I have heard 2nd hand that perhaps the 120 may not be that robust, especially the fuse, due to the light weight.?

I know nothing about nor have I seen the 120 in person. Could you please comment on this to me as I am trying to decide what plane to buy next to replace my hard flown Mantis, which is also a very good plane. Thanks for your time, no rush in answering me.

From : Don Stackhouse

The folks who are speculating that just simply are NOT familiar with the 120. It is VERY robust. It has survived long straight-ins after a servo failure and mid-airs with little or no damage (field repairable or better in those cases). The wings are strong enough for two-man F3J tows by big guys (far more load than a winch can generate). It's been flown quite extensively through a lOT of contest landings with no deterioration.

Part of that is because a lighter airplane doesn't impact as hard, but it's also due to the 120's very strong and efficient structural design. Many, if not most R/C sailplanes frankly do not have particularly efficient structures. There's a lot of extra beef in places where it just isn't needed, and often the material in the high stress areas isn't used as efficiently as it could be. The shapes are also often not the best for mimimizing weight while maximizing strength. There's often a lot of room for improvement. It is understandable that when someone (like us) goes to the trouble to achieve that improvement, some folks are going to be surprised. The Spectre's weight is not by accident, and it is not the result of skimping on things that need to be there. For example, the wing spars are designed to handle 300 pounds of towline tension.

We use some pretty sophisticated analysis methods, coupled with data from both static and flight tests of our own materials using our own processes, so we know just what can realistically be expected from them. The characteristics of the Spectre series, including the high aspect ratio wing design and the details of the fuselage structure, also save a considerable amount of weight. The wing is one of the heaviest structures in an airplane, and although the spars still have to handle the same loads, the overall wing weight is definitely minimized by the reduction in wing area from the higher aspect ratio. Fewer square inches means a lot less ounces of wing skin and foam. It also reduces the required tail size.

The pod and boom fuselage also helps a lot, just as you've probably noticed with your Mantis. In addition, we use a custom boom, with a special taper in both the diameter and the layup schedule, made to our specs to match the strength and stiffness characteristics we need in both torsion and bending, without any excess weight. This weight savings in the tail boom helps keep the nose short (improving the inertia in pitch and yaw, which makes the tail more effective, minimizing its area and weight requirements and saving some more weight up front) and also minimizes the need for nose ballast. The shorter nose also improves its buckling strength, reducing the amount of material required for the necessary strength. With a lighter fuselage and tail we need less wing to carry them, which saves even more weight, and further reduces tail size and weight. As you can see, all these effects tend to "snowball" with each other, resulting in a much slimmer and lighter airplane but without requiring any compromizes on strength. Good engineering is no accident.

Don't worry, the 120 is NOT fragile!

Don Stackhouse
DJ Aerotech