ragwing fuel system/Lycoming 360 fuel system

zero.one.victor · Post by **zero.one.victor** » Mon Feb 02, 2004 2:13 am

Please correct me if I'm wrong,but my understanding is that the Lycoming O-360 conversion for the 170 (as per the Avcon STC anway) requires an electric fuel pump to be added to the fuel system? Now,is this fuel pump to be operated all the time,or is it on for takeoff and landing only? If it is a TO & Landing only show,I'm curious if the fuel pump is plumbed with an exterior bypass line,possibly including a check-valve like the ragwing fuel plumbing,or if the fuel pump itself has an internal bypass arrangement? I looked at a Cessna 150 with the Avcon O-320 Lycoming conversion that included an electric pump for TO & landing only,the pump had an internal bypass--no external bypass lines needed.
The reason I'm asking is that I'm considering modifying my ragwing to use an electric fuel pump for TO & landing only,to replace the stock engine-driven pump arrangement. I just got a copy of an approved 337 for such a modification on another ragwing. However,the fuel plumbing included an external bypass line with checkvalve. The whole point for this mod is to clean up & simplify the fuel plumbing,so naturally I'd like to avoid the external bypass if I can.
I'm also curious what make/model electric pump is used on the Lycoming conversion.

Eric

Roesbery · Post by **Roesbery** » Mon Feb 02, 2004 3:52 am

The fuel goes from the fuel valve to the sump screen unit then to the electric pump, (which has a internal screen and the bottom twists off for checking, cleaning etc., don't have one handy, but it's the round one about 1 1/2 inches in diameter and about 5-6 inches tall, wire comes out of the side) then to the engine driven pump, then to the carb. Fuel will free flow through the whole works. The electric pump is only used for take off and landing

zero.one.victor · Post by **zero.one.victor** » Thu Feb 05, 2004 1:57 am

So they use BOTH an electric (boost) pump AND a mechanical pump? Considering it's a high wing (gravity feed),that seems like double redundancy. Is everybody else's O-360 installation like this?
Like I said,I'm also after the make/model of the electric pump. Maybe Dave Clark or somebody can look at their airplane &/or paperwork & fill me in.
Thanks,

Eric

Roesbery · Post by **Roesbery** » Fri Feb 06, 2004 4:16 am

So far as I know they are all the same, at least the ones I've seen. Was raining on ice and blowing 30K when I was at the plane today, but what I could see without removing the cowling was (Cessna 1216012) on a sticker on the electric fuel pump, also stamped on the side is (ECLIPSE) and under that is (THE SE or 5E) couldn't see it that well, and further down looked like PAT. and what looked like numbers, probably patent numbers. Looks similar to the round automotive electric pump shown in the Chief Aircraft catalog vol 22 pg 75. Maybe the cessna number means something to somebody out there.

Roesbery · Post by **Roesbery** » Fri Feb 06, 2004 4:32 am

PS Yes, the engine will run just fine and the plane will fly fine without either pump. My current plane was in need of a bit of TLC when I ferried it home after purchase, the fuel was connected directly to the carb bypasing the engine pump and the electric was among the spare parts in the back.

C170Driver · Post by **C170Driver** » Fri Feb 20, 2004 1:22 am

Fred Dyan in Fairbanks got a field approval some years ago to remove both pumps (elec. and engine driven) from his Avcon powered 172 seaplane. The approval required increasing the fuel line diameter from the fuel selector forward, including a 180 strainer.

A few years ago, we were going to "liberate" 73B from the nasty pumps, but another mechanic on the field that flew and maintained a number of 180hp 170s about came unglued. Given the capacity of the Lycoming O-360 to burn fuel at full throttle he thought not, so I relented. Fred is still flying the 172 thusly. Might try a google search and see if you can come up with his web info.

Post by **GAHorn** » Fri Feb 20, 2004 11:13 pm

My understanding is the ragwing fuel system is a derivative of the C-120/140 fuel system and has insufficient fuel flow for the C-145/O-300 engine. So a pump is required equipment for all stages of flight. (Just because a 337/field approval exists for another example of the airplane doesn't mean it was issued/approved knowlegeably.)
The ragwing needs larger fuel lines to provide adequate head pressure for a gravity system to comply with certification rules.

zero.one.victor · Post by **zero.one.victor** » Sat Feb 21, 2004 6:39 am

I beg to differ with you,George. My understanding is that the ragwing requires a fuel pump due to the routing of the fuel lines which can cause an "airlock" (for lack of a better word) after breaking the siphon action due to unporting a near-empty tank at a high angle of attack. The fuel lines go forward (and up,at a high angle of attack) and then down the front door posts,instead of back & down the rear door post. Spent a little time figuring this out in the 6-1/2 years I've owned my ragwing. I had the point driven home after draining all fuel lines & both (double) fuel tanks--fuel did not start to gravity-feed to the gascolator even after 15 gallons had been poured into the tank (tanks= 25 gallons total each wing). I had to jack the airplane tail up into a level attitude before the fuel flowed. The fuel level had to be higher than the high point in the line at the top of the front door post. The fuel pump is for sucking the fuel up & over that high point after the line runs dry,in the nose-high attitude.
Not the clearest explanation in the world but it's the best I can come up with.

