Fuel pressure, sensor

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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roger lee
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Re: Fuel pressure, sensor

Postby roger lee » Sun Nov 22, 2015 9:50 pm

7) There are many older model aircraft operating with NO FUEL RETURN LINE at all, running very simple and reliable fuel systems... and I'm not hearing any complaints!

This worked for the older fuel pumps, but not the new Corona and especially with an electric pump too. This seems to be a low wing issue and I'm not sure of a fix.
Roger Lee
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SportPilot
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Re: Fuel pressure, sensor

Postby SportPilot » Sun Nov 22, 2015 9:54 pm

.......
Last edited by SportPilot on Sun Mar 20, 2016 7:01 pm, edited 2 times in total.

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drseti
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Re: Fuel pressure, sensor

Postby drseti » Sun Nov 22, 2015 10:06 pm

In an ELSA or E-AB, anything is allowed that doesn't take it outside of the operational limitations which define an LSA. In the case of an S-LSA, anything is allowed if the manufacturer will issue an LoA and the user complies with it to the letter, and makes the required logbook entrie.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof. H. Paul Shuch, Ph.D., CFII, LSRM-A/GL/WS/PPC, iRMT
AvSport of Lock Haven
fly@AvSport.org
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designrs
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Re: Fuel pressure, sensor

Postby designrs » Sun Nov 22, 2015 10:22 pm

drseti wrote:In an ELSA or E-AB, anything In the case of an S-LSA, anything is allowed if the manufacturer will issue an LoA and the user complies with it to the letter, and makes the required logbook entrie.


... OR if the update is in accordance with an updated IPC. Correct?

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drseti
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Re: Fuel pressure, sensor

Postby drseti » Sun Nov 22, 2015 10:46 pm

Yes, I believe a modification to a component that is reflected in the IPC constitutes an authorization to replace an old component with a new one. But, be cautioned that this often requires compliance with a related or accompanying service bulletin. An example is the new style Rotax cylinder heads. If you use them, you must comply with a service bulletin which involves recalibration of your CHT indicator.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof. H. Paul Shuch, Ph.D., CFII, LSRM-A/GL/WS/PPC, iRMT
AvSport of Lock Haven
fly@AvSport.org
http://AvSport.org
http://facebook.com/SportFlying

3Dreaming
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Re: Fuel pressure, sensor

Postby 3Dreaming » Sun Nov 22, 2015 11:22 pm

designrs wrote:
drseti wrote:In an ELSA or E-AB, anything In the case of an S-LSA, anything is allowed if the manufacturer will issue an LoA and the user complies with it to the letter, and makes the required logbook entrie.


... OR if the update is in accordance with an updated IPC. Correct?


That's not how I understand it, but I suppose it could be different from manufacture to manufacture. My understanding is that ASTM requires tracking of any changes to each aircraft. You should follow what ever form of tracking your manufacturer requires.

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FastEddieB
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Re: Fuel pressure, sensor

Postby FastEddieB » Mon Nov 23, 2015 9:16 am

roger lee wrote:This seems to be a low wing issue and I'm not sure of a fix.


My Sky Arrow is high-winged, but is the functional equivalent on a low-wing, in that the engine is above the fuel tank.

I've had issues as well. My checklist calls for "Boost Pump...ON" for takeoff and initial climb.

Climbing with the boost pump on, fuel pressure is in the green. When I turn it off, fuel pressure drops precipitously, sometimes dropping to near zero before climbing it's way back up into the green. It's not hooked up to any warning mechanism, but if it was, it would surely go off. Since the engine has never sputtered, it's my "new normal", and I just watch the fuel pressure carefully when I switch the boost pump off. It's the old-style pump - I have a new-style in a box and carry it with me on trips, just in case. I'm just not motivated to mess with a working pump.

Finally, the situation seemed to get worse a few years back, and that was traced to a failing pressure sender. I relocated it off of an engine baffle to a remote location, and have had no further issues.

This was in 2011, prior to replacing the sender:

http://youtu.be/kpiH01GjBNM

Anyway, good luck. And keep in mind only a tiny bit of positive pressure is all it takes to keep the float bowls full and the fan turning. You may have a perceived problem, where no real one exists. If alarms were not going off, the whole situation might seem a lot less "alarming"! 8)
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
FastEddieB@mac.com

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bstrachan
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Re: Fuel pressure, sensor

Postby bstrachan » Mon Nov 23, 2015 10:06 am

designrs wrote:UPDATE:

I have spent MONTHS and $$$$ diligently trouble shooting this!
Replacing parts, researching everything, contacting the US importer, communicating with other owners with similar problems, etc.

Here's where it's at:

1) Mechanical fuel pressure gauge testing correlated with the Dynon readings. The problem is not electronic, sender, or Dynon.

Good that you confirmed this. That takes one unknown out of the equation. It also makes sense given the variety of measurement systems that all manifest the same problem.

2) US Sport Aircraft has updated the fuel system in the new SportCruisers. The whole system is completely different. Fuel distribution, routing, fuel pressure system, etc.. The main feature is a CHECK VALVE related to the electric pump and main fuel feed line to the mechanical pump, and also the elimination of a redundant fuel line. An upgrade kit is available for previous years.

Is a diagram of this updated fuel system available to the rest of us??? I'd like to know what they did.

3) Research indicates that ADDITIONAL RESTRICTION OF THE FUEL RETURN LINE would raise fuel pressures. I have heard of EXPERIMENTAL RV-12's having success with this. (Different rules about modification apply of course.)

4) Many aircraft with low wing, the NEW PUMP, and FUEL RETURN LINE are experiencing low fuel pressure issues, especially when operating in hot climates. Specific models that I have heard of include: SportCruiser, RV-12, Sting, etc.

