Sloan Helicopters

Frequently Asked Questions Will the helicopter blades stop rotating if engine power is lost?

NO! The helicopter will enter a configuration referred to as "autorotation". In this configuration, the blades are driven solely by aerodynamic forces resulting from rate of descent airflow through the rotor. Assuming the pilot follows procedure, the blades will continue to rotate for some time, and the helicopter may be safely landed.

Principles of Helicopter Flight, W.J. Wagtendonk, Chapter 18, page 137 Can helicopters land anywhere?

Almost. Helicopters are very versatile and maneuverable. However, the landing area must be large enough to safely accommodate both the main rotor and tail rotor blades. Most helicopter companies will have minimum landing area sizes in their operation procedures. Other deciding factors may be: Slope of the landing area the condition of the landing area, ie: logging debris as in cutblocks Gross weight of helicopter Power available of helicopter Wind direction and velocity Safe approach and departure paths Even if the helicopter pilot is able to safely land in the area, he/she may not be able to shut the helicopter engine off or even keep the engine at IDLE! If the ground is unstable, such as muskeg, the pilot may keep the helicopter in a low hover (power on hover) to ensure the safe embarking or disembarking of the passengers.

How do helicopters attain lift?

The basic concept of lift in regards to helicopters can be defined with Newton's third law: for every action there is an equal and opposite reaction. Therefore, as the helicopter blades deflect air downwards, something must go up!

Principles of Helicopter Flight, W.J. Wagtendonk, Chapter 3, pages 15 -16 What is the function of the tail rotor?

The tail rotor (or anti-torque rotor) counteracts the torque of the main rotor on the helicopter. A clockwise-rotating main rotor blade will cause the body of the helicopter to rotate counterclockwise because of torque forces applied to the helicopter. The tail rotor stops this rotation and keeps the helicopter from flat spinning. Also, the tail rotor enables the helicopter to have hover turn capability and balanced forward flight.

Principles of Helicopter Flight, W.J. Wagtendonk, Chapter 9, page 65 What are the functions of the three, main flight controls? The three flight controls are as follows:

The cyclic (the joystick)
The collective (the lever on the left side of the pilot)
The foot pedals.

The cyclic changes the pitch (or bite into the air) of the main rotor blades in a cycle. For example, the pitch on the front blade will increase and the pitch on the aft blade will decrease. This controls the attitude of the helicopter, which is how the pilot steers the helicopter. The collective changes the pitch on the blades simultaneously. If the control input is such that it increases the pitch, then the pitch will increase on all of the blades. This controls the altitude of the helicopter. The foot pedals (or anti-torque pedals) control the pitch on the tail rotor blades. As the pilot changes inputs on the cyclic and collective, he/she must then change the pitch on the tail rotor.

IT IS A FINE BALANCE THAT IS CONSTANTLY CHANGING. Why does the helicopter lift less when the weather is warm compared to a cold day?

Warm air is less dense than cold air. This degrades the helicopter's performance for mainly two reasons: On a warm day, the helicopter blades have less dense air to "bite into", therefore require more air on a warm day to attain equivalent lift compared to a cold day. The engine performance is degraded as well because the warm air is less dense, therefore more air and more compression are required to maintain equivalent engine performance, compared to a cold day. Also, the engine will operate at a higher temperature and may even reach its temperature limits.

Other factors that will degrade a helicopter's performance are:

altitude - the higher the altitude, the less the helicopter will perform moisture content - the more moisture content in the air, the less the helicopter will perform wind - (calm wind conditions may degrade the helicopter's performance. However, strong wind conditions will help the helicopter's lifting abilities as long as the helicopter is pointing INTO wind. If the helicopter is flying with the wind direction, downwind or crosswind, then the helicopter performance will degrade).

How high can helicopters fly?

Each helicopter has its own altitude limit. This limit will vary depending on the air temperature and possibly the gross weight of the aircraft. Some helicopters are rated to 20 000 feet pressure altitude. However, on warm day, this limit will be significantly less. The reason helicopters are subjected to altitude limits is because the air is thinner at higher altitudes opposed to sea level. For example: a square inch column of air weighs approximately 14.7 lbs at sea level. At 20 000 feet, a square inch column weighs 6.75 lbs. As mentioned above, both the rotor system and engine performance will degrade if the air is thinner.

From the Ground Up, Sandy A.F. MacDonald and Isabel L. Peppler, Chapter 6, page 123 Why can't helicopters fly through icing or some winter weather conditions?

If the helicopter is not equipped with anti or de-icing capabilities, then it cannot fly through icing and some winter weather conditions. The reason is that if ice and other winter precipitations adhere to the rotor blades and other flying surfaces of the helicopter, it will change the shape of these surfaces. When this happens, the lifting capability of that surface degrades RAPIDLY! It can even degrade to the point that the helicopter is no longer able to fly.