Analyzing Wing Spar Loading with Rectangular Distribution Method

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Discussion Overview

The discussion revolves around the methods for performing static analysis of a wing spar, specifically focusing on the distribution of lift forces. Participants explore different modeling approaches for analyzing a straight high wing, considering factors such as accuracy, safety factors, and displacement at the tips during flight.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the appropriateness of analyzing the wing spar using a cantilever approach and suggests placing the lift at the middle of the wing instead of at the tips.
  • Another participant notes that the choice of analysis method depends on the desired accuracy versus conservativeness, proposing a uniform or non-uniform lift distribution based on wing shape.
  • A participant clarifies that the analysis aims to determine the safety factor and tip displacement, indicating that the spar will be located at the aerodynamic center, approximately 1/4 of the chord from the leading edge.
  • One participant suggests modeling the lift as a uniform distribution for a conservative estimate, acknowledging that the root of the wing will likely bear more load than the tip.
  • A participant calculates the distributed lift based on a total lift force and half the wingspan, confirming the method of analysis being used.
  • Another participant mentions using a rectangular distribution for lift forces, stating it provides conservative results and serves as a reasonable approximation for wing loading.

Areas of Agreement / Disagreement

Participants express differing views on the best method for modeling lift distribution, with some advocating for a uniform distribution and others suggesting a more nuanced approach. The discussion remains unresolved regarding the optimal modeling technique.

Contextual Notes

Participants have not fully addressed the implications of different assumptions regarding lift distribution and its impact on the analysis results. There is also a lack of consensus on the definitions of "accurate" versus "conservative" results in this context.

pegus
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I am trying to figure out which is the most accurate way to perform the static analysis of a wing spar. Some partners told me to analyze it in cantiliver and the half of the lift force on the tip, but I do not think this is the proper way because the lift does not act on the tips. I was thinking to put the lift on the middle on the wing. This analysis is for a straight high wing.
 
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It depends what you want to use the analysis for, and whether you want the results to be "accurate" or "conservative".

A reasonable model would be to assume the lift load is uniformly distributed along the length (or even non-uniformly distributed, depending on the shape of the wing). You might also want to include the weight of the wing, and the twisting loads if the chordwise position of the center of lift is not the same as the spar position.
 
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This analysis is to get the safety factor of the spar and the displacement on the tips when the plane is flying. Is a rectangular wing, and the spar will be located on the aerodynamic center (approximately 1/4 of the chord from the leading edge), up to where I know this is where the lift acts.
 
I would (as a first approximation at least) model it as a uniform distribution. This will give you a conservative answer, since in reality the root of the wing will be a bit more heavily loaded than the tip.
 
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Ok, so if my total lift force is 30lbs, and half of the wingspan is 51" (because I am analyzing half of the wing as cantilivier), the distributed lift will be (15lb/51"), right?
 
I use a rectangular distribution for lift forces when working with spar loading. It gives conservative results and is a reasonably good approximation to wing loading.
 
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