Prop Pitch Gauge

Folding prop gear test

For the past three years the European Union funded HYbrid MARine (HYMAR) project has enabled me to collect a mass of performance data from a conventional displacement hull. This data is being used as a baseline against which we are comparing the performance of hybrid propulsion systems. The data we have collected so far provides excellent insights into the relationship between propellers, hull resistance curves, engine fuel maps, and efficiency. Our test boat, ‘Nada’, is a Malo 46 sailboat built in Sweden. The engine is a Volvo-Penta D2-75, which uses a 2.2 liter turbocharged Perkins block with about as good fuel efficiency as anything on the market in this power range. The engine operates at a maximum 3,000 rpm, as opposed to the more common 3,600 rpm, and drives the propeller through a 2.74:1 reduction gear, which is somewhat higher than is typical. The net result is to slow the shaft speed down over similar installations, enabling us to swing a larger diameter, and thus inherently more efficient, propeller than would be the norm. These propellers include a variety of technologies, and cover the range from under propping (the fixed propeller – the engine overspeeded and was still well below its full rated power output), ‘correct’ propping (the engine just reached full speed, at which point it was fully loaded), and ‘over’ propping (the prop load was such that the engine could not reach full speed). From day one we discovered how difficult it is to do objective in-the-water testing. We had initially thought the ideal conditions would be no wind and flat water. However, if there is no wind, the faster you go the more apparent wind you create, and this has an effect on the results. Our preferred mode of operation is now flat water with a 10-20 knot beam wind, which is not an easy set of conditions to find. With the wind this strong, regardless of boat speed we can still keep it on the beam where it has little effect on the measurements. Our methodology is to run back and forth over the same ground to cancel out tide effects. We start at engine idle speed and work up to full speed in increments of 200 rpm. At each engine speed we record three sets of readings in each direction. We are not getting laboratory-quality data, but what we are getting is about as good as can be done in the real world. Next, we take the boat out into the open sea and drive ‘Nada’ straight into the waves to record ‘rough water’ performance. We have had unusually stormy summers in Sweden, so we have had plenty of rough water. At higher speeds, the boat sometimes slams violently. It’s punishing work on us and the boat. The conditions are way too variable to collect objective data, so what we are trying to do is to gauge relative performance when the going gets tough. As you would expect given the wide variety of propellers, and the wide range in terms of how well they are matched to the engine, there is a wide variation in the engine speed needed to achieve a given boat speed. For example, at 7 knots the engine speed varies from 1700 rpm to 2625 rpm. The fixed 19” x 14” propeller stands out in as much as it was particularly undersized. The engine ran much faster for a given boat speed, and the top boat speed achieved was up to a knot slower than with the other propellers (see Figure 1).All other propellers reached similar boat speed up, with the most-rigged engine speeds to be slower than the propeller correctly matched. Figure 2 shows the propeller shaft kilowatts (kW) for a given boat speed (SOG) for each propeller. Take a look at the propeller set too small. It is in the middle of the pack! In other words, despite the fact that the engine runs much faster for a given boat speed, the amount of energy to the tree is necessary to arrive at that boat speed is about the same as other helices. When you think about it, it makes sense.This is not the engine speed determines the speed of the boat, but the amount of energy that is put in water. The most powerful propellers reach a given level of energy at a slower speed than the propeller engine less powerful. Figure 2 gives us a measure of propeller efficiency on this application (the efficiency of the system is not - it's something different, as we shall see in a moment). If we take a fast boat up, we can see how much energy the tree it takes to get there with different propellers. For example, at 7 knots this varies from 16 to 20 kW, which is a 25% range if we take 16 kW as the starting point, and a 20% range if we take 20 kW as the starting point. We can look at this another way, which is to take a given level of power at the propeller shaft and see how much the speed varies. For example, at 10 kW the range is from 5.8 to 6.2 knots for a variation of just 6-7%, while at 30 kW the range is from 7.6 to just under 8 knots for a variation of 4-5%. Clearly, depending on what point you want to prove, you can use the data in all kinds of different ways! In any event, to make detailed comparisons we would want to divide the propellers into three groups – under-sized, properly matched, and over-sized – and compare the propellers within each group, in which case the differences are less pronounced. For propellers that were about equally matched to the boat and engine, the biggest factor in propeller efficiency seems to be blade shape. The latest generation of folding propellers (the Volvo-Penta, Flex-O-Fold, and Varifold