Like many speeds in an airlane, maneuvering speed, Va, is related to
the wings-level, stall speed Vso by the square root of the g-load.
There is a positive side and a negative side.

For example, for Normal category, positive g operations, where the
design limit is +3.8-g, Va = 1.95 x Vso. (Note: this relationship
applies to CAS, so you must use the airspeed calibration figures in
the POH to move back and forth between IAS and CAS to find the actual
number you should see on the airspeed indicator).

If you know the wings-level, -1.0-g stall speed of the airplane (which
will in all likelihood be greater than the upright Vso), then you can
find the inverted Va, which will be 1.23 x the inverted Vso. Of
course, the inverted operating envelope is quite small.

As for your "trick" -- sure, it's something that can be done from a
steep climb followed by a pushover as the speed decays. But EVERYTHING
that is not bolted down in the airplane will float, not just the
pencil -- flashlights, flight bags, dirt, towbars, etc. And if the g
is too light, the engine may balk...

I'd recommend trying it with an instructor in an aerobatic airplane
instead.

Rich
http://www.richstowell.com


(Koopas Ly) wrote in message . com...
Me again,

Va seems to be only intended to protect against excessive positive
load factors. What about negative g's?

Can I find a Va for negative design load factors (-1.52 g) for the
C172SP anywhere?

Reason I am asking is that I want to try the "floating pencil" trick
next time I fly but I don't want to shove the stick fully forward for
fear of breaking something. I am not looking to induce negative g's,
only zero g's and zero lift. Any pointers on entry speed and power
settings? Is it easier to perform if you induce a gradual +1 g steep
climb similar to a departure stall maneuver, then upon hearing the
stall horn, give it good nudge forward on the stick? I've heard that
your airspeed may indicate well below stall, but again, your stall
speed does approach zero as your load factor goes to zero.

Likewise, would you prefer to pull 2 positive g's in a pull-up
maneuver or a, say, 60 deg. bank? Frankly, I am not too familiar with
the former so I might do something undesirable. Aside from my stall
speed going up to something like 68 kts. clean (Va ~ 100 kts), you'd
see your airspeed quickly dwindling while pulling up. I think it'd be
fruitless to add in power since heck, you're not maintaining altitude
and besides, you probably don't have any excess power anyway to do
that. Neither am I familiar with the mechanics of loops so it'd be
wiser to leave that alone. Perhaps the 60 deg. bank is more
reasonable to have some fun. Would you try to hold altitude with
backpressure and power or just leave the plane to dive and speed up in
the spiral, with a recovery before Vne? I think the maneuver would be
more innocuous with power-off a-la-emergency-descent style. Again,
I've never done a 60 deg. bank...so I should probably leave that alone
too until I try it with a passenger...oops..i mean CFI.

Seriously, if someone has something to suggest that's fun and safe,
within normal operating range and category, please suggest. It's a
buddy's bday soon and he wants to go up. Again, I am not looking for
doing anything aerobatic.

Alright, I can see the flames and derision coming from the mainland

May you have a peaceful week with no stress,
Alex