Tips and Ideas

Engine Settings

How to MonoKote

Aircraft Balancing

About Adhesives

Three Rules for Longer Lived Li-Po Batteries

Trimming an Airplane

Engine Settings

Why do Engines Lean Out and Quit?
1) The high-speed needle valve is too lean.
2) The muffler pressure line came off.
3) The fuel filter has opened up (the halves are loose).
4) There s a split in the fuel line, usually at the fuel tank.
5) The fuel tank is foaming, causing air bubbles in the fuel line.

Setting a slow, reliable idle
A month seldom goes by in which I don't receive letters from readers experiencing idle problems. As this seems to be a common problem, let s take a look at setting up an engine's idle. It isn't really all that difficult. To start with, many idle problems with non-pump equipped engines can often be traced to an improperly positioned fuel tank or a fuel tank that is too far from the engine. The centerline of the fuel tank should never be any higher than the centerline of the fuel jet and preferably 1/4 to 3/8 inches below. This helps decrease the siphoning action with a full tank of fuel. The make of the glow plug also plays an important role. Any older design, cross-flow scavenged (ported) two stroke engine should use an idle bar glow plug. Most of the newer Schnuerle ported two-stroke engines do not require an idle bar plug, but if idle problems are experienced, an idle bar plug should be used. If you aren't sure whether the engine is cross-flow or Schnuerle ported, just look into the exhaust. If there is a baffle on the far side of the piston, the engine is cross flow ported. If there is no baffle, it is Schnuerle ported. Some engines do have better idle characteristics than others due to differences in porting, timing, and compression ratio, When it comes to the actual adjustment, there are two basic methods. The first is to start with the fuel tank half full and the idle speed set in the 2,500 - 2,700 rpm range. This is where a good tachometer comes in handy and is something every toolbox should contain, not just for setting idle speed but for proper richening of the top end as well. Then, use the pinch test (i.e. pinch the fuel line). If the engine dies immediately, the idle mixture is too lean and needs to be opened in 1/8-inch increments. If the engine speeds up and the idle improves, the mixture is too rich and the adjustment should be turned in or leaned. If the engine is enclosed and the fuel line to the carburetor is not easily accessible, with a tricycle gear ship, lower the tail. If the engine dies immediately, the mixture is too lean. If the idle improves, the mixture is too rich. Remember to always make any idle mixture adjustments in 1/8--turn increments not one or two turns at a time.

With a tail-dragger, make the mixture adjustments with the tail raised to a level position, being careful not to go so high as to have the propeller hit the ground. Then, lower the tail following the same procedure as with the tricycle gear model. For the final check, accelerate the engine to full throttle. If it slows and sags and has a weak sound, the mixture is too lean and needs richening. If the engine sputters and spits out a lot of smoke, the mixture is too rich and should be leaned. After a satisfactory idle and acceleration have been established, you can try lowering the idle speed to the point where the engine will remain idleing for a prolonged period with good acceleration to full throttle. Again, the idle speed should be set with a tachometer and not by ear. Many cases of an engine dying at idle are simply because of pilots who try to idle the engine too slow. It is nice to watch an engine tick over at 1,800 rpm, but an idle speed in the 2,200 - 2,500 rpm range is more practical and reliable. Also remember, the heavier the propeller and the larger the diameter, the better the flywheel action. Increased flywheel action is always beneficial to a slow and reliable idle.

From Prop Talk
Riverside Radio Control Club
Jim Bronowski, editor
Riverside CA

The Zen of MonoKoting by Joe May

Having crashed and restored my trainer several times, I have some experience covering repairs with MonoKote. Through trial and error, using this iron-on film became easier. Iron on film has a straightforward character about it, and it's fairly predictable. With a little experience, you'll be able to tell where to pull and stretch it and where to shrink it before you seal it. To guarantee successful covering, remember these three important things:
1. If this is your first time covering, PRACTICE on something you won't mind RUINING. Get a scrap piece of balsa and cover it. Cover a solid piece and then a build a simple frame and cover that.
2. DON'T RUSH. DON'T SKIMP. Let the heat, not the pressure of the iron, do the work.
The first thing is a good lesson. The second thing is self explanatory. The third thing is what I want to cover, so to speak.

