Seminole lift detectors
- Thread starter av8or91
- Start date
tgrayson
New Member
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.
tgrayson
New 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.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. Thanks alot for confirming my orginal thinking
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
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.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?
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
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
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.
Screaming_Emu
Joe Conventional
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...beepThats 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
screennamie
New Member
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 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
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
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
you can't, the right squat mutes them both on the ground