MONTY THE ANSWER MAN ARCHIVE

Swift Fuel System...


VENTING CAN BE HARMFUL TO YOUR HEALTH...
I just got around to reading the Swift letter for September. There is something about reading about people and their flying experiences with the Swift that brings back fond memories. Reminiscing about my Swift got me thinking about my airplane and it's unique fuel tank vent system design. Not knowing what has transpired in the way of modifications to the Swifts innards over the past 35 years perhaps I should pass this one on just in case it relates to someone else’s airplane.

I think the serial number on Swift N90305 was #314, a GC-1A, but modified by the addition of a larger engine to a GC-1B. Shortly after purchasing the airplane in 1953, I noticed that on a hot day, with full fuel tanks, any movement of the airplane on the ground could cause fuel to siphon through the vent system and drain from the fuselage bottom vent. The only way the siphon could be broken was to raise the tail of the airplane about 4 feet from the ground for several seconds until the flow stopped. I can assure you that this jerk and press operation was a real crowd pleaser at the airport on a Sunday afternoon.

After researching the vent problem I found that there were several venting system designs employed through the build of the Swift. Each change corrected one problem and created another, all in an attempt to get the fuel gauge to read correctly. The one on my airplane, N90305, was supposed to be one of the better modifications made to the system. This information was provided by Temco and the FAA.

The reason that I have provided the above thumbnail information is to create the environment for explaining an incident that could have resulted in what could have been the loss of my airplane. At the time I was working in Florida and keeping 90305 hangared at the New Smyrna Beach Airport. After doing a walk around and pull and jiggle on the airplane I pushed it to the fuel pit and topped off the tanks. It was a beautiful Saturday morning and I intended to do a little sight seeing along the St. Johns River. Before takeoff I turned on my radio and checked it's operation with the airport office. As #305 lifted into the air I turned the radio off since I expected no contacts on a local flight and traffic control didn't exist in those parts. I turned South towards Cocoa Florida but after 20 minutes or so in the hot sun I headed back to the airport. I had glanced at the fuel gauge several times but since I was cruising at reduced power the continued indication of a full tank didn't seem abnormal. However, when I taxied up to the fuel pump the airport operator met me, mentioned something about smoke and began to inspect the underside of #305 explaining that I had trailed a white plume from under the airplane as I left the ground and continued to do so until it disappeared from sight.

He said that he had tried to call me on the radio but I didn't respond. Right then I knew why the fuel gauge had indicated full for so long. A quick look at the fuel gauge indicated just about empty. I calculated that when I landed I had about 10 minutes of flying time left before the engine quit. I figured that I had pumped about 18 gal. of gasoline overboard through the vent system during my 20 minute flight. After a close inspection of the vent system I discovered that muddobbers (wasps) had plugged the opening to the vent located just aft of the rear cabin bulkhead. What appeared to have happened when this vent was the bumping on takeoff had started the siphon through the vent line that is located at the top of the fuel gauge standpipe. This process kept the fuel at the top of the standpipe along with the float that drives the fuel gauge. Of course the reading always indicated at full. The vent line extension through the top of the airplane normally would have prevented the siphon to start, but unfortunately it was plugged.

The next time that #305 went into the air all vent openings were covered with a copper screen guard.

I have no knowledge of any bulletins that were issued about this problem even though I reported it to the FAA at the time. I also have no way to identify the specific system design incorporated in #314 but I suggest that anyone that has the fuel siphon problem, if it hasn't been fixed by now, add a few screens to the vent openings. Something like this could ruin your day.  --  Larry Simms (larrys@abs.net)

CLEANING FUEL STRAINER...  (4499)
From: Bob Runge <ejectr@javanet.com>
Subject: Re: Strainer
My fuel strainer seems to be installed before the fuel shut off valve in the cockpit. Therefore, if I want to clean the strainer, I have to empty the tanks or get deluged with fuel. Is there any other way I could stop the fuel flow to the strainer so I can clean it without emptying the tanks first?

Bob: Yup, thats the way they were built! Many guys have gotten some aluminum 3/8" tubing (5052 might work best) and with a tubing bender have rearranged the plumbing so they could shut off the fuel, then clean the screen. You also need an aircraft flaring tool (37 1/2 degree) Many are so neatly done it looks like factory. Myself, on the Swift I have now its all stock, so I have to drain the tanks. -- Jim

PS When I mentioned 5052 I was probably remembering replumbing pitot/static lines on a B-707. They were 5052 and bent all right, but were not flared. They used a flareless sleeve and "B" nuts. 5052 might be too hard to get a good flare and dead soft aluminum tubing might be what to use.

USABLE FUEL...
Subject: Re: Usable Fuel
From: Dennis Mee <jmmee@nh.ultranet.com>
I have a couple of questions for you, the easy one first: The type certificate shows a fuel capacity of 27.8 gal, and the factory wt & bal shows 156 lbs, (26 gal) so I assume there is 1.8 gal unusable fuel in the Swift, is that correct?

