|Weight:||297 g (10.5 oz)|
|Length:||135.8 cm (53.5 in)|
|Wingspan:||121.9 cm (48 in)|
|Wing Area:||5.8 dm2 (90 sq. in.) (x4)|
|Wing Loading:||12.8 g/dm2 (4.2 oz/sq. ft.)|
|Prop:||GWS DD 7 x 3.5|
|ESC:||CC Phoenix 10|
|Battery:||Thunder Power 3 cell 860 mah Lipo|
Note: for the latest information, visit my F-16 thread here.
My goal with this design was to capture the look of the Thunderbirds four-jet diamond formation with a single model. I had the idea for this when I noticed in pictures how the Thunderbirds fly in precise formation – wing leading edges aligned and wingtips in line. This got me thinking about four F-16s joined together in diamond formation to make a single aircraft. There were many challenges along the way, but the end result was a uniquely configured plane that was simple to build and fly.
This was definitely an unusual build for me, and I wasn’t even sure where to start. Where were the control surfaces going to go? How about the motor? Wiring? What’s the best way to join four airplanes together anyway?
I decided early on to make everything as simple as possible, and chose a 3mm depron profile design for the four jets. This had several advantages: light weight, fast building, and an ideal white base color for the famous Thunderbirds paint scheme. Each jet has 5 parts – upper fuselage, lower fuselage, wing, and two horizontal stabilizers. Design was done with Rhino, a 3D modeling program.
After a lot of head scratching I decided that the best place for the motor would be in the tail of the lead jet, while the control surfaces would be made from the wings of the trailing jet. I figured that this would give a little more control authority from prop wash like a conventional tractor design. The speed control and receiver were also mounted in the lead jet. Two servos on the underside of the trailing jet were connected to 24” extensions and wrapped around the frame rods leading forward to the receiver in the lead jet.
The framework that holds the four jets together was made from carbon rod, which overlaps in several locations to stiffen the structure. I tried as much as possible to separate the rods from the silhouette of the jets so they would look more like individual aircraft.
Markings were also made in Rhino, and exported to Adobe Illustrator for text and color. After being printed out they were trimmed and mounted on the models using spray adhesive. The trimming and spray-gluing phase was definitely the most time consuming part of the project, since everything had to be done four times. A reference photo was used for the canopy, which added a nice bit of realism.
First flight was on a beautiful spring evening with light winds. After some final photographs and control checks, it was time to fly - I throttled up to about 80% and launched with a gentle toss. The model climbed out steeply and tracked solidly due to the large side area, but unfortunately the CG was a little too far forward and the model started to nose over from about forty feet. I wasn’t able to pull out of the dive in time and crashed with minor damage. The second flight was very similar to the first, although I was able to level off before landing hard. The control throws definitely needed to be increased and the CG moved aft. After repairing the model that night, I hovered it briefly in the living room much to the chagrin of my wife! I’m really happy with the power from the little CD-ROM motor.
The second day of flying was a lot better. With the CG in the right place and generous control throws, the model flew sweetly. I tried a loop, knife edge pass (no rudder but lots of side area to hang on), and some inverted flying before another hard landing broke the nose off the lead & left jets, ending my flying day. What a blast – I had a huge grin on my face all afternoon. The model had plenty of power for vertical maneuvers, and could slow to a walking pace for flybys.
I learned a lot from this project and really enjoyed designing, building, and flying an unusual model.
Improvements for next time:
- slightly smaller size so it will fit in my car
- thicker carbon rods and triangulation of the frame structure in three dimensions for stiffness
- control surfaces on the outer jets for great roll authority
- rudder control for extended knife edge maneuvers
For the future:
I’d like to make an even larger version will full controls on each jet, flown by four pilots!
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