S1 sight gauge accuracy

[Gaston]

Hello Guys

As you know I recently began flying the S1 I have saved from the darkness.
I recently experienced a total power loss flying T & G with the S1.
and I think it could possibly help S1 pilots should the same error be neglected.
I my case I was Lucky enough that it quit at the very good place so I was able to land on a taxiway lined 45° to the left.
I didn't know one could land while in a turn, but we can, it's not very beautiful to see but it works.

the fact is that in the last few weeks before the event I've been working W&B on my S2 , and so doing, the fuel was transferred from The S1 to the S2 many times.

at the time of the incident,having no idea of the fuel level in the S1,
in the evening I checked the fuel level in the S1 looking at the sight gauge. it read about 4 us/G my plan was to fly early the next morning by 5.00 am when traffic density is low.
Knowing my flight would last about 50 minutes I added another 4 gallons in the tank, and the sight gauge showed
7.5 to 8 us/g. so with that amount of fuel I thought I was safe for a 50 min flight with plenty of reserve.

so the next morning after 50 min of flight the engine stopped at climb out on my last T & Go I had and airliner behind me at 2 miles closing in rapidly.
Runway 24 being closed for work, I knew that if I landed on the runway 29 the airliner would have to overshoot , and the airport would be closed as no other runway was available.
so I advised the controller that I was landing on taxi way GOLF , and landed...


then investigation showed that when the sight gauge showed 4G in fact the tank was empty.

there was a note adjacent to the sight gauge graduations written ''GROUND'' so I believed it was OK

but in fact the tank being a two level set up... the gauge is extremely imprecise on the ground.
there was really some fuel in the sight gauge when is was showing 4G but that was just a few last drops...
trapped in the line.

I was very Lucky with the ending , and as my sister said , there was a big amount of luck on-board with me that morning.

So Have a look at the picture included so you will understand the issue.
the sketch is not perfect but I did my best to make it evident.

that was another reason why I didn't fly much with the S1 , because I had to tear down the complete fuel system , including tank removal and cleaning of every smallest part in the fuel line.

This was one of the very rare flight I flew with a tank less than full, and I will remember it.

Hope this may help someone avoid to get caught...


Take care guys

 

[soneraii]

Hmm, good lesson here, good post, thanks for sharing. There is a lot of food for thought here.

Looks to me that if the airplane was to fly in a nose high attitude one could trap fuel in the aft portion of the fuel tank resulting in fuel starvation also. My forward lower portion of the fuel tank holds two gallons. Seems wise initially to consider that unusable fuel or ballast?? I think until I learn the idiosyncrasies of my fuel system I will fly with a near full tank.

Kevin

 

[Gaston]

Hello Kevin

forward portion of the tank on my S1 holds 3 gallons, and I know it is usable to the last drop.
for W&B purpose I consider these two volumes are different , with two different arms.

fuel CG is much more complicated than with the S2.

Gaston

 

[Schmleff]

Gaston,

Certainly a good warning for S1 pilots!

My site gauges have different calibrated numbers for that very reason. Blue numbers indicate the fuel level on the ground while red numbers indicate fuel remaining in level flight. Ill post a pict when I can get back out to the plane.

 

[Gaston]

Two colors is a brillant idea Jeff...

thank you for the post

 

[racegunz]

Hold on...... so the sight gauge read 4 gal when empty? right?(so it would make sense that if it had 4 gal. in it it would read the same?) but when you added 4 more gallons it read 7.5-8 gal.????? could you explain that to me, I'm not getting it. Or you never completely drained the tank and had no real idea how much the tank held or what it read at any level. ??? Your advice on the fuel system post is good advice, so I must be missing something in your explanation here.

 

[Gaston]

Hello racegunz

the sight gauge was not as simple as it could have been , and there were zigzag in the tube...
there was some dirt in it ,when I put the plane together ,but I thought I had sufficiently cleaned the tank and tubing but maybe there was still dirt to help trap fuel in the line and show a higher level than reality was...

after the event I removed the tank and all parts of the fuel system, and replaced the sight tube and re calibrated the gauge.

I may be missing something too,
the tube was kinked at the point it contacted the main spar box...


I took photo of the gauge showing 4 G when we knew it was empty. this photo was taken in case I had to explain the issue to TC.
I also asked an instructor from the nearby school to come and see for himself so he could back me up if needed.
which didn't happen...

My post was to let peoples know that such a danger existed

 

[Schmleff]

I have attached a pict of my site gauges. There are a couple of things to note about them for SI pilots.

The red numbers indicate the fuel level in flight, the blue show the level on the ground. Notice how close the red numbers are between 4-8 due to the shape of the tank.

To aid in seeing the fuel, I made the silver/red pattern behind the line. Its easy to see the magnification when fuel is present. You could also use a floating ball for a Piper. Univair sells them for a about $5: http://www.univair.com/piper/piper-pa-11/view-all/u10853-000-piper-fuel-gauge-float-ball/

The site gauges extend below the instrument panels that you can see the level down to the last drop. The one on the left is for the 3.3 gallon aux tank and the other is the main tank.

One of the best mods I did to the gauges was to use tiny coper lines to feed them. This prevents the indication from bouncing all over the place in turbulence.

