WINGS AND TURBULENCE

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Flooi
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WINGS AND TURBULENCE

Unread post by Flooi » Wed Sep 11, 2019 8:46 pm

Went with a friend on a midday flight in his RV7 and was impressed by how the aircraft handles midday turbulence, even though we were far from MAUW. Compared to a 172.... like chalk and cheese... even though wing loadings are fairly similar.... around 14lb per square ft. My question is this.... Is a short and high chord wing better in turbulence than a long and low chord wing of same area? Just wondering...
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Re: WINGS AND TURBULENCE

Unread post by Surge » Wed Sep 11, 2019 11:02 pm

I should imagine the longer wings the bigger the difference in terms of movement around the longitudinal axis (roll) in turbulent air.
On gliders one often experiences a wing on one side being picked up when it hits a thermal. The same effect for downdraughts except one wing is forced downwards.
I've been rolled 90 degrees within a couple of seconds when playing in the updraft from a veld fire even with full opposite aileron and sufficient speed.
Sort of like wind shear in the vertical direction and within the horizontal distance of 15 meters (G102 glider wingspan).

The RV7 wingspan is 7.7 meters vs 11 meters for the 172 so there is a fair difference in span.
On an aircraft with zero wing span there would be no or very little effect. :)

Another difference could be in control column, control linkages, control counter weights, etc. where a sudden up or downdraft could cause some change in elevator position leading to a change around the lateral axis (pitch).
I don't know enough about the two aircraft in question but in my glider the joy stick is quite short and cranked back towards the pilot. This is a short arc input. If one hits a strong updraft, the weight of ones hand on the stick tends to move it downwards (backwards) towards the pilot because of the crank angle causing the aircraft to pitch up. The positive G then compounds the problem by making ones hand even "heavier" leading to more up elevator.

Combine the two options above and one may end up with a rolling and pitching motion in turbulent air which may be more noticable in one aircraft than another.
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Re: WINGS AND TURBULENCE

Unread post by excolonial » Thu Sep 12, 2019 10:46 am

Cruise speed will also change the way you feel the turbulence in my experience. The faster you go, the quicker you pass through it. 40+ knots difference in the cruise?
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Re: WINGS AND TURBULENCE

Unread post by StressMerchant » Thu Sep 12, 2019 11:02 am

The wing properties definitely have an effect, and in particular the wing loading and aspect ratio. In general the higher the aspect ratio, the more sensitive the aircraft will be to gusts.

I used the old FAR 23 method to derive maximum gust loads for a fictitious aircraft, varying the aspect ratio but keeping all other geometry factors the same. Gust loading is very sensitive to the wing lift gradient. Different airfoils will have different lift gradients, but I have assumed above that the basic airfoil lift gradient is unchanged. The overall aircraft lift gradient will change with aspect ratio, so I included a rough correction for the aspect ratio. The numbers are just to show how the wing planform can affect the gust sensitivity.

Aspect Ratio / Max G Loading
16.3 / 4.34
12.0 / 4.12
8.3 / 3.84
5.3 / 3.44
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Re: WINGS AND TURBULENCE

Unread post by Vogoff » Thu Sep 12, 2019 11:58 am

I have often wondered about this.

The 172 feels a bit like riding waves in the ocean. The V tail Bonanza will tend to yaw rather than bump.

Meeting turbulence in my Mooney sometimes feels like I have driven into a pavement, especially at higher speeds. At other times I only notice turbulence because the airspeed increases or decreases (the change in airspeed is obviously linked to a small change in pitch required to keep altitude, but the airspeed change is measurable whilst the change in pitch is negligible).
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Re: WINGS AND TURBULENCE

Unread post by Flooi » Thu Sep 12, 2019 1:44 pm

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