Fuel management on a C172 [Archive]

Mark1234

19th Mar 2008, 09:09

Not intentionally being a smart-arse, but for some reason this stuck in my head a while back, so I just looked it up to be sure I didn't imagine it:

POH, Cessna 1976 Model 172M, Section 1 (General), Page 1-4, Underneath the Fuel Capacity table:

NOTE: To ensure maximum fuel capacity when refueling, place the fuel selector valve in either LEFT or RIGHT position to prevent cross feedingThat's not to say it's correct, but it's definately in the POH, and not something my instructor ever mentioned.

I don't have your knowledge of how it's plumbed, and there may well be imperfections in the way it crossfeeds, but surely it doesn't matter how low the join is? Fuel would still cross-feed even if you put a pipe from the bottom of one wing, draped it across the tarmac and up to the bottom of the other - it's just finding a level.

Can't really comment on the almost out of fuel scenario however..

S-Works

19th Mar 2008, 09:34

No mention of it in my FR172K manual.

dublinpilot

19th Mar 2008, 09:45

Could the fuel critical situation be so that you'd have a good idea how much fuel was left on board, when one tank ran dry?

Of course for this to work, you'd have to be running on a selected tank for the whole time....ie at no point on the flight be running on "both" thanks. Similar to the way people fuel plan in a low wing aircraft.

dp

First_Principal

19th Mar 2008, 09:50

I think you're at cross-purposes with each other!

When driving the beast keep the fuel on BOTH, as has been noted it won't make any difference switching it if you run out of fuel on one tank 'cos it will just continue to feed from the other anyway.

However if you want to refuel to the maximum potential level if you switch the fuel tap to the tank being refueled inititially that should prevent it cross-feeding to the other tank (since it's then just a direct path from that tank to the motor). If it cross-fed while you were moving from that tank to the other with the re-fueling nozzle you'd lose a little from the initial tank into the other wing tank (ie the one you're just moving to). In practice I don't think it really makes an enormous difference. Arguably if you left the tap on BOTH and were to fill the second tank up, wait for a bit and then top up again it's probably almost as good as you'd get - and with less potential for forgetting to change your tanks in the air :eek:

FP.

foxmoth

19th Mar 2008, 10:04

and with less potential for forgetting to change your tanks in the air

That is why you have - "FUEL - CORRECT TANK" (or similar) in pre TO checks.:hmm:

Small Rodent Driver

19th Mar 2008, 11:48

I would assume that his thinking is based upon exhausting one tank in order to determine that you at least have an idea what is left in the other and hence how long you have before the buttock clenching panic ensues.

SkyHawk-N

19th Mar 2008, 12:48

The Cessna fuel system is joined in the roof well down the line from the tank outlets and is gravity feed. All Cessna tanks drain unevenly and it is common to empty one tank before another. Switching the empty tank off has no effect.

The reason that quite a number of Cessnas use their fuel unevenly is due to the fuel vent pipe not being positioned correctly behind the left wing strut. It is easy for the vent pipe to be pulled or knocked out of position and even if it is out by a small measure it still has a noticeable effect. I always check the position during pre-flights and my tanks drain quite evenly. I'm not saying it's the only cause of uneven draining but it is a common issue.

When you fly the 172 selector should be set to both. When refueling it should be set to left or right to prevent cross-feeding.

SkyHawk-N

19th Mar 2008, 12:56

For info. Both the left and right tanks have two supply pipes from them, which are routed down infront and to the rear of each door. They all meet near and at the fuel selector.

There is also a crossover line which connects the two tanks this is for venting purposes. It is not designed for the transfer of fuel between the tanks but this transfer can occur due to various reasons (pressures, flying attitude, etc). The only external vent pipe is on the left hand tank.

fireflybob

19th Mar 2008, 13:03

It's a while since I flew the C172 but I recall a note in the POH/AFM that if cruising about 5,000 ft the fuel should be selected to LEFT or RIGHT in case of vapour lock in which case the opposite tank would then be selected.

S-Works

19th Mar 2008, 13:21

Mikehotel152

19th Mar 2008, 13:38

What's the effect on handling of flying on one tank for too long? Is it dangerous or merely noticable?

SkyHawk-N

19th Mar 2008, 14:07

What's the effect on handling of flying on one tank for too long? Is it dangerous or merely noticable?

Yes it is noticeable and dangerous, you drop out of the sky! :p

It's a while since I flew the C172 but I recall a note in the POH/AFM that if cruising about 5,000 ft the fuel should be selected to LEFT or RIGHT in case of vapour lock in which case the opposite tank would then be selected.

