FlyingMonkey Posted February 20, 2023 Report Share Posted February 20, 2023 Hey All... I am currently embarking on a project to replace all of my fuel and oil lines with Teflon hoses with stainless steel braiding, integrated fire sleeves, and AN fittings from Aircraft Specialty. In prep for this I pulled the entire fuel system aft of the firewall, which is frankly pretty Mikey Mouse: I have never liked the number of clam points and the fuel filter being behind the firewall. So I think when I have the new hoses made, I will have an upper firewall hose and a lower firewall hose, with the valve in between and no filter. WHAT, NO FILTER OMG YOU'LL DIE!!! Hear me out. I'm planning to buy a second filter, and place one at each wing line where they exit the windshield pillars next to the BRS harnesses. In addition to minimizing leak potential behind the panel, it also: * Makes maintaining and checking the screens easier and more accessible. * Gives a screen per wing, so if one totally blocks up, you still have fuel flow from the other wing. I can only think of one possible downside. I run 93 octane ethanol mogas, and I have a slight concern about the possibility of vapor lock. I think wrapped in firesleeve and in the location they'd be in, it would not be an issue, but I want to get the forum take on this. I will certainly do extensive ground run up and heat soak tests before flying it, and I could probably rig up some blast tubes if that seemed needed after testing. Thoughts? Quote Link to comment Share on other sites More sharing options...
Anticept Posted February 20, 2023 Report Share Posted February 20, 2023 Honestly don't bother with the filters. That's what your gascolator is for; it's a filter and a sediment bowl to catch things and get it to settle to the bottom to be drained out. You should reduce as many flow restriction points as possible in a fuel system. If you're worried about large debris, check and see if your SW has the large screens in the wings. I still think it's a design flaw that we don't have sumps in the wings (just one per side would be enough), but it's not a dealbreaker. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted February 20, 2023 Author Report Share Posted February 20, 2023 7 minutes ago, Anticept said: Honestly don't bother with the filters. That's what your gascolator is for; it's a filter and a sediment bowl to catch things and get it to settle to the bottom to be drained out. You should reduce as many flow restriction points as possible in a fuel system. If you're worried about large debris, check and see if your SW has the large screens in the wings. I still think it's a design flaw that we don't have sumps in the wings (just one per side would be enough), but it's not a dealbreaker. That is a possibility. I have never had more than a few grains in my screens, but that doesn't mean there could not be in the future if the fuel tanks start breaking down. The gascolator does have a super fine mesh screen in it. I'm more worried about trash in the fuel valve though, which is ahead of the 'lator. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted February 20, 2023 Author Report Share Posted February 20, 2023 Corey, if I keep the filters forward of the firewall do you think vapor lock is a valid concern, or just "vapor"? It seems there are plenty of other hotter locations in the fuel system (like the fuel pump!) that lock could occur, if it were going to happen. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted February 20, 2023 Report Share Posted February 20, 2023 Braided stainless will not work. There are some issues in the hose routing that can be a serious problem. Additional filters are a choke point. I have done all AN fittings everywhere but took a lot of work to get it right. I sent you an email to call me. I will save you a lot of time and $. Quote Link to comment Share on other sites More sharing options...
Anticept Posted February 20, 2023 Report Share Posted February 20, 2023 1 hour ago, FlyingMonkey said: Corey, if I keep the filters forward of the firewall do you think vapor lock is a valid concern, or just "vapor"? It seems there are plenty of other hotter locations in the fuel system (like the fuel pump!) that lock could occur, if it were going to happen. Don't bother with a filter. Again, this is what gascolators are for. I think the reason FD used an inline fuel filter is because originally they were using floscan fuel flow meters, which have a helical design causing the fuel to flow AROUND the impeller... you can see how intolerant of debris that could be. Which I should say, if you have a floscan... maybe you should keep the filter for now. Convert to the red cube when you can and get rid of inline fuel filters completely. The fuel pump is good enough to recirculate the fuel forward of the firewall. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted February 21, 2023 Report Share Posted February 21, 2023 The fine filter was there to protect the fuel flow sending unit from debris. If you have the sender then you need the filter before it. This wasn't FD's idea, but Flowscan's. Quote Link to comment Share on other sites More sharing options...
Anticept Posted February 21, 2023 Report Share Posted February 21, 2023 Which is why I advocate for the red cube. It's a straight through design like most sensibly designed aviation fuel transducers, and the filter isn't necessary as a result. Floscan doesn't exactly have a great reputation in the marine industry when it comes to debris either, and that's the industry it was designed for. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted February 21, 2023 Report Share Posted February 21, 2023 The Red Cube doesn't spec an upstream small particle filter on installation, but your better off putting one in. Why take a chance for a couple dollars. Remember: An ounce of prevention is worth a pound of cure. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted February 21, 2023 Author Report Share Posted February 21, 2023 12 hours ago, Roger Lee said: The fine filter was there to protect the fuel flow sending unit from debris. If you have the sender then you need the filter before it. This wasn't FD's idea, but Flowscan's. 12 hours ago, Anticept said: Which is why I advocate for the red cube. It's a straight through design like most sensibly designed aviation fuel transducers, and the filter isn't necessary as a result. Floscan doesn't exactly have a great reputation in the marine industry when it comes to debris either, and that's the industry it was designed for. Ah, this all makes perfect sense. I have the cheapo small engine gauges and no fuel flow, so totally unnecessary for me. I'll plan on deleting it. I love making things simpler and removing maintenance items! Quote Link to comment Share on other sites More sharing options...
