OLD TIMERS
Clarence Haught
A change of pace: Just a few years ago, contest entries in old-time rubber-power classes were minimal at best. Often there were more trophies than official scores. Happily, today this situation is improving as more and more modelers discover the joys of rubber models.
There are many possible reasons for this, including the increased difficulty in finding original ignition engines in flying condition and the high cost of all ignition engines — new, used and conversions. Notwithstanding are the noise factors, balky engines, dead batteries, vibration failures and just plain oil mess all over everything. If any of these points hits home, then perhaps you're ready for rubber power.
Old-time rubber is flown in two categories:
- Cabin — self-explanatory.
- Stick — refers to a built-up fuselage not having a cabin structure, but possessing a minimum cross-sectional area determined by squaring the fuselage length and dividing the product by 200. For example, a 36-inch fuselage (36 × 36 ÷ 200) would have a minimum cross section of 6.48 sq. in.
There are plenty of good model designs available to suit almost any fancy. Several were published in the old model magazines and the Zaic yearbooks. John Pond, P.O. Box 3215, San Jose, CA 95156, has a list of old-time rubber towline plans available for 75 cents. In addition to published plans, there are several kits on the market, for example:
- Midwest Gollywock
- Midwest Jabberwock
- Comet Sparky
- 4-K's
- Korda Wakefield
- P&W's short kit of the Korda
While good strip rubber is becoming more available after a few lean years, old timers are not quite so dependent on "high energy" rubber for good performance. Wakefield, Coupe d'Hiver and P-30 are limited by maximum motor weight:
- Wakefield: 40 grams
- Coupe d'Hiver and P-30: 10 grams each
In old-timer classes you can use what is needed as long as it does not become self-defeating in terms of uncontrollable torque or excessive model weight. The freedom to use a little more rubber eliminates the need for packing in maximum winds and thus prolongs rubber life as well as reducing model damage from bursting motors.
FAI Model Supply, P.O. Box 3957, Torrance, CA 90510, provides a good product under the FAI brand, and stocks the "new" Pirelli strip rubber. Many modelers are getting good results out of Sig and Sterling rubber. For long life and good performance, a good rubber lubricant is a must. Some of the old cooked formulas are excellent, but mixing equal parts glycerine and surgical jelly, thinned slightly with water, is hard to beat and cleans up easily with water.
Trimming a rubber model is quite easy because one may build up power gradually until the model is performing satisfactorily. However, keep in mind that rubber motors begin to weaken after repeated use and can mislead you into making adjustments that will not be compatible with a new stronger motor. It's best to make up several motors and change them after two or three flights, allowing the used motors to "rest" a week or two before using them again.
Motor size is largely a matter of trial and error, but six to eight strands (3 to 4 loops) of 3/16-inch rubber is a good starting place. The motor length should be about 1½ times the distance from the prop hook to the rear peg. Short motors tend to have too much initial power burst; long ones produce lower power but longer runs for the cruising climb. Long motors can bunch up at the end of the run and affect the center of gravity — a tensioner or braiding the strands will prevent this.
Flight-trim adjustments should be separated for climb and glide. Rubber models seem to climb best to the right. All power trim should be accomplished with thrust adjustments:
- Downthrust corrects stalls under power (assuming correct C.G. placement).
- Side thrust controls the turn.
Glide trim can be corrected by incidence changes and rudder tab. Many models are flown right under power against left rudder tab. This provides a left-turn glide and helps hold up the right wing during climb.
Many old-time rubber designs did not employ folding props, using free-wheelers instead. Free-wheeling props do add drag, but the sight of the prop ticking over as the model glides in for a landing is a heartwarming experience. Folding props are more efficient in the glide, but if they malfunction they can really upset glide trim and rate; you are stuck with whatever the original design called for — no substitutions are allowed. Either way, prop carving and building builds character. You can find ample information on the subject in the 1935–36, 1937 and 1938 Zaic yearbooks.
Give old-time rubber a try. It's a great change of pace!
FF Old Timers/Haught
Plug for a plug
Good news for those who have been having difficulty obtaining good spark plugs. Replica Engines, 14600 Ramstad Drive, San Jose, CA 95127, is offering the Japanese NGK MB8 plug for $5.00 plus postage. The MB8 is a 1/4-32 thread plug with the thread reach of the Champion V-3. This makes it usable in the smaller engines requiring the shorter plug, but it will function just fine as a replacement for the Champion V-2.
The example I have is well made and performs well. The electrodes are heavy duty, more like the Remco and the older racing plugs. Spark plugs normally have a long life but are often damaged by cracks or simply lose their seal due to age. A little maintenance in the form of a good cleaning in household ammonia will improve their service life.
Clarence Haught Rte. 5, Box 16 Coeur d'Alene, ID 83814
Transcribed from original scans by AI. Minor OCR errors may remain.
