Fuel management and fuel gauge

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Avee8or
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Fuel management and fuel gauge

Post by Avee8or »

I assume the “no takeoff” range mark is due to unporting of the fuel feed in 3 point attitude? Is this so?

Is it safe to take off when 1 tank is out of the red range if the other rs in the red range? If so, should both tanks be selected, or the fuller tank?

I had a recent flight where I had enough fuel to make destination, but had to stop short to drpo off a pax and had to add fuel as both gauges were in red zone. I could have managed differently and kept one tank out of the red saving the delayand expense of the fuel stop.
Varel Freeman

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195 N195GW
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GAHorn
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Re: Fuel management and fuel gauge

Post by GAHorn »

While good judgment would require it….. I have never found any real basis for that “no takeoff zone” in the face of the gauge. Firstly, it is not in the AFM (which is the controlling document) nor the TCDS and secondly, there is no reason one cannot takeoff provided that one has sufficient “useable fuel” for the flight plus the regulatory reserves.

If the tanks are 21 gal tanks and if only 1/4 full …that would equate to 10.5 gals , of which 5.25 gal would be useable… 1.25 gallons of which would be available for flight since about 4 gal would be required for the daytime required 30 mins reserve…… (nighttime could not be met at all regardless of any largely “cosmetic” fuel gauge placard.)

That would be an A or B model. The 170 would only have 4.375 gal of useable fuel available…. leaving you a whole 3/8-ths of a gallon of fuel for flying-around if you intend to meet the regulatory requirement for Day/VFR.

But if you remove the 30-min reserve for Day/VFR … a half-hour of flight is likely possible if the gauges are accurate. I don’t know anyone who really believes airplane fuel gauges are to be trusted. I use a measuring dipstick for every pre-flight …even tho’ my gauges appear to be “right on the money”.

The only required placards to be in front of the pilot is in the pic below, (unless you are a seaplane/skiplane operator.)

If anyone can find any written evidence in an “approved” document that limits this airplane to more than 1/4 fuel for takeoff… I’d like to know where that is found.
C8428315-28DB-42E4-87CD-4A599695FEC7.png
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
voorheesh
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Re: Fuel management and fuel gauge

Post by voorheesh »

Cessna 170 aircraft were certified under CAR 3 which has provisions concerning the determination of unusable fuel and/or minimum fuel required for safety of flight based on the number of fuel tanks and possibly potential flight attitudes. See CAR 3 §3.437 and §3.440. These speak to the need to alert the flight crew either by entry in the flight manual or by a placard. It’s possible that Cessna intended the markings on the fuel gauge to be a placard based on these rules. Very small amounts of unusable fuel are specified, but Cessna maight we’ll have chosen a more conservative value at a time when these types of airplanes were new and general aviation was in its infancy. I don’t know for sure and I can’t really remember the precise markings on the approved 170 fuel gauges since it’s been awhile since I was in one. But since you asked, that would be my suggestion as an “approved source”.

I also think its worth mentioning that considering a takeoff when the fuel gauges in these airplanes are indicating this low is asking for trouble. Especially if your guessing as to the exact amount of fuel remaining. I remember George telling us how to modify a Cessna 172 dipstick to provide a reliable indication of fuel in the tank of 170 A and B models. That’s probably the best answer to these questions. Don’t guess. Don’t takeoff unless you know the exact amount of fuel and that it is safe for our planned flights.
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Bruce Fenstermacher
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Re: Fuel management and fuel gauge

Post by Bruce Fenstermacher »

Not all Scott fuel tank indicators have the red "no Takeoff" range. One of my 170s had one with and one without. As George points out, we have yet to find a regulatory reason for the "No Takeoff" area and I never felt the need to remove the one I had nor replace the one missing. Whether the gauge had the marking or not I always treated my departures with a little more thought when the gauges were in the area. And I did legally depart in that condition a fair amount.

You see my 170 was based at a 1800ft private field with no fuel that was located on an extended base leg to a public field with fuel. We routinely took off with 10 gal total showing on the gauges to land at the public field to get fuel. And that brings up another point. While tied down my 170 was not parked level. The right wing being much lower than the left. If we didn't remember to put the fuel selector in the right hand position*, nearly all fuel from the left tank would transfer to the right. Our gauges often showed half on the right and empty on the left. I would move the 170 to level, switch tanks to both, preflight, start and taxi to the end of the runway. By that time the left tank would be bouncing on empty as fuel was being transferred from the right tank.

*For those that haven't seen how the Cessna fuel valve, either model, works, fuel can transfer between tanks in the Both and the Off positions. It can not in either the Right or Left positions unless the angle of the wings is so severe that the fuel transfers over the common air vent at the top of the tanks and that is highly unlikely except for having a completely full tank in the high position.
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GAHorn
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Re: Fuel management and fuel gauge

Post by GAHorn »

Avee8or wrote:…..Is it safe to take off when 1 tank is out of the red range if the other rs in the red range? If so, should both tanks be selected, or the fuller tank?….
Regardless of Indications…BOTH…should be selected for ALL takeoffs and landings. The TCDS is not always without errors (in fact I notified FAA just this week of yet another omission in Revision 55 which contains an incomplete sentence regarding Utility Category, as well as failing to require this “Both” requirement in Standard category).

