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Tuesday, February 12, 2008

Thermal Soaring

Thermal soaring is one of the most intriguing of all aspects. It can be hard for the average person to understand how a plane can fly for hours and gain altitude without a motor!

It takes a lot of concentration to thermal soar effectively. A sailplane can fly along the edge of a thermal and unless the pilot is carefully watching the model he may not realize the opportunity to gain some altitude. Because most thermals are relatively small (a couple hundred feet in diameter or less at 400' altitude) compared to the rest of the sky, the sailplanes will rarely fly directly into the thermal and start rising.Generally, the sailplane will fly into the edge or near a thermal and the effects the thermal has on the plane may be almost unnoticeable. As the sailplane approaches a thermal, the wing tip that reaches the rising air first will be lifted before the opposite wing tip. This causes the plane to “bank” and turn away from where we would like the plane to go.

When you are thermal soaring, try to fly as smoothly and straight as possible. Trim the plane to fly in a straight line and only touch the controls when you have to. Watch the sailplane carefully and it will tell you what it is encountering.When the sailplane flies directly into a thermal it will either start rising or stop sinking. Either case is reason enough to start circling (especially in a contest where every second counts). Fly straight ahead until you feel like you are in the strongest lift, fly a couple of seconds farther (so your circle will be centered in the strongest lift) and then start circling in a fairly tight but smooth turn. When the sailplane is low the turns have to be tighter to stay in the strongest lift. As the plane gains altitude, the turns can be larger and flatter. The flatter the turn, the more efficient the plane is flying, but don’t be afraid to really “crank” it into a steep bank when you are low. If you see the plane falling off on one side of the turn, move your circle over into the stronger lift. Thermals move along with the wind so as you circle you will be swept along with it. Be careful when thermaling, that you don’t get so far downwind you can’t make it back to the field to land. If the sailplane is flying along straight and all of a sudden turns, let the plane continue to bank (you may have to give it some rudder to keep it banking) until it has turned 270°(3/4 of a full circle). Straighten out the bank and fly into whatever turned the plane. If you encounter lift, and you won’t every time, start circling just as you did when flying directly into a thermal.

Thermals are generated all day long, but the strongest thermals are produced when the sun is directly overhead. 10:00 am – 2:00 pm seems to be the best time to get those“killer” thermals. Some of these thermals can be very large and you may find it hard to get out of them. If you find yourself getting too high, don’t dive the plane to get out of the lift. Sailplanes are very efficient aircraft and they will build up a lot of speed and could “blow up” in the rough air of a thermal. The easiest way to lose altitude is to apply full rudder and full up elevator. This will put the plane into a tight spin that will not over stress the air frame but it will enable it to lose altitude very quickly. This is especially helpful if the sailplane gets sucked into a cloud or it gets too high to see.The twirling action will give the sun a better chance off lashing off of the wing and catching your attention. When you are high enough and want to leave the thermal, add a little down trim to pick up some speed and fly 90 degrees to the direction of the wind. If you are not real high and want to find another thermal, you may want to look upwind of the last thermal. The same source that generated this thermal is probably producing another. Just watch out for “sink” which is often found behind and between thermals.

As you might expect, with all this air rising, there is also air sinking. This air is the sailplane pilot’s nightmare that can really make soaring challenging. “Sink” is usually not as strong as the thermals in the same area, but it can be very strong. Down drafts of many hundreds of feet per minute are common on a good soaring day. These down drafts can make a sailplane look like it is falling out of the air. Because of this, it is important that you do not let the sailplane get too far downwind.

When encountering sink, immediately turn and fly 90 degrees to the direction of the wind (towards you if possible). Apply a little “down elevator” and pick up some speed to get out of the sink as fast as possible. Every second you stay in the sink is precious altitude lost.

Facts About Thermal

Thermals are a natural phenomenon that happen outside, by the millions, every single day of the year. Thermals are responsible for many things including forming several types of clouds, creating breezes, and distributing plant seeds and pollen. If you have ever seen a dust devil (which is nothing more than a thermal that has picked up some dust), you have seen a thermal in action. Their swirling action is very similar to that of a tornado but of course much gentler. Most thermals have updrafts rising in the 200 – 700 feet per minute range but they have been known to produce updrafts of over 5,000 feet per minute (that’s over 50 miles/hour straight up!) These strong thermals can rip a plane apart or carry the plane out of sight before the pilot can get out of the updraft.

