Assignment Philosophy

This year there has been an attempt to replicate a real world aerospace engineering task. The drawback to trying new things is that this is an untested assignment. We will have to be able to think on our feet to get things to work. This assignment will NOT be one that you can cram in the last week. There will be teething problems, so small efforts over a long time will be much more successful than large efforts over a small time.

I have intentionally built the assignment as an HTML page, so it can be updated as new requirements and information come to light. I'm not going to move the goalposts on you by changing the overarching requirements of the assignment, but small details will be added as needed. The assessment forum will be your constant companion for this assignment, ask all questions through there. If a big enough issue arises I will update the assignment page accordingly. Conduct all your calculations in a nimble format, ie a spreadsheet, so that small changes to loads and section geometry can be easily accommodated.

Task Overview

Your task will be to analyse a proposed redesign of the de Havilland Vampire tail booms (not to be confused with a boom in your hand calculations) in an all metal configuration (as opposed to the hybrid wooden design of the original). You will need to consider both the static strength of the materials as well as the potential for buckling instabilities.

Structure

A cutaway of the Vampire is shown below. We are interested in the tail boom design, specifically the critical section just aft of the attachment with the fuselage.

Boom Cross-section

Assume the boom is a tapering elliptical section. At the critical section, the geometry is shown below. The major axis of the ellipse is 18" and the minor axis is 14". Eight longitudinal stiffeners (Longerons) are included at the locations shown. Longerons 2/8 and 4/6 are six inches above and below the neutral axis respectively. The skin is 0.05" thick.

The stiffeners are inverted hat sections with the geometry given below.

Boom Length and Taper

Assume each boom is 10' long. The boom tapers linearly from the fuselage attachment to the empennage attachment. The taper ratio (wide dimension:narrow dimension) is 1.5:1 in the vertical direction and 2:1 in the horizontal direction. Assume that the top and centre of the boom is straight and aligned with the longitudinal axis of the aircraft. Below is the view of the fore and aft boom sections when viewed normal to the longitudinal axis of the aircraft. Frames are included every 1.25' along the boom.

Loads

The critical load case to consider is the maximum negative lift on the tailplane produced by a sharp pull back on the stick. Assume that the net negative lift acts through the quarter chord of the horizontal stabiliser with no induced moment. The quarter chord of the horizontal stabiliser can be assumed to be in the same plane as the aft end of the tail booms. You will need to determine the limit and ultimate (1.5x limit) load that can be applied to the tailplane while maintaining a minimum margin of safety of 0.05.

Materials

Assume all components in your analysis are fabricated from Al 2024-T4 clad sheet.