I believe I have the same exact fuel pump in line on my 2003 Airborne 912. I've had it mounted for several years now. I always turn it on before take off and leave it on until at cruise altitude. Then turn it on again for landing. 680 some hours and never had any problems. I would love to know if it was a pump problem or a foreign substance blockage problem. Has anyone heard of this happening with a facet failing in this fashion? I can't make it to Elk River later this month but I can make it this Friday. Inquiring minds NEED to know if I should go to parallel lines or is there another explanation.
Hey David, I couldn't find your triple post, but then realized that the convo had jumped to a second page. That always screws me up too when that happens. Go to bottom of page and click on "2" or "Next" then you can see the convo continuing.
Xc when I posted I didn't see the post come up.than because I spoke about nsa I got really frightens and thought wow they really are listening and deleting my post.than I said to hell with that I'll post it again and when that didn't show up I really got scared and said to myself.my great great grandfathers were decorated vets in the revolutionary war.than I got mad and said Iam gonna say what I feel to hell (freedom of speech) right? Than I realized they were posting on front page but couldn't delete the duplicates.what do they think a paranoid society is a safe society!
Jeff - I'm rethinking the install of the auxiliary fuel pump concept. I have questions regarding an inflight failure of the primary Rotax pump. Namely, will the auxiliary pump be able to push gas through the primary pump if it fails and if so - at what pressure?
What I think would be adequate is installing the Facet auxiliary fuel pump in a parallel system. That is drawing fuel off of the main line (after the fuel filter) via a T fitting to the auxiliary. Then injecting it into the fuel supply line AFTER the Rotax pump thereby bypassing it in the event of a failure. Doing this would require two check valves. The fuel would run through the Rotax pump, through a check valve (preventing back flow) and then a 'T' fitting. The second check valve would be placed between the T fitting and the auxiliary fuel pump. In this fashion, either pump can fail and you'd still be able to supply gas to the carbs. You can also do a ground check before each flight of the auxiliary pump simply by switching it on (before engine start) and seeing adequate fuel pressure supplied to the carbs. (I have a fuel pressure sensor in my system). Then switch it off knowing your reserve pump is functioning properly. You don't need additional fuel pressure for take-offs and landings.
This adds complexity to the fuel system and I have not researched the 1/4" check valves on the market. These check valves would absolutely have to be totally reliable. But you would truly have bypass supply of fuel to the carbs with a flick of a switch.
Since I had an in-line failure of the auxiliary pump creating an inflight emergency, installing it as you currently have it I now consider to be inadequate and dangerous.
My question to the crowd here is - does anyone know of any simple and totally reliable fuel check valves with 1/4" fittings?
POOR DESIGN AND INSTALLATION OF THE FUEL SYSTEM IS THE MOST LIKELY REASON IF YOUR FLIGHT ENDS TOO SOON. This article can help prevent that.
Engine failures are rare. Almost all so called "engine failures" are returned to service without ever working on the engine itself. Its the systems that support the engine which usually fail ... and fuel systems fail more often than all other things combined. Most of those failures are easily prevented.
A WORD OF CAUTION This subject always brings out the internet "experts". If any readers doubt that real people can be as screwed up as some of the "experts" mentioned in this article they should check the archives of the engines-ul2 list starting Nov 6, 2007. Just that one discussion included many of the "expert" claims mentioned in this article.
FUEL Most American pumps have a label on them which shows the advertised octane was calculated as RON plus MON divided by two. European countries use the RON method only. If your engine manual says to use 91 RON then you can use American 87 octane gas since its the same as 91 RON.
Aviation fuel is often called 100LL. Its 100 octane but the low lead part is misleading. It does have less lead than aviation fuel had years ago but it still has much more lead than automotive gas. That lead is hard on our type engines because it fouls plugs and causes rings to stick if we use it on a regular basis. A few gallons of aviation fuel once in a while doesn't matter much but I still avoid it as much as I can.
Some "experts" claim that the volatiles evaporate out of gas rapidly so fuel goes "stale" fast. There is a tiny bit of truth in that but it certainly doesn't happen very fast. How long does gas have to sit in your car or lawn mower before you notice any difference? In my plane 3 or 4 weeks certainly doesn't cause any problems and I have gone twice that long with only a very minor difference in the performance ... and I even premix the oil with my fuel. Don't get paranoid about "stale" gas.
Gasoline picks up small flakes of rust and dirt as its pumped hundreds of miles through underground pipe lines. The large storage tanks at the end of the pipeline add water and more crap. Even the truck that delivers gas to your local gas station may contribute and of course water and crap in the gas station tank gets stirred up when the tank is filled. Gas companies try to filter the gas and most even have a filter right at the pump nozzle but some water and crap always gets to our tanks.
Some pilots filter the gas going into the tanks on the plane with felt or chamois cloth and some use a Mr. Funnel. It doesn't matter what you use to filter your fuel or how careful you are to avoid condensation in the tank, sooner or later there will be water and crap in your tank so your fuel system has to handle some of it.
ELECTRIC FUEL PUMPS The Mikuni pumps are designed to suck fuel up to the engine and can easily handle the 3 or 4 feet of vertical lift needed with our engine and tank locations. Faucet recommends mounting their electric pumps below the fuel tank because they can NOT produce much suction.
Many people think that an electric fuel pump is a way to provide an extra margin of safety. That's okay but make sure that you understand what you are doing or you can wind up LESS safe. Dual pumps can be used safely but you need to do it correctly.
If you use pumps in series each pump must provide enough fuel pressure by itself in case the other pump fails. With both pumps running there is too much pressure at the carb. To prevent that you need a pressure regulator but then you depend on ONE regulator to keep working. Wasn't your orginial concern that you depended on ONE fuel pump to keep working? What have you gained?
There was an article on two pumps in parallel published in an UL magazine which assumed that Facet pumps had a check valve built in. One friend crashed when he had fuel starvation with that setup. I made another friend do some tests before he flew that setup and we found out that he would have also had fuel starvation problems. That article was published about 2002 but that same bad assumption is still floating around on some web sites.
We normally use the Facet 40104 or 40105 pump where the fuel tanks are in the wings. Where the fuel tanks are mounted low in the plane we usually use the Facet 40106 so the carb sees enough pressure. Check them out at
The labels on top of the columns are screwed up but if you study the info you can figure out that NONE OF OUR PUMP MODELS have a check valve built in. Hint .. If you shift the label "fitting size" to your left to be in line with the fitting descriptions of the model numbers then the columns on the right will match up better and make more sense.
The bottom line is this. When there is more pressure at the outlet port than is being created by the pump, fuel will flow backwards through the pump. Any time you use more than one pump you should install a check valve on the outlet of each pump to prevent reverse flow of fuel through the pumps.
With engines mounted high and fuel pumps mounted low there is one PSI pressure on the pump outlet port for every 37 inches in height just from the head pressure of the fuel in the line up to the carb ... even with the engine off and the pump not running. For discussion, call it 1 to 2 PSI head pressure at the pump outlet when the pump is off.
Fire up the engine and the Mikuni will add 4 to 7 PSI to the top of that head pressure and give about 5 to 9 PSI total at the electric pump outlet. If the electric pump can only pump 6 PSI, fuel from the Mikuni goes backwards through the electric pump even when it is running. The end result is less fuel available for the carb than was available before you installed the electric pump.
