A & P Technology - Case Studies (Case 327)

Braided Carbon Fiber Reinforcements Provide the Strength for Critical Exit Guide Vanes on Turbofan Engines for Business Jets

The Subject:
Jet engine stator vane

The Challenge:
Reduce weight, increase fatigue strength,
and lower manufacturing costs

The Solution:
Use a braided carbon fiber sleeving tailored to
the shape of a resin transfer molded vane

The Details:
Read the case

Braided Reinforcements in Resin Transfer Molding

Case Study 327

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Fan exit guide vanes on turbojet engines are stationary, however, they must endure the pounding of adjacent rotating fan blades while remaining resistant to foreign object damage (FOD). Therefore, precise airfoil shape and high fatigue strength are primary factors in designing and producing stator vanes. In the past, high temperature metal alloys and titanium have been the materials of choice for this application, but more recently, the drive for lighter weight has led the industry to carbon fiber/epoxy composites.

Braided Reinforcements in Resin Transfer Molding Allied Signal Corporation manufacturers turbo-jet engines at their Tempe, Arizona facility. In developing the TFE 731 turbojet engine family specifically for small business jet aircraft, Allied designers studied the various forms of carbon fiber reinforcement available for stator construction. Although compression molded prepreg tape provided vanes with usable properties, the lay up time involved was excessive which kept part costs high. As a solution to this problem, A&P Technology recommended a braided carbon fiber reinforcement tailored to the shape of the mold. Vanes molded using A&P Technology's braided carbon fiber exceeded the fatigue and other performance requirements of vanes made with unidirectional carbon prepreg while dramatically reducing part cost.

A&P Technology supplies specially braided preforms by braiding an aramid sleeve and then over-braiding the aramid with a carbon fiber sleeve. Both braids are computer controlled to allow for thickness variations in the airfoil shapes. The resulting sleeve, thick in the center portion and thin at the edges, is trimmed to length at A&P Technology. Then, the molder, Intellitec (Deland, Florida) places the preforms in a multi-cavity RTM tool. Once the mold is closed, epoxy resin is injected and cured. The resulting vane is ready for use with only minor trim and deflash operations.

Allied Signal stator vanes made with A&P Technology's braided preforms are now in production and flying in engines on the Dassault Falcon 50 EX and 900B, the IAI Astra SPX, and the Lear 45. These vanes will also be introduced on the AS907 engines that power the new Bombardier Business Jet. A&P Technology's predictive software, sophisticated braiding techniques, and mandrel designs allow reinforcements to be tailored to the precise dimensions and structural requirements of the product.

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