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Fournier RF4D, Part 2

Flight Evaluation

By Bob Grimstead, RF4D owner and exhibition pilot, VH-HDO and G-AWGN

Fournier

I was introduced to Fourniers in 1970 by a lanky young Texan, Robby Dorsey, later to become Rob Dorsey, 2001-2002 president of the International Aerobatic Club. They appealed to me because they were inexpensive and I was poor, but I was so impressed with the RF4D that I continued flying them for several years, actually winning a navigation and precision flying competition in one.
 
A buddy of mine, John Taylor, formed a two-Fournier display act, which later became a trio, streaming smoke from their RF4s’ wingtips and flying balletic routines to the music of Pink Floyd. They were renowned throughout Europe, and I admired and envied them. But I chose the commercial airline life, going off to fly Boeing 747s around the world for British Airways.
 
Twenty years on, I retired to Australia, flying just for pleasure and hoping to improve my aerobatics to display standard. A local Fournier was for sale – a 1968 example (then) recently rebuilt, recovered in Poly-Fiber, and resprayed blue and white. It looked lovely and flew nicely. I had to have it.
 
Airframe Details
The Fournier’s airframe is brilliantly conceived. There isn’t a spare ounce of mass, no fitting is bigger than necessary, and every component integrates with others in innovative and efficient ways. Built of pine and spruce, with Finnish (Baltic) birch ply and Dacron covering, its sturdy structure weighs just 628 pounds. The long, 11.2-to-1 aspect ratio wings’ laminated spar and plywood leading-edge D-box form the trusty NACA 23015/23012 airfoil. This wing section was originally perfected for sailplanes, and its convex (cambered) undersurface is good for inverted flight.
 
The Lockheed U-2-like landing gear incorporates a single, retractable 500-by-5 main wheel with rubber bungee suspension and a steerable solid tailwheel. These are supplemented by two skinny underwing outriggers (roller-blade wheels on nylon rods) to keep the wingtips off the ground.
 
The engine is a French Rectimo-modified 1,192-cc 1960s Volkswagen Beetle automobile engine with single ignition and no carburetor heat, since it continuously breathes-in warm cowl air. Rectimo claimed it produced 39 roaring, snorting, thundering horsepower in international standard atmosphere at sea level (or at least it might have, 1,000 hours and 36 years ago). Mine mustered 35.1 hp on a dynamometer – making it more Shetland pony power than horsepower. The tiny wooden Hoffmann propeller looks more like a toothpick than an airscrew. The engine is started by standing ahead of the left wing and flicking the prop from behind.

Hand propping
Solo hand propping is easy from behind the prop.

This is much easier than hand-propping any other airplane, and it usually fires on the second turn after six priming rotations. Then you climb back over the leading edge into the two foot-wide, gray-painted cockpit. This is snug, but not tight, with a comfortable, g-resistant, semi-reclined seating position and a proper, five-point harness.
 
The side-hinging canopy latches and locks on the left but can be jettisoned with a lever on the right. Its postcard-sized clear view panel incorporates a scoop for pilot cooling, further enhanced by air vents behind your calves, fed by leading-edge inlets. A small baggage compartment behind the seat holds the radio’s battery and will also take a soft overnight bag or a one-man tent and sleeping bag, up to a maximum of 22 pounds.

Fournier

By your right thigh is the main gear’s lever. To raise it, you pull a trigger on its small locking handle, and then slide that backwards. The wheel swings halfway, bringing the lever upright, and you just pull it down to lie flat beside you. Extension is the exact opposite. The limit speed for transition is 70 mph, although flight with the gear down if fine all the way to redline. Two spring-loaded gear doors are pushed out of the way by the extending wheel, snapping shut when retracted. Under the belly, either side of the gear are two hardwood runners that should support the airframe should I forget to extend the gear.

Fournier
Belly skids in case you forget your prelanding checks and ignore the gear warning buzzer and annunciator light.

