tap testing
Joined: Jan 2003
Posts: 323
Likes: 0
From: Manchester
The "TAP" test has been used to detect de lamination on composite materials for years. I ,personally have used it on things as widely differing as Wessex tail rotor blades and 757 spoilers.
The test consist of LIGHTLY tapping the area to be inspected with a coin. The Tapping sound you get will change sharply when you reach an area of delamination. (The sound you get is obviously impossible to discribe, but it's a "dull" sound!).The problem is that the sound produced will change slightly when you pass over an area of re inforcement, differing thicknesses and near the edge of the componant. Experience will tell you the difference but I would recomend any one who hasn't done it before to get a LAME to "walk you through it".
The test is good but should not be relied on 100% as the sound change will lessen the deeper the dis-bond is within the material. Pleae refer to the relevent MM for the tests for that!
I hope that might be of some use to you
Rgds Dr.I.
The test consist of LIGHTLY tapping the area to be inspected with a coin. The Tapping sound you get will change sharply when you reach an area of delamination. (The sound you get is obviously impossible to discribe, but it's a "dull" sound!).The problem is that the sound produced will change slightly when you pass over an area of re inforcement, differing thicknesses and near the edge of the componant. Experience will tell you the difference but I would recomend any one who hasn't done it before to get a LAME to "walk you through it".
The test is good but should not be relied on 100% as the sound change will lessen the deeper the dis-bond is within the material. Pleae refer to the relevent MM for the tests for that!
I hope that might be of some use to you
Rgds Dr.I.
Iconoclast
Joined: Sep 2000
Posts: 2,132
Likes: 0
From: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
To: Ascend Charlie
As I had stated in a previous post; "If it is recommended for use on Bell blades I can assume either Bell has certified the product for use on their blades...”
My concern is that the WD-40 company has not approved it for this use as it may have unforeseen effects on the blades and they checked with the FAA and they have not approved it for use on any aircraft. As Nick stated the manufacturer recommends its' use and after incorporating it into the Maintenance Manual the FAA gives its' approval not to the actual product but the application as recommended by the airframe manufacturer.
If I were working for either Bell or Robinson as a Reliability engineer I would have recommended against the use of WD-40.
WD-40 was developed as water dispersant to prevent corrosion on the Atlas missiles based at Vandenberg AFB on the Pacific coast. The product is not a corrosion preventative although over the years it has been used in that application. It has also been used to eliminate squeaking in hinges and other mundane applications such as a penetrating agent for sticking nuts and bolts but that is not what it was developed for.
If a hinge didn’t loosen or a bolt broke in the process of trying to loosen it there would be minimal product liability however if a rotor blade delaminated in flight due to the use of WD-40 the liability would be unlimited.
I would strongly suggest you contact Bell and ask what kind of testing was performed and what cautions must be applied in the use of WD-40. Also tell them that the WD-40 company does not approve of its’ use in this application.
My engineer looked up the Bell maintenance books for our Huey, and there, in ink and smudge, it stated that WD-40 or equivalent is to be applied to the blades.
As I had stated in a previous post; "If it is recommended for use on Bell blades I can assume either Bell has certified the product for use on their blades...”
My concern is that the WD-40 company has not approved it for this use as it may have unforeseen effects on the blades and they checked with the FAA and they have not approved it for use on any aircraft. As Nick stated the manufacturer recommends its' use and after incorporating it into the Maintenance Manual the FAA gives its' approval not to the actual product but the application as recommended by the airframe manufacturer.
If I were working for either Bell or Robinson as a Reliability engineer I would have recommended against the use of WD-40.
WD-40 was developed as water dispersant to prevent corrosion on the Atlas missiles based at Vandenberg AFB on the Pacific coast. The product is not a corrosion preventative although over the years it has been used in that application. It has also been used to eliminate squeaking in hinges and other mundane applications such as a penetrating agent for sticking nuts and bolts but that is not what it was developed for.
If a hinge didn’t loosen or a bolt broke in the process of trying to loosen it there would be minimal product liability however if a rotor blade delaminated in flight due to the use of WD-40 the liability would be unlimited.
I would strongly suggest you contact Bell and ask what kind of testing was performed and what cautions must be applied in the use of WD-40. Also tell them that the WD-40 company does not approve of its’ use in this application.
