Currently, members of the public are permitted to acquire, import, possess and use products containing Nitromethane if the concentration is thirty per cent w/w or lower. Anyone wishing to acquire, import, possess or use Nitromethane at concentrations higher than 30% (up to 100%) has to apply to the Home Office for a Poisons and Explosives Precursors License.

At the time of writing the Home Office are undertaking a consultation on amendments to the Poisons Act 1972. There are three proposals put forward:

Option 1 – Make no changes to the existing regulations

Option 2 – Strengthen and clarify measures within the current legislation, but not change the substances and concentrations that members of the public can acquire, import, possess and use provided they have a valid license. This would effectively enable members to continue using concentrations of up to 30% Nitromethane with no requirement for a license.

Option 3 – This would lower the threshold for the license requirement from 30% to 16% nitromethane.

Members of the public can respond to the consultation either online or by completing a downloaded form. More information can be found on the Gov.UK website

The Consultation closes at 11.45pm on the 10th March 2022. When we have any further information, we will keep you updated in future editions of Propwash and here on the website.

Power

You know that changing the exhaust pipe and pipe length on your boat can have a marked effect on the engine’s power characteristics, but do you by how much and why? A two stroke 125cc engine with standard exhaust system can combust no more than 125cc of fuel air mix. A two stroke 125cc engine with good tuned exhaust system can combust approximately 180cc of fuel air mix.

Why?

Simply put, it’s because the two-stroke exhaust system, commonly referred to as an ‘expansion chamber’ uses pressure waves emanating from the combustion chamber to effectively supercharge your engine.

The speed of sound

In reality, expansion chambers are built to harness sound waves (created in the combustion process) to first suck the cylinder clean of spent gases and in the process, drawing fresh air/gas mixture (known as ‘charge’) into the chamber itself and then stuff all the charge back into the cylinder, filling it to greater pressures than could be achieved by simply venting the exhaust port into the open atmosphere. This phenomenon was first discovered in the 1950s by Walter Kaaden, who was working at the East German company MZ. Kaaden understood that there was power in the sound waves coming from the exhaust system, and opened up a whole new field in two-stroke theory and tuning.

Of course those waves don’t radiate in all directions since there’s a pipe attached to the port. Early two strokes had straight pipes, a simple length of tube attached to the exhaust port. This created a single “negative” wave that helped suck spent exhaust gases out of the cylinder. And since sound waves that start at the end of the pipe travel to the other end at the speed of sound, there was only a small rpm range where the negative wave’s return would reach the exhaust port at a useful time: At too low of an rpm, the wave would return too soon, bouncing back out the port. And at too high of an rpm, the piston would have travelled up the cylinder far enough to close the exhaust port, again doing no good. Indeed, the only advantage to this crude pipe system was that it was easy to tune: You simply started with a long pipe and started cutting it off until the motor ran best at the engine speed you wanted.

Under Pressure

So after analysing this cut-off straight-pipe exhaust system, tuners realized that pressure waves could be created to help pull spent gases out of the cylinder. Following this, The tuners realised that these pressure waves could be utilised still further by using a divergent cone to increase the strength of the negative wave and then that a convergent cone added to this would increase power still further as explained next.

The exhaust opens on the down stroke and a pressure wave emanates from the exhaust port into the header pipe. This pressure wave travels through the exhaust gases that are in the pipe at the speed of sound. It’s the pressure wave that travels at this speed, not the exhaust gases themselves. (Imagine a stream and you throw in a rock. The waves from that rock will travel down the stream faster than the speed of the water.) Anyway, the wave reaches the front divergent cone and a weak negative wave (negative pressure or ‘suck‘) (laws of physics) is sent back to the exhaust port which reaches the exhaust port while the transfers are open helping to remove exhaust gases from the cylinder which in turn helps fresh mixture from the crankcase up through the transfers into the cylinder (Some of which will enter the front part of the header).

The length of the front cone and its distance from the cylinder (header length) determines the amount of time that the pressure reducing wave from the exhaust does it work in emptying the cylinder of exhaust gas and then assisting the fresh mixture up from the crankcase into the cylinder. If header is too short then the wave energy from the front cone is wasted because the negative wave (the ‘suck’) arrives at the exhaust port while the cylinder pressure is still high after combustion. It should arrive there when the pressure in the cylinder is low but there are still exhaust gases that need to be extracted. If the header length is too long then the wave is arriving later than optimum and the exhaust gases are not fully removed from the cylinder.

