Navy T-45 Goshawk Trainers Being Upgraded With Swept Engine Inlets

The T-45 Goshawk’s new inlet design is primarily intended to reduce dangerous compressor stall occurrences during dynamic maneuvers.

byJoseph TrevithickAug 4, 2022 5:17 PM
Navy T-45 Goshawk Trainers Being Upgraded With Swept Engine Inlets
A US Navy T-45C Goshawk jet trainer with new forward-swept engine inlets. Scott Stephens
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At least a portion of the U.S. Navy's T-45C Goshawk jet trainer fleet is in the process of being modified with new engine inlets that feature a distinctively aggressive forward sweep. The inlets are intended to help mitigate potentially dangerous compressor stalls and surges that the aircraft may experience when executing high-dynamic maneuvers.

Aviation photographer Scott Stephens recently took some great pictures of one of the modified T-45Cs while it was at Meridian Regional Airport in Mississippi. He was kind enough to share his pictures with us at The War Zone.

Scott Stephens

The aircraft's markings indicate that it is assigned to the Navy's Training Squadron Nine (VT-9), which is based at nearby Naval Air Station Meridian. Some Navy T-45Cs, including this one, are also marked "MARINES" on the side. Naval Air Training Command, of which VT-9 is a part, is responsible for training U.S. Marine Corps aviators.

The "VT-9" and "MARINES" markings are visible on the side of the fuselage under the tail in this shot that Scott Stephens took of the modified T-45C in Meridian. Scott Stephens

At present, the Navy has around 194 T-45Cs, which are modified carrier-capable versions of the British Aerospace (which subsequently evolved into BAE Systems) Hawk jet trainer. That company originally developed the T-45 Goshawk in cooperation with McDonnell Douglas (which was later absorbed by Boeing). The T-45A model entered service in 1991. The C variant designation applies to a mix of new-production and upgraded A-model jets with new avionics and glass cockpits. Production of new Goshawks ended in 2009.

A spokesperson for Naval Air Systems Command (NAVAIR) confirmed to The War Zone that five T-45Cs have received the new inlets so far. The official nickname for the modified aircraft remains simply Goshawk.

A picture of another T-45C with the new inlets Naval Air Systems Command (NAVAIR) provided to The War Zone. US Navy

The NAVAIR spokesperson also confirmed that the new inlets have to do with mitigating compressor stalls and surges that the Rolls-Royce Turbomeca F405 turbofan engines that the service's T-45Cs have been suffering from over the years. Skybrary.aero defines a compressor stall in the following way:

"A compressor stall in a jet engine is a circumstance of abnormal airflow resulting from the aerodynamic stall of aerofoils (compressor blades) within the compressor. This occurs when the angle of attack of the blades of the compressor exceed their critical angle of attack resulting in one or more stages of rotor blades failing to pass air smoothly to the succeeding stages."

...

"A compressor stall occurs when there is an imbalance between the air flow supply and the airflow demand; in other words, a pressure ratio that is incompatible with the engine RPM. When this occurs, smooth airflow is interrupted and turbulence and pressure fluctuations are created within the turbine. Compressor stalls cause the air flowing through the compressor to slow down or stagnate and sometimes result in reverse flow."

Compressor stalls where the complete "reverse flow" occurs are also known as compressor surges.

With regards to jet-powered aircraft, compressor stalls and surges can lead to some degree of loss of thrust, or a total loss of power, in the affected engine, and potential physical damage. In a single-engine jet, such as the T-45, a total loss of forward thrust can be particularly dangerous, especially if it occurs during particularly aggressive aerial maneuvering. When taking off or landing, and especially while doing so on a carrier during training, it can extremely perilous.

The new inlets pronounced forward sweep is closely visible in this close-up of one of the modified jets. Scott Stephens
Two T-45s with the standard inlet design are seen here. US Navy

"T-45 engine surge is a critical safety concern for a single engine training aircraft with over 900 surge events documented, including over 70 surges requiring engine shutdown and restart emergency action," a section of the U.S. Navy's most recent budget proposal for the 2023 Fiscal Year notes.

“The Engine Inlet Modification is being developed to improve engine performance at some edges of the envelope,” Philip Paul, then Boeing’s program manager for T-45/AV-8B Programs, said in 2015, according to a story published by the Association of Naval Aviation. “The T-45 performs many flight maneuvers similar to high-performance fighter jets. Student pilots learn through exposure to these extreme operational regimes, which prepares them for these conditions that are outside of regular flight operations. The Engine Inlet Mod provides additional performance margin in these conditions that can stress airframe/engine integration.”

Paul noted at the time that the T-45 engine inlet modification had actually been developed and flight tested years before that, but had been passed over in favor of a design more in line with that other Hawk variants.

A T-45A inlet performance model, with an unswept inlet design, in a wind tunnel at NASA's Langley Research Center undergoing testing in 1998. NASA

As an aside, it's interesting to point out that the T-38 Talon jet trainer, which was originally designed in the 1950s and is still in service with the U.S. Air Force and NASA, saw its engine inlets evolve in the opposite direction. The Talon design originally had inlets with more aggressive forward sweeps optimized for supersonic flight, which were later modified to be more flat-faced for better performance and increased safety margins in lower speed regimes. NASA did the initial development work on the modification that is now fleet-wide among the T-38C. There are some T-38As that still serve as pilot proficiency aircraft for the B-2 stealth bomber and U-2 spy plane fleets, as well as aggressors for the F-22 stealth fighter force that still have the original inlets.

T-38A with its original swept inlets. USAF
A US Air Force T-38 Talon jet trainer showing the type's current unswept inlet design. USAF
A diagram showing changes in the T-38 Talon engine inlet design. NASA

The Navy's Fiscal Year 2023 budget proposal indicates that the goal is to add the new inlets to all of its T-45Cs. The service's Goshawk fleet is in the process of receiving various other upgrades, as well. These include further improved avionics and cockpit displays, Automatic Dependent Surveillance-Broadcast (ADS-B) compliant navigation and other flight systems, and new oxygen systems. The latter addition is meant to help mitigate a rash of reported hypoxia-like physiological episodes among T-45 pilots in recent years. The Goshawk is just one U.S. military aircraft to have suffered from such issues in the past decade or so.

Boeing has been putting at least some of the older T-45s through a deep Service Life Extension Program (SLEP) overhaul, as well.

All of this comes as the T-45C is entering the twilight of its career. The Navy announced in 2020 that it was looking to acquire a replacement for the T-45, which will not be carrier-capable, as part of a larger shift in how the service expects to train tactical jet pilots in the future. Last year, the Navy also announced it was looking for a similar, but not necessarily identical jet trainer-type aircraft to meet aggressor and other support requirements.

Boeing is already pitching a derivative of a version of the T-7A Red Hawk jet trainer, which it developed in cooperation with Sweden's Saab for the U.S. Air Force, as a possible T-45 replacement. A number of the competitors that lost to the Red Hawk in the Air Force's T-X competition are also being proposed now as possible Navy jet trainers. However, there are no indications so far that BAE Systems will offer a new Hawk variant or derivative.

An artist's conception of a T-7A Red Hawk variant for the US Navy. Boeing

The Navy is hoping to begin acquiring examples of whichever design it picks as the T-45's replacement by 2028.

Whatever succeeds the T-45 as the Navy's primary jet trainer, its existing Goshawks will continue to help train naval aviators for years to come and will increasingly do it with a distinct new look.

Scott Stephens

Contact the author: joe@thedrive.com

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