How to use  the multiple features in modern transmitters to control elevator, rudder, aileron and flaps?

The last years a lot of modern gliders has spread around the world. Gliders with ailerons and flaps and at the same time the new transmitters can do every thing we can ask for and sometimes more. The transmitters I know of that can do it all are Futabas FC 28,, Graupners MC 24, MC 22, X 22 and Multiplexs 3010 and 4000. Besides this there are probably the same quantity or more types that can do the same thing. Ask your dealer or ask some of the people you are going to fly with. They do certainly know what they are talking about, and if you are going to fly with them it is easier to have the same brand or even the same transmitter type.

At first glance it can look very complicated when these 4 wing "rudders" are used for ailerons, thermal flaps, launch flaps or launch preset, speed flaps, snap flaps, butterfly brake - let alone the words. I will go through the terms one by one to remove the magic.

I will not tell you how to program a plane with an MC 24 or any other transmitter. Most transmitters have very good text to follow and besides this I only know how to do it with three transmitters: 

• Royal MC (middle of the 80’ies – programmed with turn potentiometers!),

• MC 16/20 (beginning  of the  90’ies)

• MC 24 (the most advanced transmitter from Graupner today) - mine is version ca. 2000

Shortly before year 2000 some F3J pilots started to use 6 wing "rudders" instead of 4. The 6 rudders can of course be mixed into an obscene mess. I'll spare you the details and let you have a look in the manual of the updated software of the MC 24 (2004).

On Graupners homapage you can find a description (in German) on how Phillip Kolb mixes his Soarmaster. The Soarmaster is designet by the farther of HQW airfoils - Helmuth Quabeck, and on his homepage you can also find his sugestions on how to setup the successor to the Soarmaster - the Soaring Star (also in German).

The more you move your rudders the more drag you create. Any rudder input creates drag and makes the glider sink faster i.e. you loose more height per minute than you would have if you hadn't steered at all. Lots of rudder deflection (= a lot of steering and violent) creates drag, higher sinking speed, lover you gliding angle and gives you shorter flight times.

If you follow this everybody should be flying gliders that continued on course 270 degrees until they landed. This is not very convenient. Sometimes it is necessary to make rudder inputs, to steer the glider into a thermal. And this way the steering input gave you more height and hence MORE flying time with rudder input than without. It is very important that you consider which inputs that are important for your glider and the flying time and which inputs that kicks your ego and makes you impress .the opposite sex.

The picture shows my Trinitus with neutral rudders

and my wife  - maneuvers for you ego works!

I have often heard people in doubt about how the rudders work on a V-tail. I will not give you a deep theoretical explanation, but just show you how it works.

This is my Trinitus with right rudder (left rudder moves up, right rudder moves down ):

This is my Trinitus with up elevator (both rudders move up):

This is my Trinitus with down elevator (both rudders move down ):

Ailerons on a glider shall move more up than down. With equal deflection, the rudder that moves down will create to much drag an turn the fuselage in the opposite direction of the intended banking (and turning). Even with differential it can sometimes be necessary to add rudder to overcome this effect. The phenomena is called "Inverse Yaw" and it is mostly a problem on scale gliders with large span and short fuselages. 

How much differential one needs to have least drag and to avoid Inverse Yaw depends on the wings angle attack? Generally speaking the slower you fly the more differential do you need. The slower you fly the more should the ailerons move up compared to the down movement.

If you can't switch between different flying phases (with different differential) settle on about 2-3 parts up and 1 part down i.e. the aileron moves 2-3 times more up than down.

Since you can only fly with one airfoil at a time it is necessary to make a compromise - the best compromise. And the best compromise is to choose an airfoil that you can change while you are flying. This way you can have a slow airfoil and a fast airfoil in one flight. This you can do with flaps and ailerons coupled to the flaps. 

