Helicopter Dreams

Carburator ice is a big NO NO when flying a helicopter and today I experienced this little nasty phenomena. During the startup procedures my instructor noticed that I lost RPM. Since I was following my checklist I had turned the carb heat off not thinking that this could cause carb ice already during startup. By pulling the carb heat again we noticed that the RPM began to stabilize and the carb ice was gone. 17 degrees celsius but rain in the air, it’s true what you read in the books. ALWAYS APPLY FULL CARB HEAT WHEN MANIFOLD PRESSURE UNDER 18″ OR WHEN WEATHER IS MOIST/WET.

After that happenig I tried some new exercises, the first one, a bit scary called “Running Takeoff”.

1. Running takeoff

This maneuver is used to transition from the surface into forward flight when there is not sufficient power available to sustain a hover. This might occur if the helicopter is underpowered, is at high gross weight, or high density altitude.

The skids are aligned with the direction of takeoff, and power is increased until the aircraft is light on the skids. Slight forward cyclic is used to start moving the helicopter forward. During the slide, lateral cyclic is used to hold the centerline, and the anti-torque pedals are used to keep the skid gear aligned with the ground track. As the helicopter gains airspeed, the rotor system becomes more efficient, which makes the helicopter lighter, which reduces friction with the runway and allows the helicopter to gain airspeed even faster.

As the helicopter approaches translational lift, the pilot can use some aft cyclic to bring the helicopter off the ground. The reduction in friction will allow the helicopter to accelerate forward. If the pilot pulls back too far on the cyclic, airspeed will be lost and the helicopter will settle back onto the runway.

Here’s a movieclip showing a running takeoff:

Then we flew to Tullinge to practise “Stuck pedals”

2. Stuck pedals from 500 ft

When the pedals are stuck in neutral position we’re not able to control the direction of the helicopter. When lowering the collective the helicopter wants to yaw left, nothing we can do about it except for planning a flat approach to the landing spot with smooth collective movements and keep up the speed that will give us some help from the tail stabilizer. The helicopter will most likely fly with some left yaw towards the landing spot. When approaching the landing we have to reduce our speed gently and meet up with the collective to stop the helicopter. BUT, at that moment the helicopter will start yaw to the right instead. So what we do at this point, to get the helicopter down (from hovering height), is to close the throttle and meet up with the collective (as with power failure from hover). There you are, on the ground, alive!

Here’s a situation where the pilot is doing the maneuver in an emergency situation:

On our way back we did some slope landings and spot landings as well, good practise.

Accumulated flight time: 28.5 hours

080818 Flight time: 1.3 hours

I found a sneak preview movie clip showing the new Robinson R66 leaving the factory, interesting to see.

I’m a bit curious about the plans for the new Robinson R66 (five-seat jet-powered helicopter due out in 2010) and found this web site that compares the R66 with other “similar” models: Click here to read more

I must show you what a collegue of mine sent to me. A piece of symphony, lean back, put on your favourite headphones and enjoy Stockhausen’s “Helicopter String Quartet”!

Karlheinz Stockhausen says that he first conceived of “Helicopter String Quartet” in a dream, and it’s not long into the 32-minute piece that you’re right there with him, hovering somewhere between fleeting vision and unimaginable reality. The composition, originally executed in 1995, recorded the members of the Arditti String Quartet playing inside four Royal Dutch Air Force Helicopters. The choppers, meanwhile, flew patterns charted in the composer’s score. Both the helicopters and the string players were miked for sound, broadcasting in real time to a console on the ground where Stockhausen mixed them together.

Thanks for the contribution Björn!

Here is an excellent instructional video in 8 episodes from the 80’s (about 80 minutes). Sit back and enjoy, really good if you want to learn about the basics of the helicopter and the maneuvers. I like the style of the guys in the video!

Just back from 3 hours lesson of meteorology. Today we studied the Cumulunimbus (Cb) clouds and why it’s a big NO NO to fly in or close to these. We also learned some different types of fogs that I’ll share with you:

Radiation fog is formed by the cooling of land after sunset by thermal radiation in calm conditions with clear sky. The cool ground produces condensation in the nearby air by heat conduction. In perfect calm the fog layer can be less than a meter deep but turbulence can promote a thicker layer. Radiation fogs occur at night, and usually do not last long after sunrise. Radiation fog is common in autumn, and early winter. Examples of this phenomenon include the Tule fog. For clarity, Radiation fog is not radioactive.

