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5 Answers

Short Field Landing Vspeeds

Asked by: 8276 views , ,
General Aviation, Private Pilot

The PTS and 'guidance' for a short field landing is to use 1.3Vs0 "in the absense of one published". I looked through my POH's for Arrow, Archer, C152, C172, C182 and it seems like only my Cessna POH's mention a short field landing final approach Vspeed (full flaps...), but the Pipers do not. I also noticed that all 3 Cessna POH numbers for Short Field Landing are all 10kts higher than a 1.3Vs0. Does this mean 1.3Vs0 is way too slow for Cessna's but 1.3Vs0 is ok for Pipers? Does it mean I should use 1.3Vs0 for Pipers and use POH for Cessna's since it has something written down? I am in training for my initial CFI and want to find guidance on 'how to best teach' short field with a good understanding of the appropriate final approach speed for different aircraft. Thanks

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5 Answers



  1. Kent Shook on Feb 23, 2011

    Interesting. I see that the PTS specifies 1.3Vs0 in the absence of published numbers for all types of landings (Normal, Short, and Soft). In general, 1.3Vs0 is a good number to use for normal landings, while 1.2Vs0 is a good number for an actual short-field landing (as opposed to a “checkride” short-field landing, where you must follow the PTS).
     
    Also, Piper does publish short field landing speeds, but unlike Cessna (who puts them both in the “normal operating procedures” section of the manual), Piper’s short field numbers are listed at the top of the landing distance graph. For example, looking at an Archer II POH, the normal numbers are listed in section 4.29 “Approach and Landing” as 86 mph/75 KIAS, while the short field numbers are listed in the landing distance table 5-29 as 76 mph/66 KIAS. 
     
    Finally, while you must teach to the PTS, remember that the numbers change with weight. Depending on what type of airplane is being used, you may or may not be at gross weight (which is what the numbers in the book are for). If you’re at a lighter weight, you need to adjust the book values as appropriate for the weight. To do this, take the square root of the ratio of the actual weight to the maximum gross weight and multiply by the *Calibrated* approach speed (you may need to convert KIAS to KCAS) to arrive at the proper calibrated approach speed for the weight, which you should then convert back to KIAS.
     
    So, for example, looking at the Archer II again: Let’s say I’m at an actual gross weight of 2100 pounds, and I want to make a short-field landing (book: 66 KIAS). Since the MGW of the Archer is 2550 lb and 66 KIAS = 68 KCAS, the calculation goes: sqrt(2100/2550)*68 = 61.7 KCAS ~= 58 KIAS. So, you can see that using 75 KIAS (the speed shown in section 4.29) or 69 KIAS (1.3 Vs0) is going to make that “short” field landing into a not-so-short landing.

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  2. Mike Pastore on Feb 24, 2011

    Hi Matt.  You pretty much answered your own question.  Teach your students to fly 1.3 Vso if the short field approach speed is not published in the POH.  1.3 Vso is not too slow…in fact, it may be a bit fast but don’t teach them to fly slower (again, unless otherwise published).
    Part of the problem is that in heavier high performance aircraft, you can run out of elevator authority if you get too slow and end up with a really high sink rate.  The FAA does not want CFI’s teaching students to be test pilots.
    And yes, adjusting Vso based on weight as noted by the previous poster is the right thing to do….in real life and as part of any check ride.
    Regards,
    Mike

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  3. James MacGregor on Feb 24, 2011

    Funny how the same topics are asked at the same time. Simone asked this over at BCP so I’ll just replay what I said over there:

    I think a good short field landing is more of a FEEL maneuver then a text book math operation.

    On my most of my landings after I line up on final and have the runway made, i dont find myself looking at my panel until I am wheels down and cutting the strobes, xpdr, and switching to ground, taxi lights etc.

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  4. John D. Collins on Feb 24, 2011

    Matthew,

     

    The 1.3 VSo numbers for Cessna’s you refer to may need correction in order for the calculation to work.  From the manual, the VSo indicated speed for a 1981 Cessna Skyhawk is listed as 33 KIAS. This is 46 KCAS.  So 1.3 times 46, is 60 KCAS rounded to the nearest Knot.  The short field approach speed is also listed in the manual as 61 KIAS, which is 62 KCAS.  So, at least in that example the Cessna recommended short field approach speed is within a few knots of 1.3 VSo.

     

    Kent,

     

    The corrections for weight work for any speed that is based on a constant angle of attack and can be derived from the basic lift equation.  The speeds that have a constant angle of attack are the stall speed and the best glide speed.  Since 1.3 VSo is based on the stall speed, the weight conversion using the square root of the ratio of the weights will work.  It will also work with adjustments for Va for the same reason.  It will not work for other speeds such as Vx or Vy where the angle of attack is different for different weights.

     

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  5. James MacGregor CFI on Feb 24, 2011

    Also are your computations factoring in x-wind? tailwind in regards to your airspeed and flap settings, also what if you are in a one way in/out type airstrip, how would that factor in to your equation?    If you are teaching short field ops keep in mind most these strips have allot you need to keep your eyes on other then your panel.
     If you want to impress your examiner (or inspector) use a slip, keep the nose down and have a steep decent, flare at a proper altitude, tell him what your aim point is and what your touch down point is.
     
     When I did mine with a FAA I never mentioned the speed I was going to shoot the thing at, I just did what I mentioned above and the inspector was more then pleased.
     
     The FAA is looking for mastery of the aircraft and MOREOVER that you can teach, so no matter what keep talking through the whole procedure.
     
     just my .02 cents

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