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Which flow controller are you using FM 200 or FM 300. I have the FM 250 but I don't see it on his web site now. I am not planning on using a fuel filter in my system. I need to double check, I believe the Andair gascolater has the same or very close mesh size he specifies.
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It’s the 125 micron filter. Not sure which flow controller he uses on the Thunderbolt engines.Rob Caldwell
Lake Norman Airpark (14A), North Carolina
EAA Chapter 309
Model B Quick Build Kit Serial # 11B-24B / 25B
YouTube Channel: http://bearhawklife.video
1st Flight May 18, 2021Comment
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Fuel filters are a common source of engine stoppages in homebuilts. So check and clean your filter frequently. MarkComment
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What Mark said.......
Probably most fuel pump failures started with a a clogged fuel filter. Larger yachts/ships have duel (or more) and selectable filters to they can change filters on the fly, and keep the engine running.
Aviation does it different. They will have 1 filter but a filter bypass circuit, in case it gets clogged. I think several brands of fuel filters have this bypass circuit for the homebuilt market. I don't have one yet, but will be buying one.Comment
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What.... so crud can bypass the first filter and immediately clog the second much smaller filter at the injection servo...Originally posted by svyolo View Post
Jokes aside, you are going to see the filter blocking gradually, and the pressure drop will be easy enough to observe and respond to. Been there. Unless you're using crud fuel or putting sand in your tanks, the filter won't block in a matter of hours.
Design, Ops, and Maintenance are the normal controls for that risk.
Design - the fuel system relies on the following sequential filtration to gradually filter out smaller and smaller particulates:
- Tank outlet strainers
- Gascolator with finer strainer
- Fuel pump filter
- Servo filter, fine gauze
Operationally - select fuel carefully, keep tanks closed, drain tanks and gas sump at each flight, and monitor fuel pressure over time.
Maintenance - filters are all checked each 100hr, the fuel pump filter is changed every couple of years.
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Doesn't the "pressure drop when filter clogs" depend on where the filter is in relationship to the pump and/or pressure transducer? If the filter is upstream from the transducer, you'd see a drop. But if the clogged filter is downstream from the transducer, you'll see a rise, right?
I went to an Oshkosh forum on fuel system design by a guy who designed fuel systems for one of the large defense contractors. He was adamant about using only filters with a "auto-bypass" capability, and running two of them back-to-back, so you still get some filtration in the event of a filter clog. I asked him about using one of the transparent fuel filters, where you can see the filter element. He said he would reluctantly agree that those are "OK" if you check them routinely as part of your pre-flight. That's probably what I'll do - downstream from the gascolator. -
Thanks for clarifying... Still learning about fuel injection systems. (Part of why I'm still leaning towards an old dirt-simple carburetor on mine...)
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Johnathon, that hasn't been my experience with clogged fuel strainers or filters. I have been on 2 yachts where the engine failed due to a clogged strainer (1 new, 1 20 years old). The only symptom was the engine stopped and wouldn't start. I have also had fuel filters clog in cars. Once, I did have a loss of power, but the engine still ran at idle. I was still stranded. I have also had a electric fuel pump get noisy, due to a clogging filter That was the only one I caught due to a symptom.
If I remember right, I do think I remember one airplane that I flew that had a "filter bypass" light that lit based on differential pressure. I think it was a 727. Long time ago.
A British Airways 777 crashed short of the runway in Heathrow a while back. Loss (reduced) of thrust at 800' on landing. Clogged fuel filter (ice). At least 1 A330 had the same thing happen at altitude during the same timeframe, but the ice melted as they desended.. Rolls Royce Trent series engine. The fuel system met all certification requirements. There were no defects in the original design.
In a car or boat, I would rather be stranded than destroy an engine or expensive fuel component. I will call for a tow. In an airplane, I would rather make it to a runway, save the airframe, and buy a new, overpriced fuel system component.
I can't remember the brand of filter that had a bypass circuit. Andair? But, I like it. I am not going to use a VPX, but it does have 1 feature I like a lot. You can see the load on every individual circuit. It would be nice to see a circuit with a higher than normal amps (like a fuel pump) before it fails or blows the breaker.Comment
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Even if everything is properly designed and maintained, the threat of one bad tank of gas still exists.Comment
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Our R-44 (IO-540) has 2 fuel warning lights. One is "Aux Pump Failure". Second is "Fuel Filter". If I recall, the pump light sensor is tee'd into the pump-to-filter line. On pressure drop, it grounds and completes the light circuit. The filter light sensor is tee'd into the filter-to-fuel servo line. On pressure drop, it grounds and completes the 'filter' light circuit. As the filter gets blocked, the light begins to flicker. If you ignore it long enough, the light gets steady bright. I guess if you ignore it long enough, you get to practice auto-rotation...
Thinking about it, there must be some additional circuit logic that disables the filter light, when the pump light is on. I’ve seen both lights, but never at the same time.
Note that I said "as I recall". I can do more research, if needed.
BillComment
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