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Great Model Building Information & Techniques


For many people, stress is a part of life that we have to deal with. A great way to relieve stress is to take some time to create a model plane. ARCS is comprised of people who absolutely love model building. Join us in San Antonio, Texas, at our next meeting. The following material regarding the model plane propeller is from Bill Ponseigo, our club president.

Load Factor Of Model Engine Propeller

Question — which propeller should I use on my plane? Consider this: each prop has a different load factor! What is load factor? It is a term, coined by someone other than myself, which allows us as modelers to compare different props for our planes and have some idea which way to go when purchasing a new prop. To find load factor, double the diameter and add the pitch:

  • A 10/6 Prop Would Be 10+10+6=26
  • 11/7 — 11+11+7=29
  • 12/6 — 12+12+6=30
  • 22/12 — 22+22+12=56

The load factors in this example are 26, 29, 30, and 56, respectively. Now we can see a 10/7=27 as does an 11/5. So what! A 12/6=30 as does a 13/4. So what! A 22/12=56 as does a 24/8. What am I getting at? Well, each plane and motor combo flies differently, and, dare I say, each pilot expects different performance. Generally, slower planes (like bipes and trainers) should use a lower pitch prop to limit the speed of the plane and still give the thrust that's needed.

You can see that the amount of RPM a given engine can produce is governed by the propeller! So, a 10/8 prop will move (in theory at least) twice as far as a 10/4. A 16/4 will move half as far as a 16/8. We need a tachometer to tell how fast the engine is turning on the ground. We use the load factor idea to determine what other prop you may use if you want a different outcome (i.e. do you want to fly faster, do you want to fly slow, or should I say "scale like" to keep the RPMs up).

Generally, to a point, a lower pitch will allow stronger up lines, while a higher pitch will produce more speed for a given airframe. This only applies if the engine is strong enough to turn both props at the same speed. Generally, 32 to 55 cycles should turn over 10,000 RPM, and the larger the engine — the less RPM it will turn. A strong 40 will turn a 10/6 at 14,000 RPM. On a sleek airframe, it will go like crazy. Some like to go to a 9/7 to go even faster — if the drag of the plane allows it. Some use a Quikie 500, which is very slick and has less drag. Have fun and experiment.

The Weight Of Different Covering Material

Have you ever needed the weight of the different covering materials, so you can have the lowest all up weight? Here is the data that our club treasurer, Frank Patterson, has found so far. If you have any new info on these or different coverings, or if you have any questions — email Frank at treasurer@alamorcs.org.

Please click here for covering materials weights.

Incidence Gauge

Here's an incidence gauge that Jim Keck, our club secretary, has used for the last 30 years. He made it from a magazine article. It is at least $40 cheaper than the ones you buy, and it works just as well.

The original incidence gauge was built in about 1972 from an article in a model magazine. This is not an original design, but it has been modified slightly for ease of assembly. This will assist in making a straight airplane.