Breakthrough Capacitive Fuel Probe

Product Preview:  Belite Capacitance Fuel Probe

Last Revised March 8, 2016


Cap Probe

Capacitive Fuel Probe controller module.  Functional prototype shown.  Case not shown.


Probes for fuel tanks have often used the principal of “capacitance” to determine the level of fuel within the tank.  These probes are usually constructed of a thin conductive center probe surrounded by a liquid permeable sheath and a grounded jacket.  Commonly available in lengths from 12” to 24” (or longer), these probes suffer from the following problems:

  • Although many claim to be bendable, in our experience we’ve found them to frequently short and fail when bent.  Bendability is a requirement to fit through access holes and at a diagonal positioning from the hole to the bottom of the tank.
  • Presence of minute amounts of water within the fuel may cause these probes to fail. Water is a very good conductor of electricity (specifically when non-pure or contaminated.)
  • Calibration of capacitance probes is affected by changes in the dielectric quality of the fuel in the tank. Specifically, a mix of AvGas with autogas, or a mixture of alcohol within that autogas will cause capacitive probe readings to fail.
  • We believe that almost all capacitive probes on the market are designed with older technology circuits that are less immune to high electrical noise environments, such as what is found in aircraft. While this is a more subjective claim, we have solid foundation in making new claims of noise immunity with our new design.
  • Most capacitive probes require intrusive, large holes in the top of the tank in order to mount the probe puck.


Belite’s new Capacitive Fuel Probe Solves Problems

Our new probe resolves these issues and offers substantial benefits.  In particular, the probe has the following features:

  • The probe is a flexible wire assembly. It may be routed from one corner of the tank to the opposite corner, and held in place at the far corner using a simple mechanical hook.  It does not care what path it takes, as long as that path is surrounded by the fluid to be measured.  It also does not care (within reason) the length of the wire within the tank, and will accommodate any length between 6 inches and 40 inches (one meter).    The wires are jacketed with Fluorinated Ethylene Propylene (FEP).  This material is amazing.  Quoting one of the manufacturer’s websites:

For instance, in the automotive industry, chemical transference is often needed to deliver vital fluids throughout a vehicle’s complex engine. With this in mind, the flexibility and high working temperature characteristics of fluoropolymer tubing can provide custom applications in long lengths on a variety of vehicles.

Since fluoropolymer tubing is a fantastic insulator, it can offer electrical insulation and chemical resistance that makes it a great splicing aid for high continuous service temperatures in corrosive environments.


  • Our probe will not fail in the presence of water. (Water will affect the reading, but the unit will continue to function in an accuracy degraded mode.)
  • Our probe electronic module includes a calibration button which is used to set the Empty and Full position of the fuel tank. This button may be optionally routed to a pushbutton switch in the cockpit, so that the fuel probe may be recalibrated to Full after the tank is filled.  Therefore, full position calibration is automatically recompensated for type of fuel in the tank – 100LL, AutoGas, with or without alcohol.
  • This probe was designed using an integrated circuit with a novel tuned inductive filter on the probe input. This has demonstrated a great deal of noise immunity.
  • The wire assembly may exit the tank via a vent hole or any other hole. In a good tank design, this would be in that portion of the tank reserved for fuel expansion as the fuel warms up on a hot day.

Cap Probe Wire Module

Prototype wire assembly.  Not final shipping version, but a pretty good representation.

How does this new fuel probe work?  What are its features?

  • The design uses a very stable temperature compensated capacitive oscillator in conjunction with a tuned inductive filter. As fuel surrounds the wire probe, the capacitance changes.  The circuit is capable of resolving very small changes in fuel height and converts this to an output voltage, which is linear to the fuel level.  The more fuel, the higher the voltage.
  • The circuit is compatible with any type of gasoline, alcohol, or jet fuel. Kerosene is just fine.
  • The fuel probe unit provides a linear +5 volt output, compatible with almost all modern fuel display gauges and EFIS displays.
  • We specifically recommend our new RADIANT fuel gauge as a companion to the fuel probe.  While the product preview document you are reading is about the Fuel PROBE, we’ll interject for a moment and show you a few photos of our RADIANT fuel GAUGE.  Here is a screen shot of the fuel gauge:


Screen shot of RADIANT fuel gauge.  Left tank is empty and right tank has been drawing down fuel for approximately 10 minutes.  
We recommend this RADIANT fuel gauge for these reasons:  it has a great 2 minute sloshing filter built in; it shows 15 minutes of fuel trend history, and it is a full color, it is nearly weightless, it is sunlight readable display.  $200.

