Correct Orientation of 1948 Landing Light?

[CBogle]

Dear Members:

My '48 has a retractable landing light in the left wing that takes the GE4522 PAR 46 bulb. This bulb has a shield built into it that someone mentioned in another thread was supposed to protect the pilot from glare when down and lit. Assuming that this is the purpose of the shield, I would also assume that to protect the pilot, the bulb should be screwed in such that the shield is inboard, that is, on the right hand side facing the front, between the bulb filiment and the cockpit.

When I looked at my bulb installed in the aircraft yesterday, the bulb is installed such that the shield is outboard, on the left side of the filiment when facing forward.

Does anyone know with certaintly what this sheild is for and it proper orientation to the filiment when installed?

Thanks,

Curt - N4288V

[thammer]

I read that too. I've got two Grimes on my 140 and plan on checking the orientation of the bulb today. I know that the landing light mounting brackets for the 140 wing have a slight, maybe 5 degree, outboard offset that points the light slightly outboard. This is evident when you look at the notch in the bracket for the pivot point.

[GAHorn]

I haven't any specific information on this installation, but....just speculating...
The 5422 bulb undoubtedly has more uses than only for Cessna 170's. The shield will "block" the light emitted by the filament from being reflected by the outboard reflective surface, towards the cockpit. (The filament is beneath the rim of the outer lens and is not normally directly observed by the pilot. The pilot is, however, subjected to reflected light from the outer portion of the bulb.
This may be the intent of Cessna but not be the original intent of the mfr of the lamp, however. The filament also produces intense heat which will eventually darken the reflective surface, especially if the heat rising from the filament is allowed to directly impinge the reflector. A 4522 lamp (in a different installation) facing forward and oriented with the shield UP, would help protect the upper reflective surface from premature damage.

The PAR36 lamps have an index molded into the aft surface of the outer rim, in order to orient it properly with the lamp-holder. (Those who have re-oriented their 4509's so the filament is vertical will have noticed the tendancey of the lamp not to fit into an index. Later Cessna's used a slightly different lamp-holder which must itself be re-oriented to accept the bulb in any but the original horizontal-filament position.)

Does the 4522 lamp have an index on it's lip? Does the retractable landing light accomodate such?

[thammer]

Checked out the orientation of the grimes on my 140 tonight and looked over four other lights I have. The 4522 bulb has a male index notch on the back side of the rim on same side the shield arc is on. The bulb carrier inside the inner canopy has two notches, one on either side looking at the face of the bulb with the light extended. This would let you orient the bulb's shield to shade the pilot with a light on either side of the fuselage.

I haven't done a whole lot of night flying with the 140 but the few hours I have I hadn't noticed the light shining in my face. Both "shields" on my bulbs are on the outboard side of the bulb.

Incidentally, with the bulb in either of the notches the filament is horizontal. I recall seeing discussion somewhere that orienting the filament vertically was thought to prolong it's life. (besides George's post just above this one. )

Tye

[GAHorn]

Checked out the orientation of the grimes on my 140 tonight and looked over four other lights I have. The 4522 bulb has a male index notch on the back side of the rim on same side the shield arc is on. The bulb carrier inside the inner canopy has two notches, one on either side looking at the face of the bulb with the light extended. This would let you orient the bulb's shield to shade the pilot with a light on either side of the fuselage.

I haven't done a whole lot of night flying with the 140 but the few hours I have I hadn't noticed the light shining in my face. Both "shields" on my bulbs are on the outboard side of the bulb.

Incidentally, with the bulb in either of the notches the filament is horizontal. I recall seeing discussion somewhere that orienting the filament vertically was thought to prolong it's life. (besides George's post just above this one. )

Tye

I'd like it noted that I do not endorse the practice of orienting the lamp so the filament is vertical (as some articles suggest as a method of increasing lamp life.) I am not convinced that vertical filament orientation in a wing-mounted lamp is beneficial at all. (I do know that such vertical orientation reduces the illuminated area in front of the aircraft and that having tried it in my C-206 after reading such articles, I found the reduced illuminated-area unsatisfactory. Whether or not such gimmicks prolong lamp life, ... is less important to me than having the illumination directed in such as way as is useful. I'll replace lamps when they burn out, but I want maximum benefit from them whatever their life may be.)

