Why do you have to start maneuvers at Va speed?
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A question came in from a student pilot and he wanted to know why, when you start out at doing a maneuver such as steep turns, do you have to begin at Va speed?

According to the PHAK, it is the speed below which you can move a single flight control, one time, to its full deflection, for one axis of airplane rotation only (pitch, roll or yaw), in smooth air, without risk of damage to the airplane.

Steep turns, when done properly, subject the airframe to up to 2G's. Add in some turbulence and there can be a momentary 3G load. Flying at or below Va speed is your guarantee that no matter how abruptly you move a flight control, there is no way possible to overstress the airframe. More than anything else, it is just a safety valve, so to speak, to protect the airframe from damage.

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@Daddis At AOPA Where do most speed limitations come from and how are they calculated? Well, without getting too nerdy, I believe most will understand that these V speed limits are a function of the “load” or “g's” placed on the aircraft as a result of it's flight path or attitude. Engineers can calculate effects on the structure of the aircraft for any given load. A useful diagram that provides a graphical view of these is the “V-G” chart. As an instructor I introduce this chart to new students as part of their fundamental understanding of how the speed limitations of the aircraft they are flying are determined. Here is a link to one youtube explanation. There are several so if this does not work to for you I encourage searching for others or having a discussion with an instructor. It will be a worthy discussion for both you and the instructor you chose…  

. There are several.  
 

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@Prometheus At AOPA
Just remember – Va, like stall speed, goes DOWN as weight goes down.  That Va on the placard next to your airspeed indicator is for max gross weight.  At training weights, you need to correct that DOWN proportional to the square root of actual gross weight divided by max gross weight.