Blade Mass Research Articles

Formation of microsclerotia ofVerticillium dahliae Kleb. on various plant parts of two potato cultivars

Potato plants of cvs Element and Mirka were artificially infected withV. dahliae in two greenhouse experiments. Leaf blade, petiole, aerial stem, subterranean stem, stolon and root mass were separately harvested both when the canopy was still green and at maturity. After 4 weeks incubation, the plant tissue was air-dried and the numbers of microsclerotia per mg tissue and per plant were determined.

Removal of fungal and total organic matter from decaying cordgrasseaves by shredder snails

Several lines of evidence from the literature have pointed to the saltmarsh periwinkle ( Littoraria irrorata [Say]) as a potentially important shredder of standing, decaying cordgrass ( Spartina alterniflora Loisel.) shoots. Periwinkles prefer to ingest dead-shoot material and possess enzymes capable of lysis of cordgrass plant-structural and fungal-wall polymers. We offered natural, standing-dead leaf blades to periwinkles in an attempt to determine the rates at which the snails would rasp away and ingest material of the decaying-shoot system, and whether the snails would selectively remove living-fungal mass (measured as ergosterol) from the system. The larger snails tested (14 mm shell height) took 42% of the total organic mass of the blades during 6 days of exposure, and exhibited selectivity for fungal-occupied portions of blades by removing 69% of the living-fungal organic mass. Based on observed removal rates, about 2–3% ·day −1 of the organic mass of standing-dead leaf blades could be lost to snail grazing in marsh areas where the snails are most densely concentrated ( > 400 individuals · m −2 of shell length > 5 mm). In a preliminary comparison of adjacent marsh areas of equivalent canopy height, the one without periwinkles had a 4 × greater standing crop of dead leaves. Periwinkles are likely to be important controlling agents of fungal standing crops and important shapers of fungal community dynamics in cordgrass marshes, in that the standing, decaying substratum for fungal growth and the potential for fungal species successions are radically changed by the snails' activities.

Parametric aeroelastic stability analysis of a generic X-wing aircraft

This paper discusses the dynamic aeroelastic stability of a generic X-wing aircraft configuration. The analysis model includes rigid-body degrees of freedom and unsteady aerodynamic forces generated using the doublet lattice method. Design parameters are varied to evaluate the trends in dynamic aeroelastic stability. X-wing rotor blade sweep angle, ratio of blade mass to total vehicle mass, blade structural stiffness cross coupling, and vehicle center of gravity location were parameters considered. The typical instability encountered is body-freedom flutter involving a low-frequency interaction of the first elastic mode and the aircraft short period mode. In most parametric cases, those cases having the least static longitudinal stability demonstrated the highest flutter dynamic pressures. As mass ratio was increased, the flutter boundary decreased. The decrease was emphasized as center of gravity location was moved forward. As sweep angle varied, it was observed that the resulting increase in forward-swept blade bending amplitude relative to aft blade bending amplitude in the first elastic mode had a stabilizing effect on the flutter. b [B,] [C' [C] El [F] GJ [7] ^ [K] [Kf] L Lb [M'] mb nif mr [M] q

Hub Loads Analysis of the SA349/2 Helicopter

The forces and moments at the rotor hub of an Aerospatiale SA349/2 helicopter were investigated. The study included three main topics. First, measured hub forces and moments for a range of level flight conditions (mu = 0.14 to 0.37) were compared with predictions from a comprehensive rotorcraft analysis to examine the influence of the wake model on the correlations. Second, the effect of changing the blade mass distribution and blade chordwise center of gravity location on the 3/rev nonrotating frame hub loads was studied for a high-speed flight condition (mu = 0.37). Third, the use of higher harmonic control to reduce nonrotating frame 3/rev hub shear forces was investigated. The last two topics were theoretical studies only.

Structural Modification of Advanced Turbomachine Blading by Dynamic Stiffness Matrix Operations

This paper examines the application of matrix transformations from the experimentally obtained receptance matrix to the dynamic stiffness matrix to determine changes of blade stiffness and/or mass characteristics which will achieve desired modifications of blade dynamic behavior. Results for a specific turbine blade configuration are used to illustrate the approach.

