Split-S question and recovery theory

[Attila]

I’m not an aerobatic pilot, just looking for knowledge from those in the know.

Several years ago an Air Force Thunderbird crashed at Mountain Home while executing a split-S after takeoff (I’m sure many remember it). I believe that it was caused because of lack of altitude at the top. It’s obvious that the aircraft was (mostly) level and still sinking at impact. So, another hundred feet +/- may have been enough to save it. Like I said – I’m not an expert.

The questions I have are:

1 - at what point in the split-S maneuver is the abort point – 45 degrees nose down, vertical, ???

2 – after the abort point, would a pilot be able to gain more distance to the ground (flight path, not altitude) by turning to the left or right? That would provide a small corkscrew path that may have bought him that needed extra distance. Or, is it a moot-point because the turn would decrease lift and nullify the extra distance in the flight path? In other words, by curving to the side and extending the flight path, is it possible to buy enough time to save the maneuver if it’s right at the edge of failure?

I hope that all makes sense. This is simply a theoretical exercise based on my limited aviation experience, but one that I’ve never had someone knowledgeable enough to ask.

 

[N3368K]

The point to abort a low altitude Split-S is before you roll into it. Too fast and low is a recipe for disaster if you don't have the altitude.

Just an FYI. I recall reading in a WWII P-47 manual that a split-s at cruise speed at combat weight required 18,000'!


This space intentionally left blank for future sarcasm.

 

[denverpilot]

Unless you're an airshow pilot, there's no need at all to do this low-level. I was an acquaintance of two people who are long dead from attempting to do stuff low level without a plan. They wanted an adrenaline rush, and they got the one of their lifetimes, I guess you'd say, right before they scattered themselves and the aircraft all over the Colorado prairie.

As the previous poster said, if you've trained enough to do it that low, you absolutely must know all of your entry altitudes and speeds and never ever start a maneuver you can't complete. I believe the Mountain Home investigation found that density altitude (high temperatures) weren't calculated into to maneuver entry altitude properly that day, but I can't find a reference to it now.

 

[whifferdill]

Airshow pilots typically don't do low level Split-S's. It's just not very impressive and is unnecessarily risky for surface level acro. You'll never see Sean Tucker or Rob Holland do a split S down to the deck. Airshow pilots doing low level acro have altitude "gates" for various maneuvers in their sequence to ensure exit clearance to the ground. Your "abort point" is immediately upon realizing that you have not achieved your gate, before proceeding with the figure.

So your question about the "abort point" of a Split S is academic. You could abort at any point prior to reaching the vertical down attitude. Once you're vertical down, you're locked in and there's nothing you can do reduce your altitude use, assuming a max efficiency pullout. If you were to abort prior to reaching the vertical down attitude, you could reduce your altitude use by pushing out rather than pulling out, assuming the aircraft is sufficiently stressed for negative G. Turning will not help.

 

[Attila]

Thanks whifferdill. I realize now that the abort point is dependent on altitude - 30,000' doesn't have one, 10' is at the start of the roll. Didn't think that though properly.

So, a "max efficiency pullout" is going to be straight ahead with no roll - pitch only. Rolling slightly will extent your path length, but also increase the height of the figure - correct?

 

[whifferdill]

Rolling doesn't do anything to help get the nose pitched away from the ground. All it would do is change your heading and tilt the wing's lift vector such that you are reducing the rate at which the nose can be pitched away from the ground. In critical pullout situations, you want all the lift you can get, pointed as far away from the ground as possible (perpendicular).