Internet Rumors, Updates, and Evil Spammers

By Keith Hollifield

Internet Rumors - Keep in mind as you are browsing the internet forums that there are no filters or editors to separate the facts from uninformed or agenda driven rumor. There have been a couple of high-profile crashes recently where 2.4ghz radio systems were blamed by persons witnessing the event. In each case I will discuss here the actual cause was traced to something completely different and in one case the aircraft did not even have a 2.4ghz radio system installed.

Crash 1 - A large aerobatic plane being flown by a world champion pilot went into what appeared to be a lockout during a noon demo at a large event. This plane was using a 2.4ghz radio and a lockout did occur but it had nothing to do with the radio link. This was confirmed by a data logger onboard the aircraft and the problem was duplicated on the ground after the crash. The aircraft used SEVERAL high-power digital servos. The battery system used a regulator that was later found to be inadequate for the power demand during aggressive flight. During this particular flight the voltage dropped below 4 volts. This cause the receiver to momentarily power down. During the boot-up sequence it went into fail-safe while seeking the transmitter. Unfortunately it did not link with the transmitter in time to prevent impact.

Crash 2 - A world class scale jet was being flown in competition. During a "dirty pass" the plane went into what appeared to be lockout and flew into the ground. This aircraft also used several high-power digital servos and had recently been upgraded with even more powerful servos than originally installed. The cause of this crash was identical to the aerobatic plane. When all of the drag inducing items (Gear, flaps, etc) were deployed and the aicraft entered a turn the voltage dropped and the receiver rebooted.

Crash 3 - A high-end sport jet crashed in spectacular fashion at one of the premier modelers gatherings. Initial reports posted online stated that it was a 2.4ghz radio. Pictures, HD video and the owner all confirm that it was a 72mhz PCM system. The cause is suspected to be someone turning on a radio on the same channel. The irony here is that the owner had a 2.4ghz system for this aircraft but did not have time to install it prior to the event. Had he done that it is likely that the plane would not have been lost.

What we can learn from this - If you are flying 2.4ghz and using high-power servos make absolutely sure that your power supply can sustain at least 4.5 volts to the receiver during all flight conditions. Even a momentary drop below the minimum voltage can cause the receiver to reboot. A typical reboot takes 2-5 seconds and most aircraft will not remain in the air that long. This also happens to FM and PCM systems but the reboot is so fast that it either goes unnoticed or we chalk it up to a momentary glitch.

Internet Update - Many of you have noted that our online store is still not going. Here's the scoop. It is simply unmangeable to make all of our 11,500 products available and keep a real time inventory. The current plan is to pick a few hundred of the most popular products and make them available for online purchase. I hope to have the products selected and listed later this year. You can always call 859-402-2277 and we'll be happy to ship anything in our stock.

Evil Spammers - Our forum has been discontinued due to spam activity. I tried several things to reduce this but the problem just kept growing. I just don't get why these characters think it is beneficial to join using a pornographic name and try to post links to their junk. We may try again at a later date.

UPDATE 6/14/2007 - Testing Procedures for 2.4ghz Radio Systems - Horizon Hobby

Receiver Power System Requirements

With all radio installations it is vital the onboard power system provides adequate power of 4 volts or more without interruption to the receiver even when the system is fully loaded (servos at maximum flight loads). This becomes especially critical with giant scale models that utilize multiple high torque/ high current servos. Inadequate power systems that are unable to provide the necessary minimum voltage to the receiver during flight loads have become the number one cause of in flight failures. Some of the power system components that affect the ability to properly deliver adequate power include: the selected receiver battery pack (number of cells, capacity, cell type, state of charge), switch harness, battery leads, regulator (if used), power bus (if used).

While Spektrum’s receivers’ minimum operational voltage is 3.5 volts, it is highly recommended the system be tested per the guidelines below to a minimum acceptable voltage of 4.8 volts during ground testing. This will provide head room to compensate for battery discharging or if the actual flight loads are greater than the ground test loads.

Recommended power system guidelines:

1. When setting up large or complex aircraft with multiple high torque servos, it’s highly recommend a current and volt meter (Hangar 9 HAN172) be used. Plug the volt meter in an open channel port in the receiver and with the system on, load the control surfaces (apply pressure with your hand) while monitoring the voltage at the receiver. The voltage should remain above 4 volts even when all servos are heavily loaded.

2. With the current meter inline with the receiver battery lead, load the control surfaces (apply pressure with your hand) while monitoring the current. The maximum continuous recommended current for a single heavy duty servo/battery lead is three amps while short duration current spikes of up to five amps is acceptable. Consequently if your system draws more than three amps continuous or five amps for short durations, a single battery pack with a single switch harness plugged into the receiver for power will be inadequate. It will be necessary to use multiple packs with multiple switches and multiple leads plugged into the receiver.