Heat transfer and power requirements in horizontal thin film scraped surface heat exchangers

The problem of heat transfer in a horizontal thin film scraped surface heat exchanger was studied by performing 128 experiments on sensible heating of water, ethanediol, glycerol and paraffin liquid under various operating conditions, viz. flow rate, rotor speed, number of blades and mass of blades. Nusselt type correlations were developed for the scraped film heat-transfer coefficients. A new dimensionless number (blade factor) was evolved which delineates the effect of the mass of the blade on the scraped film heat-transfer coefficient. Also optimization expressions for the overall heat-transfer coefficient and temperature rise were developed in polynomial form. A mechanism governing film formation and heat transfer was conceived which could satisfactorily explain the effect of various process parameters on the scraped film heat-transfer coefficient. The literature survey also revealed inadequate information regarding the power requirement in horizontal thin film scraped surface heat exchangers. In order to develop an appropriate prediction model data on power consumption were collected during experiments on sensible heat transfer. In this correlation, the Weber number was incorporated to account for surface tension forces, which seem to be quite significant when a new surface is generated as in thin film SSHE. The effects of various process parameters on power consumption are discussed.

Calculated and Measured Blade Structural Response on a Full‐Scale Rotor

Abstract : The restricted problem of calculating the bending-moment response of a full-scale rotor to measured airloads is studied. Data are used from separate tests of an articulated rotor in flight and in a wind tunnel. Linear equations to represent the blade mass and structure are used, and the solution is obtained by numerically solving the resulting two-point boundary problem. The measured aerodynamic loads include effects caused by both rigid blade motion and elastic deformation and hence, represent an exact aerodynamic model. By comparing the calculated blade-bending and torsional-moment response with measurement, it is possible to assess the adequacy of the structural model for the calculation of calculating vibratory loads. These comparisons are good for the flap- and torsional-moments at the lower harmonics. Calculations for the chord-bending moments are less satisfactory and reveal problems with the method of deriving the chord airloads from the measured normal forces, or the representation of the nonlinear lead-lag damper.

Investigation of the structural behavior of the blades of a darrieus wind turbine

A theoretical model in which account is taken of the non-linear, non-planar structural behavior of the curved blades of a Darrieus wind turbine is described. This model is simpler and needs less computational effort than some other models, but is still accurate enough for most engineering purposes. By using the present method, it is possible to treat any blade geometry, any structural, mass and aerodynamic blade properties distribution and any combination of boundary conditions. The model is used in order to calculate the blade behavior under the influence of concentrated loads, gravity loads and centrifugal loads. In order to verify the theoretical model, predictions are compared with experimental results which are obtained from tests with small models of curved blades. Usually the agreement between the theoretical and experimental results is very good. The influence of different parameters on blade behavior is presented and discussed.

Effect of Reducing the Blade Cooling Air Temperature and Mass Flow on Blade Life and Cycle Efficiency

Reduction of the temperature of the air used for blade cooling to below the compressor exit temperature would allow the required mass flow to be reduced and might be expected to result in an improvement in engine performance. This is demonstrated and quantified in this paper. Improvements in both blade life and cycle efficiency are shown to be possible. For example by cooling the coolant by 50°C a reduction in coolant flow of 40 per cent is possible as well as an improvement of 20 per cent in blade life. Additionally a marginal increase in cycle efficiency is obtained and a 1.4 per cent increase in specific work output. A concept for an integrated cooling device for producing the required reduction in temperature of the blade cooling air is described and appraised. As envisaged at present, the device would be too bulky for airborne applications. However, with further development a feasible design might be evolved.

On tuned bladed disk dynamics: Some aspects of friction related mistuning

In this paper, a discrete multi-degree of freedom model of a tuned disk is considered. The hysteretic material damping and interblade and blade-to-disk friction forces are included. It is shown that the irregularities of the friction forces and of the harmonic excitation pattern cause mistuning of the system. Optimal conditions of friction were found analytically for the tuned case. They depend on the values of the friction forces, amplitudes and phases of excitation, represented as variations of a traveling wave of excitation. The response amplitude of the blades is minimum for optimal friction. Similar considerations were applied to find the optimal blade mass and stiffness parameters for minimal response amplitudes. These considerations give a new insight into the effects of blade mass and stiffness characteristics as they affect the reduction of vibratory response amplitudes by friction.