Very few airfoils are designed specifically to be used with active flaps, to gain the full potential. On most airfoils though one can benefit slightly with positive and negative flap deflections.. The HQW series is one airfoil that is designed to be used with both positive (=down) and negative (=up) flap deflections to gain a raise in performance at low and high speeds. Some of Mark Drelas airfoils are also designed to be used this way - AG 455-series

When you lower your flaps (=lower the trailing edge) you change the airfoil to a state where it can produce more lifting force AND you raise the lifting coefficient where the airfoil has the lowest drag. In short you get an airfoil that is better at flying slowly compared to flying with neutral flaps.

When you raise the flaps (=raise the trailing edge) you change the airfoil to a state where it can produce less lifting force AND you lower the lifting coefficient where the airfoil has the lowest drag. In short you get an airfoil that is better at flying fast compared to flying with neutral flaps.

I extreme circumstances you can raise the trailing edge to a degree where the very low lifting coefficients the airfoils is able to produce is actually negative, and you are best of flying upside down. This is good when you are showing off thermalling up side down low and far downwind.

When you have found a thermal and you are circling in it you can lower your flaps and ailerons a bit to lower the airspeed which makes it possible for you to circle even tighter. Almost everybody who has the possibility lower the flaps and ailerons the same amount of DEGREES. This way you rise the available lifting force on the WHOLE wing instead of only in the middle. 

On most gliders lowering the flaps only means that you a lowering the speed where the glider has the lowest sinking speed without the glider actually sinking slower - the sinking speed stays the same. This lower airspeed gives you the possibility to circle tighter, but it won't give you longer flights without thermals.

With an airfoil like the HQW you can lower the gliders sinking speed a bit with positive flaps movement  (=down. A lower sinking speed gives you longer flight times if you don't look at thermals (that are always there!), sink and turbulence. When you use positive flaps you are also creating an airfoil that has lowest drag at a higher lifting coefficient (=higher angle of attack), therefore it is not wise to cruise with positive flaps deflection. If you want to cruise raise the flaps to neutral or even negative (=up) if you want to leave a sinking area fast.

A positive flaps deflection of +1-3 degrees (trailing edge down) is very often sufficient and you should be able to feel it very quickly if there is any benefits from it.

2,5mm = 2,7 degrees

5,0mm = 5,5 degrees

When launching you need an airfoil which can produce huge amounts of lifting force. You get this by lowering the flaps and ailerons in the first phase of the launch. I told above that the drag increases this way, but this time we don't have gravity as energy source - this time we have either 2 person towing up front, or we have an electrical winch besides us to give us the desired power to overcome the extra drag created by the large flaps deflection. The lifting force delivered by the deflected flaps is transformed into potential energy in the line that is being stretched and ready to contract and deliver the energy back as soon as you raise the flaps and perform the catapult. As soon as you prepare to dive for the catapult remember that you are about to accelerate and fly fast. when flying fast you need an airfoil that can fly fast and therefore you  raise you flaps to neutral or any other place that you have found out gives you the best catapult and the highest launch.

The pictures show my Trinitus with  launch flaps:

ca.8mm

ca. 14mm.

When you are flying very fast you might want to raise the flaps a bit. By having the flaps raised you create an airfoil that has lowest drag at a higher speed than normal. This way you can often fly faster than with neutral flaps.

The pictures show my Trinitus with speed flaps – negative flaps raised about ca. 2mm (=-2mm):

speed flaps

Snap flaps are used mainly in F3B and F3F, where you are going to fly both very fast in a straight line and at the same time turn 180 degrees very fast and tight. You mix elevator and flaps (coupled flaps and ailerons) so the trailing edge at full up elevator goes to a point below the neutral setting (=app.. the thermal setting). If it is possible to avoid the flaps in moving up with down elevator do it.

