Excess Too (oz12587)

About this Plan

Excess Too. Control line stunt model for CO2 power.

Quote: "THIS little model was built to explore the possibilities of the Herkimer compressed gas engines for U-control use. Not only has the engine proved itself adaptable for U-control but is excellent for indoor work and for flying in restricted spaces. It has been flown in exhibitions with marked success. Those who have flown it have enjoyed the experience as much as the spectators.

When designed, speed was considered rather than stunt or sport flying since it was our intent to use the model as an instrument of research into propeller sizes for this engine. To date the model has clocked 34.7 miles an hour, which could be increased with drop-off gear and additional experimenting with propeller types and sizes.

Before installing the engine and cartridge in the model some tests were performed to determine the advisability of soldering a series of washers on the pressure line from the cartridge holder to the cylinder head. It was found that without the washers the line would frost. After about 75 washers were added to the line there was no frosting of the line, indicating that the washers were absorbing heat from the atmosphere. Since no exact calculations were made for thrust and engine run comparisons it is hard to say for sure that adding washers increases the efficiency of this engine. However, it can be supposed that there is some increased efficiency. Whether the increase in efficiency is sufficient to warrant this added weight is debatable. For this reason the plan shows a short straight line connection between cartridge holder and engine.

Incorporated in the cowling of this model are several innovations already proven in previous models, You will notice that the exhaust CO, is vented out of the cowling so as not to pollute the air which flows around the cylinder head. This has been done to keep the cylinder head temperature as high as possible. If the engine is to be cowled without a separate venting system the exhaust CO2, being very low in temperature, would then cool the cylinder head. When vented separately, air at atmospheric temperature entering the cowl is not cooled by anything other than the cylinder head.

For maximum streamlining the cartridge holder is completely enclosed within the fuselage. It is also placed so that air going past the cylinder head must flow around' the cartridge holder and bottle before being-drawn out of the vents wider the wing. It has been found that it is definitely better to mount the cartridge holder rigid inside the fuselage than to allow it to flop around sup-ported only by the copper pressure line.

The model itself is very easy to construct, the fuselage being carved from two blocks of approximately 6-lb per cubic foot balsa wood glued together lightly at the parting line. The outside contours are carved first and then the blocks are separated at the parting line and the inside carved to the thickness shown on the plans. After the two shells are completely carved and sanded inside they are carefully glued together, with the cartridge holder, baffles and formers cemented in place. The wing and tail are simple structures. It is considered that the plans are self-explanatory.

The landing gear is long and spindly due to the size of the propeller in comparison with the size of the airplane. A drop-off gear or dolly should work very well since the model has a tendency to take off and accelerate very rapidly.

Propellers varying from 7 in diameter and 4 in pitch to propellers 8 in diameter with 8 in pitch have been used. A propeller of 7 in diameter and 8 in pitch seems to give the best all-around performance. It is advisable to use stock gas model propellers of good quality and sand them down to a thin section with a slight amount of undercamber. Much weight can be eliminated and the efficiency increased tremendously. It has also been found that a stock gas model propeller is far too strong and any minor mishap will tend to, damage the ship a great deal, whereas a lighter propeller will absorb shock and break, saving the ship.

The model has been flown on lines 15 and 20 feet in length. For maximum speed .003 Tungsten wire is excellent. However, for general sport flying try fine silk thread, preferably white, since it is more visible, durable, and easy to keep in condition. For safety it is advisable to use new lines for each flying session.

For stunting, this model can be easily converted into a biplane by adding a lower wing and increasing the movable elevator area."

Direct submission to Outerzone.

Supplementary file notes

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