Anticept Posted February 21, 2023 Report Share Posted February 21, 2023 1 hour ago, Roger Lee said: The Red Cube doesn't spec an upstream small particle filter on installation, but your better off putting one in. Why take a chance for a couple dollars. Remember: An ounce of prevention is worth a pound of cure. If it were only that sure, but you're adding a restriction to a fuel system and I've had engine outs from debris clogging that thing. Gascolator design is far superior. Everythings give and take, rarely is it just benefits, and this fuel filter isn't one if you have a red cube and intact upstream in wing screens. If you have a floscan then yes, keep it, because that thing is junk and can't take any debris. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted February 21, 2023 Report Share Posted February 21, 2023 Speaking of gascolators this is the way to go if you're ELSA. Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted February 21, 2023 Report Share Posted February 21, 2023 I assume that one of the hose drains is the breather off the oil tank, but what is the other? Quote Link to comment Share on other sites More sharing options...
Madhatter Posted February 21, 2023 Report Share Posted February 21, 2023 Fuel pump seal drain Quote Link to comment Share on other sites More sharing options...
Tom Baker Posted February 21, 2023 Report Share Posted February 21, 2023 I always thought that the lower opening on the cowling was an area of low pressure. Because of rotax's instructions I have always avoided placing that line there. Quote Link to comment Share on other sites More sharing options...
Anticept Posted February 21, 2023 Report Share Posted February 21, 2023 That's correct, the fuel drain shouldn't be placed in an area of negative pressure. Cutting a couple notches in the tube should help though if you want to insist on the fuel drain being left down there. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted February 21, 2023 Report Share Posted February 21, 2023 Well I sure don't want it inside where the exhaust is. The hose lays against the bottom cowl just inside. Quote Link to comment Share on other sites More sharing options...
Anticept Posted February 22, 2023 Report Share Posted February 22, 2023 I do agree. I just put them just inside zip tied to the t mount Quote Link to comment Share on other sites More sharing options...
Jim Meade Posted February 22, 2023 Report Share Posted February 22, 2023 Was there a shield forward of the gascolator before? Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted February 22, 2023 Report Share Posted February 22, 2023 Neither the fuel pump drain or the oil tank drain hose is supposed to be out in the air steam. They should be back up in the cowled portion about 2". Leaving the fuel drain hose in the vacuumed air stream can cause it to leak. Just had two cases like this. The oil tank drain is not supposed to be in a negative or positive pressure area. The oil tank hose should also have a little "V" notch cut in it about 8"-10" back up on the hose so it can never be blocked. It is the engine's only vent for the returning oil air pressure of 5 psi to vent off. This is in the installation manual. Changing things without knowing why it was done the original way isn't usually a good idea. Knowledge is key to help guide our ideas. Research in depth first then modify. There may be more than one way to skin the proverbial cat to achieve a goal, but when you don't do your due diligence first it may turn into an elephant to skin with bad results. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted February 22, 2023 Report Share Posted February 22, 2023 Like I said the hoses lay against the bottom cowl inside. Also the shield for the gascolator was removed for the photo. V notch on the oil hose is so moisture coming from the tank doesn't freeze at the end of the hose and block the opening. This is generally for breather lines in the slipstream on most all aircraft. Quote Link to comment Share on other sites More sharing options...
Anticept Posted February 22, 2023 Report Share Posted February 22, 2023 The notch in the oil breather tube is called the whistle slot Quote Link to comment Share on other sites More sharing options...
Madhatter Posted February 22, 2023 Report Share Posted February 22, 2023 That is correct Anticept. One more point, if the breather line is in the slipstream and there is a notch on it inside the cowl there will be no low pressure differential applied to the oil tank. I have no issue in following most recommendations for FD however some are poorly thought out and and a few are risky to the mechanic or pilot. LSA is not like certified and is not scrutinized as well. The maintenance qualifications are also minimal ( no offense to anyone who goes beyond the requirements). A few days coarse for LSA vs 2000hrs classroom instruction for an A&P is a huge difference. And even after that you are minimally qualified as an A&P. There is nothing wrong with making changes but you better understand everything about it. Just my 2 cents Quote Link to comment Share on other sites More sharing options...
Anticept Posted February 22, 2023 Report Share Posted February 22, 2023 Those are rotax recommendations, not FD recommendations by the way. Everything else I do agree on. That said, to be fair with A&P schooling, a tremendous amount of it is focused on big aircraft. I want to say around 1/3rd of my courses could have been left out and I'd still be fine in GA. Quote Link to comment Share on other sites More sharing options...
Madhatter Posted February 22, 2023 Report Share Posted February 22, 2023 43 minutes ago, Anticept said: Those are rotax recommendations, not FD recommendations by the way. Everything else I do agree on. That said, to be fair with A&P schooling, a tremendous amount of it is focused on big aircraft. I want to say around 1/3rd of my courses could have been left out and I'd still be fine in GA. By saying FD I was referring to the entire aircraft. A&P today is nothing like it was in years past. I had to weld 4 hours a day for 3 months and is no longer required today. All my teachers were WW2 and prior, same ones Gene Kranz had. I was involved 24/7 in airplanes even built one in my room at the school, the room open space was 13 1/2 feet and wings 13 feet. The school administrators were not happy with it but I didn't care. As I've said before you don't have to be an A&P to be competent just persistent. The best mechanic/rebuilder/ builder I have ever known is not an A&P. His talents exceed anything I have ever seen in my lifetime. Regardless you will still make mistakes, just don't give up, ever. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.