Don't believe it? Go out to the flight line and find any plane thats running an electric pump in parallel with a Mikuni. Pull the suction line off the suction port of the electric pump and plug that line. Fire up the engine on the Mikuni and watch the gas pour out of the electric pump suction port at high engine RPMs. A 10 buck check valve from McMaster-Carr installed at each pump outlet is cheap insurance and cures that problem. Part number 7775K51 has a Viton seat which is rated for gasoline and it only takes 1/3 of a pound of pressure to open it.
If you do the same test on the Mikuni while you run on the Faucet pump you may find that it can leak back too because the flapper valves inside the Mikuni can leak pretty bad if there is any grit in them. The safest thing is to put a fuel filter on the suction side of each pump to keep them clean and put a check valve on the outlet side of each pump to prevent reverse flow.
If you provide a seperate fuel tank dip tube for each pump and a seperate fuel filter at each pump suction port you can have two completely independent fuel systems. Mcmaster-Carr sells brass barbed tees for 1/4 ID tubing as part number 44555K138. Connect the two mikuni outlets together with a tee then install a check valve on the tee opening. You can connect two more tees together to provide four openings if you have dual carbs. One line from the mikuni pump check valve, one line from the electric pump check valve and two lines to the carbs.
If the Mikuni quits, a 4 PSI electric pump on a low tank will only provide 2 to 4 PSI at the pump outlet and 0 to 3 PSI at the carb because 1 to 2 PSI is used just to raise the gas up to the carb. Will that keep you in the air? Maybe and maybe not since the carb inlet should really have at least 4 PSI. The 4 PSI pump models should only be used with wing tanks.
For high engines and low tanks use the 40106 pump if you are determined to have an electric pump. That will NOT provide too much pressure and it will keep fuel to the carb as long as there is a check valve on the Mikuni so that it can't leak fuel back into the tank.
MIKUNI PULSE OPERATED FUEL PUMPS Two stroke engines use the piston to suck the air/fuel mixture from the carb through the intake manifold into the crankcase each time the piston moves toward the combustion chamber. As the piston moves away from the combustion chamber the mixture in the crankcase is pushed from the crankcase into the combustion chamber. This creates a small vacuum then a small pressure inside the crankcase which we call a PULSE. A fitting through the crankcase wall is connected to a chamber inside the fuel pump by a piece of tubing so the fuel pump diaphram can be moved by these pulses.
Condensate forms when warm fuel/air vapor hits the cool pulse line. If that condensate can not drain back into the engine it will collect in the pulse line or the fuel pump pulse chamber. Fluid trapped in a pulse line will weaken the pulse. Fluid trapped in the pump slows down the diaphram movement. Either one pumps less fuel.
Rotax drills a tiny drain hole in the Mikuni pumps which they supply with their engines. That hole is located at the pulse port connection to drain both the pump pulse chamber and the pulse line if the pump is mounted right side up below the engine pulse connection. Click on the link below to see how to drill that hole. Some models have a 90 degree brass fitting with the hole in it at that location
I don't do that because the hole weakens the pulse and it may get stopped up over time. I mount the pump above the engine pulse connection so that any pump fluid will drain out into the pulse line and the pulse line drains back into the engine. Do NOT bolt the pump solid to the engine. Use some form of mounting which isolates the pump from vibration and engine heat
Long pulse lines, leaks in the pulse line and thin wall tubing which expands and contracts with the pulses also weaken the pulses. Weak pulses move the diaphram less so less fuel is pumped. Pulse lines must be less than 18 inches long so the pump must be located near the engine pulse connection. You can swap the engine pulse connection from one cylinder to the other to help keep the pulse line short.
It's not easy to do all that so even plane manufacturers sometimes take the easy way out. Problems may develop over time as condensate builds up in the fuel pump or pulse line.
I recommend the round Mikuni pump since it can pump up to 9 gallons (35 liters) an hour ... but that is only when they are installed correctly. Remember that they will pump less if they have any installation problems. Both outlets come from the same internal chamber so just plug off one outlet if you only need one output line.
Its VERY rare to hear of any problem with a Mikuni pump if it is installed correctly. They have been used on many brands of cycles, ATVs, jet skis and snomobiles for many years. They don't require electrical power and they are simple devices with few moving parts. Those parts are replaced during a low cost rebuild which is so easy that anyone can do it.
I think they are more reliable than electric fuel pumps so I use a round Mikuni which I replace every two years and I don't have any backup pump on my plane. If I was concerned I would install a second Mikuni pump for a backup. Most engines have pulse connections on each cylinder. There is no reason why both pulse connections could not be used at the same time to drive two Mikuni fuel pumps. Do NOT connect two pumps to the same engine impulse connection. Both would recieve weak pulses.
FUEL TANKS AND THEIR CONNECTIONS Be a little leary of fiberglass and other composite fuel tanks. Every once in a while we hear about a tank which partially disolved because of ethanol or some other fuel additive.
I don't like holes anywhere in a fuel tank except at the top. Its not a question of IF they will leak ... its a question of WHEN (and how much) they will leak. All connections should be at the top to avoid that problem.
I don't care what you use to filter your fuel or how careful you are, there WILL be crap and water in your fuel tank. Your first line of defense is to leave a little room at the bottom of the tank where the crap can settle out before it gets into the fuel lines. Make a tool to clean your tanks and use it often. Use a piece of 1/4 inch OD stainless or aluminium tubing long enough to reach the bottom of your tank through the filler opening and still leave enough for you to hold as you guide the bottom end to the low spots in the tank. Slip a piece of 1/4 inch ID Tygothane tubing over one end of the metal tube then attach a squeeze bulb to the open end of the Tygothane tubing. By squeezing the bulb you can suck out trash and water. Just like cleaning your tropical fish tank at home.
The main fuel supply should have a metal dip tube which goes through the top of the tank and ends about 1/2 inch above the bottom of the tank to keep it above any water and grit thats in the tank. Do NOT let dip tubes lay against the bottom or side of the tank. That can seal off the open end or let vibration rub a hole in the tank. Don't use copper tubing with fuel because it corrodes in gas quickly. I know that brass fittings do NOT corrode but brass is NOT the same as copper tubing which DOES corrode. Aluminium or stainless tubing will work fine. Very large engines might need as much as 3/8 OD X .035 wall tubing but 1/4 OD X .032 wall will easily handle 5 or 6 gallons per hour. Do NOT use screens or filters on the bottom of the tube. Any screen or filter will stop up easier than the tube will, you will have a hard time cleaning or replaceing it and you already need a filter right at the pump inlet anyway.
If the tank doesn't have any connections on top use a stainless steel PANEL MOUNT COUPLING through the top of the tank. McMaster-Carr #5182K375 fits 1/4 OD tubing.
This coupling is like a normal tubing coupling except it has a section in the middle which is threaded so that it can be inserted through a hole and mounted solidly in place by a nut. If you install a 7/16 viton, nylon, or PTFE washer as a gasket outside the tank it will seal in fumes. McMaster-Carr #90295A186 is nylon. To protect it use a #92141 stainless washer under the mounting nut.
The tubing nut and ferrule inside the tank are not used so the dip tube can be removed later. The tubing nut and ferrule outside the tank will hold the dip tube in place, seal around it and allow removal of the dip tube. There is a small shoulder inside the coupling that needs to be drilled out with a 1/4 inch bit before the tubing will slide all the way through the coupling.
Most tanks have a small filler opening so here are some tricks to help install connections. Large drill bits make a sloppy hole in soft plastic so drill a small hole then use a tapered hand reamer to enlarge the hole to the correct size. Don't forget to deburr the hole.
