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Thread: Too fast too furious

  1. Default Too fast too furious

    I've finally got to the point of making consistently good landings with the c172. By that I mean on center line in the first 3rd of the runway, at kts of 65 and vsi no more than -500 on the approach with about -100 on touchdown.

    BUT transitioning to larger aircraft such as the 737 I seem to be having trouble with the vsi speed. It seems that since I have to fly faster at about 140kts to land I am also having to have a greater vsi speed. Is this normal, or am I doing something wrong?

    I start my decent as soon as I reach the glideslope. Do I need to be below glideslope? Because it seems that holding the speed at 140 with vsi at 500 will end up overshooting the aiming point. It seems good for a while, but suddenly the runway starts dropping in my view and it ends up requiring a sudden drop in vsi to maintain glideslope and get to the aiming point. By then I'm hitting the ground at -500 while I flair.

  2. #2

    Default

    Quote Originally Posted by jbearnolimits View Post
    I've finally got to the point of making consistently good landings with the c172. By that I mean on center line in the first 3rd of the runway, at kts of 65 and vsi no more than -500 on the approach with about -100 on touchdown.

    BUT transitioning to larger aircraft such as the 737 I seem to be having trouble with the vsi speed. It seems that since I have to fly faster at about 140kts to land I am also having to have a greater vsi speed. Is this normal, or am I doing something wrong?

    I start my decent as soon as I reach the glideslope. Do I need to be below glideslope? Because it seems that holding the speed at 140 with vsi at 500 will end up overshooting the aiming point. It seems good for a while, but suddenly the runway starts dropping in my view and it ends up requiring a sudden drop in vsi to maintain glideslope and get to the aiming point. By then I'm hitting the ground at -500 while I flair.
    Yes, you do need to be faster than 140 kts. IF the aircraft is not set up properly and is too heavy - Approach speeds: http://www.b737.org.uk/vspeeds.htm

    The aircraft needs to be in final approach configuration, flaps set. Approach the glideslope from beneath in level flight, and allow the glideslope to pitch the aircraft down with ILS engaged. Note the speeds and attitudes.
    Those are what you need.

  3. Default

    Simplified:
    vertical speed needed=
    (glideslope angle in %) times (Groundspeed)

    at low altitude airspeed is equal to: (groundspeed plus headwind).

    Glideslope angles in fsx are all 5%
    -----
    Assuming no wind in your example, your 140 kt would be pretty close to your groundspeed.
    Your vertical speed should have been 5 times 140. Which is 820 ft per minute.

  4. #4
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    Default

    Quote Originally Posted by il88pp View Post
    Glideslope angles in fsx are all 5%
    No they are not. Take a look at London City, EGLC.

    That said, 5 x groundspeed is a good guide for vertical speed until you lock on the glideslope.

    peace,
    the Bean

    [added]Also, in aviation glideslopes are referred to in degrees, not percents. Why complicate things by having to convert between the two?[/added]
    Last edited by StringBean; 09-19-2019 at 04:33 PM.
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  5. Default

    Because with the % value the math works out. It's an easy multiplication that way.

  6. #6

    Default

    jbearnolimits, you're absolutely correct! Flying at the higher airspeeds required by the 737 requires a greater rate of descent. Here's why...

    First, let's assume you're trying to fly the same path down to the runway--the standard three degree slope downward--in a slow airplane and a fast airplane. That slope yields the same change in altitude for both airplanes over a given distance, about 300 feet per each nautical mile across the ground for our purposes.

    Now let's say the first airplane approaches the runway at 60 knots, or one nautical mile per minute. If you need to descend 300 feet per nautical mile and you fly one nautical mile every minute, the rate of descent required is 300 feet per minute.

    Not let's say the second airplane approaches the runway at 120 knots, or two nautical miles per minute. If you cover two nautical miles per minute on the same 300 feet per nautical mile slope, you can see that the rate of descent is doubled, or 600 feet for minute.

    Keep in mind this is based on speed over the ground. So the 120 knot airplane with a 30 knot headwind (which results in 90 knots over the ground) would need to descend between 300 and 600 feet per minute to maintain that same slope.

    180 knots? 900 feet per minute.

    240 knots? 1,200 feet per minute.

    Make sense?

  7. #7
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    I seem to be having trouble with the vsi speed.
    The first thing you should do is to ignore the VSI on a visual approach (and mostly on an IFR approach, as well). Establish the proper approach indicated airspeed (NOT groundspeed)and learn to visually notice where your nose would plow into the ground in a steady state descent (if you didn't flare, that is), which will be the spot that isn't moving either up OR down in the windshield. Slight power adjustments (while holding airspeed constant -- think SMALL changes in power) will let you change that "aim" point. Doing this, the rate of descent will take care of itself, and you'll soon learn to visually identify when things are correct.

    But I'd do all that in the C-172 first, then move up to, say, a Baron, and get comfortable there, then perhaps to King Air, THEN to a jet. Don't make such a big jump all at once.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  8. Default

    I see that most glideslopes are 3 degrees. How do you get a percent out of that?

    As far as vsi, I'm a pro at that, really. But never did it in real life. Just set your final speed for plane weight, flaps and watch the vsi or PAPI and maintain glideslope and LOC. I find it easier to see the runway then to see the indicators, but I can do it none the less.



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  9. Default

    Thanks for the info. Good to know I wasn't doing wrong with a higher decent rate on the larger jet. Oh and just to clarify, I am able to handle the prop planes. So that's why I am on the 737 now.

  10. Default

    I think one of my issues is impatience lol. I don't often do a full final. I tend to get too excited and turn final about 5 miles out at 2000 feet agl. Guess that's not good for a 737 lol. At least not turning final at 240kts and not in configuration to land. But it works for the c172 lol.
    Last edited by jbearnolimits; 09-21-2019 at 10:41 PM. Reason: Added stuff

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