Ironic

So I’m sitting in a friends yard watching the Blue Angels give it their best at the Sun-N-fun fly in thinking about how to modify their propulsion while all the people around me are oohing and aahing. Same with the F22 demonstration and various prop planes. I guess some of aren’t meant to watch these super skilled pilots do phenomenal things without focusing on the hardware.

Doh

 

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15 Responses to Ironic

  1. George Turner says:

    I’ve sometimes wondered what kind of short-term performance boost you’d get by spraying a storable oxidizer into the afterburner section, along with increased fuel flow. Also, someone needs to put a surplus F-404 or F-414 engine into a surplus F-104 Starfighter to make a spiffier piece of surplus.

    I once wrote a long blog post suggesting that the F-18’s patrol radius could be dramatically increased by having a drop tank shaped like a big subsonic wing, making the aircraft a biplane during the outbound leg. The F-18 has oodles of thrust but only a small supersonic wing section that can’t lift a lot off the deck, limiting fuel fraction and thus range. I am also probably the first person who ever needed to use biplane theory and Munk’s span factor for a jet fighter.

  2. Neil says:

    Hey man. Ya gotta learn to ‘let go’ sometimes.
    Cheers

  3. born01930 says:

    We had the Thunderbirds do their show here a week ago. I could watch them practice from my lanai…one of the better airshows I saw was back in the early 80’s when a couple A-10’s vaporized a concrete block in seconds. Amazing.

    Gracious host…how about elaborating on how you would modify their propulsion?

  4. George Turner says:

    Well, they could switch from JP-8 to decaborane and get a massive performance boost (in thrust and range), while still being cheaper than “green” fuel made by companies run by campaign bundlers. :)

  5. born01930 says:

    isn’t that the stuff that has a deadly poison in its exhaust? I guess it would be fine to use over enemy territory depending upon how long the poison hangs around

  6. john hare says:

    Aggressive cooling of the turbine blades would allow a hotter hot side with more power available for the same mass flow. Regenerative cooling with the fuel.

    Cagejet as I suggested a here few years back in the wing tips and tail plains for thrust vectoring and high angle of attack virtual winglets.

    I have been trying to finish a theoretical concept for using pulsed detonation in the hot section to get more functional compression ratio and fuel efficiency for a given size engine.

    A more efficient high compression ratio centrifugal compressor.

    Air turborocket instead of turbofan for better thrust-to-weight ratio even without my untested pipe dreams.

  7. Peterh says:

    “… what kind of short-term performance boost you’d get by spraying a storable oxidizer into the afterburner section, along with increased fuel flow. ”
    Increased mass flow rate and temperature, both giving increased thrust. But also more back pressure, reducing power available to the turbine. And a nozzle which may not handle the extra pressure/flow rate efficiently.

    “switch from JP-8 to decaborane and get a massive performance boost”
    And very short engine life if the extra heat load isn’t accounted for.

    “A more efficient high compression ratio centrifugal compressor.”
    First generation jet engines used centrifugal compressors. Easier to get useful compression. Later engines switched to multi stage axial compressors to get more air intake and thrust from a given frontal area.

  8. George Turner says:

    You could limit the borane fuel to the afterburner section, which also greatly reduces the insoluble wear problems that it caused. I think this was suggested back in the 1950’s before the borane idea was given up as a maintenance nightmare, combined with toxic wastelands for Air Force bases. But still, the acceleration and range would be sweet!

    I’m not sure what elements of the F-414 EPE (enhanced performance engine) have been implemented, but the all up version gives 26,000+ lbs thrust for the same frontal area, and giving better than an 11:1 T/W ratio. I think they were hoping for export customers.

  9. George Turner says:

    As an aside, the strangest compressor idea I’ve come up with is a nested squirrel cage fed from the center and feeding toward the outside, with long thin fan blades whose centrifugal force is supported by the pressure rise they impart on the stage. They ride on pivots so their angle of attack can vary, and their angle of attack is set by a little tail plane that’s mechanically activated by the deflection of the blade in bending, so the blade actively tries to remain straight, with it’s mass * G load always balanced by its lift. This of course rules out stators (which would have no G-load to compensate for the pressure difference), so the fan would have to have alternating contra-rotating compressor stages, which is doable because the blades are supported at both ends.

