Cow Patty News
Monthly Newsletter
October 2002
The Anniston RC Flyers & Talladega Radio Control Club
God Bless Amereica
What is in the newsletter this month?
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| Anniston RC Club Meeting The Anniston RC Club held its regular monthly meeting on September 9, 2002. The meeting was delayed one week due to a holiday. Eight members attended the meeting and a few got in some flying as well. The Club has decided to concrete the entrance to our field so it will be more accessible for the members. Members of our club will pour the concrete sometime this fall and volunteers will be needed.
Anniston RC will participate again this year in the Mt. Olive Volunteer Fire Department fund raising event. It will be held on October 26, 2002 and all flyers will receive a free lunch. The field will not accommodate large planes so bring your small plane and come out and have some fun with us.
Everyone is invited to attend the Anniston RC club picnic on November 2, 2002. It will be held at the Eastaboga flying field and will start around 8 am. Hamburgers and hotdogs will be served for lunch and will be furnished by the club; side dishes by club members will be welcomed. The field will be opened for flying all day long so plan to make a day of it.
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| Talladega RC Club Meeting TRCC will hold its fall club meeting on September 30, 2002. The location will be the Western Sizzlin in Pell City and the time will be 6:30 pm. The meeting will get started about 7:30 after everyone has had time for dinner. We will be making plans for the following year of activities at the field. See you there!
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| Minutes or mah (milliamp hours) By James Goss
When you are cycling your batteries most cyclers will allow you to select the results to be stated in minutes or either mah (milliamp hours). This may be confusing to some new pilots in our hobby so I thought I would give you a little background on the subject. Both mah and minutes will tell you what you want to know about your battery pack's condition. You are trying to find out how much energy your battery will store so you will know how long to expect the battery to last during a day at the field. For example, if you have a 600-milliamp battery and it is fully charged when you place it on the cycler and it takes 120 minutes to discharge down to the point where your cycler starts to charge the battery again, then you can expect to get 120 minutes of actual work from the battery.
You have got to remember that the cycler is discharging at the rate you have selected, this may be 50 milliamps or it could be 250 milliamps or any value your cycler will allow. I like to use 250 milliamps on all packs less than 1200 milliamps. 250 milliamps is a good reference because this is about what an average transmitter draws in current. Some PCM radios will pull a little more, but by and large 250 is a good value to use. With this in mind lets say you have cycled your 600 mah flight pack and it shows 120 minutes of time required to discharge the battery to the point where it drops below 4.8 volts. This is what happens when the battery uses up its stored energy, its rated voltage starts to decrease. With nicads the voltage drops very fast when this point is reached. How long you actually have to fly on this battery depends on the actual load on the battery, and that load may be greater that 250 milliamps. So you may not have the full 120 minutes of flight time even though the cycler said you have 120 minutes. Under some conditions you may only get 60 minutes instead of the 120 you expected. So using minutes is good if you have the same discharge rate on your cycler as you will have in an actual flight, but this is not likely. Your flight discharge rate for the flight pack is constantly changing as your plane goes through its many maneuvers.
Milliamp hours is a little more confusing than minutes, we all understand time so this is why the manufacturer has the discharge rated in minutes or mah. Even I know that there is 60 minutes in one hour. A lot of modelers find it easier to read the discharge in minutes and there is nothing wrong with this. It doesn't have to be 100% anyway. For the more technical minded people the mah rating will tell you the whole story about your battery and it is very accurate. The term mah gets its name because it is current referenced to time. If you have a 1200 mah battery, you should be able to get a current flow of 1200 milliamps (1.2 amps) for a time of one hour before the battery's terminal voltage starts to drop. This same battery should also furnish 100 milliamps for 12 hours, or 600 ma for two hours, or any combination of milliamps and hours that equal 1200 mah. Since your battery is rated in mah and not minutes, this is the only logical unit of measurement to use. Having the same unit rating means you can look at the battery rating and compare it to the cycled mah value. A new battery's cycled value should be equal to or greater than the battery rating.
There is a relationship between minute's discharge and mah discharge. It is easy to understand if you look at it this way. Lets say you have a discharge of 120 minutes and you were using a discharge value of 250 ma. This means that 250 ma were flowing through a load resistance for 120 minutes. To convert this to mah simply change the 120 minutes to hours, 2 hours, so we have 250 ma flowing for 2 hours. Now multiply the 250 ma times two hours to get 500 mah. Both minutes and mah are useful, but I think I like mah better because the battery is rated in mah. Minutes will work ok especially if you have a good record of the cycle time on a battery and you notice a sudden fall off in discharge time, this flags you that something is wrong. Cycling is a good way to spot a trouble in advance of total failure, but you must cycle on a regular basis if you want it to work for you.
