Designing a wing Flashcards
What makes a wing efficient?
Produces required amount of lift for least amount of drag.
2 ways achieved
Create an elliptical lift distribution and adjust its aspect ratio.
What does aspect ratio effect?
Significant effect on wing’s span wise PG. Higher aspect ratio=smaller lateral pressure gradient.
What do high aspect ratio wings do
Produce weaker tip trailing vortices and more efficient that low aspect ratios
What are the disadvantage of high aspect wings
Tip strikes landings and take-off.
Need for a stronger/heavier main spar to support longer wing length.
At high speeds aerodynamic advantages of high aspect wing are less significant.
What is the relationship between aspect ratio and CL
Significant effect on shape of CL alpha curve. A high aspect ratio produces a steeper curve and smaller critical angle.
What is the relationship between CD and aspect ratio
Aspect ratio affects how CD varies with CL.
Low aspect ratio wing suffers very large rise in drag with increase in CL.
High aspect CD increases v.little over the range of CL
What happens with Elliptical lift distribution.
Lift production reduces towards tips. Towards wing tip pressure differential steadily reduces so at tip no driving force for formation of wing tip vortices and thus minimally induced drag.
What happens with an Elliptical Planform
Elliptical wing produces a constant and reduced level of downwash across wing and thus effective AOA remains constant across wing span. Elliptical wing produces most lift for smallest total energy lost in tip vortices.
What happens with a rectangular wing.
Easier to construct, larger wing tip vortices and greater downwash towards wing tips. Sections closer to wing tip a smaller effective AOA and thus smaller section lift coefficients
What happens with taper wings
Strong vortices at root because longer root.Midspan Vortices weaker. Effective AOA is at mid span and stall is midspan.
What happens with swept wings
Downwash greatest at wing root and smaller close to tip. Downwash increases however because of tip vortex. Effective AOA and CL are greatest close to tip
What is washout
Angle of incidence at root is greater than tip angle of incidence.
What does washout help with
Improved stalling characteristics. In a stall washout helps to maintain a better stability of aircraft due to reduced AOA resulting in smoother airflow above and better effectiveness of ailerons.
What is camber change
Other way of reducing lift at the tips is to reduce camber of aerofoil section in this area. Reduced camber= reduced CL for that cross-section of the wing.
What is wing loading
Aircraft weight/wing area.
Stalling speed and CL depend on wing loading.
Small wing area heavy in weight= High wing loading
Opposite for low.
Low wing loading more efficient and improved turning performances.
