Lecture 6 - W&B in AC design_BS.pptxtudelft

1
AE3211-I Systems Engineering and Aerospace Design
Challenge the future
Delft
University of
Technology
AE3211-I Systems Engineering and
Aerospace Design
• Introduction to the Aircraft content of the course
• Aircraft balance
Dr. Fabrizio Oliviero (FPP)

2
Introducing aircraft design part

3
Course schedule
The Course is about inflecting (and use) “System Engineering” for the design of Aerospace Products:
therefore you can expect a variety of topics covered during 9 lectures.
Lecture
num.
Topic Lecturer Date Hour Format
#1 SE for Aerospace E. Gill 15-Feb 8.45 - 10.45 Hybrid (LR-CZ A)
#2 SE methods E. Gill 16-Feb 8.45 - 10.45 Hybrid (LR-CZ A)
#3
Risk Management & Concurrent Engineering
(Design for Lifecycle)
E. Gill 22-Feb 8.45 - 10.45 Hybrid (LR-CZ A)
#4 V&V for S/C Control E. Gill 23-Feb 8.45 - 10.45 Hybrid (LR-CZ A)
#5 V&V for S/C Propulsion A. Cervone 29-Feb 8.45 - 10.45 Hybrid (LR-CZ A)
#6 W&B in aircraft F. Oliviero 1-Mar 8.45 - 10.45 Echo Hall B1-B2
#7 Requirements & Design for A/C Stability F. Oliviero 7-Mar 8.45 - 10.45 Hybrid (LR-CZ A)
#8 Requirements & Design for A/C Controllability F. Oliviero 8-Mar 8.45 - 10.45 Hybrid (LR-CZ A)
#9
Requirements & Design for A/C lateral and ground
stability
F. Oliviero 11-Mar 13.45 - 15.45 Aula lecture Hall A
#10 (TBC) Recap (TBC)
E. Gill & F.
Oliviero
14-Mar 8.45 - 10.45 Hybrid (LR-CZ A)

4
Motivation for the overall AE3211-I course:
• Complete what you need to design spacecraft and aircraft systems!
• Understand how the elements from previous courses fit into a coherent framework of
how to engineer a complex aerospace product!
• Get prepared for the Design Synthesis Exercise!
• Appreciate the use of Systems Engineering (not only for aerospace products!)
See lecture 1 by Prof. Gil
Motivation

5
Motivation for this specific a/c design oriented module:
• Complete what you need to design spacecraft and aircraft systems!
• Understand how the elements from previous courses fit into a coherent framework of
how to engineer a complex aerospace product! to perform conceptual design of
aircraft
• Get prepared for the Design Synthesis Exercise!
• Appreciate the use of Systems Engineering through aircraft application examples
of:
• Requirements and Functional analysis
• Management of iterations in the design process
Motivation -2
SE is a good recipe to make a good product, but it is essential to understand and know the ingredients

6
Functions identification
Function
Generate lift
Roll control
Vertical equilibrium
Sub system
Airfoil and wing planform
HLDs
Aileron
Structural weight
Sub-function
Efficiently @ cruise
Max lift @ low speed
Change in bank angle
Sustain loads
System
Wing
EOW
System engineering problems:
• How to determine all the necessary (sub)functions?
• How to identify the needed systems?
• How to size properly the systems?

7
Functions identification
Function
Weight and balance
Stability
Controllability
Systems
Masses (already done in
AE2111)
CG location
Tail
Landing gear
• All these aspect will be faced first for the longitudinal plane characteristics
• Then we will characterize them also for the lateral-directional motions.
• We will not dive (too much…) into physics but we will try to determine possible design strategies

8
Relevance of weight&balance in a/c design
Complex or complicated? (see lecture 1)

9
Study material
• Lecture presentations
• Additional presentations will be available on BS
• Books on Aircraft Design previously cited in AE1222 and AE2111

