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    V1 cut

    The V1 and VR speeds are split by about 5 kts.

    The engine cuts out at V1 - but never increases to VR.

    I'm taking off at reduced takeoff power.

    Any suggestions?
    Bren Gee

    #2
    Hi Bren,

    how do you calculate your takeoff power settings?
    When I use the original Boeing OPT or virtualperformancetool.com I'm getting good results for the climb performance after an engine failure, close to the real aircraft.
    See my video on the topic here: https://youtu.be/NGwVTp9hWoA

    Comment


    • erjdriver
      erjdriver commented
      Editing a comment
      The virtualperformancetool.com site doesn't seem to support 777 - or should I look harder?

    • DDowns
      DDowns commented
      Editing a comment
      Adding the 777-200ER will add an EFB to all of your 777's and it includes the Boeing OPT.

    • Emi
      Emi commented
      Editing a comment
      uups, you're right erjdriver, I didn't notice I was posting in the 777 forums.

    #3
    Well to be honest, I don't have access to any tools.

    I just set the assumed temp to 65 and that gives me a "normal" 2-engine takeoff

    I guess I could try a full thrust takeoff with no assumed temp or maybe around 50 or so.

    Thanks for the link though I didn't see you explain the performance computation part.

    I looked at the site and it seems to be only for 737.

    btw - IRL have you ever tried de-rated t/o numbers. I'm IRL pilot also and have never had our
    software return a de-rated T/O.

    Thanks.
    Last edited by erjdriver; 29Oct2022, 22:29.
    Bren Gee

    Comment


      #4
      The derates are handy for contaminated surface as a way to lower Vmcg.
      Dan Downs KCRP
      i7-10700K 32GB 3600MHz 3080Ti

      Comment


      • azylman1
        azylman1 commented
        Editing a comment
        Contaminated and wet are different as I’m sure you know. Fixed derate and assumed temperature method is acceptable for wet runway, but for a contaminated runway only fixed derate is acceptable. Just a technicality but it’s helpful to be specific when dealing with these topics.

      • Want2BFlyin
        Want2BFlyin commented
        Editing a comment
        According to the FAA, "A runway is considered contaminated whenever standing water, ice, snow, slush, frost in any form, heavy rubber, or other substances are present." I'm sure the regulatory bodies of other countries have very similar definitions. So yes, a "wet" runway may not necessarily be considered contaminated, but it depends on how much water is present on the runway, and the state that water is in.

      #5
      Originally posted by DDowns View Post
      The derates are handy for contaminated surface as a way to lower Vmcg.
      I’ve never seen a derated power takeoff on contaminated runways and why would you? Lower V1 speeds due to contaminated have nothing to do with Vmcg but with stopping distance. You do not want derated power because you want the most available runway possible to stop in the event of a reject.
      Rafael Cordoves

      Comment


        #6
        Originally posted by Icaruss View Post

        I’ve never seen a derated power takeoff on contaminated runways and why would you? Lower V1 speeds due to contaminated have nothing to do with Vmcg but with stopping distance. You do not want derated power because you want the most available runway possible to stop in the event of a reject.
        I'm not following you. Boeing 777 FCTM pg 3.16 FIXED DERATE: Derated takeoff thrust may be used for takeoff on a wet runway....[which] may permit a higher takeoff weight when performance is limited by Vmcg..... [and also] permit a lower takeoff weight when MTOW is limited.

        Also same page notes that ATM reduced thrust does not change Vmcg or Vmca because these are based on full rated takeoff thrust.


        Dan Downs KCRP
        i7-10700K 32GB 3600MHz 3080Ti

        Comment


          #7
          Originally posted by Icaruss View Post

          I’ve never seen a derated power takeoff on contaminated runways and why would you? Lower V1 speeds due to contaminated have nothing to do with Vmcg but with stopping distance. You do not want derated power because you want the most available runway possible to stop in the event of a reject.
          Vmcg is the minimum speed at which directional control of the aircraft can be maintained on the ground in the case of a sudden failure of the critical engine, and the only correlation that it has with V1 is that Vmcg cannot be greater than V1. By using derated thrust when taking off on a wet runway, the yawing moment from a sudden engine failure will not be as strong, which means that the effective Vmcg will be lower. As Dan mentioned, the actual Vmcg speed doesn't change since this is calculated during the aircraft's certification and is part of that certification.

