Rolls-Royce Tay

Rolls-Royce Tay A marriage of new and old technology By Greg Napert May-June 1998 Because of its size, the Rolls-Royce Tay engine is considered somewhat of a transitional engine between corporate aircraft and transport category...

"The Tay is known as a pilot's engine because if an emergency requires the use of full throttle, the limiters within the control system will prevent engine rotor speeds, temperatures, and pressures from reaching unsafe values. One of these limiters is the LP speed governor which limits low pressure fan rotational speed. We have had events related to the LP governor, associated with a sudden increase in LP speed and a resulting exceedence at the top of climb when the aircraft levels off at cruise. We have found that this is generally caused by the LP governor setting drifting on the high side. This results in a minor exceedence of the LP assembly that is dispatched as an alert on the flight panel. If this happens, the pilot can simply pull back on the throttles to correct it temporarily and report it to the maintenance department. Typically, all that is required is a simple adjustment to the LP governor."

By-pass duct air leak
Hewitt adds, "Another area that can cause the crew to report a discrepancy between LP engine speeds is if you have any kind of an air leak at the outer bypass duct panels. This can be as simple as one of the bypass panels not being shrouded properly. A small leak of bypass air in the outer air duct could offload the LP compressor and the speed will rise marginally. Any of the access panels or a combination of panels on the outer bypass duct can cause this. It's like opening a bleed air valve and releasing bleed air — the rpm will go up. A dark stain on the trailing edge of a panel can be a tip-off to this leakage.

"We had an instance where the crew had been complaining for over a year that the LP speed on one engine was consistently higher. The maintenance department checked but couldn't find anything. It wasn't until later, when the time expired engine was removed, that we exposed a certain bushing on the inboard side of the engine that was causing an air leak. It was where the fuel burner nozzle or arm goes through the bypass panel. The sleeve had caulked, and there was air being released from this sleeve," Hewitt says.

Power run-downs
Hewitt explains, "A power run-down is a tendency for the engine to run down to sub-idle condition. We saw only one case on the GIV but more on the F-100. This turned out to be a calibration drift of the fuel flow regulator or incorrect acceleration settings. During service, you can check the acceleration time, and if the acceleration time is slow, you could have an under-fueling condition. That under-fueling condition has an effect on the operation of the engine throughout its operating range. If you've lost power, or the load on the engine changes with increased air bleeds or electrical loads, the engine doesn't have the degree of over-fueling that's required to maintain the selected power. That degree of over-fueling is set by the acceleration control on the fuel flow regulator. If your acceleration times and deceleration times are set incorrectly, it can have an effect on the engine throughout its operating range — including the engine start sequence. Results can be hot or hung starts, etc. Setting the acceleration and deceleration settings correctly will usually rectify run-down and starting problems. Occasionally, however, you do have a calibration drift of the fuel flow regulator and you will need to pull it and have it recalibrated on the bench."

Too much oil
Hewitt says, "Remember to wait 15 to 30 minutes after shutdown to service the oil on the Tay engine. By over-servicing the Tay you'll end up with oil covering the engine. If you leave it longer than 3/4 hour, then you should fire up the engine and run it at idle for a couple of minutes and then shut it down to check the oil."

Masella adds, "Despite the use of correct servicing procedures, the engine can still show evidence of air/oil mist, for example, at the engine's cooling air outlet duct. A current Mod Action from Gulfstream improves the sealing between this vent outlet and the cowl to reduce the amount of oil staining on the engine."

Ready to go
Masella says that Rolls-Royce is continuously working on making changes to improve the operating characteristics of the Tay engine. In addition to working with Lucas to eliminate P3 air leaks, upcoming changes to the Tay include elimination of the temperature limiting actuator to simplify engine controls; the addition of an air canister which serves as an "air capacitor" for the pneumatic chamber on the fuel flow regulator (to dampen the rate of engine response at altitude to prevent surges); and a modification to the fuel drain collector tank to reduce overboard spills.

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