Mrs Lil (oz15801)

About this Plan

Mrs Lil. Radio control sport model for electric power. Tailless pusher layout.

The 50 inch free flight Lil Misery (oz433) was first published in Air Trails, July 1942. This here is a later reduced scale version, for micro RC with electric power.

Note this plan is available online as a free download see: https://www.flyrc.com/john-worths-mrs-lil/

Quote: "Way back 66 years ago I designed an original free flight tailless model I called the Lil Misery. Why that name? I cant remember! The plans and a construction article for it were published in the July 1942 issue of Air Trails magazine. Lil Misery spanned 50 inches and flew great. It was powered with a spark ignition Atom engine and was very stable.

I still have the original fuselage pod with the engine in good condition but the now uncovered wing framework is very fragile due to age. I also have another one of these models which was built for me, as a gift from Joe Beshar, when I retired from the Academy of Model Aeronautics many years ago. Both these models are great to look at and now that I am 84, serve as pleasant reminders of a neat WWII-era project that turned out well when I was only 18.

Until recently I was satisfied to only look at these old models and reminisce about what used to be. Now however, I'm deeply involved with micro flight - the smallest and lightest electric motor powered RC models, and I got interested in building a much simpler half-size RC version of my 1942 model. I made this new one with a single surface foam sheet wing with a profile fuselage pod. Rudder control for turns, and motor speed for climb and descent, is provided via a lightweight RC system. The original 1942 model weighed 16.6 ounces; the new one is 1.4 ounces!

Balancing: The keys to successful flying wing model stability are Center of Gravity (CG) location and the amount of up-elevator provided by the control surfaces on the wing tips. The up-elevator out on the tips provides the angular difference between the wing airfoil ahead of the CG and the part of the wing behind the CG that acts as a tail surface. The angular difference provides the pitch stability needed for stable flight.

For this model the neutral elevator angle is fixed at about 30 degrees of what we would normally regard as up-elevator. In a model with a normal horizontal tail relatively far back from the wing the angular difference would be only a few degrees. But for this model, with the effective tail being so close to the CG, the difference must be much greater. It should be noted that the horizontal wing control surfaces are not controllable, except for manual trimming to get the model to fly straight when gliding with motor power off or at low throttle.

The CG position is at the trailing edge of the center of the wing. That's where the model should balance for initial hand glides. Then, depending on whether the model stalls or dives when hand launched without power, the CG is adjusted with modeling clay to produce a smooth glide path. More clay on the nose to correct a stall, more behind the CG to correct a dive. Note: more or less up-elevator can also help, but not more than a few degrees. The model needs at least 20 degrees of neutral up-elevator for stability. The thing to keep in mind here is that the model was designed to fly without control inputs. If the radio quits working and the motor cuts, the model should glide down safely to a good landing,

Its important to get the CG right, to avoid crashing the model on initial flight attempt. A flying wing is much more critical regarding CG location than a typical model with the tail that's back much further. I use a very simple glide test arrangement to find the correct CG location. It consists of just gliding the wing assembly without the fuselage pod and its receiver, battery and motor/prop assembly..."

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