High Heat Tendencies (300 degrees F. )

Every imperfection in the structure will be magnified when you cover over it.
The film will shrink quickly - probably causing lightweight structures to warp.
The film will stick to new wood with a vengeance, so much so that if you try to pull it off, you pull chunks of wood off with it. Now you must use filler and sand the surface smooth again otherwise your covering job will be wasted.
The film will bond to itself permanently and if you try to pull it apart, you ruin it. Throw it away.
When you pull the film and press it with an iron, you'll seal it to the surface immediately and probably with permanent ironed-in wrinkles.
The film may suck into the grain of the wood as you seal it thus showing the grain through the MonoKote. Sand the surfaces so they look and feel polished before you cover.
If you hold a heat gun too close, too long, you'll burn a hole in the film. I have not actually set the airframe on fire - but close to it.
The film will stretch more if you pull it harder. The harder you pull it the more likely it will permanently wrinkle when you put the iron on it.
When you seal along seams or joints some of the adhesive may squeeze out. If you are using a sock on your iron it will get stained, and if you don't use a sock the adhesive gets on the bottom of your iron and won't come off until you use the iron on a different color MonoKote. Then it permanently transfers to the new color. Acetone may get it off if your iron wasn't too hot.
The film will probably wrinkle later even though it looked great when you finished. It can be tightened, or melted, with a heat gun.

Lower Heat Tendencies (200 - 225 degrees F.):

The film shrinks more gradually, and it doesn't adhere permanently, quickly, usually.
You'll be able to smooth it over solid surfaces easier, and it won't bubble or wrinkle as much.
Trim strips are easier though, because with the lower heat, you get a second chance at repositioning them if you didn't get it right.

Other Characteristics:

You can stretch iron-on film without heat, enabling you to tack it into place and smooth out wrinkles before you seal or shrink it.
It's made of plastic and can be easily scratched, especially with paper towels. Use your wife's best linen napkins to properly clean it.
If you press too hard with the iron, you'll dent the surface below the covering. It will show through and you will be mad.
If you remove the backing sheet, and the adhesive sides touch, you'll damage it trying to pull it apart.
Throw it away. Don't be a cheapskate.
MonoKote sticks to the backing film very firmly, but almost never permanently.
MonoKote dulls razor blades, knives and scissors very quickly. Change often to keep your lines crisp and reduce tearing.
Even though the film is hot it can still slip off the structure being covered. It will then land in a sawdust pile on the floor, no matter where that pile is. It will not clean up, throw it away. (Hold it in place for a few seconds as it sets up.)
The color from roll to roll may not match perfectly, especially under fluorescent lights in the hobby shop. Take a few rolls to the nearest window and make sure they match. Then they probably won't match when you get them home.
MonoKote will go over MonoKote without bubbling.

Tips for Balancing a New Airplane

Here s a neat idea for balancing your new airplane in all directions at once. A model airplane has one point of balance where the wings center of gravity (CG) and the fuselage centerline intersect. That's where the secret lies, and here is how you can use that point to get a perfect balance for your new airplane. When you build the wing, install a light plywood block at this intersection (your plans will show the recommended CG). For a high-wing model, the block should be installed on the top of the wing. On a low wing model, the block should be installed on the bottom of the wing. Mark the center of the CG on the block and leave the wing uncovered so any unnecessary weight can be added for lateral balance. When you are ready to balance, install a small screw eye into the block and hang the assembled airplane from the eyebolt. Fasten sufficient (use as little as possible) weight to the main spar of the wing to achieve lateral balance. Now, move the battery, receiver, or weight as required to attain proper balance, from front to back. This simple system will result in an accurately balanced model.

From The Cam Journal
Central Arizona Modelers Inc.
Marvin Hinton, editor
Sedona AZ

Using Adhesives by Steve Trackwell

What brand you use is like Ford or Chevrolet, it's up to you. Remember they are anaerobic adhesives and set in the absence of air. Thin CA's are best for general assembly of balsa and light ply, woods that readily absorb the glue. Hardwoods and hi-density plywood do not bond well with CA's. The glue sets before it penetrates the fibers of the wood. Thin CA's also rely on a good fit of the parts being glued - no gaps.
Thick or medium CA's work best when you need to fill a gap in the joint you are gluing. They also work well to strengthen a joint by applying a second coat to form a smooth fillet of glue. Remember to store your CA's in the fridge (not the freezer) and allow them to warm to room temperature before using. If yo use a Kicker to speed the setting of CA's, allow the glue to wick into the wood before spraying the accelerator. Keep your kicker and CA' separate in your building area as fumes from the Kicker can migrate to the glue. Then you get to make a quick trip to the hobby store. Don't use CA's to bond sheet stock together when sheeting wings. it is much harder than the balsa and almost impossible to get the ridge of glue out when you sand. CA's bond our skin very well and plastic surgeons love the stuff. If you get CA in your eyes, get medical attention.