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| Technical Tip By James Goss
If you are in need of a long pushrod conduit and do not have the regular one in stock, use coroplast instead. With coroplast you can use the corrugations as pushrod housing and they really do work well. One 4 x 8 ft sheet of coroplast will give you an endless supply of pushrod guides. The corrugations run lengthwise of the sheet and are very easy to cut with your hobby knife. An 8-foot pushrod conduit is hard to come by. If you cut the guide two corrugations wide it will make it easy to glue in place because the guide will be flat. Using two will also make for a stronger assembly and three would really be strong. I have just recently discovered this technique while experimenting with one of my pusher stamps. These conduits work well and cost a tiny amount of what the regular guides cost. So if you are one that builds up your own pushrods try this method and see how you like it.
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| Finding Center Of Gravity By James Goss
Have you ever needed to locate the exact center of gravity for your large models? I have a method that allows you to determine your models exact CG location and it is accurate. This method does not require the use of complicated calculus and also does not require hanging your model from a string. Remember that the center of gravity is the sum of the weight of each component of the plane multiplied by the distance of that component from a fixed reference point. So you can see that the CG is determined by the weight of your model and how the weight is distributed. This is why everyone's model, even though identical to another as far as looks, will have its own unique CG location. Two modelers can't build the same plane and have them weigh the same. Everyone builds differently; even you can't build two of your own identical planes and have them weigh the exact same amount.
The manufacture tells us to balance the plane at a certain location and we do without questioning their CG reference point. Quite often they give us the wrong CG location and our planes never fly like they were meant to until we play around with the CG location by trial and error. A little more weight to the nose or a little less to the tail and so on. Of course if we do have the exact CG location for our plane it may still need a fine-tuning after we fly it. This method really pays off when you are trying to balance a large giant scale plane. Some planes do not have the right structural features that will allow you to place them on a balance stand or even pick them up because of their weight. Try to hold a 30-pound plane on your fingertips for a balance check without pushing a hole through the wing. It the proper balance for the plane is on a pipe spar centerline you can suspend it with a rope around the pipe if it has plug in wings, but if it calls for the balance to be 1-inch in front of the pipe you are out of luck again.
It took me a while to interpret the CG definition, but when I did it was as clear as could be. I decided all I have to do is weigh the plane from three main locations instead of weighing every component of the plane, measure these locations from a fixed reference point (the nose or the tail), multiply the distance of each point in inches times the weight at that point in ounces, sum them all up, and divide by the total weight of the plane. I guarantee you that this method will work every time and is very accurate. The three reference points can be the two main wheels and the tail wheel or nose gear, either way will work the same. I will show you an example of how easy it is. It doesn't matter what shape your plane is, it can be a normal looking plane, a round plane, a flat square plane, or any shape you can imagine. In the example I will use the Postage Stamp to show you how easy it is.
All you will need is a small set of weighing scales. For small planes I use a set of post office scales that will weigh up to 5 pounds. Digital scales will be ideal here. The Postage Stamp is a tail dragger so it has two front wheels and a tailskid.
Steps One: Set your plane's wheels on some blocks that are the same height as your weighing scales.
Step Two: Place a flat sheet of plastic, or anything that will simulate a wall for the nose of the plane to touch. You can actually use a wall, but it will get in the way when you start to measure. I use a two foot square sheet of coroplast and stand it up in front of the plane with the nose of the spinner nut touching. Try to get it square with the leading edge of the wing, not the wheels.
Step Three: Assign identities to the three wheels such as RH for right wheel, LH for left wheel, and TS for tailskid. Draw these notations on a sheet of paper in their relative positions on the plane so you will be able to keep up with what is what.
Step Four: Remove the blocks from the right wheel and place your scales under the wheel, log the weight measurement in ounces, do the same for the other two wheels. My RW measured 21.5 ounces. The LW measured 20.5 ounces. The TS measured 16.5 ounces. Depending on how your wheel gear are bent you will get different weights. To check, the three should add up to the total weight of your plane.
Step Five: Measure each wheel center to the fixed reference point and log the distance in inches. My RW measured 6 inches. The LW measured 5.75 inches. The TS measured 30.25 inches.
