I realise that the "negative 4G inverted dive" described in Top Gun is a hypothetical manoeuvre, but I was wondering what sort of speed they would be flying at. I'm guessing low subsonic Mach 0.3, but I have no idea really. I guess the 4G force, depends on radius of the vertical loop and the speed, so different radii would give different speeds. The aircraft were theoretically an F-14 Tomcat (top) and F-5 Tiger (below). I am interested in doing some CFD analysis of the 2 aircraft in close proximity, so it would be useful to have a rough estimated of the flight speed. Thanks.
The maneuver described is so non-sensical that I don't think knowing an airspeed range would help. In fact I don't think you could properly model it at all...
Start by asking yourself what the words "negative 4G inverted dive" actually mean, compare them to the movie footage of the alleged event, and then ask yourself some questions about what the aircraft was actually doing.
- If you were inverted and pushing negative 4Gs, would you be in a dive?
- If you were inverted, canopy to canopy with another aircraft that was upright, (as depicted in the scene) and the other plane was pushing negative 4Gs in a dive, would your G loading be positive or negative?
- Starting from level, upright or inverted, if you entered a dive at 4Gs, how long might you be able to sustain 4Gs before it becomes an "Split-S"?
- How much might your airspeed change during such a maneuver, and how would that affect your calculations?
And then look at the (phony) footage - what are they actually doing? Really just flying along in close formation, canopy to canopy. Maverick is inverted, but it doesn't look like they are pulling any Gs at all really, certainly the maneuver is gentle enough to leisurely snap a photo.
Even if the dive wasn't intended to be shown in the movie and happened just after Goose took the photo, Maverick's description of the event doesn't even make sense to me. My advice would be to not waste any time trying to reconcile these Hollywood anomalies with reality.
But, if the airspeed parameter is the only thing holding you back from doing something you find interesting, I would suggest you start the maneuver at around 300KIAS, and presume that by the time the plane reaches 90 degrees nose down, they would be going at least 500.
P.S. If you need any help answering the bulleted questions above please mention it in the comments.