telnar1236
Elite member
After a fair bit of time messing around with 80mm and 64mm EDF versions of the F-104 Starfighter, I have decided to revisit a light weight 50mm version that could be flown at a decently large park. Using a combination of 3D printing in LW PLA for the fuselage and vertical stabilizer and balsa and plywood plate construction for the wings and horizontal stabilizer I think I can keep the weight down around 500 grams which should give me a stall speed just under 20 mph. I also want the design to be modular to allow for different wing configurations and channel setups since the stubby scale wings of the starfighter might not be for everyone and not everyone wants the complexity of a 6-channel aircraft. To save weight, all channels will be controlled by a single servo, and the goal is for as many control linkages to be internal as possible. On top of that I plan to design a slightly modified fuselage to make a U-2 since the early versions of the U-2 were essentially heavily modified starfighters and the changes to the CAD should be pretty easy once the starfighter is finished. This is likely a long project and could take months.
The end goal of this project is a flyable F-104 (and possibly also a U-2) model for me, a set of usable free STL files for anyone interested, and to have this thread as a guide that explains some of my design process and how to build the F-104 for anyone interested without going into too much technical detail.
My design is 39.5 inches long not counting the scale pitot tube and has a projected wing area of 130 square inches (slightly larger than scale). This seems big for a 50mm EDF, but because of how long and thin the F-104 is, it actually works out about right. As previously mentioned, the target weight is between 500 and 600 grams.
It is planned to fly on a 3S 1300 mAh battery and a 40A ESC, although peak current draw should never exceed 35A. The EDF unit (I think from ChangeSun, but I'm not sure of the brand; here is the link: Amazon.com: 50mm EDF 4900KV 3S Maximum thrust770g,Brushless Motor, Applicable to RC Jet Aircraft : Toys & Games ) is rated to 770 g of thrust, but looking at RCGroups, it looks like it generates closer to 600g. A lot of brands test their EDFs at a constant peak voltage for the rated battery pack (e.g. 12.6 V for 3S) and scaling down thrust using the fan affinity laws for a more realistic supply voltage gives about 600 g as well, so that seems to be what happened here.
Here are a few screen captures of the CAD. A couple of features to note are the NACA inlets used to supplement the small scale inlets, the ESC cooling using fan air instead of ambient air which should be more reliable, the internal routing for control rods for the rudder and elevator along the top of the fuselage and the large internal space in front of the main gear bay which will hold all the servos and the receiver. Some people might also notice how big the rudder is. This is scale to the real F-104, and is necessary to allow control with a torque tube and internal control arm.
The NACA inlet design is probably familiar to anyone who has followed FliteTest for a while. It offers less drag and better airflow than most other conformal inlet designs. The ramp in the inlet is a key feature that I haven't seen used very much in RC planes because of the added complexity, but it is a key part and contributes a lot to better efficiency.
The end goal of this project is a flyable F-104 (and possibly also a U-2) model for me, a set of usable free STL files for anyone interested, and to have this thread as a guide that explains some of my design process and how to build the F-104 for anyone interested without going into too much technical detail.
My design is 39.5 inches long not counting the scale pitot tube and has a projected wing area of 130 square inches (slightly larger than scale). This seems big for a 50mm EDF, but because of how long and thin the F-104 is, it actually works out about right. As previously mentioned, the target weight is between 500 and 600 grams.
It is planned to fly on a 3S 1300 mAh battery and a 40A ESC, although peak current draw should never exceed 35A. The EDF unit (I think from ChangeSun, but I'm not sure of the brand; here is the link: Amazon.com: 50mm EDF 4900KV 3S Maximum thrust770g,Brushless Motor, Applicable to RC Jet Aircraft : Toys & Games ) is rated to 770 g of thrust, but looking at RCGroups, it looks like it generates closer to 600g. A lot of brands test their EDFs at a constant peak voltage for the rated battery pack (e.g. 12.6 V for 3S) and scaling down thrust using the fan affinity laws for a more realistic supply voltage gives about 600 g as well, so that seems to be what happened here.
Here are a few screen captures of the CAD. A couple of features to note are the NACA inlets used to supplement the small scale inlets, the ESC cooling using fan air instead of ambient air which should be more reliable, the internal routing for control rods for the rudder and elevator along the top of the fuselage and the large internal space in front of the main gear bay which will hold all the servos and the receiver. Some people might also notice how big the rudder is. This is scale to the real F-104, and is necessary to allow control with a torque tube and internal control arm.
The NACA inlet design is probably familiar to anyone who has followed FliteTest for a while. It offers less drag and better airflow than most other conformal inlet designs. The ramp in the inlet is a key feature that I haven't seen used very much in RC planes because of the added complexity, but it is a key part and contributes a lot to better efficiency.
