Help, sporatic burning smell in cockpit!

[idleup]

You all are the most experienced pilots I know so I was wondering if anyone has ever had a sporatic smell of burning in the cockpit that only lasted long enough to take a single whiff and then went away? I had this experience three times on a 45 minute flight today in my Grumman Traveler and I was very worried I was having an electrical fire. However, once landed I could not see or small anything. No wires looked melted, nothing...

It is frustrating because it makes me not want to fly, yet there is no smoke, no signs of burning and it only happens sporatically. If anyone has had something similar or has any ideas I would love to know. Thanks.

- Matt

[mburch]

If I recall correctly, the Grumman electrical system has a zener diode that's supposed to be there to help protect against an overvoltage condition, but really acts as a sort of fuse that lets out all the magic electronic smoke when your voltage regulator starts acting up. I'd suggest getting the regulator tested (or test the whole alternator if it's the internally-regulated type) and also look for that diode... I think it's back up under the panel in a dark cranny.

And now for the RV-related content: After having dealt with the above issue on my AA1B, my RV-7 electrical system uses a real crowbar overvoltage protection circuit and breaker, not the cheezy Grumman setup!

Regardless, if it were my airplane I'd go over it thoroughly and not fly again until I found the problem. An in-flight fire is a possibility I don't even want to think about. Be smart and fly safe.

good luck,
mcb

[Geico266]

Also to add the "RV element" to this thread I too have noticed a burning smell in my RV's from time to time. Then I notice I have flown through some smoke!



Sorry I can't help you with the Grumman, but it sounds like Matt has you pointed in the right direction. Pull the alternator and have it checked out.

[osxuser]

I don't know the Grumman system specifically, but might also want to look at how much load is being put on your dimming circuits. In our Cardinal, the potentiometers (sp?) would heat up, at certain flight attitudes the airflow through the cabin brought the smell of hot electrical to our nostrils without there really being a problem. This annual we are changing both over to MaxDim's, which should solve the heat problem.

http://www.maxpulsemaxdim.com/maxdimproduct.htm

[az_gila]

...the Grummans have an air vent on the side just below the level of the cowl split. The flange that holds the retaining screws on the side of the lower cowling often breaks just in front of the air inlet, and this will let "engine smells" into the cockpit.

Check the flanges on the sides of the firewall... on my Tiger they have already been reinforced with an additional angle piece on each side.... and my Tiger is a low time one at 1800 hours.

Reference here.... http://grumman.net/archives/2002/msg01733.html


A schematic for an early Tiger (IIRC the Traveller has a very similar schematic) is here...

http://www.aucountry.com/ACA_Folder/...ire_76-77.html

...the diode referred to previously is the thing in the top left of the schematic, however is seems to be a one-time over voltage item.

An easy electrical check to perform is a measure of your bus voltage - which can be easily done in flight through the cigarette lighter socket.... an over-voltage situation should show up with this test.

The other check is to clean all of the 30+ year old terminals around the voltage regulator - and dump the original mechanical one (if it's still installed) for a later electronic one - my task for my next annual...

[RV10inOz]

Check your cabin heater.

Its amazing how a squirt of WD-40 or something that gets a drop or two around that area still manages to get into the cabin heat.

On a side note, through the Jabiru firewall (ply and fibreglass) comes the cabin heater, and the smell of warming plywood gets your nose rather alert Especially on a climb out with lots of heat!

DB