Many model airplane instructions provide a sequence for construction.  Let me simply recommend that the four separate components of the aircraft — the fuselage, the fin and rudder, and the stabilizer/elevator — should be built independently of one another before they are assembled in the finished project.

First,  the wings.  Place both wing panels bottom to bottom with each other. Each wing panel should be exactly (exactly!) the same length.  If they are not, they need to be modified so that the lengths are equal.

If your wings have bent up wing tips or are polyhedral in nature, place them on your work bench, trailing edge to trailing edge. The angles should match exactly.  Build one wing first, then match the second wing to it. Simply using a measuring stick or a compass is not accurate enough.

The fuselage.  The wings may be attached to the fuselage in many different ways. If your fuselage has an integrated fin (typical fibreglass fuselage) then you need to ensure that the vertical fin is perpendicular to the wings.  Do not try to align the wings with the fin until all the internal controls are permanently mounted and the rudder post is installed.  If you have a top mounted wing, the saddles may have to be modified.  If you have a shoulder-mounted wing with a joiner rod, you may have to modify the joiner rod hole through the fuselage or the alignment pin.  Once completed, (even after painting) the fin can still be aligned by placing hot towels or heating the fuselage boom with a heat gun and twisting the boom to align the fin. Be careful not to overheat it, or you may cause some permanent damage.

The stabilizer or elevator should be mounted last.  Now that the fin is square to the wings, you need to ensure that the stabilizer is also square to the wings.  I've seen instructions that show placing a 90° triangle between the fin and the stabilizer.  I can't think of a quicker way to induce a problem.

The stabilizer must be parallel to the wing, not at right angles to the fin (although of course they should wind up that way!).  Use the wing as the reference point and eyeball it.  From a distance of 25 or 30 inches, looking straight down the fuselage, is the best way to obtain that perfect symmetry.

Now that you have all the various parts of the airplane square with one another, it needs to be balanced.  Add the appropriate nose weight to obtain the centre of gravity position indicated in the plans.  Do not add additional nose weight or glue the weight in place.  It's a very safe bet that the manufacturer has located a CG forward of its optimum performance position.  I don't know why they do this, but they all do.

Now you need to balance the aircraft laterally. The aircraft needs to be placed in such a position so that it can rotate around the longitudinal axis of the fuselage — the most convenient position is to suspend the model inverted.  If one wing tip consistently drops, you need to add weight to the opposite wing tip.  It is important to perform this step.  A laterally unbalanced aircraft will require aileron or rudder input, which will result in unequal flying surfaces.  These unequal flying surfaces will require that you change or modify the trim of your aircraft every time its speed changes.  In other words, a little right aileron trim may be necessary to keep the airplane from rolling to the left at low speeds. (The airplane wants to roll to the left because the left wing is heavier than the right.)  However, if you put the nose down and pick up speed, the airplane will now want to roll to the right as soon as the greater airflow over the offset ailerons overcome the weight of the heavier left wing.

These types of difficulties require constant pilot input.  Reduction of this unnecessary stick movement is one of our goals.  An airplane that can fly consistently over a wide range of conditions with little stick movement is much easier for a pilot to control than one that requires constant attention.

Before you take the airplane to the field for the first time, stand behind the airplane and make sure that all the control surfaces move in the same direction as the control sticks on your radio.  If you set up your airplane while standing in the front looking toward the tail, a common problem may occur.  It's typical to get the ailerons moving in the right direction, but when standing in the front, it's also typical to get the rudder mix backwards.  Stand behind your airplane, not in front of it, to make sure that all the control surfaces work in the right direction.

Charge all your batteries up, take your flight box along with glue, tools and anything else necessary that you might have to use to modify the airplane at the field, and let's go flying.

Once you get to the field and everything is appropriately assembled, it's time for your first test flight.  Find somebody who can throw your aircraft for you.  It doesn't have to be thrown hard, just hard enough to reach flying speed. Not only that, but you don't want to throw the airplane up or down, but simply level — at the horizon.  The purpose of this initial trim flight is twofold.  The first is to provide the proper elevator trim.  The second is to provide the proper amount of roll.  Keep throwing the airplane until both roll and elevator provide for a nice smooth and stable flight. If you throw the airplane hard and it pitches up immediately after leaving your hand, it's probably nose heavy.  May sound crazy but we'll spend more time on that later.

The aircraft is now set up so it can be launched on a winch or high start — please use a winch for a first flight!  It's so much more controllable! JL. However, before you do, hang the airplane upside down from the tow hook.  Use the end of the winch line or high start line.  The upside down airplane should hang tail down (just a little is all that is necessary).  If the airplane hangs tail up and wants to slide off the tow ring, then the tow hook has been placed too far aft and must be moved forward.  Do this before your first launch.  Nothing is more exciting than trying to calm a wild aircraft on launch.

