Great Building Information and Techniques

LOAD FACTOR OF MODEL ENGINE PROPELLER

The following material is from Bill Ponseigo (Club President).

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

So 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. SO WHAT AM I GETTING AT? Well, each plane and motor combo flys differently and dare 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 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, the use the load factor idea to determine what other prop you may use if you want a different outcome (ie. 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 2 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 and on a sleek airframe will go like crazy, some like to go to a 9/7 to go even faster if the drag of the plane allows it. Such as a Quiki 500 which is very slick and has less drag. Have fun and experiment.

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 Frank Patterson (Club Treasurer) 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 the Weight of Various Covering Material PDF

INCIDENCE GAUGE

Here's an incidence gauge that Jim Keck (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 works just as well.

The original incidence gauge was built in about 1972 from an article in a model magazine (I don’t have the magazine).  This is not an original design, but has been modified slightly for ease of assembly.  This will assist in making a straight airplane

Jim Keck

Please click here for the IncidenceGauge.PDF