6.6. Wing induced drag at with taking into account local supersonic flows.
Let's
consider the problem on the account of additional drag occurred at
values of
and
,
outgoing of critical values (the approximate method of the account is
offered by S. I. Kuznetsov). This drag is necessary for taking into
account at construction of the wing polar for specified
,
.
Let's
assume
that
the dependence of critical Mach number
on
,
i.e.
or
.
Let's construct this dependence in a plane of
,
(Fig. 6.22).
Fig.
6.22
Fig.
6.23. Wing polar with the account of
will be
,
then the flow supersonic area closed by shock waves is formed on the
wing. In this case there is an additional drag caused by lift
(at
).
If it assumes, that the growth of lift is not accompanied by growth
of sucking force with increasing of angles of attack at
(that at presence of the broad supersonic area on a wing is
permissible), then for a flat wing we shall have
or
.
In
addition adopting, that on transonic flow modes the proportion
is executed, then finally we receive
.
This parameter is added to induced drag, and thus we have:
(6.22)
Wing polars take the form it shown in fig. 6.23.
Values
of lift coefficients
corresponded to the beginning of wave crisis at
;
i.e. the dependence
can be found from the formula (
):
where
the factors
,
,
for a wing with a classical airfoil are equal
,
,
;
for a wing with a supercritical airfoil -
,
,
.