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No flaps approach speed C-172

Asked by: 2768 views General Aviation

I had the flaps fail on me in a 172 a few weeks ago at night.  I fly out of a 2,500 foot field.  My friend insisted that i make the approach at 70 KIAS with a slip, although i thought a lower approach speed would have been fine.  It all worked out but when i got home I couldn't find a no flaps approach speed in the POH.  

So if Vso * 1.3 = Vref (43*1.3=56 KIAS)

Then does Vs1 * 1.3 = Vref (no flaps) (50*1.3=65 KIAS)

Thanks

 

3 Answers



  1. MaggotCFII on Nov 16, 2012

    At night in your situation, a well established stabilized approach is in order. A slip at night would not be part of a stabilized approach. Also the airspeed may not be reading accurate in a slip.

    Why don’t you head out to the practice area and do some zero flap Maneuvering During Slow Flight and zero flap Power-Off Stalls. Make a quick note or two on the knee board, develop a feel for the airplane in zero flap configuration and then head back to your 2500′ runway and practice an zero flap approaches to full stop landings in the daylight!

    Try them at both your 65 and 70KIAS.

    Remembering there is always the “Go Around”!

    Then next time you will have a leg up on how the airplane is flying.

    By the way sounds like you did some good work!

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  2. John D. Collins on Nov 16, 2012

    I don’t know what model of 172 you are referring to, but in the 1978 POH, section 4, Speeds for normal operation, normal flaps up approach speed is listed 60 to 70 Kts IAS and with flaps down 55 to 65 Kts IAS . Also in the Performance section, stall speeds, the stalling speed with zero flaps is 50 Kts CAS and 44 Kts CAS with Flaps at 40 degrees.

    Using 1.3 times VS as the normal approach speed would translate into 65 Kts CAS for no flaps and 57 Kts CAS for 40 degrees of flaps. Notice that I used CAS and not IAS when I did the stall numbers and approach speed calculations. Once you have the CAS, you can convert it to IAS according to the performance chart that shows this relationship. In this case flaps up, 65 Kts CAS is 66 Kts IAS and 57 Kts CAS with 40 degrees of flaps converts to 53 Kts IAS.

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  3. Jason on Nov 17, 2012

    Hey fellas
    I was flying a 1977 Cessna 172N. Somehow i have a POH here for a 1975 Cessna 172M. It gives the flaps up stall speed, power off at 57 MPH (which is 50 KIAS). I definitely hadn’t thought of the CAS part, John.
    Guess you’re right Maggot I should do some trial and error. I actually ended up flying the approach at 70 KIAS without a slip and floated…….. forever. Oh man, my hand was on the throttle ready for a go around, absolutely!
    On a side note, went flying today and lost the landing light. (Different FBO, don’t worry :)) Landing in a black hole, feelin’ my way down… Yeah! It’s good to know you can handle things like that- makes you a more confident flyer.
    I’ll report back after some tests.
    Thanks to you both,
    Jason

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