Model Aircraft Propellers 1

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Model Aircraft Propellers Propeller selection chart Propeller aspects... Power required to turn a propeller

Model Aircraft Propellers- fromhttp://www.airfieldmodels.com/information_source/model_aircraft_engines/propellers

aution! Some propellers have extremely sharp edges especially plastic and fiberglass props. For your own safet

rape and sand this edge down. If you try to flip the propeller by hand, you will get a nasty razor cut as your fingers

de along the back of the blade.opellers come in a variety of sizes and styles and are made from five materials that I know of: Wood (Maple, Beech or balsa wood on lightweight rubber powered models) Nylon Fiberglass-reinforced Nylon Fiberglass Carbon Fiber
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Wood, Fiberglass and Carbon Fiber props give the best performance. Nylon props are the least expensive, but they

exible, cause vibration and rob power.o not use nylon propellers!

With the exception of nylon propellers (not to be confused with glass-filled nylon which are fine), all commerciallyvailable propellers work well. If you choose a propeller that the engine can swing in its comfort zone then it is a ma

personal preference after that.return t

Propeller Propertiestch is the theoretical distance the propeller will advance along the axis of rotation in one complete revolution.tch High Pitch Propeller properties:

o High speed flighto Poor Accelerationo Poor Climbo Can be difficult to slow down for landing

Low Pitch Propeller properties:o Low speed flighto Good Accelerationo Good Climbo Finer speed control throughout throttle range particularly at low throttle settings

he easiest way grasp the concept ofpropeller pitch is to draw a parallel to the gearing in your car . Low pitch propellers = low gear in your car .

It will get you up hills well but will not take you any where fast. High pitch propellers = Beginning your drive in fifth gear

It will take forever to accelerate to speed but the plane is cruising when it gets there.return t
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Propeller MaterialsWood propellers are the lightest and present the smallest load to an engine assuming all else is equal (diameter, pi

nd shape). They are capable of turning higher RPM than a heavier propeller.Wooden propellers are also the most easily broken. My opinion is that wood propellers are the most efficient and b

erforming in the air. Others disagree and they may be right because I'm not a good enough pilot to really have an

pinion. In any case, if you nose over your planes often enough then wood propellers are probably a poor choice fo

ou.berglass-filled nylon propellers are the heaviest propellers and also the most durable. These are a good choice fo

eginners because they hold up better than other types to propeller strikes. They are less efficient than wood or ca

ber propellers, however.arbon Fiber Propellers are very rigid, but extremely expensive. I have seen carbon fiber propellers only for largengines. They may be available in smaller sizes in the future.l of the above propeller materials maintain their shape well under load. Wood and carbon fiber are best.berglass-filled nylon propellers are the most flexible of propellers that I recommend, but not enough to cause

gnificant problems.ure Nylon propellers are always a poor choice unless you crash every time you fly. If that's the case, then nylon

ropellers aren't the answer for you. Stamp collecting is.ylon propellers are so flexible that they twist in use which means they are constantly changing pitch. This flexing a

eates a lot of vibration. The end result is akin to spinning the wheels of your car a lot of energy is going to wast

ylon propellers are just bad. Don't use them.return t

Weighteavier propellers have the advantage offlywheel action . Flywheel action will allow a lower, more reliable idle . N

at all properly designed engines idle reliably anyway, so this is really a moot point.nother consideration is balancing the aircraft . Personally, I think the best propeller should be chosen for flight

ualities, not for weight, but if the aircraft is close to being in balance then changing to a propeller of different weig

ay put the CG on the money.return t
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hapeow RPM engines , such as four-strokes, use wide blade propellers because four-strokes turn fewer RPM. The lowe

PM means the air that the trailing blade is entering is less disturbed. Additionally, four-strokes have more torque t

wo-strokes. Because of this, a four-stroke can swing a wider propeller efficiently.gh RPM engines , such as two-strokes are more efficient with narrow blade propellers due to the more disturbed

used by the higher RPM.return t

Number of Bladesopellers have one, two, three or four blades. Single blade propellers are counter-balanced and used on extremely

gh rpm racing motors. I've never seen these sold anywhere and suspect they are built by the user. You don't needven think about these props unless you're building control line speed aircraft. In fact, they may not even be used a

ore. I haven't been paying attention.our realm, the most efficient propellers are two bladed. Because the diameter of our propellers is so small, multi

ade propellers disturb the air that the trailing blade is entering. Therefore, 3 and 4 blade propellers are less efficie

general, the only time a 3 or 4 blade propeller should be used is for a more scale appearance or when a smaller

ropeller disk is necessary.or example, a scale, twin-engine aircraft may not be able to swing a 2-blade propeller of a small enough diameter

ear the sides of the fuselage. A three and four blade prop can be used here because it can be a smaller diameter a

resent the same load on the engine.or best performance with sport aircraft, stick to 2-blade propellers.

return t

Propeller selection chart

- fromhttp://www.top-flite.com/accys/topq5000a
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return t