I believe this is based on a very historical event with a very old model of 172. It's now considered an 'old wives tale'. This is always bought up in the US pilot forums and always dismissed.

DFC

19th Mar 2008, 15:24

There are a number of reasons for uneven flow from each tank.

Fuel vent not 100% perfect

Slight leak at the cap

Not flying with the wings level and ball in the middle (which also wastes fuel).

Since few pilots fly perfectly wings level and in balance there will always be some uneven feed. Therefore I teach pilots to select either L or R at top of the climb (first cruise FREDAI check) and then use the 30 minute / 1 hour left/right swap. Noting accurately the times each tank is used for.

Thus at any stage the pilot should be able to say how much fuel is in each tank and the tanks will be close to balanced (more important on ones with long range tanks and even more important if flying long range).

Selecting Both again pre-descent or if time available with engine failure.

Regards,

DFC

S-Works

19th Mar 2008, 16:11

Ah DFC making up his own rules again. 3 more posts and it will be in the ANO as law...... :E:E:E

My POH FR172K states to fly on both "unless it is desired to completely exhaust a tank in flight , the auxiliary fuel pump will then be required to restart the engine". It also tells me not to run the electric pumps and the engine driven fuel pump at the same time or the engine will stop unless leaned.

So if we add up some off the advise about switching tanks in flight and putting the fuel pump on in my aircraft we are setting ourselves up for a plummet.

So how about this for a thought, read the POH for the aircraft you are flying, there are subtle differences even in the same model across the variants.

fireflybob

19th Mar 2008, 16:22

A quick Google found this:-

RE: C-172 Power Loss at altitude
Airworthiness Directive
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
Amendment 39-1415; AD 72-07-02
Airworthiness Directives; CESSNA Models 172, 172A, 172B, 172C, 172D, 172E, 172F, 172G,
172H, 172I, 172K, Airplanes
AGENCY: Federal Aviation Administration, DOT
DATES: Effective March 25, 1972.
72-07-02 CESSNA: Amdt. 39-1415. Applies to the following airplanes:

MODELS SERIAL NUMBERS AFFECTED
172 28000 thru 29999
172 36000 thru 36999
172 46001 thru 46754
172A 46755 thru 47746
172B 17247747 thru 17248734
172C 17248735 thru 17249544
172D 17249545 thru 17250572
172E 17250573 thru 17251822
172F 17251823 thru 17253392
172G 17253393 thru 17254892
172H 17254893 thru 17256512
172I 17256513 thru 17257161
172K 17257162 thru 17258855
Compliance: Required as indicated, unless already accomplished.
To reduce the possibility of engine power interruption at altitudes above 5000 feet caused by vapor formation in the fuel lines, accomplish the following:
(A) Effective now, the airplane must be operated on a single fuel tank immediately upon reaching cruise altitudes above 5000 feet.
(B) On or before April 1, 1972, install at the fuel selector valve applicable Cessna placards P/N's 0509021-1, 0509021-2 or 0509021-3 as provided with Cessna Service Letter SE72-7, dated March 17, 1972, or any FAA-approved equivalent placard which reads as follows: SWITCH TO SINGLE TANK OPERATION IMMEDIATELY UPON REACHING CRUISE ALTITUDES ABOVE 5000 FEET.
(C) Compliance with the provisions of Paragraphs A and B is no longer required when the fuel system has been modified by the installation of applicable Cessna Kit No. SK172-31B or SK172-32 referenced by Cessna Service Letter SE72-7, dated March 17, 1972, or by the accomplishment of any equivalent method approved by the Chief, Engineering and Manufacturing Branch, FAA, Central Region.
This amendment becomes effective March 25, 1972.

Here is the full link:-

C172 (http://bbs.keyhole.com/ubb/showflat.php?Cat=&Board=offtopic&Number=1124813&Searchpage=1&Main=1081035&Words=+Suzyquad&topic=&Search=true)

S-Works

19th Mar 2008, 16:34

(C) Compliance with the provisions of Paragraphs A and B is no longer required when the fuel system has been modified by the installation of applicable Cessna Kit No. SK172-31B or SK172-32 referenced by Cessna Service Letter SE72-7, dated March 17, 1972, or by the accomplishment of any equivalent method approved by the Chief, Engineering and Manufacturing Branch, FAA, Central Region.
This amendment becomes effective March 25, 1972.

My bold. I am glad mine is french!

SkyHawk-N

19th Mar 2008, 17:35

Those Cessna kits mentioned provide the vent line between the two tanks I mentioned above. As this is all covered by an AD (mandatory) it should no longer be an issue (if ever it was an issue).

