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Posts Tagged ‘climb’

R/C Helicopters – Blade Pitch Setup In-Depth

July 13, 2010 Leave a comment

Setting up the pitch curve on your helicopter is one of the most crucial parts of setup.

First of all, lets define ‘pitch’. Pitch describes the angular movement of the rotor blades in relation to the horizontal plane. For example, when the angle of the blades is upward, the blades are described as having ‘positive pitch’. Likewise, when the angle of the blades is downward, the blades are described as having ‘negative pitch’.

Rotor Blade in Positive Pitch

Rotor Blade in Positive Pitch

Rotor Blade in Negative Pitch

Rotor Blade in Negative Pitch

Setting up the pitch curve

Once you have read this article, read the tutorial on Helicopter Setup then the tutorial on Radio Setup.

Setting up the pitch curve on your helicopter is one of the most crucial parts of setup. What is a pitch curve you ask? OK…

First up, I’m no aerospace engineer, so I’m not going to give you the physics behind everything. I’m gonna give you the story from my point of view.

First of all, lets define ‘pitch’. Pitch describes the angular movement of the rotor blades in relation to the horizontal plane. For example, when the angle of the blades is upward, the blades are described as having ‘positive pitch’. Likewise, when the angle of the blades is downward, the blades are described as having ‘negative pitch’.

The amount of pitch is measured in degrees above or below the horizontal plane. A normal pitch range for many helicopters is about 22 degrees in total, that’s positive and negative pitch combined.

When the rotor blades get more positive pitch, the helicopter will ascend (climb), likewise, the more negative pitch, the faster it will descend (fall). Unless of course it’s upside down, but we’ll get to that later :).

Now, back to the pitch curve situation. The amount of pitch on the blades is dictated by the position of the collective stick on your transmitter. If your transmitter didn’t have pitch curve point adjustment, you’d have a pitch curve that looks like this:

The graph on the left illustrates a ‘linear’ pitch curve. This means that moving the collective stick along will represent an equal change in the amount of pitch on the blades.

If it weren’t for the provision of pitch curve point adjustment, the amount of change of pitch in the rotor blades would be linear. Meaning that movement of the collective stick would yield equal movement of the pitch on the rotor blades. In some cases, this is fine, but what about if you want to set up different modes of flying? A pitch curve that enables you to hover nicely is probably not going to let you do inverted flying very well. For this you need to be able to adjust your pitch curves.

Most good radios have points on their pitch curves that can be adjustable. The cheaper radios have about three points, good radios have five, while the top-of-the-line radios can have about thirteen. The more points that are adjustable on your radio, the more you will be able to tune your pitch curve.

Most radios also have multiple flight modes. This means, at the flick of a switch, you can change the flight characteristics (pitch curve, throttle curve etc) of your helicopter. So for each flight mode, you can set up different pitch curves that suit different types of flying, hovering, fast forward flight, inverted etc. Flight modes are often called ‘Idle Ups’. Not sure why! Some radios have one idle up mode, others have two, some more advanced can have even more.

You need to set your helicopter’s pitch curves up as well. Make sure you use a pitch gauge to set up your curves. Doing it by eye is just useless.

Linear Pitch Curve

The graph illustrates a 'linear' pitch curve. This means that moving the collective stick along will represent an equal change in the amount of pitch on the blades.

I’ll come back to this later to show you in more detail the type of curves you can create and in what situations they are typically used. For now, that’s it! 🙂

Learning to torque roll an RC airplane

May 19, 2010 Leave a comment

Hi! We’re back to the technique lessons! This time i’ll focus on the amazing torque rolls and how you can achieve it with success.

Torque Roll

Torque Roll

You’ve seen those super low hovers and torque rolls in demonstrations and in model magazines, and you’ve probably wondered just how they are done. Super human flying ability? Hi-tech gyro gismos and big, expensive models? Certainly, you say, torque rolls can’t be in the flight plan of a sport modeler who likes to fly normal sport models can they? Well, actually, they can.

It takes practice…

It’ll take practice, of course, and plenty of it. But saying, “just practice” is like saying if you want to paint like Picasso, just start painting. The major stumbling block for most pilots is knowing just what it is you’re supposed to be practicing. And then there’s the plane. What kind of model do you need? Maybe you’re a sport modeler and don’t want an expensive “TOC” model…if that’s what it takes.

Relax. Because besides lots of practice and a good plane, learning to Torque Roll takes one more thing: a plan. And we’ve got it right here.  So read on and we’ll let you in on how the pros got to be pros at it. It’s still going to take practice, but here’s what to practice first and what to practice with.

