What you said is true for hydrolox. It is not true for methalox. It takes 3.4kg of lox to burn 1kg of liquid methane, but lox is only about 2.6 times denser. If you have equal volume tanks you will have methane left over. If your outer cylinder diameter is 10m, the same-length inner cylinder needs to be 7.5m in diameter to hold enough lox for complete combustion.
Pressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics. I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.
The BFR is likely in my opinion, to have a center engine plus two concentric rings of engines
Quote from: Impaler on 05/11/2016 12:37 amPressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics. I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.Your logic is correct, but your statement isn't correct.
Quote from: Impaler on 05/11/2016 12:37 amPressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics. I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.I doubt the tank is going to dominate the structural mass of the vehicle.
Quote from: Oli on 05/12/2016 03:47 pmQuote from: Impaler on 05/11/2016 12:37 amPressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics. I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.I doubt the tank is going to dominate the structural mass of the vehicle.Efficient rocket stages are pretty much just giant tanks. Think again.
Quote from: Robotbeat on 05/12/2016 03:49 pmQuote from: Oli on 05/12/2016 03:47 pmQuote from: Impaler on 05/11/2016 12:37 amPressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics. I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.I doubt the tank is going to dominate the structural mass of the vehicle.Efficient rocket stages are pretty much just giant tanks. Think again.I thought he meant BFS, my fault.
Quote from: Impaler on 05/11/2016 12:37 amPressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics. I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.IF the Rvac engine approaches the 5m width some have computed, 10m will be too small.I figure the BFR/BFS as just under 100m tall but maybe 15m wide, certainly at least 12.5m. If narrower, then taller.In any case, it will look very different from the pencil necked geek Falcon9.