skihigh2002
Posts: 299
Joined: Tue Jun 27, 2000 11:17 am

Stall Warning Tab On PA-44 Piper Seminole

Thu Aug 25, 2005 3:26 am

If someone could help me figure this question out, I'm a Commercial Multi-Engine pilot and I'm not sure as to the answer:

The PA-44 has two stall warning tabs because of various flap changes. But the stall warning tabs are linked to the squat switch. So, when the aircraft is on the ground they do not engage. Why is that? Other airplanes, such as the PA-32 Piper Arrow have stall warning tabs but they are not linked to the squat switch.

A possible explanation I have is the fact that once the aircraft lands you do not want the stall warning horn blaring because the aircraft is below stalling speed. But why is is different on the Seminole from any other GA aircraft?

Thanks,
Chris
 
LeanOfPeak
Posts: 496
Joined: Thu Oct 21, 2004 2:18 am

RE: Stall Warning Tab On PA-44 Piper Seminole

Thu Aug 25, 2005 3:53 am

Not sure about your question, but the Arrow is the PA-28R. The PA-32 is the Cherokee Six/Lance/Saratoga/6X series.
 
lowrider
Posts: 2542
Joined: Wed Jun 30, 2004 3:09 am

RE: Stall Warning Tab On PA-44 Piper Seminole

Thu Aug 25, 2005 4:55 am

Stall speed will vary greatly. I would guess that Piper found that the stall horn was prone to inadvertent activation on the ground or during TO/lndg roll. Call Piper, I am sure they know the answer.
Proud OOTSK member
 
KFLLCFII
Posts: 3174
Joined: Sat Sep 11, 2004 7:08 am

RE: Stall Warning Tab On PA-44 Piper Seminole

Thu Aug 25, 2005 7:45 am

Per the PA-44-180 Information Manual:

7.33 Stall Warning (para. 3)

The stall warning horn is activated by two lift detectors on the leading edge of the left wing, outboard of the engine nacelle. The inboard detector activates the horn when the flaps are in the 25 and 40 degree positions, the outboard when the flaps are in positions less than 10 degrees. A squat switch in the stall warning system does not allow the units to be activated on the ground.


My assumption is that since there is a turning prop (when the left engine is running) in close proximity to the switches, there is a good chance that the airflow produced by the prop could inadvertently activate one or both switches on the ground if the circuit wasn't linked to the squat switch. Since the outboard blade on the left engine ascends, there a strong probability that the outflow from that blade could get under the lift detector and lift it up (thereby activating the horn if the circuit was linked to the squat switch).

Why this shouldn't apply to singles? The lift deflector(s) are much further away from the turning prop than on the multis.
"About the only way to look at it, just a pity you are not POTUS KFLLCFII, seems as if we would all be better off."
 
modesto2
Posts: 2669
Joined: Sun Jul 16, 2000 3:44 am

RE: Stall Warning Tab On PA-44 Piper Seminole

Fri Aug 26, 2005 3:25 am

Based on explanations from instructors, I agree with KFLLCFII. The airflow off the #1 engine could accidentally activate either stall tab. Any other theories?

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