Drop a string through the hole then fish the string out through the filler opening. Remove both tubing nuts and the mounting nut from the coupling then push the string through the coupling. Tie a nut on the end so it can't pull back through the coupling then drop the coupling in the tank. The string will help guide the coupling to the hole as you pull it out. Hold the coupling in place as you cut the string. Install a viton or nylon gasket then a stainless flat washer to protect the gasket. Use Locktite and install the mounting nut. Put both pieces of the ferrule and the tubing nut loosely on the top of the coupling and slide the dip tube through the coupling to the bottom of the tank. Pull it back up at least 1/2 inch before you tighten the tubing nut. Some tanks with flat tops may dish down in the middle over time. Pull the dip tube further up to allow for that.
Only planes capable of inverted flight need flexible lines inside the fuel tank. Those flexible lines WILL be a real pain in the butt later. Do NOT use them.
I use a seperate 1/4 inch dip tube for my hand pump primer because defective primers can leak air into the main fuel suction line. Some people do tee into that line to supply the primer. If you must do that, use a metal or nylon tee fitting. Plain plastic fittings may break easily and are not rated for use with gasoline.
Of course vent lines must come out of the top of the tank. A cheap fitting to use for vents is a metal valve stem for tubeless truck tires from an automotive store. They have a nut for solid mounting through the tank but the rubber seal furnished with them may not be suitable for use with gasoline. Throw it away and use viton or nylon washers as gaskets as discussed above for dip tubes. Remove and discard the valve core before you slide Tygothane tubing over the fitting. If you run the vent tubing down past the bottom of the tank, fuel will not leak out if you flip the plane over. I stick a fuel filter on the open end. It keeps bugs out of the fuel tank and serves as a spare fuel filter on cross country flights. If you extend the vent line out the bottom of the plane it will keep fumes and any slosh overflow out of the cockpit. Any vent built into the filler cap can be sealed to prevent slosh leakage and fumes when the tank is vented this way.
New tanks and lines often have construction crap left in them which causes problems on the first flight. Clean and flush them out before you trust them.
FUEL, VENT AND PULSE LINES ALL these lines should be Tygothane only since gasoline fumes attack lines just like gasoline. Tygon is NOT the same as Tygothane. Be very careful. Some tubing is rated "for fuel use" and that is NOT the same as "for gasoline use". If tubing is not rated for gasoline it is not safe for our use and very little of the tubing sold anywhere is rated for gasoline. Color doesn't tell you what the tubing is rated for and makes it harder to see air bubbles inside the line. Some plastics become soft or disolve over time when used with gasoline. Other plastics become brittle after a year or so then crack or break under vibration. Rubber automotive fuel line can shed rubber particles from inside and may get soft with our oil/fuel mixtures plus you can't see air bubbles inside the line. McMaster-Carr sells clear Tygothane tubing which IS designed for gasoline use and it stays flexible for years. Part #5549K33 is 1/4 ID X 3/8 OD and #5549K34 is 1/4 ID X 1/2 OD.
The heavy wall type must be used for the impulse line and on the suction side of the fuel pump or vaccuum may cause those lines to collapse. The lines on the outlet side of the pump and the vent lines can be either wall thickness.
Automotive type worm gear hose clamps often let air leak into suction line connections because the small size we need doesn't form a circle very well. McMaster-Carr sells nylon double snap grip clamps which work well. Part #9579K63 is typical but get the right size. They also sell spring steel wire formed into a circle as "constant tension spring" clamps. Part #5324K61 is typical but get the right size. They also sell a band tightened by a nut and bolt. Part #5412K48 is typical but get the right size.
If all else fails wrap two turns of safety wire around the connection and twist it tight but don't cut into the tubing.
FUEL FILTERS There is a lot of discussion about fuel filters. Some Cessna pilot "experts" claim that any small stuff which goes through the screens they use is so small that it goes through their fuel pumps, carbs and engines with no problem. Obviously that has worked for them for a long time but you need to remember the differences in planes and engines.
Their engines are much larger so they need larger jets in their carbs. Our smaller jets are easier to stop up. The main problem is that our fuel pumps depend on two internal flapper valves being able to seal properly up to 100 times a second at 6000 RPM. Grit that gets through screens can keep those flapper valves from sealing shut properly. When that happens our pumps may not pump enough fuel to keep us in the air. Most of us install a fuel filter just before the fuel goes into the fuel pump to protect the pump from grit.
Purolator (and others) make a filter with a glass bowl to trap sediment. You can take them apart to replace the filter and clean out the bowl. It works fine on the pump output and there is no problem with them there. Unfortunately we need a filter on the pump intake and there is suction there. You may have already noticed that suction is harder to seal than pressure if you had a hard time keeping air bubbles from leaking into your suction line connections. The seal at the filter bowl was NOT designed to handle suction and if you try to use it on the suction side of fuel pumps it WILL suck air into your fuel system. Many UL pilots have known this for years and avoid them ... but every once in a while a newbie will use one then post that he has a problem with bubbles in the suction line.
Some internet "experts" claim that filters should not be used on the suction side of pumps and use those posts as "proof". You should remember that many of the "experts" use wing tanks to gravity feed fuel to a lower engine. Their fuel doesn't need to be sucked up to the engine so they are not familar with our fuel pumps or the suction needed. They claim that the bubbles are "vaporizeing" out of the fuel because a high vacuum is needed to suck fuel through a filter. Thats not true.
It is true that a high vacuum in fuel lines and/or high temperatures can cause "vapor lock" when fuel vaporizes but that is NOT what is happening here. The vacuum used normally isn't much more than we generate when we suck on a hose to siphon gas and those bubbles are present even when the temperature is below freezeing. Its real easy to prove that those bubbles are simply air leaking into the suction line ... just replace the glass bowl filter with a different type of filter and there are no more air bubbles in your suction line.
These same "experts" have claimed that our other filters leak air into suction lines. Thats not true. The ONLY reports of air leaks are those glass bowl filters and tubing connections which use the wrong clamps.
Some fuel filters use a sintered bronze element. That type element doesn't have much surface area so it won't take long for them to get stopped up. I don't recommend them.
It's hard to beat the plain old pleated paper type fuel filters which have been used in cars, boats cycles and many other applications for years. I highly recommend them. Some "experts" claim that small amounts of water in fuel will stop them up. Thats not true. A simple experiment with a filter and a squeeze bulb will easily suck water through the filter. You should trap water in the fuel tank before it can get to the filter anyway. The Cessna "experts" should think of the tank as a big gascolator. We just use a filter outside instead of a screen inside.
Some "experts" claim that its better to use a gascolator because filters will stop up. The reason filters stop up is because they are doing their job of keeping stuff out of our pumps. Simply replace filters twice a year or any time the engine will not reach full RPM or if you notice higher than normal EGT readings at full throttle and there is no problem.
SQUEEZE BULBS, CHOKES AND PRIMERS A squeeze bulb will only pump fuel to refill the carb bowls and lines which have drained down while the plane was sitting. It will NOT squirt fuel into the intake manifold to help the engine start like a hand pump primer. It will NOT enrichen the mixture to help cold engines run smoother like a choke. Some people have had so much trouble with squeeze bulbs that they refuse to use them. Squeeze bulbs should be replaced once a year to minimize problems like splitting, leaking, shedding rubber particles into the fuel or failure of their built in check valves. I do NOT recommend them.