Snap flaps makes the wing (maybe with speed flaps) able to create high lifting forces with lower drag  in the turns. It is important to remember that snap flaps doesn't "lift" the plane around in the turn - it is not a turning aid. The snap flaps lower the drag in the turn so the turning movement doesn't create as much drag as it would have without snap flaps. Compared to a turn without snap flaps it might seem as the plane accelerates in the turn. This is not true. But it doesn't decelerate as much as you are used to. Remember that when you are performing a banked turn and pulls the elevator, you are forcing the airfoil to create lots of lifting force to make the plane go in another direction than straight ahead (remember your high school physics!). It is the increased angle of attack that makes the plane turn and remember that increase angles of attack makes the airfoils lifting coefficient go up, and when the lifting coefficient raises you want the drag to stay low = the demands to the airfoil in the turn are the same as to the airfoil circling in thermals!

Some people makes it look like their planes accelerate out of the turn. This may be so, but it has nothing to do with snap flaps, it is more due to some sort of DS action along the slope edge.

The picture shows my Trinitus with snap flaps at full up elevator. The flaps are lowered about 6-7mm. Be aware that the 6-7mm are from the speed flaps raised to -2mm, so at full up elevator the flaps go down to max thermal flaps setting (=+5mm flaps)

Snap flaps (+7mm)  with maximum up elevator

When you have flown out the slot and want to land on time and on the spot the situation changes. Suddenly we want back some of the drag we have fought to remove. We want to make the glider ascend at slow speed and do it STEEP without acceleration This we do with a brake. Since we have both flaps and ailerons we don't need a separate brake.

The butterfly brake function makes the flaps go down 45-90 degrees according to you temper and pushrods and the ailerons go up 10-20 degrees. To counteract the nose up moment we add a tad of down elevator in the mixing. When you pull back on the throttle stick three things happen: The flaps go down, the ailerons go up and the elevator goes down. This way you can land very steep and slowly - AND precisely. Just before the model touches the ground you push the stick forwards to save the flaps ,servos and pushrods. It is easier than it sounds.

The picture shows my Trinitus with half and full butterfly brake - the flaps go down 22 and 52 degrees, the ailerons go up 10 and 15 degrees and the elevator compensates with 4mm and 7mm down elevator. It is not a switch, but two stages of a linear function on the throttle stick.

half brake

full brake

When you mix ailerons and flaps into the ailerons function you gain more maneuverability. Instead of only having the ailerons to function as ailerons you make the entire trailing edge to one long aileron and if you mix it so the flaps only move about ½ of the ailerons throw you get something like the Wright Brothers wing warping. Remember that rudder movement creates lifting forces in one or the other direction (up or down) and when one wing produces more lifting force upwards than before and the other wing prduces more lifting force downwards than before, the roll force is more power full and the roll rate will be quicker.

The effect of coupled ailerons and flaps is that the glider reacts quicker on ailerons input. This is nice when you need great maneuverability, but on the other hand any lifting force created has a brother named drag that tags along. Moving the entire trailing edge makes you change the airfoil on the whole wing instead of just part of it, and rudder movement is drag! Sometimes though you can be in a situation where you need very powerful steering and doing powerfull steering with only the ailerons makes the ailerons work VERY hard, and creating much drag. Switching to coupled ailerons and flaps makes the coupled rudders work less and hence creates less drag. Therefore when flying in thermals you want to steer as little as posible and with as small rudder movements as possible - use only the ailerons and in as small quatities as possible. When screaming along the slope edge trying to beat Kevein Newton or someone who is a fast F3F junkie you might want to couple the ailerons and flaps to get around the corners every 100 meters.

The picture shows my Trinitus with coupled ailerons and flaps in the speed flaps mode - the flaps move around 50% with the ailerons:

left

right

The numbers are taken from a Trinitus with 48mm broad flaps and ailerons (where they meet). At the root the flaps are 53mm broad and at the tip the ailerons are 35mm broad - this is very close to 22% of the chord. The elevator is 40mm at the V-tail base.

plus (+) deflection is positive = down

minus (-) deflection is negative  = up

I have 4 flying modes / phases with different neutral positions (ailerons and flaps) and each flying mode / phase has separate rudder movements:

1. Launch

2. Normal

3. Thermal 1

4. Thermal 2

Switch 1 back forward forward back Switch 2 forward forward back back   Launch Normal Thermal 1 Thermal 2