Multi-Engine Helicopter Shaft Speed Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Helicopter turboshaft engines experience undesirable dynamic vibrations when their shafts rotate within a specific range of speeds known as the placarded zone, and existing deceleration systems are not fully effective in preventing these vibrations.
Innovation Solution
A method and system for operating multi-engine helicopters that involve rotating one turboshaft engine at a flight speed and the other at an idle speed above the placarded zone, then synchronizing their speeds to below the placarded zone, using a clutch system and fuel flow control to prevent unwanted vibrations by maintaining the unclutched engine at a higher idle rotation speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the unclutched engine shaft is allowed to rotate freely, then the engine operation is simplified, but the shaft enters the placarded zone causing undesirable vibrations
Solution Approach 1:
The system changes the rotation speed parameter of the unclutched engine shaft, maintaining it at a higher idle speed above the placarded zone rather than allowing it to drop to normal idle speeds. This parameter change prevents the shaft from entering the harmful vibration zone while keeping the engine operational.
Solution Approach 2:
The control system continuously monitors the rotation speed of the unclutched engine shaft and adjusts fuel flow accordingly to maintain the speed above the placarded zone. This feedback mechanism ensures the shaft remains in a safe operating range and prevents vibration problems.
2Object-affected harmful factors
If the unclutched engine shaft speed is maintained above the placarded zone, then vibrations are prevented, but fuel consumption increases
Solution Approach 1:
The system applies partial action by maintaining the unclutched engine shaft at a moderate higher idle speed rather than full flight speed. This provides sufficient margin above the placarded zone to prevent vibrations while minimizing the additional fuel consumption compared to running at full power.
3Object-affected harmful factors
If both engine shafts are decelerated simultaneously below the placarded zone, then vibrations are eliminated, but the clutching process becomes complex
Solution Approach 1:
The system performs preliminary action by maintaining the unclutched engine shaft speed above the placarded zone before clutching occurs. This preliminary speed maintenance simplifies the clutching process, as the shaft is already in a safe speed range and does not require complex deceleration control during the clutching transition.
Data Source
AI summary
There is described a method of operating a multi-engine system of an helicopter. The multi-engine system has a first turboshaft engine having a first shaft, a second turboshaft engine having a second shaft, a gearbox having a clutch system, and a range of rotation speeds defined as a placarded zone. The method generally has rotating the first shaft at a flight rotation speed when clutched and rotating the second shaft at a first idle rotation speed when unclutched, the first idle rotation speed above the placarded zone; decreasing a rotation speed of the first shaft from the flight rotation speed to a given rotation speed within the placarded zone; decreasing a rotation speed of the second shaft to the given rotation speed; clutching the second shaft; and decreasing the rotation speeds of the first and second shafts to a second idle rotation speed below the placarded zone.