Step Six: Multiply the weight in ounces of each wheel by the distance in inches of each wheel from the reference point. Add the three together for a total summation. For my RW the product was 129. For the LW the product was 117.8. For the TS the product was 499. The total sum is 745.8. No unit of measurement, just 745.8.
Step Seven: Divide this number by the total weight of your plane. In my case it was 745.8 divided by 58 ounces. This gives 13 inches to be measured from the fixed reference point. This produces a CG for the Stamp that is 5 ½ inches from the leading edge on the wing.
That's all there is to it, seven simple steps that only takes about five minutes to complete. It is fast and accurate and after you do it one time for practice you will probably agree that it is well worth the effort. Test it on a plane that you know for sure where the CG is suppose to be and you will see that it indeed does work. Remember that this method does not tell you where the GC should be for best performance of your plane; it tells you where the CG is actually located.
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| Flying Your New Postage Stamp By James Goss
The Postage Stamp is not a trainer so you don't want it for your first plane. If you can already fly a trainer with precision you should be able to fly the Stamp while at a safe altitude. If you can already fly a hot fun fly, then you are in for a real treat because you can fly the Stamp two feet off the ground and hover it all day if you like. Having flight experience still requires that you get familiar with the Stamp before you start hot-dogging at ground zero. This is an unconventional plane to say the least because it operates on thrust and only receives a small amount of lift from the wing. Even though the wing is flat there is still some lift created due to the disturbed airflow over the wing. So you must understand that it is mainly the prop thrust that keeps you in the air.
You can take the Stamp off the same as you would any plane, get it moving down the runway and apply back stick. It will rotate in a short distance and you will be in the air before you know it. Once in the air you need to reduce the throttle so the plane really slows down to a nice cruising speed. Fly it around at this speed and get it trimmed so you are comfortable with it. If it still wants to fly too fast for you to feel relaxed, all you have to do is point the nose up about ten or twenty degrees and the Stamp will slow to a crawl. The main thing to remember is fly slow!!! This plane will give you all the excitement you need and without the high speed required by other fun fly planes you have flown in the past. You can fly this plane around like a helicopter and if you crash you don't have to set down and cry like a newborn baby. This plane is crash resistant and most of the time you can get it back in the air immediately.
When it comes time to land the Stamp bring it in like you would any other plane and when it gets a couple feet above the ground, point the nose up and bring the throttle up at the same time. The Stamp will set down in a vertical landing with the engine still running. With a little practice you can do vertical landings from any height. Most pilots for their first landing with a Stamp will attempt a conventional landing and set it down with too much forward speed, this usually results in a nose over and dead engine. The Stamp has very long landing gear designed for vertical landings so the prop will not hit the ground and kill the engine during it's timber.
After you are really comfortable with the Stamp you will need to start flying a few feet above the ground and really start to have fun. You can take off, reduce the throttle, and stay within a few feet of the ground for the entire flight. All you have to do is keep the nose up and the Stamp will become so stable you will not believe it. I like to fly around in this helicopter mode while doing patterns such as figure eights, circles, squares, crosses, and an occasional low altitude loop and flat spin. It is good to use the rudder for your sharp turns with the Stamp. With rudder and elevons together you can turn on a dime and instantly be going in the opposite direction. You must remember that for sharp turns you have got to bring the throttle up before you start the turn in order to maintain altitude. Flying one foot above the ground you can't afford much altitude loss.
The helicopter mode is the final phase in learning to fly the Stamp. Some pilots catch on in just a few flights while others require a little more time. It took me quite a while before I was able to fly in this mode. One of the reasons being I didn't know the Stamp was capable of doing this type of flying. It was over several months that I slowly seen what the stamp could do and one day there it was, the Stamp was hovering around like a helicopter and I had pretty good control of it. I was amazed, and still am, at how well the Stamp responded and how it could hover with ease. So it really makes a difference to know ahead of time what a plane is capable of doing. Working with the unknown will slow anybody down so this is why I like to demonstrate all the Stamp's moves before a first time Stamp pilot takes a Stamp to the air. If you already know something can be done, then it is just a matter of practice until you can also do it. This is one plane that will allow you to do just that. You will be doing tricks with this plane that you never thought possible with your other planes.
I have said many times that the Stamp will improve your flying ability no matter what style you have been flying. I will use my own experience as an example. I have flown with the rudder for many years and thought I was at least average when it comes to rudder control. I would still catch myself thinking at times which way the rudder should go for correct input. While flying the Stamp in its helicopter mode it requires constant rudder input for the nice crisp turns it will do. This has got to be the best rudder practice there is and I think it has really helped me to be able to instinctively input rudder commands. Repetition is a good way to learn and flying the Stamp in its helicopter mode you get plenty of it. Other skills will also improve, but I think the rudder input will be the most noticeable.
