Strut Airworthiness Directive (AD) (merged VI)

[Ed O'Brien]

Re: Strut Airworthiness Directive (AD) (merged I)

Although this thread will continue as will this discussion, may I add an epilogue. AND, not have it confused with an epitaph. In this way, I honor the contributors and readers of this fine owners group.

The FAA is seeded now for another purpose. There are too many planes to know and too much work to be done. There are few people who understand the lightest of these aircraft and the oldest of the GA fleet. In other words, the planes we fly. So here among the restorers and advocates is the last refuge of a proud legacy.

Our fathers and grandfathers were tormented and died in the valiant service of making aviation a safe and proud vocation. In these machines they made history and that history is of the greatest consequence to modern life. For those of us that preserve and maintain the older machines of the fleet we also preserve and maintain that struggle. We remember that service. Occasionally we are caught up in this struggle too and we soldier on. To do otherwise is to deny that history and turn our back on that legacy. Yes, I do hope that the factory, the FAA, and all of us read these threads. I hope that we've conducted ourselves as our fathers and grandfathers would have wanted. We are a good lot trying to do good work. We're in a uncertain moment. We need to remain resolute and committed. We will. Taking care of each other and this proud legacy. Please, go about your work with this history looking over your shoulder and by your side.

With abiding regards and deepest respects to the machine we fly and the people we honor in doing so... Ed O'Brien

[VictorBravo]

Re: Strut Airworthiness Directive (AD) (merged I)

Thank you, on behalf of all of the Taylorcraft owners!!!!!!!

I'm sure you have it in mind to repeat and duplicate tis test on other metal structures known to be good and bad (per your post), and since you are a real-live engineer I believe there should be some credibility to your findings with the FAA.

[1938BF50]

Re: Strut Airworthiness Directive (AD) (merged I)

Fellow Taylorcraft owners,

MODERATORS, FEEL FREE TO MOVE THIS THREAD TO THE LOCATION BEST SUITED.

For starters let me introduce myself. I am a Sr. Manufacturing Engineer for the premier high end domestic bicycle manufacturer. The scope of my work involves manipulating a host of tubing materials…. aluminum, 4130 steel, titanium, and of course carbon. We have a very complete and extensive testing department. In questioning some of my fellow engineers, test engineers and QC employees who regularly use ultrasonic and eddy current testing in their job descriptions, they unanimously thought that NEITHER would be an effective method of determining if varying degrees of corrosion existed inside a closed tube structure. Always the skeptic, I set out to prove or disprove the use of Ultrasonic testing as a capable way of testing for strut corrosion. I borrowed our very portable PANAMETRICS MODEL 22 ULTRASONIC THICKNESS GAGE for the weekend. I taught myself the use and calibration of the unit and proceeded to test the LH front strut on my 1938 Taylorcraft Model BF. I set out to neither advocate nor condemn the use of Ultrasonic equipment, only to educate myself in the use and applicability in our strut dilemma. I intentionally set up a series of test parameters that are easily duplicated for STRUTS ON THE AIRCRAFT should results prove useable.

Here are the FACTS relevant to my testing.

-Testing done over the timeframe of 08/18/07 to 08/19/07 at 70degrees and 70% relative humidity.
-Tests completed on what I believe to be an ORIGINAL pre-war Taylorcraft strut. Ellipse dimensions as indicated….major axis 3.000”, minor axis 1.310” (over painted surfaces).
-Panametrics Model 22 unit calibrated per pg. 4.3 of Manual # 910-019B.
Calibration sample .181”/.338”. mild steel.
-Unit set to read in .xxx” (three decimal place…. thousandths)
-Paint thickness sample removed from strut as measured with micrometer…approx .003” as mic’d (3) times in (3) different locations.
-Couplant fluid used was provided by manufacturer.
-Transducer calibration was rechecked and recorded at each row end (54 times total during test)
-(8) individual readings were also taken along the approx neutral axis of the remaining full length of strut at 12” intervals up to the extreme outboard end(wing attach).


I set out by removing the paint from the bottom surface of the lower portion of the LH front strut. I then layed out a grid pattern of approx ½” squares on both the upper (painted) and lower (unpainted) surfaces. Grids were labeled A1 thru G-27. Some areas were not conducive to measurements with the probe such as welds and extreme trailing edges. In total I took 291 readings on this strut using the grid layout as a template.

