Can any aircraft fly upside down (aerodynamically)?

In the case of getting caught in wake turbulence I would say that an experienced aerobatic pilot would stand a much better chance of a successful recovery, regardless of the airplane category. A recovery technique that would work in an aerobatic aircraft would also be the best you could do in a non-aerobatic one. But a non-aerobatic pilot would not know how to apply that recovery technique, because it would not be intuitive.

Interesting question.

Let’s ignore deliberate barrel rolls and outside loops (little positive g if executed skilfully).

Structurally, most rotary and flexwings can’t do negative g and I suspect that some GA crew, pax and cargo are not always adequately secured for negative g.

A problem with wake turbulence is its unpredictable nature and consequent failure of the pilot to provide correct control inputs. I’ve only experienced wake turbulence once and it was quite a surprise. Natural reaction was to resist the roll with opposing control input. That worked, but if more severe, it might have been better to continue the roll. Not an easy decision/manoeuvre for a pilot with little recent aerobatic experience.

huv beat me to it…

Competition aerobatic aircraft will have symmetrical or near symmetrical airfoils and little incidence, they also have inverted oil and fuel systems. They do not have ‘enhancements’ such as friese or differential ailerons, washout, aileron/rudder interconnect and therefore fly equally precisely both positive and inverted. Arguably inverted spin recovery is enhanced as the fin/rudder does not suffer from blanking.

Your TB20 has positive incidence and positive camber, and the engine will fail inverted given the absence of inverted systems. Lack of engine power aside, to maintain level flight inverted it will need a higher inverted pitch angle, and a higher angle of attack, therefore you will need to push on the control column to maintain level or an inverted glide. This is to overcome the camber and incidence. Any aerodynamic enhancements to help overcome adverse yaw, will now increase adverse yaw inverted – so in addition to the normal challenge of inverted turns you will have to use more rudder to overcome the very increased adverse yaw.

In short easier in a Pitts Special, but your TB20 while not authorised to do so, can and will fly inverted. Just don’t try any outside aerobatics as it is limited to -1.5G.

If you find yourself inverted or nearly so. The correct thing is to roll towards the blue. I.e roll yourself the correct way up. Pulling through a loop may result in you pulling off your wings and uses by far the most altitude.

In the C152 power stops “almost” instantly that the float in the carby hits its upper stop, and comes back just as quick, you should have enough forward elevator for at least a little negative g.

From experience a poorly executed slow roll, or plain aileron roll losses plenty of height. Because the nose of the aircraft is already well below the horizon before you are even at 90 degrees. Think what happens in a poorly executed steep turn where the entry is well below the horizon it is difficult to recover your altitude without reducing some of the bank. In a wake encounter I would expect the same.

It might be best to do nothing until out of the wake turbulence??
Overstressing is a danger. As you don’t want to continue inverted, completing the roll seems best. The engine stopping is likely irrelevant, as it will still be revolving and restart as fuel becomes available.
Some aircraft with conventional wing section/incidence are cleared for basic aerobatics. In France the bent-wing Jodel DR1050 was cleared for aerobatics.
I recall a fatal glider accident (1960+-#?)where an airline captain rolled a glider not cleared for that. The outer wing sections came off and it dived in.

Maoraigh wrote:

It might be best to do nothing until out of the wake turbulence??

We can contemplate that all we want, but still more than 99% of all pilots will apply opposite ailerons immediately when the uncommanded roll starts, and in most cases I believe that will also be the best course of action.

Maoraigh wrote:

Overstressing is a danger.

From evidence, hitting the ground is a major danger. I don’t know about overstressing. The speed is usually below maneuvering speed when wake turbulence is encountered at low altitudes.

Maoraigh wrote:

completing the roll seems best

If you are turned upside down and still in the wake, probably yes. But if the wake banks your airplane 135 degrees, what then? Or 90?

As @Ted points out, altitude is quickly lost at excessive banks. That is, unless aerobatic skills are applied. A cold-blooded aerobatic pilot could reduce altitude loss in a roll by coordinating rudder and elevator in the manner used for performing slow rolls, including forward stick while inverted. But he would still need luck to choose the fastest recovery depending of the nature of the wake.

I cannot see that low level wake turbulence is something that is easily trained or prepared for. Studying what determines the strength of the vortices, how they move, knowing the traffic in front of you and picturing where the vortices are, in order to avoid them completely, seem to be the best efforts.

cold-blooded aerobatic pilot could reduce altitude loss in a roll by coordinating rudder and elevator in the manner used for performing slow rolls

A straight and level roll is not an upset recovery technique. Nose low inverted you would unload the wing by pushing on the control column and would aileron roll to upright. Achieving zero lift angle of attack improves roll and reduces adverse yaw. Unloading the wing also results in minimal G. In effect the technique is similar to the 45 down line roll of a half cuban. The risk of pushing towards an inverted stall is unlikely as the upset is likely to leave you nose low.

Wake turbulence training is about understanding the threat and avoiding it. ATC in the USA appears to be much more risk aware about wake turbulence caution alerts and separation, although ATC in Europe does appear to be issuing more alerts and recommended separation guidelines.

One of the biggest threats is being vectored onto an ILS and the heavy ahead of you has gone around. Going missed approach at that point and requesting re vectoring for wake turbulence, would be the appropriate response.

huv wrote:

I cannot see that low level wake turbulence is something that is easily trained or prepared for. Studying what determines the strength of the vortices, how they move, knowing the traffic in front of you and picturing where the vortices are, in order to avoid them completely, seem to be the best efforts

Is the best answer. Yes, any certified will have some capability to be flown out of an upset, even inverted, but safe recovery from a wake turbulence upset is not a sure thing, and even if you did recover, overstressing is a risk. I’ve seen a few GA airplanes wrinkled by abusive recoveries from events which the pilot should have avoided entirely.

Any certified GA plane is capable of momentary inverted or negative G flight, bearing in mind that you can be inverted momentarily, and not experience negative G. It’s usually not the upset which causes the risk and damage, but the recovery. Too often, the recovery includes a dive, from which recovery within maneuvering limits may be difficult. Competent aerobatic training is useful for skill building.

In theory, I guess any aircraft can do you a 1G barrel roll on engine off if it has sufficient height and VNE/VS margins without breaking anything, knowing how to do one first time without botching the manoeuvre or the recovery is what makes it impossible…

None of this helps with wake turbulence, in theory a random but correct jerking the stick/surfaces may help making turbulent flow from the wake behave like laminar flow:

https://www.sciencedaily.com/releases/2018/01/180108121612.htm