C172 Fuel Selector

PilotRPI

PilotRPI

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PilotRPI
While on a longer flight, do any of you use individual tanks, or just keep it on both the whole time?
 
I think you do that to prevent cross-feed when doing, say, steep turns?
 
Keep it on both. If I see one of the fuel gauges going lower than the other, I'll switch it to that side for a little.
 
Usually on both if it's a short flight, but when it's 1hr each way, I'll select the tank that will help keep the wings level. It may or may not be the fullest tank depending on weight distribution in the cabin.
 
TK211X said:
I think you do that to prevent cross-feed when doing, say, steep turns?
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If your steep turn is nicely coordinated, there will be no cross-feed. :wink2:

In fact, the POH says that when uncoordinated, Both is the only valid option. The system is designed to always feed as long as at least one tank has fuel over the port. A dry port on one tank has no effect on fuel feed.

As far as I know, the only real use of the selector is:

  1. Prevent cross-feed when parked. (Should be Left or Right when parked.)
  2. Burn down one tank in cruise if you really have a big mismatch between tanks.
  3. Deal with an emergency.

Emergency example: your left fuel cap goes AWOL in cruise. Fuel is siphoning off the left wing. You aren't close to an airfield. Switch to Left immediately to use as much fuel from the left tank as possible before it runs dry. When the plane stutters, switch to Right to ensure that none of the right tank cross-feeds and siphons off. Don't slip during the landing, as you may unport the right tank and lose power.
 
I just leave it on both unless there's an issue with one tank feeding more than the other. Usually seem to balance well in one of the 172s I fly but the other feeds from the right side faster. YMMV
 
In my 172N, both all the time.

But be aware that the C-172 Type Certificate Data Sheet (Note 2K) requires the following placard:
K. Near fuel selector valve on models with serial numbers 28000 through 17258855, except those with Cessna Kit No. SK-172-31B or SK-172-32 installed:
"SWITCH TO SINGLE TANK OPERATION IMMEDIATELY UPON REACHING CRUISE ALTITUDES ABOVE 5000 FEET."
​
That serial number range includes your C-172B. Has the Cessna Kit No. SK-172-31B or SK-172-32 been installed on your airplane? If not, there's your answer.
 
That's what I was wondering about but I didn't want to lead the witness. Was wondering if anyone on here actually does that.
 
Believe me, you miss the left/right when it's gone.

I've started flying a new-to-me Cardinal RG. Unlike the previous one, this one has only an on/off fuel selector.

And this type has an annoying "feature" in its fuel vent design. They are very long, each running all the way to the opposite wingtip. If they get fuel in them 'cause the rampie overfilled the tank (I.e. Every time), the plane will suck all the fuel out of one tank until it gets below 1/4 or so. The first time this happened, I made an unplanned fuel stop 'cause I couldn't make it home only on one tank.
 
I think you want to take a look at your POH for your specific model. I know that when I flew from NY to AZ, when I was at specific altitudes, there was a recommendation that didn't always say both. There's reasons for having it on both and on one tank and I think the POH lists them.
 
Pilawt and FlyBoyAndy are correct. In the Owner Manual it states to use individual tanks on the 172B above 5000 ft due to vapor issues and venting. If on one tank and a problem develops, switch to the other and it should return to normal immediately. If on both and there is a vapor issue, switch to a single tank for a minute, then switch to the other and it should return to normal.

May have to try this from now on. Also, running on one tank always leaves something in the other, unless like the Cessna 310 post where the selector failed!
 
SoonerAviator said:
Usually on both if it's a short flight, but when it's 1hr each way, I'll select the tank that will help keep the wings level. It may or may not be the fullest tank depending on weight distribution in the cabin.
Click to expand...

That's what I do as well.. if anything it ingrains it in my mind to be conscious of tank usage so when I go to my big boy plane.
 
MAKG1 said:
Believe me, you miss the left/right when it's gone.

I've started flying a new-to-me Cardinal RG. Unlike the previous one, this one has only an on/off fuel selector.
Click to expand...

