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in drag and sink rate as the airplane slides up the back side of the power-required curve. The sink rate can be arrested in one of two ways: 

• Pitch attitude can be substantially reduced to reduce the AOA and allow the airplane to accelerate to a speed above V$_{MD}$, where steady flight conditions can be reestablished. This procedure, however, will invariably result in a substantial loss of altitude. 

• Thrust can be increased to accelerate the airplane to a speed above V$_{MD}$ to reestablish steady flight conditions. The amount of thrust must be sufficient to accelerate the airplane and regain altitude lost. Also, if the airplane has slid a long way up the back side of the power required (drag) curve, drag will be very high and a very large amount of thrust will be required. 

In a typical piston engine airplane, V$_{MD}$ in the clean configuration is normally at a speed of about 1.3 VS. [Figure 15-12]  Flight below V$_{MD}$ on a piston engine airplane is well identified and predictable. In contrast, in a jet airplane flight in the area of V$_{MD}$ (typically 1.5 – 1.6 V $_{S}$) does not normally produce any noticeable changes in flying qualities other than a lack of speed stability—a condition where a decrease in speed leads to an increase in drag which leads to a further decrease in speed and hence a speed divergence. A pilot who is not cognizant of a developing speed divergence may find a serious sink rate developing at a constant power setting, and a pitch attitude that appears to be normal. The 

fact that drag increases more rapidly than lift, causing a sinking flightpath, is one of the most important aspects of jet airplane flying qualities. 

## Stalls 

The stalling characteristics of the sweptwing jet airplane can vary considerably from those of the normal straight wing airplane. The greatest difference that will be noticeable to the pilot is the lift developed vs. angle of attack. An increase in angle of attack of the straight wing produces a substantial and constantly increasing lift vector up to its maximum coefficient of lift, and soon thereafter flow separation (stall) occurs with a rapid deterioration of lift. 

By contrast, the sweptwing produces a much more gradual buildup of lift with a less well-defined maximum coefficient. This less-defined peak also means that a swept wing may not have as dramatic loss of lift at angles of attack beyond its maximum lift coefficient. However, these high-lift conditions are accompanied by high drag, which results in a high rate of descent. [Figure 15-13] 

The differences in the stall characteristics between a conventional straight wing/low tailplane (non T-tail) airplane and a sweptwing T-tail airplane center around two main areas. 

• The basic pitching tendency of the airplane at the stall. 

• Tail effectiveness in stall recovery. 

