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The Quik Trim analog computer was
developed in 1977 for Piper and Cessna single engine aircraft. The
purpose of the computer was to enable pilots to quickly and easily
establish the center of gravity of their loaded aircraft. This also
enabled the pilot to easily determine visually if the center of gravity
was within the limits established by the aircraft manufacturer.
Shown to the left is the front face of the model for the Piper Aircraft PA-28-151 and PA-28-161. |
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The slider, shown on the left, is constrained and moves horizontally and vertically on the face of the computer. Weight for the various loads (pilot and front passenger, rear passengers, fuel and baggage) are marked. The final mark indicates the center of gravity of the loaded aircraft. If this mark is outside the red envelop, then the center of gravity is outside of the limits for the aircraft, and flying the aircraft could result in loss of control. Fuel, passengers or baggage would have to be removed to ensure that the center of gravity remained within the red envelop established by the aircraft manufacturer. |
The analog computer had some advantages at the time it was developed. Digital computers were not prevalent and the only viable alternative was pencil and paper. The alternative method could be laborious and time consuming, especially if the desired load configuration resulted in the center of gravity exceeding the established limits for the aircraft. In the latter case, the computations would have to be repeated for several cases to determine a load configuration that remained within the limits and allowed adequate fuel, passengers and baggage. The analog computer made the repeated computations not only easy, but the visual nature of the computer made the effects on the center of gravity of changing fuel, passenger or baggage loads immediately obvious. Thus, trade-offs could be accomplished quickly and easily. This facilitated center of gravity calculations and ensured that they would be made and not skipped as too onerous and time consuming.
After the introduction of the personal computer, the use of software available for center of gravity computations made the task easier. However, initally, the personal computer didn't really make the task of the computation of the center of gravity much easier. The computations were done by the personal computer, but the adjustment of the loads if the center of gravity exceeded limits still required the pilot change the load figures and re-compute the center of gravity. Again, this was an adjust and re-try process. The pilot had no visual indication of the effect of an adjustment. With the introduction of the Graphical Interface for the personal computer, this changed. The graphical interface could be programmed to imitate the process of the analog computer to provide the pilot with immediate and obvious feedback on the effects of changing any particular load.
The analog computer still has an enormous advantage over the digital computer: portability. The analog computer, including protective case and written instructions, weighs approximately two ounces, can be kept in the aircraft at all times in a seat pocket, requires no electrical power source and only a #2 lead pencil is required for its use.
Questions and comments concerning the Quik Trim analog computer should be sent to the webmaster at the address below. Questions concerning developing one for a particular aircraft model should be sent to the webmaster at the address below. Thank you .