Switching fuel tanks in route?
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
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Mike Smith
- Posts: 175
- Joined: Mon Jun 02, 2003 2:53 pm
Back to the dip stick...
George,
Since you brought it up... I bought a "glass" fuel stick you described last year, but was uncomfortable using it because of the question of accuracy. The stick I bought was for a c172 with 19 gal tanks. Yesterday I took a look at it...sawed off the bottom two hash marks and dipped it in my "A" model. The 19 gal mark comes one mark shy of the bottom edge of the filler neck. I think a full tank would show exactly 20 gals if there were 1 more mark on the stick.
My question is this...How much gas is left in the tank when the gas level is exactly at the bottom of the baffle? The stick would indicate "0", but I can see a substantial amount behind the baffle toward the back of the tank. Is that the "unuseable fuel" we hear about? I would assume that some of that fuel would move forward in level flight. Does using the stick allow for that in the way the stick has been calibrated? Your thoughts?
Also...I have seen several references to one tank burning faster than the other. Mine does too, but does that indicate that there is any problem with the fuel valve or is it just normal. There is usually 4-5 gals difference at refuel between the tanks. I normally fly with the fuel set on both all the time. I have often thought if I were to use the Right tank to exhaustion, then switch to Left, I'd have a pretty good idea of what was left, but flying til the engine quits, then switching, makes me really nervous. I know many pilots do on a fairly regular basis.
I would like to hear your some thoughts on this.
Neil
Since you brought it up... I bought a "glass" fuel stick you described last year, but was uncomfortable using it because of the question of accuracy. The stick I bought was for a c172 with 19 gal tanks. Yesterday I took a look at it...sawed off the bottom two hash marks and dipped it in my "A" model. The 19 gal mark comes one mark shy of the bottom edge of the filler neck. I think a full tank would show exactly 20 gals if there were 1 more mark on the stick.
My question is this...How much gas is left in the tank when the gas level is exactly at the bottom of the baffle? The stick would indicate "0", but I can see a substantial amount behind the baffle toward the back of the tank. Is that the "unuseable fuel" we hear about? I would assume that some of that fuel would move forward in level flight. Does using the stick allow for that in the way the stick has been calibrated? Your thoughts?
Also...I have seen several references to one tank burning faster than the other. Mine does too, but does that indicate that there is any problem with the fuel valve or is it just normal. There is usually 4-5 gals difference at refuel between the tanks. I normally fly with the fuel set on both all the time. I have often thought if I were to use the Right tank to exhaustion, then switch to Left, I'd have a pretty good idea of what was left, but flying til the engine quits, then switching, makes me really nervous. I know many pilots do on a fairly regular basis.
I would like to hear your some thoughts on this.
Neil
I have run my airplane in level flight to the point of exhaustion over the field. (At least to the point of not being able to kick the rudders and observe any movement on the fuel gauges. In other words, the 172 tanks are the same as ours.)
I then diptube-ed my tanks with the Fuel Hawk modified as described. (Yes, it is calibrated originally for 19 gal. 172 tanks, but also originally had two more gallons indexed below "zero" which I cut off, just as described.)
Now my diptube reads from 0 to 19, just as yours.
My tanks had no observable fuel in them. I added two gallons of fuel. The diptube read 2 gals. I added 2 more gallons. The diptube read 4 gallons. And so on, all the way to full where it read 19 gallons after having put in a total of 19 gallons in each tank. (I am comfortable that approximately 2 gallons aft of the baffle are not measureable with a diptube and constitute unuseable fuel.)
The 170A and B's all have 21 gallon tanks, 19 gallons of which are useable. (According to the type certificate, there are 42 gallons when the system is full, of which 37 gallons are useable, leaving 5 gallons unuseable, 2.5 gallons in each wing and it's associated plumbing.)
Since you can't dipstick the plumbing, I feel it's safe to round off each tank to 19 gallons useable, which the diptube seems to accurately measure.
