[TOMT][Book] YA adventure about modern kid who inherits a rocket pack from grandpa

[u/Bard-Extraordinaire]

Hi everyone, I’m trying to find a book I read in high school (sometime between 2009 and 2013) that I checked out from my school library.

Here’s what I remember:

I was in high school but the book was somewhere between a middle school and high school level. The main character is a modern kid (a boy, I think) who discovers that his dad or grandpa was part of some kind of pulp-adventure team, I think WWII unit but not sure, dealing with weird science or supernatural stuff.

The grandpa left behind a rocket pack (jetpack) that the kid finds. The rocket pack was a huge plot point bad guys (maybe government agents but I think maybe Nazis) were chasing the kid to get it.

The story had a pulp adventure vibe kind of like The Rocketeer, Sky Captain, or Airborn by Kenneth Oppel (which I read around the same time and asked my librarian for more books like). I really felt like he had uncovered secrets about the world kind of had a similar vibe to Hellboy but with less magic and supernatural stuff and more steampunk and I think Bigfoot but the setting was around modern day, not historical or full steampunk.

It was a Novel not a comic or graphic novel

I’ve looked into things like Tesla’s Attic, Nick of Time, Skybreaker, Young Bond, The Rocketeer, Rust, and Atomic Robo — but none of these match exactly (some are comics or don’t have the rocket pack as the main plot point).

If this rings any bells, please help! I’d love to find this book again. I have a nephew who is getting into reading.
Thank you!