There are no flaps, but another lever on your left extends a row of curved spoilers above each wing. A third lever to the right of the central black plastic main wheel cover operates the recoil starter. Connected by cable to a small cog which engages with a bigger one on the propeller’s back plate, this flips the prop over just one revolution. So it doesn’t work on the ground, but it’s perfect for airborne restarting.
 
A small instrument panel holds the usual flight instruments in the center, with engine gauges around its edges. To the left are the red stall light and a yellow one with a buzzer for landing-gear warning, which sounds with either the throttle closed or the airbrakes extended. Below these are the plunger throttle and lockable brake lever. Over on the right are choke and fuel knobs, while the float-and-bent-wire fuel gauge is in the gas cap, out on the forward decking and always in sight. An alternative aerobatic fuel cap incorporating a ball valve prevents fuel trickling out during prolonged inverted flight.

Fuel guage gas cap
Fuel guage gas cap is always in sight directly in front of the canopy

Let’s Go Flying!
Taxiing is easy enough, but sometimes takes a knack, especially in strong winds. The aircraft tilts disconcertingly from side to side on its monowheel during turns, but you soon get used to this. The brake is deliberately ineffective, and the steerable tailwheel is your only directional control, although, with care, you can apply power against the brake with some forward stick to blow the tail around. In a really strong wind, you might have to turn through 270 degrees one way to net a 90 to the other, or even get out and lift the tail around, as I had to when new to the airplane; I have since coped with 30-knot winds with little effort. Visibility is exceptionally good, despite your low seating position.
 
The most important pre-takeoff check is ensuring the canopy is latched and locked. Performance is somewhat reduced without it. (Yes, it has been done. Indeed, there are several open-cockpit “Cabriolet” conversions).
 
The takeoff is quite straightforward, although acceleration is fairly gradual. All controls come to life immediately, and thanks to the puny power, there’s little need for left rudder. (Yes, like most European motors, that VW turns the opposite way to American engines.)
 
In a strong crosswind, it’s often best to start at the runway’s downwind edge, holding the tailwheel on the ground for good steering, although this is easier than a crosswind landing since the slipstream helps rudder effectiveness. Taking off with a strong wind from the right is the more difficult case, and you have to be quick to apply drift once you‘re airborne, to prevent being blown away downwind. The manual’s crosswind limit is 15 knots, but I have flown in more than that.

Lowering the gear
Lowering the gear with a firm push, with loose shoulder strap so you can reach, locks it in place.

With such a low wing loading, the aircraft floats into the air at around 55 mph after a run of 300 or 400 yards, for a 65 mph initial climb until the wheel is up, after which you can accelerate to 80. Thanks to their push-rods and torque tubes with ball-bearing ends (rather than cables), all the controls are light and responsive, and the elevator in particular is delightfully sensitive. This can cause some overcorrection initially, especially when retracting the wheel, which requires a change of hands on the stick.
 
The low span loading confers a climb rate around 500 feet/minute with the 1,200-cc engine, although the manual quotes 600 feet/minute. It can take as much as 20 minutes to stagger to 6,000 feet on a hot day, but this isn’t a full-on contest machine, so I use any convenient thermals – there are usually plenty when it’s hot. Turning into the lift and circling at 60 mph, those long wings will often elevate us at well over 1,000 feet/minute. The 1,400-cc engine increases climb rate to 690 feet/minute, while the 1,776-cc engine gives a 900 feet/minute climb. One such 2,100-cc engine gives that RF4 a 1,200 feet/minute climb.
 
The thing that most impressed me on my first Fournier flight was the outstanding visibility from that panoramic Plexiglas canopy. You can see not only all around, including behind you, but also almost straight down over that skinny wing, both ahead and behind. It was also a little strange to be propelled by a tiny Volkswagen’s dugga-dug-dug-dug-dug, rather than a jet’s whoosh or a Lycoming’s thrum. The delightful handling, with light and well-harmonized controls, also impressed me, although the roll rate is fairly leisurely. Some rudder is needed for turns as the adverse yawis quite marked. Control pressures do rise with increasing speed, but only slightly, and all axes remain pleasantly light at all speeds up to the 155-mph, Vne (velocity not to exceed).
 
