Sizing Wing Spar for Designing a Wing Box

[tailchaser47]

hi Guys,

I am working on a project for university that requires designing a wing box. I have obtained all the aerodynamic loads such as Vz, Vx, Mz, My, Mx and now ready to start sizing spars. For preliminary analysis i have assumed that the top and bottom spar flange takes the My bending moment due to lift and the spar web takes the Vz shear force. This would give me a total area that is required for the spars (bending + shear). Now I am looking for a spar design guideline (such as the length to width ratio and radius etc) to start sizing these parts. Is there a design practice on how to distribute these areas for each spar. I plan to have 6 spars (military fighter jet) in total with the front spar at 0.25c and rear spar at 0.7c. The chord at wing root is 5.04m. Also in designing the spars how would i account for the vertical stiffeners added to the spars to reduce skin thickness (shown in the attachment). Any help is appreciated Thanks.

 

[Achy47]

Hi there,

As a scientist with experience in aerodynamics and aircraft design, I can provide some guidance on your project. First of all, it's great that you have obtained all the necessary aerodynamic loads for your wing box design. This is a crucial step in the design process.

In terms of sizing the spars, your approach of assuming the top and bottom spar flanges take the My bending moment and the spar web takes the Vz shear force is a good starting point. However, it would be beneficial to also consider the Mx bending moment and the Vx shear force, as these loads can also have an impact on the sizing of the spars.

In terms of spar design guidelines, there are a few key factors to consider. The length to width ratio of the spars will depend on the specific aircraft and its intended use. For a military fighter jet, a higher length to width ratio may be desired for increased stiffness and strength. The radius of the spars will also depend on the loads and material being used. Generally, a larger radius will result in a stronger spar, but it may also add unnecessary weight.

When it comes to distributing the required area for the spars, it's important to consider the location of the spars and the loads they will be subjected to. For example, the front spar at 0.25c will experience higher bending loads compared to the rear spar at 0.7c, so it may require a larger area to accommodate for these loads. The chord at the wing root will also impact the sizing of the spars, as a larger chord will result in higher bending and shear loads.

In terms of accounting for the vertical stiffeners, these should be considered in the design process as they can significantly affect the strength and stiffness of the spars. The addition of stiffeners can allow for a reduction in skin thickness, which can help to reduce weight. However, the placement and design of these stiffeners should be carefully considered to ensure they are effective in reducing skin thickness and do not compromise the strength of the spars.

I hope this helps guide you in your spar design process. It's important to keep in mind that every aircraft and wing box design is unique, so it's crucial to carefully consider all factors and perform detailed analysis to ensure the spars are properly sized and designed for your specific application. Best of luck with your project!