The Right Plane

No, it doesn’t take an expensive “TOC” model. It doesn’t even take a scale aerobatic plane. It does take a plane with some specific qualities though, but you can find these qualities in some fun, economical sport models.

The plane has to have a lot of elevator and rudder authority. This is important since, while in a hover, you need to be able to maintain pitch and yaw control with the only airflow over the tail coming from the prop.

Great power to weight ratio is a big help, too. While learning, and even if you are a torque roll master, at times you will need to “get out” in a hurry. The safest direction to get out is naturally the opposite direction of our nemesis, the ground. To hang on the prop and to blast out vertically, you need great, reliable power.

The catch-22 of torque rolling is that practicing up high gives you the altitude you need to recover when you get crossed up, but it’s a lot harder to do. Learning torque rolls lower to the ground is much easier, because you can see much better and make corrections faster, but one mistake and it’s that old nemesis again…CRUNCH!! So try to practice with as much altitude as you can.

Step 1

Like learning to ski, you need to know how to fall down and get back up first. You WILL make mistakes, even when you have it mastered. So, don’t worry about how to control the torque roll yet. Concentrate on learning to catch the model and fly out of any mistake without losing altitude, regardless of the attitude the model falls into. This is the key to the torque roll.

How to do it: At a safe altitude, pull the model vertical at about 1/4 throttle and begin to hover. Use just enough throttle to pull vertical, but not enough to sustain a hover. Let the model begin to fall out- it may fall to the side, the top, bottom or any combination. Practice catching it with the correct elevator and/or rudder input, and get the throttle in it. Focus on flying out level. After you start to get the hang of it and react faster, fly out vertical.

Trickiest Part: Don’t get confused and give the wrong input. Be careful, especially when the model falls with the nose toward you. That’s why we start at a nice safe altitude.

Step 2

You’ve now crossed the biggest hurdle to learning the torque roll. You can recover, no matter which way the model falls out. You have confidence that you can save the plane every time. Now you can concentrate on two new things. First, work on reacting with the correct rudder and elevator inputs to keep the model vertical. (The good news is Step 1 has already sharpened your orientation and reaction skills.) Second, learn to “fly” the throttle stick to maintain altitude in a hover but not climb or drop.

How to do it: Now it’s time to bring it down to a lower altitude. Start at about 25 feet, low enough to see the model and still high enough to give you a little reaction time before terra firma. Again pull to vertical, only this time add a little more power so that the model hangs motionless in the air. Once you’ve got the throttle figured out, concentrate on flying the rudder and elevator to keep the model vertical. Don’t worry about ailerons, they aren’t going to do much while you’re hovering. This is simply a balancing act, like riding a unicycle. The model may hover or it may begin to torque roll to the left. Don’t worry about rolling, this happens on its own and you don’t need to make it roll. The model will begin to roll once it is very close to dead vertical. The better you can hold the model vertical, the faster it will torque roll.

Hint: Choose a calm day to practice. Wind makes torque rolls much harder. You will also need lots of control surface throw to maintain control. Use as much as you can get, similar to a “3D” set-up if possible. While you’ll need this much control at times, it also makes it much easier to over-control the model, so use some expo. I suggest about 25% on rudder and 40 to 50% on elevator. Now you’ll have the control power when you need it, but a soft feel around neutral so you won’t over-control when making little corrections.

Trickiest part: Learning to keep up with the model’s orientation as it rolls to give the correct elevator and rudder inputs. It takes time to get good. One wrong input and the model will fall out, but you know how to fly out of a mistake, so set up and try again. Also don’t over-control. Even too much of the right correction will make you fall out. Flip back to low rates as the model falls out so you don’t over control and stall the plane. Use that expo feature in your radio.

Once you’ve got the hang of it, try backing the throttle down a few clicks as you are torque rolling and slide the model down closer to the ground. And that, in a nutshell, is just about it. So now that you’ve got a plan and you know what kind of plane, all that’s left is practice, practice, practice…

You’ve seen those super low hovers and torque rolls in demonstrations and in model magazines, and you’ve probably wondered just how they are done.

Super human flying ability? Hi-tech gyro gismos and big, expensive models? Certainly, you say, Torque Rolls can’t be in the flight plan of a sport modeler who likes to fly normal sport models can they? Well, actually, they can.

It takes practice…

It’ll take practice, of course, and plenty of it. But saying, “just practice” is like saying if you want to paint like Picasso, just start painting. The major stumbling block for most pilots is knowing just what it is you’re supposed to be practicing. And then there’s the plane. What kind of model do you need? Maybe you’re a sport modeler and don’t want an expensive “TOC” model…if that’s what it takes.

