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  #1  
Old 03-03-12, 12:43 AM
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ConwayB ConwayB is offline
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Any recommendations for an electronic fuel gauge?

Hi,

I have an O2 (337B) with the military fuel gauge. The aux tank readings are always spurious with full scale deflection up on one and no indication on the other, or intermittent at best. The main tanks seem OK. We've tried changing probes, cleaning contacts and micro switches, but no joy. Swapping probes doesn't seem to shed any light either. The problem appears to disappear, only to reappear again. Hard to pin down if it's a gauge problem, wiring, switch or probe issue.

I am thinking about trying an electronic fuel gauge. Does anyone know of a gauge that's STCd for a 337B that provides a good indication of fuel qty and any probes that go with it. The probes are capacitance types and I am hoping that they are not the source of the problem and that it is just the gauge.

Also, can anyone tell me what the Pennycap fuel system is and whether the O2A has this system. Many fuel gauges say they are compatible with the Cessna Pennycap system and I have never heard of it.

I am a military pilot and am used to having accurate fuel indications and making in flight calculations and decisions based on accurate figures, so eyeballing and dipping is not a satisfactory solution to inaccurate gauges. What's more, in Australia (and according to the US FARs BTW,) an accurate means of assessing fuel quantity in flight is mandatory. Fuel supplies in Australia can be few and far between, and the aircraft may be used for long range over water patrols, as well... So you can see my concern!

Thanks in advance.

To see the machine, go to www.ipas.com.au

Conway

Last edited by ConwayB : 03-03-12 at 04:39 AM. Reason: Extra info added
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  #2  
Old 03-03-12, 11:34 AM
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Ernie Martin Ernie Martin is offline
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The sentence in italics below was added 3/11/2012. The penultimate paragraph was expanded on 3/15/2012

I'm on my second 337 (a G model without aux tanks) and they've always has fuel gauge issues. On my current one, after lots of work, I've given up, relying on a calibrated stick before each flight, VERY careful flight planning, and keeping track of both current and recent fuel consumption (i.e., gal per hour at various operating conditions).

Let me add that most models have an electronic box (typically on the roof behind the headliner) that takes the inputs from the tank sensors and generates a signal for the gauges. Therefore, I don't think that using the old sensors with a new electronic fuel gauge will work.

Let me add that with separate main and aux tanks, there are techniques for reliably managing fuel on long trips -- perhaps even extending range. My first 337 was a 337D with aux tanks and I used some of the techniques to fly from Miami, FL, over the Rocky Mountains, to Boise, ID. These techniques depart from POH procedures and should be used only in special cases and by knowledgeable pilots who are very familiar with the aircraft's fuel system (the "Fuel Supply Management" page on my "backup" website www.SkymasterUS.com provides such familiarity).

I'll describe one of them for reference only. You should use it ONLY if you independently determine that it is safe to do so. As a minimum, it assumes that you know with certainty that one engine (say, the rear) consistently consumes more than the other. On a long mission you start with all tanks full (which means YOU did it or visually checked). Run on mains until the rear engine starts stumbling because the right main tank is depleted. Immediately switch the front (non-stumbling) engine to its aux tank. After confirming front engine is running fine from aux tank, switch rear engine fuel selector valve to cross-feed from the left main tank, using the electric pump to initiate flow and restart rear engine (you know the left main has fuel because a) the front engine was drawing from that tank only moments ago, and b) fuel from the left aux tank is now flowing INTO the left main due to the design of the system, where return fuel always goes to the main). After the rear engine is working flawlessly on crossfeed (about a minute) switch the rear engine to the aux tank.

While there are risks and trade-offs, covered in the next paragraph, there are several advantages. First, you will know PRECISELY what your consumption has been today (based on the time and gallons used to main-tank exhaustion). Second, you know exactly how much fuel remains (the contents of both aux tanks), so, third, you can determine exactly what your remaining range is (say you were using 9 gal/hr per engine and you have 36 usable fuel in the 2 aux tanks and you want a 30-min margin, so you still have 1.5 hours to landing).

There are risks and trade-offs The risk is that if you miscalculate and have very bad luck, both engines will die, you won't be able to draw from the full aux tanks and you'll be on a glider. If you are CERTAIN, however, that one engine (doesn't really matter which) has greater fuel consumption, then one will run out of fuel many minutes before the other one, and this works well. (BTW, even if on THIS trip the consumption was nearly identical for both engines, what are the chances that both engines will run out at EXACTLY the same time? Even if they are 5 seconds apart, this works, provided you're ready, do it right, and do it quickly.) The trade-off is that there are CRITICAL fuel management tasks ahead. In roughly 60 minutes the aux tanks will run dry, perhaps at nearly the same time, and you will need to switch to the mains using the aux electric pumps (to access the roughly 60 minutes of additional fuel that was initially in the aux tanks but was transferred to the mains by the return fuel/vapor lines). The reason for the word CRITICAL is that you don't want the tank swap while you are low and slow in the approach or pattern of the airport, and notice that if you adhere to IFR fuel reserves of one hour, that is exactly when it will happen. So, if you're landing 30 minutes after going to the aux tanks, you will be OK but if it's much after that, then the swap needs to occur while at altitude before getting low and slow. A rough rule of thumb is that the fuel in the main tank after you switch back to it will last as long as the time that you ran on the aux tank (e.g., if you ran 30 minutes on the aux, then you have 30 minutes of fuel available on the main). You can see, considering these risk and procedural issues, that the approach described here should be done as a rare exception for trips that are at the outer edge of the airplane's range and only by a competent, experienced pilot who knows the fuel system thoroughly.

While repetitive, I need to stress again that this is for reference and should not be used except in special cases, such as an aircraft with appreciable different consumption between the front and rear engine, and then only after careful analysis and preparation.

