I have an airplane and have done a gust response analysis - for a discrete vertical gust. I used the nastran example from chapter 9 section 1. How can I do a side gust analysis - gust 90 degree angle to gravity vector? Can you point me to an example.

Sanjay,

I thought about this a little more. The aero entry indicates the flight direction. Both a vertical gust and a lateral gust are orthogonal to the flight direction. Hence, a vertical gust changes alpha, and a lateral gust changes beta.

It appears to me that the Nastran gust capability is applied to vertical gust in example 9.1, and the resulting loads are due to 1g gravity loads plus the increment in the vertical direction due to the change in alpha due to gust.

For a lateral gust, the fight direction is the same as for vertical gust. To compute the result of vertical gust, I need to neglect the 1 g gravity load, and just compute the lateral load due to beta. This affects only aero surfaces that are not horizontal. So I believe my first plan for computing lateral loads in Nastran was on the correct path – the lateral gust along with the flight speed and direction defines the lateral load --- that is side force due to beta. Vertical forces need to be eliminated from the side force calculation, and so this side force must then be applied “by hand” by the user. I think that the user must apply the side gust force in a separate run, and save the time dependent side force with all vertical force removed. This side force is then dependent on time, and must then be applied to the relevant aero suraces as a time dependent forcing problem. The relevant aero surfaces are vertical fins, wing panels with nonzero dihedral, etc.

I do not think that Nastran does the lateral gust in a single step. Nastran does do the vertical gust in a single step.

Does this sound correct?

Thanks,
Scott this is my reply on Saturday.

Sanjay,

I thought about this a little more. The aero entry indicates the flight direction. Both a vertical gust and a lateral gust are orthogonal to the flight direction. Hence, a vertical gust changes alpha, and a lateral gust changes beta.

It appears to me that the Nastran gust capability is applied to vertical gust in example 9.1, and the resulting loads are due to 1g gravity loads plus the increment in the vertical direction due to the change in alpha due to gust.

For a lateral gust, the fight direction is the same as for vertical gust. To compute the result of vertical gust, I need to neglect the 1 g gravity load, and just compute the lateral load due to beta. This affects only aero surfaces that are not horizontal. So I believe my first plan for computing lateral loads in Nastran was on the correct path – the lateral gust along with the flight speed and direction defines the lateral load --- that is side force due to beta. Vertical forces need to be eliminated from the side force calculation, and so this side force must then be applied “by hand” by the user. I think that the user must apply the side gust force in a separate run, and save the time dependent side force with all vertical force removed. This side force is then dependent on time, and must then be applied to the relevant aero suraces as a time dependent forcing problem. The relevant aero surfaces are vertical fins, wing panels with nonzero dihedral, etc.

I do not think that Nastran does the lateral gust in a single step. Nastran does do the vertical gust in a single step.

Does this sound correct?

Thanks,
Scott this is my reply on Saturday.