Now, back to the fuel probe:

  • The controller board on the fuel probe has one switch. For calibration: after powering up, press it quickly to set the “low” fuel point.  After filling with gas in the tank with the probe, press it longer (a few seconds) to set the “high” fuel point.
  • A remote switch may be mounted in the cockpit. Pressing it will reset the “high” calibration point.  To avoid accidental high point resets, this requires a five second touch on the switch.  This allows automatic recalibration after every tank filling.
  • For hard core techies: the unit’s connector also provides a +5v regulated output.  This allows a differential analysis of the signal level, as the output DAC is technically ratiometric to the +5V supply.  If you understand that, you’re an electrical engineer.  If you don’t, just ignore it.
  • For hard core OEMS: this product is also available with digital RS-232 serial output, periodically broadcasting the fuel level at 9600 baud.  This allows direct digital attachment to a variety of EFIS systems, assuming support from the EFIS vendor.


What does the Belite Capacitive fuel probe cost?  When is it available?

  • The unit is priced as follows: Unit + 6” probe — $200; Unit + 12” probe — $210; Unit + 40” (1 meter) probe — $250.  Custom lengths are available; contact factory.  Includes electronic unit in small case; wire probe of 6”, 12” or 40” length; power connector and pigtail harness; short coaxial cable to connect together probe to module.
  • First shipments are projected in Q2.
  • Orders received between March 8 and April 30 receive a 25% discount. In order to reserve your delivery position and receive this discount, we must charge your card at time of order.  All such orders are expected to ship by May 30.
  • A similar special is available on our RADIANT fuel gauge.   Orders received between March 8 and April 30 receive a 25% discount. In order to reserve your delivery position and receive this discount, we must charge your card at time of order.  All such orders are expected to ship by May 30.

Want to see a demo video?  Navigate here:

Cap Probe Demo Video Screen Shot

UltraCub Rib Construction — Aluminum ribs with cap straps

If you are building aluminum ribs (or aluminum / carbon fiber strips), the top and the bottom “T Strips” have to be glued on with 2216 or similar epoxy after they are riveted in place.

2216 is a 3M epoxy which is specified for use with aluminum bonding.  Surfaces must be scoured clean (eg,: 180 grit), then cleaned with acetone, before a liberal fillet of 2216 is added on all sides.

Tape was used to stabilize the strips while glue was applied and setting.

The tip and root rib get a square aluminum tube reinforcement.

We also recommend a 5″ vertical piece of angle on each rib, to prevent vertical crushing.  (Not shown, will provide pic soon.)

Rib Construction

Rib Construction

Root and Tip Rib reinforcement Root and Tip Rib reinforcement-2

How to cook trout in the wild, with wine and Tabasco.

In today’s cooking lesson, we’re going to learn how to prepare James’ amazing!!! mildly hot trout recipe.

The very first thing to do is to clean your trout.  It’s easy — cut off the head, gut them, clean out the innards, and leave the skin on.  The skin will come off easily while being cooked, so don’t worry about it.

Then, retreat out of the wild into a cabin with a stove and a frying pan.  This is a very important step — don’t get it wrong.

Start the preparation by melting a half stick of butter or margarine in the frying pan.  I used margarine, but you should use butter.  Really.


Melting a half stick of butter in a frying pan, over low heat.

Once that has melted and is lightly bubbling, insert the trout into the pan.  It is helpful if the tail sticks slightly over the edge — this will help impress your friends.


Trout beginning to cook in bubbly butter. The trout tastes best if the tail sticks slightly over the edge of the pan. No, I’m not explaining why that is so.