The Fournier’s stall is viceless, with or without power or spoilers. The airplane’s negligible drag means it takes a while to slow down enough to reach the break, which comes at 44 mph clean, 45 with spoiler, and is preceded by the warning light around five mph higher and with minimal high-pitched buffet. Recovery merely requires reducing stick back pressure; moving it forward only causes a speed increase and greater loss of altitude. Power on, a slight wing drop sometimes accompanies the stall, but control in all axes remains good right up to the break. Recovery is in generally little more than 100 feet, with or without power. (The manual says 65 feet.)
 
Steep turns are most enjoyable, and the speed drops off very slowly in banks up to 60 degrees. You can roll to greater angles, but then you lose altitude because of the limited power. Nevertheless, it can be immensely fun twizzling around on the spot at four or five g and watching the upper wing skin wrinkling under the loads.

The maximum cruise power of 3,300 rpm gives around 110 mph true airspeed at the miserly consumption of 2.5 gallon/hour, giving you an incredible economy of around 45 mpg and nearly four hours endurance from the 10-gallon tank. Reducing to 65 mph, this frugal motor sips fuel at less than a gallon/hour for a near 10-hour endurance, or a 600-mile range. I have flown many 2:30 and three-hour legs at 3,050 rpm in the 1,400-cc engine, which gives 100 mph. It’s surprising how much baggage you can cram aboard if you’re careful with the CG (center of gravity) and maximum weight.  

Fournier
Just about all the things you can stuf into the cargo area behind the pilot seat

Show ’n Go
Back in 1970, Fourniers entered many air races. One won the British Dawn-to-Dusk contest in a single day by flying 1,234 miles in 14 hours 21 minutes, averaging 99 mph and using just 30 gallons of fuel. Air show and race pilot Mira Slovak flew his RF4 all the way over the Atlantic for an air race (in which he won his class, taking 175 hours 42 minutes) and then all across the United States to Santa Paula California. That Fournier, N1700, now hangs in the Seattle Museum of Flight, and remains to this day the smallest ever to have crossed that ocean. After crashing it, he did the whole thing a second time the other way with a replacement airplane!

Fournier

Fournier
(A responsive RF4D is a joy to formation fly with.)
 
With such responsive and well-harmonized controls, formation flying in Fourniers is a delight, not only for aerobatic displays, but also just for pure fun.

Mine also does the most delightful, gentle, elegant aerobatics, although its very basic fuel system (a gravity-fed lawnmower carburetor) means the engine stops under the slightest negative g. But the airframe is so clean she only slows a little, and hardly at all if you follow a slightly downward path through each maneuver. She burns less than a gallon per 15-minute full-throttle session. How many other aerobatic aircraft cost that little?

Fournier

RF4D Aerobatics
Loops, slow rolls, barrel rolls, quarter-clovers, Cuban eights, and reverse Cubans are all easy if you start above 110 mph, but hammerheads are rather more difficult. One buddy said, “I tried dozens of them, but all I got was a face full of dirt from tail-sliding and dropping through the vertical. First I climbed sideways, then I stopped completely, and then I fell to earth! I tried rudder at every speed – all that changed was the amount of sky.” Another friend advised: “Only go to the right. Pull quickly to just less than the vertical (so the engine does not stop), check, and then hit full rudder at fifty. A bit of opposite aileron helps.” He was right, so now nine out of ten of my hammerheads are fine. The tenth one will hover a bit before completing the turn.
 
