Photos/Videos Above vs. Build - The plane in the flight video and photos above is the prototype, with small differences with the final design (which is in the build videos). The main difference is that I abandoned the V-bend control rods and added connectors to the servo arms instead of a Z-bend on each end. The V-bends and 2 Z-bends resulted in control response that was too sloppy. The current design fixes that.
Landing Gear - The landing gear stiffener could be done in a number of different ways, such as substituting the second, inner wire with a rubber band across the middle.
Swappable - The term "swappable" is used loosely here. Technically this is a standard swappable, but the recommended motor for this plane would be overkill for most of the standard FliteTest swappables, so you wouldn't normally swap this power pod to another airplane. Fortunately the swappable power pod system is a handy design for simply mounting a motor and storing electronics so it still serves a great purpose even if you don't swap.
Thank you to my sons Willem and Nels for taking photos and video while dad flies:
A behind-the-scenes look at my luxurious basement workshop/studio, recording a build video with an iPhone :)
Added forum link.
Fuselage Plans Updated
Fuselage plans are now updated to move the ventilation exit point, to increase tail strength (see below).
Version 1 Fuselage Tail Strengthener Retrofit
Both of my FoamCubs developed a small crease in the fuselage just ahead of the tail feathers due to a weak spot in the tail where I left the bottom of the fuselage open for ventilation. This is corrected in the latest plans (above), and if you have already built the plane or are in progress, here are some instructions for an easy retrofit - it only takes a few minutes. This will be especially important for Dollar Tree builders.
- Added note on motor choice in Materials
- Added adverse yaw/coordination note in Throws, Expo