FlightplanPublished "online" by the Flightmasters
Model Aircraft Club, Inc. of Fort Smith, Arkansas. It's purpose is to inform
the membership and to promote interest in the safe building and flying of model aircraft both in
the Fort Smith Area as well as elsewhere. |
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Volume 43 Number 4 AMA Charter # 742 IMAA Chapter # 362 April 2010 |
- Editor's Corner -by Cecil Collum
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... from the president's perspectiveby Ron RobertsThis month brings some news that may not be all that exciting to read. We are having some second thoughts about the particular property we have been looking at for a new field. As we reported at the March meeting, Tom Minton is preparing a required letter to the FCRA folks that will outline our plans and schedule for improving the property into a usable flying field. So... a few weeks ago Tom took a four wheeler tour of the property to determine the extent of work that would be required so he could better be able to come up with a workable "Time Line" to put on paper. What Tom found on that excursion was very disappointing! There was a lot of water covering the area. Most of the property was either under water or so soggy that he could not pass through it. The two "sloughs" that run through the property were full and it was almost like a large lake out there. There were two Beaver dams that had backed up water and there was evidence on the tree trunks that the water had been even higher. Tom's assessment of things after that excursion is that we need to look for other property. It's not, however, like we have to start from the beginning... There is other property that may be available for us adjacent to the piece we have been looking at. It is not quite as large but it's elevation is higher, was not under water when Tom was there, and has fewer trees! We are going to talk with the folks at the FCRA and see if it might be possible to get it instead of the one we have been looking at. In the mean time, we are also looking at property just across the river in Oklahoma. We had been told that there may be some next to that "Moto-cross" park just down highway 64D. Two weeks ago Bill Womble and I met Carl Albertson at his place of business in Roland and toured the area in and around Roland and Pocola. We have heard some encouraging things. More about this at the meeting. Let me join with Cecil in encouraging you to attend the club meetings. We are facing a crucial time in the months that lie ahead because of the I-49 Interstate Project. Several of us know what it is like when a club flying field is lost. Although nothing in this world is permanent, I feel that owning the property upon which our flying field sits makes it much more so. Therefore we must join together and work diligently toward acquiring and preparing property for a new field. The club's officers can't do it for us... we must work with them to make it happen. Till next time… Ron | ||||||||||||||||||||||||||||||||||||||
- Batteries and Charging -by Cecil Collum The following segment is one of two parts on charging the batteries we use to fly and control our models. There are many ramifications to properly charging and storing these wonders of the electronic age and can cause damage to our planes, vehicles and homes if not properly done. I claim no special knowledge, the following is an amalgamation of knowledge found on the web and is presented for your pleasure. | ||||||||||||||||||||||||||||||||||||||
There are a number of battery types used in flying model aircraft and there are many buzzwords, numbers and distorted facts bandied about in various locations. The following article will attempt to demystify the various battery technologies and especially how to charge your batteries to prolong their lives. The first common rechargeable batteries were lead-acid (Pb) types and car batteries still rely on this type today. They are very heavy and contain liquid acid, making them unusable for models. Sealed and gel acid based batteries are in use but are heavy so are rarely used in flying models except as possibly the storage medium in a flying site power supply. The next generation was Nickel-Cadmium (NiCd), which are lighter than lead-acid and have a higher power density, stored energy per unit weight. Although the main type of small rechargeable battery for a number of years, there were a few major problems - they don't hold a charge for very long (losing about 2% per day even when not in use) and if you don't fully discharge them prior to recharging, they will develop a “memory”, discharging only to that point again. NiCds come in the same sizes as conventional non-rechargeable batteries, such as AA, AAA, B, C and D sizes as well as some special sizes such as sub-C and are used to fit in the unusually sized spaces in some models. “NiCad” is actually a registered trademark that is used generically such as “Coke” is used for Coca-Cola, so sometimes the chemical symbols “Ni” (nickel) and “Cd” (cadmium) are used instead to make “NiCd” of “NiCad” to avoid trademark infringement. The most common type of rechargeable battery now is the NiMH (Nickel Metal Hydride) which is available in the same sizes as NiCd batteries BUT with normally larger capacities at a smaller size and weight. NiMH batteries don't have a significant memory effect but they do lose their charge quicker than NiCds- up to 10% per day! There are new types of NiMH batteries coming into the market (and may be available now) which claim to retain 70% of the charge up to one year and which will be better for those of us who like to always have a model and radio ready to fly at a moment's notice. The latest and greatest battery technology and one that has revolutionized the electric flight fraternity is the Lithium Polymer or LiPo battery. These flat, plastic wrapped cells come with wires to a power connector and a smaller set to a balancing connector, which is used during charging. There are variants of the LiPo, including Lithium Ion and LiFePo