I’m not going to gloss over it: the three years of not being employed in engineering have become a big obstacle to your getting employed as an engineer.
- De-emphasize aerospace. Even leave the word out of your resume. It's one of the weak engineering fields for employment.
- Have neither your address nor a phone number indicative of your area of residence on your resume or cover letter - just your email address. If you're uncomfortable with that, tell each prospective employer you want to relocate to their area for some personal reason. Assume you will have to move. If you can, put your resume here so we can see and appraise it.
- All your available time look for jobs and try to contact people you've known in your field. That means suspending for a while your home engineering projects.
- As far as timing is concerned, maybe working at this hard the last two weeks of May you will get ahead of the fresh batch of graduating engineers. Expect it to be much harder in the coming summer months when they're all out looking and competing with you.
- Apply for jobs outside of just "aerospace engineer." Apply for ANY general engineering job and for lower than bachelor's degree level (i.e. engineering technician) jobs. If you have any coursework in their field emphasize that strongly in your cover letter.
- Post your resume everywhere you possibly can, including Indeed.com, LinkedIn.com, engineerjobs.com, and in Craigslist's Resume section.
- I think you should explain your not being employed in engineering for 3 years by your fascination with your engineering projects. Don't portray to prospective employers that it's the result of being rejected a lot.
- Seriously consider "starting over" by a new degree or advanced degree in an engineering field that has better job prospects. The best engineering fields now (according to the Bureau of Labor Statistics and engineersguideusa.com, the % growth expected by BLS 2012-2022 I've put in parentheses) for job openings in the next 5 - 7 years are civil (20), environmental (15), petroleum (26), computer software and biomedical (27). It will take a lot to fix your situation, but "starting over" probably will.
- Seriously consider working overseas.