1930-03-08 — Page 14

THE HONGKONG TELEGRAPH.

PROBLEMS IN PROPELLER EFFICIENCY.

Scientific Solution for Builders.

[By Chas. S. Story.]

both down

MOTORING SUPPLEMENT,"

"

cross-

SÄTURDAY, MARCH 8, 1930.

of

LICENSED

19300

EXCHANGE.

I. KNOW YOU. WON'T. MIND EX--

·CHANGING THESE

TAGS MY HUSBAND BOUGHT- ID LIKE. TO MATCH THEM TO FIDO'S LICENSE

NUMBER, AND DO YOU HAVE THEM IN GREEN AND

ORCHID?

"Parasitic Resistance." upon the body's surface, such as this stage, simply because a satis Simply described, the fuselage, bolts and struts and even window factory airscrew cannot be en- or body structure, of an airplane frames, these creating their own glacered for the plane in its in Hight, is to be considered as important amount of "paraaite original form.

littlo an elongated projectile, past which resistanco-much ke

Selection of the size and type of air flows rapidly and forcefully, angers pulling back upon the fuse screw to be used in a given job over, and under and along both lage to slow its progress.

presents its own problema-even sides. The smoothness with Rounded Fuselage Preferred.

after all matters touched upon which this surrounding stream of

To That a rounded fuselage is very above have been cared for. nir spills off this moving object de- pends upon the latter's shape much more efficient than a square, date, the two-blade propeller is the behind the point of its greatest or flat surfaced, one, is a point most efficient produced.

Much of tho disadvantage cross-section dimension, and its unrealized by most people, yet Her freedom from projecting parts or when you think of the twist of the coupled with propeller operation What will be the types of pro- away by the storm's fury,

is not hard to understand. That gearing a high speed motor down peller in use five and ten and more period of disablement is long or objects, which create "parasite, air stream about the fuselage, it at high speed can be overcome by

With aircraft short in accordance with the avail- resistance," or "drog.” years from now?

If this shape is not aerodynamic- the bigness of your cabin windows and utilizing a larger, slower pro- This makes possible a and motor designers busy upon ability of a new water screw of

But ally correct, eddies and swirls of may harm the efficiency of your peller. constant refinements and improve-proper size and strength.

bearings, since the propeller ments and changes in their pro-those factors must be proper, else air result, much like those noticed plane does not seem probable, yet lighter crankshaft and lighter ducts, we who design propellers the further performance of the in water in the wake of a motor. It is true.

boat. These have a retarding| The capacity of a designer of vibrates less.

However, new disadvantages find ourselves asking that ques-liner cannot be satisfactory. tion. Today's propeller is far) How, then, can an airplane effect upon the moving body, cut airplanes to cope with all these

speed and little points-and many others now arise, such as much greater different from the "butter paddle" efficiently perform in its screw, farting

Mistakenly.. it is and to defeat the retarding in- propeller weight and greater pro- of the past; to-morrow's propeller more a thing of balance and efficiency.

what

delicate precision, of fitness or un- thought by some that a good taper, clination of necessary departures peller diameter, the latter being will be

the task, is not and smoothness of the surface of from true streamlining, is called limited for practical use, It is not true, as many seem to fitness for

lage nose from the ground. think, that an airplane can be accurately developed to do the job a fuselage, constitute true stream- his "finess ratio"-a vague term course, by the height of the fuse-

lining. Actually, a moving air for a valuable genius. designed to maximum efficiency in hand?

a very definite It should now be apparent that Experience proves, too, that little without any thought being given, An interesting example of the stream assumes while designing, to the airscrew importance of correct selection of form, peculiar to itself, if un- it is the manner of the airscrew's is gained by gearing down motors which is to propel it.