My CTSW is similar. On/off fuel valve, no provision for preferential feeding from one tank. My airplane seems to usually feed more from the left tank, some other CTs feed more from the right, just luck of the draw.

We are somewhat lucky in that most CTs have three-axis trim. So we solve this problem by trimming to fly with the ball half to a full ball out, which lifts one wing and increases head pressure on that side so fuel flows more from that tank.

The newest CTs have a left/right/both selector, I wish I did!
 
I tend to draw more from the left in my skyhawk, but it's never an issue enough to annoy me. I don't think I've ever had to move the fuel selector from both in the air. Only time I move it is when parked.
 
I'm willing to bet most people leave them on Both all the time.

I had two friends come up just short of the runway last year. They were partners in a 172 and took turns flying that day on a 2 hour trip. The pilot with the most experience took over for the landing since it was very windy. He always flies on Both, but the other guy was concerned that the tanks weren't balanced and switched to the fuller tank early in the flight.

The guy who was landing just assumed it was still on Both because that's where he put it when they took off. The engine quit on very short final and they came up just short of the runway at a controlled airport. Nothing was damaged except egos, and they had to get a mechanic to sign off on the plane before they could depart.

Lessons learned... don't assume, and follow a checklist. The checklist on their 1963 172 actually said to take off and land on Both.

oregonboy109 said:
I just leave it on both unless there's an issue with one tank feeding more than the other. Usually seem to balance well in one of the 172s I fly but the other feeds from the right side faster. YMMV
Click to expand...
 
Correct for the 172B as well, use Both for all phases up flight unless cruising greater than 5000 ft.
 
I have a few hours in the 172 and I don't remember there being a major difference in what was in each tank after landing, leaving the selector on both. Same with the 152, where you don't even have a choice.

I prefer the L/R of my airplane. It makes it easier to know exactly what's in each tank.
 
I have always left it on Both, except on shutdown to prevent cross feed. C172S
 
By "cross feed" you guy's mean that if one tank is contaminated it wont cross to the other.. correct?
 
I generally leave it on both as well. On my check ride the DPE said "There's nothing wrong wth leaving it on both, but if you're doing long cross countries, consider using the selector to manage fuel so you KNOW how much time you have."

Since I've never flown a leg longer than 2 hours (except my instrument training) since, I've just filed it away as a tool in my box.

John
 
The CTSW has a "T" above the fuel valve, so even if I shut off the fuel valve (I always do), the tanks will still cross-feed. If the airplane is parked more than a couple of hours I will have more-or-less balanced tanks.

Since there is no selector it doesn't really matter. With a "both only" feed it's best to have equal fuel in both tanks anyway.
 
PilotRPI said:
May have to try this from now on. Also, running on one tank always leaves something in the other, unless like the Cessna 310 post where the selector failed!
Click to expand...
That admonition to cruise single-tank above 5,000' only applies to 172s built up to about the middle of the 1970 model year. But even in those, if the service kit has been installed, you don't have to worry about it.

bullwinkle said:
My CTSW is similar. On/off fuel valve, no provision for preferential feeding from one tank. My airplane seems to usually feed more from the left tank, some other CTs feed more from the right, just luck of the draw.
Click to expand...
Former Cessna aerodynamicist and test pilot Bill Thompson wrote that there was debate within the company about the design of the on-off selector in the C-150:

"Our past experience with uneven fuel feeding from wing fuel tanks (with resulting wing heaviness), and an inability to purposely run one tank dry as as to continue a long flight with more fuel in the opposite tank prompted many of us to favor a LEFT-RIGHT-BOTH-OFF fuel selector valve. At the same time, we were concerned at the number of "fuel mismanagement" accidents where the pilot would forget to switch to the tank containing fuel and experience fuel starvation at an inopportune time. We rationalized that (1) this is a trainer to be flown by forgetful pilots on short-duration flights, (2) the asymmetry of the fuel load would probably be light, and (3) this airplane would be used primarily in maneuvering rather than steady cross-country flight. Thus the simple ON-OFF fuel selector was justified.​
 
duc750sport said:
By "cross feed" you guy's mean that if one tank is contaminated it wont cross to the other.. correct?
Click to expand...

