Short Course on Multibody Dynamics

Transcript

Promemoria lezione
AA 2007-2008
Meccanica del Volo
Propulsione
Tipi di propulsione
Dipartimento di Ingegneria Aerospaziale
Politecnico di Milano
Meccanica del Volo
Motore a combustione
interna alternativo
Pratt-Whitney_R-2800
Lycoming O-235C2
Pratt & Whitney R-4360
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Rolls-Royce
Griffon
Type
12-cylinder supercharged liquid-cooled 60° Vee aircraft piston engine
Power output:
2,035 hp (1,520 kW) at 7,000 ft (2,135 m)
1,820 hp (1,360 kW) at 21,000 ft (6,400 m)
Dry weight:
1,980 lb (900 kg)
Specific power:
0.91 hp/in³ (41.4 kW/L)
Power to weight ratio: 1.03 hp/lb (1.69 kW/kg)
The Rolls-Royce Griffon engine was used in the Schneider Trophy races.
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Motore stellare a
combustione interna
Motori stellari o in linea
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The debate about the merits of the radial vs. the inline continued
throughout the 1930s, with both types seeing some use.
The radial was more popular largely due to its simplicityand better
power/weight ratio for aircraft carrier takeoffs.
Although inline engines offer smaller frontal area than radials, inline
engines require the added weight and complexity of cooling systems
and are generally more vulnerable to battle damage.
Originally radial engines had but one row of cylinders, but as engine
sizes increased it became necessary to add extra rows.
Most did not exceed two rows, but the largest radial engine ever built
in quantity, the Pratt & Whitney Wasp Major, was a 28-cylinder 4-row
radial engine used in many large aircraft designs in the post-World
War II period.
Motore a combustione
interna alternativo
La potenza erogata da
tali motori dipende:
Meccanica del Volo
• dal numero di giri.
La potenza cresce all’aumentare
del numero di giri.
• dalla pressione di alimentazione
manifold pressure funzione della
valvola di regolazione dell’aria air throttle, la farfalla.
• dal rapporto ponderale aria-combustibile
Titolo della miscela: miscela ricca o miscela povera
• dalla quota.
La potenza diminuisce con la quota di volo.
Una formula empirica porta a esprimere la
potenza alla generica quota z come
• è sostanzialmente indipendente dalla velocità di volo
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P-51 Mustang
If it is well designed, a contra-rotating propeller will have no rotational air flow,
pushing a maximum amount of air uniformly through the propeller disk, resulting in
high performance and low induced energy loss.
It also serves to counter the asymmetrical torque effect of a conventional propeller.
Some contra-rotating systems were designed to be used at take off for maximum
power and efficiency, and allowing one of the propellers to be disabled during cruise
to extend flight time.
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The first Griffon-powered Spitfire, DP845
Contra-rotating
propellers
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A Rolls-Royce Griffon powered the North American P-51 Mustang that
was an American long-range single-seat fighter aircraft that entered
service with Allied air forces in the middle years of World War II.
Jet engines
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Compressore
centrifugo
Compressore
assiale
Turbofan engines
Low-bypass
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L’uso di turbofan, con piccola
o grande diluizione, riduce i
consumi e contribuisce a
ridurre il livello di rumore
High-bypass
Bypass ratio 2 - 5
Bypass ratio 6 - 9
Turboshaft
engine
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turboelica
Carnot's theorem
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Carnot heat engine diagram
Thermal efficiency
is defined as
Carnot’s limit on the
maximum efficiency
The first law of thermodynamics requires
The second law of thermodynamics requires
The third law of thermodynamics requires the use of an absolute temperature scale
Together they imply a maximum heat-to-work efficiency of:
Carnot's theorem
Thermal efficiency is defined as
Meccanica del Volo
Carnot heat engine diagram
Carnot’s limit on the maximum efficiency
The first law of thermodynamics requires
The second law of thermodynamics requires
The third law of thermodynamics requires the use of an absolute temperature scale.
Together they imply a maximum heat-to-work efficiency of:
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Evoluzione del consumo specifico
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Evoluzione dell’inquinamento
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Turbogetto
All’aumentare della quota la portata in massa diminuisce per effetto
