personal simulation workshop - aircraftdesign.nuaa.edu.cnaircraftdesign.nuaa.edu.cn/pd-2010/1-4...

Powerplant considerations

航空宇航学院

航空宇航学院

Synthesis Process

1. Specification

2. Configuration A

3. Flight regime / Powerplant

4. Fuselage layout

5. Wing configuration 1

6. Lift, drag, mass

7. performance

8. Stage one optimization:T/Mg, mg/S

8. Stage two optimization: referee design

8. Configuration comparison

9. Concept analysis

Configuration B Configuration C

Wing configuration 2 Wing configuration 3

航空宇航学院

Introduction

• The maximum speed is one of the more

important requirements for a specified aircraft.

• Flight regime is directly related to the type of

powerplant system.

• A general knowledge of the characteristics of

various powerplants is necessary to make

correct selection of powerplant type.

航空宇航学院

Outline

• Powerplant (Propulsion) Characteristics

• Types of Powerplant

• Typical Engine Parameters

• Flight Regimes of Powerplants

• Powerplant Performance Representation

• Typical Aircraft Installed Thrust and Power

航空宇航学院

Powerplant Characteristics

• Thrust– The thrust developed by an engine is the rate of change of

momentum imposed upon propelling medium

– m_bar is mass of propelling medium

– v is velocity of propelling medium

– For an air breathing engine (jet propulsion)

( )d

T mvdt

0 0( ) ( )j F j j jT m V V m V p p A 0( )jT m V V

M is mass flow through the engine per unit time

V0 is the aircraft speed

Vj is the jet velocity

航空宇航学院


• Thrust– To compare different types of engine, a specific

thrust is defined as:

0( )SP j

TT V V

m

航空宇航学院


• Efficiency

– The overall efficiency of a powerplant system depends

on:

• a ideal efficiency

• the various mechanical and thermal efficiencies of the engine

• air intake

• nozzle

航空宇航学院


• Efficiency– Ideal propulsion efficiency

Comments:

The highest efficiency is realized when Vj is only small increment

above V0.

The most efficient powerplant is one where the thrust is generated

by imposing a small velocity increment on to a large mass of air.

For given Vj , the efficiency increases with forward speed V0

0

2

1jV

V

航空宇航学院


• Noise

– The primary sources of engine noise

• The airflow interactions with the rotating

components

• The exhaust gases

– Noise can be an important consideration

• Quieter commercial aircraft

• Stealth consideration

航空宇航学院


• Relationship between power and thrust

of propeller propulsion

T = P/V0

P is the power

V0 is flight speed

is propeller efficiency

航空宇航学院

Types of Powerplant

• Piston Engines

• Gas Turbines

– Jet engines

– Afterburning/reheat engines

– Turbofan engines

• Low bypass ratio engines

• High bypass ratio engines

– Turboprop engines

• Others

– Ramjet

– Rocket

– Electric powered propeller

航空宇航学院

Piston Engines

• Characteristics

– Thrust/Power

– Efficiency

– Noise

– Cost

• Application

– Relatively small, slow

speed aircraft

– Examples

• AD100/AD200

A four-stroke combustion cycle to convert gasoline into motion

Cranked shaft

piston

Connecting rod

Engine blockIntake port

① Intake

② Compression

③ Combustion

④ Exhaust

航空宇航学院

Turbojet Engines (Basic Jet)

• Characteristics

– Thrust/Power

– Efficiency

– Noise

– Cost

• Application

– Fighter,Trainer

– Examples

• F-7(China)

航空宇航学院

Turbofan Engines

Turbofan is evolved from the turbojet essentially by increasing the size of the

first-stage compressor to the point where it acts as a ducted fan blowing air

past the "core" of the engine.

航空宇航学院

Turbofan Engines

• High and low bypass ratio engines.

– What is bypass ratio ?

• the ratio of how much air goes through the fan, to how

much goes through the engine.

– Typical bypass ratios:

• 1:1 for a low bypass

• 5:1 or more for a high bypass.

– Application

• Low bypass engines are more efficient at higher speeds,

and are used on planes such as military aircraft.

• High bypass engines are used in commercial airliners.