10
A note on the notes*…

11
Contents & Learning Objectives of the Lecture
• Introduction and overall overview of the Aircraft Design part
• Weight&balance
• Definition
• Determine the Center of Gravity (CoG) for the empty Operative Weight (EOW) condition
• Definition of the loading diagram: Examine the effect of loading fuel and Payload on the
balance of the aircraft
• Distinguish about W&B for design and W&B for operations

12
Balance of the aircraft
Definition and assessment of the c.g. position of the empty aircraft

13
Previously…
During AE2111-II you learnt to predict the EOW through class II estimation methods.
• A typical class II method combines relevant geometry and load parameters (Nz) and corrective
coefficient to calculate weight of components

14
Applying Class II methods
What if OEWi+1 ≠ OEWi ?
Class I application Class II results
• Iterate until perc. diff < 1%
• Be aware of the consequences!!!
And if OEW1 ≠ OEW2 ?
The iteration involves all the class I
and the aerodynamic analysis!
%MTOW
OEW1
Class II application
OEWi
OEW2
Already remarked that the computation of the weight is a (doubled!) iterative process.

15
Fundamentals
Balance, stability, manoeuvrability aspect deal with moments around aircraft important poles. We will focus
our attention on the longitudinal plane, but same approaches will be applied on lateral and directional aspects.

16
Main moments and forces in the longitudinal plane
• The CoG or (C.G.) is the point where the inertial forces are applied
• The Center of Pressure is the point where the resultant of the pressure distribution is applied (and the
aerodynamic moment is nihil around this point)
• The Aerodynamic Center (or Focus) is the point where the aerodynamic moment is constant at varying
the Angle of attack. It is usually positioned along the Mean Aerodynamic Chord!

17
the equilibrium of moments (i.e. TRIM)
that the equilibrium is stable
that the aircraft can be maneuvered with the right amount of force
Relevance of stability and control in a/c design
From a functional analysis perspective, the design should ensure in every (non) flight condition:
Note that the requirements associated to these functions usually come from regulations.

18
The balance of the aircraft
However, airplane must be designed to guarantee safety and full
functionality…
• …for the whole range of c.g. positions,
• …both in flight…
• …and on the ground.
Balancing the aircraft is about managing and/or dealing with*
the position of the c.g. in order to guarantee safety and full
functionality during all the operations.
𝐷𝐴𝑇𝑈𝑀
𝑋𝐶𝐺 𝑓𝑤𝑑
𝑋𝐶𝐺 𝑎𝑓𝑡
𝑋𝐶𝐺
𝑋
While the c.g. of the empty aircraft is more or less fixed, variation in fuel and payload can generate large
variations of the c.g. position* both from mission to mission but also during a single mission

19
The balance of the aircraft
During design, the balance of the aircraft is generally achievable by one or all of the following:
• Longitudinal position of the wing with respect to the fuselage*
• Size and position of the horizontal tail
• Distribution and location of systems and payload on the fuselage
• Location of landing gears
• Implementation of a control system for the fuel flow
• Prescription of limits on the loading procedure
…and during groung operation? How can the aircraft be balanced?

20
The aircraft balance process during the design
A typical design approach to balance the aircraft consists of the following steps:
1. Determine the center of gravity position of the aircraft at operative empty weight*, for the
assumed tail size and longitudinal wing position
2. Add the c.g. variations caused by non fixed items, such as payload (pax and freight) and
fuel*.  Loading diagrams.
3. Check the maximum c.g. range against the allowable most aft and most forward c.g.
position**.  X-plot
4. If necessary, adjust the tail size*** and longitudinal wing position, and iterate from
point 1
X-plot
loading diagram

21
The process of aircraft balance (during the design)
Calculate the
CG of the EOW
Calculate the
CG of variables
masses
Build the
loading
diagram
Evaluate the
effects of
design
parameters

22
To compute the c.g. position of the operative empty aircraft, it is necessary to know the location of all
the weight components with respect to the aircraft reference system.
We rely again on Class II components CG estimation similarly to the weight estimation procedures.
Example of component c.g. location information (source Roskam)
The OEW c.g. position
Calculate the
CG of the EOW
Calculate the
CG of variables
masses
Build the
loading
diagram
Evaluate the
effects of
design
parameters

