fuel mystery

Any DA42 related topics.

Moderators: Rick, Lance Murray

Post Reply
bd32322
2 Diamonds Member
2 Diamonds Member
Posts: 13
Joined: Sun Sep 02, 2018 11:33 pm
First Name: bodi
Aircraft Type: OTHER
Aircraft Registration: various
Airports:
Been thanked: 1 time

fuel mystery

Post by bd32322 »

Hello forum members. This is my first post and its about a fuel issue my instructor and I are puzzling over. I don't own a DA42 but am training for my multi-engine rating in one. On our last flight we ran into a problem that we don't quite have the answers to, so I thought I'd ask you guys.

We topped off the tanks with about 1 inch to spare from the top. The temperature was about 70 F and we were taking off from a sea level airport. As part of the checklist I ran both engines on cross-feed on the ground and both my instructor and I checked that we put the fuel selectors back to normal mode before takeoff. I noticed that the left fuel selector lever was considerably harder to move than the right.

We took off and did some engine out training and steep turns - a decent amount of time was spent in uncoordinated flight. Then after about 45 minutes into the flight my instructor noticed fuel streaming off the right wing and we noticed that we had used 10 gallons of fuel from the left tank and none from the right. So we headed right back to the airport and landed.

Upon landing we found the right tank full - about the same as what we had before takeoff.

My suspicion is that after I put the selectors into double cross feed on the ground and put them back into normal, the right engine cross-feed never went back to normal and continued to draw from the left tank. Both engines were drawing from the left tank I think.

It could also be possible that the return line for the left engine was going to the right tank and over-pressuring the right tank and causing it to vent. However, I think that way we would have lost more than 10 gallons in 1 hour.

Anyone ran into this?

Thanks,
Bode
User avatar
Colin
5 Diamonds Member
5 Diamonds Member
Posts: 2006
Joined: Sat Aug 21, 2010 8:37 pm
First Name: Colin
Aircraft Type: DA42
Aircraft Registration: N972RD
Airports: KFHR
Has thanked: 319 times
Been thanked: 527 times

Re: fuel mystery

Post by Colin »

I have chased constant fuel tank issues since getting the plane nearly three years ago. Just in the past week I ran into the problem you describe (got into the plane after an hour flight and noticed that one tank read FULL and the other was down ten gallons). Re-checked the fuel in the wings and sure enough one still seemed *pretty* full. Worked the crossfeed levers a bit, but I don't really know how those operate (they *must* change where the return fuel goes as well as where it is pulled from, otherwise you'd be removing a bunch of fuel from your useable amount, that can't be the design).

I mean, I know the function they are meant to perform, but I don't know how they do that. The alternate air, for instance, is a flap that flips in some planes and a CFII told a scary story of being in the clouds over the Sierras, pulling the lever for alternate air, having a cable snap, and the flap essentially blocking the airflow into the engine. I mentioned the story to a head pilot for a Diamond fleet and he described the mechanism for the alternate air in a DA42, where that sort of event is impossible (concentric cylinders which are perforated, moving the lever turns one so the holes line up, if it gets stuck you are just left with the air you had before). So I don't know how the fuel lever does its job and what failure modes would look like.

The fuel hoses are meant to be replaced every eight years (I think). I can't find that entry in my logbook and I believe I will just have the whole damn thing re-done in London. New transducers, new hoses, new valves. I think there's something a little gummed up.
Colin Summers, PP Multi-Engine IFR, ~3,000hrs
colin@mightycheese.com * send email rather than PM
http://www.flyingsummers.com
N972RD DA42 G1000 2.0 s/n 42.AC100 (sold!)
N971RD DA40 G1000 s/n 40.508 (traded)
User avatar
Karl
4 Diamonds Member
4 Diamonds Member
Posts: 318
Joined: Wed Aug 04, 2010 3:58 am
First Name: Karl
Aircraft Type: DA40
Airports:
Has thanked: 68 times
Been thanked: 102 times

Re: fuel mystery

Post by Karl »

Colin,

You are correct the return fuel does go back to the tank it came from. See attchement.

I suspect in both cases the problem is caused by incorrect rigging or that the levers are worn and the valve isn't fully closing.
Attachments
20180907_111755.jpg
User avatar
ememic99
5 Diamonds Member
5 Diamonds Member
Posts: 1078
Joined: Wed Apr 09, 2014 10:31 am
First Name: Emir
Aircraft Type: DA42
Aircraft Registration: SEMAD
Airports: LDZA LDVA
Has thanked: 203 times
Been thanked: 390 times

Re: fuel mystery

Post by ememic99 »

You can confirm correct operating by checking fuel temperature. The fuel temperature, for the side which is set to crossfeed, will be considerably lower.
Post Reply