Fuel Consumption: Cessna Indicator Vs. Shadin

[Jose L. Ichaso]

Does any one`s 337 equipped with a Shadin fuel computer has diferent indications at the fuel comp. and the Cessna indicator. The avionics shop says is because it takes it`s reading from diferent places ( before and after the fuel injection unit). For exmple I have record this readings:


GPH

Cessna Ind. Shadin
6500' 22" 2400rpm 8 & 10 11.2 & 11.0

(other day flying)
7500' 21" 2400rpm 9 & 10 10.9 & 10.9


When refilling the tanks the shadin math it by 3 or four gallons. If I wouldn't have the computer, howcome can you trust this indication?
By the way,I had send this instrument to the shop to have a check and calibration with the same results.

[Bob Cook]

Jose

The cessna fuel flow indicator is based on FUEL PRESSURE to sense fuel flow.

The shadin uses a DIGITAL flow sensor (much like a miniature paddle wheel in the fuel "stream". It is located post fuel control unit.

Each sensor is different in that the calibration (flow rate) varies from unit to unit. The calibration is recorded on the side of the fuel sensor and this number needs to be inserted into the computer for calibration to be accurate. Basically it is the number of turns of the paddle wheel / unit of volume (fuel). If you give Shadin the serial number of the sensor they can tell you the calibration or correction required.

It is best to accurately record your fuel usage after a long trip and apply a correction if accuracy is CONSISTANTLY out. I find my accuracy to be within about 1 gallon per 140 gallons or less than one percent. In fact, I no longer have the Cessna flow rate indicators.

Probably a sensor was replaced in the past without applying the correction required and thus the difference in readings.

hope this helps

Bob

[Wayne Pearce]

Jose
I agree with Bob once set up with corrections put into the unit should be very accurate other than it does not seem to read when engines idling below 1000rpm during taxi, my unit is repeatably accurate over many trips and it also helps me smooth out the engines during climb.

8000ft at 21" at 2350rpm
front 39 lphr
rear 41 lphr
9000ft at 20.5" at 2350rpm
front 38 lphr
rear 39 lphr
10000ft at 19.5" at 2350rpm
front 37 lphr
rear 38 lphr

Depends a bit on temp / density, as I said very reliable would not be without it

Regards ............. Wayne