MPPalmer(at)aol.com
Guest
|
 Posted: Tue Jul 08, 2008 11:57 pm Post subject: Still on the "Case of the missing fuel" |
 |
|
Thanks all for your suggestions so far. Others have emailed me separately, off the list, suggesting I do the obvious and check our totalizer for accuracy, so that I'm chasing a red herring. (implied.)
Yes, I agree that's an obvious step. Unfortunately, in our plane, it's not so easy to do. Not accurately. See, I originally plumbed the Flowscan transducer after the FRAM fuel filter, just as it passed into the firewall and made a 90 degree turn in that old Glasair I fuel fitting they used to supply. It's a street type fitting (as opposed to a smooth mandrel bend) and proved to be too turbulent. We never got steady fuel flow readouts. So, in my brilliance, I moved the transducer to aft of the electric fuel pump, ahead of the FRAM fuel filter. The Flowscan is about 10 to 12 linear inches aft of the Faucet electric fuel pump. This works real well.... except when the electric fuel pump is on. Then the pulses from the pump pulse the transducer, causing it to read 2 GPH higher than nominal. (I can turn the pump on with the engine off and watch all day as the FF indicates about 2 GPH with no fuel moving through the system.)
The RV guys have this problem too and someone sells a $50 snubber that you Tee into the fuel line to mitigate the problem. Since we only run the electric pump on take off and landing, it's not been a real problem, and I've thought it a "feature" to have the totalizer read a little lower than actual remaining.
So that's the long story for why I haven't done the obvious and confirmed the totalizer is still accurate. But, I think I will fill the tanks and go for an hour flight without using the electric pump and see how much fuel I use on refill. When this whole "error" thing started a few months ago, I wondered if there wasn't some "fuzz" build up (a.k.a. "belly button lint") in the transducer. (I've seen this before in the finger screens way back in first flight days.) I should probably bite the bullet, disconnect the lines to the transducer and reverse flush it. (It's in an awkward position, it's hot outside! Even in our nights. And I can't see well enough with only one eye.)
I pulled one wing tip tonight and saw that all our wing tip vent fittings are behind the end rib. We had put a small inspection hole there and everything looked fine on that side.
I also ran the electric pump while setting the prop at 8 stations, twice around. I waited 2 minutes for each station, checking the header tank for any change in level or for any leaking fuel at the mechanical pump or any fumes or obvious leaks. None found.
I'm quickly running out of ideas. I will plan to top the main tank off tomorrow and blow the tip vents out again with the pressure of some fluid behind them. (Hard to explain in text, but we have a combination GI/GII wing tip vent system. I think they issued a SB or Advisory suggesting the topology we had come up with on our own... vent to the tip and tee off that to vent down to the center and stand pipe.
I haven't pulled the cowl yet to look around the carb... tomorrow's plan. But I didn't see any leaking for the half hour the pump was on tonight, pressurizing the carb.
One more possible "clue" I forgot to mention before ... when we ran out of fuel in flight on the main a few days ago, the main tank fuel gage was showing about 10 gallons remaining. (Which is what we expected was in there, but upon fill up, the tank was empty.) I should have looked at the gage again on the ground... that cork float hasn't been the most reliable thing. Maybe it stuck in flight and vibrated down on landing? But I'm wondering if I had some kind of weird suction in the stand pipe that could pull the float up (and somehow pull gas out too)? I know that when I changed out the FRAM filter this year, suction didn't break like it should have, and I ended up dribbling fuel for about 15 minutes after I broke the seal at the filter housing. It usually doesn't do that. (You know, I haven't done a visual inspection to see that the vent lines down the back of the wing are intact. Since one reporter reported a failure.... )
Keep those ideas coming, guys. No matter how obvious... or bizarre.
Thanks,
Mike Palmer <><
**************
Gas prices getting you down? Search AOL Autos for fuel-efficient used cars.
(http://autos.aol.com/used?ncid=aolaut00050000000007) [quote][b]
| | - The Matronics Glasair-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Glasair-List |
|
|
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
