Super Cirrus (oz9578)

About this Plan

Super Cirrus. Plan showing modifications to the Graupner Cirrus (oz8532) design, to improve thermal performance at the cost of scale looks.

Quote: "The Graupner Cirrus is a fine sailplane when built right out of the box, but its thermal performance and handling qualities can be increased by a few simple modifications. Since the purpose here is to present the changes and how to incorporate them into the kit construction, no detailed effort will be made to explain the aerodynamics behind the performance and handling quality changes although the actual improvements due to the changes will be discussed.

Polyhedral was added to the basic design to improve the turn capability and stability. These two properties are shown in the airplane's exceptional thermalling capabilities, and by perfect tracking on the tow with no rudder control required. The wing span is extended by approximately 4in to decrease the wing loading, thereby resulting in a lower sink rate and tighter turns. Wing tip fins were added to decrease the induced drag and also to produce outstanding stall characteristics. With the wing tip fins installed, no washout is required, which in turn results in a wing with a greater lifting capability. The horizontal tail was swept forward to better balance this control surface.

The rudder was lightened to further reduce the airplane's wing loading while also decreasing the airplane's inertia The partially balanced rudder results in much better turning capability, including quick and crisp entry and exit from spins, and excellent slow speed turns during spot landing attempts. Quik Stripe 1/8in trim tape is placed in appropriate places on the wings, horizontal tail, and rudder in order to reduce the total airplane drag by controlling the airflow over these surfaces. The Center of Gravity and tow hook positions employed result in perfect tows, and excellent flight characteristics.

Let's take a quick look at the kind of performance that can be expected from the Super Cirrus. The first flight of the Super Cirrus took place at the Soaring Union of Los Angeles (SULA) soaring field at California State College at Dominguez Hills, and resulted in a 21 minute flight which was the longest flight of the day. The next weekend saw a 10 minute test flight involving two loops, three stalls, and one spin. The Super Cirrus then put in a 30 minute flight topped that day only by an experienced contest pilot putting in a 31 minute flight with an eleven foot span airplane. The modifications are actually quite simple, and are very easy to follow with the help of the Super Cirrus modification plans and the plans provided with the kit..."

Supplementary file notes

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