172driver

19th Mar 2008, 17:41

The fuel-vent situation brought up by Skyhawk-N is indeed an issue across the Cessna range. I sometimes fly a C182 with rubber tanks and - to the despair of the chief mechanic here - this one simply cannot be brought to draw fuel evenly. Hence this a/c (and, coming to think of it, another 182 I sometimes fly) is flown on the watch hemispheric rule.

DFC

19th Mar 2008, 21:51

It also tells me not to run the electric pumps and the engine driven fuel pump at the same time or the engine will stop unless leaned.

So if we add up some off the advise about switching tanks in flight and putting the fuel pump on in my aircraft we are setting ourselves up for a plummet.

Not if you do what I said in my post.

With so many variations do we teach the common safe operating procedure which will keep you safe in all C172s or do we have the AD status checked on each aircraft hired by a PPL...........Oh and of course watch out for the old C172 that the Placard which requires the selection of L or R immediately in cruise above 5K has faded or has fallen off.

Even you admit that your POH approves the use of Left and Right positions.

Regards,

DFC

SNS3Guppy

20th Mar 2008, 10:06

What's important, here? Arguing over who knows the 172 best? Ensuring that others use your personal technique? Or simply keeping track of your fuel?

There are all kinds of ways you can manage your fuel. Some of those ways are dictated by airworthiness directive, some are by aircraft limitation or manufacturer recommendation, and some are personal preference.

The primary concern is that you keep track of your fuel and keep a way available to make the fuel available. You know, or should know, that your fuel gauges are only required to read 100% accurately when the tanks are empty. With that in mind, it behooves you to watch your fuel useage, time your fuel useage, and time your use of individual tanks. It also behooves you not to push your fuel down to the bare minimums.

A very wise addage is that you shouldn't run out of fuel if you don't burn off the bottom half of the tank. This doesn't mean that you should always have at least a half a tank; it simply means that you should always have a minimum known quantity of fuel aboard which you will not burn. Never violate that minimum number; you decide what's best for you. Don't count on burning one tank dry and then restarting; that may not be an option for you.

Know what you've got on board. You may choose to burn off one tank for an hour and then switch. You may choose to burn off both. You may choose all kinds of methods, but the main thing is that you keep track of your fuel. You should do this in writing; note the times you start, take off, switch, and calculate your fuel separately from simply watching the gauge. Perform reasonablness checks; note that half way through your trip you've burned half of the fuel you intended...if it's going down faster than you think, you have a problem. Same for if it's going down slower...

Know your airplane. Keep track of what you're burning, keep track of your fuel, do it in writing. Other than that, don't worry about what the other guy is doing.

S-Works

20th Mar 2008, 10:10

You are indeed correct my POH does approve the use off left and right positions, but it also makes it clear this is unusual and points out that you may have to use the fuel pumps to restart the engine when it stops due to fuel exhaustion.

I really see no benefit in changing tanks on a fuel system designed to be drawn from both at the same time. Why do you need to know how much fuel is in each tank when you draw from both tanks? It makes no difference that the fuel draws slightly unevenly as Cessna tanks are designed so that in the both position you can empty one tank without problem.

You are as usual coming up with a solution for a problem that does not exist.

We do not expect a PPL hirer to check the AD status, we expect the hirer to ensure that they have access to the POH and that that if they old and faded fuel switch placard is unreadable that it is replaced. We don't expect you to have to make stuff up to fix an imaginary problem.

Edit to Add:

SNS is absolutely right, I said the same thing a few posts ago. Read your POH and operate accordingly. Don't make up stuff ala DFC style.

Personally I use a fuel computer linked to the GNS430 and fly with both tanks on. Over thousands of hours it has proven to be accurate to a fraction of a litre (usually the fractions drained for fuel tests and fillinng my tug!)

DFC

20th Mar 2008, 11:39

I really see no benefit in changing tanks on a fuel system designed to be drawn from both at the same time. Why do you need to know how much fuel is in each tank when you draw from both tanks? It makes no difference that the fuel draws slightly unevenly as Cessna tanks are designed so that in the both position you can empty one tank without problem.

So when that tank empties and you then discover that the reason for it happening was that the other was not providing any fuel your actions are?

Regards,

DFC

S-Works

20th Mar 2008, 12:40

Uh! OK you need to better phrase your question as I don't understand the point of it. I assume you are saying that using your method the engine will stop earlier?

Ok lets have a look at another scenario, changing the fuel selector back and forth every 30 minutes causes it to fail and stick closed between tanks, what do you do? According to my engineer a common failure.