Propeller aspects...fromhttp://www.bolly.com.au/book/Book.php?Chapter=2&Secti

One of the biggest problems with propeller design (for all props including full size), is that it is impossible toknow what a prop is doing in a dynamic state. Often static testing does not relate to dynamic performance

very easy to develop a prop which gives excellent pull on a static test, however a prop designed to these

criteria often dont work that well in the air. As the average model propeller operates at a Reynolds number (scale effect) similar to a R/C Glider. A high

aspect ratio, elliptical based shape generally works best, whether it be for glider wings or a propeller. The reason multi blade propellers often appear inefficient is the need to use considerable lower diameter

propellers (in comparison to 2 blades), for the same horsepower available. Diameter for diameter a well
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designed 4 blade prop will in some circumstances perform better than the equivalent 2 blade propeller. Practical strength and aerodynamics means an optimum airfoil thickness of around 15 to 18% near the root,

progressively thinning to 10% at the tip. About 12% at the 3/4 span in optimum. Pitch should always climb from the root to the tip, with the rate of increase being less at the tip - even const

over the last 20% of the diameter. The quoted pitch should always be the 'peak' measurement, although to

more reliable and consistent quoting the pitch at 80% of diameter is the usual practice. The pitch distributiodescribed above is often described as 'progressive pitch', ie - the pitch progressively increases along the blad

from root to tip. The overall design and even the materials from which the propeller is constructed, also have a significant eff

on noise. The softer materials such as nylon produce a softer noise, but as they are more flexible, the flexin

will also create extra noise. To make such a prop rigid will require a thicker blade (heavier and more expensi

to produce), which in turn operate at lower rpm (due to absorbing more power), and reduce the propellers

overall efficiency. As can be seen, designing for low noise as opposed to high efficiency is a compromise. The most obvious factor in prop noise is tip speed and shape. Reducing tip speed and using a good tip shape

the most productive method of reducing noise. This will generally mean using a lower diameter higher pitch

prop than before.

- fromhttp://www.bolly.com.au/1998%20Bolly%20Book%20v3.pdf Propeller noise is predominantly a product of tip noise. The propeller tip is travelling much faster than any o

part of the blade, speed = noise.. A high drag tip shape will always create more noise than a low drag shape,

tip shape will have an effect on the props overall efficiency A well rounded or raked tip should always be used, never leave the tip square . The very end of the propelle

should be rounded on all sides, not only the leading and trailing corners, as would a model wing tip - never lit cut off square.

A propeller should NEVER be used over 885 kph without paying attention to tip shape, due to compressibilitand shock waves as Mach 1 is approached.

An optimum maximum tip speed for achieving a low noise is 644 kph. There appears to be a marked increasnoise above this speed. The best example of this is R/C Aerobatics where low noise is an advantage. F3A mo

avoid going above 604 kph tip speed.
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Power required to turn a propeller

ne can work out the power required to turn a propeller if the propeller moves a volume of air defined by the diamthe propeller and the theoretical distance the propeller would advance as defined by the pitch in one second. Th

ensity of air = Da = is 1.292 kg/cubic metre. The volume of air swept out per second = Va = PI * r * r * L r = 0.5 * DIA * 0.00254 for DIA in inches (traditionally) and r in metres L = PITCH * 0.00254 * RPM / 60 where PITCH is in inches (traditionally) and L is in metres Assume very simplistically that the volume of air swept out per second moves at a speed = Sair. Kinetic energy = Eke of the volume of air moving at speed = Sair is given by: Eke = 0.5 * Mair * Sair * Sair = 0.5 * 1.292 * PI * r * r * L * L

Eke = 2.4833E-14 * DIA * DIA * (RPM * PITCH) ^ 3 in Watts, DIA and PITCH are in inches

om data on the AXI web site for the new AXI 5320/18 brushless electric motor:prop size

in x in RPMElec power

wattsefficiency

%actual power

wattsCalc Prop power

wattsactual / calc

%16 x 8 6,900 994 85 845 1,069 79

16 x 10 6,800 1,037 85 881 2,000 4417 x 10 6,600 1,210 83 1,004 2,063 4918 x 8 6,550 1,264 83 1,049 1,158 90

18 x 10 6,350 1,490 80 1,192 2,060 5818 x 12 6,200 1,685 78 1,314 3,313 40

otes You need to be very careful with any inferences from the above calculated power. Less engine power was us

relative to the calculated value because:o the air moves at less than the theoretical maximum speed calculated from the pitch of the propeller, so the

kinetic energy of the air mass is less.o The air speed will not be a constant across the diameter of the propeller: it will be less at the centre of the

propeller and will increase and then decrease as you move from the centre of the propeller to the edge of th

propeller. Consequently, less air is moved at peak speed, so the kinetic energy of the air mass is less. Some of the actual electrical power input into the motor will go into:
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o creating heat in the motor: this is accounted for in engine efficiencyo creating air turbulenceo creating rotational energy in the air mass that does not contribute to thrusto creating noise, primarily at the tips of the propeller The typical actual / calculated value is on average 60%. This figure could be used to help us select a suitable

propeller for an engine operating at a particular RPM with a rated power output.return t

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Model Aircraft Propellers 1