2002 SNHRCC Auction

Darrell "Silver Tongue" Wagner will be the auctioneer for the evening.

Checkout the ad elsewhere in the Bull Sheet and come and enjoy an evening of fun.

CG Fixture

If you want to know where the C.G. is located on almost any configuration of model plane accurately, and I mean within a sixteenth of an inch, make this device. I've been using it for many years on everything from a 1/2A two channel to a 26 pound, 1/4 scale, Tiger Moth. It works every time, is fairly simple to use, and it's accurate.

It can be made of almost any old stuff kicking around the shop. You need a piece of 1 x 2 (or 2 x 2) wood about a foot long; a piece of 1/4 or 3/8 dowel also about a foot long; some flexible but strong rope about 1/8" in diameter (I used a piece of cotton drape cord); a pulley you can hook up to the shop ceiling (preferably over a bench where your plane can sit), and a little plumb bob.

Drill a hole parallel to the long dimension near the end of the 1 x 2. It must be snug enough so that you can just turn the dowel by hand. If it is too loose put a saw-cut through the hole and a bit beyond it, and a bolt with a wing nut (as shown in Fig. A), the friction on the dowel can then be adjusted.

A hole in the other end for the "hanging rope," a pulley, and two nails in a stud to snub the "hanging rope," and that part is ready. Next, make two equal loops of soft rope or cord to support the model. The pair I use are 40" in circumference, and they handle most 40 to 60 size models. Cut two pieces of soft cord 40" long and tie the ends together. Pull them taut over your index fingers to make sure that the lengths are equal, then put a drop of CA on each knot to assure they stay forever.

Now make a small plumb bob. I made one out of a 2" length of 3/8" aluminum rod. I chucked it in a drill press and filed a point on one end. A small axial hole at the other end and a cross-hole made a neat place to tie a piece of string or thread. I discovered later that wallpaper stores sell cute little lead bobs that are perfect. About a foot and a half of thread tied in a slipknot will allow you to adjust the height of the plumb bob.

To use this marvelous device, place the model aircraft on the bench with the center of the wing more or less below the pulley in the ceiling. Lower the dowel and support to a couple of inches above the wing. Place the 40" loops around the wing as shown in Fig. C or D, and wrap them around the dowel 4 or 5 times (same on both sides). Since the C.G. is normally well forward of the center of the chord of the wing, there will be more weight on the forward side of the, loop than the rear, and the angle of dangle will be different fore and aft. Thus the rope would like to slip forward, but the wraps around the dowel provide enough friction to prevent this. Put the plumb bob string over the dowel. Usually it is more convenient to have the plumb bob on the inside of the loop, hanging over the fuselage, or wing root.

Carefully hoist the model a couple of inches off the bench. Steady it until it reaches a state of equilibrium. By hand rotating the dowel in its hole, adjust the model to a level flight attitude. An important detail in using this device is to have the dowel parallel to the wing spar.

Adjust the slipknot on the plumb bob so that it hangs just above the model and - Voila! - It points to the Center of Gravity. Since all of the weight of the model is being supported by the dowel, the C.G. will be directly beneath the dowel (where- the plumb bob is pointing).

Put a piece of masking tape on the model where the plumb bob is pointing, and mark the spot with a felt tip pen. Or better still, put the tape on before you hoist the model, mark where the C.G. should be, and then get the good/bad news when you hoist it. While it is still up there, you can add weight to the nose or tail, adjust the attitude to level flight again by rotating the dowel, and see before your very eyes where the C.G. has moved to. After a couple of tries you should know exactly how much weight to put where.

Versatility.
Fig. C shows a high wing trainer, but the device works equally well with a low or mid wing pattern type aircraft (Fig. D). With a biplane, just put the loop around both wings (Fig. E). You say you have a J3 Cub with wing struts that get in the way! No problem; make a pair of 40" ropes with a loop at one end and a little wire hook at the other end. Feed this under the wing, around the dowel, and put the hook in the loop.

If you have flaps or strip ailerons that come close to the fuselage, and may not support the weight put on them by the ropes, a couple of things can be done. Make a single large loop of rope and sling it under the fuselage fore and aft of the wing as shown in Fig. F. Tape the rope to the bottom of the fuselage, far enough behind the wing to keep the rope off the trailing edge. Or cut a piece of balsa (or Styrofoam, or aluminum) an inch or so wide and a bit longer than the chord of the wing at the root. Place this under the wing with the rope beneath. Make sure they stay in place as you hoist the model. A delta can be tested with the single loop fuselage sling method (Fig. F) by putting a strip of 3/32" balsa beneath the fuselage. The strip must be long enough to be held by the front sling, and protrude behind the wing for the rear sling.

Take a few minutes to put one of these things together. The dimensions and the materials are almost unimportant. It's the configuration and gravity that do the job. From then on you will know exactly where the Center of Gravity is. Where it should be or where you like it to be is your problem.

I have built and used this device on a wide variety of planes from 40 size low wings to my third scale Cub and it really works well. It is sensitive, accurate and easy to build. At a future meeting I will bring the one that I built.

Red Schofield is well known flyer in Florida and can often be found on the internet news groups. He is best known for his advice on batteries and related topics at Red's Battery Clinic on the internet.

Local Hobby Shops

NEW Hobby Shop!

My name is Ted Zadlo and I recently became a member of the club.

As the owner of Pat O'Brien's Country Framer & Hobbies, I would like to extend an invitation to visit our quaint store. We specialize in aviation art, general hobbies and basic R/C supplies such as fuel, hardware, props, balsa, kits, etc. Soon we will be stocking motors and radios.

We carry SIG products, Balsa USA, Nelson paints and hardware, Graupner electric products, with more on the way. We are a dealer for Fiberclassics, Yellow Aircraft, Dare Hobbies, Clark Industries, Megatech, Tamiya, Irvine Engines, First Place Engines, B&B Mufflers and Quadra Engines.

We offer discounts to club members on all aviation art and custom framing. Special orders are never a problem.

• Store Hours: M - F 11am to 9pm and Sat 9am to 5pm
• We're convenient - Only 15 minutes from the field!
• Location: 21 Litchfield Road, Londonderry
• Phone: 434-5004
• E-Mail: fokkerman@msn.com

We are looking forward to serving you!