Ground fog is fog that obscures less than 60% of the sky and does not extend to the base of any overhead clouds. However, the term is sometimes used to refer to radiation fog.

Advection fog occurs when moist air passes over a cool surface by advection (wind) and is cooled. It is common as a warm front passes over an area with significant snowpack. It’s most common at sea when tropical air encounters cooler waters, or in areas of upwelling, such as along the California coast. The advection of fog along the California coastline is propelled onto land by one of several processes. A cold front can push the marine layer coastward, an occurrence most typical in the spring or late fall. During the summer months, a low pressure trough produced by intense heating inland creates a strong pressure gradient, drawing in the dense marine layer. Also during the summer, strong high pressure aloft over the desert southwest, usually in connection with the summer monsoon, produces a south to southeasterly flow which can drive the offshore marine layer up the coastline, a phenomenon known as a “southerly surge”, typically following a coastal heat spell. However, if the monsoonal flow is sufficiently turbulent, it might instead break up the marine layer and any fog it may contain.

Steam fog, also called evaporation fog, is the most localized form and is created by cold air passing over much warmer water or moist land. It often causes freezing fog, or sometimes hoar frost.

Precipitation fog (or frontal fog) forms as precipitation falls into drier air below the cloud, the liquid droplets evaporate into water vapor. The water vapor cools and at the dewpoint it condenses and fog forms.

Upslope fog forms when winds blow air up a slope (called orographic lift), adiabatical cooling it as it rises, and causing the moisture in it to condense. This often causes freezing fog on mountaintops, where the cloud ceiling would not otherwise be low enough.

Valley fog forms in mountain valleys, often during winter. It is the result of a temperature inversion caused by heavier cold air settling into in a valley, with warmer air passing over the mountains above. It is essentially radiation fog confined by local topography, and can last for several days in calm conditions. In California’s Central Valley, Valley fog is often referred to as Tule fog.

Ice fog is any kind of fog where the droplets have frozen into extremely tiny crystals of ice in midair. Generally this requires temperatures at or below −35 °C (−30 °F), making it common only in and near the Arctic and Antarctic regions. It is most often seen in urban areas where it is created by the freezing of water vapor present in automobile exhaust and combustion -products from heating and power generation. Urban ice fog can become extremely dense and will persist day and night until the temperature rises. Extremely small amounts of ice fog falling from the sky form a type of precipitation called ice crystals, often reported in Barrow, Alaska. Ice fog often leads to the visual phenomenon of light pillars.

Freezing fog occurs when liquid fog droplets freeze to surfaces, forming white rime ice. This is very common on mountain tops which are exposed to low clouds. It is equivalent to freezing rain, and essentially the same as the ice that forms inside a freezer which is not of the “frostless” or “frost-free” type.

Artificial fog is artificially generated fog that is usually created by vaporizing a water and glycol-based or glycerine-based fluid. The fluid is injected into a heated block, and evaporates quickly. The resulting pressure forces the vapor out of the exit. Upon coming into contact with cool outside air the vapor forms a fog—see fog machine.

Garua fog is a type of fog which occurs at the western coast of Chile. The normal fog produced by the sea travels inland, but suddenly meets an area of hot air. This causes the water particles of fog to shrink by evaporation, producing a transparent mist. Garua fog is nearly invisible, yet it still forces drivers to use windshield wipers.

Hail fog sometimes occurs in the vicinity of significant hail accumulations due to increased temperature and increased moisture leading to saturation in a shallow layer near the surface.

Flight lesson nr 7 on Thursday

Good night!

Today I’ll explain how the “Airspeed indicator” works.

The airspeed indicator displays the speed of the helicopter through the air by comparing ram air pressure from the pitot tube with static air pressure from the static port—the greater the differential, the greater the speed. The instrument displays the result of this pressure differential as indicated airspeed (IAS). Manufacturers use this speed as the basis for determining helicopter performance, and it may be displayed in knots, miles per hour, or both. When an indicated airspeed is given for a particular situation, you normally use that speed without making a correction for altitude or temperature.