Once the aircraft is launched, turn and head directly into the wind.  Trim the elevator so the airplane will fly as slow as possible.
Put the airplane in a shallow dive (30°) for about two seconds.  Pull the elevator stick all the way back and loop the airplane.  The aircraft should loop and then return to the exact same spot that the loop started.  If the airplane wanders to the left or right, first check to ensure that the rudder trim has been neutralized — not on the radio, on the airplane.  If the rudder trim is neutral, and the aircraft has been properly laterally balanced, you either have a twisted wing (OOPS) or a left and right wing at different angles of attack (double OOPS).  If you're flying a built-up wing, you can take the twist out of the wing by simply reheating the covering, twisting the wing into its new shape (actually, just past its desired alignment, as it will always pull back a little on release. JL), and reshrinking it.  Composite aircraft can usually be unwarped by placing them in the fold of an electric blanket, raising the temperature and twisting the wing back into shape.  (Not mentioned specifically, but assumed — hold it in its new alignment until thoroughly cooled! JL)

On shoulder mounted wings with alignment pins, it's easy to misalign the angle of attack of the two wings. Typically, the modeler will align the root of the wing with the wing saddle on the fibreglass fuselage.   It's been my experience that these fibreglass saddles are not created equally on both sides of the fuselage.  In the field, you may actually have to modify the location of the alignment pin in the fuselage so that the wings have the same incidence angle to each other.  (A useful check of this is to tape a straight (!) dowel under each wing, close to the fuselage, so that they protrude way out in front of the wings.  Then, from the side, check that they are exactly parallel. JL)

An airplane with a warped wing or different incidence between the two panels will result in an aircraft that will turn one way significantly better than the other.  If twisted enough, you will wind up with an airplane that will snap roll in one direction and want to fly out of the turn by itself in the other.
Matching the angle of attack on each wing half is one of the most important steps that you can perform.  If you have the necessary equipment, make the incidence change in the field before doing any other trimming.  I recommend gluing your alignment pin permanently in the wing root.  In the field, if you have to modify the angle of attack, the hole for the alignment pin must be relocated.  This can be done easily in the field.  Overdrill the alignment pin hole, coat the pin with jelly, place some thick CA in the alignment pin hole and reattach the wing (the jelly will keep the CA from bonding to the alignment pin or wing root).

Now that the aircraft is flying straight and level, without a tendency to wander to either side and turns equally well in both directions, it's time to adjust the center of gravity.  It's typical to have to add lead to the nose of a model sailplane.  It makes sense for you to have installed the servos, battery pack, and receiver as far forward in the nose of the aircraft as possible during construction to minimize this additional weight.

Whatever you do, don't permanently glue all the lead in the nose of the aircraft before you go to the field.  You need to insert any nose weight in a way so that it can be removed easily in the field.  You also need to install it in the airplane in a way so that it will not move around on its own.  It is extremely important that the weight not shift during flight!

Every model I've ever flown, bar one, required the removal of nose weight.  Now that we've got the plane flying straight and level, we need to launch it again.  It's now time for the effective (but controversial) dive test.  Again, place the model in a shallow dive (30°) and after two seconds, let go of the elevator stick.  If you built and balanced the model at the point indicated on the plan, the model will pitch up after you let go of the stick.  If the aircraft pulls up all by itself, the aircraft is nose heavy and nose weight must be removed.  I know this sounds backwards to many of you, but the reason is actually quite simple.

If you look at your model airplane from the side, the centre of gravity is that point at which if you were to place a fulcrum, the airplane would balance level.  The tail surfaces of an airplane typically produce lift but in a downward direction (opposite direction from the wing).  It is this downward force which counter-balances the weight in the nose of the airplane and the pitching moment of the wing. However, as an airplane increases its forward speed, downward lift created by the stabilizer/elevator increases.  But the weight in the nose of the sailplane remains the same.  As the aircraft velocity increases, the centre of effort moves and the airplane wants to pitch up (pull out of the dive) all by itself.  (It's probably easier to say that the downward pull of the elevator becomes more effective at the higher speed. JL)
It's actually much more complicated than this, but a discussion concerning the moving of the centre of lift relative to the CG would take a whole book.

The goal is to obtain an aircraft which only slowly pulls out of the dive.  In other words, one that has only just positive elevator.
After the airplane lands, take some of the nose weight out of the airplane.  After taking nose weight out of the airplane you must add down trim to the elevator.  Re-launch the airplane, turn into the wind, re-trim for slow flight, and  repeat the dive test.  The plane will continue to pull up but not as abruptly as it did before. Land, remove additional nose weight and add additional down elevator trim, and re-launch. You will have to keep performing this test until the aircraft only just pulls out of the dive on its own.  One BB at a time is too little.  Try taking weight 5 g at a time on a small model, 10 g on a bigger one.  This is usually equivalent to 1 to 2 clicks of down trim.

