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About Frank

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  1. Will MHD generators replace ICE?

    It helps to have the right link... I guess I responded too fast and got the wrong link. If figure 1.8 of is representative, I think the heat exchangers will make this too bulky and heavy for automotive applications. If someone figures out a way around that, it would be better. The 90% efficiency upper bound is enticing. Vibration in ICE can be cancelled and oil changes are infrequent because there is no side force on the pistons in the free-piston style engines. I'm hoping fossil fuels won't be needed in the future for automotive use because of better battery technology.
  2. Will MHD generators replace ICE?

    Still seems more efficient to run a magnet pushed by a piston through a coil of wire or convert fuel directly to electricity through a fuel cell. Maybe this would make an efficient power take-off for jet engines?
  3. Will MHD generators replace ICE?

    I glanced at the link you posted which has efficiency at 70% conflicting with wiki's (presumably more recent than 1987) 22%. The link has MHD as the receiving end of a laser transmission system for power transmission which was one way of efficiently producing plasma (that's interesting). Other ways are to use heat from nuclear to create liquid metal (LMMHD) and there is mention of brayton cycle or rankine cycle. Maybe I didn't read it right? Let's go the other way, maybe you can explain further how MHD would be used with fossil fuel - create a plasma flow somehow, but how is the plasma energy recovered once it passes the MHD generator?
  4. Will MHD generators replace ICE?

    MHD is interesting and I'll look into it more, but for this application, it looks like conversion of fossil fuel to laser energy would be inefficient. Nuclear reactors - too heavy (among other issues). Brayton cycle needs a regenerator and heat exchangers are always heavy - why turbines tend to weight more than ICE. Take these as hints/pointers for what to look for as show stoppers, I'm just responding from memory of the research I did for that same application. Come to think of it, in the ICE category, free-piston engine (or similar integrated generator/engine) generators are coming soon.
  5. Will MHD generators replace ICE?

    Only if efficiency, weight and cost are better than alternatives. Best I can tell, ICE is best now and fuel cells next if cost and weight come down. Hadn't heard of MHD:
  6. A Falcon Super Heavy version of full propellant cross-feed normally arranged in a cross, not a row as I depicted for illustration. Propellant transfers into a tank instead of trying to match pressure in direct feed to engines. The tank could be carbon-fibre and as small as allows buffering and gas elimination etc... Making it span the width of the rocket allows direct access from the sides. The smaller tank means the whole pressure of the rocket head must be borne, but is less than 100 psi, so manageable. What's neat about doing it this way is that the outer rockets don't need much modification except a port with a valve, no extra dome. So, what I called a baffle is actually called a dome (an oblate spheroid shape?) Another animation:
  7. Instead of using pipes in tanks, I inverted the extra baffles and gave them a slight slope. A sealed box would give access to the valves and ports. Two ports below the inverted baffle on either side to receive LOX (blue), via a check valve, blocked when on the boosters. A single valve for the core across the baffle so it acts as a single tank once separated, this port is also permanently closed or blocked on the boosters. A xfeed valve on the boosters just above the inverted baffle and on the low side connects to the ports below the baffle on the core. Similar idea for RP-1 (red). Here is an animated gif of the propellant cross-feed (Xfeed) time is compressed 10x, proportions are to a 40m rocket. Burn time was set to 150s for the middle once separated and results in 100s burn time with all 27 engines on (9 per fuselage), burning through 300s worth of fuel. The connecting hoses are missing, as is the rest of the rocket, but I think it's pretty clear what's happening? I have no idea if this idea is innovative, common or stupid. I haven't found anything similar on the net yet.
  8. Looking for some guidance on magnet build

    This type of thing? Basically a strong magnet in a stainless steel box. Since price is the issue, maybe source it from China - like aliexpress or alibaba. If you really want to design your own, price out ceramic magnets and figure out some sort of plastic cover maybe? Arrange magnets in a Halbach array (could be difficult to align the magnets). Redesigning tends to be more expensive for a one-off.
  9. Looking for some guidance on magnet build

