Apparent problems with Vans Capacitance Fuel Tank Sender
----- Original Message -----
From: Charles Kuss
To:
Sent: Sunday, September 23, 2007 9:23 PM
Subject: Re: [RV-8] Fuel gauge senders
Martin & Paul,
This is a subject which I have posted on many times. Short version is that the capacitance senders were actually designed by RV8 builder Dick Martin & the engineers at Electronics International. Vans uses cheapo parts and garbage spacers for the sender plates.
I am including an HTML file I've edited down from a series of communications with Dick Martin. I am also inclosing a photo and an AutoCAD drawing of the proper way to make the one piece, Delrin spacers. The cheapo nylon washers supplied in Vans kit will deteriorate after about 5 years. Once this happens, his senders will fail to function. Might as well build it
correctly the first time. I also have a file (it's at the shop) which is a tracing of the .025" 2024-T3 sender plates. You need to make 4 of them for 2 fuel tanks. I'll send those with another post tomorrow from my shop.
The photo of the Delrin spacers also includes a Delrin square shouldered O-ring to replace the cheesy thing Vans supplies with his "flop tube" kit. Ignore that item if you aren't using a flop tube. Feel free to email or phone me at 1(561)212-7785 cell
phone.
Charlie
Build It Yourself, Capacitance Type Fuel Tank Sender
Many of you have asked me for detailed instructions on how to install flat plate capacitance fuel tank sensors like the ones that I have installed in my RV8. Following is a description of how to make and install these sensors in your RV. Please keep in mind that I can talk much better than I can write.
You will need the following materials:
.025 2024 T3 aluminum sheet
10 ft of 24 ga TEFLON AIRCRAFT WIRE no substitue, other wire will deteriorate in gasoline
2 Male BNC connectors, Part # 31-236 RFX AMPHENOL NO SUBSTITUTE others will leak
2 Female BNC connectors Part # 31-326 AMPHENOL
A piece of Delrin rod 3/4"-1" dia. to make spacers from - available from plastics suppliers
2 interface modules available from Electronics International
FL2C Fuel gauge from Electronics International
Start by making the flat plate sensors. You will need 2 plates for each gas tank. Each plate needs to be approximately 35 sq. inches in area for a total of approximately 70 inches per tank. Make from 025 aluminum sheet. Make the flat plates in the approximate configuration of the T804 tank baffle . It should be 5/8 " less than the height of the T804 tank baffle. Length is about 6 to 7 inches, enough that you end up with approximately 35 sq inches of plate area. I would suggest that you place them just forward of the rear flow through hole in the T804.
Vertical spacing should be as follows: place one plate on the inner most T804 space up from the bottom of the fuel tank 1/8". Spacing from the top is not important but should be at least 1/2". Locate it on the inboard side of the T804 if you have a standard fuel pick up, and locate it on the outboard side if you have and aerobatic flop tube pick up. Place the second plate on the outermost T804 and locate it the same for and aft, but change the vertical location so that the plate is spaced down 1/8" from the top of the tank. Locate plate on the inner side of this outer baffle so that when fuelling the airplane you will not disturb the plate with a fuel nozzle or in rushing fuel.
It will be necessary to trim the ends of the tank bottom stiffeners in order to maintain at least 3/8" clearance from plate sensor. I simply trimmed the end on a 45-degree angle. The plates must be spaced off from the T804 3/8". Fabricate spacers from the Delrin to accomplish this. I have been told that Delrin spacers are available commercially, however, I couldn't find any when I needed them, so I made them myself. It is very important that you completely insulate the flat plate sensor from all the rest of the fuel tank baffles, skin etc.
The reason for the 2 sensors is so that you can get a more accurate reading of the fuel capacity in both full as well as low modes. My installation will measure to l quart increments. The 2 connectors must be connected electrically to each other. I did this by installing a piece of 24 gauge teflon wire between each sensor and then to the BNC connector installed in the T803 root end rib.
I would suggest soldering an eyelet connector rather than crimping. Attach the wire to the flat plate with a 6-32 x 3/8 machine screw and a Hi temp friction nut ( no plastic insert to deteriorate from gas). Anywhere on the sensor plate is ok, I installed mine near the center.