Our "choke" is actually just a seperate fuel path inside the carb which allows fuel to flow through a seperate jet. That enrichens the mixture to help cold engines run smoother but it doesn't "prime" the engine or fill the carb bowls and fuel lines. I don't use mine at all.
A hand primer pump squirts a little fuel into the intake manifold every time you pump it. Proper use eliminates any need for a squeeze bulb and the choke. It does take a little experience to learn how many times to pump it before starting the engine and when to pump it to keep the engine running while the carb bowls and fuel lines refill and the engine warms up a little. I recommend them highly.
FUEL PRESSURE GAUGE OR LIGHT I'm a firm believer in KISS (Keep It Simple Stupid) so I won't bother putting one on my plane. Some people do like to have a fuel pressure gauge or a light that comes on when fuel pressure drops below 2 PSI. Thats okay as long as you understand what you are really seeing. You need to see the pressure right at the carb inlet. If you just tee into the fuel line there and run a line down to a gauge mounted on the panel you will see the head pressure of the fuel in that line added to the actual pressure at the carb. You need a 10 PSI gauge but normal cheap gauges are NOT very accurate near the ends of their scales and can not survive vibration very long. You have also added the potential problem of fuel leaks and fire in the cockpit. Electronic sensors for an EIS or a pressure switch for an indicator light installed near the carb solve those problems but are they really useful?
Expect a wide variation in readings during the normal operation of the plane and make sure that the pilot understands what those variations mean. Most fuel problems are a very slow reduction in the amount of fuel delivered as a pump wears out or a filter gets stopped up. A fuel pressure gauge might let me see that problem develop over a long time but I don't need to include that gauge in my normal scan of panel instruments.
The EGT gauge IS included in my normal scan of panel instruments and it will give me early warning of fuel starvation problems by showing higher than normal EGT temperatures any time a weak fuel system can not provide enough fuel at full throttle on climbout. Even if a filter did suddenly get stopped up enough to give high EGT while I'm at cruise speed, I know that if the EGT will go back down when I reduce throttle I can limp a long way to a safe landing at reduced throttle.
Neither the fuel pressure gauge or the EGT will give any warning of a sudden failure so fly like the prop could stop turning at any time and practice emergency landings.
THE BOTTOM LINE You should NEVER attempt the first takeoff until you are 100% positive that your new fuel system will provide enough fuel under all conditions. Tie the plane down and run it at full throttle to be certain that it won't starve for gas during takeoff and check closely for leaks then be prepared for the engine to quit on takeoff. ))))))))))))))))))))))))))))))
After reading the above article, I'm more convinced that a Racor fuel/water filter gains a huge margin of safety-- and since it has the same number of connections (2) as the simple tiny filter it replaces, it does not add complexity.
Seeing the tiny debris it filters out, even AFTER I use a Mr. Funnel religiously to pre-filter all fuel, I can't help wonder if removing that fine grit helps reduce wear on the fuel pump, etc !!??
Tom, this is great stuff. We should all end up with better fuel back up systems as a result. The reason I turn mine on for take offs & landing is because that is what I was taught back in the 70's when I got my pilots license in a "real" airplane. The teachings went like this. If your mechanical fuel pump is weak or going to fail it will do it at the worst possible time, which is take offs & landings, so keep your auxiliary running during these times. I can't imagine why this would be different for a 912 vs a Lycoming. I have added to this, any time I'm low in the backcountry. I spend a lot of time flying over pretty unlandable areas. I think you might have once or twice also. We live in Idaho not Nebraska....for a reason.! I believe my plane is just as reliable as the Cessna's & Piper Cubs that are flying in the wilderness areas over unlandable terrain all the time. Until now I thought I had a pretty good backup system. I would love to have a PROVEN redundant fuel delivery system that I can run all the time if I wanted to. I'm sure the technology is out there. I guess a true backup system would mean even going to a second pickup in the tank. hmmmm. Question for anyone....What is the simplest fuel pressure gauge system for a 912?
we really need to find out why that facet pump failed you. Where are facet pumps manufactured? Have you thought about seeing if the factory would analyze it...or is that a bad idea.
(Photo Attached) When we got back to Spokane (having cut our Pre-Elk River back-country flying short because of two trikes having fuel pump problems) I dissected Ttab's accessory (secondary) Fuel pump. The one he thought CAUSED (not prevented) his engine out in the above video (taken a few weeks before our big trip).
The Facet pump is very basic: an oscillating piece of metal with a one way valve on one end shuffles back and forth in a nylon tube that has an induced electric current around it. This oscillating piece has a one way valve at one end-- thus as it moves in one direction it lets fuel flow past it and as it returns, it forces fuel forward ahead of the now closed valve- back and forth, back and forth. An additional one way valve (oriented in the same direction) is at the entry end of the pump. Very simple. There was nothing in this pump that appeared responsible for the symptom of "blocking" all fuel flow (Ttabs had it installed in series with his main pump). Possibly a little Teflon tape????
The mystery deepens!! Now with an additional Rotax Fuel Pump recall new questions are arising in our minds:
Is it better not to have a fuel pressure gauge (as most of us do not) and be blissfully ignorant of the red light / low pressure Tom thought he was having on the trip?
With what seems like a Rotax Fuel Pump recall (Service Bulletin) every year lately, is it better to install a fuel pressure gauge as an early warning? Or is it better / less complex (since pump failures usually result in visible leakage from the weep holes first and reportedly not fuel delivery failure) to just visually inspect your pump before each flight like we all do.
Was Ttabs on the right track installing an accessory fuel pump??? It was thought in this video above that that accessory fuel pump and complications actually CAUSED the engine out. Now the question is DID IT ??!!
(As a side note, we also proved multiple times on our latest adventure that the Tanarg's excellent 3-wheel-disc brake system is more than capable of easily holding back a screaming 100HP 912 at full revs. Something I don't know of other trikes being able to claim.)
Hey YFT (@Yarraft) where's those photos and description of the special knowledge you discovered about connecting fuel hose without which resistance goes up significantly? We found one of Ttabs fuel hose with a simple barbed connector had a significant amount of resistance it was one of several aha moments when we thought (erroneously) we discovered the problem.
I too await YFT's comments. I'll be working on the fuel lines again this weekend. I have a new Racor 2micron filter to install, and I'm going to completely re-wire the fuel pressure unit from the sender to the instrument panel. I also received in the mail the check valves from McMaster-Carr (recommended in the article above). Not sure about these things yet but I'd like to do some testing on them.
Also worth mentioning is I checked the air vent lines on both carbs and the fuel tank. They too have been known to cause problems like this in Tanargs.
I'm also thinking of using a 5/16 ths fuel line from the tank to the pump. Problem is it still has to go through the fuel flow sending unit (2mm jet).
The 2mm fuel flow sending jet has always bothered me. It makes me feel better that I have the Racor in front of it filtering at 2 microns though!
Ken has one of the new style fuel flow senders. Ken do you know if it has a 2mm jet? Any jet at all (best would be sensing flow by magnetic induction, or some non-invasive method)? Cost? Why did MGL stop using the previous one (which I have) altogether?
Comments
I believe I have the same exact fuel pump in line on my 2003 Airborne 912. I've had it mounted for several years now. I always turn it on before take off and leave it on until at cruise altitude. Then turn it on again for landing. 680 some hours and never had any problems. I would love to know if it was a pump problem or a foreign substance blockage problem. Has anyone heard of this happening with a facet failing in this fashion? I can't make it to Elk River later this month but I can make it this Friday. Inquiring minds NEED to know if I should go to parallel lines or is there another explanation.
