Some basic problems connected with attempts to increase the size and capacity of transport aircraft are discussed. According to the square-cubic law, the increase in structural weight is proportional to the third power of the increase in the linear dimensions of the aircraft when geomettric similarity is maintained, while the surface area of the aircraft increases according to the second power. A consequence is that the fraction of useful weight will decrease as aircraft increase in size. However, in flying-wing designs in which the whole load on the wing is proportional to the distribution of lifting forces, the total bending moment on the wing will be sharply reduced, enabling lighter construction. Flying wings may have an ultimate capacity of 3000 passengers

Yeger, S.

English

NASA Technical Reports Server

- NF/4/_T/q. 7 7¢SJ--,
NASA TECHNICAL Ivf_¢IORANDI_ NASA TM-77952
AIRCRAFT OF THE FUTURE
NASA-TM-77952 19860003850
S. Yeger
Translation of "Flugzeuge der Zukunft," Technisch-oekonomische
Information der zivflen Luftfahrt, Vol. 13, No. 2 1977, p. 88-90
(Grazhdanskaia Aviatsiia, No. 7, 1976).
L- Oa_. ''7,....._" _-
f',I0V 2 01985 ':';.
LANGLEY RESEARCHCENTER (<
LIBRARY, NASA ,_iO'i' .'I"0_ _,4:=':,_£1",02.'_"iiZL_i:C<)_.';
HAMPTON, VIRGNI,_
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546, NOVEMBER 1985
https://ntrs.nasa.gov/search.jsp?R=19860003850 2020-03-20T15:54:44+00:00Z
_- " STANDARD ll'rLE PAG
1. Rcpo,! N©. _. G©v¢,,m.r,! Acc*slior, N©'. 3. RoC;p_.nl"t Co1©1o9 H(..
TM-77952
_.T;,I.e.d$v{,;,I€ AIRCRAFTOF THE FUTURE 5.R.po,,Do,.
November 1985
6. p.,lo,m;n_ O,eon;*o_;o. Co4.
7. Aulhor(s} B. Pe,(o,rn;m90w_on;z©t;on _.por! 1"4o.
- S. Yeger
I0. Wo,k U.;tNo.
L:-- Io Co.11oct o, G,a.! No.9. P¢,lo,_;,_O o.;=o,;o,_o--o-_Aa_,.,, NASW-4006
The CorporateWord, Inc. 13.T)p-orR.po,,=-ap.,;odCov.,._
1102 Arrott Bldg. .....
Pittsburgh,PA 15222 Translation
2."Sponso,;n_A_.ncy Nora.o._ A_,-,,
NationalAeronauticsand Space Administration I_. Spon,or:n_ Agent Y Co_.
Washington,DC 20546
15.supp1....,o,yNo,.,Translationof "Flugzeugeder Zukunft,"Technisch-oekono- b
mische Informationder zivilenLuftfahrt,Vol. 13, No. 2, 1977, pp. 88-90
(GrazhdanskaiaAviatsiia,No. 7, 1976) (A77-39452).
I
14_, AEs*,©c*
Some Basic problemsconnectedwith attempts-toincr-ea_sethe Size and _padit_ )
of transportaircraftare discussed. Accordingto the square-cubiclaw, the
increasein structuralweight is proportionalto the third power of theiin- -
crease in the linear dimensionsof the_.aircra_twhen geometricsimilarityis "
maintained,while the surfacearea of the aircraft increasesaccordingto thct
•secondDower.A Consequenceis thatthefract_on-0fusefulweight--wiildecrea.'
asaircraftincreaseinsize. HoWever,in flying-wingdesignsinwhichthe
whole load on the wing is.proportionalto.the distributionof lifting forces,"
the total bendingmoment on the wing will be sharplyreduced,enabling
lighter-construction.- Flyingwings may have an Ultimate.capacity of 300Q
passengers. -.
17: K.y Wo,_s (Selected by Author(s)) I$. D;st,;bul;onSt©l,m*ni
-_" " Unlimited
19. S.cu,;ty Clo,,;(.(o(th;s ,.po,I) _. S.c,,;t_CIo,,If.(*!tMsr'_') 21- H,. of Pes*, 2_: P,;€;'7'_
Unclassified Unclassified 9 ,
$ -. "HASA-HO2
vAIRCRAFT OF THE FUTURE
S. Yeger
The steady growth of air traffic in a number of /88
countries has lead to a substantially increased number of
commercial aircraft in air traffic operations. The result has
been that the carrying capacity of many, even very large
airports, is approaching its upper limit. As a result, air
traffic specialists are confronted with the problem of managing
continued air traffic growth without further increasing the
number of aircraft.
The problem has been solved in various ways, among others by
$
designing and constructing jumbo aircraft with 300 to 500 seats
to replace several conventional aircraft. One representative of
this genre is the jumbo aircraft IL-86, developed in the USSR.
A number of specialists involved in designing, constructing,
and operating aircraft are of the opinion that the period
between 1980 and 2000 will witness further increases in
dimensions and capacities of passenger aircraft up to 1000 or
2000 seats. Opinions on this matter vary greatly, however.
