Manovering Speed

N114RW wrote:

Can someone ‘splain this to me? I have no idea if I have it right, or
not.

As I understand it, maneuvering speed is the speed above which the
aircraft may be damaged due to full control movements. Below that
speed, the plane will stall before damage occurs. I also understand
that maximum lift changes as the square of the speed, while stall speed
changes as the square root of the weight.

So, if I have an aircraft traveling at twice stall speed, it will have 4
g’s acceleration prior to stalling. If I double the weight, the stall
speed increases by 1.41, so maneuvering speed also increases by 1.41 –
assuming that the aircraft is rated a 4 g’s at both weights.
Or, to put it conversely, the maneuvering speed varies inversely
proportionately to the square root of the weight change – if I double
the weight, the maneuvering speed increases by 41%.

Do I have that right?

So, assume I am flying at 1410 lbs. weight and traveling at 4 times
stall speed. If I reduce weight to 1000 lbs., and pull back on the
stick, won’t the aircraft stall with exactly the same load on the wings,
although now 5.6 g’s? (4 * 1410 or 5640 lbs)?

Does the issue for maneuvering speed now become the motor mounts,
battery box, seats. etc? If I’m certain that the weak point is not
these things, but the main airframe itself, can I use the maneuvering
airspeed for maximum weight?

Next - how about maximum structural cruising speed?


V_A: i suppose there has been a change of the certification specification
(FAR-23 or CS-23 in europe). while you can find manoevring speeds depending
on the actual weight of the aircraft in older airplanes' manuals, current
certification specs (paragraph 335(c) in either one) define V_A a fixed
value:
"(1) V_A may not be less than V_S*sqrt(n) where --
(i) V_S is a computed stalling speed with flaps retracted at the design
weight, normally based on the maximum airplane normal force coefficients,
CNA; and
(ii) n is the limit maneuvering load factor used in design"
the designer of an airplane then has to show , that the airplane structure
can take all loads prescribed by the regulations at this speed and all
allowed combinations of weight, CG and weight distribution (e.g. max. zero
fuel weight if fuel is carried in the wings).
usually, aprupt full deflections of controll surfaces at speeds above V_A
can resut in damage of the aircraft. of course, the designer may allow full
deflections at higher speed (some aerobatic aricrafts?); refer to the POH
if in doubt.

V_C: this is the speed where the designer has to show that the airplane is
capable of taking gusts of a vertical speed of 50fps (15.24m/s), which can
result in higher g loadings than the limit manoevring load factor choosen
(usually 3.8 for normal category aircraft or 5.3 for gliders).
also here, sufficient strength of the structure has to be shown within the
entire range of weight, payload distribution and CG range.


greetings from germany

uli

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