PPRuNe Forums - View Single Post - PA-28-181 Vno below Vc minimum design speed?
Old 22nd May 2020, 14:09
  #17 (permalink)  
oggers
 
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Rarely can a question on here have been researched in such detail before being asked. It took me quite a while to get my head around the detail but was not unwelcome as a distraction from the DIY and 'exercise' groundhog day that is lockdown. The bottom line is I think djpil is correct. If the Vno is not less than 90% of VH then it complies.

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
But Vno is not necessarily = Vc. It is allowed to be between design Vc actually chosen (we don't have that figure) and the minimum permitted design Vc. For all we know, 0.9 VH (permitted) could be 139mph (entirely plausible I think) in which case Vno could be as low as that and still be compliant.
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.
If the Vc is reduced then the load resulting from a gust at Vc is reduced. Hence, with the Vno not being permitted to be higher than design Vc, this problem takes care of itself, so to speak.
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