This may be explained by certain technical problems involved in
producing gigantic aircraft, mainly with difficulties in
obtaining necessary mass relations.
Aircraft exhibiting the largest payload at a given range
possess the highest efficiency. As dimensions change, however,
the relative masses of such elements as the power plant change
while those of fuel and equipment basically do not. For this
reason, the increase or decrease of the load mass caused
*Numbers in the margin indicate pagination in foreign text.
by dimension variations is dependent above all on the aircraft's
relative structural weight which has direct influence on
economic efficiency.
The battle over reduction of the mass of such structural
elements as wings, fuselage, empennage, and undercarriage goes
clear back to the origins of air travel. Research on the laws
governing changes in dimensions and mass of aircraft parts began
at the same time. They came to be expressed in the
"Square-Cubic Law."
According to the square-cubic law, the increase in structure
weight is proportional to the cube of the increase in the linear
dimensions of the aircraft when geometric similarity is
maintained (while the surface area of the aircraft, including
€
_ the wing surface, increases proportionally to the sqare of the
linear dimensions). Since the surface load must be kept
constant to maintain take-off and landing characteristics, as
well as for flight behavior, the take-off mass has to change
proportionally to the square of the linear measurements.
Therefore, the relative structural mass increases proportionally
to the aircraft's dimensions and the payload portion will
decrease.
One consequence of the square-cubic law is an uninterrupted
increase in construction mass greater than that of other mass
portions as when linear dimensions increase. The necessary
relative portion is not preserved for the other elements, making
it impossible to produce an aircraft with the desired
characteristics. This means that the extent to which an
aircraft can be enlarged is limited. Practical aircraft /89
construction has, however, already extended beyond the
limitations on aircraft growth formally dictated by the
square-cube law.
4
The principle lies in the fact that only a portion of the
structural mass is determined by exterior forces, and it
represents mass relevant for guaranteeing strength.
The remaining portion is determined by additional
installations and auxiliary elements, with their portion
decreasing as the aircraft becomes larger. This increases the
structure's mass efficiency. At the same time, excess strength
decreases, a factor which is determined by various technological
factors and the structure's local strength margins. Stresses
increase in the elements working on pressure. Furthermore,
practical enlargement of linear measurements allows the
similarity of the aggregate and the inner structural elements to
remain in tact. This, too, helps to slow down the growth of
relative structural mass.
i
The most essential point, however, is exact consideration of
the basic forces involved in the airfoil's progression through
the square-cube law. In fact, the bending moment's resultant
which puts stress on the airfoil's elements of longitudnal bond
is determined by a force which is smaller than the thrust. The
amount of this force is smaller than the airfoil structure's
mass force, the entire load stored in the airfoil (fuel,
equipment), and the load attached tq it (engine with cockpit,
landing gear).
This type of surface discharge caused by mass force lightens
the structure substantially. An aircraft consisting solely of
an airfoil would be the ideal situation. If the entire load in
the wing can be adjusted proportionally to engine distribution,
as well, bending moment will approache zero, and the structural
mass will reache a minimum.
This idea was the basis of the flying wing aircraft which
was very popular between 1930 and 1950. In spite of its
5
popularity, however, this construction was no more efficient
than conventional aircraft forms.
The flying wing aircraft requires large dimensions and
surface areas to accommodate passengers and freight. The
