Old 27th May 2020, 16:48
  #24 (permalink)  
oggers
 
Join Date: Nov 2005
Location: Zulu Time Zone
Posts: 719
Originally Posted by AC103 View Post
Oggers, kind of you to say and thank you for your input, now what is your response to the later clarification by the FAA in AC 23-19A - Airframe Guide for Certification of Part 23 Airplanes p.26-27

FYI per the Archer III POH Speed Power chart 5-21 Vh is 133 KTAS = 153 MPH 0.9 = 135.75 MPH so a Vno of 140 MPH CAS is conceivable if we ignore the above AC but personally I would prefer not to ignore a later clarification. Understood from Piper's perspective this is hindsight.
Yes I agree the AC indicates the Vc cannot be less than the wing loading formula. However, the regulations themselves do not say that and ".... this AC is not mandatory and does not constitute a regulation". Frankly, I think the AC is badly written on that point. It says, quite literally, if designing an aircraft with a cruise speed higher than the wing loading formula, make Vc equal to 0.9VH. But in para 45a it says the designer may establish the Vc in the range, "[wing load formula] ≤ Vc ≤ 0.9VH". So imo the AC manages to be both more ambiguous and more restricitive than the regulation it was based on. At the end of the day the FARs of the time said Vc need not be higher than 0.9VH, and it seems that is what Piper did.

With regards to the problem taking care of its self, this issue is that if an aircraft design increases its MTOW on paper and then artificially reduce their Vno as their structures are not able to comply with the gust penetration requirements this is an indication of a weaker than required air frame which becomes relevant in descent and this is where it gets more interesting.
I don't entirely agree with what you are saying there. The Vno of the Archer 3 didn't change from the Archer 1. The heavier aircraft complies with gust load factors at the same airspeed as before. I assume they had enough margin in the original structure to up the weight at the same design Vc (but for all I know they may have beefed something up). In anycase, to my mind if they needed to reduce Vno in order to achieve a higher weight this is not a weaker airframe, it is the same airframe optimised for a different task.
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