Wounding capacity of rotary lawn mowers.

The rotary lawn mower possesses a powerful wounding mechanism. A typical 26-inch rotary mower blade rotating at 3,000 revolutions per minute develops a kinetic energy of 2,100 ft lb. Wounds may be inflicted by direct strike or by missile action due to a broken blade or other mass. Other serious injuries due to crushing or upset are commonly seen with self-propelled mowers. Ways of reducing these risks are enumerated.

A Theoretical Method for Calculating Flexure and Stresses in Helicopter Rotor Blades

A variational procedure is developed, in the form of an extension of the Rayleigh‐Ritz method, leading to a rapid estimation of the flapwise vibration modes and frequencies of a helicopter rotor blade. The initial data required are the blade mass and stiffness distribution and the angular velocity of the rotor blade. The normal modes and frequencies are subsequently used to determine blade shapes in flight. The aerodynamic forces only enter at a late stage of the analysis, and the effect of differing flight conditions is readily assessed. The method makes extensive use of matrix formulation and particularly lends itself to electronic computation techniques. A numerical example is given for the special case of constant spanwise blade mass distribution, although the method may readily be extended to cover this restriction. The bending moment distribution is also worked out, and flexible and rigid blades are compared.

The Avoidance of Ground Resonance

An examination is made of the way in which the ground resonance properties of a helicopter depend on the fuselage damping, blade damping, drag hinge offset, inter‐blade spring stiffness, blade mass and angular velocity of the rotor as specified by the parameters λƒ, λβ, Λ1, Λ2, Λ3 and Ω respectively. A direct method of drawing stability boundaries in the (Ω, λβ) plane is developed, and the geometry of these boundaries as the remaining parameters vary is studied theoretically at length. Arising out of the geometry, the validity of Coleman's criterion for stability is examined, and it is shown that the requirement that the product λƒ,λβ should have a certain minimum value is not itself sufficient to ensure stability for all Ω. The condition can be made sufficient by a proper and unique choice of the individual values of ?f and ??, and these values are found in terms of Λ1, Λ2, and Λ3. All other cases of stability require a larger value of the product λƒ, λβ. An alternative criterion for stability is developed which gives the minimum value of λƒ capable of ensuring stability for all Ω. This, and the preceding criterion, are mathematically exact, and follow from Coleman's equations of motion as applied to the case of a helicopter on isotropic supports. A brief account is also given of the case of a rotor having inter‐blade friction damping as against the viscous damping previously assumed.

A Method for Improving the Inherent Stability and Control Characteristics of Helicopters

The problem of helicopter control and stability is examined with a view to establishing whether satisfactory inherent stability and control characteristics may be achieved without major design modifications and without having resources to automatic control devices. I t is shown that the possibility does exist of improving both the damping and the static stability of a helicopter by a relatively minor modification of the blade mass and aerodynamic characteristics, together with the use of spring and viscous restraint in the control system. This should result in considerably improved blind-flying characteristics and a reduction in excessive control sensitivity without sacrificing maneuverability. The control characteristic of such an inherently stabilized helicopter is evaluated by means of the transient response characteristics to abrupt control manipulation.

