Stall Warning System - Revision history

Bob Steward: spelling correction

2008-02-06T00:07:11Z

spelling correction

← Older revision		Revision as of 00:07, 6 February 2008
Line 88:		Line 88:
	Unfortunately, if the delay component has failed, there are theoretically no ''good'' replacements. The OEM delay device is time-limited, and the last new device was made in 1977. However, [http://www.fletchair.com/askanexpert/stall-delay.html FletchAir] has put together some information so that you can manufacture your own replacement. [http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=9016e79bd1447c39fc7b3ded63a0d9e9&rgn=div8&view=text&node=14:1.0.1.3.9.11.11.2&idno=14 14 CFR 21.303(b)(2)] permits an owner to produce his own replacement parts (but not for use on other owner's "products"). It is essentially an exemption from Parts Manufacturing Authority requirements. [http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgOrders.nsf/0/d134929f93b3334e8625708100582c1b/$FILE/Order%208110-42B.pdf FAA Order 8110.42B 1.5(d)] reiterates this regulatory guidance.		Unfortunately, if the delay component has failed, there are theoretically no ''good'' replacements. The OEM delay device is time-limited, and the last new device was made in 1977. However, [http://www.fletchair.com/askanexpert/stall-delay.html FletchAir] has put together some information so that you can manufacture your own replacement. [http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=9016e79bd1447c39fc7b3ded63a0d9e9&rgn=div8&view=text&node=14:1.0.1.3.9.11.11.2&idno=14 14 CFR 21.303(b)(2)] permits an owner to produce his own replacement parts (but not for use on other owner's "products"). It is essentially an exemption from Parts Manufacturing Authority requirements. [http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgOrders.nsf/0/d134929f93b3334e8625708100582c1b/$FILE/Order%208110-42B.pdf FAA Order 8110.42B 1.5(d)] reiterates this regulatory guidance.

	If the horn has failed, Bob ~~Stewart~~ pointed out above that modern piezoelectric horns may be suitable.		If the horn has failed, Bob Steward pointed out above that modern piezoelectric horns may be suitable.

Jbowman90: Adjusted size of sketches

2008-02-03T11:57:24Z

Adjusted size of sketches

← Older revision		Revision as of 11:57, 3 February 2008
Line 14:		Line 14:
	== Principles of Operation ==		== Principles of Operation ==

	<div style="float: right; width: ~~100px~~; padding: 0em 0em 0em 1em;">		<div style="float: right; width: 150px; padding: 0em 0em 0em 1em;">
	[[Image:stall warning normal.png\|~~100~~ px\|none\|Stall Warning Switch Open]]<br/>		[[Image:stall warning normal.png\|150 px\|none\|Stall Warning Switch Open]]<br/>
	[[Image:stall warning stalled.png\|~~100~~ px\|none\|Stall Warning Switch Closed]]		[[Image:stall warning stalled.png\|150 px\|none\|Stall Warning Switch Closed]]
	</div>		</div>

Jbowman90: Added images showing streamlines and position of switch

2008-02-03T11:54:47Z

Added images showing streamlines and position of switch

← Older revision		Revision as of 11:54, 3 February 2008
Line 14:		Line 14:
	== Principles of Operation ==		== Principles of Operation ==

	[[Image:~~streamline1~~.png\|~~thumb~~\|100 px\|~~Low Angle-of-Attack~~]]		<div style="float: right; width: 100px; padding: 0em 0em 0em 1em;">
	[[Image:~~streamline2~~.png~~\|thumb~~\|100 px\|~~Medium~~ Angle-of-Attack]]		[[Image:stall warning normal.png\|100 px\|none\|Stall Warning Switch Open]]<br/>
	[[Image:streamline3.png~~\|thumb~~\|100 px\|High Angle-of-Attack]]		[[Image:stall warning stalled.png\|100 px\|none\|Stall Warning Switch Closed]]
			</div>

			<div style="float: left; width: 100px; padding: 0em 1em 0em 0em;">
			[[Image:streamline1.png\|100 px\|none\|Low Angle-of-Attack]]<br/>
			[[Image:streamline3.png\|100 px\|none\|High Angle-of-Attack]]
			</div>

