J

Jon Clements

Well Known Member
I have installed long range tanks in the outboard leading edges on my RV-7 and I have cut holes for leading edge landing lights in the mid section between the tanks. The hole for the lights gives me access to the space between the tanks which accomodates the plumbing for the fuel lines and vent lines to the outboard tanks. I am planning to install the standard round vans 100w landing lights in this location. The landing light is approx 4 inches in front of the plumbing etc. For obvious reasons I am concerned about have high amp 12V wires in this location and I am also concerned (to a lesser degree) about the heat generated by the lights. I am definitely planning cover all the connections in the immediate area leading to the light with heat shrink. I am also planning to cover the back of the halogen bulb with a heatproof rubber boot of some description. I am interested in broad opinions regarding how safe this would be. I don't want to install the lights if there is any risk of them causing fire if the plumbing or tanks were to leak.......has anyone else installed lights in close proximity to their fuel tanks who could comment constructively?

Thanks in advance

JON.
 
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Jon,

Just a few thoughts for consideration.

The most likley as a result of a fuel leak would be a spark igniting fuel vapor which would more likely be an explosion rather than just a fire. In this case it doesn't matter where your landing lights are relative to the tanks as if there is a leak the wing wil quickly fill with vapor throughout.

Direct heat from the light will probably not cause ignition 4 inches away of raw fuel.

I am assuming you will be using the fuel from the aux tanks early in a flight and they will be empty at time of landing which is usually when you are going to use the lights. While this does not decrease the risk of spark and vapor at least there is peace of mind that you do not have a lot of fuel in proximity to the lights.

I would just suggest making sure that all electrical connections in the wing are tight and well sealed with heat shrink so as to decrease the probability of a spark.

If you are one of those in the habit of leaving nav or landing lights on during haze or in congested airspace you should add "LIGHTS OFF" to your daytime landing checklist. This is so if you crunch the landing you do not have live wires in the vicinity of a fuel tank that may rupture.

My short opinion is you are probably OK if you wire everything with care.
 
I built the same fuel tank setup on my 9A wings, and I had that same concern. I decided to put fuel transfer pumps between the tanks, and put HID landing lights in the wingtips.
 
Possible structure problem?

I knew I had read about mounting lights inboard somewhere; so I looked it up.
This is from the Duckworks website:


Can I mount the lights inboard from the last bay?
NO. Actually, there are some very good reasons to NOT mount them inboard:
1) It violates the 'D' structure that the wing skin forms forward of the main spar. In extreme load conditions this might weaken the wing, when done inboard. Since there is little bending load at the wing tip, mounting it out there is not a problem.
2) It does not provide as wide a field of view, especially on the ground.
3) It may reduce the 'be seen' effectiveness of the lights when used for traffic awareness.
4) It will cause more glare off of the prop disc in dark background situations. You need to keep light off of the back of the prop at night. Of course, moving them inboard by one bay won't be an issue, should you have a reason to NOT use the last bay (ie wing tip tanks or something).


L.Adamson --- RV6A
 
Milt / Greg / LA -

Good feedback. Thanks.

The spark/vapour scenario is my greatest concern.

The engineering aspect (weakening D structure) has been assessed and is OK.

I have already mounted the lights but may replace them with HID wingtip lights if I decide to go the safer route. The irony though is the leading edge tanks could also leak at the outboard end (less likely) and fill the tips with fuel vapour.

One idea i had was to drill a small hole (say 1/4 inch) in the perspex in front of the landing light. This would apply positive pressure into the middle bay which would then vent out through the hole for the tie down bolts. My theory is that in this case (if there was a leak) the vapour concentration would be minimised/significantly reduced.

Any further thoughts would be appreciated

R

JON
 
HID's maybe?

You could also install HID's to help decrease the amount of heat in the wing if you are concerned.

They are not as HOT as the 100W halogen's and put out a LOT more light. Even the low cost 35W lights from Duckworks are brighter than the 100W halogens.

Just a thought.
 
Jon Clements said:
Milt / Greg / LA -

The engineering aspect (weakening D structure) has been assessed and is OK.
Click to expand...

Then this comment is for anyone else considering installing a landing light in the leading edge just outboard of the fuel tank where the skin thickness has changed to .025" thick...

I have seen first hand, the skin deformation that takes place at this location during positive G static load testing of RV wing sections. Even as bad as it looks, the wings still have passed all tests (there is a previously tested wing section on display in the hangar at Van's Aircraft that you can inspect yourself) but because of what I have seen, I would never make a cutout at this location for a landing light and I strongly discourage anyone else form doing so either.
 
Scott -

Certainly food for thought to say the least.......can you advise whether or not the wings had the perspex fitted in the opening or not during the test. The perspex (to a limited degree) replaces the structure of the aluminum leading edge. If it proved to be a significant weakness point you could expect the perspex to crack/fracture under high G loading.

It is fair to say that this issue still concerns me because I will be doing aeros (but certainly not with fuel in the outboard leading edge tanks).

Anyone else want to chime in....?

Cheers

JON.
 
eurof2 said:
You could also install HID's to help decrease the amount of heat in the wing if you are concerned.

They are not as HOT as the 100W halogen's and put out a LOT more light. Even the low cost 35W lights from Duckworks are brighter than the 100W halogens.

Just a thought.
Click to expand...

I am thinking HID's are a good option but I need to feel 100% comfortable with the lights in that location either way.....
 
Jon Clements said:
Scott -

Certainly food for thought to say the least.......can you advise whether or not the wings had the perspex fitted in the opening or not during the test. The perspex (to a limited degree) replaces the structure of the aluminum leading edge. If it proved to be a significant weakness point you could expect the perspex to crack/fracture under high G loading.

It is fair to say that this issue still concerns me because I will be doing aeros (but certainly not with fuel in the outboard leading edge tanks).

Anyone else want to chime in....?

Cheers

JON.
Click to expand...


The tests that I am referring too were done with a plain wing. No landing light opening had been cut in the skin.
The reason for my comment is because the skin deformation during the test was severe enough that it makes me have to wonder what would happen if a landing light opening were cut at that location.

Just to show how things may not be as they would seem when making modifications, and that things need to be considered carefully...

You mention not doing acro with fuel in the outer tanks. If you did, it would actually make the bending moment at the location you install the light, slightly lower because of the additional weight outboard of that point. That doesn't mean you should do acro with fuel in the outboard tanks...the additional fuel weight adds many other factors to be considered.
 
Thanks Scott -

I will get the engineer who did the numbers on the outboard LE tanks to review for me and advise. I am aware that fuel in the outboard tanks would reduce the bending moment in the middle of the wing but i certainly wouldn't do aeros with fuel in the outboard tanks. Even if you were under aerobatic weight the fuel in the outboard tanks could have severe consequences in a spin condition.

Due to the weaker skin thickness of the outboard LE the tanks have doublers and stiffening angles installed to compensate. The middle bay (with the Landing light opening) has not been strengthened.

I may consider doubling the skin to the front D section of the middle bay to improve the strength of that area subject to further feedback from the engineer.

Thanks for your feedback....it is sowing some seeds of doubt in my mind so I will review this carefully with the engineer before deciding how to resolve.

Cheers

JON.
 
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