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I would like to know how to calculate how much wind would be required to rip any particular aircraft type apart.

In the case of N3079M, (video breakdown here), it took some severe storms (estimated 40 - 50 knots) to break apart a Piper PA-28-161 Warrior II.

How can you calculate, for any particular type, what wind speed will do this?

Note - I do not believe the "maximum crosswind component" in the POH covers this, as this is for landing mostly and I know from experience that speed is way under that which the aircraft can handle structurally.

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You're thinking about it the wrong way. It's not "winds ripping the airplane apart" literally. It's gusts, or accelerations induced by pilot control input, that exceeded the airplane's G limits. Hoover is using a kind of short hand to describe the effects of flying into violent turbulence from a thunderstorm cell and losing control and overstressing the airframe. The phrasing he uses make it sound like the airplane was minding its own business and suddenly some force suddenly tore it to shreds. That's not what happened.

Theoretically, if you are below maneuvering speed, Va, in a light plane, stalling angle of attack will be exceeded before gusts can exceed the G limits of the airframe. If you've been trained properly and are about to enter really rough air, you make sure you are below Va. On light aircraft, Va applies to control inputs, not gust loads, but it's assumed to be about the same.

Transport aircraft have an additional limit called Turbulent Air Penetration Speed, below which you are protected from gust overloads by the wing's stalling AOA, independent of control inputs. This is because once the airplane gets really big, inertial effects mean the speed at which control deflections can exceed G load, and the speed at which gust loads can exceed G load, can differ quite a lot. On a transport the TAPS is usually significantly lower than Va, and is the value you observe when flying into turbulence.

Anyway, the issue isn't working out how strong violent gusts have to be to be safe from "being ripped apart". This airplane was likely broken up because they lost control in extreme turbulence, at night, and likely eventually had the speed well above Va, while still in the violent turbulence. They likely came out of it near vertical in a spiral dive, and the first thing to come off is the tail or part of the tail (ADS-B doesn't tell you what the airplane's actual airspeed was, only its groundspeed).

The moral of this story isn't about flying in rough air in itself. It's staying far away from thunderstorms, period. In the daytime you stay far away from cells. With jets with on board weather radar, you are trained to give cells at least a 20 mile berth, on the upwind side if at all possible (to avoid hail).

Flying at night, VFR, with cells in the vicinity or heading their way, without live weather radar on board, was suicidal idiocy. The "TSRAs" in the TAF, at night, would keep any lightplane pilot with half a brain on the ground. Another thing is the painted areas on weather radar (which can have a lag of several minutes if you're using a display routed through the internet and thus have a large position error) only tell you where there's water not turbulence.

If you avoid thunderstorms, it's just about impossible to get caught in this kind of situation outside of phenomena like rotors below ridge lines, or wake turbulence from a much larger airplane. So forget about calculating wind turbulence or speed limits. The exact numbers will be unknown; just stay far away from thunderstorms, and don't go on cross country flights VFR if there's a risk of getting anywhere near them.

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  • $\begingroup$ I beg to differ somewhat, but enjoyed reading your answer. $\endgroup$ Commented Dec 24, 2023 at 18:02
  • $\begingroup$ Differ away. I'm interested. $\endgroup$
    – John K
    Commented Dec 24, 2023 at 19:36
  • $\begingroup$ Done for your review. $\endgroup$ Commented Dec 24, 2023 at 20:01
  • $\begingroup$ That's basically a supplement to my post introducing new information. Good job. $\endgroup$
    – John K
    Commented Dec 24, 2023 at 22:17
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One would agree that excessive G loading, positive or negative, is the prime suspect to aircraft destruction in turbulence, but one cannot rule out stress on the vertical stabilizer from cross wind gusts.

Although it has been pointed out it is a great idea to slow down to or below the aircraft Abrupt manuvering speed in turbulence, it is not only pilot control inputs that will destroy an aircraft in a severe thundestorm.

Aircraft are advised to stay away from thunderstorms because:


1. Strong localized updrafts, downdrafts, and circular winds are common


2. Thunderstorms can develop and intensify in a matter of minutes


3. Radar information may not be in real time, and information even 15 minutes old may be dangerously inaccurate


4. Thunderstorms commonly move at over 30 miles per hour, and can move as fast as 70 miles per hour

This means the radar may have shown the storms that did in N3079M up to 15 miles from where they actually were. It is quite possible the aircraft flew directly into one.

In conditions of turbulence, the aircraft's own mass (inertia) is its worst enemy. A balsa model can withstand a strong gust because it is very light, but a full scale aircraft will experience gust loads until it has time to accelerate sufficiently to reduce the load and then ...

another gust from a different direction

One can see why flying from a 60 mph updraft into a 60 mph down draft will buckle an aircraft. Negative G load limits are usually less than positive ones.

The actually calculations could be modeled as a gust force (or a control input force) per area vs the aircraft component area rated strength. Distributing mass across the wing will do much to improve its survivability in turbulence$^1$.

Sample Calculation:

Wind Pressure (lbs/ft$^2$) = 0.00256 × V$^2$ mph
Wing area PA 28-161: 170 ft$^2$

60 mph updraft: 0.00256 × 60$^2$ = 9.2 lbs/ft$^2$

Load on Wing: 9.2 × 170 = 1564 lbs

120 mph wind shear (into downdraft): 0.00256 × 120$^2$ = 36.9 lbs/ft$^2$

Load on Wing: 36.9 × 170 = 6373 lbs

Weight Piper 28-161 Cadet: 2325 lbs

Negative G load from downdraft (windshear) = 6373/2325 = -2.74 G

G load limits: + 3.8, - 1.5

So, one might have a combination of shear and control input quickly overloading the wing, as well.

$^1$ the P3 Orion "Hurricane hunter" aircraft serve well in this role.

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