SpeedFreak IV - Sleek design 60CM wingspan super fast 150MPH+ model
Jun 02 2013 by FaTe
Big thanks to www.FrSky-RC.com for providing the Receiver unit for this project :)
The SpeedFreak design series has done nothing but show me that with careful planning and revising per version this model is capable of some truly awesome speeds. My aim for this project was 2 fold, 1st was to simply have a nice fast model. The 2nd part was to try show you don't need 6 cell lipos and all the rest to have a fast model, so here are my specifications:

60CM wingspan with a 14CM Root CORD.
60CM long from prop to tail end
Turnigy 3650kv - 450 Heli motor
Turnigy Plush 80A ESC (has UBEC)
Turnigy Nano-Techt 1600mAh
AUW 576 grams
I'm using 10MM thick balsa to create the basic fuselage shape. The intention is to have a 4CM box inside from nose to tail free to place components anywhere. With a full open lid it's critical the fuselage being very strong.
Only using regular CA glue I put the fuselage together. While only being CA together its already pretty rigid due to the thick balsa.
This is after it's first sanding over the fuselage. It's important to say everything on this project is hand sanded, no power tools used at all.
The wing and tail all cut out. The wing is 6MM balsa as a single sheet and the tail is 4MM balsa for cutting the air more.
First the fuselage needs some real strenth, so using 30g m2 Fibreglass cloth and very thin epoxy I cut 1 piece as a whole and slowly began working it in to the corners and everywhere else with a brush taking off excess as I went along. Because it's a single piece this now holds the entire stress load from engine to tail and is very strong.
The tail at just 4MM isn't strong enough but balsa is light so I used the same trick as on my DLG designs by coating the balsa with epoxy and then wiping it off again so it absorbs into the balsa and again makes it very strong.
Now everything is fully sanded down to the shape I want and to be as smooth as possible using balsa filler to get rid of any remaining gaps.
Comparing the shape against version III.
I like the dark blue tint effect I got from version 3 engine mod. To do this I spray the balsa directly with black spray paint, then I used semi-transparent blue oracover film. The black makes the film darker but because the balsa absorbs the spray paint at different amounts the patchy colour shows through as tints depending on the light angle. So you get blues, blacks and even white when the light is reflecting straight off it.
Version III suffered from lack of space and I wasn't going to repeat that mistake hence the big inside fuselage area. Here I am showing how even a 2200mAh 3S pack will fit in easily.
The motor and ESC are installed next directly in-line at the front where the most cooling will be.
The wing gets a sanding to get the basic shape, take out any overlapping defects and sand the leading edge (LE) to profile.
Being 6MM balsa it was very hard to do but I got as close to a MH-43 profile as I could. It was recommended to me by a Speed Cup competition winner.. so I took the advice lol.
To reduce drag as much as I could I put my aileron servos in-line with the wing where the control horns directly screw to the ailerons. This means 0 torque loss from having no control lines and full range of throw if I want it (which I don't).
So here you can see stage one of covering the wing by first spraying it black. Notice how it's not a solid colour and it is also a very light coating (from a distance of about 50-60CM spraying away).
Then the Oracover over and you can see the results. I love this finish lots and lots.
Of course I wanted to see what the plane looked like even though not finished.
The rudder and elevator servos are mounted side by side on proper rails so I can swap them out later for metal gear ones. The control lines are coloured black with marker pen as well as the control horns so everything fades into black hehe.
For the fuselage lid getting the shape is difficult. So I made life easier by using depron to get the shape right.
Next I fill the fuselage with toilet paper to create a spongy layer pushing upwards but not with excessive force, for this reason toilet paper is cheap and should be available (I'd hope! lol)
Below the balsa on top of the depron is a layer of epoxy drying to keep the shape, by taping down the balsa and the toilet paper pushing up when the epoxy is dry it'll be a perfect fit.
To have in-line ailerons directly connected you cannot just use the balsa aileron, it'll rip out the screws. I use 1.5MM plywood on the side where the servo horn will be. This is epoxied too the aileron and then sanded off giving screws something proper to go in for very little weight.
Back to the fuselage lid I wanted a rounded top lid but balsa was too heavy. Instead I used the depron base to fibreglass over again using 30g m/2 and epoxy + brush. I used food cling film to protect the fuselage and make the shape as flat as possible giving me an exact fit.
Now dried after 12 hours you can see the finished shape and air venting holes. All it needs is trimming and sanding.
The lid slides into the front of the fuselage on 2 small carbon fibre rods so I was mocking up the placement of the pins.
To finish the lid I used black lacquer paint to protect and seal the fibreglass below. On the back is a magnet lock and in the middle are 2 ball screws used for linkages on helicopters. With 2 little cut outs the lid pops between these 2 ball screws.
Now the fuselage is totally finished.
Being all black and expecting it to go fast I knew all dark blue / black wasn't going to make orientation when flying easy. So I choose to add a pattern on the bottom of the wing using some old silver Oracover I had left.

I used Photoshop to create a pattern of a checker board then began making it so the square seem to drip away and apart. Once I had the design as I wanted I just hand drew it on the Oracover and began cutting the squares out WHILE keeping them in order on my desk! (important!!! lol). Then I carefully began adding each one to the wing until the finished result as you see, it was not an easy task but I'm very happy with the result :)
Finished and ready to fly (RTF). On the scales again AUW (lipo battery inside) its 576 grams which is below the 600 gram target I set myself.
Looking at the bottom of this model I can only be glad I put the time in :)
I flew the model 3 times. The first time I had the Pitot tube for it's maiden but only went to 50% throttle, the Pitot tube digital display showed 120MPH top speed at 50%... lol

After that I just wanted to fly and get used too it, so later I will post a video on my Youtube channel with a top speed run. So don't forget to subscribe!