More like one wing tank feeding the other such that you're drawing from the right, but the vent line is fueling the right from the left, and you're really drawing from the left with right selected.
 
Pilawt said:
That admonition to cruise single-tank above 5,000' only applies to 172s built up to about the middle of the 1970 model year. But even in those, if the service kit has been installed, you don't have to worry about it.

Former Cessna aerodynamicist and test pilot Bill Thompson wrote that there was debate within the company about the design of the on-off selector in the C-150:

"Our past experience with uneven fuel feeding from wing fuel tanks (with resulting wing heaviness), and an inability to purposely run one tank dry as as to continue a long flight with more fuel in the opposite tank prompted many of us to favor a LEFT-RIGHT-BOTH-OFF fuel selector valve. At the same time, we were concerned at the number of "fuel mismanagement" accidents where the pilot would forget to switch to the tank containing fuel and experience fuel starvation at an inopportune time. We rationalized that (1) this is a trainer to be flown by forgetful pilots on short-duration flights, (2) the asymmetry of the fuel load would probably be light, and (3) this airplane would be used primarily in maneuvering rather than steady cross-country flight. Thus the simple ON-OFF fuel selector was justified.​
Click to expand...

You should have your own sub-forum.

We can call it "question about an airplane? Ask the guy who has the answer".

:)
 
Pilawt said:
Former Cessna aerodynamicist and test pilot Bill Thompson wrote that there was debate within the company about the design of the on-off selector in the C-150:

"Our past experience with uneven fuel feeding from wing fuel tanks (with resulting wing heaviness), and an inability to purposely run one tank dry as as to continue a long flight with more fuel in the opposite tank prompted many of us to favor a LEFT-RIGHT-BOTH-OFF fuel selector valve. At the same time, we were concerned at the number of "fuel mismanagement" accidents where the pilot would forget to switch to the tank containing fuel and experience fuel starvation at an inopportune time. We rationalized that (1) this is a trainer to be flown by forgetful pilots on short-duration flights, (2) the asymmetry of the fuel load would probably be light, and (3) this airplane would be used primarily in maneuvering rather than steady cross-country flight. Thus the simple ON-OFF fuel selector was justified.​
Click to expand...

Sounds similar to Flight Design's reasoning. They originally had a selector in their early planes, but a couple of fuel starvation incidents convinced them that "simpler is better" for most pilots.

The only tricky thing in a CT is that if one tank is empty and the other is low (3 gallons or so) and the full wing is down in a "less than perfectly coordinated" turn, you can unport the remaining fuel and have a starvation incident. But if there is any visible fuel at all in both sight tubes it's not a factor.
 
Pilawt said:
That admonition to cruise single-tank above 5,000' only applies to 172s built up to about the middle of the 1970 model year. But even in those, if the service kit has been installed, you don't have to worry about it.

Former Cessna aerodynamicist and test pilot Bill Thompson wrote that there was debate within the company about the design of the on-off selector in the C-150:

"Our past experience with uneven fuel feeding from wing fuel tanks (with resulting wing heaviness), and an inability to purposely run one tank dry as as to continue a long flight with more fuel in the opposite tank prompted many of us to favor a LEFT-RIGHT-BOTH-OFF fuel selector valve. At the same time, we were concerned at the number of "fuel mismanagement" accidents where the pilot would forget to switch to the tank containing fuel and experience fuel starvation at an inopportune time. We rationalized that (1) this is a trainer to be flown by forgetful pilots on short-duration flights, (2) the asymmetry of the fuel load would probably be light, and (3) this airplane would be used primarily in maneuvering rather than steady cross-country flight. Thus the simple ON-OFF fuel selector was justified.​
Click to expand...

I'd be interested in what the reasoning behind the early 177RGs was.

Though I think you could make an argument that it's a commercial trainer, it's actually a pretty decent cross-country platform (and seems to have been intended that way -- hence the Buick doors and easy-egress seats).
 
MAKG1 said:
I'd be interested in what the reasoning behind the early 177RGs was.

