Nemesis (oz13118)

About this Plan

Nemesis. Radio control sport pattern model. For .45 to .60 power.

Quote: "Designed not to be different but to overcome what was felt to be deficiencies in the present day multi pattern planes. That it has met this goal is apparent in that it will do all the maneuvers in the '68 pattern as well as pilot skills permit. The Nemesis, by Don Baisdon.

For those readers who are other than students of Greek mythology, Nemesis was the Goddess of Retribution, who paid back evil deeds by bring all kinds of misfortune upon the wrongdoer. In one sense the name is inappropriate for this ship since it is a rather forgiving, but since I was in a vindictive mood toward the design trend when this model was conceived, the word appealed to me. What's in a name? Well, not much, but, one thing is certain, anyone who has seen this thing land, particularly dead stick, will agree that it has to have an unusual name. The sight of anything that sleek, moving that slow, is really eerie, like a specter descending upon you.

As with most models, Nemesis evolved from design points which in my mind attributed to favorable flight characteristics of models I had previously designed or built. As with many serious modelers, I read with interest the construction articles of the more successful modelers in order to try to "go to school" on their experiences. There just aren't enough hours in one lifetime to try all the possible combinations of wing loading, power, area, decalage, plan-form, wing sections, area distribution, moments, surface deflection, etc, etc. Invariably, many design ideas lose their identity when combined or compromised with others but perhaps you can still detect in the Nemesis; Kasmirski's double tapered surfaces for appearance and structural advantages, Nelson's ideas on adequate area to provide a reasonably light wing loading, and maybe even Brett's concept of letting equipment dictate exterior outlines.

The horizontal tail planform was stolen directly from Kaz's Orion (oz927), since I had one lying around when I began the project. Even the wing of the original model was made from a revamped Orion wing kit; each rib was lengthened slightly and full span ailerons added. The overall effect of this was to lower the thickness ratio and move the maximum thickness and camber point forward percentage-wise which probably attributes to its good low speed characteristics. A semi-symmetrical section of medium thickness (14%) with a fairly low leading edge radius was chosen for penetration purposes and a definite break at the stall point. A full symmetrical section was avoided since it requires low angles of attack and hence higher speed or lower weight to demonstrate its advantages. The low-wing con-figuration was chosen over some of the attractive aspects of a shoulder-wing for .two main reasons: I wanted the horizontal tail out of the wing wake during most pitch conditions and secondly, the vertical CG location of a low-wing usually falls closer to the aerodynamic center which tends to make the rolls and other lateral maneuvers more axial.

With the aforesaid decision made, the next step was to lay out the profile of the fuselage. Most of the more popular designs used a tail length of from 2-1/2 to 3 times the length of the mean aerodynamic chord; this seemed reasonable since going beyond this posed problems in balsa length for the sides and anything under this looked a bit short coupled for comfort. The thrust line and the horizontal tail were lined up and the wing's vertical position resulted from a compromise with prop clearance, gear length and fuselage height at the maximum thickness point of the wing.

I elected to add a sub-bulkhead between the tank neck and the firewall that I could fill with foam to absorb any fuel leakage which would ordinarily run into the battery area. This added nose length, while not particularly desirable from an aerodynamic standpoint (nose length detracts from the directional stability and magnifies the propeller's gyroscopic effects) does allow space to route the fuel tubing to an optimum position and permits a fore or aft shift of the firewall to accommodate different shaft length engines.

As I mentioned previously, Tom Brett's idea of designing the airplane around the equipment appealed to me from an engineering standpoint so I was faced with the task of drawing a pleasing envelope around the various component outlines. About the only deviation that I took from purely functional was the addition of the turtledeck instead of a canopy. This is mainly because I have a long standing vendetta with bubble canopies in that they're usually so short that they manage to foul up the airflow around the vertical and get the fuel inside them or get knocked off and pose a repair problem. As it turned out, this extra area is useful to compensate for the nose length and provide the fuselage lifting force necessary for some of the newer maneuvers.

Since I had plenty of root chord and therefore equipment area length, I mounted the rudder and elevator servos side by side and the motor control servo ahead of these. With this combination, the widest component became the fuel tank and I decided to shoot the works and let this design the fuselage width.

The original 45 engine used an eight ounce tank but competition forced the use of a 60 for the vertical maneuvers. A twelve ounce World Engines tank was found to fit in the same area by shifting the batteries behind the bulkhead at the leading edge of the wing. Since equipment weight dropped about this time, the balance wasn't effected. This made sort of a happy change from the models in which you have enough equipment area to hold a square dance and actually have trouble supporting the receiver and battery pack because the fuselage is three or four inches wide inside.

Letting the tank design the fuselage width is all well and good but in this case it posed the problem of a tank hatch. From a structural standpoint I feel this is a definite mistake but the accessibility feature is great. If the engine is idling rough I can see a definite flexing taking place in the front end due to the non-continuous structure for the tank hatch, but since this has introduced no problems, I just accept it.

As long as we're at this point, we may as well dwell on design philosophy for a moment. Normally, I'm an optimist, so I try to design an airplane to fly well, not survive well. Along with this thinking. I've found that light airplanes not only fly better, but they survive crashes better..."

Direct submission to Outerzone.

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