The Fournier spins nicely, and quite quickly, to both the left and right, recovering predictably in half a turn. I’ve only flown eight-turn spins, but a South African Fournier pilot told me: “The most turns I have done is 14. My head was still going ‘round when I recovered, but it was the quickest way down from 12,000 feet over the airfield, so why not?” He also performs a Lomcevak-like tumble in his RF4, but I’m not yet that brave. Ordinary snap rolls are surprisingly easy. The rotation is nice and slow, and there’s no need to unload the elevator (although this does reduce the speed loss).
 
A quarter vertical upward roll is entirely possible, and with a “humpty-bump” pull over and another quarter roll on the down line, it makes a useful turn-around maneuver.

Fournier

Another handy turn-around is the half-flick off a climbing 45-degree line to the inverted and pull-through.

Fournier

A clean Immelmann turn needs an entry speed near Vne but can be accomplished with little sagging after some practice; the Fournier describes the prettiest, most graceful avalanches imaginable.
 
To this day, and in capable hands, the RF4 remains competitive up to sportsman level, and my little airplane has even been the aerobatic champion of Western Australia. Not too shabby for a 42-year-old, 39-hp, wooden motor glider with no inverted systems!
 
Because the Fournier glides so well, inverted flight is easy (of course the engine stops).

Fournier

Fournier
Inverted. Note canopy marking for horizon references.

To definitely kill the propeller and make it more spectacular, I turn off the fuel just before pulling into a half-loop, and then push gently off the top as the nose intercepts the horizon.

I have timed the inverted glide at exactly 500 feet/minute at 70 mph, allowing a useful inverted pass, following which I roll upright, turn through 180 degrees and make a prop-stopped gliding approach to land and finish my display.

Fournier

But It’s a Sailplane First
Which leads back to the Fournier’s original role – gliding. I’ve done some soaring in mine in strong thermals. But its former owner soared it all the time, both in thermals and ridge lift. His final, cumulus-lifted, four-hour engine-off flight used just half a gallon of fuel on a wonderful summer’s day.
 
You kill the engine and restore a wonderful silence by turning off the fuel, and then opening the throttle and reducing speed to just above the stall to stop the propeller. Positioning it horizontal with the hand-start lever minimizes the drag, giving a useful 20:1 glide ratio at 72 mph, or a sink rate of 256 feet/minute at 65 mph.

Fournier

This is far from competitive in modern gliding, which is more like 60:1 and above, but it makes the Fournier a good trainer. Better still, an infinite variety of glide angles can be achieved merely by leaving the engine ticking over and cracking open the throttle a bit when you can’t find lift (which, I confess, is how I mostly do it). Although its power-on ceiling is 19,685 feet (tremendously impressive on a mere 39 hp), an RF4 once held a world-class record by climbing to 36,800 feet in mountain wave.
 
Landing
Normal descents are made at 70 mph with the gear up and throttled back to just before the warning horn sounds, although the steepest descent (nearly 3,000 fpm) is achieved at 110 mph with throttle closed, wheel down, and spoilers extended (sideslipping if necessary to plummet even more steeply). There’s little yaw or pitch trim change with power or spoilers, but the elevator trim (operated by a small lever on the right coaming) is effective, if a trifle sensitive.
 
Pattern work is undemanding, visibility could not be bettered, and it’s easy to place the airplane where you want it, although you must pay attention to speed control with that sensitive elevator. The only important thing is to slow below 70, drop the wheel, and check that it’s safely locked by throttling back to listen for the horn, then pressing the test button to be sure. The final check? The wheel is down when the lever is up, which is far from ergonomic or intuitive.
 
The optimal smooth-air approach speed is 65 mph, adding five more for rough air or strong winds. Approaches are usually made glider-like, power-off, with gradually increasing spoiler, and aiming to be properly positioned with full spoiler at 200 feet. This isn’t difficult, although the spoilers are effective, so your final approach angle is surprisingly steep. It’s important to grasp their lever firmly; they always seem intent on jumping either all out or all in, whichever you don’t want!