The front cone needs to be long enough to generate a wave to help the fresh mixture into the cylinder but it also needs to continue working long enough to allow some fresh mixture into the first part of the header. This is the mixture which will be forced back into the cylinder. If it is too short, then it does not allow mixture into the header. If its too long, then it reduces the length of the rear cone and that needs to be long enough to force all of the unburnt mixture in the header to be forced back into the cylinder. The pressure wave continues into the rear cone and immediately sends a positive pressure wave (laws of physics!) back down the tuned pipe towards the exhaust port forcing the unburnt fresh mixture back into the cylinder. The strength of the wave increases as the rear cone gets smaller and the length is made so that the returning pressure wave from its very end at the junction with the stinger coincides with the point of exhaust port closure. When this most critical length (start of stinger to exhaust port) is correct, then maximum power is achieved. If this critical length is too short then the returning wave forces hot gases back into the cylinder, dramatically increasing cylinder combustion temperatures. If this length is too long the maximum power will not be achieved because maximum supercharging or cylinder filling will not occur, although power in the corners will be better because the tuned length will coincide more with the reduced rpm in the corners.

In conclusion we can see that the front cone length and distance from exhaust port is very important to achieve maximum cylinder filling and to pull some mixture into the header and the distance from piston to start of stinger is extremely important to get maximum filling (supercharging) of the cylinder. When we adjust the tuned pipe length on our engines we are moving several things at once, the start of front cone, the end of front cone, the start of rear-cone and the end of rear cone/start of stinger.

Theory

Tuned Pipe Diagram

The tuned length L as shown in the diagram is the length that most people use as a comparison. This is OK as a comparison but the length that is most critical is TL. Many different pipes can be used on an engine but that tuned length TL will always remain the same within a few millimetres for a specific rpm (if all other factors remain constant, nitro content, oil content, air density, temperature etc). This applies to all two stroke model engines , petrol (gas) or Glow powered (nitro). We know this from many bench and on the water tests conducted on many different engines. To elaborate: If you were running a tuned pipe at its optimised length (the length that is giving most power or speed) and that pipe had no flat in the centre section and you wanted to change to a pipe with a flat in the centre or belly section. You should measure TL on the old pipe and then set TL on the new pipe to the same length to give you a starting point for adjustment.

Tuning the exhaust system

Pipe length is decided by rpm, exhaust timing and speed of sound within the exhaust system. The last part should remain almost the same whatever you do to the exhaust timing or rpm.
1. Shorten the pipe length and rpm will be higher, lengthen pipe length and rpm will be lower.
2. If you increase the exhaust timing and rpm stays the same then pipe length will need to be longer.
3. If you increase the rpm but exhaust timing stays the same then the pipe length has to be shorter.

If you can measure the rpm of your motor and exhaust timing, then you can use a simple calculation to show how much you need to change the pipe length when altering ex timing and rpm.
Here are some simple calculations for gas engines where the exhaust gas temperature is not affected by nitro content.
(For these calculations you can measure the pipe length between whatever points you want to, but the norm is from plug to widest part of cone.)

If you take a boat that is running well and pipe length has been optimised then to alter rpm or exhaust timing the following calculations may help to find the new required pipe length.

Pipe length from manifold face to widest part of front cone. = L
Exhaust timing = E
Constant = K
Rpm = R
Just as a theoretical example, If rpm is 15,000, exhaust timing is 175 degrees (duration) and pipe length is 330mm then:

Firstly you work out the constant for your set up. So..

K = (15000 x 330) / 175 = 28286

In this example that would give a K number of 28286 and as I wrote before, K will remain the same whatever you do..

L = 175 x 28285 / 16000

Which is the new pipe length from manifold face to widest part of cone.

This would make the new pipe length 309mm.

If you wanted to increase exhaust timing to 180 degrees and run at 15,000rpm then

L = (180 x 28286) / 15000 = 339mm

Stingers

Stinger length should be separated from stinger diameter because although they are linked, in practice you would need to make a big change in stinger length to affect the backpressure. Stinger diameter is crucial to the pipes operating temperature and hence the power production. If the stinger is bigger than optimum them making it even bigger will have little effect but by sleeveing it down then you will be able to find the size that gives best power. Normally a smaller stinger will improve top end power because the exhaust gas temperature will increase which will have the effect of a shorter pipe length. If you go too small on the stinger then power will suddenly start to drop in the corners and the motor will begin to overheat. To get the best power its usual to lengthen the header and make the stinger smaller to get the best overall performance. A bigger stinger will have the effect of spreading the power band but the engine will not make the same peak hp.