Relax. Because besides lots of practice and a good plane, learning to Torque Roll takes one more thing: a plan. And we’ve got it right here.

So read on and we’ll let you in on how the pros got to be pros at it. It’s still going to take practice, but here’s what to practice first and what to practice with.

Beginners’ Guide

April 30, 2010 Leave a comment

First Model

Some people consider a glider as the obvious choice for the first model. Although a glider normally flies slower and is supposed to be more forgiving, I think that’s just a matter of taste. Being a skilled glider pilot doesn’t necessarily mean being also a skilled powered aircraft pilot and vice-versa.

Assuming that a powered model was chosen, the beginner is advised to start with a so-called trainer. This type is usually a high wing aircraft model with nearly flat bottom airfoil that produces high lift, permitting slow landing speeds without stalling. It also has some dihedral angle to give a good lateral stability.

However, a flat bottom high wing with dihedral is more sensitive to crosswind gusts, so the first flights should be done during calm weather. A beginner should avoid wings with too sharp leading edges, as it will worsen the stall characteristics.  A well-rounded leading edge is therefore preferable, as it better conveys the airflow onto the upper wing surface allowing higher angle of attack at low speed.

A trainer model should not be too small, as it would be difficult to assemble and maintain and would be more sensitive to strong winds.  It should not be too large either,  as it would be difficult to transport, require a larger flying field and
would be more expensive. A reasonable size is about 150cm wingspan (60 in) with a high aspect ratio, which means the wingspan being about 5.5 times the wing chord. A square wing is advisable, as it distributes the weight of the aircraft evenly over the entire surface of the wing. In order to allow a reasonable low landing speed without stalling, the wing
loading
should not be greater than about 60g/sq.dm (19-oz/sq. ft). Wing loading is the aircraft’s weight divided by the wing area. Some degree of wing washout also improves the stall characteristics.

The basic parts of a trainer model:

Engine – provides the power to rotate the propeller.
Propeller – (also Prop) is attached to the engine’s shaft to convert rotational motion into thrust and speed, which depends on the Prop’s diameter, pitch and the Engine’s power.
Spinner – streamlined part that covers the end of the Prop shaft.
Fin – (also Vertical Stabiliser) provides directional stability (stability in yaw).
Rudder – movable part fitted to the Fin’s trailing edge, is used to change the aircraft’s direction.
Stabiliser – (also Horizontal Stabiliser or Stab) provides longitudinal stability (stability in pitch).
Elevator – movable part fitted to the Horizontal Stabiliser’s trailing edge, is used to make the aircraft climb or dive.
Ailerons – movable parts on both sides of the wing, are used to make the aircraft roll about its fore – aft axis. When one aileron moves up the other moves down.
Wing – provides the aircraft’s main lifting force.

One may build a model aircraft based on drawings (plans). This requires some building skills and also time and effort to find out and gather the materials needed for the construction. An easier approach (albeit more expensive) is buying a kit of parts. There are many kits on the market with different levels of prefabrication depending on their price.
The cheaper kits have most of parts included, but some pieces come either pre-cut or printed on sheets of wood, so the builder is expected to do some extensive job, such as to cut out the fuselage formers and wing ribs, glue the parts together, apply the covering material, etc.
For those who are not so keen on construction, there are almost ready to fly (ARF) kits with an extensive re-fabrication, requiring one or two evenings to assemble. There are also ready to fly (RTF), which normally come complete with the power plant and some of them even with the radio pre-installed.

First Flight

It’s highly recommended to have an experienced instructor beside you during your first flight. However, it is not impossible to get succeed by doing it alone. Maximum wind speed recommended is 5-8 Km/h (3-5 mph) including gusts.

Check your plane’s CG location with empty fuel tank (if you are using a combustion model) or with batteries (if using an electric model) by supporting the model with your fingertips underneath the wings. Find the position where the fuselage gets level or its nose is pointed slightly downwards. Remember a golden rule: a plane with a CG a bit forward to it’s ideal location will fly badly, but a plane with a CG aft it’s ideal location will fly once… So, if you are not sure about how to exactly put your CG, just make sure it is more forward than aft. Within the first flights when you try to fly leveled you will notice by it’s flight characteristics and you can make small corrections on each new flight.