The next step provides some extra flavor — throw in 3 or so ounces of your favorite red wine.  The best wine is a cheap red, straight from Santa Clara, CA.  (Inside joke.)


Red wine in the pan.

Now, another critical step.  Locate an abused old pizza pan, such as shown in the following photo.


Abused old pizza pan.

Place the pizza pan over the frying pan.  You should be able to hear the butter / wine mixture lightly bubbling away.  Don’t set the heat too high — a low heat is fine.  (The stove I used in the cabin worked fine with the dial set to 2 (out of 10.))


Abused pizza pan is now covering frying pan and allowing trout to simmer in the wine / butter mix.

Allow 6 minutes to pass.  Then remove the pizza pan.  *Flip the trout using a spatula or fork.*  Your trout will now look like this:


Half cooked trout.

Insert a knife under the skin; peel off the skin.  It’s fairly easy to do.


Removing the skin off the half cooked trout.


Now the skin has been removed from this side. It’s starting to look very tasty — but wait! It’s still only half cooked.

Sprinkle four drops of Tabasco onto the half cooked fish.  If you wish, you may spread the Tabasco over the side of the fish.  Also add salt and pepper to your desired sodium level at this time.


Tobasco drops have landed. Also salt and pepper to taste.

RECOVER the pan with the pizza lid and allow to cook on very low heat for 6 more minutes.  AFTER six minutes have passed, turn the heat up to a medium / high number.


BRIEFLY turn up the heat!

After about 45 – 60 seconds at the higher heat, remove the fish from the pan.  With a little effort, you can leave the bottom layer of skin (which you just slightly seared) on the bottom of the pan.

Then, transfer the fish to fine china.  Consider adding a side of Lay’s Sweet South Heat Barbecue potato chips — a truly excellent choice.

This meal pairs well with a ridiculously cheap red wine in a plastic tumbler.


James’ hot trout with hot potato chips and red wine in a plastic tumbler.


Bon appetit! The trout flakes off the bones — and it was truly delicious.

From swimming in the stream to eating it at the table, this took about 75 minutes or less.  That’s fresh trout.

Let me know how this turns out for you.  Bon appetit!

New Motor Mount for Polini

We’ve received in some engine mounts for the Polini Thor 250.  These mounts have the advantage of allowing direct attachment to the firewall — with a couple of caveats, which I’ll get to.  It’s all amazing light and strong.

The Mounting plate is CNC machined and comes with rubber bushings to attach to the motor and to the firewall.

Polini Engine Mount

View of the Polini Thor 250 mounted to a Belite ProCub.

Polini Engine Mount-2

View behind the engine, showing the plate and one of the angle aluminum firewall reinforcements.

Polini Engine Mount-3

View of the angle reinforcement on the other side of the engine.

Polini Engine Mount-4

View from the top of the engine looking down at the firewall.

Polini Engine Mount-5

View *inside* the cabin, looking forward at the firewall and the large aluminum angle reinforcement. The middle three bolts are attached to the Polini motor mount plate.

Polini Engine Mount-6

A view from below the engine, looking up.

Polini Engine Mount-7

The motor mount plate is virtually invisible behind the motor.

Here’s the caveats:

1)  This motor is so light, you’ll need to be wary of Center of Gravity issues.

2)  The installation is so small and tight, you may need to mount the motor 4 or 5 inches away from the firewall in order to have the correct placement of the propeller relative to the cowl.  This may be done by using aluminum rectangular tubing to ‘extend’ the firewall forward.    (Not described here, but eventually coming.)

Not shown is how to mount the radiator or the water overflow tank.  (We’ve previously posted many pictures of the radiator on the ProCub / Polini installation.)

Rear Fuselage Construction, continued

Let’s continue our work on the rear fuselage.

You will have two top rear fuselage plates; they have a notch in them which goes around the rudder post.  They are laminated together as we’ve done for other pieces.

After laminating the top rear fuselage plates together using a high quality wood glue, the resultant piece is sanded and then glued to the foam using gorilla glue or 2216 glue.  The edge is also routed round; this is easily done either before or after gluing to the foam.

Rudder Test Failure-9

Top rudder reinforcement plate. Note that the edges have been routed round.

