Lavi - An Engineer's Perspective

7/25/2019 Lavi - An Engineer's Perspective

1/18

LaviIsraels Lost Winged Lion

An Engineers

Perspect ive

by John Golan

Material derived from openly published sourcesNo technical data subject to the EAR or ITAR John Golan 2016

Reflections of an Aerospace Engineer


2/18

John GolanA Brief Biography

Designer, structures analyst, and

engineering manager in the aerospaceindustry for over two decades

Participated in design, development and

field support for jet engines that power a

variety of civil and military aircraft: Bombardier C-Series to the Airbus A380

Boeing F-15 to the Lockheed-Martin F-35

As well as developmental programs

2

Past publication credits include articles inAir Forces Monthly,

Combat Aircraft,Aviation History, and the Jerusalem PostMagazine

The opinions expressed are my own, and do not necessarily

reflect those of my employers, either past or present


3/18

An Engineers Perspective

First studied the Lavi as a graduate engineering student

Teaching assistant for a senior-level airplane design class Explored the Lavi as an example of fighter design principals

As an aerospace engineertrained in airplane designyou

see aircraft differentlyAircraft features can be recognized as the product of different design

trades

3

Evaluations made on the basis of

calculated metricsnot arbitrary

aesthetics

To such a perspective:the Lavi was the product of

specific and unique Israeli

requirements


4/18

Comparison: Mission and Fuel

F-16 and Lavi provide a contemporary comparison in

contrasting aircraft design objectives and philosophies

4

F-16 was designed as a

lightweight air-to-air fighter Immediate antecedent was

Northrops F-5E Tiger II

Thin, trapezoidal wing

Minimal fuel capacity in wing

Lavi was designed as a

lightweight strike jet Immediate antecedent was the

Douglas A-4 Skyhawk

Delta wing with thick root-section

Maximum wing fuel capacity

Also frees up fuselage volume

Wing Fuel Capacity: 3,250 lb

54% of Total Internal Fuel Volume

Wing Fuel Capacity: 1,290 lb

19% of Total Internal Fuel Volume


5/18

Comparison: Structural Weight and Payload

Deeper wing root section of the Lavi also increased wing

stiffness: allowing the Lavi to carry more load at less weight

5

t

b

d hx

=

12

Load-carrying wing spars are essentially

I-beams

Moment of inertia will increase with the

height cubed

Bending stress will decreasewith the height squared

Allowed Lavi to achieve a maximum take-off weight 13

percent greater than a Block 30 F-16C with an empty weight

that was 10 percent less

Allowed Lavi to achieve more than 50 percent greater

combat radius than a Block 40 F-16C with an empty weight

that was 20 percent less


6/18


7/18


8/18

Vertical Tail Trade Studies

Both single and twin vertical tail concepts were examined

Tail-boom configuration was among the more unusual concepts Tail-boom improved control and stability at highest angles of attack

Single vertical tail eventually selected due to lower structural weight

8

Early Lavi concept featuring

tail-boom configuration

Image Credit: Tsach and Peled, 16thICAS, p. 838


9/18


10/18


11/18

Sizing the Airplane for the Mission

11

Three engine models to select from: F404, PW1120, and F100 Represented three different thrust classes of engine

Image Credit: Tsach and Peled, 16thICAS, p. 837

Lavi program was initiatedwith the F404 engine in

February 1980

Requirements later out-grew

the initial engine selection

Engine selection changed to

larger PW1120 engine in May

1981

The Lavi as Sized to its Engine Candidates

F404-440 PW1120 F100-220

Maximum Thrust, Tmax 16,000 lb 20,620 lb 23,830 lb

71.2 kN 91.7 kN 106.0 kN

Weights

Max Take-Off Weight, WTO 32,980 lb 42,500 lb 49,120 lb

14,960 kg 19,280 kg 22,280 kg

Empty Weight, WE 11,720 lb 15,310 lb 17,830 lb

5,320 kg 6,940 kg 8,090 kg

Max Internal Fuel 4,590 lb 6,000 lb 6,990 lb

2,080 kg 2,720 kg 3,170 kg

Max External Fuel 7,120 lb 9,180 lb 10,610 lb

3,230 kg 4,160 kg 4,810 kg

Wing Area, S 276 sq ft 356 sq ft 411 sq ft

25.6 m2 33.0 m2 38.2 m2

Combat Radius (nm)

Hi-Lo-Hi 970 nm 1,150 nm 1,320 nm

1,800 km 2,130 km 2,440 km

Lo-Lo-Lo 580 nm 670 nm 790 nm

1,070 km 1,240 km 1,460 km

PW1120 offered 19% increase in

combat radius at same wing loading


12/18


13/18

Lavi evolved from strike jet

experience with A-4 and Kfir F-16 influenced by F-5E

lightweight fighter experience

Design Trades: Thrust and Wing Loading

Lavi reflected compromises to meet range and payload F-16 emphasized advantages in thrust-to-weight ratio

In air-to-air role, Lavi emphasized advantages in wing loading

13

F-16 continued to add weight as

payload demands grew over the years


14/18

Design Trades: Energy-Maneuverability

Energy-Maneuverability or E-M Diagrams provide a more

comprehensive means for evaluating fighter performance E-M Diagrams plot iso-contours of specific excess power across a range of

speed and altitude or speed and turn rate conditions

Includes effects of thrust loading, wing loading andaerodynamic efficiency

Comparing E-M Diagrams of competing designs allows for a direct

comparison for the strengths and weaknesses of each

14

Preparing an E-M

Diagram requires

extensive knowledge

of each airplane Aircraft weights

Engine performance Speed effects

Altitude effects

Drag polar External stores drag

Mach number effects

g-load effects


15/18


Lavi E-M

capability

extrapolated

from published

data Lightweight air

combat

configuration

illustrated

Drag polar

data-matched

to literature

sources Engine

performance

corresponds to

maximum

(afterburning)

thrust

15


16/18


Existing published data allows for an approximate comparison of

E-M characteristics between the F-16 and Lavi

16

Lavi would have energyadvantage at higher turn

rates

F-16A would have

energy advantage atlower turn rates

Comparison in lightweight

air-to-air configuration


17/18

Design Reflects Priorities and Compromises

No single airplane can be all things for all roles

Trades that go into an airplane will be reflected in its design Degree of air-to-air versus air-to-ground emphasis

Payload and range requirements

Budget or technology constraints

Requirements and priorities will be visible in the final product

17

Lavi was aimed at

developing a light

weight, long-range

strike fighter with a

secondary air-to-air role Very different emphasis

from its contemporaries

Far exceeded capabilities

of its peers in this regard

Nati Harnik, Government Press Office


18/18

Bibliography

Golan, John, Lavi: The United States,

Israel, and a Controversial Fighter Jet

(Sterling, VA: Potomac, 2016).Shmul, Menachem, Eli Erenthal, and

Moshe Attar, Lavi Flight Control

System, International Journal of Control,

No. 1, 1994: 159-182.

Tsach, S., and A. Peled, Evolution of the

Lavi Fighter Aircraft, in Proceedings ofthe 16th International Council of the

Aeronautical Sciences (ICAS)

(Jerusalem: Aug. 28 - Sept. 2, 1988):

827-841.

18

Documents

Lavi - An Engineer's Perspective