Raptor Composite Aircraft

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Dexacare, Mar 28, 2016.

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  1. Oct 16, 2019 #2181

    TFF

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    Having some VK and SR experience, you can tell the same people designed both. Wing is one piece and retract gear with the VK but they are darn close to the same wing. I would add the cuffs if I owned a VK. Hardware is similar. Fuselage configuration is different but similarly built. The materials changed some. The SRs are more of a configuration change along with simplicity. The VK is very complicated and time consuming, where a SR just requires a check. Cirrus tried to cook the books a few years ago and the creditors took note and made them straighten up.
     
  2. Oct 16, 2019 #2182

    Doggzilla

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    And where did Glasair get its inspiration from? The already 5 year old Rutan designs which preceded it.
     
  3. Oct 16, 2019 #2183

    BBerson

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  4. Oct 16, 2019 #2184

    Andy_RR

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    Well, according to the Wikipedia font of all knowledge, the original Glasair and the Vari-Eze (Burt's first mouldless composite airframe) were both contemporaries of each other with both first flights in 1975. I think that and the fact they both use resin and fibreglass is where the similarities end.
     
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  5. Oct 16, 2019 #2185

    Venom

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    Not being diesel literate, someone help me out with a question or two. Regarding the latest Raptor fuel system modifications, do I understand correctly that the fuel system has one "lift pump" and if that pump fails then the engine quits? Is this correct? If so, wouldn't that logically mandate dual pumps? And if you were going to use just one pump wouldn't it be best to use something a little better than an automotive pump?
     
  6. Oct 16, 2019 #2186

    wsimpso1

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    Common rail diesel cycle engines typically use a low pressure pump to feed the high pressure pump that pressurizes the rail to well above combustion pressures in the cylinders, with electric injectors above the pistons. I do know that the high pressure pump is a piece of the engine, but I do not know if the Audi engine uses and engine mounted low pressure pump or if it is the electric pump that supplies fuel from the tanks.

    Redundancy in the feed pumping at the tanks makes all kinds of sense and perhaps even in the low pressure pump as well. Robustness in the high pressure pump may make sense, but I am not sure it is practical in an already designed engine.

    In mechanically controlled old style diesel cycle engines, the pump provided fuel and timing- under high pressure as the engine approached TDC- and they were engineered to be at least as robust and reliable as the base engine. With electronic controls, these have largely vanished from the market.

    I do find the discussion of "Audi engine" to be interesting, like it is some standalone company. Audi is a Volkswagen luxury brand, much like Toyota has Lexus, Honda has Acura, Ford has Lincoln, and GM has Cadillac. To imply that Audi engines are not VW is comical.

    Billski
     
  7. Oct 16, 2019 #2187

    BJC

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    The configurations are totally different, the structural design details are different, and the construction methods are different.

    Your statement seems to imply that the Falco was inspired by the VariViggen since they both are built of wood and glue.


    BJC
     
    Last edited: Oct 16, 2019
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  8. Oct 16, 2019 #2188

    aeromomentum

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    So what is/was the crash and fatality rate of the VK-30 and why?
     
  9. Oct 16, 2019 #2189

    BBerson

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  10. Oct 16, 2019 #2190

    bmcj

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  11. Oct 16, 2019 #2191

    rmeyers

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    Probably does not need the 'lift' pump. Just speculating, but since the Audi is German it more than likely uses a Bosch common rail pump. All Bosch common rail pumps have a low pressure pump integrated into the pump body with the high pressure pump. The low pressure pump is typically a positive displacement gear pump that is more than capable of drawing fuel from the tank. The low press pump draws fuel in from the tank, pressurizes it to between 25 and 125 psi and supplies it to the high pressure side. Interestingly, the first DuraMax trucks did not have an electric lift pump in the tank. Tank mounted pumps were added later. The reason? When customers inevitably ran out of fuel it would take the engine mounted common rail pump 20-40 seconds of cranking to get fuel all the way back to the engine. Customers no like. Hence add unneeded pump.

