Aerodynamic Balance Of Aircraft | Aircraft Aerodynamic Balance | Lecture 43

Summary

This script delves into aircraft control surfaces, explaining how flap type controls generate moments by altering aerofoil camber. It contrasts these with all-moving slab tail planes and spoilers, which adjust angle of incidence and disrupt airflow, respectively. The script further discusses hinge moments, stick force, and the various types of aerodynamic balances and tabs that assist pilots in controlling large and fast aircraft, emphasizing the importance of manual checks for control locks and the trade-offs between control effectiveness and reduced hinge moments at different airspeeds.

Takeaways

• 🔧 Aircraft are equipped with flap type controls that generate the required moment about the center of gravity (CG) by altering the camber of the aerofoil.
• 🛫 There are alternative control surfaces like the all-moving slab tail plane, which is used for pitch control when an elevator is insufficient.
• ⚙️ The angle of incidence of the tail plane is changed by the pilot to generate the required pitching moment, either nose up or nose down.
• 💨 Spoiler surfaces can be utilized to assist ailerons in creating the necessary rolling moment by disrupting airflow and increasing drag.
• 💪 The aerodynamic force resisting control surface movement is known as hinge moment, which the pilot must oppose to achieve the desired control deflection, also referred to as stick force or feel.
• ✈️ Larger aircraft require larger control surfaces, which in turn increase the hinge moment, potentially making it difficult for pilots to operate without assistance.
• 🔄 Aerodynamic balance techniques like inset hinges, horn balances, and internal balances are used to reduce the hinge moment by adjusting forces around the hinge line.
• 📊 Tabs are devices that reduce hinge moment by generating forces after the hinge line; they include balance tabs, anti-balance tabs, servo tabs, and spring tabs, each with different effects on control effectiveness and hinge moment.
• 🔄 A balance tab moves opposite to the control surface, reducing hinge moment but also control effectiveness.
• 🔝 An anti-balance tab moves in the same direction as the control surface, increasing hinge moment and control effectiveness.
• 🛠️ A servo tab can be used for manual reversion in the event of hydraulic failure, reducing hinge moment but also control effectiveness unless compensated by a spring tab at low IAS.
• 🔒 Servo tabs require pilots to physically check for control locks before flight to ensure full control surface movement is possible.

Q & A

What is the purpose of flap type controls on an aircraft?

Flap type controls on an aircraft are used to generate the required moment about the center of gravity (CG) by changing the camber of the aerofoil, thereby allowing the pilot to control the aircraft's pitch.

How does an all-moving slab tailplane differ from a traditional elevator in pitch control?

An all-moving slab tailplane is used instead of a traditional elevator when greater control power is needed. It allows the pilot to change the angle of incidence of the entire tailplane to generate the required pitching moment, whereas a traditional elevator only moves a portion of the tail surface.

What role do spoilers play in controlling an aircraft's roll?

Spoilers help the ailerons generate the required rolling moment by disrupting the airflow over the wing, which decreases lift and increases drag on that side of the wing.

What is hinge moment and why is it important in aircraft control?

Hinge moment is the product of the aerodynamic force acting on a control surface and the distance from the hinge line to the center of pressure. It is important because the pilot must oppose this moment to make and hold the required control deflection, affecting the 'stick force' or 'feel' experienced by the pilot.

How does an inset hinge reduce hinge moment?

An inset hinge reduces the hinge moment by positioning the hinge line aft of the control surface's leading edge, thereby reducing the distance between the hinge line and the center of pressure, which in turn reduces the hinge moment.

What is the function of a horn balance in aircraft control surfaces?

A horn balance reduces the hinge moment by placing a small area of the control surface forward of the hinge line at the outboard end. This area generates an aerodynamic force that opposes the hinge moment, helping to reduce the pilot's required input force.

What is an internal balance and how does it function?

An internal balance reduces the hinge moment by using the pressure difference between the upper and lower surfaces of the aerofoil. A seal between the leading edge of the control surface and the trailing edge of the aerofoil helps manage these pressure differences, effectively reducing the hinge moment.

What is a balance tab and how does it affect control surface effectiveness?

A balance tab is a small aerofoil mounted on the trailing edge of the main control surface. When the pilot moves the control surface, the balance tab moves in the opposite direction, reducing the hinge moment and stick force. However, it also reduces the effectiveness of the control surface by opposing the change in camber.

How does an anti-balance tab differ from a balance tab?

An anti-balance tab differs from a balance tab in that it moves in the same direction as the control surface. This increases the hinge moment and stick force, and also enhances the control surface's effectiveness by increasing the change in camber.

What are the advantages and disadvantages of using a servo tab?

The advantage of a servo tab is that it reduces the hinge moment, stick force, and control feel by moving in the opposite direction to the control surface. However, at lower airspeeds (IAS), its effectiveness is reduced, and it requires physical checks to ensure control locks are removed before flight. It can also be used for manual reversion in case of hydraulic failure.