[CBogle]

Guys:

It appears from your responses that at least in the '48 cessna 170 wing installation, due to the notches, it would not be possible to orient the bulb incorrectly. Based on all of the responses, I must conclude that the correct installation is with the shield outboard of the filiment.

I too have not had any glare problems landing at night with the bulb in this orientation. Thanks.

Regards,

Curt - N4288V

[steve grewing]

I checked my 4522 lamp orientation yesterday. The shield is on the inbd side. I can not see the lens itself from the left/front seat unless I lean forward and look at the assy from fwd of the doorpost. From that vantage point it is just visible. I turn it on in the vicinity of the airport at dusk/night and can see it reflect off the wing surface but it is not a nuisance. That and watching the amp meter spike tells me it is actually "on", sometimes I think it will shear the needle. Glad I have a 35 amp generator. It certainly does put out an abundance of light. I'm considering replacing it with leading edge mounted lights to save weight and expense.

Steve

[auxtank]

The pilot is, however, subjected to reflected light from the outer portion of the bulb.

I dont think this is true.

The outer portion of the reflective surface is angled away from the pilot. Absent a filament shield, light emanating from the filament and striking the outer surface will be reflected out the front of the lamp and not back towards the filament and the pilot. However––again, without a filament shield––light emanating from the filament in the direction of the pilot which does not hit the inner portion of the reflective surface will proceed directly towards the prop.

While positioning the filament shield on the pilot's side may protect the pilot to some degree from unreflected light, I think it is primarily meant to shield the prop from direct light.

In his article on the Grimes swing-down landing light and its installation in C120 and C140 aircraft, Neal Wright opines, "The 4522 shared another feature with like-type military landing lights in that it has a shield built in at the side of the filament. Its purpose is to prevent glare toward the side of the plane into the pilot’s eyes and prevent reflection from the prop." (Bottom of page 5) http://www.cessna120-140.org/forum/file ... s_2005.pdf

Additionally (on the top of page 6), Mr. Wright indicates that he received information from someone who had acquired two never-used swing-down assemblies. Apparently, tags still glued to the lamp face stated:

"This light is supplied for installation in the left wing. The filament shield of the lamp is toward the pilot. To make this unit suitable for right wing installation merely rotate the sealed lamp 180 degrees."

CBogle, Curt, has indicated that he has "not had any glare problems landing at night with the bulb [with the shield outboard of the filament]."

I have always flown with the filament shield on the inboard side, so I can not comment on performance in the opposite position. However, I interpret Curt's observation to indicate that filament-shield orientation is not as critical on 1948 C170 installations as it might be in some other applications.

However, Neal Wright's article seems factual, and I have no reason to believe that he made up the story about the factory stickers with instructions to install the lamp with the shield on the pilot side. So, I intend to continue to do so. YMMV.

Gordon Sandy
1948 C170

[CBogle]

Gordon:

Thanks for the insight and it appears that you may be quoting an origiinal installation source. I'll take a look at my bulb installation to determine how easy it is to change the orientation of my shield from outboard to inboard and give it a try if all it requires is re-inserting the bulb 180 degrees turned. It may be that I'm not noticing any glare issue either because I don't have anything to compare it to or it doesn't make much difference. I don't know the answer but it is worth a try. Thanks much for the input.

Regards,

Curt

[GAHorn]

The pilot is, however, subjected to reflected light from the outer portion of the bulb.

I dont think this is true.

The outer portion of the reflective surface is angled away from the pilot. Absent a filament shield, light emanating from the filament and striking the outer surface will be reflected out the front of the lamp and not back towards the filament and the pilot. However––again, without a filament shield––light emanating from the filament in the direction of the pilot which does not hit the inner portion of the reflective surface will proceed directly towards the prop.

While positioning the filament shield on the pilot's side may protect the pilot to some degree from unreflected light, I think it is primarily meant to shield the prop from direct light.