Preliminary findings indicate extremely consistent metal thickness the entire length of the strut, with the lower 12” averaging .038” +.003/-.002 over 137 readings. I have not run the statistical analysis on my findings yet but have satisfied myself that the Ultrasonic unit is an excellent tool for determining metal thickness on what I believe to be a very intact and un-corroded strut. Findings over the painted surface yield a thickness of .041” +.003/-.001 over 154 readings. These latter reading are consistent with the sample paint thickness of .003”. Another observation that I made during the testing included the following: “ratting derbis” as removed thru the upper wing attach hole amounted to nearly a half teaspoon and consisted almost entirely of weld scale and chips as a result of ( I believe) drilling the upper attach fitting at the point of manufacture.

I would like to duplicate this test on a KNOWN CORRODED strut end. Can someone (Kevin M,, Mike R.?) PLEASE hacksaw off and send me the lower 24” or so of some known defective, corroded struts as soon as possible! Should results of this further testing prove conclusive in identifying internal corrosion, I would advocate same to the FAA . Please reply to forum, e-mail (rockriverrifle “at” hotmail.com) or call me evenings at 920-648-three four six nine to discuss or make suggestions to continue testing.

THIS COULD RESULT IN A VERY USER FRIENDLY, FAIRLY QUICK, ON PLANE TEST METHOD FOR OUR TAYLORCRAFT FLEET.

[btbell]

Re: Strut Airworthiness Directive (AD) (merged I)

My T-craft and another at the airport were visually inspected and passed without any problems. The mechanic spent quite a bit of time looking them over, putting wire into the vent hole and also tapping to listen for dead spots. He felt confident they were all OK. So we are good for another three months until we decide how to proceed. I think I am going to wait this out for a few weeks to see if the second AD is issued and deal with both at the same time. Anyway, the struts to be in short supply so we could not get them now anyway.

[whake]

Re: How to Find Out Which Struts

The drilled hole in the strut is bout 1/16 inch in dia. on the back side near the bottom weld. If you poke safety wire in the hole it should come out with linseed oil on the wire, mine was clear and thick. I intend to order new struts.

[rdwater]

Re: How to Find Out Which Struts

So where do we look to find the drilled hole at the bottom of the strut? What size hole are we looking for? Thanks all, Bob

[alwaysoar]

Re: Strut Airworthiness Directive (AD) (merged)

I am wondering how best to inspect the lower strut fitting for corrosion. Aside for the obvious visual look-see, would a punch test there be sufficient? Should paint be removed to bare metal and should the welds be dye-penned? Forrest, what would you suggest. "Inspect" in a very wide-open term.

[Len Petterson]

Re: Strut Airworthiness Directive (AD) (merged)

During my working carryer I welded ships as well as doing maintinence work in the automotive industry with hydrualics a specialet.
In the ships we drilled holes and checked for plat thicknes, a possoble way to ckeck for thinkness in strut, but where to drill? What does the welding up the hole do to the strut? A Cheeryrivet in the hole?
My suggestion would be in the bottom of the lower half 2 too 3 inch up on the strut, or there a weakness has been found by punch testing.
A load test can be done with hydrualics as force can easly be controlled.
I would caution aginst it becuase, if I take marginal part and load it to max possible load and it does not brake but is invisbly damaged by the test, to a point there it would/ could fail later. In test with a force a elongation of the part has to be measured.
What method are the Piper struts tested with? Why can't we the same?
My struts are punch tested every 5 years according to Canadian rules.
If I take hammer and tap the strut ligthly with the ball and listen too the metal a person can hear a dead sound in a corroded area, and if a anti corrosion oil is used every 3 too 5 years we should not have any problems.
Why are we conserned with the struts when the strut attchment point has failed and is weaker?

Just me thinking.

Len

[mikerice]

How to find the complete AD....

Downloadable .pdfs files of both the Service Bulletin and Airworthiness Directive are posted on the Taylorcraft website at http://www.taylorcraft.com

There will be a postcard from the Taylorcraft Factory sent to the FAA database of Taylorcraft owners that refers you to the Taylorcraft website for the latest complete information on the AD. The AD is also available on the FAA website at faa.gov.

