16.1.2. The airplane wave drag.
At flight speeds with Mach numbers shock waves appear on the airplane surface and in flow, which cause occurrence of the wave drag.
Calculation is performed by summarizing of
airplane separate parts drags at
.
(16.4)
where
,
,
,
,
- wave factors drag of the airplane isolated parts of;
and
- an additional wave drag factors caused by an interference of the
wing, horizontal tail and fuselage.
At that, factors of the wing wave drag and
horizontal tail wave drag are calculated for Mach numbers
,
with taking into account the flow deceleration.
Now the authentic calculation results of wave drag
can be obtained at
.
In subsonic range of Mach numbers
calculation of the airplane wave drag is provided by generalized
ratio (Fig. 16.1), which is obtained by the experimental data
approximation for various aerodynamic configurations
,
(16.5)
Fig. 16.1. Airplane wave drag at
- airplane wave drag factor for the chosen value of number
;
- airplane critical Mach number.
The least one among isolated parts values
is adopted as the airplane Mach critical number
,
which should be reduced on
with taking into account an interference
. (16.6)
16.2. Airplane lift.
In general, airplane lift is created by the wing, fuselage, horizontal tail, power plant and other elements which enter into airplane aerodynamic configuration.
The lift of the airplane with the high-aspect-ratio wing is basically determined by lift of an isolated wing with ventral part. At that, it is supposed, that contribution from other airplane elements is indirectly taken into account in lift of ventral part.
It is characteristics for low-aspect-ratio lifting
surfaces and elongated fuselages the non-linear ratio of the lift
coefficient on angles of attack. The non-linear effects become
essential on airplanes with wings having aspect ratio equal
.
The influence of the isolated power plant onto aerodynamic lift is usually a little. However, lift can be significantly raised due to ventilation of wing surface or other elements by the prop jet or the engine jet.
As well as other aerodynamic characteristics, the airplane lift is determined as a sum of lifts created by isolated parts with taking into account their mutual influence. At that, it is expedient to allocate lift created by horizontal tail as the separate item
.
(16.7)
where
the characteristic of the airplane without horizontal tail;
- lift coefficient horizontal tail.
For airplanes with wings having aspect ratio
the non-linear lift component is not taking into account, accepting
that
.
16.2.1. Derivative of the lift coefficient.
We consider, that the airplane lift is created by wing, fuselage, horizontal tail and engine nacelles. Let's allocate the horizontal tail from the total sum
,
(16.8)
,
(16.9)
where
,
,
,
- characteristic of the airplane parts in the airplane system, at
that the lift derivatives of fuselage
and nacelles
correspond to isolated parts.
Depending on airplane aerodynamic configuration the values of derivatives and are also determined as follows:
- For the normal scheme:
,
;
(16.10)
- For the canard configuration
,
,
(16.11)
where
and
- characteristic of the isolated wing and horizontal tail which are
determined for Mach numbers
,
with taking into account flow deceleration;
and
- factors of wing or tail unit interference with fuselage;
-
derivative flow downwash.