In his article on the Grimes swing-down landing light and its installation in C120 and C140 aircraft, Neal Wright opines, "The 4522 shared another feature with like-type military landing lights in that it has a shield built in at the side of the filament. Its purpose is to prevent glare toward the side of the plane into the pilot’s eyes and prevent reflection from the prop." (Bottom of page 5) http://www.cessna120-140.org/forum/file ... s_2005.pdf

Additionally (on the top of page 6), Mr. Wright indicates that he received information from someone who had acquired two never-used swing-down assemblies. Apparently, tags still glued to the lamp face stated:

"This light is supplied for installation in the left wing. The filament shield of the lamp is toward the pilot. To make this unit suitable for right wing installation merely rotate the sealed lamp 180 degrees."

CBogle, Curt, has indicated that he has "not had any glare problems landing at night with the bulb [with the shield outboard of the filament]."

I have always flown with the filament shield on the inboard side, so I can not comment on performance in the opposite position. However, I interpret Curt's observation to indicate that filament-shield orientation is not as critical on 1948 C170 installations as it might be in some other applications.

However, Neal Wright's article seems factual, and I have no reason to believe that he made up the story about the factory stickers with instructions to install the lamp with the shield on the pilot side. So, I intend to continue to do so. YMMV.

Gordon Sandy
1948 C170

That's good info, but my earlier comment is quoted out of context. The earlier comment was speculation that the bulb has other applications and that the shield may have other uses in those other applications. In any case, some of the light which the reflector (mostly) re-directs forward also splashes over toward the pilot. If that were not true then the shield would never be claimed to affect that tendency. This can be proven by using a light meter in the cockpit and measuring the effects on the meter with the light switched off/on. Or one can simply sit in the cockpit on a dark night, turn on the lamp, and see if the lamp can be detected to be on from the cockpit by looking out there at it. If you can see that the lamp is on...then "The pilot is ... subjected to reflected light from the outer portion of the bulb."

[blueldr]

For definitive information on the oriebtation of retractable landing lights, see the below thread on"Landing Lights" for Jan. 3rd by "auxtank".

[auxtank]

That's good info, but my earlier comment is quoted out of context.

George,

Yes, I took your comment out of context, but not with any intent to misrepresent your point, only for the sake of brevity. You are right: When the pilot looks at the light in the down and on position, he or she can tell whether it is on or not! However, that does not mean that the function of the filament shield is to " 'block' the light emitted by the filament from being reflected by the outboard reflective surface, towards the cockpit."

The earlier comment was speculation that the bulb has other applications and that the shield may have other uses in those other applications.

Reading various patents pertaining to filament shields in sealed beam lamps has satisfied me that such shields were not designed to prevent direct light from reaching portions of the reflector of a lamp until sometime in the late 1970s when they were proposed for that purpose in rectangular headlamps.

A 4522 lamp (in a different installation) facing forward and oriented with the shield UP, would help protect the upper reflective surface from premature damage.

My own observation indicates otherwise. The reflector of my recently-failed 4522 shows damage to the reflective surface on the same side of the lamp as the filament shield. It appears that, rather than preventing premature heat damage to adjacent surfaces of the reflector, the shield contributes to such damage. I think this can be attributed to the fact that the shield is designed and constructed to block light and not to reflect it. This fact is supported by patent information pertaining to materials used to construct filament shields. Blocking light in such close proximity to the filament (whose temperature is in excess of 2200 degrees Celsius when the lamp is lighted) causes the shield to become excessively hot. I think if you installed a 4522 with the shield in the up position you would subject the upper reflective surface to accelerated, rather than delayed, damage.

As the photos below show: from the pilots seat, only a sliver of the face of the lamp is visible; from the front edge of the windshield (outside the plane), the shield is visible and may, or may not, be masking a portion of the filament; and from the spinner, nearly all of the shield is visible, but the filament is not visible.

I think these pictures prove that orientating the shield on the inboard side of the lamp will prevent light from being radiated directly from the filament to the forward area of the aircraft where it could create an unwanted distraction by illuminating the spinning prop.





Gordon Sandy