Stinger length is important because its part of the pipe resonance. The wrong stinger length will reduce performance at the upper end of the rpm band. i.e. between peak torque and peak bhp.. There will be maybe one or two stinger lengths that will cut the rpm off at a certain level reducing the ‘overrev’ which gives the best top speed. There will be one stinger length which gives the best overall power and over-rev. I find no way to calculate that stinger length, trial and error is the only way. It’s not dependent upon engine size, just on the pipe design. For example, my best .21 pipe runs over 100mm stinger but my best .90 runs around 60mm. One thing though, very short stingers up to 20mm long don’t normally work and extremely long stingers of 150mm to 200 mm can work very well. Once the best stinger length is found, it does not seem to vary if the pipe length is altered.

On stinger length, it is only a few percent performance difference but every little helps!!

The speed of sound within the exhaust system is dependent upon the EGT (exhaust gas temperature). The higher the temperature the longer the pipe length must be for a given rpm. EGT will vary with the following factors:

• Stinger diameter (smaller stinger = higher EGT)
• Fuel needle setting. (a leaner mixture will raise EGT.)
• Fuel mix. High oil content reduces EGT
• High nitro content also reduces EGT.

Helpful Facts

The volume of a pipe is only really related to the displacement of the engine because the various diameters of the pipe ( header, belly and stinger) are a function of exhaust port area, and if an engine has a bigger displacement, it usually has a bigger exhaust port area. It’s often said that a bigger volume pipe is less peaky or it has a broader spread of power. This is not actually so. The volume takes care of itself when the pipe is calculated. The important things are firstly (and most importantly) the length from piston face to start of stinger and secondly header length, cone lengths, belly length, and then header diameter, belly diameter and stinger diameter.

Normally a good pipe will have a belly cross sectional area of about 10 times the exhaust port area with a stinger diameter of about 0.5 to 0.6 of the exhaust port area and the header around 1.2 times exhaust port area. By exhaust port I mean the actual port in the liner not the port where the exhaust manifold bolts on. If we take 2 pipes with the same cone lengths and total tuned length then the pipe with the largest volume will will require a smaller stinger diameter to maintain the same EGT (exhaust gas temperature) within the pipe.

Again thanks to Dave Marles at Prestwich Models for this article.

Everybody knows it’s there, but few, it seems, really know much about it. Although most seem to know- at least vaguely – that’s its primary purpose is to add power. At best, there is much misinformation regarding this somewhat exotic ingredient. Let’s see what we can do to clear some of it up.

What is model fuel made of? Why do I need such a special fuel? Can I use something cheaper?

Model fuel is a blend of methyl alcohol (methanol), Nitro-methane (Nitro), and oil. Methanol is the main ingredient and provides most of the power. Nitro is added to assist the idle and acceleration, as well as increase power. The oil that’s in the fuel is the source of lubricant for the engine.
Methanol is used for two main reasons:

• It can be ignited with a platinum-element glow plug.
• It releases more energy per pound of air than gasoline. It’s also very easy to obtain and is inexpensive.

Nitro-methane is used to enhance power output. It acts as an oxidizer as well as a “hot” fuel in its own right. It’s not used in large amounts in most model engines because it’s too powerful a fuel for the way model engines are made…it’s just too “hot”. It can also be explosive if it’s not handled correctly…ever see an AA-Fuel dragster or Funny Car explode?

Oil

Oil is used to lubricate all of the moving parts in the engine. Like all two-stroke engines, there’s no oil sump, so you can’t put oil into the engine and just add fuel. The oil is mixed into the fuel. Oil used in model fuels can be made from a single product, or a blend of products. The oil that used to be the most common was castor oil. This is a product refined from castor beans (like soybean oil comes from soybeans). It’s the same oil you’ll find in the drugstore, but it’s been processed to make it less gummy and with fewer solids than the medicinal type. Lubricating castor oil is not certified for human internal use, though, so it’s not a substitute for medicinal castor oil.

