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Background
The Multiplex Fox is a simple free-flight throw glider. However, a quick search on YouTube revealed that it is a good base point for add-ons like radio control and motors to make it a miniature RC model.
The Multiplex Fox is a simple free-flight throw glider. However, a quick search on YouTube revealed that it is a good base point for add-ons like radio control and motors to make it a miniature RC model.
Material: EPP
Images
Images
Test Flight
Test Flight
The test flight had a successful outcome, leading to several conclusions:
The elevator control movement range was increased.
The center of gravity shifted slightly backward.
The normal flight was best performed at half throttle.
Rudder control was added for aerobatics and precision.
The model could fly in low winds, though it became harder to control.
A smaller, lighter receiver (~10g) was recommended.
After a few more successful flights, I made further enhancements:
Added a 1.5g micro-servo for rudder control with a carbon push-rod, totaling 3g.
Included a DVR unit and an optional DC/DC converter weighing 15g.
I repurposed a keychain spycam from eBay (20g) for the DVR unit, disassembling it to use the 9g PCB. The DVR required ~3.7V / 200mA, so I added a 2g DC/DC converter for efficient voltage conversion from the ~8V LiPo (or 5V BEC). While I tested the DVR at 5V, I opted for the DC/DC converter due to possible input rating concerns.
After these additions, the model's total weight increased to 145g (~x3).
On the new flight I noticed the following
I must use full-throttle
The flight must be done with very low or no wind at all.
The model tends to stall very quickly.
After 13min of flight, the 2cell Lipo batt was ~7.6v. After a full charge - the charger reported a 500mAh of charge. Hence, the average current consumpion was ~2.3A.
I think all the above simptoms are caused by the relativly high weight of the model (x3 from the original design).
Since the lift force relation to the air-speed is a power of 2. It means that the typical speed of the model was increased by ~x1.8, and the drag increased even more because of the "not so aerodynamic" body changes I had to make.
I don't want the model to fly any faster. Hence, changing the prop & battery configuration in order to gain more thrust is currently not an option.
Instead, I made the following changes:
Change the current receiver to CORONA 6CH micro Receiver RP6D1 - 10g ( -25g)
Assemble the two LiPo cell inside the model body to reduce the total drag.
Change the Alieron push rod setup to be like the rudder push rod to reduce the total drag and weight (-2g).
The expected typical speed of the model should be x1.6 and the total drag force will be reduced even more. Hence, better climb rate, wind resistance and flight time.
After these modifications, the model handles medium winds much better+ when there no wind it can fly with 1/2 to 3/4 throttle.
The video is of a low-altitude flight that ended with a crash. As can be seen there are high voltage power lines in the field. I "Successfully" Crashed into one of them... The propeller broke free, and it took me 10 minutes to find it. But other than that, everything is o.k.
To improve the DVR picture quality, the RC Model was modified as follows:
Improve camera placement
Fix camera vibration dumping/isolation
Use a clearer protective window for the camera
Lower the angle of the camera toward the ground, and try not to include the propeller in the FOV
This video is the best of all to this point. I removed a part of the cover in front of the camera and took off. The picture is much clearer, and I didn't notice degradation of the flight characteristics.
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