Scimitar (oz8127)

About this Plan

Scimitar. Radio control sport model. For .50 - .60 power.

Quote: "Distinctive-looking stunt ship, designed for constant high-speed and positive tracking through maneuvers. Scimitar, by Joe Foster.

SCIMITAR was designed with one basic thought. That was to try to solve a design deficiency that is prevalent in many of the small, high-speed stunt ships that are flown these days. This problem is the apparent difficulty high-speed airplanes have in tracking through the most basic maneuvers, such as loops, Immelmann turns, etc. We feel that this problem is created, at least in part, by small aerodynamic flaws that are exaggerated at high speeds.

How many ships have you seen that would track through three consecutive inside and outside loops without correction? I have flown only two. In the past we have always rationalized that some hidden warp was the culprit, even though we took great care to check the trueness of the flying surfaces and fuselage. A close examination of the flying characteristics of these crooked flying machines revealed that the heading was being lost at one spot in a loop. This was not the constant change of heading that would result from a warp. We concluded that some aerodynamic nonsense was taking place when the airplane reached a certain speed and attitude.

For example, I am sure you have seen many ships that wiggle in straight and level flight at a certain speed, or that wiggle when they are in a banked turn, or at certain head-ings relative to the wind. These are all exaggerated cases of the same aerodynamic flaw that will cause a seemingly unexplainable heading change at the top or bottom of a loop. It is our opinion that it is the uneven flow of air over the top of the fuselage, and its effect on the fin, that causes the wiggle and the resultant tracking problems.

To resolve this deficiency we incorporated into the Scimitar design three fairly obvious features. First, our wing leading edge is highly swept back. In our opinion, this improves the directional stability at all speeds. Second, we used a streamlined turtle-back fuselage design. This was done to smooth out the flow of air as it moves across the fin. Third, we kept the entire configuration as streamlined as possible, within practical limits.

Our first flights with Scimitar were very satisfying. We found that, not only had we accomplished our goal of correcting the wiggle and greatly improving the tracking problem, but we had derived two additional very desirable flight characteristics. The ship flies at a constant speed through the pattern maneuvers. This, along with its smoothness, gives it a very graceful appearance in the air, even though it is very fast. Additionally, Scimitar exhibits practically no visible dynamic overshoot about the roll axis. She does beautiful, constant-speed rolls with only a whisper of elevator correction, and stops rolling the instant you release the aileron stick..."

Fullsize plan, but the wing layout is shown at 50% size. The design uses a foam core wing.

Direct submission to Outerzone.

Update 25/10/2016: article pages, text & pics added, thanks to RFJ.

Supplementary file notes

Article pages, text & pics.

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