Thermals are formed by the uneven heating of the earth and buildings, etc. by the sun. The darker colored surfaces absorb heat faster than the lighter colors, which reflect a great deal of the sun’s energy back into space. These darker areas (plowed fields, asphalt parking lots, tar roofs, etc.) get warmer than the lighter areas lakes, grassy fields, forests, etc.). This causes the air above the darker areas to be warmer than the air over the lighter areas and the more buoyant warm air rises as the cooler, denser air forces its way underneath the warmer air. As this warm air is forced upward, it contacts the cooler air of the higher altitudes. This larger temperature difference makes the thermal rise quicker. The thermal is gradually cooled by the surrounding cooler air and its strength diminishes. Eventually the thermal stops rising and any moisture contained in the once warm air condenses and forms a puffy cumulus cloud. These clouds, which mark the tops of thermals, are usually between 2000 and 5000 feet high.

Wednesday, February 6, 2008

A Beginners Guide to RC Soaring

Sailplane or Glider?

A glider is a ship you launch to good height that gently floats back to earth. A sailplane, on the other hand, is a ship you launch to good height and it goes on up from there!

Which one you experience largely depends on whether you have taken the time to set that new lead sled up correctly. Let’s start in the workshop.

You’ve just finished building your latest sailplane masterpiece and have installed your radio gear. All control surfaces seem to be working, your battery is charged and you’re ready for the field, right?

Wrong!

There are some subtle and important steps you need to take to insure optimum performance. First of all, did you weigh your wings separately? Lateral balance not only makes your plane fly straight, it helps it perform better. Add small amounts of lead to make both wings weigh the same.

Your stabilizer should be parallel to wing leading edge and equidistant from stab tip to wingtip. Use your eyeball for the first part and a string to measure the last part. Line everything up first, then glue. Have you set your control surface throws correctly? Look at the manufacturers recommended throws.


Buy a gage and set these up--adjusting holes on the control horn or servo arm or with travel adjust on computer radios--so you don’t get more throw than you need. More throw means you’re more likely to over-control, with subsequent loss of performance and possibly even a crash. Less throw makes your flying smother.

If you are prone to over-control, dial in some dual rates with exponential on computer radios so that a large stick movement results in less control surface m
ovement. If you don’t own a computer radio, you’ll just have to be VERY careful not to move the stick too far or too much.

While were at it, center your servos, then center your control surfaces using clevis adjustment, not sub trim on your computer radio. Did you check for proper control surface movement? Viewing from the rear, stick forward, elevator down; stick back, elevator up. Stick right, rudder right; stick left, rudder left.


I am sure you balanced your ship, but let’s take a second look anyway. If you had to add lead in the nose, you might as well get a larger capacity battery that weighs more. Why not have more juice than lead? You’ll need it anyway for those longer flights you’re going to get after reading this!

While you’re into batteries, consider getting a large
r capacity for your radio. Those small 600 mAh batteries are for wimps! New battery? Did you prime and cycle it for maximum performance? Old battery? Did you cycle and charge for the new season? Best to cycle three or four times to condition the battery for the new season. (NiMH batteries don’t need cycling but do need priming.) Also, double check that balance point. Many newcomers incorrectly balance their plane because they read the ruler wrong or because they read the directions wrong! Use a good CG machine to do this.

Don’t take chances with finger balancing or a homemade rig.


After that, make sure that tow hook is in FRONT of the CG. A good rule is 3/8 inch in front, but if you have an adjustable tow hook, you may move it back to within 1/8 for higher launches. You might want to wait on moving the hook until you have a few launches under your belt.

Now to the field.


At the Field

You’ve just arrived at the field with your spanking new Glider. You put in a lot of hours building it into the perfect ship and now its time to test it out. Scary, isn’t it? Well here are a few tips to help insure your success.

Check everything carefully. Is everything nice and tight? No loose servos or batteries? You did follow the “Before You Get to the Field” instructions, didn’t you?


Always start with a range check, but before you turn on your transmitter, find out if anyone else is using your frequency!!! After assuring yourself that no one is using your frequency, turn on the transmitter, then your receiver (reverse that order when turning everything off). Keep your antenna down and walk out onto the field about 200 feet. Facing the antenna away from the model, have a helper check to see that the control surfaces are moving. O.K.?

Go back to your ship and check for proper directional movement of control surfaces. Remember, look from rear to front. Stick forward, elevator down; stick back, elevator up. Stick right, rudder right; stick left, rudder left. Do all of the control surfaces line up with their stabilizers?