23
Example of component c.g. location information
Fuselage CG: only structure +systems (the engine is always excluded)*
Tail**:

24
Wing (including movables and
systems, no fuel):
Nacelle:
Engine:
Example of component c.g. location information

25
To control the c.g. of the empty aircraft moving the wing position with respect to the fuselage, it is
convenient to arrange the various weight components into a fuselage group and a wing group
The aircraft balance process. The OEW c.g. position
The first balancing of the aircraft occurs early in the design phase where the most important variable
to be decided is the longitudinal location of the main wing.

 

i
i
i
i
CGi
CG
W
W
x
x OEW

26
What’s in the FUSELAGE GROUP?
All parts that are somehow fixed to the
fuselage or generally related to it, that is:
• Furnished fuselage with systems
• Fuselage mounted engines
• Tail
• Nose wheel
NO main landing gear, which is typically
positioned with respect to the wing MAC*
What’s in the WING GROUP?
• wing structure with movables and systems
• wing mounted engines** with fuel systems
• The main landing gear - even when
physically attached to the fuselage!
The main landing gear is positioned relatively to the
wing (i.e. to the wing a.c.) , typically at 45-50%
MAC, to guarantee ease of rotation at take off.
Why?
The position of the landing gear, as the
position of the wing, affects not only the CG
position but also the CG limits due to
clearance and stability requirements during
ground operations.

28
To obtain small tail loads, the center of gravity is always located close to the wing aerodynamic center (a.c.):
therefore, it is convenient to express the c.g. location (Xcg) in %MAC* (neglecting the effect of the wing twist).
𝑋𝐿𝐸 𝑚𝑎𝑐
mac
𝑋𝐶𝐺
𝑋𝐶𝐺 =
𝑋𝐶𝐺 − 𝑋𝐿𝐸𝑚𝑎𝑐
𝑚𝑎𝑐

29
The first step consists in the identification of an initial longitudinal wing-fuselage setting.
A “first attempt” wing position (XLEMAC) can be estimated based on known OEW c.g. positions (XOE)
from reference aircraft, as follow*:
c.g.@ OEW
(%MAC):
20-25% 35-40% 25-30%
𝑋𝐿𝐸𝑀𝐴𝐶 = 𝑥𝐶𝐺 𝐹𝐺 − 𝑥𝐶𝐺 𝑂𝐸 +
𝑊𝑊𝐺
𝑊𝐹𝐺
𝑥𝐶𝐺 𝐹𝐺 − 𝑥𝐶𝐺 𝑂𝐸
Alternatively, if the initial location of the wing is already known/determined by previous requirements, the
CG@EOW can be calculated by the classic multi-body system

30
Generation of the aircraft loading diagrams
How to load an aircraft…when you don’t have an aircraft (yet)

31
The loading diagram
Possible shifts of the CoG can be caused by the loading of:
• Passengers
• Fuel
• Cargo
The CoG can be different for each mission but is varies during a mission (burning fuel)
How can we calculate those possible position?
Calculate the
CG of the EOW
Calculate the
CG of variables
masses
Build the
loading
diagram
Evaluate the
effects of
design
parameters

32
The loading diagram
25000
27000
29000
31000
33000
35000
37000
39000
41000
43000
45000
0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400
mass
[kg]
xcg [mac]
window seats
aisle seats
middle seat
fuel
cargo
Once the position of the aircraft c.g. @ OEW is known, cargo, passengers and fuel are loaded
until MTOW has been reached.
During loading, the c.g. of the aircraft will vary as shown in this graph, called the loading
diagram (or potato diagram).
Goal of the diagram is
to assess the maximum
c.g. range* of the
aircraft

33
The cargo loading diagram
This graph is relative to a passengers aircraft with 2 cargo holds (front and rear).
In this case the cargo has been represented as two concentrated masses.
However, when the cargo is arranged in many unit loading
devices, it is better to consider the effect of each unit load
device separately.

