View Full Version : C150 Stall Warning Test - It Sucks!
Menen
25th Oct 2004, 12:59
Tried to check the operation of the stall warning vane in the port wing of a Cessna 150. Slipped off the bloody ladder twice. Climbed up for the third time and blew into the apeture in the leading edge of the wing. Nothing happened. Placed a hankerchief over the slot and this time sucked. The stall warning actuated. So how come if the dynamic airflow hits the leading edge of the wing where the stall warning system is installed, you have to suck not blow? I thought that at the stalling angle of the wing, the air would angle into the slot not get sucked into the slot? Please explain?
TheOddOne
25th Oct 2004, 13:31
Menen,
Draw yourself one of those classic streamline drawings with the wing at an AoA of about 13 deg. You should wind up with the relative airflow broken into a stream passing over the upper surface and another stream passing under the wing. The place where the hole is in the leading edge on the C150 should be neatly in between these 2 streams. There is an area right in front of the 'nose' of the wing which is now in a lower pressure than the ambient or 'static' pressure. Thus there is created a net flow OUT through this hole, and also through the noise-making device. At lower AoA's of course, the hole is being subjected to the flow passing under the wing.
It may seem crude, but it doesn't rely on any external power to make it work and it's REALLY easy to check. The key thing here is to check that the path hasn't become obstructed, by insects, etc. I must admit I've never been hygenic enough to use a cloth when testing it, though! (Is that something to do with hiding our money under the soap?) Perhaps I will in future, having recently read about the person who died when they were stung in their mouth by a wasp that had gotten inside their drink of Coke.
Cheers,
TheOddOne
the wizard of auz
25th Oct 2004, 13:34
Think about where the LOW relative pressure is going to be approaching the stall.
I might add, don't EVER blow into anything on an aircraft. It could get very expensive for you.
You sound like you might need to have a yarn with your instructor to clarify a few basics. ;)
I got pipped at the post it seems.
Hempy
25th Oct 2004, 15:10
So how come if the dynamic airflow hits the leading edge of the wing where the stall warning system is installed, you have to suck not blow?
Kinky ...:eek: :yuk:
Sunfish
25th Oct 2004, 20:45
Menen, how tall are you? I don't know ANYONE who has to climb a ladder to get to the C150 stall warning port.
By the way the real reason for using a cloth is to avoid giving the aircraft herpes.
Gday Sunfish
The reason I use a hankie I don't want a mouth full of the huntsman that decided camp in there.
Cheers Q :p
Dookie on Drums
26th Oct 2004, 11:17
The reason I use a hankie I don't want a mouth full of the huntsman that decided camp in there.
Or the wasp I saw one FI inhale!!!:E
I believe he learnt his lesson:8
Menen
26th Oct 2004, 11:28
Merci beaucoup everyone. Love the replies and the humour. If it is an Aerobat and flying upside down in level flight would the stall warning still suck and not blow?
Horatio Leafblower
26th Oct 2004, 12:45
Um.... I don't think you could get an Aerobat to fly inverted in level flight... the donk would stop...
:confused: :ouch:
*Lancer*
26th Oct 2004, 14:08
Just because the engine's not running doesn't mean you can't do it (for a while at least)! :cool:
The whole system sucks, especially when it's working
even funnier when you go down to the aircraft and see the student you have never flown with before but eveyone wants to, sucking on the pitot tube thinking its a stall warning...... :E
manamana
31st Oct 2004, 20:51
Education for all! I didn't know some C150's had suction type stall warners, I've only ever seen 150/152's with vane type warners.
You learn something everyday.:8
Tinstaafl
31st Oct 2004, 23:41
That's interesting. In the thousand odd hours I have in C150s/152s I've never seen one with an electric vane type. All were suction.
How odd... :8
The Messiah
2nd Nov 2004, 02:28
Have never sucked on one and never will. Just checked it was clear and unobstructed. How is anyone going to know?
Please don't reply that I didn't satisfy the requirements of a daily inspection because I don't care.
Please don't reply that I didn't satisfy the requirements of a daily inspection because I don't care.
He's not The Messiah, he's a very naughty boy !
messiah you do realise you can use a tissue........
Why have a stall warning in the first place if you are not going to test it? For all the days when you will never hear it or... the day you are overworked, make an error, dont relise your approaching the stall and kill yourself close to the ground or you require a change of underwear....
save the underwear.. use toilet paper on the warning instead
Another reason for using a tissue or other 'barrier.'
Preflighted a C152 at dawn on a clear Adelaide morning one July a very long time ago.
Frost on the ground, aircraft skin around O degrees C.
Preflighting pilot leaves a bit of his lips stuck on the leading edge!
Ouch!
:O