Next?

stocker

20th Mar 2008, 12:53

This may be a daft question but normally only one filler cap is vented to allow air into the tank. What happens when you select the tank that does not have this vent.

S-Works

20th Mar 2008, 14:18

Interesting question! I would assume that it draws air in across the breather pipe that connects the two tanks?

SkyHawk-N

20th Mar 2008, 15:06

I would assume that it draws air in across the breather pipe that connects the two tanks?

Yep, that's what it's purpose is.

Just for interest here is a diagram of the fuel system from the 172 service manual.

http://www.csharpprogrammer.com/files/Cessna172FuelSystem.jpg

SNS3Guppy

20th Mar 2008, 18:53

Why do you need to know how much fuel is in each tank when you draw from both tanks?

What business have you in the cockpit of any airplane if you have to ask such a question? Surely you joke.

DFC

21st Mar 2008, 09:46

Bose,

Uh! OK you need to better phrase your question as I don't understand the point of it. I assume you are saying that using your method the engine will stop earlier?

No.

I asked " What your actions are when you have an engine failure (which unknown to you at the immediate time is due to fuel exhaustion)"

Most people will

a) Fly the aircraft - Best Glide

b) Select a suitable landing area

If there is time available

Select a tank with fuel in it.................

1. Based on the unreliable fuel gauges in the Cessna, please explain how you can tell which of the tanks has the useable fuel in it when both gauges are varying from E to 1/4 in turbulence.

2. How you can determine how much fuel is in that tank

but much more importantly and here is the important point -

In your method when you select the tank with the fuel, the engine will not start because that tank is not providing fuel to the system.

If you reguluarly change tanks then in the scenario I describe the engine will stop the first time you select the blocked tank. Returning the selector to either the Both or the other tank position will make the fuel in the other tank (a known figure) available for diversion.

Ok lets have a look at another scenario, changing the fuel selector back and forth every 30 minutes causes it to fail and stick closed between tanks, what do you do? According to my engineer a common failure.

A situation that has happened on aircraft where it has been operated and left for a long period in the Both position before being moved. A well serviced and reguluarly exercised selector will be reliable.

One has to wonder why Cessna spent all that money on such a feature when in your case they could have used the same design as the C150...........as far less cost and less weight.

You also ignored the following:

You said - It also tells me not to run the electric pumps and the engine driven fuel pump at the same time or the engine will stop unless leaned.

So if we add up some off the advise about switching tanks in flight and putting the fuel pump on in my aircraft we are setting ourselves up for a plummet.

I say that using my method that will not happen. Do you not agree?

-------

What business have you in the cockpit of any airplane if you have to ask such a question? Surely you joke.

Unfortunately probably not!

One of the most frustrating parts of being a flight instructor must be the idiots who will do one thing while you are teaching them and then totally ignore it when they are let loose on their own - good fuel management and airmanship being one!

Regards,

DFC

S-Works

21st Mar 2008, 10:07

One of the most frustrating parts of being a flight instructor must be the idiots who will do one thing while you are teaching them and then totally ignore it when they are let loose on their own - good fuel management and airmanship being one!

Yes I know. Which is why as an Instructor I teach people to read the POH properly and fly as the manufacturer suggests rather than making stuff up that suits me.

DFC

21st Mar 2008, 10:54

OK then BOSE, as an instructor respond to the points I made in my last post.

Regards,

DFC

SkyHawk-N

21st Mar 2008, 11:32

Most people will

a) Fly the aircraft - Best Glide

b) Select a suitable landing area

If there is time available

Select a tank with fuel in it.................

DFC, for an 'Engine Failure During Flight' my Cessna 172 POH says ...
'Fuel Selctor valve --- Both', not 'Select a tank with fuel in it'.

Based on the unreliable fuel gauges in the Cessna

I've never had a problem with the accuracy of my Cessna fuel gauges.

DFC

21st Mar 2008, 11:45

DFC, for an 'Engine Failure During Flight' my Cessna 172 POH says ...
'Fuel Selctor valve --- Both', not 'Select a tank with fuel in it'.

"Select a tank with fuel in it" is a generic memory item that works for (almost) all aircraft.

In a C172 normally selcting both will select a tank with fuel in it so the above is not different from the POH.

However, the point I am making is that if you cruise on Both all the time and one tank becomes blocked, selecting Both or the tank with fuel in it after the engine stops due to fuel exhaustion will not restore fuel flow.

Regards,

DFC

FullyFlapped

21st Mar 2008, 12:23

However, the point I am making is that if you cruise on Both all the time and one tank becomes blocked, selecting Both or the tank with fuel in it after the engine stops due to fuel exhaustion will not restore fuel flow.

