Aircraft propellers
-
Upload
alex-mercer -
Category
Documents
-
view
229 -
download
0
Transcript of Aircraft propellers
PROJECT SYNOPSIS ON
“AIRCRAFT PROPELLERS”
Submitted by
MOHAMMAD ASAD ANSARI
MOHAMMAD ISHRAT JAVED SIDDIQUI
DANYAL SAGIER SIDDIQUI
HEMANT KUMAR CHANDRA
B.TECH 4th year (2013-2014)
(MECHANICAL ENGINEERING)
UNITED COLLEGE OF ENGINEERING AND RESERCH ALLAHABAD
Introduction
Propellers
Internal Combustion Engines
Gas Turbine Engines
Chemical Rockets
Non-Chemical Space Propulsion Systems
AER 710 Aerospace Propulsion
OBJECTIVE The main objective of the project is to understand the functioning and constructional details of the aircraft propeller. This project is an attempt to throw some light on the use of mechanical engineering designing of blade, analysis of operating force, analysis of material use and stress distribution in an aircraft propeller.
The project also intend to understand the wide application and history in the development of aircraft propeller. Aircraft propeller is widely used in most of the aircraft carrier. It is also used in many of the military operations in World War 2nd in most of the fighter planes as well as bomber planes.
C-130
Nieuport N.28C-1
Introduction to the Propeller• The rotating blade of a propeller shares
similar characteristics to a wing passing through the air
• A propeller blade generates thrust F through an aerodynamic lift force component, demands an engine torque Q to overcome aerodynamic drag, and will stall if the local resultant angle of attack of the blade exceeds max
• Additional factors: trailing vortex generation, tip losses, compressibility
Martin MB-2
Small Pressure Increase here
Greater Pressure Decrease here
The result isMORE LIFT
How lift is increased
PROPELLER SYSTEM
Small Pressure Increase here
Greater Pressure Decrease here
The result isMORE LIFT
How lift is increased
PROPELLER SYSTEM
Direction of travel
Aerofoil incline
The difference in direction of travel and aerofoil incline is called:-
The ANGLE of ATTACK
How lift is increased
PROPELLER SYSTEM
PROPELLER SYSTEMHow the blade tip travel produces the HELIX ANGLE
Forward Speed
RPMRPM
Faster Forward Speed
Changes in FORWARD SPEED and RPM will change the Helix Angle
How an increase in FORWARD SPEED changes the HELIX ANGLE
PROPELLER SYSTEM
All propeller blades are actuated by the same mechanical linkage
PROPELLER SYSTEM
Sliding Piston
Hard Stops
Fine Pitch
Coarse Pitch
Direction of
Rotation
Direction of Flight
Propeller Blade
Actuating Lever
Actuating Link
DH-98 Mosquito
Forces acting on wing airfoil section (above) and propeller blade section (below)
Momentum-Blade Element Theory
• Logically, the next level of analysis would look at a given propeller blade’s aerodynamic performance from hub to blade tip
• one can discretize the blade into a finite number of elements, while applying momentum conservation principles
Momentum-Blade Element Theory (Summary)
• The above equations for CT and CP can be integrated from the hub station (x = xh) to the blade tip (x = 1) using a numerical approach as one moves along the blade of varying and c, calculating the various pertinent parameters (C , Cd, i , etc.) in conjunction
Thrust
Power
Propeller Propulsive Efficiency
• Define as useful thrust power over overall shaft power:
Spr P
FV
JCC
dnCVdnC
P
T
P
Tpr
53
42
Also, via substitution:
A variable pitch propeller will have better efficiency over thecourse of the flight mission, relative to a fixed pitch prop.
Chart illustrating propeller propulsive efficiency for an example propeller
Compressibility Tip Loss• Depending on the blade airfoil section
design, drag divergence (compressibility) effects will become evident when the propeller blade’s resultant tip speed VR,tip exceeds a local flow Mach number Matip of around 0.85 (critical value, Macr)
• As a result, one would not typically be cruising at much greater than a flight Mach number Ma of around 0.6
22)(
MaandMatip
)1.0
(10015 crtip
alminpr,noprMaMa
Dommasch correlation:
Blade tip Mach number:
Modern high-speed blades may be thinner, and sweptor curved along the blade length, to mitigate the issues with compressibility and compression wavedevelopment at higher local flow Mach numbers
Activity Factor• Activity factor (AF) is a design parameter
associated with the propeller blade’s geometry. The more slender the blade (larger radius, smaller chord), the lower the AF value:
xxdcAF
hx p
d16
100000 31
pdcAF 1563
Typically see higher AF props on turboprop engines.
Blade Number• One has the option of setting the number
of blades, B, for a given application. While one has a minimum of 2 blades to choose from, one can presently go as high as around 8 blades on the high-performance end for an unducted propeller
• On occasion, one also sees the use of two contra-rotating rows of blades, to get more thrust delivery from one engine