I've made this request to the Glowhead Brotherhood and I'm sure I've made it before that but I'm d****d if I can remember where - oh the joys of being a septuagenarian! Problem is I have two TD Thermal Hoppers but one of them has an unusual NVA and I'm wondering if this is a genuine Cox variation or something my dad added. These engines are part of my late father's 1950s collection of aero-modelling kit that I inherited. Anybody out there able to enlighten me (or even tell me where else I posted this!!)

You might want to post your question and pictures on the COX Engine Forum -- many of the folks there are very good with engine identification and historical variations.

The Thermal Hopper did come with two options for back plates. One was the carb body you show on the left. The other was a metal or plastic tank back. The one on the right looks like it may have been the tank back version but without the tank bell on it now.

Thanks for those pointers guys. I remember reading that the Thermal Hopper used the same crank case casting as the Space Bug so a trip to Martin Hepperle's website revealed the answer. Once removed those tanks must have been a pig to reseal, maybe that's why my dad left it off, must have another rummage amongst the pile of stuff to see if I can find it. Don't fancy my chances of finding one on ebay.



Another engine almost sorted - only 20 more to go!