Welcome Guest. Sign in or Signup

1 Answers

vg and va changes in gross weight of an aircraft

Asked by: 8877 views Student Pilot

describe for me the changes in Vg and Va with changes in the gross weight of an aircraft?

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

1 Answers



  1. Brian on Nov 30, 2015

    Disclaimer: I’ve used purely an analytical method to respond to this question. Try not to let the formula’s bellow intimidate. Instead focus on the wording between the formula’s as I attempt to explain in a simple way what they represent. If you’d prefer a different explanation or wish for clarification just ask! Enjoy.

    Both speeds are Angle of Attack (AoA) related. So let’s look at the formula for lift:

    Lift (L) = 1/2 Velocity (V) squared * Density (rho or ρ) * Wing Area (S) * Lift Coefficient (CL)

    Lift coefficient is what is important here as the specific angle of attack will result in a specific CL. Surely you’ve heard the term CLmax in reference to stall speed before. Let me rewrite this in it’s plane terms before we continue:

    L = 1⁄2 V^2 ρ S CL

    So how does weight factor in? Well lift equals weight in unaccelerated flight. This means that, for the purpose of finding our unaccelerated stall speed, we can replace the above Lift variable with Weight and we have the following:

    W = 1⁄2 V^2 ρ S CL

    Now we can move some things around and set Velocity on it’s own since that is what we are looking for:

    V = Sqrt [W / (1⁄2 ρ S CL)]

    If we now take this same formula and plug in the CLmax we have our stall formula:

    Vs = Sqrt [W / (1⁄2 ρ S CLmax)]

    We can do the same for a best glide formula by using CLbg:

    Vbg = Sqrt [W / (1⁄2 ρ S CLbg)]

    —

    In each case you’ll notice that weight variable is on top. Lift coefficient, wing area, and density are held constant for the purposes of your question. So if weight, which is on top remember, goes up then Vs and Vbg will go up as well. Vice versa if they go down.

    To calculate the effects of weight use this:

    V (corrected for weight) = Sqrt [actual weight/gross weight] * V speed at gross weight

    This formula holds true for all performance V-speeds as well as Va. All other limitation speeds are not effected by weight.

    0 Votes Thumb up 2 Votes Thumb down 2 Votes


The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.