航空宇航学院

Turbofan Engines

• Characteristics

– Thrust/Power

– Efficiency

– Noise

– Cost

• Application

– This type of engine runs best

from about 400 to 1,000 km/h,

which is why the turbofan is

by far the most used type of

engine for aviation use.

• Transport

• Fighter

• Business jet

航空宇航学院

Afterburning Engines

• What is Afterburning Engines

– A jet or turbofan engine with afterburner.

• What is afterburner ?

– The jet engine afterburner is an extended exhaust section

containing extra fuel injector nozzles.

• In what case afterburning is need ?

– Performance requirements demand very high thrust for a

short period of time

• Transonic acceleration

• Supersonic dash

航空宇航学院

Turboprop Engines

• Turboprops are similar to turbofans in that they incorporate

an extra set of turbine blades used to drive the propeller.

• Unlike the turbofan engines, nearly all the thrust produced by

a turboprop is from the propeller, hardly any thrust comes

from the exhaust.

航空宇航学院

Turboprop Engines

• Thrust

– Typically range from 300 to 4000 kW power output

• Efficiency

– very efficient over a fairly wide range of speeds

• Noise

• Drawback: they have propellers.

• Application

– Smaller and slower planes such as commuter aircraft that fly

to the smaller airports.

– Large transport aircraft

• The general public does not like propellers, as they appear to

be old-fashioned and unsafe.

• The military knows better and uses them on several large

transport aircraft.

航空宇航学院

Unducted Fan Engines

• An unducted fan, or UDF, is a modified turbofan engine, with the fan placed outside of the engine nacelle.

• The appearance is similar to a pusher propeller-driven piston engine.

• It was intended to offer the speed and performance of turbofans, with the fuel economy of turboprops.

• One of the major problems are noise issues.

航空宇航学院

Typical Engine Parameters

• Specific Thrust

– The higher values relate to those engines

which have lower relative mass flows

航空宇航学院


• Frontal area

– Capture area ranges from the intake area of a jet

or bypass engine to the fan or propeller disc area.

航空宇航学院


• Disc loading

航空宇航学院


• Propulsive Efficiencies– Typical variation of ideal powerplant efficiencies as function

of Mach number

Recall ideal

propulsion efficiency

0

2

1jV

V

航空宇航学院

Flight Regimes of Powerplants

• Propeller Engines

– Efficiency change

• The efficiency increases rapidly with speed, because the

thrust from a propeller is derived by the addition of a small

velocity change to a large mass of air.

– Efficiency range

• Propeller for small, slow aircraft: < 70%

• At somewhat higher speed (M0.3-0.65): 85-90 %

– Applications

• For flight speed up to M0.5

– piston/propeller or turbine/propeller

• For flight speed ranging from M0.5 to M 0.7

– turbine/propeller

航空宇航学院


• Turbofan Engines

– Aircraft with flight speed ranging from M0.7 to M 0.9

• Turbofan engines with the higher bypass ratios (4-8) are used on

relatively longer range aircraft.

– Some aircraft at M0.5 to 0.7.

• While their efficiency at these lower speeds is less than that of a

propeller engine, their relatively small size can enable a more

compact aircraft to be designed which is more efficient.

• Such aircraft are often in the small business/executive class.

– Application to supersonic flight

• Turbofan engines with the low bypass ratios(0.4-1.0) are used on

military aircraft, such as fighters.

航空宇航学院

Turbofan Engine used on long range aircraft

Boeing 777

航空宇航学院

Turbofan Engine used on business jet

P&WC PW308A

航空宇航学院

Turbofan Engine used on the fighter

F-22

Pratt & Whitney F119-PW-100

航空宇航学院


• Basic Jet Engines

– There is little future application for a basic

jet engine due to the development of the

afterburning low bypass ratio engines.

