Fournier RF-4 (oz6789)

About this Plan

Fournier RF-4. Radio control model powered glider. For Astro 10 electric motor.

Quote: "Combining the best of two worlds, the Fournier uses electric power to find its place in the sun, followed by the silent majesty of flight that can only be experienced by the soaring pilot.

This Fournier RF 4 was especially designed for the Astro 10 electric motor, and with this propulsion system the plane flies very realistically. For example, take-off consists of a straight run followed by a few low hops culminating in a gradual climb-out. One pass around the field is usually enough to gain pattern altitude. The ship will loop from level flight and do near perfect wing-overs, especially to the left using engine torque. Rolls are not possible without ailerons, but snap rolls and spins are possible if large elevator deflections are used. The ship will thermal even at the high gross weight associated with electric propulsion (52 oz) since, even at this weight, the wing loading is only 13 oz per square foot. Flying speed is quite low and the ship is very stable in flight.

With the power plant removed, the ship has been flown as a slope and thermal sailplane. The radio battery was placed in the motor tube and the radio moved forward over the CG. In this configuration the ship thermals well and is a striking change from the run-of-the-mill sailplane. The tow hook was placed to one side of the landing gear strut.

Although designed for electric propulsion, for those of you who wish to put a glow engine in this plane, I suggest a .10 or .15 be used. A throttle is not actually required, unless desired, as dead stick landings are a cinch with the excellent glide ratio of the RF-4.

The new three channel radio systems are well suited to this design. It has been flown with ailerons which work well (use 1-1/2 x 15 inch ailerons) but they do detract from the thermalling ability. The aircraft is a crowd pleaser and fun to fly. It can be hand launched if no smooth runway is available.

I hope you enjoy building and flying the Fournier RF 4 as much as I have, and wish to thank both Dave Shadel and my brother, Bob Boucher, for their many helpful suggestions and assistance in designing, building, and flight testing this new aircraft. My special thanks to Bob for taking the prototype to the 1973 Nationals and entering it in R/C scale where he aptly demonstrated its realistic flight characteristics under electric power. Now let's get on with the construction.

Constructing The Wing And Tail. Begin the wing construction by taping the wing plan to a flat board which should measure at least 12 x 36 inches. Remember, your completed wing will only be as straight as your building board! If you use a 72 in board you can build both wing panels simultaneously. Now, cover the plan with a piece of Saran Wrap or similar product. Do not use waxed paper.

Carefully select your wing sheeting, making sure to match them as closely as possible, and pin directly over the plan in the correct position. Next, butt glue a 3/32 x 3/8 x 36 in hardwood spar to the aft edge of the bottom sheeting... "

Update 11/10/2016: Added article, thanks to RFJ.

Update 26/11/2025: Added kit review from MAN January 1972, thanks to RFJ.

Quote: "Field and Bench: Astro-Flight RF-4 Fournier kit, Kraft KP3S series 71., OS .10 R/C Engine. By Charles Kennedy.

Happy combination of plane, system and engine made for a happy review for this Field and Bench. With gliding on an upswing, subject is timely one - plenty food for thought.

Having cut my R/C glider teeth on Astro-Flight's Malibu, I was very inter-ested in undertaking a second glider model. RF-4 provided an interesting semi-scale project and proved to be another fun project. Combine this with Series 71 Kraft KP3S and an OS10 and all sorts of possibilities come to mind.

Now to the model. Kit examination disclosed building instruction booklet, proof of scale booklet, full size plans and the usual array of balsa strips and sheets. Wing ribs and fuselage bulkheads are die cut. I checked to see if all the parts were there and read the instructions before starting on the wing panels.

1/16 balsa sheet bottom was cut and laid down over plans; 5/16 square leading edge was glued in place. Then I realized that with a solid bottom sheet, I couldn't see the rib locations, so off came the bottom and down went some pencil marks at leading and trailing edges to locate rib positions. Next, wing and spars were glued in place.

When dry, wing was removed from building board and leading edge shaped to accept upper sheeting. Wing half is re-pinned to board, placing wash-out blocks under leading edge to give a total of 3/16 wash-out at the tip. Wash-out is important to pre-vent unexpected spins in the RF-4.

2-1/16 top sheeting is applied next—wet at leading edge, dry at trailing edge. Top trailing edge should be chamfered where it joins the bottom sheeting. Ribs were then cap-stripped. Second wing half was finished in a similar fashion. Next the center section was constructed and the two wing halves joined to it, I added two 1/16 plywood doublers at the dihedral joints, although they are not called for on the plans.

Tips were blocked 5 in each to form correct dihedral angle and, when dry, joint was nylon-taped and coated with Titebond. Five inches of dihedral at each tip is recommended when no ailerons are built into the wing; three inches recommended when using ailerons. As the radio set to be employed was a Kraft 3 channel, no ailerons were planned.

Total of 10 inch dihedral looked excessive to me so I called Roland Boucher of Astro-Flight and questioned the amount of dihedral. He stated 5 in was correct and that's the way it should be built. I said yes, sir - then Roland proceeded to tell me I incorrectly constructed his Malibu (Field & Bench, MAN 12/70) in that I did not completely sheet wing top. My response was I built the RF-4 incorrectly as well by leiving a portion of the wing top between 2 in leading and trailing sheets uncovered. So for all you Malibu and RF-4 builders, sheet the top of the wing completely (even though the plans don't show it!)

Speaking of plans let me comment on the RF-4 plans. Astro-Flight has elected to describe the RF-4 construction by means of a six page, step-by-step instruction book and consequently there are minimal construction notes on the plans. Also there are no scale details on the plans. As a result, there is a great deal of improvisation required on the part of the builder with respect to construction. This is no problem for an experienced builder, but for a beginner, it's trouble. Thus, I do not recommend the RF-4 be undertaken by the novice builder unless he can obtain help..."

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