Crazzyflyer's Rc Planes: Fun With Foam

Building with construction foam is an inexpensive alternative to conventional materials and offers some unique advantages. It's very strong and in most instances requires very little reinforcement. It's readily available at the local hardware store in dimensions large enough to suite most project requirements. A 2 ft x 8 ft x 2 in sheet will set you back about $10-$15 bucks. The 2" thickness allows for creating contours and air foils as well as a margin for error. The thinner pink foam is available in 4ft x 8ft x 1 in sheets for smaller projects and is similarly priced.. The pink foam is best suited for projects were a flat surface or no contours will be used. The pink foam is also less dense than the blue so it may require reinforcement in some instances.

Witch ever you chose have some fun with it. Draw a 2 dimensional image of the air frame you want. Trace it on the foam. Cut out the pattern. Add vertical components, movable flight surfaces, electronics and go flying. It's a vary fast building method and lets you explore different air frame options at a price most anyone can afford.

The image above are my two proto types for the final built up rendering below. They helped a great deal in figuring out were I went wrong with my design. When I designed this saucer shaped blended body aircraft I inadvertently placed the center of lift at the center of the wing/body far behind the C of G. This makes for a very unstable aircraft. It flies great nose high but as soon as you trim the plane to a level flying attitude the nose drops and you find yourself in a steep dive. Fortunately this plane has enough elevator authority to recover. In the final built up model I installed a Knard to reduce this tendency and improve level flight stability. The other problem with this model was proper C of G. Although this would be considered a Delta Wing design it actually requires the C of G at about 25% of the leading edge like most convention planes. This meant a great deal of weight was added to the front of the aircraft. Not the best outcome, but what can you do. Remember I'm in the out lands with this plane. Even the Air Force couldn't make this design viable. The model below has the solution built in.I mentioned previously that a Knard was added for stability. This had the added bonus of placing the motor farther forward. I crated a new battery location within the extended fuse. I was able to reduce the amount of weight needed for proper C of G from 3 pounds to a meager 8 oz. This meant that the airplane went from almost eleven pounds all up to just over 8 pounds. That huge. This design also requires an aggressive angle of attack for take offs as evidenced by the photos below. This doesn't create any problems during landings. Once the air plane sets down it stays down. I will be modifying my proto type today with the Knard and I'll update any changes to flight performance.

The completed upgrades to those model let me shed about 3oz. Total weight 29oz. The Knard is functional and should make for an interesting maiden. I'll let you know. I mixed the elevator with the aux on the receiver for those wondering how to set it up.

For those wondering, yes the Knard has functional flight surfaces. This should aid in elevator authority as well as trim for level flight. Assuming I get the incidence right.