This test method is one of the complex test method which consists of more than one environmental effects combined. The vibroacoustic/temperature procedure is performed to determine the synergistic effects of vibration, acoustic noise, and temperature on externally carried aircraft stores during captive carry flight. In a captive carry arrangement, the payload craft, such as a rocket, missile, aeroplane or spaceplane, does not separate from the carrier aircraft.

Such a determination may be useful for, but not restricted to the following purposes:

 

1. To reveal and correct design weaknesses (Test, Analyze and Fix (TAAF) test).
2. To determine whether a design meets a specified reliability requirement (Reliability Demonstration test).
3. To reveal workmanship or component defects before a production unit leaves the place of assembly (Screening test).
4. To estimate the Mean Time Between Failure (MTBF) of a lot of units based upon the test item’s time to failure of a small sample of the units (Lot Acceptance test).
5. To determine the relative reliability among units based upon the test item’s time to failure of a small sample of the units (Source Comparison test).

 

Photo: Demonstration of Turkish “Bozdoğan” (in front) and “Bozok” missile attached to Turkish UCAV “Bayraktar Akıncı”. “Bozok” in the photo is an example to captive carry flight configuration. (AA Photo)

 

For captively-carried stores, this method is intended primarily to test electronics and other electro-mechanical assemblies within the store for functionality in a vibroacoustic/temperature environment. As an incidental part of the testing, thermal variation may induce changes in moisture exposure of the store and the effects of such exposure must be noted when interpreting the test result data. Typical applications include:

 

a. development of a more reliable store design prior to production.
b. assessment of the potential for the satisfaction of the reliability requirement for a store.
c. manufacturer’s internal testing to assure delivery of reliable units during production.
d. determination of the acceptance of a lot prior to delivery.
e. determination of the relative differences in quality from two sources for establishing production buy proportions.

 

Operation.

Operating any materiel item produces stress that can cause failure. In the case of external aircraft stores, operation generally means providing full electrical power, that produces thermal, electromagnetic, and electrochemical stress. Duty cycles (on/off), low and high voltage, power ripple, and voltage spikes may also be significant stresses. Even when the stress of operation is negligible, it is necessary to operate the materiel under test to detect the presence of failure. Many failures induced by temperature and some vibration-induced failures are reversible, at least initially. As the test continues, reversible failures tend to become irreversible. Thus, it is important to conduct tests of functions while the environmental stresses are present.

 

Temperature.

The most severe temperature shock to internal components may come from powering the materiel when it is cold. To induce all the stresses related to temperature in their proper proportion, use a thermal model of the store to predict the temperatures and rates of change at several internal points under service mission profiles.

 

Vibration.

Vibration may cause mechanical fatigue failure of parts, abrasion due to relative motion, dislodging of loose particles that can cause electrical shorts and degradation of electronic functions through microphonics and triboelectric noise.

 

Moisture.

Moisture, in conjunction with soluble contaminants, can result in corrosion. In conjunction with electrical power, it may result in shorts. The freezing of water in confined spaces may produce mechanical stress. The test cycle should provide for the diffusion of water vapor and condensation.

 

Shock.

Shock can cause failure through mechanical stress similar to that induced by vibration. Shocks that are more nearly transient vibrations (many zero crossings), such as aircraft catapult and arrested landing shock, may be included in this test. Short duration shocks such as pyrotechnic shocks associated with the store or sub-munition launch, flight surface deployment, etc., are generally too difficult to reproduce at the store level.

 

Altitude.

Barometric pressure is generally not a stress for external stores. However, variation in pressure may enhance the penetration by moisture. Reduced pressure may increase the temperature due to reduced power dissipation and there may be increased electrical arcing. Test separately for resistance to arcing. Moisture penetration will generally take place without pressure variation and, in most cases, the amount of water entrained is not important so long as it is enough to provide internal condensation. Reduced heat transfer may be realized by restricting air circulation rather than reducing the ambient pressure.

 

Photo: Turkish missiles “Bozdoğan” and “Gökdoğan” in captive carry flight configuration. (Courtesy of TUBITAK SAGE)

 

Effects of the vibroacoustic/temperature environment.

Possible effects of a combination of vibration, acoustic noise, and temperature include all effects that these factors can cause separately (see Methods 514.6, 515.6, and 520.3). In addition, increased stress as a result of moisture from thermal change may produce possible effects seen in Methods 501.5, 502.5, 503.5, and 507.5. The combined vibration, acoustic noise, and temperature environments may interact to produce effects that would not occur in any single environment or a lesser combination of environments. Items in the discussion to follow point to significant effects of mechanisms applicable to this method.

 

All test methods given above are already covered in our previous blog entries. You may read them from here: https://pals.com.tr/blog 

 

DID YOU KNOW?

 

PALS is attending on IBC 2022 this year as Exhibitor. After 2 years of COVID break of the convention, PALS will be showing a great attendance. Our Sales team and most of our experts will be at our booth. Including Author of this blog letters will be personally attending to the exhibition. We are inviting our readers to drop by in our booth and meet with PALS team even for just to say “Hi”. We would be more than happy to welcome you and offer famous Turkish tea. 

 

 

If you wish to set a meeting with our sales and technical team to learn more about PALS products and services, don’t hesitate to contact us from https://pals.com.tr/contact