If I had to select one characteristic about the Stamp that I like above all the rest it wouldn't be hard. Above all I like the fact that I can fly the Stamp in close where I can see it well. In another article I describe orientation awareness and how it will be improved by flying the Stamp. As time goes on I see this more and more to be true.
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| Hovering By James Goss
It seems that in the field of 3-D flying, hovering has become the benchmark that most pilots use to choose their fun fly planes. I have been trying to hover some of my models now for about two years and have had good luck with some and none at all with others. Now I am not talking about hovering your plane into a head wind, the type of hovering I am in reference to refers to hovering your plane with its nose pointed straight up and with no wind at all. Hover, bring the plane down close to the ground and then pull back up to repeat it again. Every now and again let it do a torque roll and then lock it back into a stationary hover. A series of torque rolls also looks neat, especially if the wind is blowing the plane down the center of the field. I think any plane will hover if it has enough engine power and control surface movement. How long it stays in a hover depends a lot on the plane as well as the pilot.
Let me say at the beginning of this article that hovering a large or small model plane can be dangerous for other pilots as well as for you and all the spectators around. 3-D flying deals with maneuvers while the plane is at or near a stall condition. A hover is about as stalled as you can get. You already know that a plane can do some crazy things when it is stalled and sometimes you have no control at all over the plane; it has a mind of its own. This is where it can get dangerous if you are flying too close to other people. Pilots that are flying their own planes are not watching what is going on with the other planes in the air. I think it is a good idea to practice taking your eyes off your plane and looking around to see what the other planes are doing. I always do this during each flight and have no trouble finding my plane again; it just takes a little practice. When you take your eyes off your plane in flight it is still going to be in the general vicinity when you look back, it is not going to just fall out of the sky. (Unless you are flying a super fast plane, in this case it may be in the next county when you look back.) If possible always hover at a location across the field and then if you loose control your plane can hit the ground without doing any damage to anyone or anything other than your plane. Remember, when your plane falls out of a hover it takes a lot of engine power to recover without loosing any altitude, most planes do not have it. At our club field I try to do most of my hovering across the field and over a soybean field. In all cases you can't predict which way your plane will go when it falls out of a hover. It may do one thing this time and something completely different the next time. So always have a large safety zone around your plane that will give you plenty of recovery time.
So what does it take to hover a model plane? First you need an engine that has about a 1:1.5 or greater weight to thrust ratio. An engine that has enough power will pull your plane straight up from a hover with good acceleration. A lot of fun-fly planes with small engines will hover the plane for a while, but when it falls out of the hover it will loose a lot of altitude fast. This is not what you want if you are hovering three feet above the ground. The engine has got to pull your plane straight up and not let it fall to the side. Next it takes a plane that is built for hovering with plenty of control surface and control surface movement. When the plane does fall out of its hover you may need a lot of rudder or elevator to gain control again. I am talking from 45 to 60 degrees of control surface movement. Most important of all you need a reliable engine, one that will not quit while your plane is at ground level. Even at a few feet above the ground when a model falls due to a dead engine, most planes will still receive a lot of damage. I have seen giant scale as well as small planes have their fuselage break into several pieces when they fell from a height of only three of four feet. I think it is safe to say that it is possible for all engines, gas and glow, to quit at any time during a flight. You may have fifty flights without a dead stick and then it happens when you are least expecting it. So relinquish the thought that your engine is above quitting on you during a hover, it will happen sooner or later. If I am planning on a lot of hovering during a flight I like to adjust my engine on the rich side because when the nose stays pointed up for a minute or so the engine may go lean and quit. I also like to fly a few circuits to make sure my engine is at normal running temperature and is running reliable in the vertical mode. A while back I was just getting ready to enter my first hover during a flight and had about 40 or 50 feet of altitude. The engine spit and sputtered a few times and down she came. The plane was a 60-inch fun fly with a YS-120 engine and a total weight of 8.5 pounds. I had just enough altitude for the plane to recover and level up before it hit the ground. So it is important to know how much altitude your plane needs to recover and always use this amount or greater for your first hover of each flight. When your engine quits and gravity takes over, your plane will try to fall at a rate of 32.2 feet per second per second while it is in a vertical attitude. This means that if your plane is at a 50 ft. altitude and your engine quits, it will take only 2.05 seconds for your plane to hit earth. Remember that during the first second the object only falls half the distance, about 16 feet because it is going from a standstill. So the first second averages out to half of 32.2.