Route the wire up to the fuel tank vent line and twist it around the vent line and route it through SB437-4 plastic bushings on the tank baffles. ( I cut a 1/16 x 1/16 notch on the I D of the bushing). 1 twist every 2 inches is sufficient. Route the wire from the outer sensor to the inner sensor to the BNC connector. I also put a few dabs of Proseal on the wire and vent tube to prevent vibration of the wire.
Locate the BNC connector l " aft of the fuel tank vent fitting in the T803 root end rib. Per DWG 18 "Inverted Fuel Alteration section". When you have soldered the stripped end of the 24 ga Teflon wire to the BNC it is very important to thoroughly insulate the wire from the BNC back over the wire insulation at least 1" with Proseal. If you don't do this it is possible for moisture to follow the outside of the wire to ground. Completely cover the BNC connection with Proseal on the inside of the tank. That completes the sensor installation.
When installing the instrument, you need to place the interface module as close as possible to the BNC connector outside of the fuel tank. I installed mine 3 inches down line from the fuel tank. Technical questions about calibrating the instrument can be answered by Ron Robinson, the engineer at Electronics International in Oregon who helped me engineer this installation. I bought my instrument from Vans, he had the best price.
Some of you that I talked to, indicated that you were going to build your own instruments. I think that's a good idea if you are an electronics expert, however, I don't understand electronics well enough for that. I will save money on some other part of the plane. Please don't ask me to elaborate on this project on the internet. It took me an hour to write this. I will be happy to talk to anybody about it on the telephone if you call me. I finally have a fuel gauge that works and is accurate.
Dick Martin Green Bay, Wis RV8 80124 N233M (920) 432- 4845 mornings cst
Jerry,
I just attempted to call Dick Martin this morning regarding the Capacitance senders. However, the phone number [ 920-432-8545 ] has been disconnected. Do you have a working number for Dick?
Hi Charlie,
Try 920-432-4845 and see if that one is good. This is Dick's work number.
The plates are attached to the second and fifth ribs. (RV-6A) Very easy to install. Hardest part was making a notch in the vent tube bushings to run the wiring through. When I was done installing, I tested by using a multimeter set on ohms, to put a load through the plates. Touch the positive lead to one plate and the negative to the other plate and if the needle moves, the wire between the plates is good. Touch the plate nearest BNC and the center pin in the BNC to see if the wiring between the two is good. Next check to see if the plates are grounding out on the tank (which is bad). Touch one plate and touch the tank skin or rib. If you get a reading, the plates are not isolated from the tank and will not work. The only other way to test them is to put fuel in them with the guage hooked up which is DANGEROUS! I'll trust my meter test. Let me know if I can answer any questions.
Jerry Calvert RV-6A
----- Original Message -----
From: Charles Kuss
To:
Sent: Sunday, September 23, 2007 10:31 PM
Subject: RE: [RV-8] Fuel gauge senders
Paul & Martin,
Make sure to purchase the Amphenol brand bulkhead electrical connectors from a local electronics supplier. Vans sells crappy Chinese made units which will leak fuel. I believe that the part number for these units was included with my last post.
Charlie
PS You can buy 7/8" or 3/4" diameter Delrin rod from either McMaster-Carr or MSC. I suggest you buy two feet of it. If you only buy one foot and make a mistake, you'll need that 2nd foot of Delrin stock. Only Teflon or Delrin (generic name is acytate) plastics are completely fuel proof. All other plastics will degrade while submerged in fuel. Teflon is very
hard to machine accurately. Machining Delrin is easy. I made my parts on a friend's metal lathe in his machine shop.
Enclosed are a few photos of my fuel tanks prior to installing the rear baffle. I copied another local builder's mod regarding installation of the "anti hang
up" bars for the left fuel tank. I am installing a flop tube in the left tank, hence the need for the plates. Vans design of these parts severely limits future access into the tank via the access plate on the inboard rib.
On the advice of another local RV owner (A&P, IA mechanic) I also installed REAL fuel tank nutplates. These are part number NAS1073-08 Vans use of standard
nutplates to retain the access plate is why a lot of builders have fuel leaks here. They think the cork gasket is leaking. It's not. The fuel leaks between the threads of the standard MS21047-L08 nutplates and the #8 screws. The fuel actually leaks out from under
the heads of the screws.
Make sure you secure the Tefzel wiring to the vent tube with some ProSeal (or similar). This will prevent future damage to the wiring from sloshing fuel.
Charlie
--- PAUL FERREIRA wrote:
> A million thank you's and salutations!
