tap testing

[4ero]

From what I have seen the tap test on 44 blades is not always performed during a daily.

It seems to be universally understood (I personally have not seen any reports nor questioned the validity of the info passed to me by fellow pilots) that at least one tragic event was due to heat generated by an orbital sander of some sort causing the glue under the skin to debond.
I feel this belief contributes to the test not being done on a daily basis by many R44 drivers.

In another thread allsorts of potential hazards were listed, from WD40 to sunlight, to sharp temperature gradients.


So…

How many of you perform the tap test during every daily on your 44’s?

Of those that have done it, how many potential delaminations have been discovered?



(Dear Moderator, please close this thread at the first whiff of personal agenda, finger pointing, or general off-topic abuse.)

[joyrider]

I've got a 44 rating but have never been shown how to perform a "tap test". I believe it's done at the MPI by an engineer. More details please

[helimatt]

joyrider,
pm me and I'll email you the details
regards

[Lu Zuckerman]

To: 4ero

.In another thread allsorts of potential hazards were listed, from WD40 to sunlight, to sharp temperature gradients.



No matter what you were told by Robinson do not use WD-40 on rotor blades. WD-40 is a water dispersant and it also has penetrating ability and can effect the bonding materials used on the blades. WD-40 is not approved for any use on any aircraft and as such Rocket Chemical can not be held responsible if there is delamination. A film of WD-40 on the blades will attract sand and dust causing disruption of the airflow over the blade surface.

:E :E

[4ero]

Joyrider,

it's ad/r44/18 and should be done daily.

The most common method is lightly bouncing a 20c along the blade just behind the spar listening for on ominous dull thunk.

I have been shown to run across the top only, can a blade not delaminate from below? (much harder to tap)
.

[Ascend Charlie]

Lu:

I am flabbergasted! The maintenance release on our 206 B and L machines specifically required applying WD40 to the main and tail blades weekly.

So, what is the go???!!:confused:

[Head Turner]

Blade performance requires a clean surface which can be achieved by careful polishing with a simple wax polish.
WD 40 can damage the bonding as mentioned above. I have seen it used on metal blades to inhibit rust formation and potential icing.
A highly polished Enstrom blade will give 1/2 inch of extra power.
by reducing drag.

Tapping blades is a way of giving you the benefit of knowing all is well with the bonding on the intended flight.

[Lu Zuckerman]

To: Ascend Charlie and Mr Selfish

I am flabbergasted! The maintenance release on our 206 B and L machines specifically required applying WD40 to the main and tail blades weekly.



I was under the impression that WD40 was specifically named in the Jetranger flight manual, As suitable for application to the MR blades?

If it is recommended for use on Bell blades I can assume either Bell has certified the product for use on their blades or someone just thought it was a good idea. In either case the product must be listed as a consumable product in the maintenance manual. The same is true for the R-22 and the R-44 and as such must be approved by the FAA.

When this subject came up a while back I contacted the WD-40 Company and they specifically indicated that they have not certified it for use on aircraft and if the product is misused and causes damage they are not responsible. I can only assume that if it is used in accordance with Bell and Robinson recommendations and something happens any litigation will go after Bell or Robinson.

WD-40 contains petroleum distillates and these are the elements that can break down bonding materials. They can also seriously damage elastomeric rotorhead elements if there is any overspray. Some waxes contain petroleum distillates and should not be used on bonded blades.

:E :E

Verify, verify,verify. Since Bell recommends the use of WD-40 I figured something had changed since I contacted the WD-40 Company in September of last year. I just got off the phone and they indicated that in September of last year they got several E-mails I assume from members of this forum resulting from, my post on the subject of WD-40. With that amount of interest WD-40 Company contacted the FAA and they indicated that the FAA for any use on aircraft or helicopters does not approve WD-40.

Question both Bell and Robinson about this non-approval.

:E :E

[Vfrpilotpb]

On heavy good vehicles, Railway rolling stock large machinery and ships, the application of a 2lb hammer lightly tapped will without doubt satisfy most engineeres to the tightness of the relevent nut or bolt, on steel plate panels that can also be tapped you will also find any that are not tightly fastened or clamped by bolts, but I fear the application of a 2lb two faced hammer or even a tiny panel pin hammer would have a rather displeasing effect on the surface of any rotor blade or propeller.

Like wise I distrust the suggestion that this "Tap Test" is supposed to be carried out by using a two cent coin. I have many friend over here in the UK who own R44's and I have never seen any of them carry out a Tap Test on their daily check,

Is it actually in the R44 manual?

