Originally Posted by
john_tullamarine
Perhaps I am to learn something here ? And that is a serious, not a frivolous, question.
First, I had no intent to cause you distress - if I did, then my apologies, good sir ... and, certainly, I have no interest in getting into a micturating contest ... quite unproductive and unbecoming.
Also keep in mind transport aircraft are certified using procedures that require staying within 35 feet of the centerline using only aerodynamic controls during VMCG testing
No problem with that other than 35 ft probably should read 30 ft ? Not of great note in the overall scheme of things, though, noting that the rules do change over time.
You are probably right 30 v 35 but there is a limit. The point is during certification you must keep the airplane within X feet of the centerline using aerodynamic controls only...no nose wheel steering or asymmetric thrust. Line crews want to avoid running off the side of the runway but can use the full width of the runway. So some pilots ignore/discount AFM limits because they are rules but they think they can outperform the AFM limits.
.. during VMCG testing we don't care about drag but about control. So in this case we want a short arm for the rudder because that reduces the rudder's effectiveness giving us a worse case scenario.
Indeed, as per the rulebook and FTG. But whence, then, comes your previous statement on Vmcg ? That was the cause of my concern.
Now, here may be the learning point which I seek - first, I have no direct experience (either as a pilot or PE) with those aircraft having a forward CG fiddle factor. I am presuming that the OEM reason for this is that the general reduced stall speed spinoffs associated with being a bit aft of the most forward limit are eminently saleable ? On the other hand, should there be a provision whereby Regulator and Applicant can negotiate a very restrictive (forward) CG envelope with attendant Vmcg recertification in the manner which your previous comment implies, then I have no knowledge of that. If that be the case, could I trouble you to provide some appropriate and authoritative reference material for my benefit ? For this, I would be more than appreciative.
There is NO fiddle factor. You comply with the AFM which may incorporate supplements that expand on the limits. Said supplements involve engineering and additional testing. There may also be mandatory changes to hardware and software. Accordingly the manufacturers charge big bucks to upgrade your capabilities.
I've taken the trouble to have a looksee at your profile and you appear to be appropriately qualified and experienced to comment on this topic.
Thank you for checking I get tired of comments by or from people with little or no relevant training and experience. I used to work at a major supplier of aeronautical information where if you paid me a penny for every time I was asked, "Why are you disagreeing with me? What are you talking about? I've got 300 hours and what you are talking about doesn't make sense because that's not how I do it in the C-172 or Seminole!" We were discussing a performance question about a B-757. I love working with people who ask good relevant questions AND realize when they have reached the event horizon of their knowledge.
PS For whatever reason, I didn't see your second post last night.
I really don't see its relevance but the Vmcg question needs to be addressed for the benefit of the new chums .. please ? The first sentence appears to make little sense in respect of the certification animal.
Probably very few of us have heard about these things let alone understand them or how to calculate them. The point is to raise awareness and understanding.
Providing some education (at an appropriate level) for the new chums is a major thrust in my approach to PPRuNe. I think we all appreciate that the Industry is a bit light on when it comes to theory training for pilots. It is for that reason that we need to get to some endpoint with the Vmcg comment from an, apparently, technically competent chap ?