If one tank is blocked, and the other one is empty, then nothing's going to help anyway, is it ? I suppose there's a theoretical advantage in knowing that you've got a blocked tank, but personally, given the nature of the cock, I reckon you're probably at least as likely to bust the thing or have it jam stuck at "Off" as you are to get a tank blockage ...

I used to own a 172N and flew hundreds of hours in it, at all altitudes pretty well up to its service ceiling. Aside from PTO checks, when both tanks would be selected and tested individually, the fuel cock never moved from "Both", as per the POH. No problem. As for accurately knowing how much fuel is on board, I personally never relied on the gauges : I'd know how much was in before take off, and then all the rest is just timing (and always using a max consumption rate whether I was actually consuming at that rate or not).

I now fly a 210, which has no "both" position. I have a bit of a shudder every time I switch tanks, as the selector has to pass through "off" to get to the other tank. Cessna changed this in the next model to include a "both" position ...

DFC

21st Mar 2008, 12:39

I reckon you're probably at least as likely to bust the thing or have it jam stuck at "Off" as you are to get a tank blockage ...

Move the selector from right to left or vice versa via the Both position ensures that it can't ever be stuck in the Off position.

If it was as likely to break as some here make out then Cessna would have been required to modify the design and we would have had more ADs and more frequent inspections etc.

The vast majority of problems come from people who leave it in the both position and then have a problem with the lever being stuck - often when they need to select ther Off position rather than L or R.

Regards,

DFC

Ken Wells

21st Mar 2008, 17:17

In the late '80's we had a flyout from Woodvale to Avaranches in Brittany I flew one of the clubs 172 Kilo Golf ; with a student. We had a great time and spent three days there.

Next to the airfield is Mont Saint-Michel ; in those days it was unrestricted airspace now it is a no fly area.

We flew around the Mount at low level admiring the view in a left hand circle. After a few seconds the engine spluttered and faltered. I righted the aircraft and planned to land on the sand bank doing my checks . The fuel tank was selected on left tank. I immediatley selected both and the engine came back to life. Due to the low content of the right tank, the fuel did not flow as it was selected on the lower tank in the turn.
From then on I always flew on both tanks.:=

SNS3Guppy

21st Mar 2008, 17:31

I now fly a 210, which has no "both" position. I have a bit of a shudder every time I switch tanks, as the selector has to pass through "off" to get to the other tank. Cessna changed this in the next model to include a "both" position ...

You may or may not be aware of the fuel system in your Cessna 210, as many pilots who fly them aren't (including the instructors who check them out). Your fuel system involve wing tanks, but also kidney header tanks with their own sumps at the bottom of each door post, inside the airframe where you can't see them. A fuel drain will be found for each tank on the underside of the airplane, even with the wing strut (on 205's, 206's, and early 210's with the strut)...or where the strut would be if the 210 had one (most 210's).

This small collection tank accepts vapor return and bypass fuel from the fuel pump, and utilizes the same fuel line that serves it from the wing tank, to vent the kidney sump. What this means is that under conditions involving increasing vapor in the fuel (hot conditions when a lot of hot, vaporizing fuel is being bypassed and returned to the kidney sump)...you can have an engine failure. The wing tank is trying to feed the kidney sump, which is trying to feed the fuel pump through the fuel selector, but hot, gaseous fuel is returning up the feed line from the tank, causing a blockage. It's addresed in the Cessna Fuel Flow Fluctuation procedure in your handbook. However, the Cessna procedure is wrong, and can lead to an unrecoverable engine stoppage. The primary goal when large fuel flow fluctuations occur, which are occuring for the reason I have described, is to switch tanks. Get cool, uncontaminated fuel to that engine ASAP.

Running your airplane in a both position would put the airplane in a position of contaminating both fuel tanks with hot, vaporized fuel. Running it in one and then the other, rather than a "both" position, is crucial to safety. This same fuel arrangement doesn't exist on the 172; they're entirely different systems. The fuel arrangement I've described is part of the 200 series fuel systems, excepting the 208. You'll find it on the 205, 206, 207, and 210. You probably won't encounter the problem very often; I had a complete engine failure only once in the 210 as a result of FFF, but it will have your full attention when it happens. Switching tanks, engaging the boost pump, and adjusting your mixture (and throttle) is important when it occurs. Following the Cessna procedure, which erroneously directs the pilot to use the boost pump first, only aggravates the problem by increasing the amount of hot bypass fuel being sent back to the kidney sump, and consequently increases the back pressure and resistance to flow as that hot fuel and vapor returns up the wing tank feed line. Swapping tanks to a source of cooler, clean fuel is the most crucial step, followed by boost, and a throttle and mixture adjustment (the manual won't tell you to close the throttle, but if you've just had an engine failure at a high power setting (when it's most likely to occur with FFF and high fuel flow), the sudden surge as the engine comes to life can detune your crankshaft and ruin your engine...or even cause a catastrauphic failure.