Ernie

Last edited by Ernie Martin : 03-15-12 at 12:05 PM.
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  #3  
Old 03-03-12, 04:41 PM
rick bell rick bell is offline
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shaddin - better than sliced bread and friggen accurate
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  #4  
Old 03-03-12, 06:08 PM
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hharney hharney is offline
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https://www.ultra-fei.com/index.php?page=auracle2120


http://www.aerospacelogic.com/index.php
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Last edited by hharney : 03-03-12 at 06:11 PM.
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  #5  
Old 03-03-12, 11:01 PM
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Skymaster337B Skymaster337B is offline
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A calibrated fuel stick for a Skymaster...where can I get one?
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  #6  
Old 03-04-12, 12:28 PM
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Ernie Martin Ernie Martin is offline
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Here is one source: www.mypilotstore.com/mypilotstore/sep/1177

It's easy to calibrate. I have the FuelHawk shown in the link; the calibration for my 337G with extended range tanks is shown below :

Mark Gallons (Usable)
0 31.8
1 37.8
2 42.7
3 46.1
4 49.4
5 52.5
6 54.8
7 57.0

Ernie
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  #7  
Old 03-04-12, 02:14 PM
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Gord Tessier Gord Tessier is offline
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Hi Ernie, isn't the 1973 337G 59 gallons useful. Your gauge tops at 57?
Just wondering.
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  #8  
Old 03-04-12, 02:53 PM
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Ernie Martin Ernie Martin is offline
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Seven is the highest wet marker. Completely full (59) is at a line somewhere between 7 and 8.

Ernie
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  #9  
Old 03-04-12, 08:46 PM
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Gord Tessier Gord Tessier is offline
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Ahhh, ok now I get it. I just ordered one. I was always filling the tanks and relying on the Shadin to tell me how much fuel I had left. I never felt really comfortable doing that.
Thanks Ernie.
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  #10  
Old 03-07-12, 09:26 AM
jchronic jchronic is offline
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Being highly fuel-conscious on our extended overwater surveys, I agree with the kudo to the Shadin. Over time, with a visual verification of full tanks on departure, and careful tracking of fuel adds after landing (I keep a running spread sheet), I've found it to be consistently accurate within 1-2 gallons. I try to maintain my fuel gauges, but just as a 'sanity check against' the Shadin and time flown/fuel burn - and in case of a leak somewhere that doesn't register on the Shadin sensors.

At our usual (low) altitudes and distance offshore I can't risk waiting for an engine to stumble before switching tanks. So when using the aux tanks, I burn the mains for 1 hour, then switch one engine to aux at a 'cardinal' time (e.g. on the hour or at 15, 30, or 45 mins after) and note the time on my kneeboard. Then 15 mins later, switch the other engine to aux, burning both aux tanks exactly 1 hour.

Since our survey cruise is 100 knots, there's aux fuel left at the end of an hour. If I need to use it, I go back to each aux tank - one at a time - for another 15 minutes. Again, at a higher altitude I'd wait for the fuel flow to start dancing around, but not where we are.

Joe
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  #11  
Old 03-10-12, 02:54 PM
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n86121 n86121 is offline
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Fuel Management

I use the mains until there is abouot 30 min to 1 hour left - 16 gals.
I have a shadin set to warn me "low fuel" to switch to aux at 76 gals used from mains.
That assures me fuel in the mains for landing.

Then I switch to aux.

When there are about 4 gals left in each aux, i.e. 30 used out of 38,

I switch back to the mains for landing.

I assume each tank may be 4 gals low, just because...
Un-level filling, combustion heater use, whatever.

I set the totalizer to assume only 120 gallons, not 128.

It would be really nice if the aux tanks could be ported somehow into the mains....

As they did with later models.

D
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  #12  
Old 03-11-12, 07:40 PM
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Ernie Martin Ernie Martin is offline
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For clarity, I added a sentence in italics to my March 3 post above.

Ernie
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  #13  
Old 09-22-19, 08:10 AM
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patrolpilot patrolpilot is offline
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Quote:
Originally Posted by Ernie Martin View Post
Here is one source: www.mypilotstore.com/mypilotstore/sep/1177

It's easy to calibrate. I have the FuelHawk shown in the link; the calibration for my 337G with extended range tanks is shown below :

Mark Gallons (Usable)
0 31.8
1 37.8
2 42.7
3 46.1
4 49.4
5 52.5
6 54.8
7 57.0

Ernie
Thank you, Ernie! Proof that there is no such thing as an old topic. I just bought a G, and this was to be the first order of business!

Of course, I will verify the numbers for my airplane but hoped to establish a minimum fuel load for takeoff referenced to the "zero" point that you have measured. That is the only thing about the extended tanks, lack of a visual check, but I'm happy to have the airplane. Too bad that Cessna never engineered a drip stick on the inboard tank. I've used them plenty of times on the airliners I've flown. Probably enough pilot vs. fuel problems to begin with. Why fly if you can't see it?
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Old 09-24-19, 12:52 AM
wslade2 wslade2 is offline
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I have been looking at CiES fuel sensors and Aerospace Logic display since I got into my plane in March. Have spoken with both CiES and Aerospace Logic. Also Possibly newer Electronics International engine monitor with the CiES sensors. Been slowed down with other maintenance items. Of course always dip the tanks.
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  #15  
Old 09-25-19, 03:04 PM
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The more I look at them; I'm thinking the Insight Gem 4 Skymaster over the JPI 760. I like the display a lot better. I'm also thinking of the Strike Finder as well. I have the ForeFlight stuff on the iPad, but I love doubling up on information.

I had a WX-10 in my Piper Pacer commuter, it saved my bacon many night.
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