Peter R-B
Vfr

[Lu Zuckerman]

The tap test on rotor blades has been employed since the early 1950s when Sikorsky first introduced metal blades. It was discovered that the individual pockets on the blades were delaminating and the pockets were secured with black tape similar to electricians tape. Sikorsky recommended that the mechanic perform a tap test using either the edge of a coin or a small hammer. If a hollow sound were detected the black tape would be applied and continuously applied until the blade went in for major maintenance.

The requirement for the tap test on the R-44 and R-22 should be covered in an advisory circular and eventually incorporated in the maintenance manual.

The US Navy found a cure for the problem. They secured the pocket on the spar by drilling a small hole and driving several sheet metal screws into the blade spar. Naturally when Sikorsky found out about it they removed the blades from service.


:E :E

[Arm out the window]

I know it will be hard to describe in words what we are supposed to be listening for during this tap testing, but would anyone who has heard what delamination sounds like care to attempt it?

[NickLappos]

The airframe manufacturer can recommend almost anything, like WD-40, for its blades, and WD-40 people can do nothing to start or stop its use. The WD-40 people will not "approve" anything, even use of WD-40 on salad, because it is not their place to do so, and they have nothing to gain by such an endorsement. Would you tell some guy in an email to use your product on some flying machine? Are you smoking cigarettes without labels?

pprune is a great place to swap stories and wisdom, but a bad place to start arguing with published procedures.

If the Original equipment manufacturer (OEM) tells you to do it, you can, and probably should, even if Lu and the WD-40 guy he called say not to. Why? Because the manufacturer of the helicopter is the applicant, and the owner of the maintenance and operating procedures, and they know. They really know, because that it their job. Imagine that it is not WD-40, imagine it is knowing the thickness of the skin, or the bonding agent under the skin, or the other million things it takes to build that machine. The FAA explicitly endorses anything in the flight manual and virtually anything in the maintenance manual, and the OEM fully endorses both.

Just be sure the OEM manual says to do the WD-40 procedure (read the paragraph yourself!) then go ahead and do it, it is just fine. But if it is in your opertaing company documents, and not explicitly in the OEM maintenance manual, then watch out!

[belly tank]

Would anyone care to say what products you CAN use on rotor blades?

Or is this something to talk to the manufacturers about?

[helimatt]

Gday Vfrpilotpb,
The tap test is an airworthiness directive in Australia which is required as part of the daily inspection. I dont know if any other countries have issued any thing similar, but Robinson have a service bulletin/ letter out on it.
Cheers:ok:

[4ero]

So it appears the tap isn't really going on much. and after reading the AD I wasn't actually doing it properly myself.
(should be on both sides of the base at the D-spar / Skin Seam)

AOTW: It's like looking for a secret passage in an old library. You tap along the blade looking for

ting - ting - ting

if you get a

ting - ting - thung

close the doors and put you hand in your pocket for a blade.


Has anyone found a potential delamination yet?

[Leftpedal]

I've never done a tap test on the R44 either - what number is the service bulletin and can anyone point me to a copy. Is it on the Robinson website?

[Ascend Charlie]

Lu:

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.

Makes me feel a bit happier. At least Bell is OK with it, but maybe Robbo blades are a different matter.

[sprocket]

I suspect that Bell and/or other manufacturers have given WD-40 the approval under the assumption that the paintwork on all rotor blades is in good condition with all of the bonding joints (at least) sealed or covered.
In the real world a lot of the bond lines and edges become eroded which exposes the adhesive and allows absorbtion of chemicals and water. Keeping the paintwork good in these areas is probably the hardest yet most important task.

In some cases I have seen 206 blades less than 12 months old corroding/delaminating at bond lines yet the blade it had replaced went to full life under the same conditions (and maintenance procedures).

The manufacturers have to be responsible for their product quality but how can a buyer detect faulty bonding until its too late?

[Arm out the window]

Thanks, 4ero.
I've only just had the pleasure (or otherwise as many people have been telling me; quite liked it myself - s'pose it's one of those things you're not supposed to tell people about!) of flying the R44, the tap test was shown to me briefly but not explained in depth; good to get a bit more info.

[belly tank]

Our engineers actually gave us a template when the AD came out.

the template is only made from cardboard and it fits over the leading edge with hash marks on the cardboard inboard section to identify the area to be tap tested. a useful little tool but you get the idea after a few tappety taps where to tap!!

they never said i had to wear tap shoes whilst performing the tap though!

cheers

BT

[Dr Illitout]

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.

[Lu Zuckerman]

To: Ascend Charlie

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.

:E :E

[sandy helmet]

Been a long time since I flew a 44 but didn't the tap test go hand in hand with a daily crack inspection with a 40x magnifying glass?