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The Fournier RF4D's strength printer friendly version
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Bob Grimstead
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Posted Wednesday, April 25, 2007 @ 01:01 AM  

Hi Folks,

Thirty-odd years ago, when I first started flying RF4s, I repeatedly heard the rumour that, although only approved to +6/-3g, this airframe had been designed to an ultimate load of 13g (corroborated by Jane's All The World's Aircraft), and tested to destruction at 13.8g. This was also mentioned in a couple of magazine articles around that time, but I could never establish whether the rumour originated with those articles, or those articles merely perpetuated a verbal rumour.

Looking for an answer to Collin's previous question in Rene's own book, I came across the following statement on page 218 (badly tanslated by moi).

'The RF4's wing which, during static tests, held on to 13.8g, was recalculated to 11g after a correction for wood....'

He goes on to say (I think) that, if cropped for the RF7, this spar should be good for 13g breakage, or 9g approved.

OK, so our airframes are no longer new, and this was only the wing, not the fuselage, but it's all reassuring stuff -- especially since there's no such thing as wood-fatigue. The RF4D is one strong little airplane!

Yours, Bob

PS, I reckon that when or if my spar ever snaps, it will be where the outriggers bolt to the spar, at the inboard end of the ailerons and the outboard end of the spoilers. That seems to be the most highly stressed area, and goodness only knows what damage those rattling outriggers have imparted to the spar there over the years.

Bob Grimstead
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Posted Tuesday, June 3, 2008 @ 09:36 AM  

Hello Folks,

I've recently found some strange information about the RF4's strength.

My Australian Manual (dated 1968) Section 2.4 states unequivocally that it is stressed to +6/-3g at the fully aerobatic weight of 370kg ( 816 lb).

However, our British Fournier came with a Manual dated 1985, and Section 2.4 of this says - Deleted.
So does the copy on the CFI Europe web site.

Presumably, this means there are no longer any g limitations to be observed?!

Unfortunately, the LAA take the view that it should arbitrarily be limited to +4/-2g.

Since I routinely fly to +6/-2g (and occasionally, accidentally, more) I would like to get those British limits increased.

Does anybody know the reason for Section 2.4 having been deleted, and to what limits do you all fly?

Yours, Bob

Donald
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Posted Tuesday, June 3, 2008 @ 02:20 PM  

Bob,

I would imagine your reasoning re. Section 2.4 to be 180° out. If your Australian manual Section 2.4 states +6/-3g and the British manual Section 2.4 reads 'deleted' I would take that to mean that the +6/-3 limit has been disallowed. That would allow the overseeing body, the LAA, to set the limits. That it's an arbitrary limit of +4/-2 may be irritating but in the UK we do rather tend to take a conservative stance on such things. God knows how we ever had a global empire. The rest of the world must have been useless.

It used to be said of engineering in the PFA, now LAA, that if deHavilland didn't do it that way then you ain't going to either.

Cannot help you with getting it fixed, though.

Don

Bob Grimstead
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Posted Friday, June 6, 2008 @ 02:20 AM  

Hi Don,

Yeah, my comment was rather tongue-in-cheek.

And we all know what happened to de Havilland, don't we.....

I'll just have to remember to re-set my G meter after every flight won't I?

Yours, Bob

Sam M.
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Posted Monday, December 8, 2008 @ 10:13 PM  

Hey Bob, whats the most amount of G's you have pulled, or pushed?

Bob Grimstead
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Posted Tuesday, December 9, 2008 @ 09:57 PM  

Hi Sam,

As I read my g-meter at the end of the last aerobatic contest, it showed +5.9/-2.8g, but I have occasionally pulled and pushed a little bit more than that.

However, I feel ashamed if I complete a display with much more than +4.5/-1.5g on the dial, and generally +4/-1g are all you need to accomplish most of the manoeuvres. You only need higher numbers when you are trying to make small radius turns for a competiton, not in display flying, where minimising the g means minimising your height loss.

HOWEVER... after forty years, every airframe is now different, so if you want to know what g-forces your own Fournier will withstand, wear a parachute, climb very high (10,000 feet, I'd say) and then gradually, bit by bit increasing the g-force, make a series of tight turns until the G-meter reads what you expect to be your personal limit.

Beware, contrary to myth, wood does not creak or groan before breaking. It just snaps with no warning, so if your airframe does break, the first thing you will know is when something goes 'bang!' and you are trapped in the cockpit with the wing folded over the canopy, or some such other nightmare scenario.

The most important thing is to inspect your wing root fittings beforehand (all four of them) to ensure they are tight, with no play. That forty-foot wing exerts a lot of leverage! Also check the horizontal and vertical stabilizer fittings and security.

Your only true safeguard is inspection. Unlike a metal airplane, wood will not deform to show you that it's been overloaded. It just breaks.

Be careful Sam, approach all such test flying gently, step by step, and taking all possible precautions.

Yours, Bob

Bob Grimstead
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Location: Perth, Western Australia or West Sussex, England
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Posted Wednesday, April 27, 2016 @ 09:03 AM  

--------------------
Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

Jorgen
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Posted Wednesday, April 27, 2016 @ 04:02 PM  

What a funny clock- tea time, is it?:D

May the 4's be with you/ Jörgen

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