Sonex Onex and SubSonex Undergo Load Tests
The Onex tail holds strong under 1,730 pounds
SubSonex Wing Load Test Case 8: 3,095 pounds
Wing deflects 7 inches during a load test as Sonex Founder John Monnett looks on.
November 11, 2010 — EAA was invited recently to the Sonex Aircraft’s Hornet’s Nest R&D facility to witness load tests on several components of their Onex and SubSonex airframes. The Onex is a folding wing design under development that can fit through a 7-foot garage door. The SubSonex is the much-talked-about single-place turbojet that received a larger engine a year ago only to meet with some setbacks during testing last spring. After a design review and AirVenture 2010, the test program resumed. The Onex’s tail was put to the test as well as the SubSonex’s left wing.
During a load test, varying weight is added to locations across the entire wing (in the case of the SubSonex). Due to the weight, the wing is expected to deflect from its original position. The weight is then removed and the wing should return its original position. Then the wing structure is inspected for any damage. The process is repeated as many times as needed with increasing amounts of weight and loaded in different areas to simulate in-flight loads. Each of these scenarios is called a case.
With as many as 15 to 20 cases during a load test, there is plenty of tedious work as dozens of sandbags need to be loaded and unloaded for each loading scenario. There is suspense as the loading cases get more extreme. At Sonex a forklift was used to support the tail and wing while the sandbags were loaded. Once they were in place the lift was lowered and creaks and groans could be heard as the component took on the full weight.
While not always required to prove the aircraft is safe, wings and other components are often tested to destruction so that engineers can gauge the exact failure point. A successful load test usually occurs when the component remains intact through a certain number of planned cases. After that the weights are added in 10 percent increments to help ascertain the exact point of failure. With the Onex, Sonex President Jeremy Monnett was prepared for serious damage or complete failure as the weights climbed. The tail, however, was able to withstand 220 percent over its design limit without any damage. The test was discontinued at that point as the tail was proven to be safe and reliable far beyond any realistic flight loads that could be imposed. The wing tests also proved successful.
EAA Radio: Hear the SubSonex wing test