Eagles Flying Association

Tips & Tricks

ULTRA HIGH FREQUENCY ADVANTAGE

I thought that this may be of interest.

Although specific to Spectrum / JR systems , it also has some interesting general info, particularly on model-generated interference. It is not aimed at protracting any argument for one system over another, it is merely an informative read.

Del

The Spectrum DSM system operates in the ultra high 2.4GHz ISM (Industry, Science and Medical) band. This ultra high frequency offers several advantages over conventional 27 and 75MHz systems. First, all model-generated radio interference from noisy motors, speed controllers, bad bearings, metal-to-metal noise, etc. exists below 300MHz. At 2.4GHz (that’s 2400MHz) the operational frequency range of the Spectrum system is 8 times higher than the range of this model-generated RF noise, making the system immune to these types of interference. Secondly, 2.4GHz is an internationally accepted band, so it’s not necessary to change radio equipment when travelling to overseas events. And because the 2.4GHz wavelength is very short, the required lengths of the antennas are much shorter. The receiver antenna is 8.5” and can be cut down to 3.6” if desired, making antenna mounting within the model easy. The transmitter antenna is a mere 3.5” long; eliminating the “fishing rod” that normally extends into view. FCC learned valuable lessons from other bands and applied those lessons to the 2.4GHz band. And unlike the 27 and 75MHz band, the FCC limits the power output in this 2.4GHz to a maximum of 1watt, thus preventing other 2.4GHz systems from overpowering each other. In other words, there are no “high power” commercial users interspersed in the 2.4 GHz band.

THE BENEFITS OF DSM

Spektrum’s DSM system eliminates all types of radio interference, including model-generated noise from motors, ESCs, bad bearings, etc. and from outside sources like pagers, cell phones, wireless computer systems and other RC radio systems, and offers these benefits:

· No more waiting for an open frequency—just turn it on

· Ultra fast 5.6ms response time

· No tuning or maintenance to perform (ever)

· Built-in fail-safe drives servos to pre-programmed position if signal is lost

· Ultra precise resolution

· Operates on international 2.4GHz ISM band so no need to change bands when travelling to international events

· Short 8.5” or 3.6” receiver antenna length and 3.5” transmitter antenna length

· 40% less current draw with the transmitter means 40% more battery life

· Telemetry ready

HOW DSM WORKS

Collision avoidance eliminates the possibility of more than one Direct Sequencing Spread Spectrum system from transmitting on the same frequency. Here’s how it works: When the transmitter is turned on, the system scans the 2.4GHz band looking for an open channel. When an open channel is found, the system locks in and transmits on that channel.

This process takes about 2 seconds. In the unlikely event that an open channel is unavailable, the transmitter continues to scan without emitting a signal until an open channel becomes available. The transmitter will remain on that selected channel until it’s turned off. Each individual module is factory programmed with its own unique serial code called GUID (Globally Unique Identification code). Once a receiver is programmed to a specific module (called binding) the receiver will only recognize that module ignoring signals from any other sources. And with over 4 billion possible GUID codes, it’s virtually impossible for a receiver to listen to anything other than its bound transmitter.
When the receiver is turned on, it scans the 2.4GHz band and searches for its specific transmitter’s encoded signal. When found, it locks in on that channel. If the signal is lost, the receiver goes into a hold mode, positioning the servo to a preset fail-safe position until the signal is reacquired. If the receiver is turned on before the transmitter, it will continuously scan the band until the encoded transmitter signal is present. During this period, the receiver drives the servos to the preset fail-safe position. All Direct Sequencing Spread Spectrum systems are required by the FCC to incorporate active collision avoidance, making it impossible for more than one transmission on a single frequency. BINDING

Each module has its own unique code (called GUID). The receiver must be programmed to a specific module so that the receiver will only recognize that module, ignoring signals from any other sources. This process called binding is push-button-easy and takes only about 30 seconds. During the binding process the servo fail-safe positions are also set. It’s necessary to bind the receiver to the module during first installation and is recommended when the receiver is moved from one model to another. Multiple receivers can be bound to a single transmitter module, common when using one transmitter to operate several models.

BOTTOM LINE

With Spektrum’s DSM system, you no longer have to worry about transmitters being turned-on on your frequency, or interference caused from noisy motors, speed controllers or other interfering sources. The receiver will only recognize its corresponding module and it’s virtually impossible for a receiver to listen to anything else! Plus the DSM system is telemetry-ready, and with optional telemetry modules the engine temperature, speed, rpm, signal strength, battery voltage etc. are displayed in real time via Spektrum’s handheld display or via a PC.

ENGINE TUNING GUIDE

- Supplied by Dave Burstow -

Dave Burstow © 2007

Despite lots of articles, I still see people struggling with engines on the flight line. Mostly this relates to bottom end settings of the low speed mixture screw rather than the main needle, so it may be worth a repeat of some of the basics as a step by step guide………........

We all know that the most important thing to a satisfactory flight is an engine that ticks over well, responds quickly to throttle, and doesn't stop until after you land! If all your engines do this you can stop reading now (smartass), if not, read on. Now, I don't claim to be any red hot engine expert, but I have learnt a few things that could help if you're getting problems. I have seen a lot of people (including many that I thought would know better) on the flight line having trouble with engines that can easily be made to run right. I should add that I am talking about common engine makes, 2 or 4 stroke glow, with a main needle and either an air bleed screw or a low speed mixture screw - anything much more outlandish and I'm lost too!