Always use an epoxy with a minimum of one hour cure time. Longer times work best in high strength areas. The longer the glue has to penetrate the wood fibers the stronger the joint. Three and five minute epoxies should be reserved to loan to your neighbor when they need a favor (they set too quickly). Always store your epoxies at room temperature. If your workshop is heated only when you are in it, take them with you back to a warm environment. Avoid freezing. If your epoxy gets cold, warm in it a tepid bath of water, never use a microwave to heat epoxy. Follow the manufacturers instruction, and mix equal amounts or ratios, depending on the type of epoxy you are using. Some epoxies are mixed by weight not volume. Thin epoxies only after they have been thoroughly mixed. Remember that epoxy cures by a chemical reaction with heat as a by product. Heat speeds the curing process. So, if you are mixing a large amount of epoxy, mix it in a wide shallow tub and less heat will be generated. Thin epoxy with Denatured Alcohol. If you have money to waste, buy Reagent Grade Isopropyl Alcohol. It's the purist you can buy, but save the money for that special engine you want or an extra servo or two.

Safety First: Both CA's and Epoxy should be used with adequate ventilation. Some of us are allergic to the stuff they put in these products. Non-sterile exam gloves are really cheap at Costco, just peal them off and pitch them in the garbage. Finger cots can be purchased at your local drugstore. Paper dust masks do not offer ANY protection from the fumes given off by these products.

3 Simple Rules for Li-po Safety

I've puffed, exploded, deadened, shorted, crashed, smeared, and punctured many a li-po pack, but I've seen actual flames very few times. I'm extremely black-and-white about all aspects of li-pos. There are the accepted practices when charging, discharging and storage - and then there are any other ways to perform the same -period. The accepted practices will yield a full and happy pack life (over 600 cycles from some brands), and any deviation will result in reduced life at best, and a 2,000 degree unstoppable torch in your living room or vehicle at worst.

I generally don't like broad generalizations, especially when educating hobbyists, but this is one area that I use them. When we compare NiMH/NiCad packs and li-po packs, I lump them under the same umbrella: When abused enough, both can explosively vent. Now with the thousands upon thousands of hobby enthusiasts I've interacted with since the beginnings of electric flight, those that have experienced that explosive venting with "round cells" are extremely few, while those that have experienced it to one degree or another with li-pos are a far greater number.  So are Li-pos more dangerous? I don't consider them to be, no. But they do have more than one "rule" to keep them happy. With round cells, they will only explosively vent if they are charged at a fairly high rate well beyond their capacity. This may happen either through charger error or negligence. But simply put, adherence to this one and only one rule will guarantee it will never happen to you. Adherence to all three of my li-po rules will similarly guarantee that explosive venting/flames/puffing or anything at all dangerous or pack life degrading will not happen.
So what are the "3 rules of li-pos"?

Rule #1: Never, under any circumstances, allow the voltage to fall below 3.0v per cell.
Under any circumstances means exactly that - any circumstances at all. Including: while under a heavy discharge load, resting (no load at all), or a very tiny discharge load. Never below 3.0v per cell under any circumstances.
A good ESC with the proper and accurate cutoff voltage configurable to 3.0v/cell under any/all discharge conditions is imperative to have. Several li-po brands (the smart ones) have started to not warranty packs if they were used with an ESC with either no LVC (low voltage cutoff) or an LVC setting anywhere below 3.0v/ cell.

Rule #2: Never allow the pack to get over 140 deg F.
Just as above, each and every foray above this temperature has a cumulative effect of degrading both output performance and cycle life. The longer it stays hotter, and the more times you get it hotter, the worse it will get, with the results the same as above.

