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Thread: M0.7~0.85

  1. #46
    Moderator Topaz's Avatar
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    Re: M0.7~0.85

    Quote Originally Posted by bmcj View Post
    ...The Rose Rocket (as well as the Mach Buster) are at least in the advanced building stages, though I have not heard any news of either in the last few years.
    Huh. The tractor-prop aircraft ("Rocket") is by a guy named "Rose"? I just did an image search for the MachBuster. Found a picture, but the page it's cached from on airliners.net isn't coming up any more. Turns out that the MachBuster is also by a guy named "Rose": David Rose.

    Cooincidence? I'm guessing "no"...
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    Discussion Thread for the Project: Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

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    Re: M0.7~0.85

    good by
    Last edited by pie_row; November 29th, 2009 at 09:08 PM.

  3. #48
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    Re: M0.7~0.85

    good by
    Last edited by pie_row; November 29th, 2009 at 09:07 PM.

  4. #49
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    Re: M0.7~0.85

    Quote Originally Posted by bmcj View Post
    Intrepid looks interesting, but is only an artists rendition (in a 10 year old article). Has anyone seen any recent news on this?
    It seems that M.Hollman was involved in that design or he was going to design something similar, aircraft was never built. Others

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  5. #50
    Registered User Autodidact's Avatar
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    Re: M0.7~0.85

    Quote Originally Posted by pie_row View Post
    The power required...
    Sounds like at the altitude you need to fly at to obtain the high speeds, it's difficult to find enough oxygen to feed the piston engine; would a tank of nitrous-oxide help? And why are tubine engines more efficient up high - don't they need oxygen too? (Sorry pie_row, didn't mean to hijack the thread)
    Last edited by Autodidact; November 20th, 2009 at 04:22 AM.

  6. #51
    Moderator autoreply's Avatar
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    Re: M0.7~0.85

    Quote Originally Posted by pie_row View Post
    The big P&W was maintaining full take off power to 40,000ft.
    I can't find a statement against this, but I can find data of most other P&W's, getting only a bit boost. In fact none of the others gets more that 1/3rd of the original power at 30,000 ft.

    With two stages of turbocharging at 4:1 for each stage* (16:1 total) you can turbo normalize full sea level power to 80,000ft.
    But you forgot to include the power required to drive the turbo. In this case that's over 100% of your original power.

    With composite construction adding a P cabin doesn't add the lbs like with aluminum.
    No?
    How come the IV-P is much heavier compared to the normal 4 or other aircraft despite the fact that it was designed with pressurization in mind?

    Quote Originally Posted by Autodidact View Post
    Sounds like at the altitude you need to fly at to obtain the high speeds, it's difficult to find enough oxygen to feed the piston engine; would a tank of nitrous-oxide help?
    Definitely, but then you're carrying an awful lot of mass higher up.
    And why are tubine engines more efficient up high - don't they need oxygen too? (Sorry pie_row, didn't mean to hijack the thread)
    Turbines (and turbofans) power decreases linearly with density. Efficiency is directly proportional to the pressure ratio and to the temperature difference.

    The pressure ratio (pressure before combustion divided by ambient pressure) remains constant, even if you go up high. The temperature decreases however and that's the reason turbines are more efficient higher up, a bigger temperature difference between before and during combustion is simply more efficient.

  7. #52
    Moderator Dana's Avatar
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    Re: M0.7~0.85

    It's not that turbines are more efficient up high, but up high you're cruising at a high TAS, and they're more efficient at high speeds, since the thrust doesn't fall off as speed increases like a prop does.

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  8. #53
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    Re: M0.7~0.85

    Quote Originally Posted by Dana View Post
    It's not that turbines are more efficient up high, but up high you're cruising at a high TAS, and they're more efficient at high speeds, since the thrust doesn't fall off as speed increases like a prop does.
    Well, props, turboprops and turbines all loose thrust above their designpoint.

    It's only that the design point of many turbofans is above their cruise speed a bit. Given the much denser air below their efficiency at 230 kts or so at sea level is comparable to the efficiency high up during cruise, low they're making much more power/thrust and the air is a bit less cold which lowers efficiency by maybe 10/20%, but that's it.

  9. #54
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    Re: M0.7~0.85

    good by
    Last edited by pie_row; November 29th, 2009 at 09:07 PM.

  10. #55
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    Re: M0.7~0.85

    Mach number has barely anything to do with efficiency, it's temperature only, that's a fundamental of the thermodynamic formulas as used for jets.
    That the pressure ratio (with some engines) rises at cruise is true, but that's because the turbine temperature is limited by material properties and by going to the full pressure ratio the turbine would melt.

    Quote Originally Posted by pie_row View Post
    Quote:With composite construction adding a P cabin doesn't add the lbs like with aluminum.
    “No?
    How come the IV-P is much heavier compared to the normal 4 or other aircraft despite the fact that it was designed with pressurization in mind?”-autoreply

    Burt Rutan built an airplane called the boomerang it was pressurized. The fuselage weighed 200lbs. The Cessna 210 P added 200# with the P.

    Yes, the fuselage itself isn't the problem, everything around is. Pressure seals, heavier windows, much heavier doors, all the pumps, safety stuff easily adds up to a couple hundred pounds. I've rode the stories about the Lancair IVP and that's considerably heavier than the unpressurized IV which is otherwise identical.

  11. #56
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    Re: M0.7~0.85

    good by
    Last edited by pie_row; November 29th, 2009 at 09:07 PM.

  12. #57
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    Re: M0.7~0.85

    Quote Originally Posted by pie_row View Post
    I forget the exact model number but it was a variation on the R 4350. had a two stage turbo charging system. And they controlled the boost with a propulsive nozzle so you got some thrust. About 250lbs/1,000hp. At 545mph that would be getting close to ½ of the thrust of the prop. Or close to 1/3 of the total. The big P&W was maintaining full take off power to 40,000ft.
    You are probably referring to the same engines that were used on the Republic XF-12 Rainbow.

    M0.7~0.85-republic_rainbow.jpg

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  13. #58
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    Re: M0.7~0.85

    Quote Originally Posted by bmcj View Post
    You are probably referring to the same engines that were used on the Republic XF-12 Rainbow.
    "Und make it schlicht!"
    Last edited by Autodidact; November 20th, 2009 at 01:12 PM. Reason: I can't spell

  14. #59
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    Re: M0.7~0.85

    good by
    Last edited by pie_row; November 29th, 2009 at 09:06 PM.

  15. #60
    Registered User bmcj's Avatar
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    Re: M0.7~0.85

    The Rainbow had rearward facing exhausts inside an augmenter tube (inside the nacelle... there were no outside protuberances from the nacelle structures) to add thrust, increase cooling flow, and reduce cooling drag.

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