However, increasine horsepower: lairacrew equipment came recently hampered in its flow; the more attack upon the air before it which of less than 500 h.p.

increasing propeller Far too many aircraft builders to our attention. The builders of perfectly the surfaces of the body determines the manner of its have given extreme eare to the la tri-motored airplane changed centred in this stream conform to delivery of the air stream past the demands aerodynamic correctness of their their motive power equipment, its shape, the more perfect is that fuselage and this manner of de diameters, and soon we reach a livery, in turn, determines very point where the great diameter of plane's design, have studied care substituting new engines which body's streamlining.

of larger When a new factor, in the form definitely what is to be the true a screw introduces new difficulties. Sometimes, the motor speed is in- fully the power plant best suited required propellers to the purposes for which it was diameter. These were secured of a rapidly revolving propeller, is shape of the fuselage,

that the propeller Two important factors of this creased s0

diameter may be decreased, but meant, and then, with no care at and tried without first consulting introduced into this relationship

some loss of all, have selected a propellera propeller engineer, and it was between air stream and fuselage, shape are the greatest

When the propeller whose type merely pleased their found that the overlapping of the obviously, the flow of the stream sectional area of the fuselage, and this results in unthinking fancy, and have ex- two outer screws into the stream of air is very materially affected, the distance of this area from the efficiency.

Experience has engineer considers the three and period of time. Certainly, if the the horizontal balance is taken to pected first-rate performance from from the central and more forward If the propeller is of the tractor propeller itself.

The "prop" is then balanced in the plane, Barring some accidenserow caused a loud and dangerous type, and is mounted on the nose determined that, generally speak-fourbladed propeller, since either time between major overhauls can be correct. tal blessing of the gods, it can't slap" A propeller man was then of the fuselage, it initiates the ing, the ratio of this area to that of these is smaller than a two-be extended from 350 to 600 or 700 be done. Propeller equipment is consulted, and upon his recom- movement of the air stream, of the propeller disc should be blade screw of similar power, he hours, the operator will be grate- a perfectly vertical position, and put must decide whether he wishes to ful for lessened overhead-and his checked to see that it does not mendation, the outboard motors throwing it back along all sides between 1.5 and 1.3, or, no mere matter of accident.

moved further For the ultimate success of awere

from

the of the body and laying down its another way, the fuselage which sacrifice a small percentage of altered. schedule of flying time swing away from this position.

repeated, and the result again.... projected air vehicle, practice and fuselage, so as to clear the three own laws as to what lines the fuse-absorbs between 20 and 36 per efficiency, which, for practical pur-cannot seriously affect his busi- Reversed, end for end, this test is

Cut the wideopen speed of our checked. long experience dietate that the streams of each other. This, of lage shall have, and how other cent. of the propeller disc area poses, can be neglected in most s

Incidentally, extreme care is gives the best general perform-cases in commercial plane design. best procedure

plane course, meant redesigning of the parts shall be related to it.

Thus it is seen that this matter motors to between 1,500 and 1,600

have the shaft and For example, since this pro-ance. (Propeller disc area is the of selection of correct propeller r.p.m., and cruise our planes at a taken to designer and propeller engineer to structure of the wings to accom

of the imaginary disc work in complete and close har-modate the new stresses-a very peller-created stream flows back in area mony from the time first plans are costly business.

a twisting manner about the fuse. described by the turn of the equipment is one of trial and motor speed of 1,300-1,400 r.p.m., mandrel clean for these tests, since. error of repeatedly being forced and I contend we will all profit in a tiny speck of sand between shaft more generally and propeller may defeat the drawn. The Airscrew, far from Examples are numerous, on the lage, the fin which projects above screw).

Likewise, this greatest dimen- to decide which disadvantage we longer-lived,

inspector's purpose, and indicate being an accessory of secondary other hand. of highly successful the fuselage just ahead of the

It may be interesting for the static balance when it actually to accomplish importance, Is [11 intimate, modern airplanes whose makers rudder must be set a little off sion of the fuselage must be cor- choose, or can best afford to risk, efficient equipment.

distanced from the

reader to tell something here of does not exist. integral, basic component of the recognized from the start the im- entre at the forward edge, in rectly,

the care we must exercise in It might seem that such precise whole plane itself, and must be soportance of constant ec-operation order that it may split this twist-propeller, in order that the air advantages we wish to secure.

stream may flow with as little. High Speed Adjustments. Olding stream accurately.

securing perfect balance in our leare in balancing a great wooden considered, for success sake, as with the propeller maker. much as are the wings, the fuse-heads at the designing of aircraft

It is my confirmed belief, which propeller products. Minute atten- object like a propeller is stretch- Now, the forward movement of resistance as possible lage, the tail section, or the con-produce remarkably efficient types the airserew-propelled fuselage is widening taper of the fuselage, hold in the face of considerable tion must be given each propeller ing accuracy to an unneeded limit. trols.