	The images to the right show the streamlines around an airfoil at progressively higher angles-of-attack. However, they do not show the separated streamlines typical of a stall. Notice that there is a streamline that terminates near the nose of the airfoil. The point of termination is called the stagnation point because this is where the flow reaches zero speed. More to the point, any streamlines above the stagnation streamline flow above the airfoil and any below the stagnation streamline flow below the airfoil.		The images to the right show the streamlines around an airfoil at progressively higher angles-of-attack. However, they do not show the separated streamlines typical of a stall. Notice that there is a streamline that terminates near the nose of the airfoil. The point of termination is called the stagnation point because this is where the flow reaches zero speed. More to the point, any streamlines above the stagnation streamline flow above the airfoil and any below the stagnation streamline flow below the airfoil.


	Stall warning devices take advantage of this phenomenon. On the Grummans, a small tab sticks out of the leading edge. For normal angles-of-attack, the tab is positioned so that it is located below the stagnation streamline so that the normal flow forces the tab down and keeps the stall horn switch in the open position. As the angle-of-attack increases to stall, the stagnation point moves below the tab, and the streamlines act to lift the tab and close the switch thus activating the stall horn. Cessnas use a pressure activated switch rather than a tab but basically measure the location of the stagnation point in a similar way.		Stall warning devices take advantage of this phenomenon. On the Grummans, a small tab sticks out of the leading edge. For normal angles-of-attack, the tab is positioned so that it is located below the stagnation streamline so that the normal flow forces the tab down and keeps the stall horn switch in the open position. As the angle-of-attack increases to stall, the stagnation point moves below the tab, and the streamlines act to lift the tab and close the switch thus activating the stall horn. Cessnas use a pressure activated switch rather than a tab but basically measure the location of the stagnation point in a similar way.

Jbowman90: Stall Horn moved to Stall Warning System

2008-01-31T12:01:28Z

Stall Horn moved to Stall Warning System

← Older revision		Revision as of 12:01, 31 January 2008
(No difference)

Jbowman90: short commentary on the time-limited nature of the OEM delay device

2008-01-31T04:56:16Z

short commentary on the time-limited nature of the OEM delay device

← Older revision		Revision as of 04:56, 31 January 2008
Line 24:		Line 24:
	== Preflight Checks ==		== Preflight Checks ==

	To check the condition of the stall horn on Grummans, the master switch must be on. For certain serial numbers, a delay was built into the stall warning system to prevent it from activating spuriously during slow flight and in turbulence. This delay was designed to be 0.9 seconds +- 0.1 second. After S/N AA-5A 0055 and AA-5B 0181, the delay was determined to be unnecessary and was discontinued. For AA-1 aircraft, this delay could also be optionally installed using Grumman American Accessory Kit # AK-123. This delay is important because some owners have preflighted their stall horn and wrongly concluded that it does not work without knowing about the delay.		To check the condition of the stall horn on Grummans, the master switch must be on. For certain serial numbers, a delay was built into the stall warning system to prevent it from activating spuriously during slow flight and in turbulence. This delay was designed to be 0.9 seconds +- 0.1 second. After S/N AA-5A 0055 and AA-5B 0181, the delay was determined to be unnecessary and was discontinued. For AA-1 aircraft, this delay could also be optionally installed using Grumman American Accessory Kit # AK-123. This delay is important because some owners have preflighted their stall horn and wrongly concluded that it does not work without knowing about the delay.

	== Troubleshooting ==		== Troubleshooting ==
Line 79:		Line 79:
	As some of the commentary above indicates, repair and replacement can be expensive. The switch appears to be approximately $900 new or $350 for an overhaul.		As some of the commentary above indicates, repair and replacement can be expensive. The switch appears to be approximately $900 new or $350 for an overhaul.