Hey David, I couldn't find your triple post, but then realized that the convo had jumped to a second page. That always screws me up too when that happens. Go to bottom of page and click on "2" or "Next" then you can see the convo continuing.
Xc when I posted I didn't see the post come up.than because I spoke about nsa I got really frightens and thought wow they really are listening and deleting my post.than I said to hell with that I'll post it again and when that didn't show up I really got scared and said to myself.my great great grandfathers were decorated vets in the revolutionary war.than I got mad and said Iam gonna say what I feel to hell (freedom of speech) right? Than I realized they were posting on front page but couldn't delete the duplicates.what do they think a paranoid society is a safe society!
Jeff - I'm rethinking the install of the auxiliary fuel pump concept. I have questions regarding an inflight failure of the primary Rotax pump. Namely, will the auxiliary pump be able to push gas through the primary pump if it fails and if so - at what pressure?
What I think would be adequate is installing the Facet auxiliary fuel pump in a parallel system. That is drawing fuel off of the main line (after the fuel filter) via a T fitting to the auxiliary. Then injecting it into the fuel supply line AFTER the Rotax pump thereby bypassing it in the event of a failure. Doing this would require two check valves. The fuel would run through the Rotax pump, through a check valve (preventing back flow) and then a 'T' fitting. The second check valve would be placed between the T fitting and the auxiliary fuel pump. In this fashion, either pump can fail and you'd still be able to supply gas to the carbs. You can also do a ground check before each flight of the auxiliary pump simply by switching it on (before engine start) and seeing adequate fuel pressure supplied to the carbs. (I have a fuel pressure sensor in my system). Then switch it off knowing your reserve pump is functioning properly. You don't need additional fuel pressure for take-offs and landings.
This adds complexity to the fuel system and I have not researched the 1/4" check valves on the market. These check valves would absolutely have to be totally reliable. But you would truly have bypass supply of fuel to the carbs with a flick of a switch.
Since I had an in-line failure of the auxiliary pump creating an inflight emergency, installing it as you currently have it I now consider to be inadequate and dangerous.
My question to the crowd here is - does anyone know of any simple and totally reliable fuel check valves with 1/4" fittings?
Long but interesting article:
)))))))))))))))))))))))))))))))))))))))
By Robert Mezler
POOR DESIGN AND INSTALLATION OF THE FUEL SYSTEM IS THE MOST LIKELY REASON IF YOUR FLIGHT ENDS TOO SOON. This article can help prevent that.
Engine failures are rare. Almost all so called "engine failures" are returned to service without ever working on the engine itself. Its the systems that support the engine which usually fail ... and fuel systems fail more often than all other things combined. Most of those failures are easily prevented.
A WORD OF CAUTION
This subject always brings out the internet "experts". If any readers doubt that real people can be as screwed up as some of the "experts" mentioned in this article they should check the archives of the engines-ul2 list starting Nov 6, 2007. Just that one discussion included many of the "expert" claims mentioned in this article.
FUEL
Most American pumps have a label on them which shows the advertised octane was calculated as RON plus MON divided by two. European countries use the RON method only. If your engine manual says to use 91 RON then you can use American 87 octane gas since its the same as 91 RON.
Aviation fuel is often called 100LL. Its 100 octane but
the low lead part is misleading. It does have less lead
than aviation fuel had years ago but it still has much
more lead than automotive gas. That lead is hard on our
type engines because it fouls plugs and causes rings to
stick if we use it on a regular basis. A few gallons of
aviation fuel once in a while doesn't matter much but I
still avoid it as much as I can.
Some "experts" claim that the volatiles evaporate out of
gas rapidly so fuel goes "stale" fast. There is a tiny
bit of truth in that but it certainly doesn't happen
very fast. How long does gas have to sit in your car or
lawn mower before you notice any difference? In my
plane 3 or 4 weeks certainly doesn't cause any problems
and I have gone twice that long with only a very minor
difference in the performance ... and I even premix the
oil with my fuel. Don't get paranoid about "stale" gas.
Gasoline picks up small flakes of rust and dirt as its
pumped hundreds of miles through underground pipe lines.
The large storage tanks at the end of the pipeline add
water and more crap. Even the truck that delivers gas
to your local gas station may contribute and of course
water and crap in the gas station tank gets stirred up
when the tank is filled. Gas companies try to filter
the gas and most even have a filter right at the pump
nozzle but some water and crap always gets to our tanks.
Some pilots filter the gas going into the tanks on the
plane with felt or chamois cloth and some use a Mr.
Funnel. It doesn't matter what you use to filter your
fuel or how careful you are to avoid condensation in the
tank, sooner or later there will be water and crap in
your tank so your fuel system has to handle some of it.
ELECTRIC FUEL PUMPS
The Mikuni pumps are designed to suck fuel up to the
engine and can easily handle the 3 or 4 feet of vertical
lift needed with our engine and tank locations. Faucet
recommends mounting their electric pumps below the fuel
tank because they can NOT produce much suction.
Many people think that an electric fuel pump is a way to
provide an extra margin of safety. That's okay but make
sure that you understand what you are doing or you can
wind up LESS safe. Dual pumps can be used safely but
you need to do it correctly.
If you use pumps in series each pump must provide enough
fuel pressure by itself in case the other pump fails.
With both pumps running there is too much pressure at
the carb. To prevent that you need a pressure regulator
but then you depend on ONE regulator to keep working.
Wasn't your orginial concern that you depended on ONE
fuel pump to keep working? What have you gained?
There was an article on two pumps in parallel published
in an UL magazine which assumed that Facet pumps had a
check valve built in. One friend crashed when he had
fuel starvation with that setup. I made another friend
do some tests before he flew that setup and we found out
that he would have also had fuel starvation problems.
That article was published about 2002 but that same bad
assumption is still floating around on some web sites.
We normally use the Facet 40104 or 40105 pump where the
fuel tanks are in the wings. Where the fuel tanks are
mounted low in the plane we usually use the Facet 40106
so the carb sees enough pressure. Check them out at
http://www.facet-purolator.com/solidstate.asp
The labels on top of the columns are screwed up but if
you study the info you can figure out that NONE OF OUR
PUMP MODELS have a check valve built in. Hint .. If you
shift the label "fitting size" to your left to be in
line with the fitting descriptions of the model numbers
then the columns on the right will match up better and
make more sense.
The bottom line is this. When there is more pressure at
the outlet port than is being created by the pump, fuel
will flow backwards through the pump. Any time you use
more than one pump you should install a check valve on
the outlet of each pump to prevent reverse flow of fuel
through the pumps.
With engines mounted high and fuel pumps mounted low
there is one PSI pressure on the pump outlet port for
every 37 inches in height just from the head pressure of
the fuel in the line up to the carb ... even with the
engine off and the pump not running. For discussion,
call it 1 to 2 PSI head pressure at the pump outlet when
the pump is off.
Fire up the engine and the Mikuni will add 4 to 7 PSI to
the top of that head pressure and give about 5 to 9 PSI
total at the electric pump outlet. If the electric pump
can only pump 6 PSI, fuel from the Mikuni goes backwards
through the electric pump even when it is running. The
end result is less fuel available for the carb than was
available before you installed the electric pump.