Now you are ready for the next step. It is helpful at this point if you have a buddy to assist. Pick up the sailplane and run forward with it about 15-20 feet. The idea is to get the plane up to flying speed. When you have enough speed, toss the plane out in front of you, keeping it as level as possible. Whether you or a friend does the toss, be ready to input some control surface movement to compensate for dives, stalls or veering left or right. Some guys will run farther and let the ship “bounce’ up and down in their hand to get some idea of what the plane is going to do when released.


Ideally, your ship will glide straight out ahead of you and gently come to earth about 50 feet later, with little or no control surface input. If not, you may have to check your CG, lateral balance, or compensate by adjusting your trims. If you throw the plane hard and it pitches up immediately, you probably have too much nose weight.

Once the toss proves satisfactory, it’s time for the true test. Launch! But first, check to see if your tow hook is in the proper position, hang the plane upside down from the tow ring. It should hang slightly tail down. If it hangs tail up and wants to slide o
ff the ring, you’ll need to move the hook forward. (Note: if one wing hangs down more than two inches lower than the other, see the previous section on lateral balance.

When you do launch, toss the plane hard on launch to get it up to airspeed. Don’t just let it go from your hand. You may want an “old timer” to take her up for the first time, but if you do it yourself, try to launch and fly hands-off as much as possible. Remember, you’re not looking for thermals at this point. You are just trying to get a good feel for the flight characteristics and trim needs for this particular model. Fact is, you should launch and land that new ship 20 or 30 times before you really start thermal hunting.


One thing you don’t want to do in this sport is hurry things up. Take your time. Explore your ship slowly and you will be rewarded with better piloting skills. Practice makes perfect.

Check out the “Trimming” instructions from here.

Trimming Your Lead Sled

Little at a time method.

Try several flights with no wind (early morn or evening). On each flight, try a few tight thermal turns at altitude with slow speed (some up elevator slows your ship in turns). Remove ¼ ounce lead on each flight until plane becomes unstable or tip stalls in turns (Note: dial in additional down trim as you remove weight)

Pay attention to slow speed handling and pitch cha
racteristics. When plane gets mushy, tip stalls a lot or starts slow oscillated pitching, add back in a ¼ ounce lead and call it good.

Note: you will probably need to add nose weight under windy conditions, try ½ ounce at first OR Start with dive test –launch and trim for slow flight (up trim). Come around and fly perpendicular to yourself.

Perform a shallow dive, about 30º then let go of stick. Gradual pull out = O.K. Immediate pull up into a climb = too much up trim holding too much nose weight land and remove nose weight, then re-launch, re-trim and do the dive test again
repeat until the pullout is very gradual (teaching point; if your ship is flying too fast, move CG rearward by removing nose weight; if your plane porpoises a lot, you probably need to remove nose weight) (during the dive test, if the dive angle increases—tuck under-- add nose weight) When it is flying more smoothly, go to early morning test.

Early morning test.

Again, this involves several flights under no wind conditions. Launch (no zoom) and fly straight ahead, hands off as much as possible. Trim the rudder to fly perfectly straight. When she sinks far enough, turn straight back and land. Time each flight and change the elevator trim to optimize the flight times. Once you have determined the optimum trim setting (close to stall), remove 1/8 ounce of nose weight and start the process all over again. Your flight times will increase throughout this process. Eventually, though, she becomes unstable and you have to give so much input to keep it straight and level that flight times start to decrease again. When this happens, put ¼ ounce weight back in the nose and your good to go.

Note: if you’re having to fight for control of your
plane all the time (as with porpoising), you’ve either got too much nose weight (probably the case) or too little. Either way, you’re going to have to adjust the nose weight to get smooth control.

Flying for Fun

Unless you are a competition pilot with a flat wing, full house sailplane, you’re probably just out to have a little fun soaring. Here’s how to enhance your experience. Let your sailplane do the flying. The number one problem with beginners is overcontrol. Too much up elevator will cause a stall, leading to difficulty in trying to regain control to get the plane flying smoothly again. Near the ground, this problem spells BIG trouble. Move that stick in small increments. (Usually, just letting go of the controls will right your ship, without any input from you.) Also, if you overcontrol, you’ll never know when your plane passes through a thermal. Again, let the plane do most—but not all--of the flying. If you read “At the Field,” you will find that it is important to get a good feel for the flight characteristics of your model. You can’t do that when you are constantly yanking the stick. Also, you should have already trimmed your rudder for perfectly straight flight. If you move rudder very much, you won’t be able to see the signal your plane makes when it hits a thermal.