However, the fuel flow meter I have is very accurate. Over the burn of all 18 gallons, I have never seen it more than a tenth of a gallon from what was actually used. That $160 gauge really changes the cross country usability of the airplane.

 

[Pttim]

The ball you mentioned Jeff is an awesome idea. I put a small orifice in the fitting from tank to site gage. I have no bounce of fuel but would like a better indicator. [ball]. Orifice size is about a 53 drill size.

 

[N8053H]

Anyone do fuel system testing before first flights? In both nose high and nose low conditions. Checking both flow rates when full and almost empty.
This could have been caught during these test.

The FAA put out a paper on this a couple years ago.

Tony

 

[Pttim]

Anyone do fuel system testing before first flights? In both nose high and nose low conditions. Checking both flow rates when full and almost empty.
This could have been caught during these test.

The FAA put out a paper on this a couple years ago.

Tony

Please check the topic of fuel system, this is about site gage accuracy.

 

[N8053H]

Anyone do fuel system testing before first flights? In both nose high and nose low conditions. Checking both flow rates when full and almost empty.
This could have been caught during these test.

The FAA put out a paper on this a couple years ago.

Tony

Please check the topic of fuel system, this is about site gage accuracy.

Yes and this should have been caught during this testing.. My point.....

 

[racegunz]

Easy guys, I am taking all this to heart because I'm about to start fabricating my S1 gas tank and don't want to do it twice! When testing my present plane I did do the flow testing( sort of) per the FAA paperwork, also added fuel 2 gal. at a time to check the gauges......they are horribly inaccurate, but consistent, that with my now added fuel flow meter I'm very confident. I do not wish to make my S1 so complex, I will indeed run a sight tube that can see down to the last, and will now take extra effort to make sure none can be trapped at any point. Gaston's pain our gain.....so to speak. ;D

 

[Schmleff]

Correct me if I am wrong, but the only time the FAA requires a fuel gauge to read accurately is when the tank is empty.

I have heard a few guys say that a fuel gauge is not required in an experiment, but I have never taken the time to study that one out

For the first few years I flew mine, I had the site gauge marked as full, 3/4, 1/2 and empty. I never flew it based on the gauge, I based the fuel quantity on time. It was only after I had 3 separate tanks that could feed the engine and no starter that I really dug into it ; )

 

[Gaston]

Guys

Note that this S1 is not a new plane , it's been flown 60+ hours before I acquired it. so the fuel system efficiency was already proven.

Note also that it flew with a 2180 so probability that it could not feed the smaller 1834 were very low, as per my estimation.

Furthermore, the fuel flow was grossly checked while in shop, and I measured well over 13 GPH
approximate, and this, with a lower than half full tank, which was more than safe and this was good enough for me...
and I really do not see how the fuel sight gauge inaccuracy could have been caught, unless fuel flow would have been estimated according to fuel gauge variation...much more complicated and hazardous than measuring a fuel volume flowing in a given time...

and finally , This post was about fuel gauge inaccuracy, and not at all related to fuel flow issue...

and my goal was only to help others avoid such a critical issue.
you take it or leave it ... it's only between the ears.

Gaston

 

[Schmleff]

Gaston,

I re-read the thread again and am still trying to figure out what caused your gauge to read the way it did. If it had not done anything like that during testing, I wonder if it could be vapor lock related. Could you add to your drawing where your main fuel outlet and the line to the sight gauge is connected? Also, could you draw in the zig zag's in the sight gauge line?

As for my comments, I usually comment with a broad brush, often beyond the intent of the initial post as was the case here. When critical safety issues come up (as I mentioned elsewhere), I want to make sure that someone reading our threads years from now gets related tips that may save their lives. In all other cases I try hard not to railroad other peoples posts

 

[Gaston]

I'll have a look into this Jeff...
I understand your point , and I have no problem with any comments.
I'll upgrade my sketch the best I can, and I look to see if I have a photo of the zigzag...
I will try to make a better description of the issue
the zigzag were caused by too long tubing between fuel tank and the point where the tube passes below the spar.
where it was kinked because of the angle..

more to come as soon as I can

PS don't understand what you mean ''not railroad other peoples post ''

 

[Schmleff]

Gaston,

I am working on my fuel system now and can see an issue that would cause what you described. I will make a sketch and post it later.

 

[Schmleff]

Gaston,

Two questions.

At what angle is your top top longeron when the plane is on the ground?

How far down does your tank extend below the top longeron in the front section?

 

[Gaston]

Sorry Jeff for the delay...
been much busy completing installation of the transponder in the S1and a first CC flight in the S1

I added some details on the sketch of my fuel tank...
this is only approximate routing of the sight gauge tube(blue line and zigzag are exaggerated for evidence of routing.found no photos of the system before it was redone...

Can't tell the angle of longeron for now, will probably measure it tomorrow...

front section of the tank is about 6 inches below longeron will measure that precisely also.

the tank vent is on the top front of the tank, and I noticed that in final for landing fuel was expelled by the vent...
Tuesday I flew a small 140 miles Cross Country and when setting for level flight with full fuel
fuel was also expelled from the vent, at almost every bump ( very bumpy sky) until fuel level was lower...

first 15 minutes were very impressive,I had to convince myself not to turn back and land...
on the returning flight my correcting inputs were much smoother,and more precise...
nice little bird, but I need more flying time to master it...

Gaston