Why there is thermos bottle in structure of Myrsky?
Torstai 13.7.2017 - Reino Myllymäki
If you look at the old photos of the VL Myrsky II, you can find a thermos bottle in the middle of the studs, wires and pipes. What is the function of that Airam thermos bottle?
The Airam thermos bottle is a balance bottle of the variometer. The variometer get the static pressure from the pitot tube as the speed and altitude meters.
When the aircratft is climbing, the air pressure lowers and there is a growing pressure difference in the variometer. The variometer does not meter the pressure difference directly since the comparison pressure comes from the balance bottle. The pressure of the bottle is changing slowly and therefore the difference is different than theoretically it should be.
The balancing bottle is a standard Airam thermos bottle. The capacity is 0,44 litres including the 0,5-1,0 meter long capillary pipe.
The variometer has has 8 to 10 second delay. If the climbing changes rapidly to the lowering, the variometer can indicate still climb during the start of the sinking. Otherwise the variometer indicates the climbing and the lowering and their speed.
The original Airam balancing bottle has been donated to the project by the Airam. The bottle's place is above the map box in the left side of the cockpit. So, it easy to understand if somebody presume it pilot´s hot chocolate bottle!
Historical photo: The Finnish Aviation Museum. Other photos: The Finnish Air Force Museum.