	Unfortunately, if the delay component has failed, there are no replacements. However, [http://www.fletchair.com/askanexpert/stall-delay.html FletchAir] has put together some information so that you can manufacture your own replacement. [http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=9016e79bd1447c39fc7b3ded63a0d9e9&rgn=div8&view=text&node=14:1.0.1.3.9.11.11.2&idno=14 14 CFR 21.303(b)(2)] permits an owner to produce his own replacement parts (but not for use on other owner's "products"). It is essentially an exemption from Parts Manufacturing Authority requirements. [http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgOrders.nsf/0/d134929f93b3334e8625708100582c1b/$FILE/Order%208110-42B.pdf FAA Order 8110.42B 1.5(d)] reiterates this regulatory guidance.		Unfortunately, if the delay component has failed, there are theoretically no ''good'' replacements. The OEM delay device is time-limited, and the last new device was made in 1977. However, [http://www.fletchair.com/askanexpert/stall-delay.html FletchAir] has put together some information so that you can manufacture your own replacement. [http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=9016e79bd1447c39fc7b3ded63a0d9e9&rgn=div8&view=text&node=14:1.0.1.3.9.11.11.2&idno=14 14 CFR 21.303(b)(2)] permits an owner to produce his own replacement parts (but not for use on other owner's "products"). It is essentially an exemption from Parts Manufacturing Authority requirements. [http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgOrders.nsf/0/d134929f93b3334e8625708100582c1b/$FILE/Order%208110-42B.pdf FAA Order 8110.42B 1.5(d)] reiterates this regulatory guidance.

	If the horn has failed, Bob Stewart pointed out above that modern piezoelectric horns may be suitable.		If the horn has failed, Bob Stewart pointed out above that modern piezoelectric horns may be suitable.

Jbowman90: Added Parts Repair and Replacement

2008-01-31T04:43:51Z

Added Parts Repair and Replacement

@@ Line 24: / Line 24: @@
 == Preflight Checks ==
-To check the condition of the stall horn on Grummans, the master switch must be on.  For some models of Grummans, the stall horn is ''designed'' to have a several second delay ostensibly to avoid spurious activation of the horn near but above stall.  Some have preflighted their stall horn and determined that it does not work without knowing about the several second delay.
+To check the condition of the stall horn on Grummans, the master switch must be on.  For certain serial numbers, a delay was built into the stall warning system to prevent it from activating spuriously during slow flight and in turbulence.  This delay was designed to be 0.9 seconds +- 0.1 second.  After S/N AA-5A 0055 and AA-5B 0181, the delay was determined to be unnecessary and was discontinued.  For AA-1 aircraft, this delay could also be optionally installed using Grumman American Accessory Kit # AK-123.  This delay is important because some owners have preflighted their stall horn and wrongly concluded that it does not work without knowing about the delay.
 == Troubleshooting ==
@@ Line 53: / Line 53: @@
 This kind of horn has been used as an inexpensive alarm sounding device for alot more years that than I can remember and basically it is a smaller (quieter) version of the way most auto horns were fabricated for years... and unless the coil inside is fried (open) you can normally free up the stuck reed by exercising it with your finger...  just press the reed up and down so that you hear a clicking sound this will indicate you have free'd up the reed and the bimetal strip should react to the em [electromagnetic] coil when it is energized.  I gave my assembly a quick shot of lps silicon spray, wiped it off, retested with the battery and "good to go",  master on, trip the stall switch, just like new.
 </blockquote>

Jbowman90: Added homebrew repair technique for stuck reed in horn

2008-01-31T04:02:30Z

Added homebrew repair technique for stuck reed in horn

← Older revision		Revision as of 04:02, 31 January 2008
Line 28:		Line 28:
	== Troubleshooting ==		== Troubleshooting ==

	The stall horn switch is located about midspan on the 4-seaters and is accessed via an access panel on the bottom of the wing. The switch on the 2-seaters is located near the wingtip and can be accessed by removing the fiberglass wingtip. The switch is held in place by a screw on the wing leading edge. The screw sits in a slot allowing for adjustment of the switch up and down. The horn ~~itself~~ is usually installed ~~near~~ the NACA inlet on the pilot's side.		The stall horn switch is located about midspan on the 4-seaters and is accessed via an access panel on the bottom of the wing. The switch on the 2-seaters is located near the wingtip and can be accessed by removing the fiberglass wingtip. The switch is held in place by an adjustment screw on the wing leading edge. The screw sits in a slot allowing for adjustment of the switch up and down. The horn is usually installed under the NACA inlet on the pilot's side on an L-shaped bracket.