in our test) all have blades with substantial camber and all performed consistently well. The MaxProp feathering propeller, which has very flat blades, lagged a little. However, there are things the folding propellers cannot do which the feathering can. Most important from the perspective of the HYMAR project is the ability to ‘trick’ a feathering propeller into remaining open when under sail so that it can be used to generate power off a free-wheeling propeller. This is difficult, and perhaps impossible, to do with the folding propellers (we will run some experiments on this later this year). The thing that really jumps out is the undersized fixed propeller, which was in the middle of the pack in terms of SOG v kW, but is now shown to have a substantially worse fuel economy. However, let’s ignore this for the moment and look at the rest of the propellers. Once again, we can parse the data in a couple of different ways, looking at the amount of fuel consumed for a given boat speed, or the boat speed achieved for a given level of fuel consumption. For example, at 6 knots the fuel consumption is between 3.5 and 4.5 liters per hour while at 8 knots fuel consumption is between 10.5 and 13.5 liters. In both cases, this gives a variation of 22-30% (depending on whether you calculate this from the lower or the upper rate), which is quite significant. At 6 liters per hour fuel consumption, the speed ranges from 6.7 to 7.1 knots for a variation of around 6%, which is not particularly significant. If we look at the numbers one way, there’s a big difference in efficiency, and if we look at them another way, there’s not much! A fuel map shows us how much fuel an engine burns per unit of energy produced at different engine speeds and loads. The energy is measured at the flywheel rather than the propeller shaft and as such does not take account of losses in the drive train. In Figure 4, we have torque on the vertical axis and engine speed on the horizontal. The graph would be easier to understand if we had kilowatts on the vertical axis, but unfortunately I don’t have this map (any kind of a fuel map is hard to obtain – the engine manufacturers tend to keep them close to their chests). At this point on the graph, we can see the engine is burning 230 grams per kilowatt-hour (g/kWh). The total hourly fuel consumption is therefore 26.39 x 230 = 6069.7 grams. There are approximately 840 grams in a liter, so this equates to 7.23 liters. If we refer back to the previous graphs we will see that this translates to around 7.5 knots, which translates to something over 25 shaft kW, so the pieces fit together as well as can be expected given that we don’t know the losses between the flywheel and the propeller shaft, and also bearing in mind that the fuel map is derived in the laboratory and will be different to what is experienced in real life. In Table 1 I have the measured propeller shaft torque at different engine speeds for three propellers. The Flex-O-Fold is too big for the boat: the engine cannot get above 2,471 rpm. If we were to run the boat at full speed for any length of time we would probably damage the engine. The Volvo-Penta propeller is well matched to the engine: it allows the engine to reach just under its full rated speed. The fixed propeller is way too small: the engine overspeeds and is still nowhere near fully loaded. In Figure 5 I have plotted the three propeller curves on the fuel map without accounting for drive train losses. Now we see the answer to the fuel efficiency question.Over-rigged Flex-O-Fold is near the top efficiency of fuel card on most of its operating range. The well-matched Volvo-Penta is close at higher loads, but falls a bit lower loads: in practice, we will not see much difference between it and the Flex-O-Fold. The propeller is fixed undersized always ineffective in the areas of fuel card - for a given amount of energy to the propeller shaft, it will burn fuel much more. Although my plotted propeller curves need to be shifted by some unknown amount to account for the drive train losses, and the differences between laboratory testing and the real world, the relationships between the three curves will remain pretty much the same. Figure 5 illustrates another interesting possibility. We could have a propeller that is less efficient than another propeller in terms of how many kilowatts it takes to get a boat up to a given speed, but which operates in a more efficient part of the fuel map such that the overall system efficiency (as measured in terms of fuel consumption) is higher.In other words, the propeller turns out to be less effective in general more effective. The optimum efficiency is obtained by combining a high efficiency propeller to the top of the card fuel efficiency is possible without incurring the risk of engine damage. The Gori propeller is intriguing in that the blades can be opened in two different directions, with a different side leading to the water. There is a substantial difference in height between the two modes of operation, which I call "normal" and "overdrive". In overdrive mode, the propeller we tested had a similar performance to that shown for the Flex-O-Fold, including overpowering the engine at higher engine speeds, and as such was one of the more efficient propellers but could damage the engine if used improperly (see Figure 6). In normal mode the Gori was a little undersized for the boat and marginally less efficient than some of the better matched propellers. A slightly larger propeller would have pushed the overdrive side even harder while providing a better match to the boat in the normal mode.  