Load on Propeller Blade caused by Torsional Vibration of Shafting

The Author ever stated that the torque fluctuation of the intermediate shaft must be considered when calculating the strength of propeller. The present paper explains the relation between torque fluctuation and bending moment at the root of blade of propeller by its own inertia.The wave form of one complete period on film which recorded by Author's torsionmeter can be expressed as follows : Δ-Δm=Σγn sin (nω0t+ψn), where Δ=displacement of image from zero line (cm), Δm=mean displacement of image from zero line (cm), n=wave number of the component of harmonics included in one period, ω0=2πN/60 for 2-cycle engine, = πN/60 for 4-cycle engine, N=revolutions of shaft per minute, γn=amplitude of the component (cm), ψn=phase angle of the component.Assuming the positions of nodes of forced vibration to be the same as those of free vibrations, fathermore neglecting the inertia of shaft, the formula for amplitude of shaft at propeller position referred to any one of the mode of vibration isθL=1/Ip2Σqγn sin (nω0t+ψn), where.L=virtual moment of inertia of propeller (g.cm2), p/2π=natural frequency per second for the mode of vibration under consideration, q=torque per unit displacement of image (dyne. cm-1).Practically, it is enough for this purpose only to consider the vibration with one node.The angular displacement, angular speed and angular acceleration of propeller are φ=2πN/60t-1/Ip2Σqγn sin (nω0t+ψn), ω=2πN/60-1/Ip2Σnω0qγn Cos (nω0t+ψn), α=1/Ip2 Σ (nω0)2 qγn sin (nω0t+ψn).Assuming that the distribution of virtual mass along the blade is similar to the distribution of actual mass of blade and the boss is sphere, the virtual moment of propeller and the bending moment at root of a blade areI=zk'ρ1∫R0 RγAR2dR+ρ2π/60 (2Rγ) 5, M=-α·k'ρ1 [∫R0RγAR2dR-Rγ∫R0RγARdR], wherez=number of blades, k'ρ1=virtual density of blade (g.cm-3), ρ2=density of boss (g.cm-3), 2Rγ=dia. of boss, 2R0=dia of propeller, A=sectional area of blade at a rad. R.k' is larger than unity. M is the vector quantity whose direction coincides with axis of propeller shaft.Assuming that the contour of blade is elliptic and sectional form of blade at any radius is parabolic, the above formulas can be simplified as follows

Choice of Airfoils for Rotating-Wing Aircraft

T E National Advisory Committee for Aeronautics has for some time been directing its efforts toward the improvement of safety in flight, and with that purpose in view has done extensive research on rotating-wing aircraft at the Langley Memorial Aeronautical Laboratory. At present an extensive program of research on rotating wings is under way in the propellerresearch wind tunnel, where autogiro and gyroplane models 10 feet in diameter are to be tested to determine the influence of varying such basic properties of the rotor as the pitch angle, the airfoil section, the plan form, and the blade mass. Similar tests are being made on a model of a cyclogiro rotor 8 feet in diameter. The following analysis of the choice of airfoils for these rotors is supported by work that has already been completed; much valuable information concerning this and related subjects is anticipated from the current program. Rotating-wing aircraft may be divided into two main classes: those normally employing power-driven rotors for sustentation, such as the helicopter, helicogyre, and cyclogiro; and those employing autorotating wings for sustentation, such as the autogiro and gyroplane. The autogiro and helicopter are familiar types. The helicogyre is an aircraft supported by a power-driven lifting propeller which is rotated by means of an additional propeller on each blade of the main screw. The cyclogiro is supported by a paddlewheel rotor on each side of the fuselage, rotating about the lateral axis. The gyroplane is quite similar aerodynamically to the autogiro except that the blades on the gyroplane rotor are free to rotate only about the span axis, and the opposite blades are rigidly joined; lift on opposing sides of the rotor is equalized by rotation of a blade pair about its span axis. The aerodynamic characteristics of an airfoil section required for the optimum performance of a rotating wing are the same regardless of the type under consideration. I t is true, however, that the choice of the proper airfoil is more critical for the autorotating systems than for the power-driven; for this reason, the following discussion will be concerned with the autogiro and gyroplane rotors. The aerodynamic similarity between these two types is so complete that the analysis applies with equal validity to both systems. The autogiro is a windmill of low pitch operating at large angles of yaw and maintaining a condition of zero aerodynamic torque during a state of steady autorotation. This condition means essentially that the average moment, during one revolution, of the blade element chord forces about the axis of rotation is zero, the chord force on any element being the sum of two components of opposite sign, and being derived from the lift and drag of the element. The torque variation with rotor speed is such that a decrease in speed in any state of operation generates an accelerating torque, and conversely; the rotation is therefore stable. The optimum airfoil for a rotor of given geometrical form is defined as the airfoil that gives the largest maximum lift-drag ratio of the rotor. I t has been shown by Lock (British R. & M. 1127) that by consideration of the energy losses in the rotor, the ratio of drag to lift can be expressed as