Don't believe it? Go out to the flight line and find
any plane thats running an electric pump in parallel
with a Mikuni. Pull the suction line off the suction
port of the electric pump and plug that line. Fire up
the engine on the Mikuni and watch the gas pour out of
the electric pump suction port at high engine RPMs. A
10 buck check valve from McMaster-Carr installed at each
pump outlet is cheap insurance and cures that problem.
Part number 7775K51 has a Viton seat which is rated for
gasoline and it only takes 1/3 of a pound of pressure to
open it.
If you do the same test on the Mikuni while you run on
the Faucet pump you may find that it can leak back too
because the flapper valves inside the Mikuni can leak
pretty bad if there is any grit in them. The safest
thing is to put a fuel filter on the suction side of
each pump to keep them clean and put a check valve on
the outlet side of each pump to prevent reverse flow.
If you provide a seperate fuel tank dip tube for each
pump and a seperate fuel filter at each pump suction
port you can have two completely independent fuel
systems. Mcmaster-Carr sells brass barbed tees for 1/4
ID tubing as part number 44555K138. Connect the two
mikuni outlets together with a tee then install a check
valve on the tee opening. You can connect two more tees
together to provide four openings if you have dual carbs.
One line from the mikuni pump check valve, one line from
the electric pump check valve and two lines to the carbs.
If the Mikuni quits, a 4 PSI electric pump on a low tank
will only provide 2 to 4 PSI at the pump outlet and 0 to
3 PSI at the carb because 1 to 2 PSI is used just to
raise the gas up to the carb. Will that keep you in the
air? Maybe and maybe not since the carb inlet should
really have at least 4 PSI. The 4 PSI pump models
should only be used with wing tanks.
For high engines and low tanks use the 40106 pump if you
are determined to have an electric pump. That will NOT
provide too much pressure and it will keep fuel to the
carb as long as there is a check valve on the Mikuni so
that it can't leak fuel back into the tank.
MIKUNI PULSE OPERATED FUEL PUMPS
Two stroke engines use the piston to suck the air/fuel
mixture from the carb through the intake manifold into
the crankcase each time the piston moves toward the
combustion chamber. As the piston moves away from the
combustion chamber the mixture in the crankcase is
pushed from the crankcase into the combustion chamber.
This creates a small vacuum then a small pressure inside
the crankcase which we call a PULSE. A fitting through
the crankcase wall is connected to a chamber inside the
fuel pump by a piece of tubing so the fuel pump diaphram
can be moved by these pulses.
Condensate forms when warm fuel/air vapor hits the cool
pulse line. If that condensate can not drain back into
the engine it will collect in the pulse line or the fuel
pump pulse chamber. Fluid trapped in a pulse line will
weaken the pulse. Fluid trapped in the pump slows down
the diaphram movement. Either one pumps less fuel.
Rotax drills a tiny drain hole in the Mikuni pumps which
they supply with their engines. That hole is located at
the pulse port connection to drain both the pump pulse
chamber and the pulse line if the pump is mounted right
side up below the engine pulse connection. Click on the
link below to see how to drill that hole. Some models
have a 90 degree brass fitting with the hole in it at
that location
http://www3.sympatico.ca/murray.j/mikuni_pump.htm
I don't do that because the hole weakens the pulse and
it may get stopped up over time. I mount the pump above
the engine pulse connection so that any pump fluid will
drain out into the pulse line and the pulse line drains
back into the engine. Do NOT bolt the pump solid to the
engine. Use some form of mounting which isolates the
pump from vibration and engine heat
Long pulse lines, leaks in the pulse line and thin wall
tubing which expands and contracts with the pulses also
weaken the pulses. Weak pulses move the diaphram less
so less fuel is pumped. Pulse lines must be less than
18 inches long so the pump must be located near the
engine pulse connection. You can swap the engine pulse
connection from one cylinder to the other to help keep
the pulse line short.
It's not easy to do all that so even plane manufacturers
sometimes take the easy way out. Problems may develop
over time as condensate builds up in the fuel pump or
pulse line.
I recommend the round Mikuni pump since it can pump up
to 9 gallons (35 liters) an hour ... but that is only
when they are installed correctly. Remember that they
will pump less if they have any installation problems.
Both outlets come from the same internal chamber so just
plug off one outlet if you only need one output line.
Its VERY rare to hear of any problem with a Mikuni pump
if it is installed correctly. They have been used on
many brands of cycles, ATVs, jet skis and snomobiles for
many years. They don't require electrical power and
they are simple devices with few moving parts. Those
parts are replaced during a low cost rebuild which is so
easy that anyone can do it.
I think they are more reliable than electric fuel pumps
so I use a round Mikuni which I replace every two years
and I don't have any backup pump on my plane. If I was
concerned I would install a second Mikuni pump for a
backup. Most engines have pulse connections on each
cylinder. There is no reason why both pulse connections
could not be used at the same time to drive two Mikuni
fuel pumps. Do NOT connect two pumps to the same engine
impulse connection. Both would recieve weak pulses.
FUEL TANKS AND THEIR CONNECTIONS
Be a little leary of fiberglass and other composite fuel
tanks. Every once in a while we hear about a tank which
partially disolved because of ethanol or some other fuel
additive.
I don't like holes anywhere in a fuel tank except at the
top. Its not a question of IF they will leak ... its a
question of WHEN (and how much) they will leak. All
connections should be at the top to avoid that problem.
I don't care what you use to filter your fuel or how
careful you are, there WILL be crap and water in your
fuel tank. Your first line of defense is to leave a
little room at the bottom of the tank where the crap can
settle out before it gets into the fuel lines. Make a
tool to clean your tanks and use it often. Use a piece
of 1/4 inch OD stainless or aluminium tubing long enough
to reach the bottom of your tank through the filler
opening and still leave enough for you to hold as you
guide the bottom end to the low spots in the tank. Slip
a piece of 1/4 inch ID Tygothane tubing over one end of
the metal tube then attach a squeeze bulb to the open
end of the Tygothane tubing. By squeezing the bulb you
can suck out trash and water. Just like cleaning your
tropical fish tank at home.
The main fuel supply should have a metal dip tube which
goes through the top of the tank and ends about 1/2 inch
above the bottom of the tank to keep it above any water
and grit thats in the tank. Do NOT let dip tubes lay
against the bottom or side of the tank. That can seal
off the open end or let vibration rub a hole in the tank.
Don't use copper tubing with fuel because it corrodes in
gas quickly. I know that brass fittings do NOT corrode
but brass is NOT the same as copper tubing which DOES
corrode. Aluminium or stainless tubing will work fine.
Very large engines might need as much as 3/8 OD X .035
wall tubing but 1/4 OD X .032 wall will easily handle 5
or 6 gallons per hour. Do NOT use screens or filters on
the bottom of the tube. Any screen or filter will stop
up easier than the tube will, you will have a hard time
cleaning or replaceing it and you already need a filter
right at the pump inlet anyway.
If the tank doesn't have any connections on top use a
stainless steel PANEL MOUNT COUPLING through the top of
the tank. McMaster-Carr #5182K375 fits 1/4 OD tubing.
This coupling is like a normal tubing coupling except it
has a section in the middle which is threaded so that it
can be inserted through a hole and mounted solidly in
place by a nut. If you install a 7/16 viton, nylon, or
PTFE washer as a gasket outside the tank it will seal in
fumes. McMaster-Carr #90295A186 is nylon. To protect
it use a #92141 stainless washer under the mounting nut.
