United States. National Advisory Committee for Aer.

Annual report of the National Advisory Committee for Aeronautics online

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aD cooling appliances— e. fi[., „ „, « ,

water connections and any oil left in the engine. It wul also include all fuel and oil

flopplied for six hours' ran and aU oil containers and pipes therefrom.

jne gross wei^t per horsepower is the total weight of the engine divided by the
fcnre & horsepower, below which the output has not been allowed to faU throughout
tSe aixhours' run, with a tolerance of 3 per cent for small variations and inaccuracy
ofineasarementB.

(d) 8hax>e of engine to be suitable for fitting m an aeroplane.

2. DE8DIABLB ATTRIBUTES OF AN AEBOFLANB ENGINE.

(a) Light total weight, (b) Economy of consumption, (c) Absence of vibration.
{i) Smooth running \^ether m normal or inclined position and whether at full power
or throttled down, (e) Slow running under light load. (/) Workmanship, (p)
Bflenoe. (A) Simplicity of construction, (t) Absence of deterioration after test.
0) Suitable shape to minimize head resistance, (k) Precautions against accidental
Btoppege— e. g., dual ignition. (Z) Adaptable for starting otherwise than by pro-
peller swinging, (m) Accessibility of parts, (n) Freedom from risk of fire, (o)
Absence of smoke or ejections of oil or ffuoline. (p) Convenience of fitting in aero-
plane, (a) Relative invulneiabili^ to small-ann piojectUes. (r) Economy (in
bulk, weight, and number) of minimum spare part equipment. («) Excellence of
material, (t) Reasonable price, (t^) Satis&u^tory running under climate varia-
t&oos of temperature.

In the recently issued specifications issued by the United States
Navy Department a number of items appear bearing on engine-
fiervice requirements which are abstracted and reproduced wiow
for comparison.

''They shall be well balanced and produce no excessive vibration
at any power. To be capable of being throttled down to 20 per
cent of the revolutions per minute for full power. The weight of
the engine complete, with ignition system, magnetos, carburetors,
pumps, radiator, cooling water, and prqpeller not to exceed 6 pounds

25302*— S. Doc. 268, 64-1 ^18



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194 AEBONAUTIOS. *

per brake horsepower. Engine to be fitted with some type of com-
pression release as a means of stopping it. To be fitted with a
practical means of starting from puot's seat when installed in an
aeroplane. All moving ps^ not lubricated by a splash or forced
lubncation system to be readily accessible for inspection, adjust-
ment, and oiling. Ready means shall be provided for checking
and making adjustment to the timing of the engine. To have an
accurate and positive lubricating system which wm insure a uniform
consmnption of lubricating oil proportional to the speed of the engine.
All parts subject to corrosion to be protected from the effects of
salt water. To be fitted with an approved attachment for obtain-
mg the revolutions per minute. To be provided with means for
preventing fire in case the engine is turned upside down. A hand-
throttle lever and connections to carburetor to be provided that
can be applied for convenient operation by the pilot. This lever
to be designed with a positive means of retaining it at the throttle
adjustment desired by the pilot. All bolts and screws without
any exception to be provided with an approved positive means
for preventing backing out due to vibration. No soft solder to be
usea in any part of the power plant."

Among the conditions for acceptance tests the following stipulation
will be noted: ''Motor to be run at fuU power for one-half hour under
conditions approximating operations in the aeroplane in a heavy
rainstorm."

At the present time many of the important conditions that an
aeronautic engine must fulfill are pretty well settled, at least in kind,
if not degree, but every day sees some new attribute announced as
desirable, so that while it can hardly be said that aero service require-
ments for engines are now reducible to rigid specifications, they can be
formulated with enough precision to enable an engine designer and
manufacturer to imdertake production with some prospects of success
or acceptance. In so proceeding, however, no designer or manufac-
turer can afford to ignore past experience in engine construction nor,
on the other hand, may old constructions be slavishly reproduced, for
what was acceptable yesterday may not be to-day, and certainly will
not be to-morrow.

All these service requirements can be classified imder three head-
ings for future more or less minute analysis.

