| Engine Size (cu. in.) |
Starting Propeller |
Alternate Propellers |
|---|---|---|
11-7, 11-7½, 12-4, 12-5 |
||
11-7½, 12-4, 12-5, 12-6 |
||
12-8, 13-5, 13-6, 14-5, 14-6 |
||
17-6, 18-5, 18-6 |
||
18-8, 20-6 |
||
Each of the three propellers shown at the left are designated as 10-6, but they are from different manufacturers and are made of different materials. The top prop is wood, the middle prop is non-reinforced polyester and the bottom one is glass-filled nylon. When choosing a wood prop, look for grain lines that are straight and run from tip-to-tip. Avoid wood props with curved grain that runs of the leading or trailing edge.
A higher pitch prop will pull the airplane faster in level flight. A lower pitch prop will cause the airplane to takeoff faster and climb quicker. Some full scale airplanes have adjustable pitch props so they can use the most efficient pitch in each situation. The pilot will determine the pitch for takeoff and climbing to altitude and adjust to a higher pitch for better level flight speed and fuel economy. Compare it with the drive/overdrive of a car.
For your model, don't be affraid to try different props, not only in pitch but also size. Eventually you will feel comfortable with a certain prop for your particular model and stick with it. By each propeller change you most likely have to re-adjust the needle valve.
Try different prop diameters also. For example, let's say you're running a .60 2-stroke engine and start out with a 11-7 propeller. The model will very likely fly real nice. Next, put on a 12-6 propeller, readjust the needle valve, and fly again. Watch as the model takes off in a little shorter distance and you will be able to pull the nose up a little steeper on the climbout without stalling. The level flight speed, however, will be slightly less than with the 11-7 prop. So, while the engine turns both propellers at approximately the same RPM, the flight characteristics of the aircraft are slightly different with each size propeller. Don't be afraid to try another different size propeller and note any further changes. Usually, the changes will be very small, and there will be always a tradeoff of somekind--what you gain in aspect of performance you may lose in another. By trial and error you will eventually determine which size prop best suits your particular model and how you want it to perform.
Wooden or Plastic Prop?: Choosing a good propeller is all up to you. It can be a plastic (or fiberglass) or wood. Generally a wooden prop is preferred because the blades are strong, giving you truer, and more efficient performance than the plastic or synthetic propeller. Most competition flyers choose wooden props for these facts alone.
On the other hand, plastic props are more durable than a wooden one altough the plastic prop sometimes fly apart especially with larger engines. Again however, if you're just starting out learning to fly, a plastic prop would be a better choice since propellers tend to fly to pieces when they hit the ground on a wrong or rough landing. When you advance in flight and are comfortable with landing in all directions and different wind conditions you may want to change your prop to APC or Wood.
Prop Balancing: A good propeller is a balanced one, no matter what the material it is made of. All propellers should be carefully hand balanced using a commercially available prop balancer, something like the cheap 'Hand-Held' balancer below.
An unbalanced prop causes excessive vibration which can lead to structural failure and radio problems. Lightly sand the front side of the heavy blade until the prop balances. Avoid sanding the tips or changing the shape of the propeller.The sharp edges of injection molded synthetic props can be sanded lightly to remove any molding flash. Don't sand any more than necessary and re-balance the prop when finished.
Always check your prop carefully after each flight to be certain it hasn't been broken, cracked, or nicked. Even a small nick in the leading edge can cause the blade to separate on the next run, so discard all propellers with any kind of flaw.
How to balance your prop with a Magnetic Balancer [click here!] There are a couple good examples and hints.
"Prop balancing" still under
Safety First! When people hurt themselves with a model airplane, it almost always involves the propeller. Props are dangerous and you must be constantly on guard to avoid accidents. A spinning prop is like a buzz saw -- it can and will cut right through fingers, arms, legs and bones. I know, because I had a prop going thru my left middle finger and bone about 8 times. Notice the "Chicken Stick" being used for starting.
o Always treat a running engine with total respect and attention!
o Always have someone hold onto your model while you starting it!
o After starting, move around behind the prop to remove the glow
plug battery and to make needle valve or engine adjustments!
o Never, under any circumstances, reach over a running prop!
o Be concious of the prop arc! Don't let spectators stand in line with
or in front of the spinning propeller, and don't stay there yourself
any longer than necessary.
o To make the 'arc' visible, paint the tips of the propeller with a bit
of white or silver paint.
One last thought on safety and propeller selection. A wood prop will usually break if it hits your hand while a
plastic or APC will not. A plastic or APC prop will usually cut much deeper, causing more serious damage to you than
a wood prop. This safety aspect of wood propellers should not be overlooked. Two years ago, a fellow club member
asked to hold up his aircraft so he could check the needle valve for the correct idle setting. The plane was a
delta-wing type with a pusher prop at the back. Letting my attention slip for a second I grabbed right into the
(APC) propeller which in turn cut several times through skin, nerves and bones of my left middle finger. Luckily
for me there were other members present who applied first aid. I learned a good lesson that day not to under estimate
the power and destructive force of a propeller!Prop Preparation: Propellers usually need some amount of preparation before bolting them in place. Often times the center hole will have to be enlarged to fit the engine's crankshaft. Always use a special-purpose "prop-reamer" or a drill press to enlarge the hole. Be careful to make the enlarged hole straight and perpendicular to the prop hub.
To Make Props Last Longer: You will break fewer propellers if you do one simple thing. Always bolt the prop on the engine so that when the piston first comes up against compression (in the normal direction of running) the prop is horizontal! In a power off landing, the prop will windmill to that position and be much less likely to come in contact with the ground. Again, do NOT use a damaged or nicked propeller! As a matter of fact, you should destroy a damaged prop to avoid injury to someone else picking it up and using it on his/her aircraft if you intend to chuck it in the garbage can.
Sig Manufacturing Co, Inc has been one of the Radio Control industry leaders since 1951, manufacturing an extensive
line of radio control, control line and free flight model aircraft kits as well as numerous accessories and a complete
assortment of balsa for the modeler who enjoys scratch building. About 80% of the above information has been
reprinted from SIG's booklet "The Basics of Radio Control".Back to Hints & tips
Copyright © 1998 - Tony van Roon