AT THE HANGAR WITH BIG RICK

Why do Engine Inlets Suck?
(Challenger 300/350)

INTRODUCTION

There’s few reasons why I say that. First, I needed a catchy title that would peak your interest… you’re here, aren’t you?

Another reason is because, that’s what they’re supposed to do; inlets draw in air uniformly to prevent compressor stalls. The inlet is a duct which ensures smooth airflow into the engine despite air approaching the inlet from all directions (crosswinds, aircraft pitch and yaw). The Inlet must accommodate both accelerating and diffusing air flow to provide linear air flow to the engine.

The Bombardier Challenger 300/350 Engine Inlet

INLET PERFORMANCE

There is a lot of science involved with Inlet Performance. (I wish I would have paid more attention in my calculus class). NASA has determined that to solve for Inlet Spillage Drag, you will need to know the value of K = lip suction factor.   So, as we can see, it’s more than just a shiny face.

The main reason for this article is to discuss the airworthiness issues with the Challenger 300/350 Engine Inlets. It is well known throughout the Challenger community that the Inner Barrels are susceptible to erosion, corrosion and delamination.

AIRWORTHINESS ISSUES

The corrosion causes the aluminum acoustic skin to deteriorate and the screen mesh to delaminate. The results could be catastrophic if the stainless-steel screen mesh is ingested into the Engine.

Corrosion of the inner barrel surface is caused by moisture intrusion and accelerated by salt or chemicals such as acid rain.

The inlet has an inner skin that is a known corrosion point

The Inner Barrels are constructed with Aluminum honeycomb and acoustic skin, covered with Stainless Steel Screen Mesh, held together with stainless-steel fasteners. (Fun fact, did you know there are 63,000 holes in each acoustic skin).

When there is dissimilar metal construction, then add a little moisture, speed up the process with salt air and you have a perfect recipe for the occurrence of galvanic corrosion.

SOLUTIONS FOR YOUR INLET

What can be done about this problem?

The way to solve this is to remove one or more of the factors that cause the corrosion. It would be difficult to remove the moisture element, even if you don’t fly in rain, the condensation will occur when you are at altitude and then back on the ground. There is not much that can be done about the salt air or acid rain.

That leaves the dissimilar metal factor that can be improved on.  The standard OEM intake present 244 opportunities for erosion, delamination and corrosion to the inner acoustic skins. There are 242 fasteners holding the assembly together plus the 2 leading edges of the inner barrel. By eliminating these points of entry, the corrosion cannot be accelerated by moisture or the elements.

If you suspect you have erosion, corrosion (white or lighter area) or the screen mesh is starting to delaminate issue on the Inner Barrel then you should have the Inlet inspected as soon as possible for a repair or an overhaul. Contact CARE@CARE.aero to schedule an inspection.

BigRick

Rick Mutschler

Rick is a retired U.S. Navy chief with over 40 years of aviation experience. His passion for aviation took flight while serving on aircraft carriers in the Navy. Motorcycles are Big Rick’s other passion. While he’s always searching for the elusive 1958 Harley-Davidson Panhead, he’s the proud owner of a H-D CVO Road Glide and a Big Dog K9 Chopper. Every year, Rick and his veteran brothers burn rubber as they travel coast to coast in a long distance bike tour. CARE is proud to call Rick part of the family for 19 years and counting!