dalla diminuita densità. Sino alla tropopausa, si può esprimere la
trazione T ad una quota assegnata z come
Il consumo specifico cresce all’aumentare della velocità di volo e
rimane circa costante al variare della quota; valore indicativo:
0,8-1,0 N(N h).
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Gloster E.28/39
The W2/700 engine flew
in the Gloster E.28/39,
the first British aircraft to
fly with a turbojet engine,
and the Gloster Meteor.
In September 1939, the Air Ministry issued a
specification to Gloster for an aircraft to test
one of Frank Whittle's turbojet designs.
Working closely with Whittle, Gloster's chief
designer George Carter laid out a small lowwing aircraft of conventional configuration.
The jet intake was in the nose, and the tail-fin
and elevators were mounted above the jet-pipe.
Le camere di combustione
circonferenziali
A contract for two prototypes was signed by the
Air Ministry on 3 February 1940 and the first of
these was completed by April 1941
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Me 262
The Messerschmitt Me 262 Schwalbe (German "Swallow") was the world's first
operational jet-powered fighter aircraft. It was produced in World War II and saw
action starting in 1944 in bomber/reconnaissance and fighter/interceptor roles.
Officially named Schwalbe, because the swallow is one of the fastest birds
known when going into a dive to capture and eat an airborne insect, German
pilots nicknamed it the Turbo, while the Allies called it the Stormbird.
While the Me 262 had a negligible impact on the course of the war (approximately
150 Allied aircraft losses for 100 Me 262 losses), its design was highly influential
on postwar aircraft development.
DH-106 Comet
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Vickers Viscount
The British de Havilland Comet first flew in
1949 and is noted as the world's first
commercial jet airliner
On 10 January 1954, BOAC Flight 781 a De
Havilland Comet 1 took off from Ciampino
Airport in Rome, Italy en route to Heathrow
Airport in London, England on the final leg
of its flight from Singapore. At about 10:00
GMT, the aircraft suffered an explosive
decompression at altitude and crashed into
the Mediterranean Sea, killing everyone on
board.
Meccanica del Volo
BOAC Flight 781
After extensive testing of the Comet
1 G-ALYU ("Yoke Uncle") which had
been donated for testing by BOAC,
investigators at the RAE concluded
that the crash had been due to
failure of the pressure cabin at the
forward ADF window in the roof.
This 'window' was in fact one of two apertures for the aerials of an electronic
navigation system, opaque fibreglass panels taking the place of the window
'glass' - as a result of metal fatigue caused by the repeated pressurisation and
de-pressurisation of the aircraft cabin.
In addition, it was discovered that the stresses around pressure cabin apertures
were considerably higher than had been appreciated, especially around sharpcornered cut-outs, such as windows.
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ugelli
postbruciatore
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Trent 900
Leading the way on the Airbus A380
Engine Specification
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SL 0.25M,
flat-rated to 30°C/86°F
Thrust
70,000-76,500lb
Certificated up to 80,000lb
Bypass ratio
Inlet mass flow
8.7-8.5
2655-2745lb/sec
Fan diameter
116in
Length
179in
Weight
14,190lb
Stages
Fan, 8 IPC, 6 HPC
1 HPT, 1 IPT, 5 LPT
Certification 29th October 2004
GE90-115B
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Fan/Compressor Stages: 1F/4LPC/9HPC
Low-Pressure Turbine/High-Pressure Turbine Stages: 6/2
Application Examples:
Boeing 777-200LR
Boeing 777-300ER
Max Diameter (Inches): 135
Length (Inches): 287
Dry Weight (Lb.): 18,260
Max. Power at Sea Level (Lb.): 115,300
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GE90-115B
E’ il motore più grande e più
potente al mondo.
Certificato per 115000 lb
52.000 kg, ha sviluppato in
prova una spinta di 127900 lb,
58000 kg.
Il diametro misura poco meno
di tre metri e mezzo. Visto da
vicino lascia particolarmente
stupiti,
fa
decisamente
impressione.
Statoreattore
scramjet
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supersonic combustion ramjet
Boeing X-43
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Guinness
World
Records
recognized
NASA's
X-43A
scramjet with a new world speed
record for a jet-powered aircraft
Mach 9.6, or nearly 7,000 mph.
Pegasus booster rocket ignites to send
the X-43A on its record setting flight on
Nov. 16, 2004. NASA photo

Short Course on Multibody Dynamics

Transcript

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