航空宇航学院

Powerplant Performance Representation

• Thrust Representation

– Flight speed

– Flight altitude

– Engine operation conditions

• Specific Fuel Consumption

– Flight speed

– Flight altitude

– Engine operation conditions

航空宇航学院

Thrust Representation

• Turbojet & Turbofan

– T = T0

• T0 is the datum sea level static dry thrust

• T is the available operating thrust at any given

condition

• is a factor dependent on flight speed, altitude, engine

operation conditions and bypass ratio,R

– For 0<MN<0.9: = F [K1 + K2 R+(K3 + K4 R)MN]s

– For MN > 0.9: = F [K1 + K2 R+(K3 + K4 R)(MN-0.9)]s

航空宇航学院


• Turbojet & Turbofan– For 0<MN<0.9: = F [K1 + K2 R+(K3 + K4 R)MN]s

– For MN > 0.9: = F [K1 + K2 R+(K3 + K4 R)(MN-0.9)]s

» S is altitude factor ( see table 3.2)

» F is a factor to allow for use of afterburning

» TW and TD are the sea level static thrust values in wet

and dry operation conditions respectively

» K1 , K2 , K3 , K4 are assumed to be constant for a

given powerplant in defined Mach number and

operating condition ( see table 3.2).

(1.32 0.062 )

W

D

T

TF

R

航空宇航学院


Powerplant thrust parameters

航空宇航学院


• Propeller Characteristics

– The efficiency of a propeller, , is function both of

the advance ratio, J, and thrust coefficient, cT.

– Thrust coefficient

• Influenced by the pitch to diameter ratio

– Advance ratio （进距比）：

J = V/(nDp)

V0：the forward speed (m/s)

n : the rotational speed (rev/s)

Dp: the propeller diameter (m)

What is pitch ?

The distance that a

propeller would travel in an

ideal medium during one

complete revolution,

measured parallel to the

shaft of the propeller.

航空宇航学院


• Propeller Characteristics (con’t)

– The value of (nDp) is limited both by M and

noise considerations

• Small directly driven piston engine: nDp = 90m/s

• Turboprop trainer and related types with 4 bladed

propellers: nDp = 80m/s

• Small general aviation and region turboprops with

3 to 5 bladed propellers: nDp = 75m/s

• Large turbo propeller driven transport aircraft with

up to 6 bladed propellers: nDp = 63m/s

航空宇航学院



– The maximum efficiency

• For 0.4<J<1.0 =0.82J0.4

• For J>1.0 =(0.82J1.6) /(10 j)

– Where j=0.3(logJ) 2.4

– The limited efficiency

• limit=1.8z0.15(nDp) 1.6JP00.095 10 –7

– P0 is max. engine shaft power (kW)

– is the air density

– z is the number of propeller blades

航空宇航学院



– The thrust in flight conditions

• T= P0 10 3/ V0 N

• T= P0 10 3/J(nDp) N

– The thrust in static conditions

• Ts= (cT)s (nDp) 2Dp2 N

– (cT)s = 0.0085 z 0.15(P0/A)0.65

» (P0/A) is power disc loading (1.273 P0/Dp2)

» P0 is the static power (max. rated), kW

航空宇航学院



– The propeller rotational speed, n, is chosen

in conjunction with the diameter to give the

best compromise between tip speed and

efficiency in a given (nDp). Typically :

• Direct drive piston engines n = 45 rev/s

• Geared turboprop engines n = 433(P0)-0.4 rev/s

航空宇航学院



– Typical power disc loading

• Direct drive piston engines: (P0/A) = 4.7 P0 0.5 kw/m2

• Turboprops: (P0/A) = 1.45 P0 10 5 /(nDp)2 kw/m2

– The diameter of the propeller

• Direct drive piston engines: Dp = 0.52P00.25 (m)

• Turboprops: Dp = 3(nDp) P00.365 10 -3 (m)

– Where P0 is defined by Eq. (3.9m) in the textbook

航空宇航学院


• Turboprop

– Maximum power take-off conditions

• At the take-off stage

Ts = 1.73z 0.15(nDp)2.7 P0

0.095 10 –4 N

• At second climb stage

Tss = (0.82 P0 10 3 )/ [(nDp)V 0.6] N

» V = 1.1(VUS)HH

» VUS is true unstick speed （离地速度)

航空宇航学院


• Turboprop

– Climb/cruise power and thrust

• For climb/cruise conditions at M>0.25

1.05 0.883 0.733

01.62 [ / ) 0.75 ]NT P M N

The related total aircraft static thrust:

0.8620.8620.883

0.15 2.7 0.733 41.14 ( ) 0.75 10s E P

E N

TT N z nD N

N M

航空宇航学院


• Piston propeller

– Types: unsupercharged and supercharged

– For no supercharging cases

• The power is approximately proportional to relative density to

the power of 1.1.

