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[TowerTalk] Universal Freestanding Tower

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Subject: [TowerTalk] Universal Freestanding Tower
From: (Bill Coleman)
Date: Wed, 13 Feb 2002 16:51:40 -0500
On 2/11/02 6:24 PM, Randall Williamson at wrote:

>To be very technical airplanes are work hardening and stress cracking
>and breaking down that is why there is a maximum hour limit on the

I owned a 1964 Cessna 150D for almost 10 years. I was the forth owner. 
This aircraft had over 9300 hours on it when I sold it.

Cessna publishes no maximum hour limit for this airframe. Very few parts 
come even close to "working hardening". Indeed, most cracks are caused by 
stress risers and intense vibration -- such as around the engine cowling. 

And heck, those parts aren't structural.

Back in the 1980s, there was a DC-3 with well over 100,000 hours of 
flight time, still going strong. I suspect it is still flying today. No 
sign of a life limit.

Certain aircraft parts do have life limits. Anything on a heliocopter, 
for example. And certain presurised aircraft may have such limits.

But, for the most part, life limits don't exist for aircraft. Why would 
they exist for towers?

> The antenna is work hardening too, but the cost of inspection
>and the availability make it a unlikely candidate for x-ray or dye
>penetrating sprays for inspection. The strength to weight ratio make
>them difficult to just give a visual inspection, by the time failure is
>visible to the naked eye it has already fallen. 

Wasn't there just a thread here about TH6 and TH7 antennas that have been 
up for decades? Why haven't they cracked up?

I stand by my assertion that a properly designed and maintained aluminum 
structure has no reason to "work harden" or otherwise fail.

The problem isn't with Aluminum. It is how it is used.

Bill Coleman, AA4LR, PP-ASEL        Mail:
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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