Eric

Dave Clark · Post by **Dave Clark** » Sun Feb 22, 2004 12:45 am

If the lines are 3/8" then Eric is right, it's the routing that's the problem. Why can't you just re route to the later configuration?

Eric, I finally got to the hangar. The electric pump is a Facet auto pump and the only part number on it is 574A.

zero.one.victor · Post by **zero.one.victor** » Sun Feb 22, 2004 3:16 pm

I need to measure the lines & see what size they actually are. I haven't heard of anyone re-routing the lines,but that actually seems like it'd be the best solution. Too simple,maybe?

Thanks for the p/n Dave.

Eric

zero.one.victor · Post by **zero.one.victor** » Mon Feb 23, 2004 6:43 pm

I looked in my '48 IPC at the fuel system drawings. Part numbers for the fittings --for example, AN-815-6D union--indicate the fuel lines from the wings are 3/8" OD. I'm gonna pull off the door post trim today & measure one to make sure.
Anyone got their A or B-model IPC handy? How about looking at the fuel system pages & seeing what size couplings & stuff are called out? Dave, I don't know if you're referring to ID or OD when you say 3/8" lines-- I assume OD,since that's how the sizes are called out for the AN fittings.
I have a copy of a 1993 letter from Cessna that came with one of my electric fuel pump 337 copies. They state "To meet fuel system requirements as far as fuel pressure in certain attitudes the engine driven fuel pump was necessary. In 1949 the fuel system was designed to meet the requirements without the aid of a fuel pump which was deleted from the engine installation. The Type Certificate does still require a fuel pump to be installed on those aircraft that originally had the engine driven fuel pump."
Nowhere do they mention WHY the pump was required--whether it was line size,or routing,or divine intervention.

So I can see why it'd be hard to get line re-routing approved,but (relatively ) simple to get the electric pump OK'd.

Eric

3958v · Post by **3958v** » Tue Feb 24, 2004 12:35 am

Eric I too have wondered why the fuel pump. When I first bought the plane it someone had removed the pump on mine. I reinstalled one because I felt it was the right thing to do. But I tried various power on stalls with as little as 1/4 tanks and I could not cause fuel starvation. The only thing that I could say might have been a problem was unporting a tank which I did at altitude in a slip. It took about 5-10 l o n g seconds before the engine restarted after leveling the wings and switching to both tanks. If that happened to the factory test pilots that may have caused them to feel that a fuel pump would be helpful. I would be interested to compare the routing of our fuel lines to the routing used on the 140 since our tank designs are about the same. Again I stress that I have installed a fuel pump and highly recomend anyone without one to either put on the electric or an original engine driven pump and check valve on. Bill

zero.one.victor · Post by **zero.one.victor** » Tue Feb 24, 2004 1:52 am

I measured the fuel lines at the wing root area today and sure enough they are 3/8" OD.

Eric

Post by **GAHorn** » Tue Feb 24, 2004 4:26 am

I still believe the ragwing's fuel system is merely the descendant of the C-120/140 fuel system, which is inadequate for the C145 engine's increased fuel demands. As you pointed out, the ragwing fuel lines go down the forward doorpost. I don't see where you feel we differ Eric.
The certification rules specify the head pressure required at full throttle which are influenced by engine fuel demands. I don't think it was any test pilot's suggestions, but instead it was the certification rules that had to be met. Since Cessna was utilizing the 120/140 wings/fuel system for expediency, they used the expedient of adding a fuel pump to meet the rules.
When the fuel system was redesigned in 1949 with the A-model, the routing was changed to alleviate the lack of sufficient fuel flow in all attitudes. This allowed them to dispense with the pump. (The metal A-model wing and fuel system was subsequently also used in the C-140A.)
It has been said that an STC exists to remove the pump if fuel lines of increased size are installed on the ragwing. I'm not familiar with that mod, and it may be anecdotal. I should have made that clear on my earlier post.

Dave Clark · Post by **Dave Clark** » Tue Feb 24, 2004 2:46 pm

Eric

I just read again your original question. My electric pump does flow internally if switched off but I don't know at what rate because the engine driven pump is always pulling gas through there. Which brings up the point that you'll be getting less pressure without the engine driven pump when the electric is turned off. But I don't think a simple bypass loop with a check valve has to be messy or complicated, I can mentally picture it out of aluminum tubing right at the pump, which I assume you would mount on the firewall. So if I were you I'd talk to the friendlies about an approval based on the 337 copy you have, then go ahead with it if they say they'll bless it.

BTW, the Avcon conversion requires a fuel pressure gauge. I think my green range is 6 to 9 psi. and is probably not accurate enough to tell if the electric pump restricts the flow vs. a direct line.