34
The passenger loading
Usually we rely on a statistical prediction of the passenger
distribution normally managed by the different airliners.
The “window seating rule” can be adopted.

35
The fuel loading diagram
However different and separated fuel tanks can be
installed in a wing and a fuel flow control system can
be used to manage the tanks emptying sequence.
Keeping fuel at the tip of the wing increases the
bending relief action.
For simplicity we can assume that the fuel c.g. is located in correspondence of the tank c.g.

36
The loading diagram
25000
27000
29000
31000
33000
35000
37000
39000
41000
43000
45000
0,000 0,050 0,100 0,150 0,200 0,250 0,300 0,350 0,400
xcg [mac]
mass
[kg]
window seats
aisle seats
middle seat
fuel
cargo
This is the loading diagram of a passengers aircraft.
Use a 2% margins to account
for the c.g. variations caused by
passengers and attendants
moving, landing gear retracting,
food and drinks served, etc.
Calculated with
class II methods
OEW
MZFW
MTOW

37
Centered. The most convenient, because of the small c.g. range
Tilted forward. The OEW c.g. is quite close to the tail, due to the
aft fuselage mounted engines. Passengers and fuel shift the c.g.
strongly forward. More difficult to balance
Tilted backward. The OEW c.g. is slightly close to the nose, due to
the forward wing mounted engines. Passengers shift c.g. backward.
Less difficult to balance due to the longer tail arm
The loading diagram

38
The loading diagram
25000
27000
29000
31000
33000
35000
37000
39000
41000
43000
45000
0,000 0,050 0,100 0,150 0,200 0,250 0,300 0,350 0,400
xcg [mac]
mass
[kg]
window seats
aisle seats
middle seat
fuel
cargo
The ground controllability and
stability limits depend on the
landing gear positioning
The extreme front and aft c.g. position must be compatible with the limits dictated by aircraft
controllability and stability, both in flight* and on the ground
The ground controllability and
stability limits on flights
depend on the tail (or canard)
size and positioning

39
Effect of longitudinal wing shift
• Position 1. (the one used for the initial tail sizing)
• Slightly forward wing positioning (e.g. position 1 -10%)
• Slightly backward wing positioning (e.g. position 1 +10%)
In order to affect the c.g. range (i.e., the position of the most fore and aft c.g), the designer has the
opportunity to modify the longitudinal position of the wing (group) with respect to the fuselage.
To study how the c.g. ranges changes with the longitudinal wing position, we can generate 3 loading diagrams
for 3 different wing positions (expressed in terms of XLEMAC/lfuselage ratios):
Finally, a plot can be generated that describes the c.g. range variations for different longitudinal position of
the wing w.r.t. the fuselage (XLEMAC/lfuselage vs. Xcg/MAC)
Calculate the
CG of the EOW
Calculate the
CG of variables
masses
Build the
loading
diagram
Evaluate the
effects of
design
parameters

40
loading diagram wing postion 1
25000
27000
29000
31000
33000
35000
37000
39000
41000
43000
45000
0,000 0,050 0,100 0,150 0,200 0,250 0,300 0,350 0,400
cg [mac]
mass
[kg]
window seats
aisle seats
middle seat
fuel
cargo
wing position 1
2% in-flight variations
Initial wing positioning
c.g. max range at wing position 1
Effect of longitudinal wing shift

41
loading diagram wing postion 1
25000
27000
29000
31000
33000
35000
37000
39000
41000
43000
45000
0,000 0,050 0,100 0,150 0,200 0,250 0,300 0,350 0,400
cg [mac]
mass
[kg]
window seats
aisle seats
middle seat
fuel
cargo
wing position 1
2% in-flight variations
Effect of longitudinal wing shift on c.g. travel
laoding diagran wing position 2
25000
27000
29000
31000
33000
35000
37000
39000
41000
43000
45000
0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400
xcg [mac]
mass
[kg]
window seats
aisle seats
middle seat
fuel
cargo
wing position 2
Wing shifted forward
(OEW c.g. moves back on MAC)
c.g. max range at wing
position 2