The tubing nut and ferrule inside the tank are not used
so the dip tube can be removed later. The tubing nut
and ferrule outside the tank will hold the dip tube in
place, seal around it and allow removal of the dip tube.
There is a small shoulder inside the coupling that needs
to be drilled out with a 1/4 inch bit before the tubing
will slide all the way through the coupling.
Most tanks have a small filler opening so here are some
tricks to help install connections. Large drill bits
make a sloppy hole in soft plastic so drill a small hole
then use a tapered hand reamer to enlarge the hole to
the correct size. Don't forget to deburr the hole.
Drop a string through the hole then fish the string out
through the filler opening. Remove both tubing nuts and
the mounting nut from the coupling then push the string
through the coupling. Tie a nut on the end so it can't
pull back through the coupling then drop the coupling in
the tank. The string will help guide the coupling to
the hole as you pull it out. Hold the coupling in place
as you cut the string. Install a viton or nylon gasket
then a stainless flat washer to protect the gasket. Use
Locktite and install the mounting nut. Put both pieces
of the ferrule and the tubing nut loosely on the top of
the coupling and slide the dip tube through the coupling
to the bottom of the tank. Pull it back up at least 1/2
inch before you tighten the tubing nut. Some tanks with
flat tops may dish down in the middle over time. Pull
the dip tube further up to allow for that.
Only planes capable of inverted flight need flexible
lines inside the fuel tank. Those flexible lines WILL
be a real pain in the butt later. Do NOT use them.
I use a seperate 1/4 inch dip tube for my hand pump
primer because defective primers can leak air into the
main fuel suction line. Some people do tee into that
line to supply the primer. If you must do that, use a
metal or nylon tee fitting. Plain plastic fittings may
break easily and are not rated for use with gasoline.
Of course vent lines must come out of the top of the
tank. A cheap fitting to use for vents is a metal valve
stem for tubeless truck tires from an automotive store.
They have a nut for solid mounting through the tank but
the rubber seal furnished with them may not be suitable
for use with gasoline. Throw it away and use viton or
nylon washers as gaskets as discussed above for dip
tubes. Remove and discard the valve core before you
slide Tygothane tubing over the fitting. If you run the
vent tubing down past the bottom of the tank, fuel will
not leak out if you flip the plane over. I stick a fuel
filter on the open end. It keeps bugs out of the fuel
tank and serves as a spare fuel filter on cross country
flights. If you extend the vent line out the bottom of
the plane it will keep fumes and any slosh overflow out
of the cockpit. Any vent built into the filler cap can
be sealed to prevent slosh leakage and fumes when the
tank is vented this way.
New tanks and lines often have construction crap left in
them which causes problems on the first flight. Clean
and flush them out before you trust them.
FUEL, VENT AND PULSE LINES
ALL these lines should be Tygothane only since gasoline
fumes attack lines just like gasoline. Tygon is NOT the
same as Tygothane. Be very careful. Some tubing is
rated "for fuel use" and that is NOT the same as "for
gasoline use". If tubing is not rated for gasoline it
is not safe for our use and very little of the tubing
sold anywhere is rated for gasoline. Color doesn't tell
you what the tubing is rated for and makes it harder to
see air bubbles inside the line. Some plastics become
soft or disolve over time when used with gasoline. Other
plastics become brittle after a year or so then crack or
break under vibration. Rubber automotive fuel line can
shed rubber particles from inside and may get soft with
our oil/fuel mixtures plus you can't see air bubbles
inside the line. McMaster-Carr sells clear Tygothane
tubing which IS designed for gasoline use and it stays
flexible for years. Part #5549K33 is 1/4 ID X 3/8 OD
and #5549K34 is 1/4 ID X 1/2 OD.
The heavy wall type must be used for the impulse line
and on the suction side of the fuel pump or vaccuum may
cause those lines to collapse. The lines on the outlet
side of the pump and the vent lines can be either wall
thickness.
Automotive type worm gear hose clamps often let air leak
into suction line connections because the small size we
need doesn't form a circle very well. McMaster-Carr
sells nylon double snap grip clamps which work well.
Part #9579K63 is typical but get the right size. They
also sell spring steel wire formed into a circle as
"constant tension spring" clamps. Part #5324K61 is
typical but get the right size. They also sell a band
tightened by a nut and bolt. Part #5412K48 is typical
but get the right size.
If all else fails wrap two turns of safety wire around
the connection and twist it tight but don't cut into the
tubing.
FUEL FILTERS
There is a lot of discussion about fuel filters. Some
Cessna pilot "experts" claim that any small stuff which
goes through the screens they use is so small that it
goes through their fuel pumps, carbs and engines with no
problem. Obviously that has worked for them for a long
time but you need to remember the differences in planes
and engines.
Their engines are much larger so they need larger jets
in their carbs. Our smaller jets are easier to stop up.
The main problem is that our fuel pumps depend on two
internal flapper valves being able to seal properly up
to 100 times a second at 6000 RPM. Grit that gets
through screens can keep those flapper valves from
sealing shut properly. When that happens our pumps may
not pump enough fuel to keep us in the air. Most of us
install a fuel filter just before the fuel goes into the
fuel pump to protect the pump from grit.
Purolator (and others) make a filter with a glass bowl
to trap sediment. You can take them apart to replace
the filter and clean out the bowl. It works fine on the
pump output and there is no problem with them there.
Unfortunately we need a filter on the pump intake and
there is suction there. You may have already noticed
that suction is harder to seal than pressure if you had
a hard time keeping air bubbles from leaking into your
suction line connections. The seal at the filter bowl
was NOT designed to handle suction and if you try to use
it on the suction side of fuel pumps it WILL suck air
into your fuel system. Many UL pilots have known this
for years and avoid them ... but every once in a while a
newbie will use one then post that he has a problem with
bubbles in the suction line.
Some internet "experts" claim that filters should not be
used on the suction side of pumps and use those posts as
"proof". You should remember that many of the "experts"
use wing tanks to gravity feed fuel to a lower engine.
Their fuel doesn't need to be sucked up to the engine so
they are not familar with our fuel pumps or the suction
needed. They claim that the bubbles are "vaporizeing"
out of the fuel because a high vacuum is needed to suck
fuel through a filter. Thats not true.
It is true that a high vacuum in fuel lines and/or high
temperatures can cause "vapor lock" when fuel vaporizes
but that is NOT what is happening here. The vacuum used
normally isn't much more than we generate when we suck
on a hose to siphon gas and those bubbles are present
even when the temperature is below freezeing. Its real
easy to prove that those bubbles are simply air leaking
into the suction line ... just replace the glass bowl
filter with a different type of filter and there are no
more air bubbles in your suction line.
These same "experts" have claimed that our other filters
leak air into suction lines. Thats not true. The ONLY
reports of air leaks are those glass bowl filters and
tubing connections which use the wrong clamps.
Some fuel filters use a sintered bronze element. That
type element doesn't have much surface area so it won't
take long for them to get stopped up. I don't recommend
them.
It's hard to beat the plain old pleated paper type fuel
filters which have been used in cars, boats cycles and
many other applications for years. I highly recommend
them. Some "experts" claim that small amounts of water
in fuel will stop them up. Thats not true. A simple
experiment with a filter and a squeeze bulb will easily
suck water through the filter. You should trap water in
the fuel tank before it can get to the filter anyway.
The Cessna "experts" should think of the tank as a big
gascolator. We just use a filter outside instead of a
screen inside.
