Wing Skin & Structure Cracks in a 170A

[Metal Master]

Having read in another posting about wing cracks I thought some might find this interesting.
In the early days of my 170 A’s life it was owned by the Nebraska- Kansas Pipe line company in Phillipsburg, Kansas it was used as a corporate aircraft delivering company personnel to various locations and as a pipe line inspection aircraft. N1208D SN# 19762

The Total time on the airplane is around 4,300 hours I have not calculated the total time exactly yet as I have not finished repairing it. Last logbook entry in May of 2004 was 4,276.5 total time.
I listed all of this because of the cracks I found in the wing during the repairs to the wings. I found cracks in the skin aft of the fuel tank where they intersected the ribs. The cracks were short about ½” maximum length and were in fact also transmitted into the ribs directly where the skin cracks appeared. The cracks were at the rivet locations on the second and third ribs part number 0523209-1 and - 2 Item Number 63 and 64 in the 170 A parts catalog Figure 3. Cracks at one location on each rib both upper and lower surface.

Additionally I found a crack in the 5th lightening hole out board of the point where the wing starts to taper on the rear spar part number 0523400. no associated crack in the wing.

Pipe line service has been a factor in early fatigue damage of airframe structures. I do not know why this is, perhaps George could enlighten us in this respect. Assuming of course that the pipeline service was indeed a factor causing these cracks. They appear to have been there a long time.

All of these cracks seem to be of a nature as having been caused by repeated flexing of the wing and not having been cause by accident damage. None of the structure in these was flexed out of place by the ground loop incident for which this aircraft is being repaired. The crack in the inboard area of the wing had evidence of fretting corrosion in the area of the cracks, which indicated relative motion between the components over a long period of time.

All of these cracks were hard to detect because they were so fine. In the end after first noting the crack in the spar I had to identify the crack location in the spar by die penetrate method because it was so fine. Each time I went back to look at it, it was difficult to locate.

I replaced the skins part number 0524002-26 and lower skin part number 0523002-28 Items Number 84 & 89 in figure # 3 and repaired the ribs locally where the ribs were cracked. The same cracks appeared in both left and right wings in the same location.

[GAHorn]

Well, I'm not surprised frankly. The constant low-level flight of patrol aircraft is especially strenuous. When you consider the differences between patrol flying and other types missions it may be more obvious.
Patrol flying involves long periods of cruise speeds at 500 feet and below, where thermals generally propagate. If you are cruising at 115 mph at 500 feet and pass over a green pasture, then cross an asphalt road then over the next green pasture...in any season, but especially in the summer, then you've subjected the airframe to a brutal beating. The air is heated over the pavement and it is rising, and it's much cooler over the pasture and relatively calm. Over the pond/stream/river it's actually possible to be sinking. (It's making the airframe absorb UP/DOWN/UP/DOWN at a much more frequent cycling and at much higher speeds than the average airframe. The average airframe takes off, climbs to find the smoothest air possible for the trip, then lets down and lands.) Discovery of a farmer on a 'dozer cutting a new stock-pond right over the right-of-way (ROW) calls for a hard pull-up, visual investigation, then a dive at the farmer to get his attention so you can drop him a note of warning.
Not even flight training aircraft are made to suffer so. Most of their pattern work is less than cruise speeds, either climbing out or descending at 70 mph or so. The airframe doesn't have to absorb the punishment of thermal jolts at cruise speeds.
You can only bend the paper-clip so many times before something breaks/cracks.
(I used to work for KANEB, ....Kansas-Nebraska pipeline company. Are you certain of the name of the former owner of the aircraft in question?)

[Metal Master]

(I used to work for KANEB, ....Kansas-Nebraska pipeline company. Are you certain of the name of the former owner of the aircraft in question?)

Yes! The name listed as owner on the early form 337's in block 2 which were actually CA-337 forms then is KANEB. Also the early log books were used as a flight log and list each flight including the original factory test flight and many flights around the area of Phillipsburg and Hastings. The pipeline patrols are listed in the block titled "Nature of Flight" as pipeline Patrol. When the airplane was used to move personnel the persons names are listed in the nature of flight column.

The original log takes the aircraft through 8/28/1952 and 715.45 hours. The subsequent airframe logs are missing to 10/20/65. However the engine logs are complete. The original “N” can be seen etched into the top of the right wing sheet metal even though the airplane had been subsequently painted. It was N1208D then and now.

Pilots names listed are Ray Henderson, Leonard Condit, Cm Broadwater, the last two having flown the majority of the flights.


Regards,

Jim

[GAHorn]

Leonard Condit's grandfather was a guy I knew and a fellow fraternity bro', Cliff Condit, CAA (fore-runner of FAA) pilot's license No. 8. I saw his license before he died in the late '90's, it was signed off/issued by a guy named Orville Wright.
But I never personally flew any of the KANEB pipeline patrol planes. I flew their corporate airplanes which were based in Houston, College Station, London-KY, and NC. Small world.

[lowNslow]

Is pipeline patrol done in slow flight with the flaps extended? Just wondering, if so, if that would be a contributing factor for skin cracks.

[GAHorn]

Pipeline patrol is flown at normal cruising speeds at altitudes varying between 300 and 500 feet on average. Strenuous manuevering may be a part of the routine, as hard pull-ups, wing-overs, and buzz-jobs are part of the norm (in order to get the attention of contractors, etc. on the line who may be working noisy equipment and/or to get worker's to come out of noisy compressor-stations to drop them a note, etc.)
The low level includes an extraordinary stress on the airframes due to turbulence, as the airplane will spend 98% of it's life never getting above 1000 feet.