1. Field of the Disclosure
The present disclosure is directed to tools for measurement of engine torque.
2. Description of the Related Art
Determination of entire torque is an important element of engine performance, but it is an essential element in some circumstances, particularly propeller aircraft engines.
In many countries including the USA, aviation authorities such as the FAA require that an aircraft engine be dynamically tested for engine torque over a range of speeds to insure that the aircraft engine is suitable for the airframe.
Dynamic testing, i.e. with the motor in the airframe and the propeller attached, is necessary to be run when the aircraft is in flight. Such dynamic testing by prior art systems has been difficult and dangerous.
There are also other problems with prior art approaches. They require a signal cable. The transmission of the signal from the torque sensor to the aircraft instrumentation must be achieved via a multi-conductor signal cable. Because the cable is in relatively close proximity to the rotation of the propeller and starter ring gear, there is a risk that the cable will be caught up in the propeller. Heat, vibration and chafing reduce cable life, as well.
The prior art systems are also heavy due to the added weight of the slip-ring housing and associated bearings. This is a problem when flight testing aircraft that are close to the front of the weight and balance envelope. The sensor moves too much weight too far forward. At times, this condition will require a test flight be conducted without a flight engineer, to reduce weight. This requires the pilot to not only fly the aircraft, but monitor the data acquisition equipment as well. If the bearings were to seize, the entire assembly might be destroyed, not to mention damage to the engine, propeller and hazard to the crew.
Prior art devices are not strong enough. The torque sensing element must be of a two piece design to facilitate assembly through the outer slip ring housing. This junction of the torque sensing element is the limiting factor regarding the overall strength.
Prior art devices have bearings between the slip ring housing and the torque sensing element and are of constant concern. The bearings are heavy and difficult to replace. Typically the unit must be returned to the manufacturer for replacement. The average life of the slip ring housing bearing is less than 400 hours.
Prior art devices have brushes. The carbon brushes used for signal transmission are a regular source of maintenance. The normal brush wear deposits carbon dust inside the brush housing requiring constant cleaning. The brushes also frequently become lodged in the housing causing signal degradation.
Clearly this is not an effective solution, but because of FAA requirements, aircraft engine manufacturers and rebuilders have been forced to use it.
The present disclosure addresses both of these problems with an innovative solution.