bwainfan
Well-Known Member
- Joined
- Feb 10, 2007
- Messages
- 60
Matthew:
A few thoughts for you:
First, we normally take off at a speed significantly above stall speed in order to have positive rate of climb and stall margin for gusts. Typically lift-off speed is about 1.2 x stall speed, so Cl is about 70% of Clmax at that point.
The issue about CLmax for LAR configurations is as much about the fact that they are tailless airplanes as it is about aspect ratio. Without a tail, we can't trim flaps, or highly-cambered airfoils. This limits the max CL.
For reference: The highest CLmax I'm aware of for any tailless airplane was bout 1.4, on a swept-wing design that had large flaps inboard. For most tailless configurations CLmax varies from a low of about 0.8, to a high of 1.1 to 1.2. (The highest I have ever measured either in flight with my own airplane, or in the wind tunnel over my career has been in the 1.2 range)
For preliminary sizing of a LAR configuration I would probaly use 1.0, but do calcs for 0.8 also just to get a sense of how it affects the design.
A few thoughts for you:
First, we normally take off at a speed significantly above stall speed in order to have positive rate of climb and stall margin for gusts. Typically lift-off speed is about 1.2 x stall speed, so Cl is about 70% of Clmax at that point.
The issue about CLmax for LAR configurations is as much about the fact that they are tailless airplanes as it is about aspect ratio. Without a tail, we can't trim flaps, or highly-cambered airfoils. This limits the max CL.
For reference: The highest CLmax I'm aware of for any tailless airplane was bout 1.4, on a swept-wing design that had large flaps inboard. For most tailless configurations CLmax varies from a low of about 0.8, to a high of 1.1 to 1.2. (The highest I have ever measured either in flight with my own airplane, or in the wind tunnel over my career has been in the 1.2 range)
For preliminary sizing of a LAR configuration I would probaly use 1.0, but do calcs for 0.8 also just to get a sense of how it affects the design.
Actually, it’s landing not takeoff that is the critical scenario when considering ultralight, microlight, or light sport categories with maximum stall or landing speeds. Since the simple spreadsheets I mess around with don’t make allowances for any special behavior at low aspect ratios, I am wondering if there is any way to generalize about LAR designs at low speeds and high angles for attack to help me size the wing area.