	The indicators that the stall warning system is not working correctly include		The indicators that the stall warning system is not working correctly include
Line 46:		Line 46:
	# Activates in turbulence. The component that produces the delay may have failed. The delay is meant to prevent nuisance activation of the stall horn by relatively short duration angle-of-attack excursions cause by turbulence.		# Activates in turbulence. The component that produces the delay may have failed. The delay is meant to prevent nuisance activation of the stall horn by relatively short duration angle-of-attack excursions cause by turbulence.

	~~''Note:~~ ~~For~~ switch ~~failures, some~~ owners have reported blowing dust out/off of the switch ~~has brought~~ it back to life. Use low pressure compressed air such as the stuff in cans used for cleaning computer components. Spraying electronic contact cleaner into the switch may remove oxidation from the internal contacts. Also check for oxidation and corrosion on the external terminals.''		If switch failure is suspected, first mark the position of the switch on the leading edge. Remove the adjustment screw, disconnect the wiring, and test the switch using a multimeter. Some owners have reported blowing dust out/off of the switch bringing it back to life. Use low pressure compressed air such as the stuff in cans used for cleaning computer components. Spraying electronic contact cleaner into the switch may remove oxidation from the internal contacts. Also check for oxidation and corrosion on the external terminals.

			Horn failure can be tested by applying 12V directly to the horn terminals. One owner reported ...

			<blockquote>
			This kind of horn has been used as an inexpensive alarm sounding device for alot more years that than I can remember and basically it is a smaller (quieter) version of the way most auto horns were fabricated for years... and unless the coil inside is fried (open) you can normally free up the stuck reed by exercising it with your finger... just press the reed up and down so that you hear a clicking sound this will indicate you have free'd up the reed and the bimetal strip should react to the em [electromagnetic] coil when it is energized. I gave my assembly a quick shot of lps silicon spray, wiped it off, retested with the battery and "good to go", master on, trip the stall switch, just like new.
			</blockquote>

Jbowman90: Added material to the troubleshooting section. May need some more expert input and actual cases from GG.

2008-01-31T03:47:23Z

Added material to the troubleshooting section. May need some more expert input and actual cases from GG.

← Older revision		Revision as of 03:47, 31 January 2008
Line 28:		Line 28:
	== Troubleshooting ==		== Troubleshooting ==

	To be ~~completed~~ ...		The stall horn switch is located about midspan on the 4-seaters and is accessed via an access panel on the bottom of the wing. The switch on the 2-seaters is located near the wingtip and can be accessed by removing the fiberglass wingtip. The switch is held in place by a screw on the wing leading edge. The screw sits in a slot allowing for adjustment of the switch up and down. The horn itself is usually installed near the NACA inlet on the pilot's side.

			The indicators that the stall warning system is not working correctly include

			* Does not work at all
			* Operates in flight but not on the ground
			* Operates on the ground but not in flight
			* Activates at relatively high speeds
			* Activates in turbulence

			''Note: If you suspect a switch failure and want to remove it for testing, be sure to mark the position on the leading edge. Otherwise flight testing will be involved in getting it set in the correct position after troubleshooting.''

			# Does not work at all. If the stall warning system does not work at all, first try testing it on the ground. Be sure to engage the switch with the master switch on for at least several seconds. If it works fine on the ground, the switch may need adjustment upwards. The switch may be positioned too low to be activated by the movement of the stagnation point near stall. If it does not work on the ground, the culprit could be a bad switch, bad horn, blown fuse.
			# Operates in flight but not on the ground. During preflight, are you holding the switch up for several seconds? Some of the stall warning systems operate on a delay to prevent nuisance activation. Also, some owners have reported that the culprit turned out to be low battery voltage that prevented the horn mechanism from activating. Once the engine was running and bus voltage was at 14V, the horn worked fine.
			# Operates on the ground but not in flight. The switch may be positioned too low. The stagnation point never moves underneath the tab even at stall conditions, so the tab will never be lifted to the on position. Loosen the adjustment screw and move the switch up in 1/4 inch or smaller increments each flight until it activates at least 5 kts above stall.
			# Activates at relatively high speeds. The switch may be positioned too high. For normal angles-of-attack, the stagnation point is moving under the switch and activating it. Loosen the adjustment screw and move the switch downward in 1/4 inch or smaller increments each flight until it activates at least 5 kts above stall.
			# Activates in turbulence. The component that produces the delay may have failed. The delay is meant to prevent nuisance activation of the stall horn by relatively short duration angle-of-attack excursions cause by turbulence.

