Yes, I know what you mean. I know of a couple of PhD's who should not be working engineers.
The problem I see is that someone who has worked under all the requirements to acquire a P.E. license probably won't be willing to take a teaching position. Just finding someone who has the qualifications would be tough enough, and the real drive it takes to get to that level of engineering is based on a love for the work, and that personality is rarely found alongside a honest desire to teach. And that's not even getting to the subject of compensation.
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I did go to college for 1 year. I quit my job as a maintenance tech in a plant to go to college full time to get my Electrical Engineering degree. (I had the post-911 GI bill for a free ride, plus housing allowance)
That is when I started my LLC, so that I could do side jobs for my ex-employer for extra cash.
One of the courses for 1st year Eng students was "Introduction to Engineering," taught by guy probably 70+ years old.
He told us his story; boiled down, he graduated college, went out and worked with a team designing containment systems for fluid tanks for a few years and then went back to college as a professor, all before I was born.
He used to teach physics but got tired of that and wanted to teach the newbies who still had sparkles in their eyes.
One day I brought in a device that I had made for my previous employer, before dropping it off later that day.
I tried to engage him in discussion about things that he had designed, and he had nothing to offer.
He said that his participation on the one Engineering team he had ever been a part of, was limited to basically busy work; crunching numbers, drafting, etc. He had no patents, nor anything that seemed like an original idea.
He, or rather that discussion that we had, is part of the reason why I left school.
I felt like I was being taught by people with no real-world experience. The blind leading the blind..
After that I started to reevaluate the path I was on.
I informed myself of the salary of a degreed Engineer upon graduating. A rookie Engineer's average salary was less than I was making as a Maintenance Tech before I quit.
And, by that point I had other customers and figured out that the salray was less than I could make self employed, working 20-30hrs per week (not including health ins.).
That was all the motivation I needed. I didn't feel that FREE college was worth my time.
Maybe if they had a more qualified person at the gate to welcome in the newbies, I wouldn't have been scared away.
But there probably wasn't any more qualified person to be had, because as you point out, the qualified people are not willing to take a teaching job.
The qualified people have the passion for the jobs they're qualified for. Teaching is a totally different passion.
There's a maxim for that: "those who can, do. Those who can't, teach." <- a little harsh and not applicable 100% of the time, but it's a maxim for a reason.