3. If using a regulator it’s important the above tests be done for an extended period of 5 minutes. When current passes through a regulator heat is generated and this heat causes the regulator to increase resistance which in turn causes even more heat to build up (thermal runaway). While a regulator may provide adequate power for a short duration it’s important to test its ability over time as the regulator may not be able to maintain voltage at significant power levels.

4. For really large aircraft or complex models (35% and larger or jets) multiple battery packs with multiple switch harnesses are necessary or in many cases one of the commercially available power boxes/ busses is recommended. No matter what power systems you choose always carry out test #1 above making sure that the receiver is constantly provided with 4 volts or more under all conditions.

5. The latest generation of Nickel Metal Hydride batteries incorporate a new chemistry mandated to be more environmentally friendly. These batteries when charged with peak detection fast chargers have tendencies to false peak (not fully charge) repeatedly. These include all brands of NiMh batteries. If using NiMh packs be especially cautious when charging making absolutely sure that the battery is fully charged.  It is recommended to use a charger that can display total charge current. Note the number of mAh put into a discharged pack to verify it has been charged to capacity.

'til next time....

Shaking Off The Rust

By Keith Hollifield

Winter is breathing its last gasp. Spring rain is just around the corner. Are you ready to get those airplanes and helicopters out again?

Many of you have new projects that will need to be maidened. Almost all of us have had a major reduction in our flying hours over the last few months. These are a few tips that can make the return to regular flying successful.

1) Check your batteries - All batteries that have been out of regular use need to be checked. The best way to do this is cycle them (Charge then Discharge) on a good charger with a digital readout for capacity. The capacity should be at least 80% of the rated capacity at a 2C discharge. If you don't have a charger capable of this ask around. There are plenty of us that have them. If you would like to get one for yourself I recommend the Hyperion line of chargers. They range from $64.99 to $169.99 and the basic one will handle most flyers' needs.

2) Tune her up - If you have a nitro engine hopefully you put after-run oil in the engine when you put it away. If not, make sure the engine is not gummed up from sitting. I have successfully loosened engines by working nitro fuel into the crankcase and around the piston. Once the engine is turning freely check the glow plug. Is it blackened? If so, put in a new plug and pick up a couple of spares. If you have a four-stroke engine now is the time to check valve clearance. Your instruction manual should outline this process. Give the engine a good visual inspection looking for any cracks or other areas that could cause an air leak.

3) Control is key - Check all of your control surfaces. These tend to get knocked around in the shop and during transport. Make sure all of your hinges are secure. Control horns should be firmly attached with minimal slop. Replace any part that does not look right. CA Hinges can be replaced if necessary by cutting the old ones and installing new ones slightly to the side of the old position. Helicopter pilots should check all ball links for excessive play. Replace any that have noticeable slop.

4) Radio system check - Do a good range check on your radio. Have a helper change the position of the model so that your receiver and radio are tested from every angle. Check all servos for damaged gears by applying a little pressure on the servo horn and moving the servo through its range of travel. If you feel any notchiness or if the motor spins freely at any point you have a bad gear. Replace it before you fly. Check the slop in your servos by moving the servo horn back and forth. A well designed new servo has virtually no slop.

5) Connections - Check all wire connections for servos, batteries and switches. EVerything should be free of corrosion and securly connected. Make sure any servos connected through an extension have some sort of mechanical lock that keeps them from separating. You can use fishing line tied to either side of the connector for a cheap solution. If you want something a little easier get the safety clip from Parsons Products. Check your swtiches for positive on-off action. If the switch slides easily with little to no locking action then it is time for a new one.

6) Airframe - Check the overall condition of your airframe. Are the wheels / Gear worn? Is the engine securely fastened to the mount. Do the wings/rotors have excessive movement? Is everything inside still where it is supposed to be? Are the servo mounts secure? Reglue anything questionable.

7) Fuel system - Check your fuel tank for any abnormalities and signs of leaking. Make sure all the fuel tubing is in good condition. Now is a good time to replace your fuel filters.

8) Field box - You won't get much flying done if your support equipment fails. Check your field box battery. Make sure your glow ignitor has plenty of juice. Do you have plenty of spare props/rotors? Does your fuel pump still work?

9) Sim Time - One of the best ways to get your mind ready to fly again is using a simulator. Just a little bit of time on the sim can reacquaint your hands and eyes with the controls. It is a lot cheaper and quicker to work out the bugs with a virtual aircraft. My favorite sim is Realflight G4 from Great Planes. If you haven't flown a sim come by the shop and check out our demo.

10) Have a plan - Whether it is your first flight ever or just another entry for the log book the best way to have a successful flight is to plan for one. Think of or even write out some goals for the flight. For a maiden flight I often have a very short plan of takeoff, trim, left turns, right turns, slow pass, land. Keeping the first flight simple and short allows me to set up the plane for further testing, change any control movements that I didn't like and inspect the plane for any vibration induced failure before putting it at risk during a high performance maneuver. For successive flights I will begin to test vertical climb ability, aerobatic maneuvers, top speed and any extra controls such as landing gear.

Good luck and fly safely.

'til next time...