Fly a pattern search. When you’re off launch, turn to the left or right and fly at about a 45° angle until you find thermal activity. If you are getting uncomfortably far out, turn into the wind and come back. Don’t turn with the wind, as you will lose ground and fly in air you’ve already flown in.

Stay out in front of yourself, unless you’ve found that elusive thermal and follow it downwind to gain altitude.

When you see your plane coming down significantly, you have a choice. Either find a thermal quick or join the landing pattern. My advice for beginners, join the landing pattern. In fact, you should practice landings more than anything else, and this should be a separate activity from hunting for thermals.

Landing

Landing can be a scary time for sailplane pilots, especially if you’re new to the sport. If you’re at this point, try these tips:

Don’t bother using spoilers or flaps, if you have them. These will just confuse the issue (and possibly cause a crash). Deploy spoilers and you’ll dive; deploy flaps and you’ll balloon or stall.

Wait to use these until you have some flying experience and can quickly compensate for these effects. (A computer radio can be programmed to automatically compensate for these effects)

Be careful when using up elevator to slow down. You can easily stall this way and, close to ground, that usually means a crash. When landing, avoid using the elevator.

Mentally create your landing pattern and practice it as often as you can, This should be a separate operation from flying for fun and hunting thermals. That’s because your mind should be focused on this one task to get good at it.

Start by entering the pattern at about 50 feet up for a good safety margin. Put in one or two clicks of down trim. This will speed things up but increased speed means better control. Going slower may give you more time to react, but it also creates more opportunity for accidents like stalling. Come to your left or right, as you prefer, and sink to about 20 feet. At this point, you should be about 100 feet out to your side. When you get about 40 feet behind you, start a gentle turn to the left (or right). When your ship gets about 20 feet out from your side, make another gentle turn toward you. Watch that up elevator!


If you are too high on approach, you can turn downwind slightly and come around from the other side of you. You can also zig-zag behind you on final approach to bleed off altitude and energy. If you are too low, shorten the approach by spending less time between turns. Practice, practice, practice!

Keep the wings straight and level, then let her settle in. You can give slight up elevator when she is about a foot above ground. This will slow the model. (Remember, when you are looking at the nose of your plane coming toward you, move the stick in the direction the wing is dipping. This is opposite of when you are looking at the tail of your plane in front of you.) If it rolls right past you and seems not to want to land, just let it go. It’s better to walk a distance to your plane than to pick up the pieces at your feet. Next time, fly a little further past yourself before making the turns.

When it’s windy, don’t fly past yourself. Make your first turn when your ship is at a right angle to you or even in front slightly. That’s because the wind will carry it downwind by the time your make your final approach.

Have fun!

Monday, February 4, 2008

10 Simple Flight Safety

1. No flying overhead.

2. Avoid flying over any spectators.

3. Before executing a low pass or low flying stunt, always check that the path is cleared of other flyers or park users.

4. Always fly within the perimeter defined by the boundary of the park, never over highway or roads.

5. Always sound out ("Landing") to alert others before coming in for landing. Always sound out ("Man on Runway") before going onto the runway while others are flying.

6. To avoid mid airs collision when flying as a group, always makes your intention clear and fly in the same direction as others.

7. Ensure frequency is cleared before turning on your radio, this is especially so when someone else is already flying.

8. Do not to hog the runway.

9. Avoid flying alone at the field, accidents do happen, your flight buddy could well save your life during such emergency.

10. Remember your model is not a toy but a piece of potentially lethal machinery, never compromise safety of human life, crash your model to abort flight if need be.

Clubs' Rules

Model Airplane Clubs Rules

• The flying field must always be well maintained and kept free from debris. Club members are responsible for keeping trash picked up and properly disposed of.

• All automobiles are to be parked in the designated area and behind the pit line at all times.

• Transmitters in use on the field must have the proper frequency ribbons displayed.

• When arriving at the field, you are responsible for checking that your frequency is not in use prior to turning any RC equipment on.

• Flying is only allowed at designated club sites.

• No flying is to be done behind the pit line.

• People learning to fly, who have not yet been cleared by a club instructor to fly solo, are required to get assistance from an experienced flyer prior to flying in front of any spectators.