This web site is designed for 800 x 600 screens with 16 bit resolutions.
It's best viewed with
Click Here To Start.
Tips by the Radio Control Flying Club of Toronto
|This area is dedicate to groups and individuals who have contributed articles to this website. Please feel free to contribute! THANKS
- Taming the Stall
- Loaded Digital Voltmeter Adapter
- Color Schemes for Better Visibility
- Buying Used Equipment
- What Adhesive to Use what for Maximum Strength
TAMING THE STALL
.or got lost somewhere on my desk )
We've gone on a bit about what a stall is, and some techniques to prevent stalling our planes when we don't want to. Now we'll look at how we can tame a planes stall characteristics somewhat. But first, we need to look at how different wings stall. In general, as angle of attack (AOA) is increased, a straight wing, like on most trainers, will first start to stall inboard, at the wing root near the fuselage. And that's good. Although there is a loss of lift, all the messed up airflow is near the
root, and the tips are still flying, meaning we also have aileron control out there where it's most effective. So we get a nose drop, but the plane stays reasonably level and we don't lose control. But tapered wings are more efficient, and we'll see them on most higher performance planes. And the more highly tapered the wings are, the more likely they will stall first out at the wing TIPS. Stalls on such planes are very different; when a wing stalls first at the tips, a wing drops, you have no
aileron control, and a simple stall instantly becomes a snap roll. Your first indication of a stall is when the plane flips onto its back, out of control! Summarizing, we can see that if the stall begins out at the wingtips, we'll see a wing drop (often violently). But if the stall begins at the wing root, all we get is a nose drop, with the plane still under some control. What we'd prefer should be pretty obvious! So what's the answer? How do we make a plane do its stalling properly, in at the
wing root? Washout is one answer. This is best done during the building stage, and involves "twisting" each wing during construction so that the tips "fly" at a slightly lower angle of attack than at the root, near the fuselage. Normally only a matter of about 2 degrees difference, the lower AOA at the tips mean that the root will always stall first. Many kits, even for straight winged planes, include washout in construction - as the wing is laid out on the building board,
the trailing edge is set up higher out near the tip of the wing, giving you washout when the wing is complete. Another way to accomplish the same thing is to use a different airfoil out near the wingtips; one that naturally stalls at a higher angle of attack than the airfoil at the root. This is very easily accomplished when cutting a foam wing, but is seldom seen in built-up construction. "NASA droops" will do this also, and could be added to an existing wing. The NASA droop is a
leading edge "anti-stall" modification, usually applied to the outer 35-40% of a wing. The easiest method to modify an existing plane to cure nasty stalling habits is the use of stall strips. Applied to the inner 20-25% of the wing, the stall strip is a small change to the leading edge that produces turbulence to that part of the wing at higher angles of attack, causing the stall to begin at the root. (see fig) Thus we will have a slightly higher stall speed, but the stall will at
least be manageable. Plus - the beauty of the stall strips is that you can just pin them on and experiment till you get the effect you want, then make them permanent! So if you have a vicious stalling plane on your hands, don't just try to cope till you crash it - add some droops or stall strips - let the plane age gracefully, THEN crash it!
LOADED DIGITAL VOLTMETER ADAPTER
Reviewed by: Clifford "Red" Scholefield - Gainesville, FL, USA
Expanded scale loaded voltmeters have become the accepted means of field checking a receiver battery pack to see if it has the capacity for another flight. The meters that are available for $10 to $15 are all of the analog variety and of limited use other than for what they were developed. With the dramatic drop in price of digital multimeters, many R/C modelers consider them to be "necessary" support equipment. These meters have an extremely high impedance (resistance) and therefore
display what is essentially the open circuit voltage of the battery pack. The open circuit voltage of a Ni-Cd battery pack reveals very little regarding the state of charge of the pack. For this reason, the expanded scale voltmeter with a built in load is the recommended way of checking the status of the pack. Even this is not ideal since the discharge curve of Ni-Cd batteries is very flat. A better method of checking a Ni-Cd battery pack is with a "loaded" digital voltmeter with an
inherent higher resolution. The problem with using a loaded digital voltmeter is that no one makes such a device. This should not be a deterrent to modeler. The construction starts with two pin jacks to match the leads or probes on the digital multimeter; one red for the positive lead and a black for the negative lead. A resistor of the appropriate value could be used but that is kind of boring since it just lies there and resists. A brighter idea is a light bulb, which clearly shows it is
providing a load for the battery. After careful experimentation, a # 44 bulb (6.3V-250mA) was found to load the pack with 220 mA. This is fairly close to the load imposed by the R/C system. If a higher load is needed, either a PR12 or PR13 bulb provides a drain of about a 500 mA. A normal battery pack should be able to sustain 500mA for an hour. The bulb can be used to roughly check the battery pack capacity. When the bulb dims significantly, the battery pack is near the end of the charge. A