			''Note: For switch failures, some owners have reported blowing dust out/off of the switch has brought it back to life. Use low pressure compressed air such as the stuff in cans used for cleaning computer components. Spraying electronic contact cleaner into the switch may remove oxidation from the internal contacts. Also check for oxidation and corrosion on the external terminals.''

Jbowman90: Minor language and spelling changes

2008-01-31T02:33:39Z

Minor language and spelling changes

← Older revision		Revision as of 02:33, 31 January 2008
Line 1:		Line 1:
	== Introduction ==		== Introduction ==

	Although the Grummans typically give a good tactile warning when a [http://en.wikipedia.org/wiki/Stall_(flight) stall] is imminent, the stall horn adds an additional aural warning. For those that have not noticed, the tactile warning is the shaking of the yoke due to wing wake impingement on the horizontal tail near and while in the stalled condition. In this article, the applicable regulations are presented, ~~basic theory~~, why preflight checks of the stall horn sometimes fail, adjustments, and general troubleshooting.		Although the Grummans typically give a good tactile warning when a [http://en.wikipedia.org/wiki/Stall_(flight) stall] is imminent, the stall horn adds an additional aural warning. For those that have not noticed, the tactile warning is the shaking of the yoke due to wing wake impingement on the horizontal tail near and while in the stalled condition. In this article, the applicable regulations are presented, principles of operation, why preflight checks of the stall horn sometimes fail, adjustments, and general troubleshooting.

	== Applicable Regulations ==		== Applicable Regulations ==
Line 12:		Line 12:
	Because of the tactile feedback due to the aerodynamic qualities of the stalls in Grummans, an audible stall warning may not be technically required. However, the Grummans were certificated with the stall horn.		Because of the tactile feedback due to the aerodynamic qualities of the stalls in Grummans, an audible stall warning may not be technically required. However, the Grummans were certificated with the stall horn.

	== ~~Basic Theory~~ ==		== Principles of Operation ==

	[[Image:streamline1.png\|thumb\|100 px\|Low Angle-of-Attack]]		[[Image:streamline1.png\|thumb\|100 px\|Low Angle-of-Attack]]
Line 26:		Line 26:
	To check the condition of the stall horn on Grummans, the master switch must be on. For some models of Grummans, the stall horn is ''designed'' to have a several second delay ostensibly to avoid spurious activation of the horn near but above stall. Some have preflighted their stall horn and determined that it does not work without knowing about the several second delay.		To check the condition of the stall horn on Grummans, the master switch must be on. For some models of Grummans, the stall horn is ''designed'' to have a several second delay ostensibly to avoid spurious activation of the horn near but above stall. Some have preflighted their stall horn and determined that it does not work without knowing about the several second delay.

	== ~~Troublshooting~~ ==		== Troubleshooting ==

	To be completed ...		To be completed ...

Jbowman90: Minor formatting corrections

2008-01-31T01:23:15Z

Minor formatting corrections

← Older revision		Revision as of 01:23, 31 January 2008
Line 24:		Line 24:
	== Preflight Checks ==		== Preflight Checks ==

	To check the condition of the stall horn on Grummans, the master switch must be on. For some models of Grummans, the stall horn is '''designed''' to have a several second delay ostensibly to avoid spurious activation of the horn near but above stall. Some have preflighted their stall horn and determined that it does not work without knowing about the several second delay.		To check the condition of the stall horn on Grummans, the master switch must be on. For some models of Grummans, the stall horn is ''designed'' to have a several second delay ostensibly to avoid spurious activation of the horn near but above stall. Some have preflighted their stall horn and determined that it does not work without knowing about the several second delay.

	== Troublshooting ==		== Troublshooting ==

	To be completed ...		To be completed ...