which are used in other applications such as electric scooters, cell phones and laptop computers but LiPos are the only commonly used for modelling. For all these types of batteries, a single cell gives only a set voltage out- for example, a NiCd gives 1.25 Volts, NiMH 1.2 Volts and LiPo 3.7 Volts per cell. Although the voltage stays the same, the capacity varies with physical size- for example, an AA size NiMH will typically have over twice the energy capacity of a smaller AAA size battery. There is no actual “set voltage”. Most numbers in the battery world are “Nominal” - they are about right but will vary depending on the state of charge of the battery, how rapidly you drain it of current or even the temperature. The above figures are the normal nominal values for each battery type. Capacities are also somewhat nominal - they vary with age of the cell, how it was treated in the past, and especially how rapidly you drain it's current. If you drain it quickly, you may get only half the total energy you could have gotten if you drained it more slowly. To get the voltages (capacities) required for models, cells are combined into power packs with a number of cells electrically connected in series (plus to minus) which increases the voltage or in parallel (plus to plus, minus to minus) which increases the capacity of the pack. This explains why packs are available in odd steps such as 4.8 volts, 6 volts, 7.2 volts. These are packs of 4, 5 or 6 cells in series. Lipos are often described as “3S” (3 cells in series, 2 cells in parallel) or “3S2P, which translates into English as 3 cells in series, in parallel with another 3 in series. A “3S2P battery has 3 times the voltage and twice the capacity of a single cell and contains 6 actual cells welded together. Amps and Volts: When discussing electricity current is measured in Amps and voltage in Volts. An Amp is a large unit when we are discussing the amount of current used by our models, so milliamps are the unit of measurement we normally use. A milliamp is one thousandth of an amp (1/1,000 or 0.001 amps). If you think of electricity like water in a pipe, the voltage is the pressure and the current is the flow. One can have a small pipe with high pressure, a large pipe with low pressure or anything in between. Model electronics tend to be at the low pressure, high flow end, usually 5 to 20 volts and from 100 mAh to 50 amps and more. “C” is the symbol used to indicate the capacity of a battery pack. For example, for a 2200 mAh battery “C” is 2200. “C” is often used when discussing maximum charge and discharge rates, with a “10 C” for the 2200 mAh battery above having a current capacity of 22,000 mAh or 2.2 Amps. | One often sees “mAh” used when discussing batteries as this is the abbreviation for “milliamp-hours”. A 2,000 mAh battery can give 2,000 milliAmps for one hour or 500 mA for four hours, nominally. In actual practice, if you drain the battery at a rate of about 1C (2,000 mA for the above battery) one should get that, but if you drain it much faster than that you will get much less. At 10C (a 10A drain) you may get only 600 mAh from it. Charging: Charging is the area in which we get into the most trouble. When one purchases radios, etc., with rechargeable NiCd or NiMH batteries, even some models, a charger is supplied, usually a “wall-wart”, a box that plugs into the wall receptacle with a thin cable that goes to the airborne and transmitter packs. These chargers are slow chargers - they supply a very small charging current and are intended to charge the batteries over a period of 10-14 hours. At these low charge rates (about 1/10th C or 50-70 mA for most batteries supplied with radios), these batteries are very tolerant of poor charging such as charging too long or using varying voltages or currents. They do an adequate job but it is very frustrating when one forgets to plug them in the night before a flying session. Fast chargers are the main topic of this section. One may fast charge MOST batteries but there are some that can be damaged by fast charging, so be certain of your batteries BEFORE fast charging. There are many fast chargers on the market but by necessity they all do the same thing and have the same options. Many can fast charge a number of battery types and most now available, including the many almost identical chargers coming from the Far East on sites such as Ebay can handle at least NiCd, NiMH and Lipos. Charging NiCd Batteries: NiCd and NiMH batteries both require constant-current charging - for example, the charger must be control the current it feeds into the battery and it measures the voltage the cell is currently producing throughout the process. The voltage will rise slowly throughout the charging process, but when the battery is fully charged it actually dips slightly. A fast charger will detect this dip in the charging process, referred to as “-dV” or “negative delta V”, the mathematical expression for the “change in voltage” and stop charging. Adding more at this point will simply overcharge the battery and will not add any more energy to it. The size of the dip varies slightly with the size of the cell, but for the sizes used in our airplanes, a peak voltage sensitivity of 12 mV is OK and will safely detect the fully charged point. The voltage values one will see are actually per cell - for example, for a 4 cell pack the sensitivity will be 48mV but all chargers in use today set it as a “per cell” value and multiply it up by the number of cells in the pack automatically. NiCd batteries are best charged at a rate of about 1 C - for example, 1.0 A for a 1,000 mAh battery. They will get warm but not hot as they approach the fully charged point, which will usually take about 80 minutes at 1C due to inefficiencies in the chemical charging process. Many chargers will show the voltage they are reading back from the pack and the amount of charge they have put in so far, usually in mA, a figure that will typically be in the hundreds or thousands as the pack approaches the fully charged state. Fully