connector will be needed that will mate with the charge plug on the model. Finally, some type of enclosure will be needed to house the components and assembly may begin. A small plastic box about the size of a small matchbox will make a neat compact unit. It is nice if the box is clear or at least translucent so the bulb can be seen as it lights when the battery is loaded. Otherwise, the integrity of the box must be compromised by adding another hole in addition to the three needed for the jacks
and battery lead. One of the leads can be soldered directly to the tip of the light bulb base. Attaching to the side of the bulb base may cause a problem because the material may not accept solder. A small brass clamp can be made from 1/32" thick stock by 3/16" wide and secured to the bulb with #2 hardware while leaving a small section to which the lead is soldered. The clamp can be made so that it can be soldered directly to one of the jacks providing a secure mount for the bulb. All
that is required now is to plug the meter into the red and black jacks on the load box and the battery lead into the battery connector on the plane. If the loaded digital meter indicates 4.8 volts or greater, it has sufficient charge for additional usage. If it indicates less than 4.5 volts, it is dangerously low and should not be used. The use of a battery pack with a reading below 4.8 volts is marginal and is dependent on the equipment, number of servos, activity of the servos, and other
factors. Before being used at this level, the capacity should be checked. On a day when the equipment is not being used, it should be allowed to discharge until the meter reads 4.6 volts. Then the system should be turned on and ground checked every 5 to 10 minutes. The servos should be actuated to determine how long it takes before they start to twitch. This will give a rough calibration as to the meter reading that should indicate the bottom limit for use.
COLOR SCHEMES FOR BETTER VISIBILITY
(more beginners notes and possible refresher)
By Ken Blackwell
Color schemes and patterns are very personal. However, there are a few fundamentals that should be considered when designing your color layout for your airplane. You want to make your model as visible as possible considering adverse visibility conditions. Before you design your layout, look at what others are flying to determine if you can see the airplane
attitude under a wide range of visibility conditions. You have to be able to see it to be able to control it! The following are some characteristics that have been proven.
(1) There should be a large pattern contrast between wing top to bottom. For example 2 or 3 large span wise bars or strips on the top contrasted by a big check (4-6 boxes per wing panel) will do the job. Small patterns will fade into a blur at the distance we fly.
(2) Large white or yellow wing tips on the topside show up really well making the top of the wing highly visible. It almost looks like a neon sign flashing in a turn/roll at the end of the field.
(3) White or yellow wing and stab leading edges show up much better on approach to landing and make it much easier to judge attitude on approach to landing.
(4) A white or yellow band (about 3") down the side of the fuselage helps in determining attitude when flying wing-level, making it much easier to determine whether the airplane is climbing or diving..
(5) Colors should be sharply contrasting such as white or yellow against insignia blue, missile red, or dark green. Most airplanes use either white or yellow as their light color. Look to see which is most visible to you. Also, remember that under many lighting conditions colors change to monochrome or dark Vs light. At large distances and
under low light conditions the eye can no longer distinguish colors. Two colors that really look neat together at 20 paces may turn into a stealth airplane at flying distances. Small patterns with non-contrasting colors may cause you to be unable to tell up from down under poor visibility conditions. Finally do it your way but remember, if you cant see it you certainly cant fly it and may be headed for premature re-kiting.
Buying Used Equipment
by Bryan Jones:
[from The Flightline, Pearland TX, Bryan Jones, editor.]
Seemed like an appropriate article to include as swap shop season resumes.:p>
Have you ever been presented with a deal too good to be true? Sometimes they are good deals, other times... well. One thing we have in our benefit living in the Houston area is a very large group of RC airplane flyers. There are several outlets for buying and trading model airplanes and their
related accessories. Regardless of where you go to find the used equipment you desire, there are a few tips I have learned you may want to consider.
Airframes These are the easiest items to inspect. The first and easiest items to check is the covering or paint. Having a well-applied and thoroughly sealed covering or coating is important in keeping oil and other materials from the underlying wood or fiberglass. Water or oil soaked structures
will eventually weaken and fail. Look in the engine compartment
for the sealing I have mentioned. Exposed wood is easy to spot. Another area critical to an airplane's structural integrity is the wing saddle and attachment structure. Look here for cracks or evidence of previous repairs. Generally, any joint having been repaired will be weaker than originally constructed. If the joint shows sign of repair, this indicates design or crash damage. Assume it is crash damage and inspect the tail feathers and other exposed inner surfaces in the fuselage.
