Landings and Stall Warning Question

[Bob - S50]

Question for the group.

 

[kortopates]

I think you're placing too much confidence in the precision of the stall horn activation. From the maintenance manual: The stall warning should actuate at no less than 5 kts, nor more than 10 knots preceding the stall and shall continue to until the stall occurs in the power off configuration.

That's a 5 kt range assuming all your reported data is based on properly configured stall warning horns of mostly 35-50 year old airplanes 

Much better to go by airspeed IMO and how quickly one does the roundout based on the height they begin it.

From S&M manual:

Edited December 7, 2017 by kortopates

[RobertGary1]

Pretty hard to notice airspeed late in the flare, and the indicator is pretty inaccurate at those near stall speeds anyway. If you're curious you might have a observer notice it for you while you focus on touch down.

 

-Robert

[Shadrach]

On 12/7/2017 at 3:33 PM, kortopates said:

I think you're placing too much confidence in the precision of the stall horn activation. From the maintenance manual: The stall warning should actuate at no less than 5 kts, nor more than 10 knots preceding the stall and shall continue to until the stall occurs in the power off configuration.

That's a 5 kt range assuming all your reported data is based on properly configured stall warning horns of mostly 35-50 year old airplanes 

Much better to go by airspeed IMO and how quickly one does the roundout based on the height they begin it.

From S&M manual:

Could not disagree more. For the stall horn to sound, AOA must be increased to the point that airflow has reversed derection at the stall horn vane location on the leading edge. It is a far better indicator than the ASI of what airflow over the wing is doing at low speed. 

The 5-10 knot range in warning speed is due to the ASI's lack of precision at low speeds and high AOA, not the stall horn's. 

Edited July 3, 2018 by Shadrach

[Bartman]

We have adjusted my stall horn and it's full up in the travel slot and the tab on the switch is free and not bent.  However, I rarely hear the stall horn even on full flap-full stall landing but I do hear it chirp momentarily pretty often on takeoff especially if it is gusty.  At altitude in full flap landing config it comes on just over 5kts above stall speed and blares continuously in slow flight and until I recover from the buffets or when she stalls, but not when landing.  I have had it adjusted, had the IA look at it, and finally I just got used to it.  And not I'm not landing too fast and I know what a full stall landing feels like and looks like and my yoke is in my chest when the mains touch.  I haven't gotten a bounce due to landing to fast in years, often off at 1,000 ft exit, and always off by the 2,000 foot exit on home runway.  It's not me, its the switch. 

Maybe there is an internal adjustment inside the wing in addition to the sliding external adjustment but  thats not what the manual shows.

[Bartman]

And if anybody else had my problem and solved it I would be very happy to know what you did.

[Bartman]

Alright now this is really strange. About a month ago when working on the glue removal on the cabin door I walked around the plane and my jacket caught the stall switch. Of course I looked at it, then turned on the master and confirmed it still worked. It was not a particularly forceful event when I caught it on my jacket and I'm sure most of us have done it before. Also there was no perceived difference in the appearance or the effort required to raise the tab and the horn operation was unchanged. The strange thing is while my stall horn always worked in preflight but rarely even in a full stall landing, now it has sounded the last 3 landings. 

Go figure. 

[Hank]

Who needs a hangar fairy when you've got a good jacket?  

[steingar]

If your landings are short to your satisfaction and smooth to your Mrs. satisfaction, who cares about a stall horn?

[carusoam]

Early on in O ownership....   For a few months I went without hearing the stall warning...

It turns out, the switch went inop.... I always tested the mechanical part, but assumed the electrical part was working...

Back then I had pretty good speed control...

A bump on final approach typically will sound the horn...

Today, I make sure the power is on for the full stall horn test.  Reach in the window to turn the power on/off....

PP thoughts only, not a CFI...

Best regards,

-a-

 

[Htwjr]

If my stall horn is going off just before the mains touch it is a good landing.

[jaylw314]

17 minutes ago, Htwjr said:

If my stall horn is going off just before the mains touch it is a good landing.

I've always wondered what the stall warning means in ground effect with flaps down.  Both of them will affect at what AOA and speed the stall warning goes off, so I imagine having the stall warning go off during landing isn't necessarily an informative thing...

I assume the stall vane is calibrated to a specific configuration at a specific speed in level flight.  I don't know what those specifics are, though.  My guess is that it's not Vs0

[carusoam]

The stall vane gets tripped as the split line moves lower down the leading edge...

Take a look at where the vane is... that gives you a feel for how far down the split line is...

The higher the AOA, the lower the split line... followed by turbulent airflow separating from the wing...

AOA will be effected by flaps and ground effect and the plane’s slowing air speed...

So I was told once... by a PP Thinking out loud....

Best regards,

-a-