43
loading diagram wing position 3
25000
27000
29000
31000
33000
35000
37000
39000
41000
43000
45000
-0.100 -0.050 0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400
xcg [mac]
mass
[kg]
window seats
aisle seats
middle seat
fuel
cargo
wing position 3
Wing shifted back
(OEW c.g. moves forward on MAC)
c.g. max range at wing
position 3

44
Most forward
Most aft
c.g. max range at wing position 2 (forward)
c.g. max range at wing position 1
c.g. max range at wing position 3 (backward)
A plot can be generated that describes the
c.g. range variations for different longitudinal
position of the wing w.r.t. the fuselage
(XLEMAC/lfuselage vs. Xcg/MAC).
Remember this plot because it will be used in
the following lecture to design the aircraft
according to stability and controllability
criteria!

45
The cargo loading diagram for a freighter
In case of freighter, there are hundreds of loading possibilities so that the design problem is
faced in the inverse way:
Given the final fore-and-aft position of the cg, what are all the possible location of the cargo cg
for different amount of payload.
  limit
limit
cargo
cargo cg
OE
cg x
x
x
W
OEW
x 


CG
cargo
cargo 1 x
W
OEW
x 












46
The aircraft balance process during operation
How relevant is W&B during normal aircraft operation?
“Between 2008 and 2016, the probable causes of 136 general aviation (GA) accidents (in US only) were
related to pilots improperly conducting preflight performance calculations for W&B”
“82 air transport (FAR/CS 25) accident in the period 1970-2005 whose the primary cause was related to W&B
mistakes”

47
The aircraft balance process during operation
The typical operational approach to balance the aircraft (pilot is responsible) consists of the
following steps:
1. Given the center of gravity position of the aircraft at operative empty weight* add the c.g.
variations caused by the actual non fixed items, such as the embarked payload (pax and
freight) and fuel**.
2. Check the weights are within the operational limits
3. Check the maximum c.g. range against the allowable most aft and most forward c.g.
positions*.
4. If necessary, adjust the position of the payload, or unload excessive weight

48
The loading diagram for operations
For commercial flight there is a ground operator who
is responsible of supervising the load operation and
he/she decides disposition of cargo and amount of
boarded amenities. He/She prepares the load and
balance sheet.
The commander pilot checks that the information
contained in the load and balance sheet are
compatible with the CG range limits of each flight
(and ground) condition.
Most of the times, the operating activities are
managed through automated processes and
software (e.g. each baggage weight measured at the
check in is then included software to estimate weight
and location of each LD)
These limits are given by the specifications identified during the AC design!

49
W&B systems
“Primary onboard aircraft weight and balance systems could resolve most of the weight and W&B such systems is
currently insufficient to enforce the use of these systems on commercial aircraft as primary means for
determining the weight and balance. However secondary weight and balance systems could still be of some value
in preventing weight and balance related accidents.”

52
During this lecture…
1. the concept of aircraft balance and methods to control it
2. to compute the OEW CG of the aircraft and the effects of shifting the wing groups on CG
location
3. to compute the operational c.g. range of an aircraft (i.e. generation of loading
diagrams) and its dependency on the overall vehicle architecture
4. to distinguish between W&B tasks during the conceptual design of the aircraft from W&B
activities during the actual aircraft operations
You have learnt:

53
Questions?

Lecture 6 - W&B in AC design_BS.pptxtudelft

Recommended

Recommended

More Related Content

Similar to Lecture 6 - W&B in AC design_BS.pptxtudelft

Similar to Lecture 6 - W&B in AC design_BS.pptxtudelft (20)

Recently uploaded

Recently uploaded (20)

Lecture 6 - W&B in AC design_BS.pptxtudelft