4 ms·

There are very specific regulations relating to how transport category aircraft have to behave. One of these is the reason the 737 MAX has the specific MCAS beh

by Zak 7y ago

There are very specific regulations relating to how transport category aircraft have to behave. One of these is the reason the 737 MAX has the specific MCAS behaviors that are probably responsible for two crashes: causing the aircraft to stall must require continually increasing the pitch-up control input (or something substantially similar), and that wasn't the case at low speed, high thrust, and high angle of attack. It may be difficult to achieve the required flight characteristics without software augmentation in a flying wing, even if RC hobbyists can usually fly them manually without crashing. The 737 MAX has raised the question of whether it's a good idea to approve transport category aircraft that require help from software to have acceptable flight characteristics.

rtkwe 7y ago
MCAS wasn't required for the MAX8 to fly it was required for it to maintain the common type rating with the existing 737 fleet. With training the MAX8 would have been fine to fly and pilots would have known to pitch down or decrease throttle when experiencing the engine induced pitching.
- sokoloff 7y ago
  MCAS provides for the certification requirement of continually increasing stick forces with increasing pitch, which was otherwise not met at high angles of attack and high thrust settings. MCAS (or another means to accomplish the same goal) was required for the aircraft to meet certification requirements, regardless of whether it was to share a common type rating with the rest of the 737 fleet (so long as it shared the landing gear with the rest of the 73' line, it was going to have this adverse aerodynamic raw result). https://www.risingup.com/fars/info/part25-175-FAR.shtml https://www.risingup.com/fars/info/part25-175-FAR.shtml
  - rtkwe 7y ago
    That regulation seems to be at a static thrust level right? > 75 percent of maximum continuous power for reciprocating engines or the maximum power or thrust selected by the applicant as an operating limitation for use during climb for turbine engines; and Wouldn't that give a stable pitch response because the thrust relative to the center of mass is constant? Also if the MCAS is always pushing the plane out of the given AoA (which seems to be what it's logic is, if AoA > x trim down until AoA < x) would that be considered outside the flight envelope anyways? The stick force curve goes screwy for every aircraft in a stall.
    - Zak 7y ago
      It's an aerodynamic issue with the 737 MAX: the engine cowlings themselves produce lift at a high angle of attack, and the engines are mounted farther forward than they are on other 737s.
mikeash 7y ago
Airbus and Boeing have been flying fully fly-by-wire airliners for decades. It works just fine.
- Zak 7y ago
  Those aircraft, as far as I know would meet certification requirements without the software adding control inputs that are opposite to what the pilots command.

by Zak 7y ago

rtkwe 7y ago

MCAS wasn't required for the MAX8 to fly it was required for it to maintain the common type rating with the existing 737 fleet. With training the MAX8 would have been fine to fly and pilots would have known to pitch down or decrease throttle when experiencing the engine induced pitching.

sokoloff 7y ago
MCAS provides for the certification requirement of continually increasing stick forces with increasing pitch, which was otherwise not met at high angles of attack and high thrust settings. MCAS (or another means to accomplish the same goal) was required for the aircraft to meet certification requirements, regardless of whether it was to share a common type rating with the rest of the 737 fleet (so long as it shared the landing gear with the rest of the 73' line, it was going to have this adverse aerodynamic raw result). https://www.risingup.com/fars/info/part25-175-FAR.shtml https://www.risingup.com/fars/info/part25-175-FAR.shtml
- rtkwe 7y ago
  That regulation seems to be at a static thrust level right? > 75 percent of maximum continuous power for reciprocating engines or the maximum power or thrust selected by the applicant as an operating limitation for use during climb for turbine engines; and Wouldn't that give a stable pitch response because the thrust relative to the center of mass is constant? Also if the MCAS is always pushing the plane out of the given AoA (which seems to be what it's logic is, if AoA > x trim down until AoA < x) would that be considered outside the flight envelope anyways? The stick force curve goes screwy for every aircraft in a stall.
  - Zak 7y ago
    It's an aerodynamic issue with the 737 MAX: the engine cowlings themselves produce lift at a high angle of attack, and the engines are mounted farther forward than they are on other 737s.

mikeash 7y ago

Airbus and Boeing have been flying fully fly-by-wire airliners for decades. It works just fine.

Zak 7y ago
Those aircraft, as far as I know would meet certification requirements without the software adding control inputs that are opposite to what the pilots command.