Relaxed static stability is adopted on some aircraft in order to
Answer: A
Allowing the centre of gravity aft of the classical limit cuts the download the tail must produce and permits a smaller surface. The aircraft is then flown through a control system that supplies the stability the airframe lacks.
Please log in or register to report this question.
Tail volume coefficient relates the tailplane's
Answer: B
Combining area and arm into one dimensionless number captures how much pitching authority the tail provides. Comparing a new design's value against historical ranges is a quick check that the empennage is not grossly mis-sized.
Please log in or register to report this question.
An aircraft has its centre of gravity at \( 25 \) per cent MAC and a neutral point at \( 38 \) per cent. Its static margin is
Answer: C
Correct answer: 13 per cent
The static margin is the distance from the centre of gravity to the neutral point, expressed as a fraction of the mean aerodynamic chord: \[ 38 - 25 = 13\ \text{per cent MAC.} \] A positive margin means the centre of gravity is ahead of the neutral point, which is the condition for static longitudinal stability - the aircraft returns towards its trimmed attitude after a disturbance.
Please log in or register to report this question.
If the centre of gravity moves aft to \( 35 \) per cent MAC with the neutral point unchanged, the static margin becomes
Answer: D
Correct answer: 3 per cent
\[ 38 - 35 = 3\ \text{per cent MAC.} \] Moving the centre of gravity aft reduces the static margin, and at 3 per cent the aircraft is only just stable: the pitch control is very light, the response quick, and the trim drag low. This is the trade the aft limit governs, and it is why an aft centre of gravity is desirable in cruise but must be bounded.
Please log in or register to report this question.
A tailplane of \( 30 \) m\( ^2 \) sits \( 18 \) m aft of the centre of gravity, on a wing of \( 120 \) m\( ^2 \) with a mean aerodynamic chord of \( 4.5 \) m. The tail volume coefficient is
Answer: A
Correct answer: 1.00
The tail volume coefficient compares the tail’s moment-generating capacity with the wing’s: \[ V_H = \frac{S_t\,l_t}{S_w\,\bar{c}} = \frac{30 \times 18}{120 \times 4.5} = \frac{540}{540} = 1.00. \] Values near unity are typical for a transport. Because it is a ratio of an area times a length to an area times a length, it is dimensionless and comparable across aircraft of any size.
Please log in or register to report this question.
Assertion (A): Relaxed static stability requires a full-authority flight control system.
Reason (R): The airframe alone does not supply the stability the pilot needs.
Select the correct answer from the options below.
Answer: B
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason is exactly why. Relaxed static stability means designing with the centre of gravity at or behind the neutral point, so the airframe no longer returns itself to trim after a disturbance. The stability must then be created artificially by a flight control system reacting faster than a pilot can, which is what makes full authority and the redundancy behind it a precondition rather than an enhancement.
Please log in or register to report this question.
Assertion (A): Static margin is quoted as a fraction of mean aerodynamic chord.
Reason (R): Expressed that way it is comparable between aircraft of different size.
Select the correct answer from the options below.
Answer: C
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the purpose, which is the same one that lies behind quoting centre of gravity in percent MAC. Non-dimensionalising by the mean aerodynamic chord makes a static margin of 10 per cent mean the same degree of stability regardless of the size of the aircraft, so limits, handling criteria and experience transfer between types.
Please log in or register to report this question.
Consider the following statements about longitudinal stability:
1. Static margin is the distance from centre of gravity to neutral point.
2. A positive margin means the centre of gravity is forward of the neutral point.
3. Moving the centre of gravity aft increases the static margin.
Which of the statements given above is or are correct?
Answer: D
Correct answer: 1 and 2 only
Statements 1 and 2 are correct: the static margin is the centre of gravity to neutral point distance, and it is positive when the centre of gravity is forward of the neutral point. Statement 3 reverses the relation - moving the centre of gravity aft brings it closer to the neutral point, so the margin decreases, which is precisely why an aft limit is needed.
Please log in or register to report this question.
Consider the following statements about relaxed static stability:
1. It reduces trim drag and permits a smaller tail.
2. It requires artificial stabilisation through the control system.
3. It improves the aircraft's natural handling qualities.
Which of the statements given above is or are correct?
Answer: A
Correct answer: 1 and 2 only
Statements 1 and 2 are correct: a reduced or negative static margin cuts the tail download needed to trim, so trim drag falls and the tail can be made smaller, and stability must then be supplied artificially. Statement 3 is the opposite of the truth - the natural handling qualities are worse, which is exactly why the control system has to make them good.
Please log in or register to report this question.
Match each stability quantity in List I with its definition in List II.
List I
A. Neutral point
B. Static margin
C. Tail volume coefficient
D. Mean aerodynamic chord
List II
1. Tail area times arm, over wing area times chord
2. Centre of gravity position giving neutral stability
3. The reference length for quoting positions
4. Gap between centre of gravity and neutral point
Select the correct match.
Answer: B
These four connect the weight and balance work of this topic to the stability and control that follows from it. The centre of gravity estimate is only meaningful once its position relative to the neutral point is known.
Please log in or register to report this question.
