Limitations and Gust Responses Flashcards
Prop aircraft under CS23 are subject to two speed limitations which are … and …
Vne and Vno
Aircraft under CS25 speed limitations are … and …
Vmo and Mmo
what is Va?
it is the speed at which the aircraft will stall when achieving its …
the design manoeuvring speed
max load factor
what does the maneouvring load diagram display, and what is it also known as?
Displays load factor limitations and speed limitations together, and indicates the combinations of these where we can fly
built up by considering 3 different factors: stall speeds, g limits, and speed limits
AKA V-n diagram
G limits in CS 25 with flaps up are …
sometimes these are referred to as the …
+2.5 g and -1.5 g
AKA ‘load limit factor’
Light aircraft g limits are …
+3.8g, -1.52g
Light utility g limits are …
+4.4g, -1.76g
formula for calculating Va, or the accelerated stall speed?
Va = Vs x sqrt n
what is the significance of Va with reagrd to the regulatory max g limit?
, below this speed, the pilot can apply full elevator deflection and the aircraft will stall before its g limit is reached. Above Va, large elevator deflection may cause the aircraft to reach its g limit before stalling, possibly deforming the airframe
(at higher speeds the aircraft can pull more g without stalling)
what is Vc and what does it set for?
Vc is the design cruise speed, a high-speed limit in level flight. It is set so that, in the event of a specified upset in the cruise, the aircraft can be recovered to level flight before Vd is exceeded
(provides a margin to allow for uncommanded speed increases)
What is Vd?
Vd is the design dive speed. The max speed limit that is set after test pilots have put the aircraft in to a dive, and is normally limited by buffet and vibrations
what is the positive g limit for CS 25 aircraft with flaps extended?
2 g
what is the effect of extending flap on the manoeuvring load diagram?
Extending flaps increases CLmax and decreases stall speed, while the g limit is reduced by CS25 to 2 g
The shape of the slow speed part of the curve on our V – n diagram is changed, and the flight envelope is reduced in size
What is Vb?
Vb is the design speed for maximum gust intensity – a speed achieved when an aircraft experiences a gust of 66 fps while flying at Va
At this speed the stall will occur at a load factor greater than 2.5 g, at a point where the 66 fps line crosses the stall line
Vb is a point at a higher airspeed and higher load factor than Va
where do the gust lines extend from on the gust envelope diagram?
unlike the stall lines, the gust lines originate from where n=1 and V=0
what influences the size of the gust response when flying straight and level in smooth air?
The alpha at which we are flying in smooth air will influence the size of the gust response
In the top image the gust increases alpha to 6 degrees, a 20% increase
The lower image increases alpha to 4 degrees, a 33% increase
So the aircraft with the higher alpha will experience smaller percentage changes in both lift and load factor in the gust
Its gust response will be less and we will measure a lower gust load factor
In other words: increased alpha decreases gust load factor, and we get a smoother ride