Castor oil has been replaced in most fuels by some kind of synthetic oil. The synthetic oils used in model fuels are basically synthetic versions of castor oil. The synthetic oils are used because they are: 1) less expensive than castor oil; 2) less gummy than castor oil; and 3) leave less mess on the model than castor oil. They are not “better” oils, but oils with different characteristics that are highly desirable. For “problem” engines, a fuel with some castor is highly desired, because it is actually a better lubricant at the operating temperatures a model engine can generate.

Blending

Nowadays, “Premium” fuels contain a blend of synthetic and castor oil, hoping to combine the best characteristics of each. “Sport” or “regular” fuels are usually 100% synthetic oil. Very few model fuels use 100% castor oil, but they are still available from some fuel manufacturers.
An “ideal” fuel blend for most model engines would be 20-22% oil, 10-15% Nitro, and the rest methanol. The various percentages of the ingredients are percentages of the volume of fully-mixed fuel. These numbers are controversial.
Some fuel manufacturers claim that their lubricant is so good that you need less of it, so they have lower oil content. Many advantages are claimed from this…some are even true. Lower oil will allow an engine to throttle up faster because there’s less oil to get in the way of the combustion process. There’s also less oil to give you a margin of error in case the engine gets a bit lean for some reason.
A lot of times, oil quantity is reduced so that the cost price of the fuel is lower, and the fuel manufacturer can increase profits by keeping the price at the same level as full-oil fuels. In fact, cost is the main reason most fuels are blended with about 18% oil. While it’s lower than the “ideal” fuel, it still has enough oil to give good protection.
Just about the only thing that can be added to a basic fuel are some ingredients that help the glow plug fire off the mixture inside the engine…these are called “ignitors”. Propylene oxide is an example of an ignitor that’s been added to fuel in the past. Some rust-inhibiting compounds can be added to help slow down rusting of the bearings and crankshaft, but their effect is limited because only a small amount can be added to the fuel before the fuel’s performance is affected.

Storage and fuel care

Yes, there are ways to care for fuel so that it will stay good while it’s being stored.
First off, it should not be stored in unsealed containers. This allows air to get into the fuel container. Moisture in the air will be drawn into the fuel because methanol has a very strong attraction for water. The two will mix easily and readily. Once model fuel becomes contaminated with water, the engine’s performance will suffer. It won’t idle, it will be hard to set the needle properly, it will tend to run hot…all in all, it will be a mess.
When somebody has running problems, one of the first things to recommend is to try running the engine with brand new, fresh fuel.

Nitromethane is just one of a family of chemicals called “nitroparaffins.” Others are nitroethane and nitropropane. Nitroethane can be used successfully in small quantities. (Top fuel drag racers, which generally run on straight nitromethane, sometimes add a little in hot, humid weather to prevent detonation). At one time, nitroethane was only about half as expensive as nitromethane, but its cost now is so nearly the same, using it to lower cost is hardly worth the trouble. Neither of the nitropropanes will work in model engine fuel. Incidentally, nitromethane is made of propane, in case you didn’t know (and I’ll bet you didn’t).

Powerrrr!

Yes, NITRO = POWER! But there are conditions and contingencies. First of all, it doesn’t add power because it’s such a “hot” chemical. Not at all. This may come as a surprise to most readers, but the methanol (methyl alcohol) in the fuel is by far the most flammable ingredient – nearly twice as flammable as nitromethane. As a matter of fact, if nitro were only 4 degrees less flammable, it wouldn’t even have to carry the red diamond “flammable” label! In actuality, nitromethane must be heated to 96 degrees F. before it will begin to emit enough vapours that they can be ignited by some sort of spark or flame!

So, how does it add power? We all know (I think) that although we think of the liquid part substance, we put in fuel tanks (in our automobiles or model airplanes) as the fuel, in truth, there is another “fuel,” without which the liquid part would be useless. Remember what it is? Right – just plain old air (in reality, the oxygen in the air). Every internal combustion engine mixes air and another fuel of some sort. In our case, a liquid – glow fuel. The purpose of the carburettor is to meter those two ingredients in just the right proportions, and every individual engine has a requirement for a specific proportion of liquid fuel and air. Try to push in too much liquid without enough air, and the engine won’t run at all. That’s the purpose of the turbocharger on full-size engines – to cram in a lot more air than a simple carburettor or fuel injection system can handle.