Though I think you could make an argument that it's a commercial trainer, it's actually a pretty decent cross-country platform (and seems to have been intended that way -- hence the Buick doors and easy-egress seats).
Click to expand...

I did my commercial ride in a gutless....back in the 80's. It was an ok step up from a vanilla C172.....but the 182RG was much better.
 
MAKG1 said:
I'd be interested in what the reasoning behind the early 177RGs was.
Click to expand...
Dunno. Thompson doesn't mention it in his chapter on the 177RG. Looks like only the '71 and '72 model years of the 177RG had the "on-off" selector, and they went to the "left-both-right-off" selector for 1973. As far as I know, all fixed-gear 177s had the four-position selector.

:dunno:
 
duc750sport said:
By "cross feed" you guy's mean that if one tank is contaminated it wont cross to the other.. correct?
Click to expand...
I was referring to parking on a unleveled ramp. While parked, if the plane isn't level, fuel will settle in the lower tank if the valve is in Both position.

If fuel truck fills the upper tank first, by the time he fills the lower you probably don't have a full tank on one side anymore. I also think, depending on how steep the bank, the lower tank could eventually leak fuel as the other feeds into it.
 
jaymark6655 said:
I was referring to parking on a unleveled ramp. While parked, if the plane isn't level, fuel will settle in the lower tank if the valve is in Both position.

If fuel truck fills the upper tank first, by the time he fills the lower you probably don't have a full tank on one side anymore. I also think, depending on how steep the bank, the lower tank could eventually leak fuel as the other feeds into it.
Click to expand...

This happens in my airplane if parked on a bank. Fuel will run from one tank to the other, and if the tank overfills it will spill out the vent. It's messy and you can lose a lot of fuel that way. Ask me how I know. :(
 
For the most part if you have a BOTH selection you can consider the two tanks as one.

My old Champ has only an ON/OFF selector and has only one gauge mounted to the right tank. It's an airplane that you want to dip the tanks before takeoff and watch your time. The gauge only serves the purpose as an instrument that if you look at it and have to ask yourself "why is it doing that?" then you should probably look for a place to land.

My old Luscombe has two ON/OFF valves, one for each tank and you are never supposed to operate with both open at the same time. It does have a gauge in each tank though but still you need to start off with a known quantity and keep track of the time you run on each tank.

No autopilots either :rolleyes:
 
If taking off from above 5000ft, do you go for a single tank also?
 
SkyHog said:
If taking off from above 5000ft, do you go for a single tank also?
Click to expand...

My understanding is that for take-off and landing (in particular), Both is required because uncoordinated flight could unport a tank. This is a much greater risk than the very rare vapor lock.

Curious why the low wings, where both is not an option, do not have this issue...
 
arnoha said:
My understanding is that for take-off and landing (in particular), Both is required because uncoordinated flight could unport a tank. This is a much greater risk than the very rare vapor lock.

Curious why the low wings, where both is not an option, do not have this issue...
Click to expand...

Fuel pump.
 
MAKG1 said:
Believe me, you miss the left/right when it's gone.

I've started flying a new-to-me Cardinal RG. Unlike the previous one, this one has only an on/off fuel selector.

And this type has an annoying "feature" in its fuel vent design. They are very long, each running all the way to the opposite wingtip. If they get fuel in them 'cause the rampie overfilled the tank (I.e. Every time), the plane will suck all the fuel out of one tank until it gets below 1/4 or so. The first time this happened, I made an unplanned fuel stop 'cause I couldn't make it home only on one tank.
Click to expand...


I would love to see pictures of that Cardinal. Something tells me its either been modified from original valve or its hidden under "carry on" junk.

Must be a 1971 or 72 per type certificate. Doesn't make any sense why they did that when the 68 doesn't even feed evenly on "BOTH".
 
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bnt83 said:
I would love to see pictures of that Cardinal. Something tells me its either been modified from original valve or its hidden under "carry on" junk.

Must be a 1971 or 72 per type certificate. Doesn't make any sense why they did that when the 68 doesn't even feed evenly on "BOTH".
Click to expand...

It's a 1971. Decent little airplane aside from this quirk.
 
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