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Led lighting, and LED replacement bulbs now on CS-STAN issue 4

It's not a huge heatsink.

My order of magnitude estimate for the thermal resistance, in still air, lamp in its normal orientation (i.e. shining horizontally), fins vertical, is about 5 deg C per watt.

At $300 each, these better have a decent life...

Shoreham EGKA, United Kingdom

I think using some heat conductive (aluminium oxide) grease would be a good idea.

Better use beryllium oxide or aluminium nitride if you can find them. BeO is as good a heat conductor as metallic aluminium (220 W/m·K), AlN is 170, while Al2O3 is only 40.

By the way, Peter, did you do any research on Aeroleds vs. Alphabeams that influenced your choice?

LKBU (near Prague), Czech Republic

The Aeroleds drew more current (on paper) so I thought they would be brighter

Plus I read a favourable review by another TB owner.

Otherwise they are all very similar.

Can you get berrylium oxide grease? The stuff is extremely toxic. Many years ago I used to use BEOX power transistor washers. Today one can't even buy them.

Shoreham EGKA, United Kingdom


The standard 4509/4591 halogen lamps have a quoted life of 25 hours

Are you sure? I used the 4509 for many years and they used to last around 100-125 hours. You are correct regarding the standad 4509.

Before and after

But as mentioned the cockpit annunciators do not work anymore. I am going to do an STCd mod to the current sensing PCB and sell it for USD 25,000. Shall I start a poll on how many would be interested? There will be a 90% discount to avionics shops, so demand should be more or less automatic.

I could not do any clever heat transfer arrangements because the lamps sit in very simple aluminium surrounds which have very little metal in them, so there wasn't any point in getting the heat to conduct into them.

The LED lamps are a bit thicker (in front of the mounting face) so the spring wire clips which hold the old lamps in place are no longer right and need to be slightly modified with pliers

Finally, the plastic bezel which goes around the lamps doesn't quite fit anymore and needs a little bit of trimming to accommodate the lamp shapes. If you don't do this, the plastic (probably very brittle from years if being heated by the old lamps) will crack when you put the screws in...

Total installation time 1hr.

The improvement in brightness is spectacular.

Shoreham EGKA, United Kingdom

If anybody wants the old lamps, drop me an email - it's in my profile. Free and free postage in the UK

They lamps are not marked with a P/N but I believe they are

GE 4509 landing light

GE 4519 taxi light

I would keep them as spares but already have a pair of spares in the toolbox.

Shoreham EGKA, United Kingdom

GE4509 is 14 Volts, so it is more likely a 4591 28V.

United Kingdom

This is the current sensing relay board in a TB20GT, and some pre-GT serials, though I have no idea of the changeover points

The three relays (2 lights, pitot tube is the rightmost one) switch at 2.2A 2.2A 1.6A.

An obvious mod which somebody might want to have a go at is to find a more sensitive version of these relays. The manufacturer of the relays "TEPA PARIS" does not come up on google, however, and I have never come across relays such as this. I imagine they are reed relays, and probably of a low current rating because Socata put 15 ohm resistors in series with the contacts, to limit the inrush current of the incandescent lamp in the panel annunciator.

Early TBs had a different board

which looks like it has the same connections but actually the current sensing, and relay contact, terminals are swapped over!

The original lamps are now sold, BTW.

Shoreham EGKA, United Kingdom

I don't know how keen you are to do this, but you could replace the reed switches with a more sensitive one. We used to buy a lot of reeds from Hamlin, and I believe they still exist as part of Littelfuse.

The sensitivity is quoted in Ampere Turns, so your choice is either to leave the coils alone and change the reeds, or to add some turns. The latter might need some thought to avoid excessive heat generation, but enamelled wire is available in so many sizes and the DC resistance is in the wire tables.

If you change the reeds the top tip is not to bend the leads, or cut them if possible.

Most reed switch contacts take 0,5A easily but you need to limit the peak current, hence the resistors

Darley Moor, Gamston (UK)

I used the Whelen PAR's on my old plane, the Commander. They reduced the wattage draw from around 500W down to less than 80W, still providing same brightness if not more. I'm going to replace them on the Aerostar as well, but here I'll probably go with the Alphabeams, as they're brighter. The Aerostars small central lightbox restricts the lights spread a bit, so the brighter the better. I wish there was a mod to put an extra landing light in each wingtip, as well. That would really help on dark nights. But I'm afraid there isn't.

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