1.3 Vs0?

[ayavner]

Hi all - just trying to reconcile something in my brain.. you always hear of the appropriate landing approach speed as being 1.3 * Vs0. Yet most POH's quote an approach speed that is much higher than that.

 

For example, the J170 POH says Vs in landing config is 40 knots. 40 * 1.3 = 52, however the manual states 65 is the approach speed. I've seen similar discrepancies in other aircraft I've looked at.

 

So.. where does this Vs0*1.3 come from?

 

 

[Birdseye]

Probably a case of CYA. A bit for dad, a bit for mum and a large bit for the litigation lawyer.

 

 

[djpacro]

Pages 4 & 5 at https://www.faasafety.gov/files/notices/2014/Oct/FAA_P-8740-49_OnLandingsPart_II_[hi-res]_branded.pdf maybe enlightening.

 

 

[Birdseye]

An interesting read. Specifically the comment "Use 1.3 Vso on short final only". I'd regard it rather like the 'big jets' Vat - something to aim for the over the threshold, not on the extended final that most seem to fly these days.

 

 

[Jay_1984]

Hey,

 

As I understand it, 1.3Vs is the minimum safety margin for landing in short field situations. It would be the slowest safe speed which would result in minimal float on landing as you're riding the back of the lift/drag curve and getting to stall speed quicker reducing the runway needed to come to a stop. The higher figure given in the POH comes from the airspeed obtained at the best lift/drag ratio and gives a minimum angle of descent. This would be more suitable for regular landings.

 

BTW, I don't think of myself as an expert in this, just what I think I remember from training. Happy to be corrected.

 

 

[facthunter]

The link provided by djpacro has most of the info you will need.

 

A few points.

 

You approach speed (indicated ) will vary for gusts/turbulence , wind speed, actual aircraft weight, landing flap used. If it is a short strip you will want to fly slower but still maintain a safe margin above stall. If you use power on approach you may fly a little slower as a technique. (another story in itself but you still have your margins)

 

You should achieve a stabilised approach at a comfortable height above the aerodrome surface. This will vary a LOT but in NORMAL ops you might consider 400' for complex aircraft and lower for more simple types, once you have a fair bit of experience. Don't be rushed at this stage. Set the plane up well for the landing.

 

IF you are in a high density altitude situation your ACTUAL approach and touchdown speed will be higher. Be ready for the feeling of going too fast, same as if you are landing downwind.. Nev

 

 

[Yenn]

Facthunter. I know you are correct and what you mean, but by ACTUAL speed you really mean True Airspeed, which is visible as higher speed as groundspeed. We use indicated AS on the approach as it is the speed directly related to lift. I hope this makes your ACTUAL more understandable.

 

 

[ayavner]

thanks guys, i'm just sitting back and absorbing, nothing to add just yet!

 

djp, i've downloaded that and went back and got part I as well... good stuff, and i do like that the FAA tries to show a little humour to keep it from being so dry.

 

 

[facthunter]

Sorry if ambiguous. At a high Density altitude your airspeed indicator will under read. (Read less airspeed than you are doing). The stall speed will still be the indicated figure. Nev

 

 

[ben87r]

I use 1.3 Vso (weight corrected VREF) around 75kn MTOW) as the speed to be at around 50-80', but, the approach speed will be well above this (90-100kn turning final/2nm final) and slowly reducing speed down final. Keeps the speed up for most of final and if windshear or turbulence is encountered easy to keep the speed up a tad.