charged NiCd cells will typically show about 1.45 V, which will drop to about 1.3V after a small amount of use and stay around there until shortly before it runs out when the voltage drops sharply. If one charges at low rates, say under 0.5C, then the voltage peak may not happen (it is caused by chemical changes and at low rates may not be as pronounced). This is true for NiMH cells, as well. Charging NiMH Batteries: NiMH batteries are charged in a similar manner as NiCds, but the voltage peak when fully charged is smaller. If you use a NiCd charger it may well miss the dip and overcharge the battery. The sensitivity should be set at 6mV per cell. NiMH packs should also be charged at a rate of 1C for best effect. Some chargers don't switch off when they reach fully charged but instead wsitch into “trickle charge” mode where they apply a very low charge current that can be used indefinitely - just enough to cancel out the the self-discharge that NiCd and NiMH all suffer from. The required trickle charge rates for NiMH are much lower than for NiCd, another reason not to use a NiCd charger for NiMH batteries. Many chargers have a “safety cut-off” which limits time, charge or both. Note that setting “2C” as the cut-off means that you will have to change it for different batteries. Watch for part two next month... | |||||||||||||||||||||||||||||||||||||
UPCOMING EVENTS
The following events have been scheduled by the Flightmasters or other organizations. Mark your calendars so
you don't miss any of them. Checking the Event Listing, there will be quite a bit of activity in the western
half of Arkansas this year. Get out there and enjoy all the events you can, even if you have to drive 150 or
so miles. I plan to attend the Petit Jean, SMALL, CAMAA and MARCS Float Fly this year and renew my friendships
with many of the pilots from Central Arkansas. These fellows will make you feel at home even though you may
be a complete stranger when you arrive. You won't be a stranger when you depart and you will have made friends
from other parts of the state and learned how others solve the same problems we all have. To the writer, this
is the most important part of our sport.
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23 & 24 |
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An article in FLY RC and MODEL AIRPLANE NEWS magazines have an article concerning a new world's record speed flight by a radio-controlled, conventionally configured, turbine model aircraft, as verified by the Guinness World Records during a series of flights conducted on 26 January 2010 in the Dominican Republic.
The record was set by David Schulman and Axel Hache'. The record speed is 325.23 mph but the highest speed attained was 345 mph.
Meeting Notes from last meeting:
He was found guilty of insubordination and sentenced to suspension from the Service for five years without pay. Mitchell declined to accept the sentence and resigned his commission. He died in 1939 and President F.D. Roosevelt promoted him posthumously to the permanent grade of Major-General (two stars). This was reconfirmed in 2004 by President GW Bush.
Many years later, the Japanese proved Mitchell correct when they sank the British Prince of Wales and the Repulse while underway off Singapore in WWII.
The airplane was conceived and built in 1939 by North American Aviation, who would also create the Mustang fighter. There were almost 10,000 built and they were used in every theater and by 22 nations. While the US Army Air Forces were the biggest user, the US Navy and Marines also used the Mitchell, designating it the PBJ-1. The Army also used the Mitchell for Photo Reconnaissance, terming it the F-10.
On 18 April 1942, about 700 miles off the coast of Japan, sixteen US Army B-25s took off from the aircraft carrier Hornet, enroute to Tokyo and four other cities in the Doolittle Raid. Damage was minimal but the
There were several variants of the B-25, with the G and H models carrying the 75 mm field gun in the nose. Crewmen said the plane stopped in mid-air or flew backward when the fieldpiece was fired. The gun wreaked havoc on Japanese transports and warships. Other variants carried as many as eight .50 caliber machine guns in the nose as well as carrying single and twin packs on the fuselage sides below the cockpit and waist, dorsal and tail guns. Late in the war, B-25s were used to strafe Japanese shipping and ground troops with devastating results.
In the European Theater, B-25s flew in every action by Allied forces, including the raid on the Monte Cassino monastery in Italy. The Russians loved the plane and flew it as if it were a fighter, doing all sorts of aerobatics with it. It was used extensively by Russia during the Great Patriotic War and devastated the German forces.
On 28 May '45, a B-25 lost in thick fog, flew into the Empire State Building in New York City. It struck between the 79th and 80th floors, causing an elevator car operated by Van Buren native Betty Lou Oliver to crash to the ground. She survived but fourteen others weren't so lucky.
In 1992 another B-25, Heavenly Body, took off from an aircraft carrier in California to mark the 50th anniversary of Doolittle's Raid. At least one PBJ-1 landed on a carrier after the war. So endeth the tale.
1.The friction clip provided on the high speed needles of our carburetors will frequently lose tension, allowing the settings to fluctuate wildly. If you have this problem, cut a short length of fuel tubing, slip it over the clip and needle valve and your problem is solved.
2. One member had a problem with the glow plug end of his on-board glow system, so he cut off the offending part, selected a wheel collar to fit over the glow plug stem, placed the wire into the collar, tightened everything onto the plug and temporarily solved that little problem.
3.While repairing wing damage one member needed to reinforce a sub-spar that had broken, so he backed the spar with a Popsicle stick, glued everything together and covered his wing.
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