POWEB-WEIOHT RATIO, BELIABUJTY, AND ADAFTABILrTT.

If the engine complete with full tank is light enough it can be
used — and is most useful when most light^ and this weight involrea
many factors, each of which must be considered — some mdependent
of others but many interrelated. The longer the contemplated
flight, the more change there must be in the relation between specific
fuel and oil consumption of the engine and the weight of the engine
proper; so in any consideration of this item length of flight must be
mcluded. Not yet, however, has the engine or night art reached the
point where it is prepared to fix a minimum weight, though each year
sees a definite maximum. In fact, one of the problems of the day for
the aero engine designer is to discover means for lowering more and
more both this maximum pepmissible weight that many can attain.



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AEB0KAXJTIG8. 195

and the minimum possible attainable by only a few of the best — and
with increasing flignt lengths this is becoming more and more a matter
of raising tibermal efficiency, engine s|>eed, and cylinder mean effective
pressure, with correspondmg reduction of lubricating oil. On the
weig:ht question, therefore, it is not the service conditions that
gpecUy what is wanted other than that it shall be as low as possible,
but rather the en^e designer is put on his mettle to say how far it is
possible to go with due consideration to the other two elements —
reliability and adaptability.

ReliabiUty is demanded always, but how much? Some writers
call for absolute reliability and others try to specify in numerical
terms a value for one or another of its elements. For example,
in the 1913 German tests, any engine that dropped to 85 per cent
of its normal speed was rejected, and this stipulation was retained
for the 1914 competition. Again, in the British conditions, the
only power rating allowed was the least attained at any time in six
hours. Now absolute reliability is impossible, for this would mean
continuous, iminterrupted operation without variation in any respect,
except at the operator's will. No such engine has ever been built
nor will it ever be built. Obviously what is wanted is as great a
reliability factor as the engine designer and builder can secure con-
sistent with other factors, so here again, as with the unit weight
factors, the problem is one for the producer to say how far the relia-
bility can be assured, rather than tor the user to specify and reject,
especially on laboratory tests. However, rejection on such grounds
is far more justifiable than acceptance, for the engine so accepted
may fail on its first flight, due to some accident or to faulty operator's
adjustment. What is needed here is, first, analysis of the reliability
factor into its elements and by cooperation between engine desiCTier
and user, an agreement on reasonable values for each, so one will not
promise, nor tne other expect the impossible, but each imderstand
clearly the limits — and more important, the reason for the Umit —
that means may be sought to eliminate the disturbing cause.

About the same situation is true with the third lactor, adapta-
bility, and its elements — such as shape, vibration, silence, accessi-
bility, uniformity of torque. They may be specified to-day only in
the qualitative or comparative way, though some of them are capable
of formulation, quantitatively, such for example as torque variations.
So far it has not seemed feasible to impose any such limits but to
leave the field wide open to the designer with an expression of desire
for as high a degree of success as is possible with each.

The reason for this state of affairs in the art ia clearly due to its
youth and the necessity at present, and for some time to come, for
the maximum possible encouragement of invention, desim, research,
uid manufacture, until it becomes clear to all just how far it is pos-
sible to go in any direction after enga^g all available resources of
talent, material, money, and plant. When, after such a period, one
or more standard types of engme or enjrine parts — or even of air craft
itself — have been established, then wifl it be feasible to specify more
particularly and numerically all the elen/ents of each of the factors
of unit weight, reUability, and adaptabiUty.

In the meantime^ the problem is one of review of engines produced
and an analysis oi their construction and performance as a whole
and with it a similar analysis of fundamental possibilities. This must



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196 AEBONAUTIOS.

include a more or less standard examination of each of the essentia)
parts of the engines and the relation of form and arrangement to
the perfection or imperfection With which the part performs its par-
tial duty or fimction. Even now, as Soreau, reporting the French
tests, points out, the relative importance of low engine weight proper,
reUabuit^P' and life, and consumption of fuel and oil^ orij^aUy con-
sidered in this oraer, has been reversed, experience indicating that
the last is now first and the first last.

