0-Four9ier RF-4
The 0-Four9ier RF-4, also referred to as the Fournier RF-4 designed for .049 power, is a semi-scale aerobatic motor glider from France.
Quote: "Construct a **56-inch span** model resembling the Fournier, intended for **.049 engines**."
Witnessing the acrobatic performances of full-size Fournier-powered gliders can be a captivating experience. Their slow, graceful maneuvers and stunning mirrored flying, particularly with one glider inverted and the engine off, stand in stark contrast to the typical high-energy displays, leaving a lasting impression.
Many modelers enjoy aerobatics, but a significant number also appreciate the opportunity for gentle soaring. This variation appeals to the creator, who often finds themselves torn between selecting a vintage model or an acrobatic one for flight. The desire to merge these two types led to the conclusion that the Fournier would be an ideal subject. With a powerplant of .8 cc (.049), the model would be a manageable size for transport and versatile enough to fly almost anywhere with a PAW 80 Classic engine.
Upon starting the design, some challenges became apparent. The fuselage of the model was unexpectedly large for its size, and the wing taper was excessive. Adjustments were made to slim down the fuselage and reduce the wing's taper. Strip ailerons were incorporated for simplicity, while the scale moments were maintained, and the tailplane size was slightly increased.
The final design preserved the essence of the Fournier while resulting in a more practical model. This was validated during a test flight at a private airstrip, where, coincidentally, a full-size Fournier was parked nearby. The model drew admiration from the pilots present, with the modifications only becoming apparent once pointed out.
Before construction begins, it's crucial to recognize that maintaining scale moments may lead to a tail-heavy model. Using very light wood for the tail assembly, potentially constructed from strip wood, is advised. The rear end should not be strengthened unnecessarily, ensuring space for a full-sized 500 mAh battery in the nose for optimal performance, especially for thermal catching. Additional weight may still be necessary, which can be addressed later.
Flight Performance
Following the approach of many contemporary writers, the focus will shift to flight performance before construction details.
Three servos are utilized for the rudder, aileron, and elevator. Alternatively, one could operate the throttle instead of the rudder or fly using only aileron and elevator controls.
Equipped with the Cox Texaco engine, appropriately propped with an 8 x 3.5 Master prop, the model is well-powered. It ascends steadily, providing ample height for at least three and a half minutes of gliding, while also executing loops, rolls, and Cuban Eights.
Once trimmed, solo hand launches are smooth; the model climbs in a gentle, flat trajectory, minimizing the need for a frantic hand-to-transmitter transition. A soft push is all that’s required to launch, eliminating the need for running or awkward motions.
The ailerons are highly effective, with even a 1/8th movement on low rate being almost excessive for gentle soaring. The rudder displays strong performance, with the set throw of 1 inch in either direction being overly generous— the writer typically avoids using it. The elevators function smoothly and powerfully.
For aerobatic maneuvers, high rates should be selected for the ailerons. It’s essential to remember that the flight relies on the wing rather than power. Although the model will not loop right after a roll, it can loop and roll in succession. Loops are consistent and effortless, while rolls require more precision. The roll rate is slow; a shallow dive followed by a gentle upward pull and aileron input is necessary. Downward input should be applied during the inverted segment of the roll but removed to avoid entering a steep dive post-roll.
The model exhibits a fast, flat glide that can be slowed with about three clicks of upward trim. All controls maintain strong response during gliding; for low-altitude soaring, selecting a low rate for the aileron is advisable. The model demonstrates commendable penetration.