The rear rudder post receives a 4″ strip of 2 oz glass on each side.  After sanding, we apply some lightweight spackle over the glass to smooth the joint.

Carbon fiber cloth is cut to fit over the top and the bottom plate.  Each piece is, in turn, epoxied in place.  The overlap area should be at least 4″.  Cut around the exit point for the rudder cable.

There are two pieces of vertical stabilizer foam:  the main and the front piece.  They are glued to the rear rudder post and to the front rudder post using gorilla glue.  The front piece is also ‘pinned’ into the rear fuselage foam using scrap pieces of 1/4″ aluminum tubing:  a 12″ piece and a 6″ piece.  Drill a quarter inch hole, clean the scrap pieces of tubing; and insert into the holes using water mist and gorilla glue.

Rudder Test Failure-10

Orientation of 1/4″ aluminum pins in front rudder piece.

The above photo shows the carbon fiber cloth reinforcement which was epoxied over the wood and fuselage.  A bottom piece is also epoxied over the bottom wood piece; the overlap area should be at least four inches.

Carbon Fiber over bottom wood

Carbon fiber cloth epoxied over bottom wood. Note cloth overlaps with carbon fiber cloth which was epoxied on the top wood. Make cut in cloth for rudder control cable tube as necessary. Overlap area is at least 4″.

After the glue sets, we route a round edge to the top and front edges of the vertical stabilizer, and then apply a 4″ fiberglass reinforcement over all edges, and also over all tube / foam glue joint areas.  The front foam piece is also glassed to the fuselage using 4″ pieces on each side and around the front.

There are three more pieces of wood to be installed in the rear fuselage.  The first is the lower front fuselage reinforcement.  The pieces are laminated together as shown:

Lower front fuse wood reinforcement

Lower front fuselage wood reinforcement laminated together.

This piece fits on the lower bottom of the fuselage, where it butts to the cabin.  The notch allows proper operation of the elevator bellcrank.  In order to install it, the foam is cut out exactly 1/2″ (the thickness of the piece), and the part is Gorilla glued in place.

lower front wood with gorilla glue

Lower front wood with generous Gorilla glue.  Note use of peel ply below to ease cleanup.

In order to make it easy to glue, and in order to ensure that the Gorilla glue didn’t get over the fuselage, the fuselage is lifted into place.

lower front wood gluing with weights

The fuselage is carefully squared to the wood piece, and held in position with same added weight.

The view on the floor:

lower front wood gluing with weights 2

The view of the gluing process. Note that the Gorilla glue is expanding outward and down, making cleanup easy.

Next we laminate the lower front load spanner.

Lower front load spanner being laminated using high quality wood glue.

Lower front load spanner being laminated using high quality wood glue.

And we place it over the bottom of fuselage, using a sharpie pen to mark areas to be cutout.

lower front wood load spanner_-2

Cutout areas marked.

lower front wood load spanner_-3

1/2″ depth waste areas routed out.

lower front wood load spanner_-4

Test fit. This example wasn’t cut as exactly as it could have been. You can do better.

lower front wood load spanner_-5

Use only 2216 glue to attach this piece.

24 hours later, after the 2216 glue has set, sand the entire surface smooth.  Large gaps must be filled with additional 2216 glue.  Small gaps (less than 3/16″ depth) may be filled with spackle.  There was a slight warpage in the wood piece, it was also sanded out.  Note that the front piece has also been sanded to uniform fit perfection.


After sanding.  Small gaps may be filled with spackle.  Large gaps must be filled with additional 2216 glue.

The next piece of wood to be installed is the trim ring around the cargo area.

The two pieces are laminated together.  Here they are, before lamination:

Cargo trim rings, before lamination.

Cargo trim rings, before lamination.

The location of the foam cutout is marked with a Sharpie.

cargo trim rings-2

Cargo trim ring shown in place with sharpie marking the route line.

cargo trim rings-3

A router bit set to a depth of 1/2″ (the depth of the trim ring) helps make a clean cutout.

cargo trim rings-4

The trim ring is glued in place with Gorilla glue.

After the glue is set, excess glue is cutout and removed.