Rule #3: Always store the pack at 1/2 charge when it won't be used for an extended amount of time.
This is a fairly new one. Li-pos simply haven't been around long enough to fall into inactive hands for extended periods of time! I don't know the "whys" or "hows" involved, but a pack stored (more than a month or two) at full charge, over time will lose capacity and discharge capability and eventually it will "puff" and be useless. So if you think it may be a month or two before you fly a pack again, discharge half the capacity of a full pack or charge up a spent pack and then discharge down to half capacity for storage.

So there you have it - 3 simple rules for a long and happy cycle life with your li-pos. If you follow them, I feel li-pos are no more dangerous than any other electron storage device (ie. battery).
But what happens when the rules are broken, or more importantly: When exactly is the user at risk of an explosion and fire from a Li-po pack?

There are three instances a li-po will explosively vent and potentially involve flames:
1. A serious impact or similar physical damage to the pack when it is fairly charged (bad crash, puncture, damage to the silver envelope and etc.)
A damaged pack should be destroyed (soaked in saltwater) as soon as possible, and if necessary, stored outside in a safe place should it catch fire until it can be destroyed.
2. Direct short.
A sustained direct short can cause explosive venting and flames almost immediately. Even a very tiny amount of time (1/100th of a second) spent in a shorted condition can reduce lifespan and output capability significantly, if not outright destroy the pack. Keep this in mind when you solder connectors on new li-po packs! Even a tiny short from one wire brushing another can have large effects.
3. Charger error, charger user error, or most commonly: charging a damaged pack.
Contrary to the above, where you pretty much know you're in immediate danger from a damaged/shorted pack - this is where most of the li-po paranoia and fires come from. "I had just put it on to charge 10 minutes before, and all of a sudden it's puffing up and starting to shoot flames for no reason". I've heard that quite a few times. They want to blame the pack and, they want to blame the charger, want to blame the power supply, to blame everything and except who actually is to blame - themselves.

Charger errors are still very possible in this day of almost everything being automatic. li-pos are even more volatile to being at over 4.2v/cell as they are being under 3.0v/cell. It doesn't take but 10 minutes when charged at the next cell up rate to cause a catastrophic pack failure. I recommend folks to not charge li-pos unattended (as in in the garage when you are inside the house doing something else). I charge here at my desk at work with the charger and pack in my view as I work on my computer, or at home beside my desk/workbenches when I'm sitting at them only. Mostly because due to testing, we have a lot of packs very near the end of their lives due to over-discharging, or simply cycle life, and I know the only time they are subject to bad things happening is while on the charger.

With my own personal packs, I have no problem leaving the room or even not monitoring them at all, because I know they have not been abused in any way and are absolutely safe.
Charging a damaged pack is where a vast majority of li-po paranoia comes from, because it seems to be completely at random and may strike at any time. In fact, continuing to discharge below 3.0v/cell can damage a pack so severely, and in so few cycles, it very well may fail catastrophically on the charger when "everything seemed normal, and just like yesterday". So where's the average hobbyists defense against the "random li-po killer inside their charger"? Obviously it all comes down to the 3 rules of li-pos. When they're followed, nothing bad happens. Period.

My support staff and I are presented daily with folks that persist in breaking rule #1 "because I know what I'm doing". I recommend to my staff to make sure and teach them about logging cycles, and write down how many man the pack takes in each time. Or at the very least, jot it down once a month. This shows the consumer that the mah in is dropping steadily (depending on the level of damage being done), and when it gets to close to 75% of the original new pack mah, it'll start to fall rapidly each cycle, and it's time to retire that pack. Then we offer them a simple experiment - on a second pack, run the cutoff at 3v/cell, and keep track the same way as well. Invariably, the customer calls back in a few months praising us for our wisdom and cursing the pack brander who told them it was OK to slowly and steadily kill their packs (and put them in danger as well, to put a personal point on it).

When you don't follow the 3 rules above, it's just a matter of time before it happens.

Taken from the Castle Creations Website

Trimming an Airplane

The following chart may be used to systematically set up and trim a model for straight flight and aerobatic maneuvers. Please note that for best results, trimming should be done in near-calm conditions. Before you decide to make a change, be sure to try the test several times before making adjustments. If any changes are made, go back through the previous steps and verify that they are not also affected. If they are, make further adjustments as necessary.