I don't want to cover the myriad of things that COULD lead to bad engine runs - this could fill a book, but remember that an engine, once tuned up, should need almost no adjustment. If it suddenly goes very off-colour, you should be looking for a non-tuning fault like a folded clunk tube, a gasket or bearing problem, the odd vital screw missing from the carburetor, air leaks, plug problems, blockages or duff fuel. Start with the recommended plug, fuel, prop and cooling for your engine, or none of the following is likely to give you a good state of tune.

You need to make sure you have a carburetor which is fully open at full throttle/full trim, and with an opening that is just fully closed with the throttle and trim closed With all of this and usually 2 -3 turns out on the main needle you should have an engine that will at least start, that will run up to full RPM and which can be leaned out.

This is where the fun starts. People will tell you that engines run straight out of the box, factory set. I haven’t seen many like this, and certainly none of the wide range of engines I have owned have behaved like this, or am I just unlucky?

Let's get a few things clear. We're talking here about mixture adjustment at the bottom end of the rev range. This governs some vital things like a stable tick over, instant throttle response and an engine that keeps going in the air when you throttle back. The two most common types of carb have an inset screw or knurled nut on the opposite side of the main needle, or an air bleed hole and spring screw on the front body of the carb. For the first type, screwing it IN will LEAN the mixture, and screwing it OUT will RICHEN the mixture. For the second type, the OPPOSITE applies. Air bleeds tend to be far less critical, but when you make adjustments on either don't move setting screws more than 1/4 turn at time, and remember where you started from.

REMEMBER - DO YOUR CARB ADJUSTMENTS FROM BEHIND THE PROP, TETHER THE PLANE FOR EXTENDED FIDDLING, AND DON’T HOG THE PEG!

If you have an engine that will run at tick over, start from here. If you have an engine that won't run at tick over or low revs, or is hopelessly out of adjustment, reset your starting points: For an air bleed, sight through the hole and adjust the screw so that half of it is filled. For a mixture screw type, hold the barrel hole closed against a modelling pin, connect a spare bit of fuel tube to the fuel inlet nipple on the carb, and, with main needle set normally (2-3 turns out), and throttle closed, adjust the screw until you can just blow down the tube and hear air escaping. Open the screw 1/4 to 1/2 turn from this point.

Start the engine at full trim, open up to full throttle, lean out the main needle to your satisfaction with the aircraft nose up, and back it off a couple of clicks. Let the engine warm up. Adjust trim to a sensible idle. Remember at this point that your ears will tell you most about what the engine is doing.

Once at idle:

* If the revs dropped off audibly when the glow was disconnected after starting, the bottom end is RICH, or;

* If the engine idles but gets progressively slower and slower and finally stops, the bottom end is RICH, or;

* If the engine stops abruptly when trimming back to idle, or shortly thereafter, the bottom end is LEAN.

By making adjustments to the bottom end mixture in small steps (!!with engine stopped!!) and checking as above, get the engine at least to the point where it can be trusted to idle without stopping. Let it idle for a full minute, then, (!!make sure the plane is secured!!) abruptly open up to full throttle.

* If the engine revs rise as fast as you can open the throttle with no cough, spit or fart then congratulations, you've cracked it. All you need to do now is recheck mixture on the main needle at full throttle (again lean out so it doesn’t sag nose up, then back off a couple of clicks), and fly.

* If the engine dies abruptly with little or no exhaust smoke, the bottom end is still LEAN.

* If the engine runs rough, coughs and dies but the exhaust smokes noticeably before doing so, the bottom end is still RICH.

* If the revs rise slowly and hesitantly, running very rough in the mid range with lots of exhaust smoke, the bottom end is RICH, but the engine is not too far off. Minor bottom end leaning is needed.

The next bit is easy but tedious. Since it is generally unwise and unsafe to fiddle with bottom end mixture screws when the engine is running, due to their proximity to the meat slicer, you will need to start and stop the engine several times, making small adjustments (quarter turn or less) each time and checking the effect on the engine against the above symptoms. You'll soon know if you're adjusting the screw in the right direction, if you're not things will simply get worse rather than better! Remember your starting point so you can go back to it, and continue to start, check, stop and adjust. Keep checking against the above criteria, and keep listening to what the engine is doing. When you are happy you have everything nearly how you want it, go back and check the main needle setting at full revs. This can be affected by what you have done to the bottom end, and you will need to make some final adjustments to both to come to a final balance between top and bottom needle settings. Note 2 strokes should be set a tad rich on the ground – they’ll lean out once in the air and further as the tank drops. For 4 strokes, the same applies, but it is more difficult to hear the revs peaking out. Use a rev counter, find peak revs, then back the needle off to drop the revs 300-500rpm – your engine will run well and last longer this way.

The ideal result of all of the above will be an engine that starts quickly and easily, responds immediately to throttle, idles cleanly and doesn't stop in the air. Some makes of engine are better than others, so don't try to reach perfection. You can try different fuel, prop and plug combinations, but my advice is, if continued fiddling doesn't give you the last 1% of a perfect engine run, stop fiddling and spend the time flying instead.

PROP POWER & MISC CALCULATOR

- Supplied by Tony Honor 2008 -

You will need Microsoft Excel installed on your PC to run this application

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FUEL MASS CALCULATOR

- Designed & Supplied by Tony Honor 2008 -

You will need Microsoft Excel installed on your PC to run this application

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