Fournier

The spoiler lever controls your descent angle just like a throttle – back (open) for steeper, forward (closed) for shallower – so very accurate touchdowns can be achieved. If you seem to be landing short, you merely ease the lever forward, reducing spoiler deflection and extending your landing point without changing speed, power, or trim. If you really muck it up, you retract them, put the lash to those Shetland ponies, and gently go around. You become so practiced at gliding approaches, a real forced landing ought to be easy.
 
With spoilers fully extended, the flare starts a little earlier than you might expect, and at first that light elevator can lead to overcontrolling. An experienced tailwheel pilot might initially find a smooth touchdown difficult because the Fournier’s ground angle is considerably less than its stalling angle. So if it’s stalled-on for a “three-point” landing, the tailwheel touches first, and the main wheel hits teeth-jarringly hard. (Ask me how I know this.) Nosewheel pilots shouldn’t find this a problem, and a proper touchdown is easily achieved by holding the correct attitude, then lowering the aircraft to the ground.

Fournier

With their very slow touchdown speeds (below 40 mph), Fourniers can be inclined to weathercock, so I generally land on the runway’s downwind edge, lowering the spoilers slightly and easing the stick fully aft as soon as she stops flying for optimum tailwheel steering. On soft ground, if you let the upwind wing lift a little, the downwind outrigger wheel digs in, helping you keep straight.
 
Finally, you must hold on to that spoiler lever once you’re on the ground. If you let go, they can pop back in, and you pop six feet above the runway with decaying airspeed. The only solution on a short strip is to open the throttle and go around. If you do that, leave the wheel down so you don’t forget to lower it again.
 
Once you’re firmly on the ground, the rather poor brake needs plenty of force, even at taxi speeds. But the main wheel is so far forward there’s no fear of tipping the airplane on its nose, so it can be pulled as hard as you like. Landings rarely use more than 250 yards. Thanks to this, I operate my English Fournier from a narrow farm airstrip which is only 400 yards long, although I can’t recommend this except to the most experienced pilots.

Fournier

 I’m hopelessly biased, but I can’t improve on these words I first wrote 35 years ago: “The Fournier is a nice little airplane, versatile, economical, and a delight to fly. It quickly becomes a part of the pilot, seeming to need little more than his will to perform most maneuvers. Its slightly unusual facets merely make it more interesting to fly, encouraging the pilot to explore its whole range of abilities and strive to fly it ever more accurately. Its few vices on the ground are quickly forgotten in the air, where in its natural environment it performs like the thoroughbred it is.” 
 
Other Pilots’ Opinions
World-renowned display pilot and broadcaster Brendan O’Brien said, “I think my favorite aeroplane is the Fournier RF4. A very economical single-seater, it fits you like a glove, performs elegant aerobatics, and is a joy to fly…I actually broke 4,468 class speed records in 14.2 hours in a Fournier but claimed only 210 records, which were ratified by the Fédération Aéronautique Internationale.”
 
Ex-Skyhawks Fournier display team leader John Taylor said, “I am biased of course, but I still think the Fournier is in a class of its own.”
 
Former display pilot Matthew Hill said, “The Fournier is a strong old bird. One pulled 7g and showed no signs of complaining at all. If for any reason it goes quiet, you can look ahead for a place to land rather than underneath you! Fourniers are now much in demand because they’re very quiet and have low fuel consumption.”
 
UK display and corporate pilot and aviation journalist Peter Turner said, “Glad to hear you have bought an RF4. You will love it. It is one of the nicest aeroplanes I have flown.”
 
South African display pilot Peter Goldin said, “My Fournier is one of the sweetest flying planes and very pretty. It can do many aerobatics (about 50 percent of my flying). I once pulled 7.7g, and there was no damage at all. It goes cross-country at reasonable rate, sips fuel, and glides a long way. I once climbed it to 18,300 feet by a large cumulonimbus, cut the motor, and glided about 50 miles home.”
 
Silence Twister builder Peter Wells said, “The Fournier RF4 is widely regarded as the finest single-seat light aircraft ever made...”

 
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