specific surface load is small with low flight mass and
relatively large surface area. The thrust coefficients attained
during flight are small, as well. Therefore, the attainable
aerodynamic efficiency in air travel by no means reaches its
maximum value.
Speed increases intensify this disadvantage: As thrust
increases, lift/drag ratios deteriorate even more. It was more
advantageous to use a smaller wing which could be flown at
maximum efficiency in air travel. This allowed for J
accommodation of the load in a fuselage elongated in flight
direction. The fuselage possessed a small cross section.
However, this made it possible to reduce the total drag only by
retaining the conventional set-up.
Calculations reveal, however, that the flying wing aircraft
is advantageous for a lO00-seat aircraft. The airfoil
dimensions required to attain maximum aerodynamic efficiency are
so large that the flying wing can accomodate passengers,
baggage, fuel, and equipment.
At present, model procedures are being prepared, and methods
have been developed to calculate the mass of aircraft parts, so
that it is possible to control structural mass changes while
making large alterations on the aircraft (even without
maintaining geometric similarity).
0 I000 _00 3000Poss.
Figure 1: Change of payload portion on the total mass of
a commercialaircraft as a function of the
number of seats.
Figure 1 shows the payload portion of an enlarged,
conventional subsonic aircraft with an assumed range of 3000
kilometers.
First, the mass of an imaginary aircraft is calculated
without each payload portion (GKoM = 00. Then payload is
increased slightly, so that the total mass Go becomes greater
for a payload portion Gxos = G<_ > 0.G
o
Continuing this procedure by adding to the seating capacity,
we _eka_mine that the payload portion increases rapidly. After
reaching a maximum, Gx0s decreases again, since the relative
' structural mass becomes larger.
The figure shows that there is an optimum size for aircraft
with a smaller number of seats at GKoM = max. The maximum
payload portion corresponds to aircraft dimensions for which
stress has reached its highest point and strength margin its
lowest point. A two-story fuselage is best suited for more than
500 seats. Such a fuselage is smaller than a one-story
fuselage, can be more densely loaded, and has a smaller mass. A
three-story fuselage is recommended for aircraft with more than
1500 seats.
O_M
bo
f
o 1ooo 2oo8 sooo_.
Figure 2: Change of payload portion of the total mass as
a function of number of seats for various types
of commercial aircraft. A - Conventional
set-up (I - single deck fuselage, 2 - two-story
fuselage, 3 - three-story fuselage); B - Flying
wing aircraft with cockpit, accomodations for
€
passengers in cockpit and in airfoil, and C -
"Pure" flying wing aircraft.
Different aerodynamic aircraft designs under given
circumstances are compared in Figure 2. A conventional aircraft
with two-story fuselage and a seating capacity over 1000 begins
to be disadvantageous with regard to GKOM when compared to a
flying wing aircraft with a small cockpit in place of the
fuselage (and accommodating passengers in the cockpit as well as
in the wing). Partial use of the airfoil for loading payload
permits a moderate enlargement of the surface and high
aerodynamic efficiency values in flight.
Use of a pure flying wing aircraft is most advantageous for
further enlargements of dimensions and increase in seating
capacity over 2000, as well as for corresponding surface load
enlargement.
8
Thus, the use of new designs and aerodynamic solutions and
the introduction of multiple-story fuselages, aircraft without
empannage, and flying wing aircraft lead towards shifts of the
maximum attainable payload portion in larger aircraft. This
increases the cost-effectiveness of aircraft with lO00 or more
seats. More refined construction methods, materials, and
equipment, as well as more efficient engines encourage this
scientific-technological development for the future.
(Taken from Grazdanskaja aviacija 7/1976; Translator: Dr.
Peter Bork)
IJI[/Jfiiii_liiiiiiiiiiiJIrI
3 1176 00188 7927


Aircraft of the future

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server