    I have refrained from commenting on this aircraft project until now, but I possibly have something constructive to contribute. In one of the recent posts it was stated that the gentleman building the airplane believed that he was not getting sufficient power from the engine and that he needed a bigger lift pump. Referring to my admittedly 'summary' description above it should be clear that increasing the lift pump capacity will do nothing. Increasing the lift pump pressure could cause real problems if it overpowers the regulated fuel supply to the high pressure side. Without knowing the specific model of pump it's hard to say. Nothing good will come of it though.

    And while I have my typing hat on now, a comment to perhaps clarify something for those who are not diesel savvy. On a normally aspirated diesel engine the only way to change the 'fuel mixture' is to change the combustion chamber shape or fuel injector nozzle geometry. That is to say there is effectively no way to change the mixture on a NA diesel. It always operates lean, that is with excess oxygen at all times. With a forced induction engine, for example turbocharged, that is not always true. There can be times when the airflow in is less than the fuel being supplied needs. This then does become a 'rich' running condition. This is apparently what is happening with the engine here in question.

    This also explains the very high EGTs he is seeing. He is not melting pistons or burning valves for the reasons stated below;
    Simple short explanation: He is burning the excess fuel in the exhaust pipes, not in the cylinder. In this case the EGT is not representative of combustion chamber temps but is instead showing actual flame in the pipe itself.
    More accurate explanation: How can he be burning fuel in the pipes if there is already too little air? Remember that a diesel is a stratified charge engine. We like to say the fuel droplets are looking for air molecules to react with. There can actually be sufficient oxygen in the combustion chamber to react with the fuel but too little time for the air and fuel to find each other. So the combustion process is still going on when the EX valve opens and just keeps going in the exhaust pipe. Depending on how hot it gets, there may or may not be any soot deposits in the pipes. (FYI, that's why common rail engines are so efficient. At 26107 psi the fuel droplets can be very small indeed!)
     
  12. Oct 16, 2019 #2192

    wrmiles

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    With regard to the pumps, turbine engines do not have redundant high pressure engine driven pumps. Although they usually have some suction feed capability, it is difficult to cover the entire envelope, therefore electric, ejector or engine driven boost pumps are used. These are required to be redundant.
     
  13. Oct 16, 2019 #2193

    BBerson

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    I am curious, what is it about a Diesel engine that allows running a lean mixture beyond stoichiometric?
     
  14. Oct 16, 2019 #2194

    akwrencher

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    There are a number of differences, direct injection, compression(Heat) ignition, heavier fuel. There is no fuel mixture in a diesel, it starts burning as it is injected into superheated air. Timing is controlled by injection, not spark. All these things make them a very different animal. Perhaps someone with more formal background can expound.
     
  15. Oct 16, 2019 #2195

    Rik-

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    Turbine engines also cannot handle much more than 15 psi input pressure or it cavitates the inlet pump. They do have a high gpm supply pump.
     
  16. Oct 16, 2019 #2196

    Rik-

    Rik-

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    technically a diesel always runs lean as throttle isn’t govern by air but rather fuel supply
     
  17. Oct 16, 2019 #2197

    BBerson

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    I know it runs lean. But wondering about "limits of inflammability" .
    For example, my book shows the limit of inflammability of petroleum is 1.5-7.8 percent of air by volume.
    So I would suppose that means the mixture could be as lean as 1.5% fuel vapor in air, or as rich as 7.8% fuel vapor in air.
     
    Last edited: Oct 16, 2019
  18. Oct 16, 2019 #2198

    Voidhawk9

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    Not a diesel expert, but I believe this comes back to the aforementioned stratified nature of the fuel / air mix in the combustion chamber.
    Fuel is injected into the compressed air, and somewhere in the region where air and fuel is mixed appropriately combustion is occurring, while the fuel charge is still not fully mixed with the air in the chamber - there is 'excess' air further away from the injector that has not (yet) participated in combustion.
     
  19. Oct 17, 2019 #2199

    flywheel1935

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    Just a thought, why all the discussion with regards to the diesel engine,???? its never going to fly !!!!!!!!!
     
  20. Oct 17, 2019 #2200

    TFF

    TFF

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    Because this is an EFI diesel, is the emissions timing still there? Mechanical pumps have one shot at injection. The EFI shoots fuel at other times which makes it “clean” and less smoke.
     

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