Wings are a little more of a mystery than the fuselage. Without breaking the wing, place it over your knee and apply bending pressure. Listen for cracking noises (Stop then!). Look for splinters falling out any openings. Check control surface tightness and proper operation. Look for wing tip damage. Wing tip damage comes in two forms: first, the underside scrapes
caused from ground loops and hard landings. Second the crunching effect on the end of the wing tip caused by cartwheels. Cartwheels will trash a model quicker than almost anything.
Engines Purchasing a used engine is not quite as easy as purchasing an empty airframe. The first item of concern is external damage. Look for dirt, particularly that packed in between the forward cooling fins or around the carburetor. This is a pretty
good indicator of a crash. Don't forget looking for the broken cooling fins and bent needle valves. Once you have checked the engine externally, look at the cylinder head. Assure all head bolts are present. Check the crankshaft. Look for damaged threads.
One thing I strongly recommend is checking the shaft for run out with a dial indicator or similar instrument. I wouldn't accept any more than 0.002" TIR (total indicated run out) on .60 and smaller engines; 0.003" TIR on all others. Bear in mind, this measurement should be weighed in relation to the rest of the engine and these run out measurements are pretty high.
Look into the exhaust port on the cylinder. If the muffler is attached, remove it. Slowly turn over the engine while feeling the condition of the bearings and the piston/cylinder liner fit. Look down the port at the piston and the liner. Look for gouging and excessive scraping or scratches. Feel the engine as it is turned over. Notice any grinding or gritty feel in the bearings. Try and find out if the engine has ball bearings or sleeve bearings
on the shaft. A ball bearing engine (with good bearings) is more valuable.
Hang onto that dial indicator we used earlier and set it up to check shaft looseness. When you get the indicator set up, pull the shaft in the opposite direction than it is being pulled when you set up the indicator. On engines 60 or smaller, 0.001" to 0.002" is reasonable. Larger engines can withstand 0.003" to 0.005" looseness.
Finally, check the thrust on the shaft. While holding the engine in one hand, push and pull the shaft while turning it. Note any noises or unusual feels such as metal on metal rubbing or gritty feel. This is not particularly a problem in the inactive or reverse thrust direction, but may be a real problem indicator in the active or normal thrust direction.
I have purposely skipped the four-cycle engines for a couple of reasons. First, this subject deserved more space than available and second, I would have to research the issue more before writing.
Radio Gear This is a more challenging area than the previous two. Bear in mind the consequences of a complete radio failure... not pretty. Keep this in mind when you are about to make that killer deal. I have a few easy items to look for when buying used radio gear. These items typically do not
indicate the actual condition of the internals but are a very representative indicator.
First, the general external appearance of the transmitter, receiver, and servos are important. Look for dirt, glue, or fuel residue. None are good. Even more important, check the switch harness from one end to another if you must use a used item. I don't recommend it. I only use switches I have purchased new. One failed switch or switch lead and the game is over.
The external condition of the transmitter is a good indicator of how the entire system was treated by its previous owner. Check the bottom and back of the transmitter case for excessive scratches. This indicates the amount of use the system has had. Less scratches, less use, good, good. Check the feel of the gimbals. Smooth and tight. Check the trim switches and auxiliary switches. Extend the antenna, checking for bends or damage. Turn on the
transmitter and check the output/power needle response. Obviously the batteries may be dead or undercharged.
Look at the receiver antenna. Is it in good shape? A kinked or stressed antenna indicates rough use and possible damage. Look for cracks in the case. Check for narrow band certification. Check for bent pins in the open sockets.
The servos are the least important items, but don't forget, it only takes one well-placed servo failure to wreck your plane. First, check the outward appearance. The leads are important as well. Look to see if the wires are damaged where they are attached to the plug. Look for plug damage.
CAREFULLY check the gear train by rotating the servo head. If you strip the servo, you may have to buy a wrecked servo. Don't do this step if you don't feel sure of what you are doing. If you do, feel and listen for broken gear teeth.
Flight battery pack -- be very careful. I wouldn't recommend using a flight pack if you don't have a cycler/charger to verify the capacity and health of the battery. Don't forget to look at the lead. It's just as important as the battery switch.
Finally, connect the components of the system and operate with the transmitter. Check each channel individually, check dual rates, check programmability (if applicable), check servo response (noise, chatter, dragging, speed, etc.).
If possible, perform a range check -- collapsed antenna at 200 feet minimum fully operational. These are just a few items to keep in mind when purchasing used equipment. Even if everything checked out as described here, there is a possibility that the equipment was near breaking down or someone was trying to sell away a hidden problem.