Transmission range check should be performed on the ground before the flight. This is usually done with the Transmitter aerial collapsed (this is not applicable for 2.4Ghz radio systems). The control surfaces should respond without glitch at a distance of about 80 meters (263ft). This distance is only an approximately guide line, as the actual range may vary depending on the environment.
The effective range may only be half of this value if located at mountain bowl site or close to a public radio transmitter, radar station or similar. The range may suffer adverse effects if the receiver aerial is close to metal parts or model components reinforced with carbon fiber. Some transmitters allow the aerial to be totally collapsed inside a metal case (again not applicable to 2.4Ghz radio systems), which also may reduce the radiation. In this case the lower section of the aerial should be extended during the test. The check should be repeated with the power system running, alternating the throttle setting between idle and full-throttle.

The range will be much higher when the model is in the air, normally about 1Km or as far as one can see the model.

Take-off:

If you hand launch your model, throw it against the wind horizontally and straight ahead, not up.
If you take-off from the ground, taxi the model towards the wind and let the model gain ground speed before applying elevator. Once in the air try to climb at a very small angle, not abruptly upward, which would cause loss of airspeed and stall.

The model is more sensitive to the motor torque effect during the relatively low take-off speed and may begin to turn left (or right). Use the rudder or ailerons to prevent the model from turning during the climb stage, otherwise the model may initiate a spiral dive.

Don’t try any turns until the model has gained speed and reached a “safe altitude”. Be very gentle with the controls and practice gentle turns high in the air before you try to land. To prevent losing altitude when turning the model, just give little up elevator at same time you make a turn.

Try to keep the model in sight and do not fly too high or too far away. You may reduce the throttle while high in the air so you may get an idea how the model behaves at low speed – try to glide it while high and use just a bit of elevator to keep the nose leveled – even thought initially you will feel it is too slow and it may fall, just keep doing it so you have a real feel of how slow it can fly (as you have the model high in the air with slack to recover if something happens). This will give you an idea of the kind of speed you will use when approaching for a smooth landing (which will NOT happen on the first times… – you have been warned).

To prevent getting confused about which way to turn when the model flies towards you, turn your back to the model slightly while keeping watching it, so you can imagine “right” and “left” from the model’s point of view. At this stage, you should have already practiced with a good computer flight simulator and you should be already comfortable with this situation. If not, better to spend a few more hours on the simulator if you don’t want to crash your expensive plane.

Some trimming may be needed in order to reduce or eliminate roll, bank and/or pitch tendencies. A flat bottom wing often tends to “balloon” up into the sky, keeping climbing when full throttle is applied. This may be reduced during the flight by adjusting the elevator trim or by reducing the throttle. In worst cases it may be needed to increase the motor’s down-thrust angle and/or decrease the main wings incidence angle.

Landing:

Reduce throttle to about half or even less (depending on the power and torque of your power plant) so you have to slightly pull up the elevator to keep the altitude. Turn the model towards the wind and let the model sink gradually towards the landing area by easing the elevator.

During the last fifteen to twenty meters (45 to 60 feet) of descent, (which depends on the model’s characteristics) you should idle the throttle. The model will start sinking at a higher rate now. Try to keep the model in a shallow dive and don’t use the elevator to gain altitude or to prolong the flight at this stage, otherwise stall is likely to occur.
Just keep a slightly downward attitude throughout the final approach in order to maintain the airspeed.
The higher the wing loading, the steeper the approaching angle may be. However, it is not recommended approaching angles greater than 45 degrees.
If you notice that the model is sinking too fast or is too low to reach the landing field – just increase the throttle first before applying elevator to maintain or gain altitude to prolong the flight or to repeat the landing approach.
Pull up the elevator slightly about 30-60cm (1-2 ft) before the touch-down so that the propeller or nose gear don’t hit the ground.

Be prepared to repeat unsuccessful landings several times, since it’s often a matter of trial and error before one gets used with how the model behaves. If you are using a flying field with grass around the track (highly advisable), on the first tries just worry about the landing approach. Don’t try to land in a specific spot, avoid turns when the model is flying low or at low speed. Just let your model glide into the ground straight-ahead. With time and more experience, you will get better and better an soon will be landing exactly where you want. Even experienced pilots sometimes have hard landings, as this is the most difficult maneuver.

Avoid the proximity of buildings, roads and electric power lines. Don’t fly close to or towards people and animals.
The bigger the field for your first flight, the greater will be your chances for success. And remember, if the weather conditions are not adequate for your first experiences, control your excitement and come back later when the weather is better. This is a great way to prevent mistakes that will cost you a lot of money in repairs.

It’s also advisable to join the nearest model aircraft club there you may meet experienced fliers who can provide lots of useful tips and hints.

Good luck!