Interesting, my approximation to an English r is more like a muted w than anything involving curling the tongue and still there's a major difference between r and l sounds. (The r in my native language is also fairly unique, possibly regional.)
Edit: Just checked with a mirror and nope: raised tongue with the sides of the tongue pressing against the upper molars and a curled tip.
Let's not gloss over the war criminal and Nazi aspects, shall we? To this day people are hurt/killed by missiles developed from the ones he co-developed.