• The power is also approximately proportional to engine speed.

航空宇航学院



– For supercharging cases

• Maintain sea level power to 5 km altitude, or

• increase sea level power by a significant amount.

The power then decreases as the relative, density

decreases, as unsupercharged engine.

– Variation of power with forward speed is

negligible

航空宇航学院



– The static thrust

Ts = 42P00.85 N (per engine)

– Climb

Tcl = (0.82P 10 3) / [ Vcl0.6(nDp)

0.4] N

• Assuming that max. continuous climb rating is

90% and typically, (nDp) = 90 m/s

Tcl = 0.1221.1P0 10 3 / Vcl0.6 N

航空宇航学院


• Piston Propeller

– Cruise

• Cruise speed less than 90m/s: J <= 1.0

Tcr= 0.1151.1P0 10 3 / Vcl0.6 N

• Cruise speed greater than 90m/s: J >1.0

Tcr= 0.341.1P0 10 3 / Vcl0.84 N

航空宇航学院

Fuel Consumption Characteristics

• Turbojet and Turbofan

– Dry (no reheat)

c = c’(1-0.15R0.65)[1+0.28(1+0.063R2)MN]0.08

– Up to 11 km, c should be assumed to be constant

– c is the specific fuel consumption

– R is the bypass ratio

– c’ is a factor which should be determined by reference

to the actual specific fuel consumption of a given

powerplant at a critical condition

» Supersonic engine R<1.0 c’ = 0.95 N/N/h

» Low bypass ratio subsonic engine c’ = 0.85 N/N/h

» Large subsonic turbofan c’ = 0.70 N/N/h

航空宇航学院


• Turbojet and Turbofan

– Dry (no reheat)

• When the engine is operated at some thrust less

than the design value in a given flight condition

– cOD = c[1+0.01(T/TOD – 1)] for T/TOD <10

» cOD and TOD refer to the off-design conditions

– Afterburning (reheat)

– c= 1.05(TW/TD)(1+0.17MN) 0.08 N/N/h

» This applies up to 11 km, above which c should be

assumed to be constant with altitude.

航空宇航学院


• Turboshaft Engine

– The specific fuel consumption in climb/cruise condition

(c)p = 2.88(1-0.025P0 10 -3 )(1-0.2MN) N/kW/h

– In terms of thrust

(c)T = MN 0.117(1-0.025P0 10 -3 )(1-0.2MN)/ N/kW/h

• The above equations refer to shaft power, not flight power.

航空宇航学院


• Piston Engines

– In terms of power settings

• (c)p = c’[1+0.24(P0/Pr)][1+1.5(Pr/P01.1)] N/kW/h

– P0 is the maximum rated power

– Pr is the power required in a given flight condition

– c’ depends on the actual engine and its mode of operation,

typically is 1.0 or less.

– In terms of thrust

• (c )T = (c)p (V/) 10 -3 N/N/h

航空宇航学院

Powerplant Mass

• The mass of a given type of powerplant

is closely related to the static thrust.

• Typical values will be presented in the

chapter 6 for mass prediction.

航空宇航学院

Typical Aircraft Installed thrust and Power

Typical static thrust to weight ratios-Jet and fan driven aircraft

航空宇航学院

Typical Aircraft Installed thrust and Power

Typical static thrust to weight ratios

Propeller-driven aircraft

航空宇航学院

Summary: The purpose of this chapter

• To gain/review a general knowledge of the

characteristics of various powerplants.

• To obtain the thrust and efficiency formula for

performance evaluations, given some preliminary

parameters (static thrust T0, (nDp) , number of blades).

– Thrust/Power available at takeoff

– Thrust/Power available at climb

– Thrust/power available at cruise

personal simulation workshop - aircraftdesign.nuaa.edu.cnaircraftdesign.nuaa.edu.cn/pd-2010/1-4...

Documents