I believe the tricycle 172 must have it's diptube calibrated with 2 gallons below the "0" mark in order to accomodate the unuseable fuel that may sit at the center of the tank in the tricycle stance of the 172 aircraft. Cutting that 2 gallons off the bottom of the diptube accounts for the 2 gallons of unuseable fuel which rests at the rear of the 170A/B tank (aft of the baffle) in the 3-point stance.
Most high wing Cessnas, when fed from both tanks simultaneously, will actually appear to use fuel more rapidly from one tank than the other. This is because the tanks share a common vent line. Actually both tanks are feeding equally toward the engine, but one tank (the left in most 170A and B's) appears to feed more slowly because it is also being replenished by the dual-vented right tank (remember the vented fuel cap) via the vent line. In other words, a certain amount of fuel will transfer while both tanks are relatively full from the right tank thru the vent line to the left tank. This occurs for two reasons. One is: the right tank is vented not only by the vent line gooseneck, but also by a vented cap. Therefore it's head pressure is potentially higher. The second reason is because at the time of highest fuel consumption (takeoff and climb) p-factor causes the pilot to keep the airplane straight by increased right-rudder application. This keeps the fuel level in the right tank pressed against the vent line further encouraging fuel transfer toward the left tank.
Since the end result is that fuel is leaving the left tank only toward the engine, but is leaving the right tank toward the engine AND toward the left tank, the result is a right tank that empties intially somewhat faster than the left. After approximately the first hour of flight, this transfer naturally stops, and both tanks will continue to feed the engine equally, but the left tank (no longer be replenished from the right) will read higher because it is indeed containing more fuel.
I hope this explanation helps.
(I run my airplane from takeoff to touchdown on Both, and live with it.)
I then diptube-ed my tanks with the Fuel Hawk modified as described. (Yes, it is calibrated originally for 19 gal. 172 tanks, but also originally had two more gallons indexed below "zero" which I cut off, just as described.)
Now my diptube reads from 0 to 19, just as yours.
My tanks had no observable fuel in them. I added two gallons of fuel. The diptube read 2 gals. I added 2 more gallons. The diptube read 4 gallons. And so on, all the way to full where it read 19 gallons after having put in a total of 19 gallons in each tank. (I am comfortable that approximately 2 gallons aft of the baffle are not measureable with a diptube and constitute unuseable fuel.)
The 170A and B's all have 21 gallon tanks, 19 gallons of which are useable. (According to the type certificate, there are 42 gallons when the system is full, of which 37 gallons are useable, leaving 5 gallons unuseable, 2.5 gallons in each wing and it's associated plumbing.)
Since you can't dipstick the plumbing, I feel it's safe to round off each tank to 19 gallons useable, which the diptube seems to accurately measure.
I believe the tricycle 172 must have it's diptube calibrated with 2 gallons below the "0" mark in order to accomodate the unuseable fuel that may sit at the center of the tank in the tricycle stance of the 172 aircraft. Cutting that 2 gallons off the bottom of the diptube accounts for the 2 gallons of unuseable fuel which rests at the rear of the 170A/B tank (aft of the baffle) in the 3-point stance.
Most high wing Cessnas, when fed from both tanks simultaneously, will actually appear to use fuel more rapidly from one tank than the other. This is because the tanks share a common vent line. Actually both tanks are feeding equally toward the engine, but one tank (the left in most 170A and B's) appears to feed more slowly because it is also being replenished by the dual-vented right tank (remember the vented fuel cap) via the vent line. In other words, a certain amount of fuel will transfer while both tanks are relatively full from the right tank thru the vent line to the left tank. This occurs for two reasons. One is: the right tank is vented not only by the vent line gooseneck, but also by a vented cap. Therefore it's head pressure is potentially higher. The second reason is because at the time of highest fuel consumption (takeoff and climb) p-factor causes the pilot to keep the airplane straight by increased right-rudder application. This keeps the fuel level in the right tank pressed against the vent line further encouraging fuel transfer toward the left tank.
Since the end result is that fuel is leaving the left tank only toward the engine, but is leaving the right tank toward the engine AND toward the left tank, the result is a right tank that empties intially somewhat faster than the left. After approximately the first hour of flight, this transfer naturally stops, and both tanks will continue to feed the engine equally, but the left tank (no longer be replenished from the right) will read higher because it is indeed containing more fuel.