Both tanks on for takeoff and landing.” is a REQUIRED PLACARD according to the AFM and applies to Standard and Utility categories.

(on another note, some 170s have been refurbished using 172 fuel selector placards which state that immediately upon reaching a cruise altitude above 5,000 that the lever should be selected to only ONE tank. This is NOT APPLICABLE to a 170 of any model…and actually should not be applicable to pre-68 C-172 aircraft equipped with the Continental engine….but the entire 172 fleet has been erroneously included in that restriction. There’s no harm in following that instruction, but it’s unnecessary with Continental engines as none of them experienced the “burp” of the birth-defected* Lycoming-equipped airplanes.

* = my skepticism of Lycomings (due its’ own thread.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
counsellj
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Re: Fuel management and fuel gauge

Post by counsellj »

PM Sent
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n2582d
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Re: Fuel management and fuel gauge

Post by n2582d »

Bruce Fenstermacher wrote:... *For those that haven't seen how the Cessna fuel valve, either model, works, fuel can transfer between tanks in the Both and the Off positions. ...
If the late-style (aluminum block) fuel valve allows fuel to transfer between the left and right tanks with the valve in the off position, it's probably a good indication that the valve leaks and needs to be rebuilt. This has been discussed here.
Gary
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JimNelson
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Re: Fuel management and fuel gauge

Post by JimNelson »

While I would never take off with less than 1/4 tank of gas, it does figure into my flight planning. I plan to arrive with more than 1/4 tank so that if I muff the landing and have to go around, I'm not "taking off" with less than 1/4 tank. So 10.5 gallons to stay above 1/4 for go-arounds, another 4 gallons for a 30 minute reserve.

And... there's a handwritten note in the book that says "RT draws 60%, LF 40% with fuel select set at both. Range limited to 3.3 hours to have 1/4 tank for G/A safety." Another note says "Now fuel every 2.6 hours." So to take into account the uneven fuel use, the 1/4 tank go around, the 30 minute reserve, full fuel range is shorter than expected.
1950 170A
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voorheesh
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Re: Fuel management and fuel gauge

Post by voorheesh »

JimNelson wrote:While I would never take off with less than 1/4 tank of gas, it does figure into my flight planning. I plan to arrive with more than 1/4 tank so that if I muff the landing and have to go around, I'm not "taking off" with less than 1/4 tank. So 10.5 gallons to stay above 1/4 for go-arounds, another 4 gallons for a 30 minute reserve.

And... there's a handwritten note in the book that says "RT draws 60%, LF 40% with fuel select set at both. Range limited to 3.3 hours to have 1/4 tank for G/A safety." Another note says "Now fuel every 2.6 hours." So to take into account the uneven fuel use, the 1/4 tank go around, the 30 minute reserve, full fuel range is shorter than expected.

To me, this is a a smart way to approach fuel planning for a 170 with “warnings” on the fuel gauges. The problem is we don’t seem to know why the markings are there. It just seems wise to take them into account and be on the safe side of the question.

I’m a flight instructor with several brand new pilots going through early training and I’m trying to have them take this same attitude as they gradually take on more responsibility and decision making. Ask questions, don’t ignore warnings, we all make errors, but better on the side of safety.

I’m an outsider on this forum because I no longer own or fly a 170, but remain interested and see this group as an excellent resource. So I also want to thank the original poster for bringing the issue of these fuel gauges to our attention. He too has a good approach to aviation and brings us an example of how there is no such thing as a dumb question.
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GAHorn
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Re: Fuel management and fuel gauge

Post by GAHorn »

It’s common with GA and light-planes to have a destination that is a single-runway.

What if you arrive with minimum fuel in the tanks…and the runway is blocked by the gear-up or ground-loop accident which occurred just a few minutes ago?

I once left AUS in a state-owned 206 with a destination of E38 (Alpine, Tx…which has two runways)…with the wx forecast to be VFR at the destination…..and 30 mins before arrival checked with FSS for E38 weather…to discover the airport closed because of an accident. (Some rejected lover decided to commit suicide with a slow-roll in a Bonanza at 300’ AGl.)

Alternate airports should always be part of your plan …even on clear days. Thirty minutes ain’t always enough.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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KAP54
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Re: Fuel management and fuel gauge

Post by KAP54 »

I would guess that this comes from the original 170 (ragwing). The flight manual states that takeoff with less than 1/4 fuel is not recommended. Due to the routing of the fuel line, a fuel pump is required. This was changed on the later A & B models. Perhaps it was possible to lose fuel flow if the pump failed on takeoff with less than 1/4 tank. Just a thought.
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ghostflyer
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Re: Fuel management and fuel gauge

Post by ghostflyer »

My aircraft originally had what Bruce had . Only one gauge had the markings of of 1/4 tank take off restrictions . Both gauges were of the same manufacture . I originally thought it was the indication to have that amount of minimum fuel on board for a takeoff. No,way I was going to take off with 20 liters on board . I drained the tank once to check the amount of fuel on board with quantity indicated. Some of my placards in the aircraft were incorrectly marked . One of the original owners didn’t calculate correctly the difference between imperial and metric.
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