Taylorcraft.com webmaster

[fearofpavement]

Re: Strut Airworthiness Directive (AD) (merged)

Question: How are we supposed to be notified of these SB's and AD's? I have heard of neither except on this forum. Is it incumbent on the factory and FAA to notify us?

AD's get mailed to the registered owner. The dissemination of service bulletins is a bit fuzzier.

(I haven't received the AD yet for either of our BC-12D's as of August 18)

[cpirrmann]

Re: Strut Airworthiness Directive (AD) (merged)

Question: How are we supposed to be notified of these SB's and AD's? I have heard of neither except on this forum. Is it incumbent on the factory and FAA to notify us?

[cpirrmann]

Re: Strut Airworthiness Directive (AD) (merged)

To a layman (that's me) it would seem that since the bolts at either end represent a hinge, that all of the stress is tension and compression on the strut no matter what the wing is doing as long as it's attached to the fuselage. Therefore, the weakest points would be the attach points at the spar and fuselage (as we have seen). It would seem that the strut would have to fail any punch test before it was weak enough to fail in those two directions (or the occasional 'passenger using it as a step' test).

[VictorBravo]

Re: This guy has the strut thing figured out. plain and simple

Figure out the circumference of the strut by wrapping a string all the way around from front to back, then measuring the string.

Multiply that circumference by .049 (I think that's the wall thickness), and you will get the cross sectional area of the strut metal.

Multiply that figure by 90,000 PSI tensile strength (according to the AC Spruce catalog for 4130).

The number you get should represent the minimum tensile strength of the strut (assuming the bolts do not tear out and there is no corrosion.

You should get some huge number like 25,000 or 40,000 pounds if my calculator is correct.

Next, calculate the maximum amount of stress that the airplane can put on the strut (the aerospace engineer next door might be helpful with this).

HINT ! Since the struts are at an angle, and the distance between the upper fuselage spar attach is about twice the distance as the vertical distance between the upper and lower fuselage attach... there may be some leverage or force multiplication going on that exceeds the raw number of G's the airplane can pull!!!

Then cut the calculated strength of the strut in HALF, for corrosion, bad welds, nicks, and for the wife and kids.

If there is still a big strength reserve, chances are you are safe.

Perhaps the aforementioned "Mystery Writer" can excercise his old slide rule a little and calculate just how much force the Taylorcraft airframe can develop on a wing strut, given the geometry of the airframe attach points. I can't do the calcs because of acute, chronic lack of knowledge, which El Mysterioso so gleefully pointed out.

Again this might be far more than just the gross weight times 6. How's about a Taylorcraft like mine with the Harer STC (1500 pounds gross) at 6G?

[stormman]

Re: This guy has the strut thing figured out. plain and simple

well these are just guessaments but lets say the gross weight is #1200 X 6 Gs =7200#. You have 4 struts devided by 4 = 1800 pounds so each strut needs a pull test of 1800 pounds. now since a grade 5 1/4 inch bolt has a pull strength of 40,000 pounds or so I am told .Also my 1/2 climing rope has a strength of 6700 # Now im no rocket guy but im willing to bet the crapiest strut hanging from a hoist on one end and will support my gmc pickup hanging from the other end over the grand canyon. Not so sure I would use my 1/2 in rope though. But I have seen it lift the front end of a pickup off the ground. So to make a simple test , get a chain hoist hook one end to the hook the other end to the ball hitch on your pickup and lift the back wheels off the ground. To try for a little humor we could use 4 lenghts of my climing ropeat 6700 x 4 = 26,800 or about 26,800 devided by 1200# gross weight = 22.3333 G,s on 1/2 inch rope and im betting on the bolts shearing first way past 6700# Remember this is written in simple Arkansas humor but you get the point, its that simple.

[M Towsley]

Re: This guy has the strut thing figured out. plain and simple

Norm,

Can you define 'proof-load' for me? I don't seem to have anything nearby that can do that. Just curious as to how it is done and how 1,800 owners could do it. Maybe it is just that simple. Thanks.