Originally Posted by
chevvron
The Boxkite was another which was underpowered using I think a VW engine which was 'cowelled in' to disguise it and hence causing overheating problems.
Again, from memory of reading the loaned book (which I must try and get a copy of, but the current prices are excessive) - IIRC the replica aircraft were powered with 100bhp Continental 0-200 engines, and they initially had major concerns about over-powering and so made provision for throttle restrictors.
But when they got to flight testing they found they needed all the available power - the modern engines developed their power at much higher rpm than the edwardian-era ones, and so they turned muuch smaller props. These props just didn't develop the thrust at low airspeeds needed to overcome the very high drag of these airframes.
The very low airspeeds also provided much lower airflow over the cylinders, and that led to overheating. Various tricks were used to reduce the overheating, but the final cure was to simply drill out the jets in the carbs and run the engines very rich to fuel-cool them (a much-used technique in motorbike, kart and smaller single-seat car racing). This must have made them prone to intake icing, but I don't know what they did to address that.
My apologies to Joan - once said the memory clicked into place!
PDR