No doubt, some of you are now thinking about those articles you've read where an aft CG produces an event known as "pitch instability" or "tuck under".  As the CG of the aircraft moves back, the elevator of your aircraft becomes more efficient.  In other words, it requires less control throw to obtain the same pitch movement (climb or dive).

Many new pilots don't like this increased pitch sensitivity, so they add weight back to the nose of the sailplane.  You can accomplish the same result by simply reducing the control throw at the elevator.  If you have a radio with dual rate functions, just reduce the amount of control throw.  The same goes for the computerized radios.  If you have a simple 4-channel radio without dual rates, move the clevis at the elevator control horn all the way to the outboard position.  If that's not enough, move the clevis at the servo arm as close to the center hole as possible.  (This latter is true but not a clever idea!  It invariably introduces slop in the linkage and causes more problems than it solves! JL)

If your model has a full flying stabilizer, the trim adjustment of the stabilizer to obtain the proper incidence in the dive test is relatively easy to do.  On an aircraft with a separate stabilizer/elevator, this could be much more difficult.  You may need to re-trim the stabilizer so that after the dive test, the elevator and the stabilizer are perfectly lined up — no up or down deflection on the elevator.  Shim the leading or trailing edge of the stabilizer as necessary to obtain the neutral elevator so that in the dive test, the airplane only just pulls out of the dive on its own.

(The Dive Test is illustrated neatly in an article (CG & the Dive Test) which can be found in the SSC Information Centre under Articles from Southeasters at --
www.rc-sa.co.za/ssc   JL)

 1  Build and balance the airplane as per the CG on the plans.
 2  Remove 2,2 oz. of nose weight.
 3  Reduce the elevator deflection by one-half.
 4  Double the rudder throw.
 5  Move the tow hook all the way to the forward most location.

Two and a half ounces (40+g) of nose weight is a lot of weight in a 2 metre sailplane.  Not only that, but its removal significantly increased the thermal performance of the airplane.

To return to the trimming of the original airplane, we now need to complete its trim by providing the appropriate amount of control throw.

The first item to be adjusted is elevator throw. Determine the tightest thermal turn you wish the plane to perform.  While in the turn, your elevator stick should be nearly bottomed out.  If you have a lot of additional stick throw, it's unnecessary and will never be used.  Reduce the amount of control throw still further on the airplane, and eliminate the additional stick movement.  You will find, that by softening the elevator input, the sailplane is more gentle and easier to fly at a distance.

Launch the aircraft and disable any rudder mix that you may have.  Roll the airplane left and then roll it right. If the airplane rolls along the fuselage center axis, without yawing left or right, your differential is just right.  If you roll left, but the airplane yaws left (nose down), you have too much differential.  If the airplane rolls left and yaws to the right (nose up), you need to increase your amount of differential.

Once the proper amount of differential is obtained, then turn on the rudder mix.  If your differential is correct, it won't take much rudder mix at all (the rudder mix on my Prism is less than 3/8 inch at full aileron deflection).

Too much rudder mix can actually stall the inboard wing in a turn.  Many may find this difficult to believe, but if you have an airplane that tip stalls easily, try reducing the amount of rudder mix and increasing the aileron differential.  That tip stall may go away.

Soft controls result in a gentle flying airplane.  A gentle or smooth flying airplane thermals better.  It's just that simple.  If you have more control throw on any surface than you absolutely need, you have too much.  To give you an example, the other day I trimmed out a fellow pilot's airplane that was "twitchy." Although it was twitchy, it was very flyable.  At a distance, where it was difficult to see, it became nearly unflyable.  After some experimentation, we reduced his elevator throw from 100% to 30%.  Not only that, but his radio had exponential rates and we bumped his exponential rates up to 35%.  The airplane now became extremely smooth, very easy to fly, and with an aft CG, it thermalled like a bandit.

It's unfortunate, but a common statement I hear from many fliers is, "It's flying good enough, I don't want to touch it."  There's a big difference between "good enough" and "excellent performance."  There's no reason why every airplane in your inventory shouldn't be an "excellent performer."

A sailplane that flies perfectly out of the box doesn't exist. If you expect yours to, you will be disappointed. Be patient and don't be afraid to make those necessary trim changes. You will be glad that you did.

I'd like to thank the members of the Seattle Area Soaring Society for showing me these useful tips over the last several years. Without their help, guidance and support, my airplanes would not fly as well as they do.