Posted Sunday, June 1, 2008 @ 11:26 AM  

We all know how important it is to have the mainwheel locked down before landing, but I recently discovered it’s also important to have it stay locked up during flight.

Like all the others, the red RF4 (G-AWGN) Matthew and I recently bought is now over forty years old, so it has changed through the years, and feels a little different in some ways from my Blue Australian one. Among other things, the Bauer/Scherer metal spring suspension had been incorporated, and it has a superior Teleflex brake cable. Maybe the linkage was less well lubricated. Anyhow the wheel’s operation felt a little different to my other Fournier’s.

Nevertheless, it still came as a surprise when, while pulling 4g, the wheel came crashing down in flight. As a precaution against collapse, the engine was stopped and a glide approach made to a gentle touchdown with no further problems. You could see something was wrong, because the wheel lever was touching the cockpit floor.

Investigation revealed that the locks had gone past the down lock cut-outs in the wheel casting’s quadrant and lodged against the upper end of the quadrant. Luckily they stayed there and supported the aeroplane’s weight, although the mechanism was obviously misplaced, and the aeroplane sat noticeably higher.

Those U-shaped up and down lock cut-outs often become rather V-shaped over the years, but these were still clearly sharp-edged. This is because the castings are not original, and nearly new (the main casting was replaced a couple of years ago after it had cracked) so I really could not see why the wheel did not stay up and locked. I can only think it was not properly locked up in the first place. In future I shall be sure to push and pull that lever to be sure it’s properly locked up.

Anyhow, further investigation unearthed some obvious damage. The pivoting casting had whacked into the woodwork at the rear of the wheel cut-out in the fuselage underside (which appears to have some function as an over-travel stop) and had cut deep grooves into it.

Enquiries to other Fournier owners revealed that this kind of thing had happened before, usually causing distortion to the mainwheel’s backing plate, on the rear of the fuselage’s main bulkhead. (This is the plate that the fifth, crutch, or negative-g seat belt attaches to).

The good news was that I have a couple of Matthew’s spare Fournier fuselages in my garage, so a replacement plate was available. The bad news – we would have to separate our Fournier’s wing from its fuselage to replace it!

Those of you who have done it (myself included) know just what a pain this task can be.

In the ‘maintenance’ area, I will post a checklist for anybody else who wants or need to undertake this laborious process (it took two of us two days to get apart, and myself working alone three and a half days to re-assemble).

G-AWGN (the Old Wagon) is now flying again, and long may she continue to do so.

This was the first RF4 I ever flew, after an RF5 check-out by Rob Dorsey in November 1970.

Yours, Bob

Posted Thursday, September 2, 2010 @ 07:36 AM  

The other day, I discovered that there's another area of damage likely when your wheel whacks down in flight like that.

Take another look at the second picture.
If you peer closely, you can see that the plywood floor has cracked away from the plywood fuselage sidewall.
I didn't look closely at that, because I was too concerned about fixing all the other damage & inspecting the wheel mechanism.

A couple of months ago, at annual inspection time, I had removed the canopy for its annual emergency release function check, and happened to be looking down into the fuselage from the right wing-root. I saw a line of daylight!

Further investigation revealed this. I had thought it was just another crack in the paint!

Push in a little screwdriver, and you can see it better.

Repair was quite straightforward. The tricky bit was realising that repair was needed in the first place.

I just prised open the crack as wide as I could without splitting the wood or glue any further. Blew out any debris with an air line, and cleaned both surfaces as much as I could (I think I used acetone on Q-tips, I can’t remember for sure).

Then I drilled and countersunk a line of holes for small brass screws to hold it all together while the glue set (and afterwards).

Next, I mixed up some slow-setting two-pack epoxy adhesive (Araldite) and put that into a syringe and squirted it into the crack all the way along, and from both sides.

Finally, I screwed up all the screws, wiped off the surplus glue and went home for a couple of days to let it all cure fully.

I would suggest this is an area for inspection next time you’re making your pre-flight check (in case this has happened in the past) and at any time your wheel comes down unexpectedly in flight – talking with other Fournier owners, this seems to happen more often than you might think.
Also, that long lever is only thin-walled aluminium tubing, so it can kink, or worse, snap off in flight – don’t laugh, it has happened.

Finally, be sure to include a check that your wheel IS properly locked up when you make your HASELL check before flying aerobatics. It’s the S for SECURITY bit.