ORIGINAL: Rotaryphile
Correct dive height to attain 115.5 mph terminal velocity, neglecting air resistance would be about 445 feet, and probably about 600 feet with air resistance.
Correct dive height needed to attain 181.4 mph without air resistance would be about 1100 feet, and probably about 1500 feet with air resistance factored in.
Both appear do-able if the airplane hangs together and doesn't turn itself into a dangerous missile.
Have you an explanation for consideration of density altitude? I've been recording it since the 70s whenever I do any kind of testing, especially prop tests. Most would be amazed exactly how much it differs, even from day to day. And not many would realize how much it affects our model performance. It's probably the one most important unknown that makes a great deal of our testing of little real value.
As an aside, nowadays it's actually quite easy to take very accurate readings of it. There are handheld "weather stations" quite reasonably priced that do quite an excellent job of recording just about everything.