Originally Posted by Mad (Flt) Scientist
At a normal takeoff speed (once the plane is safely airborne) it will be flying about 25% faster than stall speed, and will be capable of generating about 1.5'g', so it's true to say that you can't structurally break a plane on takeoff with lift alone. However, the maximum permitted speed in a takeoff configuration (Vfe) will be about 75-100% higer than takeoff speed - say twice the stall speed. Which means that you could in theory generate 4'g' if you went as fast as permitted then pulled as hard as you could. That WILL break something, I'd expect.
And in theory, you could create 8 G or something if the OEW is, say, 50 % of MTOW and the plane is taking off light.
So, for planes that rotate on takeoff (many donīt because the wing is at a high AoA on takeoff run, either because the tail is low on a short tailwheel or less freqently because although the fuselage is level the wing is at a high angle of incidence):
The maximum allowed speed in takeoff configuration, Vfe, is around, as you say, say, 200 % of stall speed. However, can the plane actually run on ground at Vfe, or are there other speed limits, like tire speed limits?
The normal speed when rotation is attempted is then 125 % of stall speed?
The minimum speed when it is allowed to attempt rotation is 110 % of stall speed, if the plane can stall on ground - usually cannot, then the minimum allowed speed to attempt rotation is accordingly higher as determined by tailstrike clearance?
Airplanes in takeoff configuration are to be able to take +2 g at MTOW... presumably more at less than MTOW. They have to be capable of 1,21 g or more at minimum allowed Vlof... and would be capable of 1,5 g at normal Vlof?
What are the typical g-s actually achieved at a normal liftoff - what would constitute a too abrupt takeoff and what would be regarded as too slow and floating liftoff?
Originally Posted by Mad (Flt) Scientist
MTOW for structural purposes has to cover ALL design manouvres - not just during takeoff, cruise and landing normal operations, but various extreme cases. The extra margin you get in normal operations provides additional safety margin and allows for a decent fatigue life. And, yes, a plane at its structurally certified MTOW can takeoff, certainly on a 'normal' day - otherwise there'd be no point in designing the structure to take the relevant loads!
For simplicity, MTOW (= 'structural MTOW') is the usually quoted value when doing simple comparisons because it's (generally) a single value and is indicative of aircraft performance limits (since most designs will balance out strure vs performance limits to optimise the design).
How is MTOW measured?
While it is usually not allowed, there are plenty of planes alleged to have flown overloaded... And I said usually... Wasnīt it the case that in Alaska, planes are officially permitted to fly overloaded?