5) In my opinion, it is VERY LAME that at least one major manufacturer requires the electric pump to be on at all times. That should NOT be required or necessary!

I totally agree.

6) This is an INTERMITTENT problem that SOME aircraft experience under SOME conditions, making it especially troublesome.

That's the rub. I don't recall having any low fuel pressure indications at all for the first couple of years I owned the Sting. Then it got to the point where I could count on having at least one low pressure episode every flight. The worst was coming back across the Grand Canyon about a year ago. I got continuous low fuel pressure light every time I turned the AUX pump off, continuing for about 20 minutes. Then the fuel pressure went back to normal with the AUX pump off, for the rest of the flight. Nothing else changed. Temperature, altitude, power setting, the kind of fuel, all remained the same. So why did the low fuel pressure situation go away????? And recently, I've had no low fuel pressure indications for the last month or so. Mechanical problems don't "fix themselves" in my experience. What is going on here???

7) There are many older model aircraft operating with NO FUEL RETURN LINE at all, running very simple and reliable fuel systems... and I'm not hearing any complaints!

It is extremely FRUSTRATING that "improved" systems and "improved" parts subject owners to theses worrisome issues.

** Looking at all available information and options to resolve this issue and expect progress. **

A suggestion. It's not FUEL PRESSURE that keeps that big fan-like thing on the front of the airplane turning, it's FUEL FLOW. Maybe the Rotax/Bing setup does not require much pressure to provide an adequate fuel flow (I'm talking about 1 PSI or less, which is hard to measure accurately and which is BELOW the threshold on my EIS). I say this because although lots of people are reporting this low fuel pressure indication, I have not heard of a single incident of engine stoppage or forced landing due to "low fuel pressure". I just ignored the low fuel pressure light on two occasions (once climbing out with WOT). The engine did NOT falter or hiccup and the fuel pressure came back up all by itself after a short time. So, I am considering installing a fuel flow meter. The problem is that fuel return line. You have to have two flow sensors and an indicator that can measure the difference between the flow in the feed line and the flow in the return line, which is the flow to the engine. These are available but expensive. But if you measure the same fuel flow at the same power setting regardless of what the fuel PRESSURE reads, you could conclude there is no problem. Might be worth doing.



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bstrachan
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Re: Fuel pressure, sensor

Postby bstrachan » Mon Nov 23, 2015 10:12 am

I hadn't seen Fast Eddie's comments when I wrote mine, but it sure sounds like we're on the same page.

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drseti
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Re: Fuel pressure, sensor

Postby drseti » Mon Nov 23, 2015 10:37 am

FastEddieB wrote:My Sky Arrow is high-winged, but is the functional equivalent on a low-wing, in that the engine is above the fuel tank.


Actually, Eddie, your plane has a high wing -- and an even higher engine. ;)
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof. H. Paul Shuch, Ph.D., CFII, LSRM-A/GL/WS/PPC, iRMT
AvSport of Lock Haven
fly@AvSport.org
http://AvSport.org
http://facebook.com/SportFlying

Nomore767
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Re: Fuel pressure, sensor

Postby Nomore767 » Mon Nov 23, 2015 10:54 am

drseti wrote:
FastEddieB wrote:My Sky Arrow is high-winged, but is the functional equivalent on a low-wing, in that the engine is above the fuel tank.


Actually, Eddie, your plane has a high wing -- and an even higher engine. ;)


But not when he flies it upside down!

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designrs
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Re: Fuel pressure, sensor

Postby designrs » Tue Nov 24, 2015 8:47 am

>> The problem is that fuel return line. You have to have two flow sensors and an indicator that can measure the difference between the flow in the feed line and the flow in the return line, which is the flow to the engine. These are available but expensive. But if you measure the same fuel flow at the same power setting regardless of what the fuel PRESSURE reads, you could conclude there is no problem. Might be worth doing.

My fuel flow meter comes AFTER the return line. So I always see actual fuel flow.

>>And keep in mind only a tiny bit of positive pressure is all it takes to keep the float bowls full and the fan turning. You may have a perceived problem, where no real one exists. If alarms were not going off, the whole situation might seem a lot less "alarming"!

Exactly! This PERCEIVED PROBLEM has caused me months of aggravation, lots of $$$, and sucked a much of the enjoyment out of my flying experience!! While I do not have a Dynon malfunction, and there is something going on with my fuel pressure, alerts and alarms are keeping me from enjoying a perfectly good airplane that runs just fine.

Now doing fuel system upgrade to newer SportCruiser specs including: New fuel lines (I'm almost due for rubber anyway), elimination of a redundant fuel hose on the supply side, and a check valve related to the electric pump.

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bstrachan
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Re: Fuel pressure, sensor

Postby bstrachan » Thu Dec 03, 2015 1:12 pm

2.2 hr cross-country yesterday in the Sting. Fuel pressure solid >3 PSI all the time. Free air temp at cruise altitude ~48 F. Shell gas? Cooler winter temps? Who knows.

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designrs
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Re: Fuel pressure, sensor

Postby designrs » Sun Dec 06, 2015 11:46 pm

I tested Shell Premium gas in Florida... 10% ethanol.
Guess I have to visit Utah for ethanol free and fill up!

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MrMorden
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Re: Fuel pressure, sensor

Postby MrMorden » Mon Dec 07, 2015 9:43 am

designrs wrote:I tested Shell Premium gas in Florida... 10% ethanol.
Guess I have to visit Utah for ethanol free and fill up!


The 93 octane premium here in Georgia from my local BP station tests out at about 5-6% ethanol. Not bad.
Andy Walker
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA


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