At ER=25, I would expect to see more like SL~310s
With 1950 psi chamber pressure, I'd say that this is rather unlikely. More likely around 300s, especially if they go for an O/F ratio closer to 3.8 to improve density instead of optimizing only for Isp which was the basis for the 3.3 O/F ratio above.
On the Vulcan configuration which gets lift-off thrust from solids anyway, the BE-4 will probably have a somewhat longer nozzle and thus have a roughly similar and possibly slightly higher Isp than the RD-180 at altitude, but on the other hand have noticeably lower Isp at launch pad due to the lower chamber pressure. On Blue's own flyback booster where they need a short nozzle for landing and where liftoff thrust would be bottlenecked by the engine, they will probably go for a rather low expansion ratio and low Isp.With that said, for a first stage total thrust to keep gravity losses down is much more important than a <5% Isp increase. The BE-4 only really needs a decent specific impulse. If it has a small enough physical footprint and is cheap enough that you can fit more engine thrust at the bottom of the rocket for a similar production cost, that configuration is going to be superior regardless of whether or not the specific impulse is slightly higher.
The BE4 should have high T/W as it uses additive manufacturing which helps to keep weight down.
Quote from: STS-200 on 03/18/2016 10:56 amAt ER=25, I would expect to see more like SL~310sWith 1950 psi chamber pressure, I'd say that this is rather unlikely.
Can anybody guess at throttle range of BE4. Blue plan to do vertical lands so deep throttling it one primary design features.
Quote from: Nilof on 03/18/2016 11:34 amQuote from: STS-200 on 03/18/2016 10:56 amAt ER=25, I would expect to see more like SL~310sWith 1950 psi chamber pressure, I'd say that this is rather unlikely.No it isn't. If the illustrations are close to the truth the area ratio is somewhere in 23-25 region. 16.77 is way too low to match.Your analysis has 1 atm nozzle exit pressure, that is too high. All real booster engines are overexpanded at sea level, many have the exit pressure at about 0.6 atm. This improves overall performance during flight.I did some SWAG analysis in 2014. Back then 130bar (1885 psi) Pc produced result close to the imagery and the few known facts. ~3% error, yay!
Like the smaller BE-3 upon which it is modeled, a main feature of the BE-4 is its reusability, and it’s being designed to fly a minimum of 25 missions. Bezos explained his philosophy on how to build a successful reusable engine: “Our strategy is we like to choose a medium-performing version of a high-performance architecture.” Here’s what that means: The Russian RD-180 engine is a high-performing version of a high performance architecture. It uses the best materials and pushes the performance envelope. It is the Ferrari of engines. But that comes with a cost. When it fires, the RD-180 engines produces extremely high chamber pressures of up to 3,700 psi. By comparison, the BE-4 engine produces a chamber pressure of 1,950 psi.Developing an elite engine like the RD-180 was a decade-plus project, on par in complexity to the space shuttle’s main engines. It required expensive materials. On the plus side, this provides a lower weight engine and a higher thrust-to-weight ratio. But the engine’s specific impulse isn’t all that much greater than the BE-4, which can be built more easily, and because it doesn't push performance limits can be reused
Quote from: TrevorMonty on 03/18/2016 11:31 amThe BE4 should have high T/W as it uses additive manufacturing which helps to keep weight down.Huh?
I saw the < sign. I now read the article. But I still cannot believe they are not aiming to be at least somewhat better than RD-180. Even with an initial value which can be improved upon later. After all they use methane instead of RP-1 which should allow for higher ISP, if not better T/W.
Comparing the two engine developments – Aerojet Rocketdyne pursuing the classic government funding route, while Blue Origin has a billionaire owner who can act lightning-fast – the two companies’ situations do not favor Aerojet Rocketdyne.“Compare it to having two fiancées, two possible brides,” Tobey said of ULA’s approach to the two. “Blue Origin is a super-rich girl, and then there is this poor girl over here, Aerojet Rocketdyne. But we have to continue to go to planned rehearsal dinners, buy cakes and all the rest with both.“We’re doing all the work on both, and the chance of Aerojet Rocketdyne beating the billionaire is pretty low. Basically we’re putting a whole lot more energy into BE-4 for Blue Origin.”Using methane would be new for the U.S. space sector, imposing risks, but Tobey said the BE-4 engine is only 60 percent of the cost of the AR1, a clear advantage in today’s cost-driven market.Of both engines, he said: “They are never going to outperform the RD-180."
I dislike "performance." If you mean Isp, say Isp. If you mean T/W ratio, say T/W ratio.On the latter, Merlin 1D kicks RD180's butt all over town. Merlin 1D with recent thrust upgrades gets T/W of 200.
In fact, the thing I find most impressive is that people says that the tolerances on that engine are ridiculously loose.
Not a really relevant parameter for comparison. Try installed T/W. Compare Atlas V thrust section to F9 thrust section. Installation wise, I bet RD-180 kick Merlins butt all over town. Atlas V/RD-180 had no need for 9 feed lines.
Quote from: Robotbeat on 08/09/2016 01:34 pmI dislike "performance." If you mean Isp, say Isp. If you mean T/W ratio, say T/W ratio.On the latter, Merlin 1D kicks RD180's butt all over town. Merlin 1D with recent thrust upgrades gets T/W of 200.Not a really relevant parameter for comparison. Try installed T/W. Compare Atlas V thrust section to F9 thrust section. Installation wise, I bet RD-180 kick Merlins butt all over town. Atlas V/RD-180 had no need for 9 feed lines.
Quote from: Jim on 08/09/2016 01:58 pmNot a really relevant parameter for comparison. Try installed T/W. Compare Atlas V thrust section to F9 thrust section. Installation wise, I bet RD-180 kick Merlins butt all over town. Atlas V/RD-180 had no need for 9 feed lines.But they can't throttle down to what is effectively less than 10% thrust either. Yes, I appreciate the KISS principle in rocket design, but they could never have pulled off the booster landings with only one or two very powerful engines.