Because Owning And Flying Your Beechcraft Can Be Done Safely AND For Less Money!
  Fuel Flow Transducer Mounting

 

Recently a Beech Lister and fellow Baron owner had his plane in for some starter maintenance. When the shop began to prime the engine to test the starter, fuel began to leak all over the engine from his fuel flow transducer mounting configuration

 

Here is what his configuration looked like:

 

 

Can you see what's wrong with this picture?

 

The leaks were the result of the previous installer using hard lines for the transducer install! And aluminum lines to BOOT!

 

Both JPI and EI have specific install instructions to use flexible hose for this critical connection to the fuel spider. There is way too much vibration going on up there on top of the engine for any hard lines to survive. This owner was extremely thankful that the leak did not happen in flight with his family on board. Very scary!!!!!

 

Check your Fuel Flow install to be sure your installer read the instructions <nbg>!

 

Here is his revised install, thanks to a fortuitous find by the shop replacing his starter:

 

 


 

Here is another Beech Lister's transducer install on a Bonanza:

 

 


 

Here is another fuel flow transducer install on an IO-470N

 

 


 

So, if you have a digital aftermarket fuel flow system installed, give your set up a look to be sure it uses flexible lines over the engine and avoid a potentially very scary and dangerous situation.

 


 

Fuel Flow Transducer Install WATCH OUT!

 

Many folks are installing digital fuel flow instruments these days. They are awesome pieces of instrumentation and when properly installed and calibrated can give us something on the order of 1% accuracy of our fuel consumption and when connected to a GPS signal give us fuel remaining at destination instantaneously!

 

Here is an install watch out that has been identified by Dan M. with sleuthing help from Mike Busch. The Beech Talk thread is HERE and Dan's narrative follows:

 

The fittings differed internally, and were reversed - very likely when the Shadin was installed 12 years ago. The plane has burned through 5 cylinders since then. Takeoff power was reduced when at low elevation airports (not good for clearing trees). The only reason the engine did not destroy itself was it's low compression ratio (7:1).

Reversed the fittings, reset the metered pressure back one turn to undo prior test, and started it up. Full power, full rich, fuel flow went to 21.5 gph with the factory pressure gauge right at the SL takeoff mark.

I have attached a photo of the fuel manifold. Notice the capped restricted elbow fitting (I applied yellow torque seal for future identification). The normal elbow fitting is behind, pointing away, and connected to the fire-sleeved fuel hose in the background. The brass plug near the top with the tiny hole is the vent for the diaphram.

 

 

So before "Joe Mechanic" starts hooking up your transducer line to the fuel manifold, you might want to be sure you and he know what's coming out or NOT COMING OUT of that fitting!

 

The fitting on the spider manifold with a "restrictor" orifice are usually used to provide the pressure reading to the factory fuel flow (or pressure readings converted to FF gallons/hour) gauge inside the cabin, therefore, you do not want a full pressure spray of gas inside the cabin if the hose cracks. Others have commented these fittings SOMETIMES can be found painted red.

 

The problems seem to arise when the restrictor fitting is inadvertently or mistakenly placed on the supply side!

 

Here is a bulletin on it:

 

Continental: IO470K; Improper fuel fittings; ATA 7324 A technician states, "(We performed...) the fuel injection setup per TCM SID 97-3E, but the electronic fuel flow computer showed flow below specifications. We were unable to increase flow sufficiently by increasing pressure. (Subsequent inspection revealed the...) inlet elbow fittings (P/N's 631658 and 628437) had been previously reversed, probably twelve years prior during installation of an electronic fuel flow transducer. Part

631658 has a restrictor orifice, while 628437 does not. The parts look identical externally. It takes a very careful (observation) to see the internal difference. The TCM engine overhaul manual does not mention this.

The TCM parts manual shows the different part numbers, but does not describe the differences. This would be a very easy mistake to make, and very difficult to diagnose later. (Again), this problem probably started twelve years ago, and was not detected or corrected until now. This airplane had five cylinders changes during this time - (most likely) caused by lean operation at full power. The aircraft (may not have...) generated full power on takeoff due to a very lean, full rich mixture. It is critical to communicate this to mechanics and owners to prevent a dangerous condition."

 

PS: Good Call on installing a FF instrument and hooking it to your GPS! Takes a lot of the old school estimation out of "Wonder if I have enough fuel to make it?"

 


 

Here is a narrative by Beech owner Mike T. regarding his search for fittings for his fuel flow transducer install:

 

I finally found a source of the steel fittings I need to install FloScan transducers on a pair of TCM engines.

 

I wasn't having success with suppliers of aviation-type hardware but checking with suppliers of hydraulic fittings got quick results.

 

What I need are 1/8 - 1/4 male-male NPT FF pipe nipples, SAE 104137. They cost less than $2 each. Parker is one mfg.

 

These particular fittings might not be appropriate for any individual engine. It depends what fitting is on the flow divider, which may or may not conform to the TCM parts catalog. (Going down the aviation road got scary as one potential vendor got an "expert" involved who mentioned the necessity of meeting "aerospace standards" and such.)

 

Hydraulic supply houses might be a good source for other types of fittings we use. Some sell a big variety of AN fittings, for instance, dwarfing the selection offered by popular aviation vendors. (A couple of years ago I paid an aviation house almost $30 for a brass elbow fitting that's readily available in the real world for $2.05.)

 

Certainly, it's up to the installing mechanic to determine suitability.

 

 

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