Now, suppose we were to find a way to run more liquid through our model engines without increasing the air supply? That would add power, wouldn’t it? Well, guess what – we can! An internal combustion engine can burn more than 2 ½ times as much nitromethane to a given volume of air than it can methanol. Voila! More Power! That’s how it works, and it isn’t all that complicated. Nor do we have to spend a lot of time thinking about it in the course of a normal day’s running. However, there are some factors we do need to consider. As a practical matter, virtually all our everyday running can be done on model fuel containing from 5% to 15% nitromethane. There’s probably no reason why 5% won’t work perfectly well. Need a little more power? Move up to 10% or 15%. In most of our sport engines today, that’s enough. Most of the popular engines on the market today are built to run on something very near that blend. Typically, European engines will successfully run on lower nitro blends, because they are built to do so. Why? In Europe, nitro is pretty expensive?

More than power

Nitro does more than just add power. It also helps achieve a lower, more reliable idle. One good rule of thumb for checking to see if a particular engine needs a higher nitro blend is to start the engine, let it warm up for a few seconds, set throttle to full idle and remove the glow driver. If it drops rpm, move up to a 5% higher nitro blend. If there is no discernible drop, you should be fine right where you are. One of the most popular misconceptions is that by adding substantial nitro, the user will immediately achieve a huge power jump. Just isn’t so. Most will be surprised to learn that in the 5% – 25% nitro range, you will probably only see an rpm increase of about 100 rpm static (sitting on the ground or on a test stand) for each 5% nitro increase. On the water, it will unload and achieve a greater increase, and it will probably idle better, too. If you have a model that’s doing well, but just isn’t quite “there” power wise, go up 5% in nitro. If that doesn’t do it, you need a bigger engine, not more nitro! Most of our popular sport engines in use today aren’t set up to run on much more than 15% or 20% nitro.

Increasing the nitro has the effect of increasing the compression ratio, and each specific engine has an optimum compression level. Exceed it and performance will probably suffer, not gain, and the engine will become much less “user friendly.” High performance racing engines, for example, are tuned entirely differently – compression ratio, intake and exhaust timing etc. – and are usually intended to run on much higher nitro blends. The first question that comes to mind, then, is, “Why aren’t all engines designed to run on no nitro, so we can all save a lot of money?” Ask any of the World-class competitors. Those engines are a difficult to tune and run, and are definitely not user-friendly! In fact, they are well beyond the skill levels of most average modellers.

There’s a price to everything. Another statement we read or hear frequently is that nitromethane is acidic and causes corrosion in engines. It isn’t acidic, and the manufacturers say it doesn’t happen – can’t happen. However, at least one noted engine expert and magazine writer insists that it does.

Costs

Why does nitro cost so much? While I have no clue as to the cost of manufacturing, other than it takes a multimillion-dollar investment in a large refinery to produce it, there is one pretty good reason: There is only one manufacturer of nitromethane in the Western Hemisphere. Figure it out for yourself. Also (and this will come as a big surprise), our hobby industry only consumes about 5% of all the nitromethane produced; and full-size car racing about another 5% or so. This means we have no “clout” whatever, and simply must pay the asking price. Where does the rest of it go? Industry, It’s used for a variety of things – a solvent for certain plastics, insecticides, explosives (yes, it was an ingredient in the Oklahoma City bombing) and I’m told it’s an ingredient in a well-known prescription ulcer medication (no wonder that stuff is so expensive!).

Boom!

Please note that while nitromethane is an ingredient in making some explosives, under normal use, it in itself, is not explosive. (Remember, the bomber used fertiliser, too). Hardly a month passes that someone doesn’t ask, “I hear more nitro will make my engine run cooler. Is that true?” Nope. The higher the nitro content, the higher the operating temperature. Fortunately, in most of our sport engines, the difference in operating temps between 5% and 10% is negligible, and there are lot of other factors (proper lubrication, etc.), that are much more important.

Finally…

Remember in the beginning of this, we said that nitro adds power because we can burn more of it than we can methanol, for a given volume of air? This also means that the higher the nitro content of the fuel, the less “mileage” (or running time) we will get. What’s the practical side of this? If you go to a higher nitro blend, be sure to open your needle valve a few clicks and reset before you run. Otherwise, you’ll be too lean, and could hurt your engine. Conversely, if you drop to a lower nitro blend, you’ll have wind it in a little.

