Seminole lift detectors

av8or91

Well-Known Member
Why is there 2? I havent recieved a clear or good enough answer from my instructor. I know the outboard is 0-10 degrees of flaps and the inboard is 25-40 degrees of flaps.
 

tgrayson

New Member
Why is there 2? I havent recieved a clear or good enough answer from my instructor. I know the outboard is 0-10 degrees of flaps and the inboard is 25-40 degrees of flaps.
A flapped wing will stall at a lower AoA than a non-flapped wing, which alone suggests that a single stall warning vane can't be accurate for both conditions.

That's an all-things-being-equal sort of thing, which they often aren't. Most decisions about where to put a static port, or pitot tube, or fuel vent, or stall warning vane are done by trial and error, and the only explanation you'll get is that "it works." The airflow around a wing at any particular point often deviates from what the simple theories say it should be.
 

av8or91

Well-Known Member
Thats what I was thinking but instructor kept saying something along the lines of how the engines were mounted on the wings and could inadvertenly activate the stall warning horn:confused:. Thanks alot for confirming my orginal thinking:)
 

tgrayson

New Member
Thats what I was thinking but instructor kept saying something along the lines of how the engines were mounted on the wings and could inadvertenly activate the stall warning horn:confused:. Thanks alot for confirming my orginal thinking:)
He's speculating and so am I, although what I said is based on known characteristics of wings. Piper has not said specifically why they have two. All you can know for sure is that they found one inadequate. :)

For the engines to have anything to do with it, you'd have to have a mechanism for why the flaps make any difference to the airflow at the locations where the vanes are located. One that's plausible is that the lower pressure over the wing produced by the flaps moves the slipstream more inboard, which is something that does happen on some airplanes.

I've only heard of this setup on the Seneca and Seminole, both twins, and not aware of it on Piper's larger singles. Anyone know?
 

msmspilot

Well-Known Member
He's speculating and so am I, although what I said is based on known characteristics of wings. Piper has not said specifically why they have two. All you can know for sure is that they found one inadequate. :)

For the engines to have anything to do with it, you'd have to have a mechanism for why the flaps make any difference to the airflow at the locations where the vanes are located. One that's plausible is that the lower pressure over the wing produced by the flaps moves the slipstream more inboard, which is something that does happen on some airplanes.

I've only heard of this setup on the Seneca and Seminole, both twins, and not aware of it on Piper's larger singles. Anyone know?
I'm pretty sure it's the same on the Saratoga. I haven't flown one in a few months, and it's late, but that seems right.
 

HangerBum

Well-Known Member
I do not know about other piper products but I know Beechcraft put them on the Duchess. The Duchess has one on each wing. I have flown both and I would agree that it has to do with the angle of attack. The stall indicators are located quite a ways out on the wing so I do not believe the engines would have anything to do with it.
 

tgrayson

New Member
The stall indicators are located quite a ways out on the wing so I do not believe the engines would have anything to do with it.
That's what I'd think too. The slipstream at the prop has about the radius of the prop arc itself, so I'm skeptical it'd have influence very far out on the leading edge.
 

tgrayson

New Member
I'm pretty sure it's the same on the Saratoga. I haven't flown one in a few months, and it's late, but that seems right.
Retrieved my Saratoga POH from the attic and it does indeed have two lift detectors.

Av8or91, ask your instructor to explain why the Saratoga has the same configuration as the Seminole, and watch him squirm. ;)
 

jynxyjoe

The Kickin' Chicken!
It is to make the Seminole even slower, louder, and most importantly it creates that extra resonance to vibrate the spinal column for that extra measure of comfort.
 

Screaming_Emu

Joe Conventional
Thats what I was thinking but instructor kept saying something along the lines of how the engines were mounted on the wings and could inadvertenly activate the stall warning horn:confused:. Thanks alot for confirming my orginal thinking:)
I believe where he got that idea from is the reason there is a squat switch which disables the lift detectors on the ground. Would be a long taxi if you had the right kind of crosswind going which blew the slipstream out towards the lift detectors "beep....beep..bee...beep
 

screennamie

New Member
What the hell is a Seminole "lift detector"


Cheers
George
I was thinking the same thing having flown the Seminole for my CMEL. I'm guessing from the conversation so far its the stall warning switches on the leading edge of the left wing.

There's lots of reasons why there's two. tgrayson has it right, also a wing will tend to stall near the root first working outwards leaving positive control to the ailerons.

Also the whole engine nacelle thing blocking or advancing stall characteristics of the wing. The root will act at the nacelle instead of the fuselage. I can see where your instructors coming from but tgrayson gets the blue ribbon.
 

Nihon_Ni

Well-Known Member
I believe where he got that idea from is the reason there is a squat switch which disables the lift detectors on the ground. Would be a long taxi if you had the right kind of crosswind going which blew the slipstream out towards the lift detectors "beep....beep..bee...beep
I don't believe there's a squat switch cut-out. If you can preflight the horn by lifting the vane, then there probably is not a cut-out. In my Seneca, you could preflight both vanes on the ground.
 

Cessnaflyer

Wooooooooooooooooooooooooooooooo
I do not know about other piper products but I know Beechcraft put them on the Duchess. The Duchess has one on each wing. I have flown both and I would agree that it has to do with the angle of attack. The stall indicators are located quite a ways out on the wing so I do not believe the engines would have anything to do with it.
Thats interesting. On the single version of the dutchess, the sundowner, it only has one flap.

One thing I heard from a Boeing engineer that I thought was funny, "It's weird that we can keep 100's of people safe with only using theory on how to make an airplane.
 

tgrayson

New Member
One thing I heard from a Boeing engineer that I thought was funny, "It's weird that we can keep 100's of people safe with only using theory on how to make an airplane.
Probably making a joke with respect to how laymen seem to think that “theory” means speculation, guessing, as in not proven. Not how scientists use the word “theory” of course. All of our knowledge of the world is embedded in theories, even the ones that are the most well-supported by the evidence and that no sane person would ever question, such as the germ theory of disease. Theories always remain theories, no matter how obviously true they are.

Now if that engineer has said they only use hypotheses to keep people safe, I'd be concerned.;)
 

Blip16

Well-Known Member
I don't believe there's a squat switch cut-out. If you can preflight the horn by lifting the vane, then there probably is not a cut-out. In my Seneca, you could preflight both vanes on the ground.
you can't, the right squat mutes them both on the ground
 
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