          As an example, let's say that the 777's Vmcg is 120 knots (it probably isn't, this is just an example). I am not sure if the 777 has a critical engine, but for the sake of this example let's say that the right engine suffers a complete loss of thrust at 115 knots with full-rated power still being provided by the left engine. The aircraft is going to immediately yaw to the right. If the runway is dry, you may be able to keep the aircraft on the runway while bringing the throttle back to idle on the left engine. If the runway is wet, you are almost guaranteed to be going off the right side of the runway. If derated thrust is being used on the takeoff, the certified Vmcg will still be 120 knots, but the effective Vmcg may now be 110 knots. The same failure on a wet runway will not produce as strong of a yawing moment as it would at full-rated power, so you will most likely be able to keep the aircraft on the runway this time.
          Tim Lincoln
          My YouTube Channel

          Comment


          • azylman1
            azylman1 commented
            Editing a comment
            Well, V1 is never lower than Vmcg, so in this case you would reject the takeoff and not continue veering off the runway.

          • Want2BFlyin
            Want2BFlyin commented
            Editing a comment
            I didn't state it very clearly, but in the example scenarios that I mentioned Vmcg was below V1, and therefore both ended with a rejected takeoff. It's just one ended in the grass and the other did not.

          #8
          Getting back to the original question..and suggestion.

          I tried a full thrust takeoff and doing a V1 cut - the engine cuts out about 5 kts shy of V1 and barely reaches VR.

          And this is a light airplane.

          The only variable that I added was that it's a relatively high altitude airport 5K msl.


          This is not correct behavior.
          Bren Gee

          Comment


            #9
            Originally posted by erjdriver View Post
            Getting back to the original question..and suggestion.

            I tried a full thrust takeoff and doing a V1 cut - the engine cuts out about 5 kts shy of V1 and barely reaches VR.

            And this is a light airplane.

            The only variable that I added was that it's a relatively high altitude airport 5K msl.


            This is not correct behavior.
            Are you pulling the throttle lever or relying on something else to simulate the ENO? There is a RTO test by FAA that allows an engine failure within 5 kts of V1 so I'm wondering if this is related.

            Something isn't right. A lightly loaded 777 that hasn't been derated or have an ATM applied will take off like a rocked on a single engine. Something is wrong with your testing.
            Dan Downs KCRP
            i7-10700K 32GB 3600MHz 3080Ti

            Comment


              #10
              I pressed toga buttons and see thrust go up - yes on 2-engines the plane accelerates too fast.

              and then I programmed v1-cut in the FMS - i don't touch the throttles.

              I'll post the weight if you'd like and takeoff is in denver.
              Bren Gee

              Comment


                #11
                The aircraft weighs 486K lbs.

                I tested at full thrust at sea level airport (V1/VR are the same) and the behavior seems closer to normal.

                Same config but at 5400 msl (V1/VR split by about 5 kts) - and engine cuts out about 5 kts before V1 and then acceleration is very slow and barely reaches VR.

                Bren Gee

                Comment


                  #12
                  That actually makes sense. You can expect noticeably lower performance from the engines at Denver than you would at LAX. Should it be quite that bad? I'm not sure. But you will definitely notice a difference. Now try it with temperatures near what would normally be seen in the middle of summer compared to temperatures that are normal for the middle of winter.
                  Tim Lincoln
                  My YouTube Channel

                  Comment


                    #13
                    I understand performance will be worse at higher temps.

                    But I had OAT at 20c at Denver at a very light load and full thrust - the plane should accelerate past Vr with no issue on single engine.

                    Appreciate someone else try it - MTOW 487K lbs

                    Bren Gee

                    Comment

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