Some "experts" claim that its better to use a gascolator
because filters will stop up. The reason filters stop
up is because they are doing their job of keeping stuff
out of our pumps. Simply replace filters twice a year
or any time the engine will not reach full RPM or if you
notice higher than normal EGT readings at full throttle
and there is no problem.
SQUEEZE BULBS, CHOKES AND PRIMERS
A squeeze bulb will only pump fuel to refill the carb
bowls and lines which have drained down while the plane
was sitting. It will NOT squirt fuel into the intake
manifold to help the engine start like a hand pump
primer. It will NOT enrichen the mixture to help cold
engines run smoother like a choke. Some people have had
so much trouble with squeeze bulbs that they refuse to
use them. Squeeze bulbs should be replaced once a year
to minimize problems like splitting, leaking, shedding
rubber particles into the fuel or failure of their built
in check valves. I do NOT recommend them.
Our "choke" is actually just a seperate fuel path inside
the carb which allows fuel to flow through a seperate
jet. That enrichens the mixture to help cold engines
run smoother but it doesn't "prime" the engine or fill
the carb bowls and fuel lines. I don't use mine at all.
A hand primer pump squirts a little fuel into the intake
manifold every time you pump it. Proper use eliminates
any need for a squeeze bulb and the choke. It does take
a little experience to learn how many times to pump it
before starting the engine and when to pump it to keep
the engine running while the carb bowls and fuel lines
refill and the engine warms up a little. I recommend
them highly.
FUEL PRESSURE GAUGE OR LIGHT
I'm a firm believer in KISS (Keep It Simple Stupid) so I
won't bother putting one on my plane. Some people do
like to have a fuel pressure gauge or a light that comes
on when fuel pressure drops below 2 PSI. Thats okay as
long as you understand what you are really seeing. You
need to see the pressure right at the carb inlet. If
you just tee into the fuel line there and run a line
down to a gauge mounted on the panel you will see the
head pressure of the fuel in that line added to the
actual pressure at the carb. You need a 10 PSI gauge
but normal cheap gauges are NOT very accurate near the
ends of their scales and can not survive vibration very
long. You have also added the potential problem of fuel
leaks and fire in the cockpit. Electronic sensors for
an EIS or a pressure switch for an indicator light
installed near the carb solve those problems but are
they really useful?
Expect a wide variation in readings during the normal
operation of the plane and make sure that the pilot
understands what those variations mean. Most fuel
problems are a very slow reduction in the amount of fuel
delivered as a pump wears out or a filter gets stopped
up. A fuel pressure gauge might let me see that problem
develop over a long time but I don't need to include
that gauge in my normal scan of panel instruments.
The EGT gauge IS included in my normal scan of panel
instruments and it will give me early warning of fuel
starvation problems by showing higher than normal EGT
temperatures any time a weak fuel system can not provide
enough fuel at full throttle on climbout. Even if a
filter did suddenly get stopped up enough to give high
EGT while I'm at cruise speed, I know that if the EGT
will go back down when I reduce throttle I can limp a
long way to a safe landing at reduced throttle.
Neither the fuel pressure gauge or the EGT will give any
warning of a sudden failure so fly like the prop could
stop turning at any time and practice emergency landings.
THE BOTTOM LINE
You should NEVER attempt the first takeoff until you are
100% positive that your new fuel system will provide
enough fuel under all conditions. Tie the plane down
and run it at full throttle to be certain that it won't
starve for gas during takeoff and check closely for
leaks then be prepared for the engine to quit on takeoff.
))))))))))))))))))))))))))))))
After reading the above article, I'm more convinced that a Racor fuel/water filter gains a huge margin of safety-- and since it has the same number of connections (2) as the simple tiny filter it replaces, it does not add complexity.
Seeing the tiny debris it filters out, even AFTER I use a Mr. Funnel religiously to pre-filter all fuel, I can't help wonder if removing that fine grit helps reduce wear on the fuel pump, etc !!??
Tom, this is great stuff. We should all end up with better fuel back up systems as a result. The reason I turn mine on for take offs & landing is because that is what I was taught back in the 70's when I got my pilots license in a "real" airplane. The teachings went like this. If your mechanical fuel pump is weak or going to fail it will do it at the worst possible time, which is take offs & landings, so keep your auxiliary running during these times. I can't imagine why this would be different for a 912 vs a Lycoming. I have added to this, any time I'm low in the backcountry. I spend a lot of time flying over pretty unlandable areas. I think you might have once or twice also. We live in Idaho not Nebraska....for a reason.! I believe my plane is just as reliable as the Cessna's & Piper Cubs that are flying in the wilderness areas over unlandable terrain all the time. Until now I thought I had a pretty good backup system. I would love to have a PROVEN redundant fuel delivery system that I can run all the time if I wanted to. I'm sure the technology is out there. I guess a true backup system would mean even going to a second pickup in the tank. hmmmm. Question for anyone....What is the simplest fuel pressure gauge system for a 912?
we really need to find out why that facet pump failed you. Where are facet pumps manufactured? Have you thought about seeing if the factory would analyze it...or is that a bad idea.
Great article, thanks for posting that, Thanks for posting the Video also TTAbs
(Photo Attached) When we got back to Spokane (having cut our Pre-Elk River back-country flying short because of two trikes having fuel pump problems) I dissected Ttab's accessory (secondary) Fuel pump. The one he thought CAUSED (not prevented) his engine out in the above video (taken a few weeks before our big trip).
The Facet pump is very basic: an oscillating piece of metal with a one way valve on one end shuffles back and forth in a nylon tube that has an induced electric current around it. This oscillating piece has a one way valve at one end-- thus as it moves in one direction it lets fuel flow past it and as it returns, it forces fuel forward ahead of the now closed valve- back and forth, back and forth. An additional one way valve (oriented in the same direction) is at the entry end of the pump. Very simple. There was nothing in this pump that appeared responsible for the symptom of "blocking" all fuel flow (Ttabs had it installed in series with his main pump). Possibly a little Teflon tape????
The mystery deepens!! Now with an additional Rotax Fuel Pump recall new questions are arising in our minds:
(As a side note, we also proved multiple times on our latest adventure that the Tanarg's excellent 3-wheel-disc brake system is more than capable of easily holding back a screaming 100HP 912 at full revs. Something I don't know of other trikes being able to claim.)
Hey YFT (@Yarraft) where's those photos and description of the special knowledge you discovered about connecting fuel hose without which resistance goes up significantly? We found one of Ttabs fuel hose with a simple barbed connector had a significant amount of resistance it was one of several aha moments when we thought (erroneously) we discovered the problem.
I too await YFT's comments. I'll be working on the fuel lines again this weekend. I have a new Racor 2micron filter to install, and I'm going to completely re-wire the fuel pressure unit from the sender to the instrument panel. I also received in the mail the check valves from McMaster-Carr (recommended in the article above). Not sure about these things yet but I'd like to do some testing on them.
Also worth mentioning is I checked the air vent lines on both carbs and the fuel tank. They too have been known to cause problems like this in Tanargs.
I'm also thinking of using a 5/16 ths fuel line from the tank to the pump. Problem is it still has to go through the fuel flow sending unit (2mm jet).
The 2mm fuel flow sending jet has always bothered me. It makes me feel better that I have the Racor in front of it filtering at 2 microns though!
Ken has one of the new style fuel flow senders. Ken do you know if it has a 2mm jet? Any jet at all (best would be sensing flow by magnetic induction, or some non-invasive method)? Cost? Why did MGL stop using the previous one (which I have) altogether?