Clearly, with judicious use of the propeller a boat operator can achieve high levels of efficiency much of the time, but this takes a certain amount of operator management and there is the risk of engine damage if the propeller is used improperly. The Bruntons ‘Autoprop’ is another interesting propeller. It is a self-pitching propeller, adjusting the pitch according to the blade loading. This results in a considerably different, much flatter propeller curve than with other propellers that creates greater opportunities for efficiency optimization. In terms of the fuel map used in this article, an idealized propeller curve from an efficiency perspective would be as shown in Figure 7, although this is unacceptable in practice in as much as it sacrifices considerable power at the high end (full power falls from 55 kW to 38 kW). A couple of things are striking. One is how little fuel it takes to move the boat at slow speeds, which is a function of how little energy it takes (refer back to Figure 2: Speed Over the Ground v Shaft Kilowatts). The other is how rapidly the fuel consumption increases above a certain speed. For example, at 6 knots fuel consumption is approximately 2.4 liters an hour; at 7 knots it’s 4 liters; at 8 knots it’s 7.6 liters; and at 8.6 knots it’s 16.4 liters. What we are seeing here is the impact of the hull resistance curves associated with displacement hulls. At slow speeds, the principal resistance to motion is friction between the wetted surface area of the boat and the water. So long as the boat’s bottom is clean, this resistance is low and as a result it takes little energy to move a displacement boat in calm water. As the boat moves through the water, it makes waves. At slow speeds these waves are small and close together but with increasing speed the waves increase in size and lengthen until we arrive at a point at which there is a wave at the bow and one at the stern with a clearly defined trough between  them – in other words, the length of the waves the boat is making is the same as the waterline length of the boat. For years, we’ve all been taught to think in terms of the maximum or ‘hull speed’ for most displacement boats (I am not addressing racing boats here) being that point at which the wavelength more-or-less equals the waterline length. This is defined by the formula: 1.34 x v(waterline length in feet). It takes surfing conditions for most displacement boats to significantly exceed this speed. ‘Nada’ has a waterline length of 12.05 meters = 39.56 feet. The square root is 6.29 feet, so this gives us a nominal hull speed of 1.34 x 6.18 = 8.43 knots. We can tell when we reach this speed because the stern wave we are generating is under the stern counter. If we go any faster, this wave starts to move aft of the boat until we are dragging it behind us, which requires enormous amounts of energy.This definition of hull speed and we put in place on the resistance curve of the hull at which the fuel is above 14 points liters an hour and is up more or less logarithmic. If we accept a maximum speed of only one node less fuel consumption drops to less than half, and if we fall another node, it is up to a quarter! In other words, for the last two nodes is three times more power is needed for the first 6.43 knots. To put that in perspective, a financial standpoint, to $ 3.00 a gallon last two nodes which currently costs about $ 8 per hour or $ 4 per mile, while the first 6.5 knots costs 35c one mile. We’ve also run some tests with a mildly barnacled propeller, and then the same propeller in a polished state, to see what effect a few barnacles would have on performance, and it really was just a few. It was equally shocking (see Figures 8 and 9). At any given speed, the fuel consumption was approximately 50% higher with the barnacled propeller while for any given level of fuel consumption the speed fell anywhere from half a knot (at higher levels of fuel consumption) to a full knot (at slower boat speeds and lower levels of fuel consumption).For example, at 7 knots fuel consumption increased from about 4 liters an hour without barnacles to about 6 liters per hour with geese. If we secured the fuel consumption to 3 liters per hour regular speed from about 6.5 knots, no barnacles to about 5.5 knots with geese. We found that further improvements in fuel economy with conventional propulsion systems can be achieved by careful matching of the curves of the propeller and engine fuel cards. We also know that in many applications, we can make further improvements to the hybrid optimized. However, both of these approaches require significant technical resources. Ironically, the single greatest conservation measure we could probably apply to boating at the present time is ridiculously simple and non technical. It is to install a nautical mile per litre (or litres per nautical mile!) meter or even a ‘cost-per-nautical mile’ meter, at the helm station. Most owners, especially of displacement vessels, would be truly shocked at the doubling and quadrupling of fuel consumption and costs that occur when they try to squeeze out the last knot or two of boat speed. That last bit of speed is incredibly costly in terms of fuel consumption. They would immediately ease up on the throttle.

