Hi folks, Not been in here before!!

I have a build thread going on a sailplane in 'Sailplanes - Thermal' but this machine has interrupted things!!

I am a full-size pilot and a friend asked me to 'look at something' in his workshop, the 'something' was a 1/4 scale Fournier RF-4! He is the owner of the real aircraft with this registration but not a modeller or model flyer.

He's asked me to check it over and fly it for him, I couldn't refuse!

It's been built very nicely, it is 110" span and weighs just under 10 lb (4.4 kg). It is fitted with an OS FS61 which I think is a discontinued engine and it has retractable gear.

The model type was the 1978 World Champion (presumably F4C?) in the designer's hands.

Hope to fly it later this week and will report back.

Cheers

Gary

Very nice photos of a great model aircraft. Thanks for sharing.

For those interested, contained within the July 2011 R/C Model Aeroplane magazine is a free construction article pull-out 72 inch wingspan plan for the Fournier RF-4 along with another related Fournier RF-4 article.

Soft landings,

Joe

OS FS 61 with exposed rocker arms IS mid-1980's, one of the first 4 strokers. Very nice engine, not all that powerful, but has enough to fly that plane as it should be flown. IIRC the valves need setting fairly often.

howell

Cheers guys, this has come out of the blue but it's such a nice model I thought I should share some details and photos.

This OS FS61 might be from slightly later, it has a single rocker cover with four 'ribs' on it, looks very similar to my OS FS40 Surpass from the mid-1990s but has a much smaller silencer. It doesn't look like a lot of power but others seem to be using this size engine but possibly two-stroke. I've had one flight in a full-size RF-4 and it goes very well on a VW Beetle motor!

The short kits are still available, it would be a good subject for electric conversion which I'm sure has been done already, we'll see how it flies and there might be a kit on order for myself!!

Speaking to the owner tonight I mentioned that it has a flap function for the ailerons and he said the previous owner used them for landing. I explained that would be bad for tip-stalling reasons and he said 'crow braking' so the previous owner must have been moving them up and not down which makes sense. I'll probably not play with them unless it glides for ever (which it probably will!)

This model has no airbrakes, they are detailed on the plan I think and there seems to be another difference; the wings are fully sheeted where the models shown on Mick's website have open fabric-covered structure (like the full-size).

Cheers

Gary

I flew the Fournier last night, have to say I'm very impressed by it.

The take off took a long run but then it seemed overpowered in the air, I think it was the combined drag of the wheels in the grass even though it was quite short.

I stalled it at height and it has a quite nasty wing drop which developed into a spiral dive, recovery was easy but I kept a safe speed on from then. It would need to be provoked, I did not try a stall in turning flight but expect it would do the same with not much warning. Did not try any aerobatics but I'm sure it can do them.

Had to do a couple of landing approaches as without airbrakes and the motor on a slightly high tickover it just kept sailing by!!

One landing had a tiny 'wheelbarrow' bounce and the prop clipped the grass, stopping the engine, there's not a lot of clearance.

I really am tempted to order a kit but I have far too many build projects on the board already (but it would be nice to have one for a rainy day!).

At some stage I will have to give it back to the owner, not just yet though!!

Cheers

Gary

What a great find. I really must make the time to build a 50% version. Ad to the lack of spoilers it's pretty easy to retrofit some Graupner 250 mm blades and will certainly make landings a lot easier.

Cheers, with a headwind it would not be too difficult to land without brakes, luckily I kept the engine running on some landings so I was able to taxi it back from the other end of the field!

I'm busy converting it to 2.4 as I wasn't happy with the original old radio gear installed.

I learnt that the wings are not original which would explain why they are fully sheeted (could even be foam) instead of Mick's scale open structure.

There is a very nice kit RF-4 by West Wings, much smaller and electric-powered. By coincidence I flew one a few weeks ago, very nice as well!

Cheers

Gary

Gary, my friend has a Fournier RF -4 110in wingspan. He has had 3 unsuccessful landings because of tip-stalling. In attempts for success, he has tried a faster approach (higher tickover) but it has just sailed on past the end of the strip. Any comments or suggestions ?

