The problem area is the main wing-to-fuselage attatch point, and specifically the forward bolts.
For those of you who don't already know, the main spar has two bolts permanently attached to it.
These 14mm bolts have plates welded to their heads, and these plates are screwed to crush blocks (René thought of everything) on the rear of the spar. Their threaded ends protrude forwards by maybe four inches, and insert into the main bulkhead in the fuselage, under your knees.

Over time, that fuselage bulkhead wood dries out and shrinks a bit, allowing a little bit of play to develop in those holes. Fly a lot of aerobatics as I do, and the bolts fret in the holes, enlarging them more. After a while, you will hear a 'klunk' when you make a G reversal as the bolts shift. This is not in high G or flick/snap manoeuvres, but only on G reversals -- mostly the slow roll, when you go from positive to negative to positive. Probably, you will also see some fretting of the wing root fairings, where they rub the paint off the fuselage sides.

To see for yourself, simply remove the nuts (22mm spanner/wrench) and look with a mirror. This is what I saw...

Sorry about the second photo. I was working upside-down in a confined space, and the camera was too close, so it didn't focus properly.

I have had this symptom for a while, and was putting off doing anything about it because I had a series of displays booked. Just before the last one, I started flying rolling circles, and the repeated klunking became unbearable. It was annual inspection time anyway, so I separated wing and fuselage for repair. The repair scheme is taken from our British (red) Fournier's logbook, in which it was written some years ago. Next time I go back there, I'll get the exact words, but it was something like: 'In accordance with Sportavia factory recommendation, holes drilled over-size, ash plugs inserted, holes re-drilled.' Not difficult, just hard to get at.

With the wing off, this is what the holes looked like:

The bolts were fine, just a little polished.

Here is my good friend and ace aeroplane restorer, Rob Felton doing the work.

First, get an appropriate size of hole cutter.

I can't remeber whether we used 3/4 inch or 7/8 inch. Size is actually not hugely important, because under the bulkhead's ply skin there is quite a large (5cm square?) block, presumably of ash.

Then, make up a jig. The holes must be 99.5 mm down from the top edge of the bulkhead, but I can't remember how far in from the sides. Rob took a long time making this very precisely.

Then, open out the holes until the damaged, crushed wood is gone.

At this stage accuracy is not too important.

Cleaned out holes:

Then Rob turned up two ash dowels to fit, glued them in place, and carefully sanded off the slightly protruding ends. He used the Atraldite wood glue, but I can't remember the number. It has good gap-filling properties, that's the important point.

Finally, using his jig, and measuring many times to ensure accuracy, he drilled the new holes with a 14mm twist drill bit. the result. Now to paint, finish and re-assemble.

No more KLUNK.

Yours, Bob

[Edit by Bob Grimstead on Wednesday, February 11, 2009 @ 00:12 AM]

I remember when assembling our RF it was a tight fit.
then again our rf only has 375 hours TT.

The problems will come when we try to reassemble.

I might have to take a file to the holes and taper them or ease them slightly, although I sure do hope not.

If you look under the dismantling / wing-off post, you'll see we had to use a wooden wedge to get the red one's wing off, but that's a good thing.

The tighter the fit, the better, and the longer the assembly will last.

How are your aerobatics going?

Yours, Bob

Slow rolls. Start with lots of aileron rolls, which are easy -- see the aeros page.
Before you slow roll your RF4, you should slow roll another glider -- a two-seater, with an instructor. Gliders are slippery and airspeed can quickly become dangerously high. The following advice is of course advisory, and I take no responsibility for it, but it's the best I can give you.
For proper slow rolls, first strap yourself in very tightly, so you can't move off the seat. If you can't, don't do it. Be sure to be strapped in very tightly -- lap & crutch, not shoulders, you may need to move your right shoulder forward if you don't have the cranked stick.

Take a wax (Chinagraph) pencil with you, or lipstick, or something to mark the canopy. Then climb to a good height. 3,000 feet is good, 4,000 feet is better.
Fly full-throttle, in balance and straight-and-level, then lower your nose slightly and trim to ten mph over the max straight-and level speed (but ensure you're ten mph below Va). Leave the trim there and note exactly where it is. That's your aerobatics trim position. Now mark a blob where the horizon is on your canopy. Then level out and make a three-inch horizontal line where your mark is. Put a central vertical line on that, so you have a cross. Check it, then land and drop off your marker.

Climb back up again. Now trim to that position again and hold that cross on the horizon. You should have no forward stick pressure but you should be in a full-throttle gentle descent at around 110-120 mph (BUT BELOW Va). Now apply FULL right stick. Clamp your feet gently on the rudder pedals so they don't move.
Hold that stick hard against your right leg. As you roll right, the nose will yaw up and to the left -- that's great. As you go through 90 degrees of bank and start becoming inverted, positively move the stick an inch or two (or three, or four) forward, but keep it hard against your leg. You'll have to push a bit, a few pounds pressure, whatever is necessary. You want to keep your cross on that point on the horizon. That way you'll lose a couple of hundreed feet, but stay at a good high airspeed. The engine will stop producing power, but at that speed the prop will be windmilling furiously, so there's no chance it will stop. Keep pushing gently to hold the cross on that point, and KEEP THE STICK AGAINST YOUR LEG.
Whatever you do, do not allow your cross to fall below below the horizon. If it does, push slightly harder to bring it back to the horizon. NEVER PULL!
Keep rolling and it will soon be over. If you can, use some top (right) rudder (no more than half deflection) in the third quarter to hold up the nose. If you can remember, you can ease off the aileron here a bit. If you don't, no worries, the roll rate will only speed up. When your wings become level again, centralise all controls and note your airspeed and altitude. Now go home and have a well deserved think about it. If your finishing airspeed was much higher than the start, you need to hold the nose a little higher, and vice versa.
That's it.
When you become more used to them, you can fly level slow rolls, but the airspeed and roll rate will both drop off as you go around.

Have fun, and stay high.

Yours, Bob

Ive done a ton of slow rolls in a Decathlon, that will have to do for now, as there isn't any aerobatic gliders around.
when i start doing them ill try to post a video.

Thanks for this important post. I am going to check N2182 it has over 2000 hours.

Collin

I just flew a Decathlon again for the first time since in Santa Paula, about a hundred years ago.

I can't believe how heavy its controls are after the little RF4!

The only real difference I could see, is that you will not need to use so much top rudder in the first quarter with the Fournier, because the aileron's adverse yaw neatly swings the nose up for you (although you do still have to use a little bit of top rudder).
And of course, the Fournier rolls so much more slowly you have pelnty of time to think about your control inputs as you go around.
I can't wait to get mine flying again.

Yours, Bob