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On May 16, 2:06 pm, N114RW <qwerty_...@charter.net> wrote:
> Can someone 'splain this to me? I've no idea if I've 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've 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've that right?
>
> So, assume I'm 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 am certain that the weak point isn't
> these things, but the main airframe itself, can I use the maneuvering
> airspeed for maximum weight?
>
> Next - how about maximum structural cruising speed?
The maneuvering speed (Va) is dependent on weight and
aircraft design structural strength. The Va goes down as weight
decreases because it will respond more readily to a full control
input. Full-up elevator, say, will result in a brief upward climb
before the stall, and a lightly loaded airplane will rise more than a
heavier one. That upward path reduces the angle of attack and so the
thing doesn't stall as soon as ti would if at gross. If we make that
full-up application at quoted Va when lightly loaded, we might
overstress the airplane just because it won't stall soon
enough.Stalling unloads things and allows the airplane to follow a
less radical chnge in flightpath, reducing the load on everything from
the seats to the battery box.
Engine mounts are much stronger than the rest of the
airplane. It's a requirement for crashworthiness, I think. Many
airplanes will fail the tail before the wing; the Bonanza and 210 come
to mind. Lots of those have come apart in the air when their rich but
ignorant pilots flew into IMC and lost control, spiralled out of the
cloud and pulled up hard when the trees appeared. The stabilizer
breaks, the airplane flops forward over onto its back, and the wings
fail in negative g loading.
I cannot bring myself to stress an airplane at Va. I work
on these things and know how light tthat structure is. Too many years
working on other, much heavier machinery, I suppose.
Dan
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Re: Manovering Speed
