All aircraft gain weight over time and as such, it is vital to accurately weigh an aircraft. This is particularly the case in larger aeroplanes, with paint applied, painting and not stripping, configuration changes and cabin equipment modifications. On smaller crafts, such as lighter planes and helicopters, additional equipment such as cameras and communications apparatus will also add to the weight, as may certain repairs.
Weight distribution is critical as passenger loading and cargo loading all affect the balance. Balance is essential to ensure aircraft stability and control ability, all determined by finding the Centre of Gravity (CoG). Although the CoG is not a fixed point, the aircraft manufacturers set limits and any deviations from this may seriously compromise both stability and control.
New aircraft are also weighed during development especially when test flights are being carried out to test load capacity, stability and safe operating limits.
There are a number of methods used to weigh aircraft. The most popular uses scales or ‘platforms’ under each wheel. The aircraft under test is towed ensuring each wheel is positioned accurately on the weighing platforms. Each weighing pad contains accurately calibrated load cells that measure the weight at each wheel and combine these together to give the overall weight of the aircraft.
Although extremely accurate and cost effective for smaller aircraft, when one considers an aeroplane such as the A380 that has 22 wheels, this option can seem expensive.
The other accepted method is to use under axle jacks with a calibrated load cell placed on top of the jack. The jacks are then raised lifting the aircraft off the ground transferring the load from the ground to the load cell.
However, cost is not the only consideration - safety, ease of use and time all have to be taken into account. In order to ensure the most accurate readings, aircraft weighing should take place in a closed environment to avoid air currents and all equipment should be properly calibrated by the scale manufacture and zeroed before use.
There are a number of specialist companies throughout the world that provide systems for aircraft weighing and one such company, Jackson Aircraft Weighing Service, (JAWS), based in Florida, is a full service aerospace weighing company with sales, calibration service, on-site weighing and rental scales for aviation applications. Aircraftscales.com and Helicopterscales.com are divisions of Jackson Aircraft Weighing Service. They believe they are currently the only full service manufacturer that offers products for rental or short term lease but, more importantly, they can offer unbiased advice on the optimum system for any particular aeroplane, helicopter or UAV.
In both the platform and jack methods, output from the load cells needs to be transferred to an indicator. Traditionally this is done with a wired system where a cable is connected from each of the load cells to an instrument where the readings are displayed. For some users, this is adequate and many companies are still happy with this approach which works extremely well. Companies like JAWS still supply wired systems but over the years have been developing more sophisticated, yet easy to use, wireless systems that have many advantages over the wired systems.
The first and most obvious advantage is the lack of wires. Not only do they pose a health and safety risk but, in certain applications, replacing damaged cables can be awkward and expensive, while fault finding on complex systems can also be time consuming.
A number of years ago, engineers at JAWS saw the opportunities opened up by wireless systems for the aviation weighing market and tested several wireless suppliers before choosing to work with UK-based telemetry specialists Mantracourt. General Manager of JAWS, Larry Jackson commented: “We chose to offer wireless systems only after complete testing and development, Mantracourt was the only company that offered what we needed - support, software and development - they are still our partner today.”
In fact, JAWS is now in the process of accelerating its wireless options and conducting retro-fits from wired to wireless conversions. This provides all their customers with product lines complete with fully vetted software applications, printouts, handheld displays and in general a very high quality production capability.
Mantracourt Electronics is a leader in high precision measurement electronics and supplies OEM sensor manufacturers and system integrators around the world with measurement solutions. However, it was the company’s latest wireless offering, T24 and the fact that Mantracourt’s electronic engineers worked closely with JAWS technical aviation weighing specialists to devise customised solutions that meet the exact requirements of JAWS customers.
Mantracourt’s T24 is a modular wireless telemetry system for multiple data acquisition in real time. The range comprises a versatile set of products, based around proprietary acquisition devices that can be mixed and matched to provide high quality remote readings for critical applications. The system comprises a range of transmitters, interfaces, displays and output modules that can be simply and easily configured to suit individual applications. The transmitter modules have been designed to collect data from a large range of industrial sensors and in the case of JAWS, specially calibrated matched load cells. The low power, battery equipped, radio units allow data collection over many years without externally supplied power and so are more cost effective than hardwired systems.
To further add to the versatility of T24, Mantracourt provides data logging and visualisation software. This allows users to log up to 100 channels and build visual mapping displays. Alarms can be set that can indicate under and over range and can alert users to loss in communication, low battery and error reports. The Mantacourt development team worked with JAWS to meet their special process calibration requirements and printable output applications.
Another consideration JAWS had to take into account was the fact that its weighing units were not only vital bits of safety equipment so had to be extremely accurate at all times but they knew that as they supplied the rental market then the equipment would be subjected to continuous and often harsh use.
Summing up the working relationship between Jackson Aircraft Weighing Service and Mantracourt, Larry Jackson added: “When you build the best, your team and partners must be the best. Performance and quality in aviation can never be compromised.”
Wireless systems are becoming more prevalent throughout industry and as they start to become incorporated in such critical weighing applications as in the aviation industry then it is even more important that they are reliable, secure and free from interference. As has been shown above, choosing a wireless system supplier that can work closely with your team to develop a customised solution is vital and keeps companies ahead of their competitors.