How much do you trust sight gauges?

My personal minimum is a four hour reserve, so I get a little leeway.
 
Stewartb said:
Who's sight gauges? I have some in my Cub that I don't trust at all when they get low. I use sight gauges to validate other indicators, like what my expected burn is based on time. Sight gauges aren't perfect.
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The angled wing root sight gauges in my Husky bounce around too much to be very useful, especially when low.
I've heard some owners insert a fitting with an orifice in the lower tank connection to dampen things out.
Did you do something similar when building the Supercub?
 
That's standard practice, so yes. My exp uses Atlee Dodge sight gauges and even with the best available it isn't anywhere close to accurate. Not a problem. I have a watch and I like 60min in reserve.
 
asicer said:
You are on your way home VFR on a CAVU day in an airplane (single engine land) equipped with marked sight gauges. 15 minutes out, your timer expires indicating that you hit your fuel reserves. However, your sight gauges are showing about 20 minutes of fuel remaining plus reserves. You tip the wings/nose and verify the readings against the AI. There is an airport directly below you, another halfway home and a straight non-busy freeway connecting them all.

Do you press on? Or do you divert?
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Anytime you are asking whether you should divert or not the answer is to divert.
 
wanttaja said:
The sight gauge on my airplane is a metal rod sticking up through the fuel cap with a cork at the bottom.
It actually tends to stick; the slipstream will pin the rod to the tube until the gas level goes down low enough that the weight overcomes the friction.
cork1.jpg

So I tend to go more by the clock.....

Ron Wanttaja
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Same with the Cub.
I have had occasion to land with the sick 1/3 up, and on touching down it dropped to the bottom of the tank.
:eek2::hairraise:
 
To me that isn’t a sight gauge. It’s a float that’s read directly rather than the more modern electrically translated float gauges. A sight gauge allows you to see fuel.

A2F982E0-16F7-4E4B-B9F5-B38F34BFB640.jpeg
 
Tom-D said:
Runway close in a moments notice.. that aircraft 2 minutes ahead of you blew a tire/crashed, and you can't land.

Now what?
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Have a contingency to only allow flight into your reserve to destination or alternate airports with two or more runways. See? PLANNING.
 
According to the presented premise if I trust the watch, I've got 30 minutes until things get quiet. If I trust the sight gauge I've got 50 minutes until things get quiet. I'm 15 minutes out and CAVU. Do I press on or land and fuel up? Depends. How well do I know the plane and have I run tanks dry on it in the past?

If its a plane I know well and prehaps have run tanks dry on in the past, I'd probably be very comfortable continuing on. Blame it on my banner flying past. It wasn't unusual for unexpected headwinds to put you into your reserve fuel on longer tows. In that scenario I'd continue on and fill the tank when I landed to verify how much fuel was actually in there on landing. Then I'd set about trying to troubleshoot why my time calculation was so far off from the sight gauge indication.

If its a plane I don't well, this scenario becomes impossible. In a plane I don't know well, I'd have landed 4 airports back and topped up. I don't like to get anywhere near reserves in a plane I don't know well.
 
Tom-D said:
Runway close in a moments notice.. that aircraft 2 minutes ahead of you blew a tire/crashed, and you can't land.

Now what?
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I land. There's going to be runway before or after the incident airplane. There's grass next to the runway. There's probably a taxiway. The rulebook is there for a reason. But in some situations, the rulebook is best used to prop the door open before impact.
 
Juliet Hotel said:
I land. There's going to be runway before or after the incident airplane. There's grass next to the runway. There's probably a taxiway. The rulebook is there for a reason. But in some situations, the rulebook is best used to prop the door open before impact.
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Invoking the emergency may cost more than you want to cope with.. Landing at a closed airport will get the wrong people asking question about your fuel management skills.
 
Tom-D said:
Invoking the emergency may cost more than you want to cope with.. Landing at a closed airport will get the wrong people asking question about your fuel management skills.
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Let em' ask. If you mean to intimidate me into believing the mean old FAA is going to take away my certs or lock me up in the hoosegow because headwinds put me into my fuel reserves and I landed in the grass... Well you're going to have to try harder than that.
 
Juliet Hotel said:
Let em' ask. If you mean to intimidate me into believing the mean old FAA is going to take away my certs or lock me up in the hoosegow because headwinds put me into my fuel reserves and I landed in the grass... Well you're going to have to try harder than that.
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No intimidation intended,, awareness.
 
cgrab said:
Sight gauges are the most accurate form of fuel gauge (assuming they were installed and marked properly) so I would go with the sight gauge. That said, my plane has Cessna gauges so I dip the tanks, write down what is in each tank on my knee board and calculate when I will have 10 gal in my tank flying at 7.5 gal/hr. I start the clock at engine start and keep an eye on the time in my tanks. When I have 10 gal I will land at an airport with fuel.
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What kind of ‘sight gauges’ are we talking about?

I have only seen a true sight glass gauge in one airplane (an EAB). Seen a lot of sight gauges on ships, but rarely in an airplane.

Virtually all the sight gauges I’ve come across in airplanes are actually gauges that display based on a mechanical float or bobber.

And I’ve see WAY too many of those float/bobbers stick and give false high readings.

And then there are the occasional cork bobbers that can get saturated over time and actually sink giving a false low.

In short, if my watch is telling me I’m low, but the gauge isn’t, I’m going by the watch.

If the gauge is showing lower than my watch, I’m going to err on the side of caution and verify.
 
