Trying to achieve turbonormalizing the home-built way

Discussion in 'Firewall Forward / Props / Fuel system' started by geosnooker2000, Aug 11, 2019.

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  1. Aug 20, 2019 #61

    SVSUSteve

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  2. Aug 20, 2019 #62

    BJC

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    Last edited: Aug 20, 2019
  3. Aug 20, 2019 #63

    rv6ejguy

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    Vne regarding flutter is based on TAS, not IAS. Lots of articles on Van's aircraft discussing this.
     
  4. Aug 20, 2019 #64

    BJC

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    Yup, lots of incorrect guesses, opinions, and beliefs on this subject everywhere. Most are wrong.


    BJC
     
  5. Aug 20, 2019 #65

    Turd Ferguson

    Turd Ferguson

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    I have flown some planes that had chart to adjust the value of of the placarded Vne. Did they not get the memo Vne is always the same indicated value?

    A glass cockpit airplane can adjust where Vne is displayed as you fly. All with the magic of electrons.
     
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  6. Aug 20, 2019 #66

    geosnooker2000

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    Here they are. In both cases, the info is on page 5-24 (cruise performance)
    https://inflightpilottraining.com/wp-content/uploads/2018/12/SR22-POH.pdf
    http://takeflightsandiego.com/assets/documents/SR22T G5 POH.pdf

    Note the differences on pages 2-4 (Airspeed limitations). They ARE represented in KIAS, not in KTAS. For the turbo, at least, I suppose if they had gone with KTAS, they wouldn't have needed two different values in the table.
     
  7. Aug 20, 2019 #67

    pictsidhe

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    IAS is what the gauges tell you in an aircraft. It is easier to hit Vne up high, so it ia likely specified in terms of IAS as high as Vne could be achieved. Increase your ceiling, that IAS Vne is no longer safe. Maybe it will be ok, maybe your wings will buzz off. Do you really want to assume it will be fine?

    Change anything, it's a new plane, and needs to be tested as such. The 'oh, it'll be fine' attitude to deviations from standard kills a lot of experimenters.
     
  8. Aug 20, 2019 #68

    SVSUSteve

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    I stand somewhat corrected as I was simply referring to the IAS readingS that are published in POHs. However, if you’re just plodding along smashing bugs, that line on the ASI should be sufficient (assuming that the design has been properly tested). Obviously, if you’re going up into the flight levels etc you have to be more careful and account for changes etc. You know that I am the person on this forum least likely to advocate a cavalier attitude with regards to safety. I apologize if it came across that I was doing so.
     
  9. Aug 20, 2019 #69

    Turd Ferguson

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    The turbo handbook says Vne is reduced linearly from 17,500 feet to 25,000 feet. 205 to 175. What is that suggesting?

    Being a Part 23 airplane a Cirrus had to publish IAS numbers to comply with the regs. That doesn't change the applicable laws of physics. They have enough margin build into the plane that the difference between IAS and TAS is irrelevant - at least till you get to 18,000 ft.
     
    Last edited: Aug 20, 2019
  10. Aug 20, 2019 #70

    TFF

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    When you are flying, your airspeed gauge will read KIAS only. You have to calculate KTAS for your conditions. Now with the Cirrus and any glass cocpit, its done for you. But the Cirrus has the table which is nice, in chapter 5. The pilot has to juggle all the limitations even if he could go faster. One day you could the next you can't. If you made the same table and put in your airframe limitations, you will be caping out once the true airspeed crosses with the VNE, because the VNE is low. At some point the gains stop if you believe in the boundrys. The Cirrus have 205 KTS VNE at sealevel. Thats 236MPH. Above 17500 they have to use 175 indicated; big correction.
     
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  11. Aug 20, 2019 #71

    Turd Ferguson

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    As you climb, indicated airspeed decreases; (ref "q") Dynamic pressure decreases which is what your airspeed system is measuring.
    The going rate is ~2% per thousand feet but it is not linear, especially when you get above 18,000 ft.
    Since indicated airspeed moves further away from the fixed value painted on the scale as you climb, it is harder to "hit Vne up high" with indicated airspeed.
     
  12. Aug 20, 2019 #72

    rv6ejguy

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    Many turboprops and jets have a Barber Pole on the ASI which shows Vne corrected for altitude. This is because Vne isn't based on IAS regarding flutter.

    IAS is close enough for most slow planes flying below 10,000 feet. It isn't close enough up in the flight levels.
     
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  13. Aug 20, 2019 #73

    BJC

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    And, if Vne is set by flutter, the difference between IAS and flutter speed.


    BJC
     
  14. Aug 20, 2019 #74

    rv6ejguy

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    I had a hand in two RV7s fitted with turbo Subaru engines. These would easily bust Vne (210 KTAS) at anything above 10,000 feet in level flight with modest manifold pressure- say over 40 inches. Planes with low Vnes are not the best candidates for operating high with turbochargers. Can be done if careful but sometimes it's better to choose a different airframe, better suited to the fast mission.
     
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  15. Aug 20, 2019 #75

    E28POWERM20

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    A BD-4 with a turbo would be very attractive here. The current BD-4C version has a 261mph VNE. You can even build it with longer wings for better high altitude performance. Can be built from plans as well.

    If you don't need 4 seats, the options really start to open up.
     
  16. Aug 20, 2019 #76

    pictsidhe

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    What is the Vne on the long wing version?
     
  17. Aug 20, 2019 #77

    E28POWERM20

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    That's a good question, I only know it's an option.

    Edit: The VNE is still 261mph with the longer wings, but only at 2000lb gross weights and lower. No testing was ever done at higher gross weights.

    Source: Bede Representative.
     
    Last edited: Aug 20, 2019
  18. Aug 20, 2019 #78

    BoKu

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    Have a chat with Steve Smith about this at the races. He has a compelling argument, backed with some research, that tying flutter-bound Vne to TAS is unnecessarily conservative. It appears that a value that splits the difference between TAS and IAS is more generally applicable.
     
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  19. Aug 20, 2019 #79

    SVSUSteve

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    Can you elaborate on why that might be?
     
  20. Aug 20, 2019 #80

    BoKu

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    Sorry, that is aerodynamics above my pay grade. I'll ping Dr. Smith and see if he can send me a link.
     
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