Follow the manual, but know your airplane. The two aren't always 100% in harmony. The goal isn't to use what you find as a do-list, but a check list, and the checklist follows action; acts of common sense.

S-Works

21st Mar 2008, 22:07

Move the selector from right to left or vice versa via the Both position ensures that it can't ever be stuck in the Off position.

If it was as likely to break as some here make out then Cessna would have been required to modify the design and we would have had more ADs and more frequent inspections etc.

The vast majority of problems come from people who leave it in the both position and then have a problem with the lever being stuck - often when they need to select ther Off position rather than L or R.

Regards,

DFC

And if you the 'problem' of the tanks draining unevenly was as bad as you indicate to require the tank change every 30 minutes they would issue an AD for that.

Horses for courses, methinks.

DFC

21st Mar 2008, 22:21

We flew around the Mount at low level admiring the view in a left hand circle. After a few seconds the engine spluttered and faltered. I righted the aircraft and planned to land on the sand bank doing my checks . The fuel tank was selected on left tank. I immediatley selected both and the engine came back to life. Due to the low content of the right tank, the fuel did not flow as it was selected on the lower tank in the turn.
From then on I always flew on both tanks

That is why Cessna require the tanks to be on both unless in level flight and have various comments about uncovering the tank outlets in various modes of operation.

-----------

Bose,

I am surprised that as an "instructor" you ignore the oportunity to directly address the points I made earlier.

When you read my post again you will see that I never suggested changing the tanks every 30 minutes.

Perhaps you are the only instructor I know who does not believe in keeping the aircraft in lateral balance and trim and thus avoiding unnecessary drag.

Regards,

DFC

SNS3Guppy

21st Mar 2008, 22:22

And if you the 'problem' of the tanks draining unevenly was as bad as you indicate to require the tank change every 30 minutes they would issue an AD for that.

Not necessarily. I've flown several PZL Dromaders which experienced fuel imbalance problems greater than that...and for which no AD will ever be forthcoming.

That's why it's "fuel management," not "fuel and forget."

S-Works

21st Mar 2008, 22:29

I never argued against your comments about keeping the aircraft in balance. I also did not disagree with your comments on the actions in an engine failure. So I did not see the point in reply to perpetuate a fight. Your final comment was not worth the effort in arguing as it is just as usual a made up scenario that tries to prove your point.

I merely pointed out that the aircraft should be flown in accordance with the POH not have 'rules' made up to suit. We all now how you like to make rules up.

I realise from the 'quotes' that you do not consider me to be a proper 'instructor' and I am sure that I must bow to your vast experience however dogmatic it may be.

S-Works

21st Mar 2008, 22:31

Not necessarily. I've flown several PZL Dromaders which experienced fuel imbalance problems greater than that...and for which no AD will ever be forthcoming.

That's why it's "fuel management," not "fuel and forget."

Yeah we can all come up with appropriate horror stories. Thanks for the input though and agreed fuel management is a very appropriate philosophy to adopt.

DFC

21st Mar 2008, 23:16

I merely pointed out that the aircraft should be flown in accordance with the POH not have 'rules' made up to suit

You can do both. Airmanship demands quite a lot of "'rules' made up to suit" safety.

Yes I did put the "instructor" in because I don't know if you are actually one but I doubt if an instructor would say;

Interesting question! I would assume that it draws air in across the breather pipe that connects the two tanks?

unless they slept through a large part of the FIC.

Regards,

DFC

SNS3Guppy

22nd Mar 2008, 03:36

Yeah we can all come up with appropriate horror stories.

There's no horror story there. That's every day, normal operations...and in that particular airplane the ONLY way to balance the fuel is to fly in a slip or a bank. You suggested that any propensity to develop such an imbalance would require an AD...and that's just not true.

Further, operational necessity may require the use of one tank rather than both. I've been in situations where the limited availability of fuel required putting what was available in one tank and running it off that tank, rather than dividing that between two...and yes, in the venerable 172.

There is, indeed, more than one way to skin a cat, and frequently, more than one reason for doing it.

S-Works

22nd Mar 2008, 11:47

Quote:
I merely pointed out that the aircraft should be flown in accordance with the POH not have 'rules' made up to suit
You can do both. Airmanship demands quite a lot of "'rules' made up to suit" safety.

