Stall warning

[guillaume78150]

Maybe an academic question but when landing, the stall warning never light up... I flare the aircraft around 75mph, too fast ?

[Piper_EEWL]

If the stall warning doesn't come on you're to fast yes
It's not that easy to land the Comanche with the stall warning on though I have to admit. A key factor to success I found is having it trimmed correctly since chopping the power will reduce elevator effectiveness a lot.

Also since this is Accusim did you check if the stall warning works? Maybe you blew the fuse?

[guillaume78150]

I stalled the aircraft (intentionally) at 10.000' and it works...
I use to approach around 95mph and reduce power before the threshold. It's true it makes the plane less reactive and kiss landing is a matter of luck.
Fingers crossed, I never broke anything so far.

[Scott - A2A]

If you perform a very hard turn, you can get that light to trigger much higher than stall speeds.

Scott.

[DHenriques_]

Maybe an academic question but when landing, the stall warning never light up... I flare the aircraft around 75mph, too fast ?

The key to understanding your question is in understanding that the stall warning system is referenced to ANGLE OF ATTACK and NOT airspeed ! Stall and the airspeed indicator are only linked at one point when landing. Remember, you can stall an airplane at ANY airspeed or in ANY attitude.
When landing and in your flare, if the stall warning horn or light hasn't actuated that is an indication that your angle of attack hasn't yet reached the point where it actuates the visual/audible signal. You can be fairly certain this being the case that you are not yet slow enough to have increased your angle of attack to the stall point.
Remember always that airspeed is related to angle of attack. Ideally when your angle of attack increases to the stall point and the airplane is at gross weight and at 1g when landing, the point where the stall angle of attack and airspeed will meet is at the marked lower end of the landing configuration reference line on the airspeed indicator.
Dudley Henriques

[guillaume78150]

Thanks Dudley. Which brings the question, does a "proper" landing means stalling the aircraft (I always thought it was better to keep a security margin in case of wind shear) ?

If you perform a very hard turn, you can get that light to trigger much higher than stall speeds.
Scott.

I experienced that...with a glider. The instructor was a former French Air Force F84 pilot and told us the aerodynamic rules at Mach 1 at FL400 with a swept wing were the same at 70 mph at FL10 on a straight wing with no engine.

[DHenriques_]

Thanks Dudley. Which brings the question, does a "proper" landing means to stall ?

Actually, the term "full stall landing" might be a bit misleading. Done correctly, a "full stall landing" will occur with your gear making contact with the runway just as your lift coefficient passes though your CLmax line.
Basically what this means is that just as your wheels touch down the wing is transitioning through it's max lift point and on into a decreasing area of lift; basically your stall point.
I have always taught students to visualize this as a point where sink rate can no longer be held constant with back pressure and the aircraft can no longer be held off the runway due to the increasing sink rate.
If you hold the airplane off until it's in full stall the result is usually a "plopped on" landing. If you catch it just right however, the landing will be the classic "greaser" everybody likes to experience as the gear meets the runway with "just a little bit of lift" left on the wing.
Dudley Henriques

[guillaume78150]

Tomorrow is a day off. Back to the airport for take off and landing.

[bobsk8]

https://www.youtube.com/watch?v=t-5qmN3HLoQ&t=35s

[guillaume78150]

Thanks for the link, good one.

... If you catch it just right however, the landing will be the classic "greaser" everybody likes to experience as the gear meets the runway with "just a little bit of lift" left on the wing.
Dudley Henriques

It works... The trick is to keep a bit of power until the wheels touch. But it must be accurately set as with too much of it, the Comanche tends to "float" above the runway, low wing effect ? Obviously 95mph is too high, but the Comanche does not slow easily.
I remember flying a Cessna 206, the aircraft was easy to land, stall warning beeping loudly and visual contact with the runway thanks to the high wing. It's true it stalled and kiss landing it was not easy.

[William Hughes]

The Comanche tends to float because almost everyone tries to land it too fast. I was practicing power off stalls the other day with the gear out and the flaps down. Just me in the aircraft and the mains full. The flutter-banging started at about 50 knots and the actual stall was around 47 knots. A power off stall in that regime in that aircraft doesn't actually break, the nose lowers a bit and the aircraft sort of mushes down while trying to drop a wing.