RC Helicopters are getting more popular · USA Free Articles

Over the years, the radio controlled (RC) helicopters have gained tremendous popularity, with devoted model plane flyers. Standing on terra firma, with a hand-held transmitter, the RC ‘helicopter pilot’ can soar the helicopter high within the skies and execute intricate manoeuvres, not only for the pleasure of the ‘flyer’ alone, but even for those observers, who watch in awe. Apart from the quick growing as a recreational hobby, RC helicopters are put to severe makes use of, like aerial photography, filming and distant inspection and observation for civil and military purposes. RC helicopters are generally created of balsa wood, carbon fibre, and aluminium or fibreglass. The RC helicopters are available in a number of designs, which includes scale models of actual machines. Having a hand-held transmitter, ‘the pilot’ can send signals to a receiver in the helicopter. The more manoeuvrable models with advanced transmitters and receivers can control the throttle with the main engine speed, variable pitch from the propeller, cyclic controls for pitch and roll and also the tail rotor for yaw. Thus, the aerobatic capabilities from the RC helicopter are limitless, which includes hovering, backward flight, and nearly all the manoeuvres an actual helicopter can perform. The distinct forms of RC model helicopters available are:*Nitro (internal combustion engine)*Electric*Gas turbine *Petrol/gasoline.Gas turbine and electric helicopters are fast evolving and becoming a lot more common. Nevertheless, the nitro engine powered copters are most typical. Understanding to fly a RC helicopter just isn’t tough, as some may assume. With the availability of flight simulator software program, the novice ‘pilot’ can learn all that needs to be on a computer, including the aviation and operational manoeuvres. RC helicopters are complicated gadgets and require the following equipment and accessories: *Helicopter kit *Radio program, which includes a transmitter, receiver, servos and battery *Gyro or equipment to control the tail plane from the helicopter *Engine*Fuel*Exhaust*Field equipment that supports the helicopter *Maintenance tools for repair and tuning as hex drivers, pitch gauge, glow plug wrench, ball link pliers and set of screwdrivers of frequent sizes. You’ll find other categories of model flying planes. Competitions are held in various parts from the globe, which include a number of categories of RC helicopter occasions. These events invariably attract a big number of competitors. Two of the most renowned competitions on the international aero modelling competitors scenario, would be the 3D Masters which are held each year in the Northampton University in England, exactly where this competitors showcases the very best of RC helicopters from all over the world and also the other competition is organized by The Flying Giants Community, Triple Tree, South Carolina, USA. It is only within the globe of RC helicopters, you are going to get the thrill of creating your machine hover at a height, then climb high and move in any direction, you wish. You don’t demand a runway to fly helicopters. Just a small piece of ground is enough to make it land and take off. So, why wait! Go out for the nearest model plane shop and have a look at, what is accessible, to take you into the thrilling new planet of RC helicopter flying!

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