Apparent LSS in day VMC aircraft
 

Reading Tim Cripps' write up on the Savannah in the current Pilot, combined with some in-depth discussions on another aeroplane with another TP recently, has caused me to think deeply on this.

I spend most of my time certifying aeroplanes for day-VMC ops, usually by PPLs. Here in the UK it's always taken as sacrosant that apparent LSS must have a clearly positive gradient, and we routinely (as was certainly the case with the Savannah, as anybody with access to the September Pilot will see) end up modifying aircraft in the UK certification process to improve the low, neutral or occasionally even divergent (CH601 for example) LSS seen on a lot of foreign aeroplanes.

Allied to this, the UK is unusual in requiring a minimum value of manoeuvre stability (15 lbf / 7daN to reach N1) in most cases. Admittedly most foreign types I've flown don't have a problem meeting this, but one or two have.


Now pretty much all of us in the UK agree that our position is a good and reasonable one - whether you're talking to associations like BMAA/PFA, CAA, or manufacturers like Pegasus who recently put the German FlightDesign CT through UK certification and ended up redesigning large chunks of it. So within this sceptred isle, we have a consensus - and all for good reasons, controllability by low hours pilots, accurate height and speed control, reduced risk of Nz overstress, etc. Yet, nationally, we seem to feel that we're the only people in step, and the rest of the world is wrong.

So what's going on here? Are we being OTT, and the rest of the world has the better idea? Is it simply that we look at aircraft in more depth here, and pick up things that tend to get missed elsewhere?

I'm not trying to make any kind of point here, I'd really just like to try and understand why here in the UK we seem to be at odds with much of the rest of the world?

G

Yes, Genghis, you're on your own against the rest of the world now. The Australian authority had a similar approach until a few years ago. Even home-built aircraft designs which had many example flying in the USA were subject to "first-of-type" performance and handling assessments. All of that has gone with our new regulations, including Experimental "category", and automatic type acceptance from a few countries.

... as a consideration ..... it was often interesting that the regulatory TPs who did those Ozzie assessments .... were often heard to say something along the lines of "it is a nice little aeroplane ... but wouldn't it be lovely if it flew like an aeroplane ?... " .. in relation to things such as long stab and strange directional qualities ..... and a host of other minor matters.

I can still quite clearly recall my first flight in a Wittman Tailwind (if my memory serves me correctly) ... it was a nice little machine but had the disconcerting habit of, quite suddenly ... and without any prompting ... adopting a stable yaw of, probably, 25-30 degrees .... not a problem .. but it didn't really add to whatever attractions the machine may have had ....

Now over here, we'd generally argue that such characteristics are not in themselves dangerous, because they can be controlled. (Same could be said of an aircraft with negative LSS) BUT whilst he or she sorts them out, they divert the pilots attention from other tasks like navigation, lookout, etc. and thus do degrade the safety of the aircraft in use ?

G