So 1.3 x 50 knots is 65 knots. If I make the final approach in that W&B condition at that speed the aircraft lands promptly and nicely. But the book says a clean max gross stall speed of 64 knots, and to be safe a lot of pilots will make the calculation for a final approach speed of 83 knots! So they have to bleed off a lot of speed while floating just above the runway and waiting for the aircraft to slow down. If they get a bit high during the process she'll come down with a bump when she finally does stop flying.

Higher speed aggravated stalls in the clean condition do indeed break suddenly and with little warning. One moment you are looking at the sky, and the next moment, you are looking at the ground with the airspeed rocketing up.

Stall accidents I worry about are full power in the takeoff condition (gear up, flaps up, full power, attempting to get over a tree), or low power maneuvering on final (low power, gear down, flaps down, maneuvering to reach the runway). You want to keep your speed up during base and long final in case you need to dodge something as a high g turn might suddenly stall the high-AOA wing (the low inside one as you roll out of a turn - slower moving and aileron deflected down increases AOA).

[guillaume78150]

Should the stall warning beeps too, mine does not...

[Piper_EEWL]

No there's no audible warning as in the Cessnas. The light on the panel comes on. That's it.

[guillaume78150]

Vielen Dank.

[DHenriques_]

The Comanche tends to float because almost everyone tries to land it too fast. I was practicing power off stalls the other day with the gear out and the flaps down. Just me in the aircraft and the mains full. The flutter-banging started at about 50 knots and the actual stall was around 47 knots. A power off stall in that regime in that aircraft doesn't actually break, the nose lowers a bit and the aircraft sort of mushes down while trying to drop a wing.

So 1.3 x 50 knots is 65 knots. If I make the final approach in that W&B condition at that speed the aircraft lands promptly and nicely. But the book says a clean max gross stall speed of 64 knots, and to be safe a lot of pilots will make the calculation for a final approach speed of 83 knots! So they have to bleed off a lot of speed while floating just above the runway and waiting for the aircraft to slow down. If they get a bit high during the process she'll come down with a bump when she finally does stop flying.

Higher speed aggravated stalls in the clean condition do indeed break suddenly and with little warning. One moment you are looking at the sky, and the next moment, you are looking at the ground with the airspeed rocketing up.

Stall accidents I worry about are full power in the takeoff condition (gear up, flaps up, full power, attempting to get over a tree), or low power maneuvering on final (low power, gear down, flaps down, maneuvering to reach the runway). You want to keep your speed up during base and long final in case you need to dodge something as a high g turn might suddenly stall the high-AOA wing (the low inside one as you roll out of a turn - slower moving and aileron deflected down increases AOA).

The way I've always explained this to students entering the landing phase is that the purpose of touching down at the stall indication is to make the touchdown at the lowest possible airspeed. What's indicative here is imparting the mindset to the student that it is entire possible to land the airplane at a speed higher than the stall speed. Once this concept sinks in the student begins to associate the flare into what it should be; that being the slowing down of the aircraft to reach touchdown at the slowest speed which of course will occur as the wing transitions through it's max CL at the stall point.
What happens if the student DOESN'T understand this concept usually results in touchdowns somewhere before the wing reaches its max CL while in sink at some airspeed above stall but beneath the lift needed to cancel out the sink rate.
This in turn is the cause of the student not using increased back pressure to cancel the sink rate while holding the aircraft off the runway as it slows down.
All this explained to the student using the KISS principle simply involves explaining to the student that the more airspeed the student has over the threshold the longer the student will have to hold off the touchdown.
It helps as well to explain to the student that the published suggested final approach airspeed is simply what the manufacturer has determined to be an airspeed over the fence that allows for a flare that lands the aircraft using a reasonable amount of room for the flare and touchdown.
This is of course a general explanation that works for most students. Naturally a good CFI will alter any explanation to reflect an individual student's ability to understand what is being taught.
Dudley Henriques