Dennis,
The actual full fuel figure varies a little - from tanks empty to full I've seen 27.8 to 28.3 gallons register on the pumps, and others have noted wider variations. I suppose Globe wanted a round figure that was reasonably close. There may be a gallon or so unusable in the 3 point attitude, but level I think it can all be used. I have heard of guys burning their tanks dry, and landing on the aux. - not me! Yes, officially, there is 1.8 gal of unusable fuel. I use 26 gal capacity on a w&b when its to my advantage to show a lesser weight. (all the time in a Swift!)  --  Jim

LEAKING FUEL DRAIN VALVES...
Subject: Re: Fuel drain valves
From: Dennis Mee <jmmee@nh.ultranet.com>
Both of my fuel drain valves are leaking. The sump drain leaks around the valve handle when turned on but slowly stops when turned off, perhaps a worn shaft. The strainer drain leaks through the valve and continues to drip when turned off, perhaps a bad seal. Joe doesn't have of these twist type drain valves, I assumed they are original, any ideas on repair or replacement? I remember seeing these type drain valves on other airplanes but can't remember which one. My fuel selector valve is leaking through from the aux to the main tanks and does not shut off completely, I've been trying to get a replacement valve from Merlyn for some time but can't wait any longer, I'll have to get something to replace it elsewhere. Since I have to drain the system I'd like to fix them all at the same time.

Dennis:
Boy, its been a long time, but I think I have replaced an "O" ring in those drain valves Try having a 1/8" pipe plug handy, remove the leaky valve and temporarily install the pipe plug before you lose too much gas. I think I had it down where I only lost about a cupful. Compare the Merlyn valve to standard brass gas valves at your local hardware store or maybe you'll have to go to the gas company. (Natural Gas) Maybe you can find a replacement. Better yet, maybe you can dismantle the one you have and either lap the leaking parts or apply "fuelube" - which will make it easier to operate also. Fuelube is a paste type lubricant for fuel valves. It is available from Aircraft Spruce or any of the major aircraft suppliers. -- Jim

FUEL STRAINER REMOVAL...  (8499)
From: Dick Aaron <raaron@pica.army.mil>
Dear Jim,
I'm writing to thank you for saving me untold grief and also preserving my sanity. While not having written before, I've been an avid follower of your contributions to the Swift Internet Newsletter and have learned, and re-learned, many useful tips. In doing the annual on 2405B, I encountered what I thought was a non-functioning fuel shut-off valve in the course of cleaning the fuel strainer. After draining the tanks and assessing what was involved in removing the valve I went home and had some ice cream to calm down.

In the spirit of monitoring the frequency, I thought that I better check the record first. Lo and behold, there in the archives was your letter to Bob Runge about the fuel strainer being before the valve. Who'd have thunk such a thing was possible?! Why did they do that? It wasn't that way on my other Swift. I discovered this a day or so before I was planning to bite the bullet and take a day off from work to take the valve out. I figured a 40% disassembly of the Swift should do it. Can you imagine what would have happened to me if I did this and then discovered that it was the plumbing???!!!!!!!! By the way, is there any reason that the strainer assembly can't be moved back about 3" to make it easier to service? Thanks again, and if you're ever near this part of New Jersey I'll buy you some ice cream. -- Dick Aaron N80625, 2405B

Richard,
No, many Swifts have this done so cleanly that it looks like a factory installation. The secret is to use a tubing bender and make it look professional, it certainly is an improvement to be able the shut off the fuel and remove the strainer. -- Jim

BELLY TANKS AND GC...  (9499)
I have installed belly tanks, but the STC has no reference to weight and balance. I measured the centroid of the belly tanks at 51.5". the centroid for the wing tanks is 47". the mathematical result is 48.1". I have a 15# ballast in the tail. I acquired a 9.5# globe ballast and figured the aft Shift would allow me to remove the 5.5#. My max wt(1970#) most aft cg is 33.4, and the empty wt cg is 29.8. Am I playing with fire here or doing the right thing? John Ewing N80913 <jonwewing@cs.com>

(Editor's note: Jim is still sans computer as I write this so we'll have Don pinch-hit one more time...)

From: Don Bartholomew <spectro@nanosecond.com>
Organization: The Aeroplane Factory
To check the numbers, I need the empty weight that corresponds with the 29.8" location. Also, does this number include full or empty oil, and how much oil? I also need either the empty weight and arm with the tanks installed, or the weight of the tanks and hardware to figure the new empty weight.  This recommendation is based on experience: Drain the useable fuel, fill the oil, and weight the airplane. While it is level, drop plumb bobs and measure the ACTUAL arms from the firewall to the center of the main axles and from the axles to the centerline of the tail weighing point (usually the centerline of the tail wheel axle). These numbers vary between aircraft and the tail arm IS NOT what was used by the factory computations. The factory typically used 145.56" and measuring to the tail wheel axle measures around 159.5". This makes a big difference in computations!  With this information, calculate the cg and try loaded conditions to see where you are. Run calculations with less tail weight and see how things are. Use your actual personal weight rather than the FAA "standard" person (170"). If you get me the scale weights and arms, I can run some examples for you. -- Don and Helo

On to page two of fuel system stuff...