To Test For... Test Procedure Observations Adjustments
1. Control neutrals Fly the model straight and level Use the transmitter trims for hands-off straight-and-level flight. Change the electronic sub trims or adjust clevises to center transmitter trims
2. Control throws Fly the model and apply full deflection of each control in turn Check the response of each control:
Aileron high rate: 3 rolls in 4 seconds
low rate: 3 rolls in 6 seconds
Elevator high rate: to give a smooth square corner
low rate gives approximately 130 foot diameter loop
Rudder: high rate 30-35° for stall turns
low rate maintains knife-edge
Change ATV (for high rates) to achieve desired responses
3. Decalage Power off vertical dive (crosswind if any). Release controls when model is vertical (elevator trim must be neutral). a) Model continues straight down
b) Model starts to pull out (nose up)?
c) Model starts to tuck in (nose down)?
a) No adjustment
b) Reduce incidence
c) Increase incidence
4. Center of gravity Method 1: roll into near vertically banked turn.
Method 2: roll model inverted
1a) Nose drops
1b) Tail drops
2a) Lots of forward stick (down elevator) required to maintain level flight
2b) No forward stick (down elevator) required to maintain level flight, or model climbs
a) Add weight to tail
b) Add weight to nose
5. Tip weight (coarse adjustment) Fly model straight and level upright. Check aileron trim, maintain level wings. Roll model inverted, wings level. Release aileron stick a) Model does not drop a wing
b) Left wing drops
c) Right wing drops
a) No adjustment
b) Add weight to right tip
c) Add weight to left tip
6. Side thrust and warped wing Fly model away from you into any wind. Pull it into a vertical climb, watch for deviations as it slows down a) Model continues straight up
b) Model veers left
c) Model veers right
d) Model rolls right
a) No adjustment
b) Add right thrust
c) Reduce right thrust
d) Put trim tab under left wing tip
7. Up/down thrust Fly the model on normal path into any wind, parallel to strip at a distance of around 100 meters from you (elevator trim should be neutral as per test 3). Pull it into a vertical climb and neutralize elevator a) Model continues to straighten up
b) Model pitches up (goes toward top of model)
c) Model pitches down (goes toward bottom of model)
a) No adjustment
b) Add down thrust
c) Reduce down thrust
8. Aileron differential Method 1: fly model toward you and pull into a vertical climb before it reaches you. Neutralize controls, then half roll the model
Method 2: fly model on normal pass and do three or more rolls
Method 3: fly the model straight and level and gently rock the aileron stick back and forth
1a) No heading changes
1b) Heading change opposite to roll command (i.e. heading veers left after right roll)
1c) Heading change in direction of roll command
2a) Roll axis on model centerline
2b) Roll axis off to same side of model as roll command (i.e. right roll, roll axis off rightwing tip)
2c) Roll axis off to opposite side of model as roll command
3a) Model flies straight ahead without yawing
3b) Model yaws away from roll command (i.e. right roll, yaw left)
3c) Model yaws toward roll command (i.e. right roll, yaw right)
a) Differential settings okay
b) Increase differential
c) Decrease differential
9. Dihedral Method 1: fly the model on normal pass and roll into knife-edge flight; maintain flight with top rudder (do this test in both left and right knife-edge flight)
Method 2: apply rudder in level flight
a) Model had no tendency to roll
b) Model rolls in direction of applied rudder
c) Model rolls in opposite direction in both tests
a) Dihedral okay
b1) Reduce dihedral
b2) Use mixed to produce aileron opposing rudder travel (start with 10%)
c1) Increase dihedral
c2) Mix ailerons with rudder direction 10%
10. Elevator alignment (for models with independent elevator halves) Fly the model as in Test 6 and pull up into an inside loop. Roll inverted and repeat the above by pushing up into an outside loop a) No rolling tendency when elevator applied
b) Model rolls in the same direction in both tests—halves misaligned
c) Model rolls in opposite directions in both tests. One elevator half had more throw than the other (model rolls to side with most throw)
a) Elevators are in correct alignment
b) Either raise one half, or lower the other
c) Reduce throw on one side, or increase throw on the other
11. Pitching in knife-edge flight Fly the model as in test 9 a) There is no pitch up or down
b) The nose pitches up (the model climbs laterally)
c) Nose pitches down (model dives laterally)
a) No adjustment needed
b) Alternate cures:
1) move CG aft
2) increase incidence
3) droop ailerons
4) mix down elevator with rudder
c) Reverse “b” above

From the Flying Cardinals of Northern Kentucky, Inc., Hebron, Kentucky