    Since the blades don’t experience any significant stresses (in theory), they could be made out of just about anything. Since they’re shape isn’t a compound curve, they could be extruded instead of machined. Since they’re supported at both ends, they wouldn’t have the usual tip losses.

    The downside is that they would experience high-G maneuvers as a periodic, uncompensated loading (hopefully nowhere near their resonance frequency), and they would never survive a compressor stall or bird strike. For a fixed installation they might work, though.

  10. john hare says:

    The squirrel cage set up I wrote about used the same blades as compressor and partial admission turbine. This allows the blades to be cooled by the incoming air during much of the cycle.

  11. john hare says:

    I did a quick BOTE on your compressor with the centrifugal force on the blades balanced by the pressure rise and came up with well under 1% of the force being countered by the pressure at sea level with altitude being worse. It would still be the blade strength to weight that counted.

  12. George Turner says:

    Ah. I knew there was some reason I gave up on it for flight. It’s been a long long time since I ran numbers on it, but I recall that I ended up looking at really large diameters (hundred feet plus) to reduce the centrifugal forces while maintaining a high-subsonic blade velocity. Another issue I encountered was that the blades had to get either bigger (increasing the mass per unit area through simple size scaling of a solid) or denser, because each stage has a progressively greater pressure difference. I think it ended not being practical unless you were building some multi-GW powerplant. Oh well.

    I recall another odd thought I didn’t pursue, which was using a revolving set of high-intensity lasers (like spokes) to ionize air, each accompanied by an electric arc, to try an make a fan section without physical blades. The basic question is whether any kind of MHD propulsion effect could instead be arranged in rapidly rotating stage sections to provide compression, regardless of how inefficient it might actually be. But that sounded so complicated and strange that I figured that at best it might turn into a cool movie prop or Halloween decoration, and decided not to think about it further.

  13. john hare says:

    I can’t speak intelligently on MHD and ionization. Acknowledging that, there is a thought I once had to use MHD in the compressor section as a non physical stator. It would seem to allow much tighter effective clearances and a continuous compressor blade. For a visual, think of it as a very large wood screw in a tunnel with a constantly decreasing section with the MHD drag effects constantly converting velocity to pressure inside the channels.

    I can’t even start to do the math on the MHD drag as stator to determine if it would work at all. If it would, compressor blading would be stronger and cheaper with the possibility of using compressor section generated electricity for something else like an arcjet afterburner

  14. George Turner says:

    BTW, I ran across a Rand report (pdf) from 1979 that urged the DOE to switch our Brayton cycle powerplants to an approximated Ericsson cycle, which uses isothermal expansion and compression to achieve much higher efficiencies (matching Carnot or Stirling cycles) at low pressure differentials, at the expense of a slightly increased blade count and more shafting. They recommend it for fossil fuel, nuclear, and solar power applications.

    Perhaps Kirk Sorensen would find it interesting for his FLiBe work.

  15. George Turner says:

    Speaking of aviation fuels, a few months ago I was debating the replacement of tetra-ethyl lead by benzene, which makes our modern gasoline several hundred times more toxic than the old stuff. Of course the benzene is normally burned and so doesn’t build up in the environment like lead did, but my house mate is monitoring an overturned tanker spill that dumped into a major cave system that feeds a lake, so I became aware of the benzene issue.

    So I wondered if bismuth could serve the same function as lead, and sure enough, I ran across a 1926 report on various compounds that were tested for their anti-knock potential. Triaryl bismuth (which you might drink before getting an X-ray) had one-fifth of tetraethyl lead’s effects, so using five times more of it gives the same result. There’s also a new and better way to synthesize triaryl bismuth.

    So my thought was that the compound could possibly be used for aviation gasoline and for classic cars that can’t run on modern unleaded, if bismuth is compatible with aviation engine bearings. Perhaps an industry expert or A&P would know. The bismuth would build up in the environment, just as lead did, but as the main ingredient in Pepto-Bismol, it’s perfectly harmless.

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