Yes I did put the "instructor" in because I don't know if you are actually one but I doubt if an instructor would say;
Quote:

Interesting question! I would assume that it draws air in across the breather pipe that connects the two tanks?
unless they slept through a large part of the FIC.

Regards,
DFC

It's quite alright, an easy mistake for you to make. Most of us don't believe you even fly let alone instruct so I guess we are even. Fortunately there are enough people on these forums with my signature in there logbooks and licenses to prove my credentials. Can you say the same......
:p:p:p:p

And as for editing my post to suit your point if you actually read he whole quote it was a rhetorical answer... Again an easy mistake for one just looking for a fight to make.

Interesting question! I would assume that it draws air in across the breather pipe that connects the two tanks?

DFC

22nd Mar 2008, 19:12

Interesting question! I would assume that it draws air in across the breather pipe that connects the two tanks? Today 03:36

Never assume.

It makes an ass of u in front of me. - Regular FIC basic line!

I never claim to be anything to push forward my opinions - take it or leave it. What you believe makes little difference.

However, most people who fly the C172 know the situation and positioning of the (where fitted) tank interconnecting line and for example it's effect on fuel flow from each tank even when the fuel is selected to Right and the tanks are 100% full.

Regards,

DFC

S-Works

23rd Mar 2008, 17:43

Interesting question! I would assume that it draws air in across the breather pipe that connects the two tanks? Today 03:36

Never assume.

It makes an ass of u in front of me. - Regular FIC basic line!

Last time.

And as for editing my post to suit your point if you actually read he whole quote it was a rhetorical answer... Again an easy mistake for one just looking for a fight to make.

A and C

23rd Mar 2008, 18:16

I can see nothing wrong with Bose-X fuel management, selecting both tanks and monitoring the fuel flow rate & total would seem to cover most things.

I would also expect him to monitor the blocked fuel tank indicator. For those of you unfamiliar with this it is a large yoke fitted in front of the pilot that you will have to turn away from the fuel tank that is not feeding to maintain level flight.

S-Works

23rd Mar 2008, 21:29

FullyFlapped

23rd Mar 2008, 23:57

DFC :

I never claim to be anything to push forward my opinions - take it or leave it
Ha ha ha ha ha ha ha ha ha ha ha he he he he he he ooooh stop it it hurts ;):ugh:;):ugh:;):ugh::=:D:yuk::oh:;):p:ugh:;);)

DFC

24th Mar 2008, 10:40

For those of you unfamiliar with this it is a large yoke fitted in front of the pilot that you will have to turn away from the fuel tank that is not feeding to maintain level flight.

For those unfamiliar with the C172, they will always have some imbalance which will require aileron deflection to keep the wings level when cruising in the Both position. As I said many posts ago this is particuluarly noticeable on those aircraft with the long range tanks fitted.

Of course, some idiot will come up now and try to tell us that they can take-off with 100% full tanks, keep Both selected and keep the tanks balanced throughout the flight!

As I asked BOSE earlier - perhaps he could explain where the fuel comes from with 100% full tanks and the fuel selector positioned to the "right" position?

Then he could exmplain where it somes from with the tank selected to "Both"?

Regards,

DFC

SkyHawk-N

24th Mar 2008, 10:55

Of course, some idiot will come up now and try to tell us that they can take-off with 100% full tanks, keep Both selected and keep the tanks balanced throughout the flight!

Here is THAT idiot :ok:. As I previous stated my 172 rarely suffers from uneven fuel drain from it's tanks. I put an equal amout of fuel in each tank, fly on 'Both' and 9 times out of 10 they are equal on arrival.

172driver

24th Mar 2008, 11:02

Joining the ranks of the idiots here :p

Most 172s I fly (and all the RGs) have long-range tanks, I fly them from full with selector on both and hardly ever experience an imbalance.

Note, however, what I said in an earlier post about 182s.

YMMV

SkyHawk-N

24th Mar 2008, 11:33

172driver, you are an idiot! Welcome :ok:

S-Works

24th Mar 2008, 11:38

Quote:
Of course, some idiot will come up now and try to tell us that they can take-off with 100% full tanks, keep Both selected and keep the tanks balanced throughout the flight!
Here is THAT idiot . As I previous stated my 172 rarely suffers from uneven fuel drain from it's tanks. I put an equal amout of fuel in each tank, fly on 'Both' and 9 times out of 10 they are equal on arrival.

Yep and me, realise only a few thousand hours on my own Cessna gives me very little experience so it must just be blind luck that when I fill up my variance between tanks is a couple of liters.

