The Colombian Air Force (Fuerza Aérea Colombiana – FAC) has been using the T-34 Mentor and T-41D Mescalero aircraft to train new pilots for four decades. However, late in 2006 it decided to replace them, beginning a project to manufacture a new aircraft for training purposes – the Calima T-90 – and marking a crucial first step in raising the capabilities of the Colombian aerospace industry in terms of its knowledge and infrastructure.
In a commercial agreement between the FAC, the Aviation Industry Corporation of Colombia (CIAC), and US aircraft manufacturer Lancair International, four non-commissioned officers specializing in avionics, opposed engines and composite materials were sent to Lancair’s facilities to begin the design and manufacture of components for the new airplane. By September 29, 2010, the first Calima T-90 was manufactured and delivered to Colombia. Since that moment it has been fulfilling its function as a training aircraft in many new pilots’ courses in the FAC’s Military Aviation School, which is based in Cali, Colombia. A total of 26 T-90s have now been delivered.In 2012 an agreement was made by the CIAC, FAC and the Military Industry of Colombia (INDUMIL), for a project to design an alternative manufacturing process of the principal, central forward spar of the Calima T-90, to better suit atmospheric conditions in Colombia, with a view to keep the original configuration spar, manufactured in Oregon.
A number of thermomechanical studies were undertaken as part of the project to produce two spars more suited to local conditions. The first spar was sectioned into coupons that were subjected to laboratory tests to collect data for simulations. The second was subjected to a full-scale flexural load test to better understand its properties. This structural testing confirmed 10% more strength in bending and a 2 lb weight saving compared with the original spar, while failure under static load was also more suited to local flying conditions. All tests were conducted in the University of the Valley in Cali, Colombia.
This work paved the way for another new project in 2014 – the design and implementation of the Calima T-90 wing static test. The project was sponsored by Colciencias (Administrative Department of Science, Technology and Innovation), along with the CIAC and FAC, and was a critical step in the development and engineering of the new training aircraft.
The objectives of the project were fourfold. First, to design and build a module for static tests to enable the verification of the failure load of the wing plane; second, to manufacture one wing plane with the same characteristics as in one of the 26 Calima T-90s already flying, and to subject it to loading in the module, but implementing the new spar from the previous project; third, to use the built module to run the wing plane static test, controlling and monitoring loads, deformations and deflections up to the maximum level; and fourth, to create and share the report of the assessment process and test results.
With the building of this module for static tests, which can also undertake dynamic tests, the capacity to realize full-scale aerospace tests was born in Colombia. In recognition of the ingenuity involved, the wing static test module is named Icaro, because it can show on the ground what Icarus [Ícaro in Spanish] discovered in the sky.
Static test module design
The test module was designed for easy disassembly and is also scalable, while it is also wider than the dimensions estimated in the initial proposal, so it can be employed for positive load testing for the Calima T-90, as well as for airplane components with root lengths up to 1.7m and a lift load capacity up to 20 tons. With a relatively modest investment of resources it could be scaled up to perform negative load and dynamic tests, as the hydraulic actuator and metallic structure were designed to meet this goal.
The positive load wing test was successfully executed on April 12, 2016, marking the first time a full-scale aircraft wing plane test was performed in Colombia. The test employed a hydraulic actuator with one whiffletree to distribute the load. Thus, the development of the test module and its use in the static test of a wing of the Calima T-90 aircraft was used to provide valuable information required to obtain FAR 23 certification for the Calima T-90.
The test itself lasted more than 12 hours, and to achieve certification for the wing plane, which was awarded by the Section of Aeronautics Certification of Defense – SECAD – it had to adhere to strict technical and documentary protocols based on FAR 23 and its supporting references as advisory circulars, among others.
During the test, the wing plane was subjected to forces equivalent to those expected in normal flight loads. Specifically, the Calima T-90 was subjected to a first stage equivalent of 4.05g, and during the force application the operation of the control surfaces
– the flaps and ailerons – were tested. All responded smoothly and without any loss of functional capacity. Then the wing plane was inspected, receiving approval to proceed with
the next step of loading – a cycle to reach the ultimate load of the wing plane, corresponding to 6.075g.A new inspection saw the continuation of the test to a third stage, in which the aircraft was subjected to increasing loads to achieve rupture, which occurred at 6.3g. During every second of the test, video and sensor data were captured and stored in a datalogger, recording every movement the wing plane made as a result of the loading.
“The results show that the aircraft under critical flight conditions for a category normally behaves very well and has a structure with a very good performance,” says project director Cesar A Rodriguez, principal researcher, Colciencias-FAC 666-2014. “The information collected will define critical areas and opportunities for improvement of the aircraft, as well as valuable information to ensure continued airworthiness. Breakage was concentrated in a predictable area without additional failures in the rest of the wing, which shows that the effects are concentrated in one place – this is the first step for many studies that the analysis of the information collected during the test may bring forward.”
The construction of Icaro and the successful execution of the wing plane test to failure loads has helped the Colombian aerospace sector acquire some vital new skills. It has helped fully explore the airplane’s design, and to better understand load distribution, security factor, deformation and critical points of the aircraft structure. The project has also delivered the capacity to design and build a test module to expand the capacity of the original module, as well as benefit from the experience and knowledge that comes with executing and monitoring the static test, and evaluating the development of the wing plane according to new design conditions.
Overall, it has helped all partners involved acquire basic knowledge about structural static evaluation, helping to increase the predictability of structural life. Furthermore, it has generated a new business unit to sell similar services and kit, but most importantly of all, it ensures accurate prediction of the reliability, durability and performance of the Calima T90 against possible failures that could result during stable flight conditions.
Cesar Augusto Rodriguez Adaime was the principal researcher in the design and implementation of the T-90 wing static test