Part 1 (b).— MEANS EMPLOYED UP TO THE PRESENT TO PROMOTE
AERO-E^GINE DEVELOPMENT, INCLUDING POSSIBLE MEANS NOT
EMPLOYED.

Any new art develops as fast as encouragement is offered or as
fast as the necessary means are made available and intelligently -
used, and, of course, mversely as the difficulties involved. It would
be hard to find any class of machine among those developed in mod-
em times that haa to face the same inherent difficulties incident to
the nature of the problem, or one that received, at least for the firat
few years, so little real encouragement and assistance as this one,
the aero engine. The initial step is one of conception, which must
be subseauently checked by construction and trial. This must be
followed by commercial perfection, which requires endless research
by test and computation — ^not only on the machines as a whole but
to a larger degree on each element of the problem that analysis indi-
cates to have separate entity, and on ^oups of elements tnat have
coordinate functioning. Construction is here again necessary, not
only of the complete machine, but also of variante on each part, and
of instruments, appUances, models, and apparatus that do not them-
selves ^ter into tne result but are essential to its attainment. Fi-
nally, with commercial perfection, further construction work is neces-
sary to create the means of rapid large scale reproduction within the
limits of dimensions needed for interchangeaoility of parts, i. e.,
establishment of the manufacturing plant. It must be understood,
however, that these three steps that must be undertaken in this
order on general principles may not be repeated many times over
even when concerned with the same product, such as the aero engine,
or that the earUer step ceases when the latter is inaugurated, for this
is not true. These three stages or periods of development may, for
the want of better terms, be designated as, first, the period of inven-
tion; second, the period of design; and, third, the period of manufac-
ture. Design can not be undertaken before invention, whether that
invention be of the patentable sort or not. Yet invention undoubt-
edly proceeds long after design has been firmly established and, of
course, while manufacturing may not be undertaken until both in-
vention and design have accomplished a reasonably commercial
perfect product, it goes without saymg that both invention and design
will continue during the whole of the manufacturing period.

With the exception of invention, which needs litUe enooura^ement
beyond a stimulation of the imagination, the primary factor m sug-
cessful development is mondy, for, with sufficient fimds, the necessary
professional sKill, labor, materials, and plant mav be secured for carry-
ing out the steps of design and manufacture. Of course, money may
be, and usually is, misspent in these developments, especially^ whea
the control is m the hands of persons lacking engineding skill and



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AEB0NAUTIC8. 197

^perience, so there should be added the reqiurement that organiza-
tion be associated with money.

No better illustration of this situation can be given than that of the
steam turbine, whose period of development practically coincides with
that of the aero engine, but which has been broi^ht to a state of com-
mercial perfection that the aero engine has not even approached,
partly by reason of the better understanding of the service require-
ments that are not yet fully formulated for the flying machine, but
almost entirely because of we differences in the means employed for
the development. The steam tmrbine had its invention stage, and
while invention still proceeds it is largely superseded by rational de-
sign for manufacture, under skillful guidance, under proper organiza-
tion, suitably financed and satisfying an ample, well-understood mar-
ket demand. The aero en^e is stOl lawely undeveloped, invention
is still more active than design, and the aSnost microscopic, painstak-
ing research required to establish the data necessary for design is
almost wholly lacking, so naturally manufacturing in the true sense
of the term is correspondingly nonexistant, thou^ a few individual
models of engines are being reproduced in fair numbers.

