The PA-28-181 Archer III does not seem to be compliant with Vc min regs, it looks be 7MPH short. Other PA-28s appear OK but not the Archer III:
Vc min for 15lbs/sq.ft wing loading =
147mph EAS
PA-28-181 Vno =
140mph CAS
What I am missing?
From the
PA-28-181 Archer III TCDS p. 21,37
Airspeed Limits:
Never exceed 171 mph (148 knots) CAS
Maximum structural cruising 140 mph (121 knots) CAS
Maneuvering @ 2550 lbs. 128 mph (111 knots) CAS
Maneuvering @ 1634 lbs. 102 mph ( 89 knots) CAS
Flaps Extended 115 mph (100 knots) CAS
Certification Basis:
PA-28-181: CAR 3 effective May 15, 1956, including Amendments 3-2 and 3-4; paragraphs 3.304 and 3.705 of Amendment 3-7 effective May 3, 1962; FAR 23.207, 23.221, 23.955 and 23.959 as amended by Amendment 23-7 effective September 14, 1969; FAR 23.1557(c)(1) as amended by Amendment 23-18 effective May 2, 1977; and FAR 23.1327 and 23.1547 as amended by Amendment 23-20 effective September 1, 1977. FAR 36, Appendix G, Amendment 36-16 for the PA-28-181 (Archer III), S/N 2890206 through 2890231, 2843001 and up, and 2881001 and up.
Regs: Design air speeds are defined in CAR 3.184 and CFR 23.335 no amendments to these sections are listed in the certification basis above so
3.184 in CAR 3 effective May 15, 1956 p.12 rather than CFR 23.335 is the defining regulation on design speeds for this type:
3.184 states:
§ 3.184 Design air speeds. The design air speeds shall be chosen by the designer except that they shall not be less than the following values:
Vc (design cruising speed)
= 38 √ W/S (NU)
= 42 √ W/S (A)
except that for values of W/S greater than 20, the above numerical multiplying factors shall be decreased linearly with W/S to a value of 33 at W/S=100: And further provided, That the required minimum value need be no greater than 0.9 Vh actually obtained at sea level.
Vc is not published in the TCDS but Vno is.
Vno is defined thus:
§ 3.740 Maximum structural cruising speed
(Vno). This operating limitation shall be:
(a) Not greater than Vc chosen in accordance with § 3.184.
(b) Not greater than 0.89 times Vne established under § 3.739.
(c) Not less than the minimum Vc permitted in § 3.184
So Vno essentially = Vc
Additional data for the PA-28-181 Archer III:
W/S = 2550lbs/170sq.ft=15lbs/sq.ft
From 3.184 above the following applies:
Vc (design cruising speed)
= 38 √ W/S (NU)
38x √ 15 = 147.17 mph
Vc = 147.17 mph
Vno = Vc
However Vno as per TCDS = 140 mph CAS
Not sure what is going on here? Wondering what is actually meant by:
And further provided, That the required minimum value need be no greater than 0.9 Vh actually obtained at sea level.
Surely 38 √ W/S is the minimum compliance standard while faster aircraft need not prove 30ft/s gust protection at any more that 0.9Vh but must still adhere to 38 √ W/S as the minimum standard.
V-n diagram from 3.185 for reference if required.
V-n CAR 3.185