APPENDIX 2. DETERMINING POWER-OFF STALL SPEED OF ULTRALIGHTS

The information contained in this appendix is intended to assist in a determination of an ultralight's ability to comply with Section 103.1(e)(2), a maximum power-off stall speed which does not exceed 24 knots. Computations made in accordance with the information provided may be accepted as satisfactory evidence of compliance. When using this information, no factors other than those provided here should be considered. (The values provided here are for relatively square, rectangular wings; they are not valid for noticeably swept or tapered wings.) Relevant considerations for this computation are:

Empty weight. The dry empty weight of the vehicle (excluding floats and/or parachutes), as established through some form of evidence satisfactory to the inspector, should be used.
Pilot weight. The pilot's weight will be assumed to be 170 pounds. In the event that an ultralight is being operated under exemption allowing two-occupant operations, the pilots' weight will be assumed to be 340 pounds.
Fuel weight. The weight of the fuel (6 pounds per gallon) is included and for the purpose of this computation will be assumed to be filled to capacity.
wing area. The total wing area (square feet) should be determined. Ailerons and flaps may be included, but canards (which generally have a higher stall speed than the main wing) are excluded.

STEP ONE - Add the weight factors.

                 Example: Empty weight ..... 240 lbs.
                          Pilot weight ..... 170 lbs.
                          Fuel weight ......  30 lbs.
                                            -----
                                             440 lbs.

STEP TWO - Divide the total weight by the total wing area to obtain the wing loading of the vehicle.

                 Example:       Weight     440
                              --------- = ----- = 2.9 (Wing Loading)
                              Wing Area    151

STEP THREE - Select, from the wing profiles provided below, the lift factor which applies to the ultralight in question.

       Lift Factor     Wing Profile                 Wing Description

          1.4                        Single/double surface with camber of less
                                                    than 7 percent (see Appendix 3) and all
                                                    symmetrical and semi symmetrical airfoils
                                                    without flaps, regardless of camber.

          1.6                               Relatively flat-bottom, double surface
                                                    wings with camber of 7 percent or more.

          1.8                   Single surface with camber of 7 percent
                                                     or more or double surface with flaps
                                                     extending up to 50 percent of the total
                                                     wingspan.


          2.0                                  Double surface with flaps extending
                                             more than 50 percent of total wingspan.

STEP FOUR - Determine the power-off stall speed of the ultralight through the use of the chart below.

INSTRUCTIONS:

Enter the bottom of the chart at the computed wing loading of the ultralight (Example: 2.9).
Proceed straight up the wing-loading line to the point where it intersects the applicable lift factor curve (Example: 1.6).
Note horizontal line which also intersects at that point, proceed to the left side of the chart via that line. Read power-off stall speed (Example: 23.2 knots).

NOTE: If your computed wing-loading point is lower than the applicable lift factor line at the base of the chart, the stall speed would be lower than provided on the chart.

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Jon N. Steiger / stei0302@cs.fredonia.edu / SUNY College at Fredonia