IK04 said:
That would be an example of inadequate preflight planning.
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Easy to say, but I had the dork in front of me land gear-up, closing the airport. And I really had to pee.
 
Fearless Tower said:
What kind of ‘sight gauges’ are we talking about?
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My neighbors plane has a clear tube on each side of the cockpit that runs from the top to the bottom of his tank in the wing. Much like that on a coffee pot. On the bulkhead are two scales. One is marked ground and one is marked air. Since he has a tailwheel plane the indications change when his plane is in flight. He is able to look at the fuel that is available in his tanks. This is the only type of sight gauge I would trust.
 
cgrab said:
My neighbors plane has a clear tube on each side of the cockpit that runs from the top to the bottom of his tank in the wing. Much like that on a coffee pot. On the bulkhead are two scales. One is marked ground and one is marked air. Since he has a tailwheel plane the indications change when his plane is in flight. He is able to look at the fuel that is available in his tanks. This is the only type of sight gauge I would trust.
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Heh. When I was learning to fly I told my instructor we needed to fuel up first. He says, " Look again and tell me what it reads," as he hoisted the tail of the Super Cruiser up onto his shoulder. "It reads about half way," says me. "Climb in," he says.
 
Trust? I do not think it means what you think it means?
 
Hi, OP here. In case anyone is still following this thread, it's time to come clean. OK, so here's the deal, the scenario in post #1 wasn't hypothetical. I faced this situation for real a while ago. En route, the headwinds were stronger than forecast and ate into my fuel reserves.

I elected not to divert. Here's why:
  1. These were glass tube sight gauges and not the J-3 type bobber on a stick.
  2. My personal minimum is for a 1hr reserve, so I was pretty certain I would still land above the FAR91 minimum 30minute reserve if I didn't divert.
  3. I actually had more than the 2 airports between me and my destination I mentioned in post #1
  4. At my departure point, ramp parking was full so I had to park in the grass. I wasn't sure the plane was level when I Iooked inside the tanks so the takeoff fuel quantity had some uncertainty in it.
  5. When I hit the unexpected headwinds, I took extra care leaning the mixture than I normally do, so the fuel burn could have been lower.
  6. I was at 6500AGL and my destination airport was class D where I could expect a straight-in (@Dave Arata actually had a very good question that I artfully dodged). Continuing would have been at cruising-descent power while my fuel burn calculations were all at high cruise power. Also, spiraling down from that altitude would have been extra 11 minutes plus 3 more to fly the non-towered pattern entry which is more than a little inconvenient.
After I landed, I saw 1 hour of fuel in my tanks.

So in one sense, I did nothing wrong and everything worked out. However, before that flight I had @Ryanb 's rule which was to only trust the most conservative indication and I violated that. So in another sense, I screwed up by violating my conscience.

Even though this flight was years ago, I still think about it from time to time and wonder: Did I really make a rational decision? Or did I let get-there-itis cloud my judgement by placing more trust in the sight gauges than I should have?
 
asicer said:
Even though this flight was years ago, I still think about it from time to time and wonder: Did I really make a rational decision? Or did I let get-there-itis cloud my judgement by placing more trust in the sight gauges than I should have?
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Get-there-itis is certainly something to be cautious of. But at some point you have to trust yourself and your judgement. Otherwise you end up never going more than 3 airports away and even then only on the calmest CAVU days. In the situation you describe, I would've done just what you did and I'd have been fine the choice.
 
asicer said:
You are on your way home VFR on a CAVU day in an airplane (single engine land) equipped with marked sight gauges. 15 minutes out, your timer expires indicating that you hit your fuel reserves. However, your sight gauges are showing about 20 minutes of fuel remaining plus reserves.
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asicer said:
  • My personal minimum is for a 1hr reserve, so I was pretty certain I would still land above the FAR91 minimum 30minute reserve if I didn't divert.
After I landed, I saw 1 hour of fuel in my tanks.
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The reason your personal fuel minimum is 1 hr is so you don't have a fuel crisis in a case like this. If you had no personal "pad" you'd face the decision you've anguished over, but in my opinion everything went as planned. :cool:
 
Given that situation I would have done the same. The way your scenario was written I thought your timer expiring was referencing the VFR 30 min. reserve requirement, not a 1 hr personal minimum and in effect giving you a 15 min cushion...
 
idahoflier said:
The way your scenario was written I thought your timer expiring was referencing the VFR 30 min. reserve requirement, not a 1 hr personal minimum and in effect giving you a 15 min cushion...
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Yeah, I intentionally made it nebulous in order to focus on the question in the thread title. However, I did leave a small clue when I said "hit your reserves".
 
IK04 said:
That would be an example of inadequate preflight planning.
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not necessarily …. the runway (assuming one) could suddenly get closed for a bunch of reasons
 
I’m too cheap to burn up my special reserved gas, so I’d land ASAP and borrow gas from a local farmer. Or logger. Pretty much anyone with free mogas. Ethanol free, of course.
 
WannFly said:
not necessarily …. the runway (assuming one) could suddenly get closed for a bunch of reasons
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That's not my point. Thorough planning would have mandated either an airport with more than one usable runway or enough fuel to fly to another airport, plus reserves.

It's part of the PACE concept of mission planning: Primary, Alternate, Contingency and Emergency.
 
asicer said:
Yeah, I intentionally made it nebulous in order to focus on the question in the thread title. However, I did leave a small clue when I said "hit your reserves".
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Well, then to get a little closer to answering your original question, I trust sight gauges a LOT more than I trust electro-mechanical gauges, though they do suffer from the same problems in unstable air.
 
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