I've been perusing AC 103-7 and its appendices, and I want to check what I think I know.
First off, assume a "max" UL... empty weight 254 lbs, 5 gallon fuel capacity, 24 lb ballistic parachute, 220 lb pilot, 20 lb payload.
For the purposes of AC 103-7, the takeoff weight of this aircraft is 254 (empty) + 30 (fuel) + 170 (nominal pilot) = 454 lbs.
Now, the "assumed CL_max" is dependent on top camber anyway. Assume no flaps on this beasty; so to fall into the 1.6 category with a two surface wing, "top surface camber" must be at least 7%. Two examples of such airfoils are the 0014 (7% by definition, even though no camber by normal definition) and the 23112 (7.65% upper surface). Let's use the 0014 for discussion purposes.
By chart, the maximum wing loading is about 3.15 lbs/ft^2. At 454 lbs, this comes to 144 ft^2. So 32 ft span by 4.5 ft constant chord gives a nice hershey bar that gives this area.
Would this actually be a legal (for stall purposes) ultralight?
Actual take off weight would be 548 lbs, and actual CL_max would be around 1.4 for a 0014. So actual stall speed would probably be between 28 kts and 29 kts, almost 20% higher than the legal limit. But everything's okay, because I chose to demonstrate by AC 103-7 rather than measured values, yes?
Edit for follow-up question: Does all of this still apply if some characteristic of the plane (tail authority, for example) prevents it from actually stalling, limiting minimum demonstrable speed to 1.3x stall speed?
First off, assume a "max" UL... empty weight 254 lbs, 5 gallon fuel capacity, 24 lb ballistic parachute, 220 lb pilot, 20 lb payload.
For the purposes of AC 103-7, the takeoff weight of this aircraft is 254 (empty) + 30 (fuel) + 170 (nominal pilot) = 454 lbs.
Now, the "assumed CL_max" is dependent on top camber anyway. Assume no flaps on this beasty; so to fall into the 1.6 category with a two surface wing, "top surface camber" must be at least 7%. Two examples of such airfoils are the 0014 (7% by definition, even though no camber by normal definition) and the 23112 (7.65% upper surface). Let's use the 0014 for discussion purposes.
By chart, the maximum wing loading is about 3.15 lbs/ft^2. At 454 lbs, this comes to 144 ft^2. So 32 ft span by 4.5 ft constant chord gives a nice hershey bar that gives this area.
Would this actually be a legal (for stall purposes) ultralight?
Actual take off weight would be 548 lbs, and actual CL_max would be around 1.4 for a 0014. So actual stall speed would probably be between 28 kts and 29 kts, almost 20% higher than the legal limit. But everything's okay, because I chose to demonstrate by AC 103-7 rather than measured values, yes?
Edit for follow-up question: Does all of this still apply if some characteristic of the plane (tail authority, for example) prevents it from actually stalling, limiting minimum demonstrable speed to 1.3x stall speed?
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