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Welcome to the 2.4GHz spread spectrum radio revolution! No other advancement in RC radio technology has changed our hobby in such a profound and positive way. As big as PCM was – it doesn’t come close to the freedoms that all spread spectrum radios have.
Interference issues are more or less all gone! No more frequency conflicts! No more Worries!
Actually, the RC radio world has been rather slow to adopt 2.4GHz spread spectrum technology considering it has been commercially available since the 90’s with cordless phones, cell phones, and later wireless computer technologies such as Wi-Fi and now Bluetooth. In fact, spread spectrum was co-invented way back during WWII to prevent radio signal jamming of torpedoes by a famous actress of the day Hedy Lammar

Read the full article on :
www.rchelicopterfun.com

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LiPo batteries, short for Lithium Polymer battery, are a type of rechargeable battery that has taken the electric RC world by storm, especially for planes, helicopters, multi-rotor/drones and Fast Electric boats.
They one of the reasons electric propulsion is now a very viable option over fuel powered models.
LiPo batteries have many things going for them that make them the optimum battery choice over conventional rechargeable battery types such as NiCad, or NiMH.

Read the full article on :
www.rchelicopterfun.com

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Let’s start with basics: Exhaust timing raises power band on a 2 stroke engine, but with too high timing comes a loss of torque. With modern boat set ups and remote adjustable pipe movers, you have the best of both worlds being able to adjust pipe length whilst in motion and under load.

Induction timing is another critical part of a 2 stroke engine for power gains. Closing the timing later and/or opening earlier can increase power, but this has to be balanced with transfer port time and exhaust. For example, too high exhaust or late closing induction can cause engine bogging and the higher the tuning the more temperamental an engine can become. But when you get it right you can get more torque and rpm and bhp.

Torque is key in model boats as it allows you to swing bigger or higher pitch props. With high nitro content fuel, you can gain a lot of torque and can raise other timings for improved performance.

Head squish is also a power gain area, but too high a squish will result in power loss, but the engine may rev higher. If the cylinder head volume is not correct, this will cause detonation, (Visible pitting on the head and piston) and too low squish will cause a loss of performance. A correct volume head with high nitro and correct engine timings will give you a powerful motor.

It’s all a balancing act to get the best boat performance – Pipe, fuel, gearing, props, engine mods.

Engine bogging can be seen quite often. Too high a timing of ports or the pipe being too short can cause this. Testing is the key to getting everything working together.

There are various engine tuning programs available for example Prestwich can supply one.

For tuning, typically you will need a Digital Vernier, Dremel with diamond burrs and polishing stones.

Thanks to Dave Pillman for this article. Related Article

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There are four basic type of unbalance: Static, Kinetic, Dynamic and Whip. Propellers are balanced using Static or Dynamic means.

Static unbalance is gravity at work. If a propeller is placed between centres on frictionless rollers the heavy or weighted portion will rotate to the bottom immediately. This is corrected by adding or removing weight from the propeller.

Dynamic unbalance is a twist caused by two forces in two separate planes. If weights were placed 180 degrees opposite the other, no single point would roll to the bottom, because the prop would be balanced both statically and kinetically. By rotating the propeller at an appreciable speed each weight would cause its own centrifugal force in separate planes. This would cause an end to end rocking motion.

The following is courtesy of Prestwich Models. Prestwich can supply a full range of CNC machined props for all applications.

• Assemble the prop balancer and find the shaft that is a close fit into the propeller.
• Put the shaft between the magnets so that it touches one magnet and is close to the other. It may be necessary to adjust the width of the balancer to do this.
• The prop will rotate and then stop. Mark the prop with a marker pen at the lowest point.
• Spin the prop again and it should stop in the same position. Draw a vertical line downwards from the shaft on the lower blade. This is the area where you must remove material to balance it.
• If the prop stops with the blades level the material can be removed from the hub or better still from the lowest edges of each blade. Material removed from towards the tip of the prop will have more of an effect on the balance.
• Remove material with a file from the front of the blade ONLY, i.e. the convex side which is the same side as the drive dog slot. Use a fairly large file, the small swiss type files are not coarse enough.
• Keep checking the balance of the prop. When it is balanced it will be possible to spin the prop and will not stop in the same position each time.
• To sharpen the prop use the file again making file strokes towards the edge of the prop until it is sharp. This must only be done on the convex side, front side.
• Sharpening the prop can be done before balancing but if not then rebalance after sharpening.
• The trailing edge of the prop (thick edge) should be squared off so that it has sharp edges , i.e. 2 sharp edges.

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