I must admit that I'm not totally comfortable with it yet, it does feel like it wants to roll further into turns but I don't think it's tip stalling (more to do with higher airspeed and lift on the outer wing, a known problem with large wing span full-size gliders, especially near the ground in the wind gradient). There doesn't appear to be any washout in the wings of this Fournier, not sure if the full-size has any.

Setting the ailerons slightly negative at neutral might help although I haven't done that. This model is rock steady on the approach with the wings level and is not causing roll control worries near the ground.

I have been using 'wheeler' landings with the tail high and flying it on to the ground positively (that also keeps the angle of attack lower which might be why I'm not seeing any bad behaviour). There is a risk of overcontrolling with the elevator (pitch oscillations) due to the higher speed compared with a fully held-off landing, I did it last night and had to open up the power and go around but I think a gust caught it at the wrong moment!! I have a lot of exponential dialled in to soften the elevator around neutral.

I think the technique is to find the slowest safe airspeed and trim accurately for it, fly a large circuit at fairly low level and make the final turn (very carefully!) about 100 yards away. I have a habit of adding two clicks of down trim on the downwind leg of the circuit for gliders just to be on the safe side.

If the tickover is too high it will go for ever without airbrakes, I have retuned the engine and got the tickover nice and low. It might be useful for your friend to understand how full-size pilots control the approach (or at least how I taught it as a gliding instructor), the left hand (throttle or airbrakes) is controlling the 'picture' (undershooting/overshooting the reference point) and the right hand (elevator) is controlling the airspeed (trying to keep it constant using the trim to help).

Only other thing I can suggest is cutting the engine on the approach, slightly risky because you lose the option of going around but it's no different to landing a glider!!

I've been promised a flight in the real G-AWBJ, I'll check some things out while I'm up there! I have flown another RF-4 and I remember landing it fully held-off on the mainwheel and tailwheel together with no problems.

Cheers

Gary

An afterthought is to check the wings for any wash in, that wouldn't help!

I forgot that I took some photos last night with my Tiger Moth as they are both the same scale.

GB

Many thanks for your suggestions Gary, which we will try when he returns from hols and if the rain has stopped by then!
Regards, Malcolm

Hi guys I know on highly swept wings that the addition of turbulator strips make a big difference to tip stalling on the upper surface. I believe the full size has something like 5 degrees washout in the wing. If you were to run a razor saw up to the forward spar you could induce washout and run some ca down the joint for a permanent fix. Or just make new ailerons. Raising your ailerons on landing say 5 degrees and would certainly prevent tip stall. I've also found that a mix of say 20-40% rudder mix makes a huge difference in the turns to overcome the adverse yaw you'll experience at low speeds, I found this on my 40% 1-26 glider (similar wing planform)

Hope this helps Rossco

I better not take a razor saw to someone else's model!! I'm not having tip stalling problems but the other chap might be, it's difficult to tell without seeing what it's actually doing.

My Multiplex DG600 has turbulators on the optional wing tip extensions, an original design feature shown in the instructions, they seem to work!

GB

Hi. Just found this thread. I finished a second Fournier about 3 months ago. Faithfully followed the plan : it has working spoilers (half inch L section plastic driven by separate servos, retract as supplied by MR - dont waste time trying to construct it from piano wire, as the springing is essential, Enya 46 4 str, washout as shown. Flies great but you need to get used to it as it feels a bit odd at first. It will not tip stall as long as you keep a bit of speed on and do gentle turns. The airbrakes are essential for accurate landings - I have mine set up in two stages : pos 1 for slowing it downwind, pos 2 for final approach, where I apply some forward stick to avoid stall. The brakes just compensate by preventing speed build up. It was going dead stick when I started to throw it around a bit so have just invested in a new Enya No 3 plug! Wow they now cost 6 quid! This model looks beautiful doing scale manoevres on a calm day. I have simulated the smoke by tying red and blue ribbons to each wing tip. There was some talk about wing failure, as it is built in two sections, but if you engineer it accurately and re inforce the entire centre section with glass it will be ok. My first Fournier is pictured on Micks website - two guys holding identical models. I am on left. It was at Croydon airport in the late 90s I think. This one flew nicely but I never managed the retract properly. Don Coe (Hastings club) also has a beauty - see You Tube.
I now fly at CADMAC club, Northumbria (when there is not a gale blowing!)