Manufacturers who have not because of any haphazardness retarded in some degree by its own and also that it may spill off the disagreement, since my contention in the final inspections before de- Enough inequality of weight to be ignored this fact have learned in procedure, but because of this bulk in the air stream, this re- tail with as little retardant as may is supported by much available livery to the user. The tests are discerned in such tests, however, bitterly and expensively to pay it uniform care in attention to every tanling effect being called "head be.

data, that if we were a little less simple, yet extremely important.. is sufficient, when multiplied by A completely finished "prop"- the terrific speed of revolution of cases, resistance," or, in some

Efficiency of Two Blades, respect.

feverish to attain high speed per- Just why does the propeller as "drag." The amount of this re- It is through oversight of these formance in the commercial air-varnish, trade mark, and all-isa labouring propeller, to create a We need only to turn for a sume such importance in airplane tance determines, in large part points that much difficulty arises plane, and by cutting our top mounted on a shaft which in turn bad pounding vibration, upsetting moment to another sphere of design? Why will not any good the efficiency of its performance, when a nearly completed new speeds five or so mile, we brought sits in ball bearings. Very care- smooth performance.

Having produced a fine propel activity for light upon this truth.product, of suitable and This efficiency is likewise affected plane design is brought to the down our motor and propeller fully, it is brought to rest in an An ocean liner, having weathered power, fit an airplane's needs? It by the smoothness of the body's propeller maker for proper equip-speeds, we could achieve longer exactly horizontal position. Four ler, we have but prepared for ser a terrific storm at sea, hobbles into may be well to consider the subject conformity to the air stream's ment. It is not uncommon to have life in motors, motor mounts, square inches of ordinary news- vice a product whose care and We port with a propeller gone, torn primarily for a moment.

form, and by any projecting parts to rebuild a plane completely at plane body structures, and propel-, paper (usually about .0025 inch upkeep and operation all bring

lers, due to lowered vibration, and thick) are placed on one blade tip. new, fascinating problems.

improve thus we could

our If the blade swings rapidly down- jare studying all the time the many ward, the test has resulted satis- elements affecting propeller life, bperating efficiency.

Such procedure has already factorily, but must be repeated by and the results of our studies are been demonstrated to give greater placing the same acrap of paper on available always to the man whe payload capacity per horsepower the other blade tip. If the rate buys or sells or uses airscrews

and the expense of upkeep is of swing of this blade toward the in short, to everyone engaged in always distributed over a greater floor is equal to that of the other, aviation.

for ін

Compared to Steamships.

feature.

size

THORNYCROFT

RIGID SIX-WHEELED MOTOR VEHICLES

over the

I

in

order

"

those

127731

STUDEBAKER EIGHTS...

PROVED BY THOUSANDS OF MILES APPROVED BY THOUSANDS OF OWNERS

сем

COMBINED EFFORTS

of RELIABILITY OVERCOME ALL DIFFICULTIES

THIS FICTUR

ILLUSTRATES THE MEANING OF

“DOUBLE ASSURANCE'

SECURED BY USING

THORNYCROFT

JOHN I THORNYOROFT & Oo., Ltd. UNION BLDG., H.A.

FAMOUS MOTOR VEHICLES

SHELL

MOTOR.PIRIT. LUBRICA LING OILS AND GREASES.

THE ASIATIC PETROLEUM 00,, (8,0,) Ltd. ASIATIO BLDG., HK

MORE

ORE than twenty new nights have been hurriedly introduced at recent International Motor Shows to meet buyers' demands for eight-cylinder power and smoothness.

-Three years ago Studebaker introduced economical eights at the price of sixes. These President, Commander and Dictator Eights have won Studebaker more official performance records than are held by any other car. You want a time-proved, thrifty champlon sight. You want Studebaker-built by the world's leading builder of eights and backed by 78 years of manufacturing experience.

a

Delivered prices from H.K. $4,640 to H.K. $8,130 THE HONG KONG HOTEL GARAGE 25 Queen's Road Central Tel. Central 4769;