Kline Fogleman Air-foil

"I presume you mean narrower chord, but wider span?"

Exactly that, but I understood what Klippy meant. Now I am wondering, what would be the effect of extending the 'chord' of the aileron past the trailing edge of the wing? Would this in effect be similar to a cuff in reverse, or would it be more likely to tip stall ?

Mr Antony Fokker certainly had no qualms about extending the aileron beyond the wing trailing edge.
To be fair the Triplane wing had a very narrow chord to start with and there were ailerons on only one of them!

I don't think broad chord ailerons themselves alter the stall characteristics (tip or otherwise) of the wing but they are likely to increase the effect of adverse aileron yaw which can promote an entry into an incipient spin that will have a rotation opposite to the bank.

The weather is diabolical, so no flying for the next few days! I thought I may as well resurrect this project, which got sidelined for the Viggen build. I decided to ditch the idea of being able to convert it to a KFM 3 & get the ailerons as close to the wing I am comparing it against. Both halves are now covered & ailerons cut to size, with a simple tape top hinge. The control horn is deliberately set 5 mm back from the hinge pivot point, & the servo arm centred slightly forward in order to give some mechanical differential. Rather than a flat plate, the wing has a profile that resembles a proper KFM 2. The centre joint looks a bit scruffy at the moment, but once the two halves are glued in place this will be capped.

Not according to this guy Eric. Skip to 3.30 minuets if you don't want to watch all of it.

The video is quite correct but done that way it significantly reduces the mechanical advantage of the servo as the aileron goes up just when the aerodynamic load increases.
Raking the servo arm forward maintains a better geometry to handle the increased load on the servo, linkage and hinges.
Another advantage of a raked forward servo arm is that the smaller deflection of the down going aileron means it has a much improved mechanical advantage.
At extreme airspeed the upgoing aileron servo might get stalled but the down going one will go down ensuring at least some roll control.

All important attributes and for 'free' if you are use small light aileron servos.

That's a very eloquent explanation Simon, thanks.

There is no doubt the the KF air foil sections do work well at model sizes but it does depend on the definition.

As far as I can tell the big advantage KF at model sizes is it better controls the airflow over a wider range of angles of attack than a conventional section. This can make the plane very forgiving. An important attribute in RC flying where the feed back on what is happening is entirely visual and at a distance. They are also well suited to simple foam board construction techniques.

On the other hand a KF is not so good in terms of aerodynamic efficiency. This is of little consequence in most model power planes as the efficiency of everything else is pretty low as well but where high aerodynamic efficiency is required, as in a competition glider, KF sections are not used.

Quite some time ago NASA demonstrated from wind tunnel tests that full size light aircraft KF sections showed no significant flight envelope benefits coupled with lower lift to drag ratios.

A delta like that has a very abrupt drag rise as a certain AOA rather than a true stall.
What I think we are seeing is the point where the drag rapidly exceeds the available thrust rather than a sudden loss of lift. The result is a sort of pancake descent in a near stable condition.
Without more thrust the only way out is to lower the nose quite dramatically to allow the thrust to quickly raise the speed but being a delta the lift falls away dramatically so resulting in a steep descent & big loss of altitude.
If you have sufficient thrust to accelerate the plane fast enough to regain normal flying speed before contacting the ground you likely would have been able to avoid the situation in the first place.

You take a delta into the drag exceeds thrust regime when low down at your peril.