----- Original Message -----
From: Charles Kuss
To:
Sent: Monday, September 24, 2007 9:12 PM
Subject: Template for capacitance fuel sender info
Guys,
Enclosed is a tracing of one of Vans capacitance fuel sender plates. You will need to make 4 of these (2 for each fuel tank). Make them from .025" 2024 T3 aluminum. The only part of Vans capacitance fuel sender kit I found worthwhile was the drawing sheet they send with the kit. Better to simply order the drawing from Vans for $3. It's drawing OP-? I don't have that drawing at hand, so I don't have the drawing number handy. Sorry. I re-designed the spacer blocks (3 needed for each plate) for the plates.
The parts supplied in Vans kit are absolute trash. His idea of making a spacer is to give you 36 1/8" thick Nylon washers, like what you could buy at a hardware store. Nylon breaks down over a period of years when immersed in gasoline. Worse yet, you have to stack 3 of these washers together to obtain the clearance needed. The washers also have a hole drilled in them for a 1/4" bolt, not the #8 machine screws used in the kit. #8 bolts are .160" in diameter, compared to the .281" diameter holes in the washers. To fill in the slop, he provides a short length of vinyl tubing to be placed over the #8 screws. This is supposed to do two things.
#1 The tubing insulates the screws (and by extension the sender plates) from touching the sender plates. If the sender plates contact the #8 screws, the fuel senders will short to ground. This will render your fuel gauge inoperative. The tubing is only about .040" thick. If the screws should ever loosen up, the only thing keeping your sending units from shorting out, is that .040" thick soft vinyl tubing, not much in the way of electrical integrity. An electrical short will require removal of the fuel tank and cutting holes in the fuel tank's rear baffle to make repairs. Once repairs are complete, you'll have to fabricate access plates for the rear baffle to seal the access holes. Much easier to just design and build the thing correctly from the start.
#2 The tubing is supposed to act as a spacer to take up the "slop" between the #8 screw and the center holes of the Nylon washers.
My re-designed spacers are made of Delrin (generic name acytate), which is totally impervious to petroleum based chemicals. My spacers also have a shoulder on them. This shoulder insures that you have 136" of very tough Delrin keeping the plates from shorting out, rather than .040" of very soft vinyl tubing doing this job. Using my spacers will require you to increase the #8 attaching screw pass through holes from .166" diameter to 7/16" in diameter. I did this using a Unibit, but any 7/16" diameter drill bit will work.
Install one countersunk aluminum washer and one Delrin washer (dimensions to make these are shown on the AutoCAD file sent earlier) under the head of each of the #8 screws. I used flush mount #8 screws on my RV-8A, but you can omit the countersink in the aluminum washer and used the more common pan head screws. I used the flush screws so that there wouldn't be a protruding head sticking out for something in the fuel to catch on. (I always think in "worst case scenarios"). I used some of the left over .063" aluminum Vans supplies with the wing kit (for the fuselage center section) to make the aluminum spacers. The Delrin spacers and washers I made from round stock I purchased from McMaster-Carr, on a lathe. You can also find Delrin at your local plastics supplier.
FYI, Bob Weir of RST shows you how to make your own capacitance converter modules. You can buy the ready made units from Electronics International (and buy their pricey gauge) OR you can build Bob's unit and use the standard (and much cheaper) Stewart Warner or Mitchell resistive gauges. Converting the Stewart Warner units to have lighting will cost a lot more.
To read Bob's DIY article, see
http://www.rst-engr.com/rst/articles/KP89SEP.pdf
Vans sells the Stewart Warner gauges. These are cheaper than the Mitchell units sold by Aircraft Spruce and others. However, the Stewart Warner units have no provisions for night illumination. If you like night flying, buy the Mitchell units. They come with lights included. Mitchell sells 0 to 15 psi and to 30 psi gauges. The higher pressure units are for fuel injected engines. Bear in mind whether you will be using a carburettor or fuel injection when ordering your fuel gauges. For Mitchell gauges see
http://www.aircraftspruce.com/catalog/inpages/mitchfuelpress.php
I hope this helps.
Charlie Kuss
PS If you don't have any CAD software installed on your computer, Bob Nuckholls includes a copy of an older version of AutoCAD on his AEROELECTRIC CONNECTION CD. You can download this CD for free off of his web site. See
http://www.aeroelectric.com/CD/
This info is indispensable for doing your electrical system.