The millions of dollars needed for rational perfection for manufac-
ture become available to the suitable organization ordinarily only
when a permanent market is clearly in sight and when the service
requirements of the product are reasonably definite. In the case of
the aero engine, this market has been absent or at least very uncer-
tain and the service requirements very hazy— both so much so that
under ordinary conditions the aero en^e could not have reached
even the degree of perfection so far attamed, tmsatisfactory as it may
be, without other incentives or different sorts of encouragement than
the ordinary article of commerce receives as, for example, i^ain the
steam turbme. This special element in perfecting the aero engine is
that of governmental aid based on military necessity, a comparatively
recent force in the situation but now a very strong one in Europe, but
almost wholly lacking in America. The military establishment can
purchase what it nee£ in the market only when there is a reasonably
strong civilian demand for the same article, strong enough to warrant
the financial investment necessary for its perfection — and such is the
case with the automobile and traction engine. On the other hand,
when there is no such demand, however active invention may be.
rational design and manufacture will be abs^it and must be suppliea
by the Army and Navy through their own organization and plants,
or, as an alternative, reasonably steady annuad governmental appro-
priations for purchasing sufficient quantities by the military depart-
ments may be made the oasis of support for civilian production . Such
is the case, for example, with ordnance and to some extent with ships.
For several vears after the demonstration that engine-driven air
craft could make successful flights the only encouragement offered to
development was that of adventurous sport. Men whose incomes
were sufficient became purchasers of macnines for their own amuse-
ment and others bought machines for making exhibition flights before
paying audiences for the profit to be derived. Both sorts of operators
took diances with the iinperf ections of the machine in a spint of ad-
venture or speculation, but practically all made short nights that
made no sucn demand on the engines as is now standard. Men such
as Eiffel, and Deutsch de la Meurtne, should be mentioned for their con-



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198 AEBONAUTIOS.

tributions of large sums of money for scientific investigations, not of
engines, however, and the national subscription funds of France and
Germany, all of which assisted in development. In many cases, even
with these short flights, the engine was taken apart, cleaned, re-

E aired, and readjusted before eadi ascent. Even as late as Septem-
er, 1912, Mr. Earle L. Ovington, writing in the Scientific American
reports:

Usually every 15 hours of running, and at most every 20, my mechanics (skilled
men) went through the interesting process of separating eveiy smgle component part



of my motor, one from the other. The valves were regroimd and retimed, because
of valve-gear wear, new valve sprin«93 were inserted, the tappet rods were adiusted,
and the whole motor was given a ricia inspection. Tne Gnome, in common with most
rotary motors, uses castor oil as a lubricant, hence at each cleaning g^t quantities
of carbon were removed . I claim that any engine requiring such attention may rightly
be termed ''delicate.'' How far would you get in an automobile if you haa to take
the entire engine to pieces and readjust practically every working jirt of the whole
motor every 15 or 20 hours of service?

In an article in the Auto Car of March 28, 1914, we find the follow-
ing statement:

The Gnome en^e requires cleaning out after about 24 hours' oontinous running
if it is to be kept m tune. The French military regulations demand that the Renault
be cleaned out after 200 hours' running. Users of other aeroplane engines have told
the writer that cleaning carbon out is hardly ever necessary.

With such an imcertain and capricious market perfection of the
aero engine could hardly be expected in a whole hietime, especially
as the amount of business in any one country would scarcely suffice
to support one producing establishment, and that one unable to bear
the expense of the high-salaried engineers competent to supervise
the work and when, at the same time, the stimulus to the imagina-
tion created by the idea of the mechanical flight produced thousajids
of inventions and inventors, each seeking ana many finding financial
support, under the influence of the excitement of the time rather than
from any sound business basis. Failures necessarilv must be nunoier-
ous under such conditions, and every failure, whetner of mechanism
or finances, set back the art and discouraged the rest.

During this period the miUtary oigamzations of all the nations
watched results and piu*chased a few machines for experimental
purposes, out of which grew the conviction now so firmly established
aad^so thoroughly demonstrated in the present European war that,
however impenect the aeroplane, it is a military necessity and must
be perfected. Perfection oeing impossible or too slow without
governmental aid, plans were formulated by the Eiux>pean nations,
one after the other, and, in addition to creating a corps of flying men
with suitable cooperation with the mihtary establishment, competi-
tive tests for aero engines were organized by Germany 1912—14;
France 1909, 1911, and 1913 in cooperation with the Ligue
Nationale A6rienne and the Automobile Club de France; Italy 1913 :
and England 1914, in which substantial money prizes were offered
for successful machines and in some cases buying orders given to
winners in the contest. It was the intention to make each of these
contests an annual event so as to not only continue the development
of engines under this incentive, but to show clearly the annual
progress by comparison of the entries in successive years on the basis
of their performance, in relation to their form, materials, and propor-
tions. The contests so far held are summarized in Appendix 1,
which also reproduces the conditions and such of best results with



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AEBONAUTIOB. 199

some discussions and interpretations as are obtainable from pub-
lished reports. Unfortunately the European war has interrupted
reports oi such tests as were completed m 1914 and prevented^ the
canying out of others, so that the latest information of this class is
not now obtainable.