The reason no correction is needed is that an airspeed indicator and aircraft performance are affected equally by changes in air density. An indicated airspeed always yields the same performance because the indicator has, in fact, compensated for the change in the environment.

(Source: Rotocraft Flying handbook)

So today I’ll try to explain how the “Altimeter” works.

The altimeter displays altitude in feet by sensing pressure changes in the atmosphere. There is an adjustable barometric scale to compensate for changes in atmospheric pressure.

The basis for altimeter calibration is the International Standard Atmosphere (ISA), where pressure, temperature, and lapse rates have standard values. However, actual atmospheric conditions seldom match the standard values. In addition, local pressure readings within a given area normally change over a period of time, and pressure frequently changes as you fly from one area to another. As a result, altimeter indications are subject to errors, the extent of which depends on how much the pressure, temperature, and lapse rates deviate from standard, as well as how recently you have set the altimeter. The best way to minimize altimeter errors is to update the altimeter setting frequently. In most cases, use the current altimeter setting of the nearest reporting station along your route of flight per regulatory requirements.

(Source: Rotocraft Flying Handbook)

During the last Meteorology course we talk about winds and air pressure. Have you ever thought about what causes winds and what a low/high pressure is? I’ll try to explain it to you.

Air moves because of differences in both temperature and air pressure, also called atmospheric pressure. Atmospheric pressure is the pressure exerted by the atmosphere at Earth’s surface due to the weight of the air. As the Sun heats Earth’s surface, the surface heats the air above it. As the air molecules warm up, they move farther apart. This reduces the or heaviness of the air and creates an area of low air pressure. On the other hand, molecules in cool air are closer together, making that air denser and heavier. Cool air creates an area of high air pressure.

Wind is caused by air flowing from high pressure to low pressure. Since the Earth is rotating, however, the air does not flow directly from high to low pressure, but it is deflected to the right (in the Northern Hemisphere; to the left in the Southern Hemisphere), so that the wind flows around the high and low pressure areas. This effect of the wind “feeling the Earth turn underneath it” is important for very large and long-lived pressure systems. For small, short-lived systems (such as in the cold outflow of a thunderstorm) the wind will flow directly from high pressure to low pressure.

The closer the high and low pressure areas are together, the stronger the “pressure gradient”, and the stronger the winds. On weather maps, lines of constant pressure are drawn (as in the example, above) which are called “isobars”. These isobars are usually labeled with their pressure value in millibars (mb). The closer these lines are together, the stronger the wind. The curvature of the isobars is also important to the wind speed. Given the same pressure gradient (isobar spacing), if they are curved anticyclonically (around the high pressure in the above example) the wind will be stronger. If the isobars are curved cyclonically (around the low pressure in the example above) the wind will be weaker.

Crystal clear, huh?

It might sound easy but it takes some time of training to get the take-offs and landings working smoothly. So what to think of?

Take off to the hover

• Pre take off checks (won’t go into detail here)
• Gently raise collective to about 17” then more gently
• As the helicopter becomes light on skids it will start to move. Be aware of where the helicopter wants to move.
• Correct the rotation caused by the tail rotor with pedals, be prepared with left pedal since helicopter wants to turn right.
• Correct pitch, roll (left/right/front/back) movements with cyclic.
• When stable, raise collective some more - be active with cyclic and pedals.
• As the helicopter leaves the ground adjust with cyclic for attitude change.
• Establish a 5ft hover
• You’re flying!

Landing from the hover

• Establish steady hover into the wind
• Lower collective and fly the helicopter to the ground
• Make a firm landing with no sideways or rearward movement
• On ground contact lower lever to avoid any bounce. You might need a bit of right pedal.
• Lower collective
• When collective fully down reduce RPM to 80%

Misslanding
It’s important that you “fly” the helicopter to the ground and that there’s no sideways or rearward movement when ground contact is made. If a skid will dig there’s a risk the helicopter will tip over (dynamic rollover). If you experience any sideway movements during landing you should immediately raise the collective and return to a stable hover.

Dynamic rollover
If incorrectly positioned the lift and thrust forces from the main rotor will cause the helicopter to roll about one skid. If not immediately corrected by lowering of the collective lever these dynamic forces will cause the helicopter to roll over. This can often occur when the aircraft is on sloping ground and rapid lifting of the collective lever causes a roll about one skid.