    Here is a free program that will help you design your magnet. Not knowing much about the design, I'm concerned that if you get such a powerful magnet working it will interfere with equipment in the shop or even cause harm. Also the magnetic field won't act uniformly under the square metal plate. This program will help you get a feel for what is possible.
  10. To keep the RP-1 tank at the bottom, adding a baffle to the LOX tank and holding a portion in reserve for post-separation allows LOX to flow into the lower section from the boosters and post separation from the top section of the LOX tank. The extra baffles would improve the rocket structure as well. The same baffle trick can be used for RP-1 if pumping is an issue, like this: The cores (middle) and boosters (sides) at 3 different times - launch at top, midway to separation at middle, at separation at bottom. Green is LOX propellant crossfeed, yellow is RP-1 crossfeed, blue is LOX and red is RP-1. There are baffles between green and blue and between red and yellow which allow gravity crossfeed with some extra plumbing and valves. Then the 15% extra delta-v expected from crossfeed can cover the loss for reuse. The BFR plan calls for transfer of cryogenic propellant by micro acceleration, so LOX transfer under large acceleration calls for similar plumbing work/knowhow. Starting with cryogenic LOX crossfeed only might minimize risk of failure, compared to transferring RP-1 or liquid methane (for BFR).
  11. I get an increase in payload of ~5% using gravity feed tank to tank, 2 extra bulkheads in the boosters (mass not accounted for), LOX tank at bottom of main core (which may need some extra plumbing – mass not accounted for). Not really worth it? It seems throttling back the core engines to 70% reduces crossfeed advantage, but it seems like throttling back incurs some loss I haven't accounted for? It looks like this - stacks represent core and boosters tank placement. red is RP-1, blue is LOX, green is crossfeed LOX. Main core mass LOX: 243t (always metric tonne) RP-1: 161t Total mass: 404t Booster mass LOX crossfeed: 85t LOX: 242t RP-1: 95t Total mass: 422t Stage1 xfeed Propellant mass: 910t Total mass: 1,468t Isp: 301s Delta-v: 2,855m/s Stage2 xfeed Propellant mass: 338t Total mass: 530t Isp: 311s Delta-v: 3,097m/s Stage 3 xfeed propellant mass: 108t total mass: 178t Isp: 342s Delta-v: 3,119m/s Crossfeed payload mass: 66.1t Stage1 Propellant mass: 1,123t Total mass: 1,465t isp: 301s Delta-v: 4,296m/s Stage2 Propellant mass: 125t Total mass: 313t Isp: 311s Delta-v: 1,550m/s Stage 3 Propellant mass: 108t Total mass: 174t Isp: 342s Delta-v: 3,224m/s Total delta-V for baseline: 9,070m/s FH as I modelled it payload: 62.6t Payload improvement: 5.61%
  12. Large Hybrid Model Rocket

    Maybe try paintball solenoids, should be high pressure, lightweight and cheap. Found type info, but no spec sheet. here a spec sheet Need a pressure regulator (100 psi max).
  13. Large Hybrid Model Rocket

    I'm curious what you used as an oxygen tank. I read some discussions (can't remember where) about the pros and cons of NOx (because they are available in small and light cartridges) and other things such as paintball cartridges. Also wondered if some sort of pressure regulator is used or just a tiny orifice? So you're looking for a servo controlled valve or maybe a pulsed solenoid, something like a throttle body injector? What did you choose to vary the flow rate?
  14. I need help on my rocket engine thrust equation

    I can't answer your question directly, but I found a spreadsheet that probably has all the equations ready for your numbers to be plugged into:
  15. Large Hybrid Model Rocket

    I build a fairly cheap 3d-printer from an aliexpress kit. Not as easy as the shiny brochures, but works. My neighbour and I are talking about building a rocket and he's even considering smelting metal. 3d printed waste casting would help with that too. Big plans, not enough time. I don't know if you missed the question or it's top secret , but does a reaction wheel come as a unit?