Besides these eovemmental contests with cash prizes and pur-
chasing orders, which are undoubtedly the biegest sin^e influence
80 far brought to bear on the rational development of the aero
engine, there are some other coordinate factors to be noted, and these
are dvilian contests conducted by oi^ganizations interested pro-
fessionally in promoting the art or by individuals, reports of which are
also given in Appendix 1, with £ne Oovemment contest reports.
Amon^ these private contests are to be noted in France Competition
of LaLigueNationale A6rienne, 1911; Automobile Club of £Vance,
1913; England, Alexander contest, first for British-built engines,
1909, ana second for any enmie, 1912.

Finally^ there must be noted amon^ these influences for good in the
rational development of the aero engine the establishment of labora-
tories for testing engines alone or flying-machine supportiog and
control elements alone, or both engine and air craft, and reference
is made to the paper by Dr. A. P. /^ahm, May, 1915, reproduced in
Appendix 2, with other laboratory references in addition to those
contained in the contest reports of Appendix 1. Some of the results
obtained in these laboratories are not published and apparency
but little work has been done on engi^ies. It is assumed that most
of the laboratory work on engines so far done is such as to be of value
only to individuals seeking to perfect their own engine^ or, believing
it perfected, seeking an independent test report to enhst capital for
manufacture or to serve as an advertising inducement to purchasers.
As a consequence, the conclusion must be that the largest single
factor in the recent rapid development of the aero engine is govern-
mental, involving the establishment of official organizations to study
the problems, the operation of laboratories to determine by test tlie
resnlts attained bv designers and producers, especially wnen laige
and regular purcnasing orders are involved to support civiUan
development and manmacturin^ establishments, or in the absence
of sumdent orders, and perhaps m addition to them, the distribution
of sufficient cash prizes, whetner originating in governmental appro-
priations or private and institutional donations.

Great as has been their influence for good in aero engine develop-
ment, these contests have not yet been under way long enough to
bave accomplished more than a small fraction of what may be so
attained, nor can this contest means be r^arded as either sufficient
or without faults. There is an ii^erent danger that the results of
snch tests be misinterpreted, and in fact there is even a bare possi-
bility that they may exert a retarding influence on the art. Natur-
ally competitors design engines and enter them to win a prize and
&e conditions of the contest become the controlling factor in the
preparation of an engine for entir. If these conditions place undue
wei^t on factors that are not of primarjr importance to the engine
as it works in place in actual flight, it is easily possible that not
only may the best engine from the actual service standpoint be
rejected but. worse than that, the bulk of these workers who are
en^paged in aevelopment will be led away from lines that are truly
legitunate in order that by following the lines prescribed by the rules



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200 AEBOKAUTIOS.

they may secure the necessary cash to continue. In view of this
possibility too much care can not be exercised in the preparation and
regular revision of these^ contest rules and conditions m order that
the result may be what is wanted and what is needed by the whole
art. instead of a perfect attainment of a merely hypothetical standard.
Attention is called to these rules in the appendix and especially
to the alterations in later (German rules as compared with the earlier,
all directed toward greater latitude and greater reliance on the
judgment of competent engineers and proportionately less, on the
numerical values of those quantities that are subject to measure-
ment and which require experienced cultivated judgment to inter-
pret into terms of engine goodness which often depends as much on
mtan^ble things such as workmanship, ru^edness, simplicity, and



Online LibraryUnited States. National Advisory Committee for AerAnnual report of the National Advisory Committee for Aeronautics → online text (page 16 of 77)