Originally Posted by
cncpc
This relates to a couple of Cessna aircraft I have flown that had Robertston STOL installations.
On application of 10 degrees or greater flap, the aircraft rolls left and will continue to roll inverted if the pilot does not intervene. The force required to roll wings level and hold them there is quite noticeable. It has to be held until landing.
The roll instability is there on takeoff as these aircraft call for 10 flaps on takeoff, but while it is noticeable once the wheels lift off, it does not require as much force at lower speeds. Same on approach.
It seems to me that the certificate of airworthiness is invalid when this situation exists as the aircraft does not meet the standards under which it was certified. Is that a correct assumption?
Unfortunately Sycamore is missing something potentially important - Pilot_DAR was unfortunately in a seaplane crash a little while ago and is mostly out of circulation still, so he's probably not the right man to ask for help right at this minute. If I was in Canada, I'd gladly help, but I'm not.
Sounds to me that what you are suffering from here is not necessarily a roll instability - sounds to me more like an undemanded roll input. If this is *only* happening at a particular flap setting I'd be suspicious particularly of the flap mechanisation on the particular aeroplane, rather than the STOL kit. Really obvious things to check would be the actual flap position on each side through range - easily checked using a suitable phone app to an adequate standard for a quick and dirty look at this.
If it is the result of the STOL kit, if the kit is STCd - which means it's presumably been flight tested by a grown up in some previous installation and found to be satisfactory - then the other likely culprit is that the STOL kit (vortex generators IIRC) have been installed incorrectly.
Either way, I think that your first port of call is to get the aeroplane checked over for rigging and correct installation of the STC by your friendly neighbourhood licenced engineer / A&P.
G