Knuckledragger00

“Stall” warning on rollout, very annoying..

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9 minutes ago, N201MKTurbo said:

Everybody keeps talking about airspeeds and such. The stall vane is an angle of attack sensor. if the relative wind is below the plane of the tab it blows it up. If the wind is above the plane of the tab it blows it down. 

With the wheels on the ground, the angle of attack and airspeed are decoupled. When you rotate the plane for takeoff, you are raising the angle of attack above the stall angle of attack as evidenced by the fact the plane isn't flying yet. So the stall warning should sound. If you did a no flaps takeoff and just flew the plane off without rotating it, it probably wouldn't sound. 

The switch may have a weak or broken spring. There is a spring that holds the switch down requiring a certain wind speed to blow it up from the normal down position. This is what keeps it from going off all the time.

There's a spring in there?  Mine feels like it's just the weight of the vane.  Now that I think about it, if you're not stalled, the wind should actually be blowing down on the vane anyway, so there shouldn't need to be a spring in there, right? 

Also, when you rotate the plane on takeoff, the stall warning would only go off if you were rolling with the wings at an angle greater than the critical AOA.  Given how much I remember the nose is pitched up in level slow flight with flaps down, I can't say I ever remember rotating that much on takeoff, so I think that would be a pretty dramatic "yank her off the runway" type of nose rotation before you'd trigger the stall warning.

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17 minutes ago, N201MKTurbo said:

Everybody keeps talking about airspeeds and such. The stall vane is an angle of attack sensor. if the relative wind is below the plane of the tab it blows it up. If the wind is above the plane of the tab it blows it down. 

With the wheels on the ground, the angle of attack and airspeed are decoupled. When you rotate the plane for takeoff, you are raising the angle of attack above the stall angle of attack as evidenced by the fact the plane isn't flying yet. So the stall warning should sound. If you did a no flaps takeoff and just flew the plane off without rotating it, it probably wouldn't sound. 

The switch may have a weak or broken spring. There is a spring that holds the switch down requiring a certain wind speed to blow it up from the normal down position. This is what keeps it from going off all the time.

Actually will sound before wheels leave the ground.  Interesting thought about the spring however.  I do keep thinking about how common this issue is with the TKS equipted Bravo’s also!

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MKT,

everyone is talking airspeed and AOA because we can’t separate them by what KD is describing...

The stall horn is expected to be the issue...

But... being new to the plane... there is some concern for what ifs...

Like what if he is really flying that closely to stall without recognizing it?

The LB adds some oddities... the Tks adds some difference...

The mechanic that didn’t adjust the stall horn properly?  What if he did?

There is a maintenance manual that is really good at describing the procedure for adjustment details...

interesting point regarding the spring... something that has become part of my everyday walk-around...listen for the tone.

The LB while on the ground has an AOA a few degrees higher than other Mooneys... it is possible to keep the nose off while landing and the stall horn sounding...

a super smooth landing can get scary when the horn sounds that long....

A full stall landing 5’ above the pavement looks and sounds incredibly similar... :)

PP only, not a CFI nor mechanic...

Best regards,

-a-

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Anthony what the heck is a super smooth landing 

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Dan,

(Having the stall warning unexpectedly sound for more than a peep is unnerving... for me.)

as for the one super smooth landing....

It was a 1 in 1,000 landing for me...

its an every day landing for 201er, Ross, Paul, and others...

I had one the other day... the stall horn was more than a momentary peep on landing.

The touch of the mains was so light it was hard to recognize...

I wasn’t sure... to celebrate the well orchestrated landing, or hit the throttle to cushion what was inevitably going to happen next... 

I went with make sure the throttle was out again and relax any pull on the yoke...

 

The why... what made that happen...

Nice weather... and possibly George’s Circular Approach technique.

Better Speed control, minimizing configuration changes in the pattern, really stabilized approach... continuous arc style.

or it was just a one off lucky event...  :)

 

Notes on the stall horn...

1) it is measuring AOA by knowing where the air split line is, for the air to go over the wing. Split line moves down with an increase of AOA, when the vane is above the split line... the switch turns on...

2) It is binary... either on or off...

3) It can’t be used as a primary tool to control flight attitude, other than to lower the nose to make it stop...

4) when it sounds, the airspeed is typically deteriorating with the large increase of drag... immediate actions are required to hold off things like departure stalls...

5) adjustment of the stall horn is usually physically moving the vane’s location more up or more down the face of the leading edge... moving it down, delays the horn... moving it up will have it sound sooner...

6) millimeters really count.  Making adjustments properly, probably includes drawing lines on the front of the wing next to the vane... a way to put the vane back to where it started, or measure the difference to the new location...

7) Sort of a bracketing technique...? That would need a flight to define the effects of the new vane location.

8) if you are doing the flight testing, you should be discussing the adjustments directly with the mechanic... If your mechanic is doing the flight testing he would be explaining what he did better... from experience...

9) find a mechanic that has the Mooney maintenance procedure for adjusting the vane.  It isn’t easy to access to make adjustments....

10) Too important to ignore, or guess, or not have right...

 

21 years or so of continuously learning how to fly.... PP thoughts only, not a mechanic... not a CFI...

Best regards,

-a-

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I have a tks equipped Bravo and have never experienced posters symptoms on takeoff

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I have a TKS Bravo, and I will hear the "stall" warning after rotation if loaded at gross, especially if you don't have full rudder trim engaged.

Also, I think the default G1000 vr bug is 60kts, where Vr for a mooney should be 66 at gross. 

I have looked at a number of data runs from the G1000 (do you have the -34 software?).. and the plane doesn't lift off until about 75kts. 

You should be able to compare the spring feel of your stall vane and another long body.. the spring isn't much force. 

So check the stall in flight.. and if it is within spec (5-10kts) in flight then it is probably the spring.. if it is not in spec in flight, it should be adjusted. 

Here is the excerpt from the maintenance manual: (PM me if you want the whole thing) 

 

3. Stall Warning Indicating System Adjustment (Fig. 27-23).

The stall warning switch is adjusted when the airplane is test flown at the factory. Should it require readjusting, proceed as follows:

A. Locate switch installation on under surface of left wing leading edge and loosen the two phillips head screws, one on either side of the vane.

B. If stall warning has been activating too early, pull vane BACK and DOWN.

NOTE
NEVER TRY TO ADJUST SWITCH BY BENDING VANE. This part has been heat treated and can- not be bent without damaging or breaking vane or switch.

C. If stall warning has been activating too late, push vane UP and FORWARD. Moving vane, with the phillips head screws loosened, moves entire unit up or down inside wing, causing switch to be closed earlier or later. Re-tighten screws after making each adjustment.

As a rule of thumb, moving vane tip 1/4 inch will change the time the stall warning actuates by about 5 KTS indi- cated air speed.

The only way to test the accuracy of the setting is to fly airplane into a stall, noting speed at which the warning horn comes on and speed at which full stall occurs.

For Garmin G1000 system equipped aircraft, the So- nalert tone is heard and approximately one second lat- er “STALL” is annunciated over the speaker.

The stall must be made in various configurations, clean, gear and flaps down and power on and power off. It may be necessary to make several alternate ad- justments and test flights before the desired setting can be reached.

The stall warning should actuate at no less than 5 KTS. nor more than 10 KTS. preceding the stall and shall continue until stall occurs in power off configuration. The rate of speed reduction shall not exceed one knot per second with airplane trimmed to 1.5 times stall speed.

The switch setting should be checked and adjusted as necessary whenever a wing or wing leading edge is re- placed or extensively repaired or if a new switch is installed. The switch should require no adjustment in normal service.

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