F21 fuselage/strut fittings

[Robert Lees]

One of the posts which, it would seem, has passed into the great ether for all eternity, is mine about F21 fuselage/strut fittings, so I re-post here. Those who responded, please feel free to re-post your responses for the purposes of completeness.

Here in the UK, we have had an F21 failure of the above item, fortunately found during routine inspection. I need not comment on the result had it failed in flight. For B models, this was the subject of an AD in 1947 (AD 47-16-03 refers), and all aircraft of that vintage should have log book entry to demonstrate compliance.

The UK authorities here will (under ICAO rules) be required to notify both the FAA and the TC holder of this discovery, but in the meantime, an inspection of post-1947 aircraft models might be in order for peace of mind. Indeed, I have re-inspected my project for the same potential problem; none found.

The original AD was apparently issued after a subject aircraft suffered failure; it was apparently a float-equipped plane.

Photos attached.
er...Admin: attachment file size needs to be reviewed...appears to be 50kB, so I cannot upload

Rob

[Steve Long]

Re: F21 fuselage/strut fittings

Hello Robert,

I have an F21 - an 81 Model that I use on wheels, skis and floats. After receiving your post last week or so I had the mechanic thoroughly check that fitting as he pulled the floats off to convert to wheels. He found no problems, but I appreciate your posting and the photos that accompanied it really helped. Thanks. Steve Long

[Robert Lees]

F21 fuselage/strut fittings Update 2005

Does anyone know if the design of the lower strut attach fitting changed between the B models and the F models?

This issue is likely to develop to a re-issue of the 1947 AD, with extended applicability to all models, so any help would be appreciated.

Rob

[alwaysoar]

Re: F21 fuselage/strut fittings

This AD gives me the willys. I am not sure where the failure occurred in the original plane. Is it where the fitting attaches to the fuselage, or in the "fingers"? I routinely inspect the fingers on my preflight, and do a dye-pen at annual, but where the attachments are welded to the fuselage longerons in harder to see. Rob, where are those original pictures?

[Robert Lees]

Re: F21 fuselage/strut fittings

This link discusses the matter a little more. My understanding that it is in the fingers.

[birdlegs]

Re: F21 fuselage/strut fittings,and others too

Rob; as the results from this thread roll in, count me as one who got a real good look at this. When I pulled my wings the AP/IA gave me a brief Re: how to proceed, He stressed several times not to put any forward force on the lift struts, the attach fingers are not designed for any such force, only acceptable movement is slightly up & down, any increase could stress the bracket. Use healthy amounts of oil too, it cleans off.

[alwaysoar]

Re: F21 fuselage/strut fittings

I've been think about the fore and aft wiggle. My struts do not perfectly line up, thought I can't imagine why--it would seem if this were a problem that there would be aerodynamic issues, but it flies true--so that after I mount them on the fuselage fittings, I have to move them forward to get them to the wing fittings, or at least the aft strut. So what I think I'll do in the future is to go ahead and tighten down the fuselage bolts before I try to attach the struts to the wing fittings to prevent stress on the fingers. I inspect the fingers routinely and with the naked eye I see no cracks. At annual, I use dye penetrant on the fingers. But, this is worrisome. However, if you've ever looked at a J-3 Cub's fuselage fitting, the T-craft by comparison looks very rugged and overbuilt.