A4 / V2 Rocket in detail: Turbopump

[Homer J Simpson]

[Miyuki]

Maybe they said it in video I didn't watch it all
But why they use stream powered turbine and no just gas turbine with fuel they already have ?  Was it problem at materials or was it just simpler to regulate to have second fuel for steam turbine ?

[Kleinstein]

At that time gas turbines where just a new thing and high temperature materials were not that well available. Jet engines just started development. Also burning alcohol with oxygen gives very high temperature - hardly practical even with modern materials.
Cooling the burn chamber with the liquid oxygen and using the gas generated their is likely hard to control.

AFAIK the kind of steam driven turbine from hydrogen peroxide fuel was also used in torpedoes, though at a lower power level. So they could have reused some knowledge from there.  There is not that much control going on - they seem to have just measured the power of the pumps in a test run and than adjusted with the flow reduction. Burning the fuel faster will also shorten the time the engine runs - so this compensates somewhat with the final speed and it seems like they has an extra measurement for the speed.