One for the experts.:-)

Can you tell what it is without arguing with yourselves?   Have posted this at 1.20 AM so can add a link tomorrow with the answer if required. Have a look at the extra for a clue too.

It is now 10.45 and a few have got it so here is the link to confirm http://www.lightaircraftassociation.co.uk/pdf/DataSheets/Isaacs%20Spitfire.pdf