Turbulence effect on big v small aircraft

[DrZoos]

I did a mid arvo flight during the week with 29 degree and not much wind .. Theres a spot off the end of our runway that nearly always has some local turbulence much higher then other areas. But this day it was severe.

 

i made a normal approach. It was So rough i couldnt / didnt get it right so i went around . Funny from my perspective Virgin behind me did the exact same.

 

2 nd time round i came in higher landing much further up the runway, worked well. Virgin must have had the same thought since he used the entirety of the runway to stop, which is very unusual for them.

 

It got me thinking about the effect on big v small. Clearly an equal force will move a larger mass less then a smaller. But given the big aircrafts wing surface is larger and thus exposed to a higher amount of the turbulent air, it got me thinking that maybe we assume the difference in the way turbulence affects us is not correct. Ie that flying through the same air would be much worse in the smaller aircraft.

 

Or is it just down to wing loading?

 

Im interested to hear viewpoints.

 

 

[Ultralights]

pretty much down to wing loading.

 

 

[DrZoos]

I guess the lack of flex in our short wings may also contribute

 

 

[Old Koreelah]

Wing loading is a major factor, as the rotary-wing people say. While our large, slow fixed wings are being pummelled around, a gyro's rotor (which is just a very thin, fast-moving wing with high wing loading) is barely affected by turbulence.

 

 

[Marty_d]

pretty much down to wing loading.

Guess the old F-104 Starfighter didn't have much problem with turbulence then!

 

 

[facthunter]

The Virgin flight probably just added a little extra speed. They compensate for gusts and w/v. Wing loading gives better penetration , but short wingspan and tail moment arm affect things too. Larger aircraft are much easier to handle in choppy conditions. Nev

 

 

[DrZoos]

Ive heard people say before that speed helps Nev, but doesnt the Velocity Squared in the lift formula argue that velocity actually increases the effect of turbulence. And isnt that why max turbulence penetration speed is always much lower then VNE... or max crusing speed. I know people increase speed in turbulence incase of wind gusts dropping etc , but doesnt the actual increase of speed increase make it rougher ??

 

Or are you saying he simply came in faster to give himself a safety margin in the turbulence?

 

 

[facthunter]

Your target speed is increased for safety margins and control considerations, on approach in gusty winds.

 

Increasing speed increases structural loads and roughness (the harshness in bumps), in turbulence. This relates to a cruise situation. Nev

 

 

[Powerin]

. And isnt that why max turbulence penetration speed is always much lower then VNE...

As far as I remember turbulence penetration speed is calculated from stall speed more than anything else. At this speed a potentially damaging gust from below or a vertical updraft will stall the wing, unloading it, before the structural G limits of the wing are reached. Turbulence penetration speed provides an automatic safety net to prevent structural damage. Go faster and the maximum structural limit of the wing can be exceeded before the wing stalls.

 

 

[dutchroll]

In a large aircraft such as the Airbus, the target approach speed may be increased up to a certain amount - a technique reserved for gusty wind conditions. This is used to help maintain energy on final approach, in the event that a gust causes a loss of energy (i.e., undershoot shear, etc).

 

The "turbulence speed" is a different principle all together. This is the speed which the manufacturer has determined gives a combination of the best protection against the effects of gusts on the aircraft structure, while still maintaining an adequate margin to buffet onset in those conditions. Although FARs do offer a complex formula which the turbulence speed may not be less than, they also give some flexibility for choosing an optimum speed between the high and low speed buffet boundaries.

 

And yeah, ultimately wing loading or weight, and structural rigidity have a lot to do with how much turbulence is "felt". There was always a very noticeable difference in turbulence in a B767 when at max takeoff weight (185 tonnes) versus a much lighter domestic weight (say around 120 tonnes). And you could follow a B737 through exactly the same patch of sky where he reported turbulence as "moderate", but in the 767 you could only really report it as "light" based on the definitions of the various categories!

 

 

[djpacro]

Some simple arithmetic gets to g loads due to a simplified gust: http://flysafe.raa.asn.au/groundschool/FAR_23-335.pdf