There is a lot of controversy about which prop to use while hovering. Do you need a large diameter with low pitch or a small diameter with large pitch? I think it depends on your plane and all planes seem to be different to some degree. I know on my smaller fun fly planes a large diameter and low pitch work best for me. On .46 size planes I like to use a 12.25x 3.25 prop. It gives my planes good speed regulation while going vertical. Remember that prop diameter is for thrust and pitch is for speed. All we need in a hover is enough thrust or pulling action to cancel the gravitational pull of the earth. The only speed we need is the air flowing over our control surfaces to correct for a fall out. While in a hover the low pitch prop seems to create less torquing of the airplane. It is easier to hover a plane when it is stationary and not trying to torque roll. I will talk about torque rolls later.
Now that you have a plane and engine needed for hovering all you need to do is practice. Entering the hover can be from any position that you like. Most pilots will bring their plane in as if they were going to land it and just before it touches down they will give it a little throttle and pull vertical. Of course they didn't learn to hover like this. You will need to start out at a safe altitude, maybe 100 feet or so to get the feel of it and as you get better you can work lower to the ground. You may wonder why we hover so close to the ground. Not only does it look good it is much easier to hover when you can see your plane. You must be able to see when your plane is on the verge of falling out of its hovering position or what I like to call its sweet spot. If it is close enough you can see this and head it off at the pass so to speak. So for good hovering it is almost a necessity to be close to the ground (the danger zone) for that reason. If you are hovering at 300 feet in the air you may not be hovering at all, your plane may still be going up and you just don't realize it. While in a hover I choose to have the top of the fuselage face me and I watch the nose and not the tail. For me it is easier this way because the rudder is not reversed. If the plane's nose falls to the left I give it right rudder. If it falls to the right I give it left rudder and so on. The elevator also works better for me this way. You are still flying its just that your plane is not moving, so it is logical to use the same train of thought as you do when you are flying with the wings producing lift, up is up and down is down.
Next, how do you get your plane to descend? Once you learn to hover you will want to learn how to get your plane to loose altitude while keeping it in a hover. Of course if you chop your throttle the plane will reduce its altitude, but keeping it in a hover is a hard trick to learn. You have got to manage the throttle by reducing and increasing it in small increments. If you give it the gun all at once your plane will probably start to torque roll and if you can't handle torque rolls you will loose the hover and the plane will fall to one side or to the front or rear. The way I do it is to gently reduce the power and let the plane fall a foot or two and then stabilize it again by giving it more throttle. You will normally need to give it more throttle than it requires to hold it in a hover until it stabilizes again and then back off. When it is back in its sweet spot chop the power again and repeat until it is as low as you want it. If everything is going well at this time you may want to pull back up and do it all over again or fly off in a knife edge. I have one plane that I can get to descend if the wind is not too strong and I am having a good day. Getting a plane to descend while in a hover is one of the hardest 3-D maneuvers I have tried. With practice it is becoming a little easier as time goes on.
I guess the overall most impressive 3-D maneuver that we can do is the torque roll. Some planes will torque better than others and it depends mostly on the engine. For every action there is an equal and opposite reaction (who was it that said that?) If your plane is in a hover it will eventually start to torque roll, some faster than others, but it should start. If it rolls around fast with a uniform rate it is easier to keep it under control because you only have to correct it when it is in your favorite position. If it rolls around and stops with the reverse side of the fuselage facing you it will take some quick thinking to input the correct controls. Rudder is now backwards and what makes it even harder is that the elevator is also backwards as compared to its operation while the fuselage top is facing you. Once you learn to hover for a few seconds you will need to practice the hover with the fuselage turned to the opposite direction than that from which you learned. The first time you let the plane rotate around and you keep it in a good hover as it rotates, you will feel a real accomplishment. It is always a good feeling to know you are advancing in any hobby or sport.
It seems to be true that a larger plane will hover better than small plane if it has enough engine power. First of all you can see the plane better and it doesn't need to be right on the ground to make out what is going on. A large plane seems to fall out of its hover at a slower rate so you have more time to think and react with the correct inputs needed to keep the hover going. Again let me say that there is no prettier picture than a large giant scale plane doing torque rolls a few feet above ground level. Of course everybody interprets beauty in his or her own way. What's enjoyable to me may not be so for others. But overall I think most all pilots will enjoy seeing a plane hover in the grass and then pull away still in one piece.
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The Anniston RC Club Meeting