As I asked BOSE earlier - perhaps he could explain where the fuel comes from with 100% full tanks and the fuel selector positioned to the "right" position?

From the pumps before the flight?

Slopey

24th Mar 2008, 11:50

Idiot here also (and a new one at that) - 172, long range tanks, no imbalance. Maybe I should fly it sideways more often.

S-Works

24th Mar 2008, 12:19

Idiot here also (and a new one at that) - 172, long range tanks, no imbalance. Maybe I should fly it sideways more often.

I am sure DFC will be happy to show you how to and then teach you all his rules for dealing with the resulting lack of information on the fuel contents that apparently results from this.

SkyHawk-N

24th Mar 2008, 12:30

Idiot here also (and a new one at that) - 172, long range tanks, no imbalance. Maybe I should fly it sideways more often.

Obviously you aren't using the Cessna "Tilted Head" technique properly. If you are flying and finding that you are not using this technique you will end up with level fuel tanks, hardly a satisfactory situation. :*

Granite City Flyer

24th Mar 2008, 13:55

Put me down on the idiot list please. 2000hrs in 8 versions of the 172 over 7 years.

mad_jock

24th Mar 2008, 14:33

4 pages on leaving the C172 fuel selector on both????

Fecks sake it's not rocket science.

Or is this one of those discussions which will only drop off the bottom when something else comes along to argue black is white etc.

I have 400hours in C172's and never bothered fannying about with the fuel selector. And the only time I have ever seen it used was by a ferry pilot who had butchered the fuel line for the right tank to install the ferry tank. Highly illegal and definatly none standard. Last seen climbing at 5' per min after using 1800m of runway to just get it off the ground

S-Works

24th Mar 2008, 19:47

MJ, where would the fun be? ;)

DFC

24th Mar 2008, 20:47

As I asked BOSE earlier - perhaps he could explain where the fuel comes from with 100% full tanks and the fuel selector positioned to the "right" position?

With Bose the instructor unwilling to answetr a simple question;

The C172 in most cases has two tanks feeding to a common point.

Only one tank has a vent.

The second tank (the right) vents via an interconnector to the other tank.

Most people assume that with 100% full tanks the and the fuel selector positioned to "Right" the fuel will feed from the right tank - i.e. the level in the right tank will reduce.

Unfortunately not.

With the selector set to Right, any fuel that leaves the right tank is replaced via the interconnector and the space thus left in the left tank is filled with air via the vent.

This continues until the interconnecting line is uncovered and air flows from the vent via the left tank to the right tank.

Therefore in the situation of 100% full tanks and fuel selected to right, the level in the left tank reduces.

Seems that not many people know that or that it is nigh on impossible to get perfectly balanced fuel flow when Both is selected unless the inaccurate flying manages to balance things out (but of course such flying burns more fuel).

Now that you know that BOse, do you want to hazard a guess at the second part of what I asked?

Regards,

DFC

Julian

24th Mar 2008, 20:53

I am a complete idiot as well, always flown on 'both' in 172s when I have hired them on my hols.

Maybe we could all meet DFC at his home airfield for a mass instructional day from him one weekend? :E

J.

DFC

24th Mar 2008, 21:49

I am a complete idiot as well, always flown on 'both' in 172s

I did not say that pilot who fly on Both were idiots.

I said;

Of course, some idiot will come up now and try to tell us that they can take-off with 100% full tanks, keep Both selected and keep the tanks balanced throughout the flight!

The original basic C172 system in general does not permit that. Why do you think that they gave the pilot a selector to balance the tanks?

Regards,

DFC

S-Works

24th Mar 2008, 21:58

The original basic C172 system in general does not permit that. Why do you think that they gave the pilot a selector to balance the tanks?

To give you a reason to make up rules and then try and spend days convincing us all that we are having been doing it wrong for several thousand hours whilst operating as per the manufacturers guidelines?

mad_jock

24th Mar 2008, 22:31

DFC it doesn't matter at all.

The out of balance is going to be there anyway if you have one person on board. Your average yank at 100kg at 0.5 meters is going to give you more moment than 10kg (if that) at 1.5m

No plane will ever be in perfect balance it's called the real world.

The gyroscopic and all them other forces will put out of balance as well.

Personally I think they put it in so if you got fuel pissing out of one tank either from the fuel line, the filler cap or tank drop you could isolate that side to stop it syphoning through the connection.

Or it was a change in the design regs that you needed to be able to isolate the tanks.

Or they put it in so ferry pilots can stick a 50 gallon drum on the back seat and hack into the fuel lines