I hope this explanation helps.
(I run my airplane from takeoff to touchdown on Both, and live with it.)
Dipstick
Thanks George,
I had forgotten about the gas in the plumbing. Your explanation helps confirm my suspicions on unuseable fuel, and the uneven fuel useage makes perfect sense as well. Thanks for the education, and your work on this website. It is a constant sorce of enlightenment and entertainment for a newby like me.
Neil
I had forgotten about the gas in the plumbing. Your explanation helps confirm my suspicions on unuseable fuel, and the uneven fuel useage makes perfect sense as well. Thanks for the education, and your work on this website. It is a constant sorce of enlightenment and entertainment for a newby like me.
Neil
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Bruce Fenstermacher
- Posts: 10318
- Joined: Tue Apr 23, 2002 11:24 am
George your explanation of unegual fuel usage seems like it might work. BUT I have a vented cap on both tanks and the left still drains slower (or is it filling from the left) than the right.
My left wing which usually ends up with more fuel than the right is heavier then the right even with the fuel level. Because of this left wing heavy condition I usually put twice as much fuel in the right then the left to balance the plane and use the right tank only or both to keep the plane balanced.
Switching fuel and using either left or right seems natural to me cause my first plane was a Cherokee which doesn't have a BOTH position (most Pipers don't) and you alway have to switch tanks.
My left wing which usually ends up with more fuel than the right is heavier then the right even with the fuel level. Because of this left wing heavy condition I usually put twice as much fuel in the right then the left to balance the plane and use the right tank only or both to keep the plane balanced.
Switching fuel and using either left or right seems natural to me cause my first plane was a Cherokee which doesn't have a BOTH position (most Pipers don't) and you alway have to switch tanks.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Re: Dipstick
Not just the newbies! It's just a matter of how often the rest of us say THANKS! We are very lucky to have George and this forum.N170GA wrote:Thanks George,
I had forgotten about the gas in the plumbing. Your explanation helps confirm my suspicions on unuseable fuel, and the uneven fuel useage makes perfect sense as well. Thanks for the education, and your work on this website. It is a constant sorce of enlightenment and entertainment for a newby like me.
Neil
Joe
51 C170A
Grand Prairie, TX
51 C170A
Grand Prairie, TX
Bruce, the best explanation I can offer for those with dual vented caps (assuming the're working correctly-check your red silicone rubber flap valves) is contained in the secondary reason I offered previously. The highest fuel consumption rate occurs during takeoff and climb when additional right rudder is required to keep the airplane on a straight course due to P-factor. This puts the fuel in the right tank against it's inboard bulkhead and encourages fuel to transfer from the right tank to the left tank, thereby replenishing at least in part, that fuel which has been fed from the left tank to the engine. Therefore, if both tanks begin the flight equally full, and although both tanks feed the engine equally, the left tank being replenished through the vent line/interconnected plumbing will contain more fuel than the right after a takeoff and climb.N9149A wrote:George your explanation of unegual fuel usage seems like it might work. BUT I have a vented cap on both tanks and the left still drains slower (or is it filling from the left) than the right.
My left wing which usually ends up with more fuel than the right is heavier then the right even with the fuel level. Because of this left wing heavy condition I usually put twice as much fuel in the right then the left to balance the plane and use the right tank only or both to keep the plane balanced.
Switching fuel and using either left or right seems natural to me cause my first plane was a Cherokee which doesn't have a BOTH position (most Pipers don't) and you alway have to switch tanks.
My tanks are usually within a gallon of each other at fill up - i.e. they require the same amount of gallons to be made full. I run a vented cap on the right tank, non-vented on the left (as sitting in the plane). If I have an extra 5 gallons of gas and pour it into the right tank, overnight the two tanks almost equalize in quantity while sitting in the hangar. When fueling the plane, have always tried not to waste too much time moving from one side to the other, because the full side will transfer to the more empty side. Thus, if you filled the right tank, then went over for a while and looked at scenery, then, came back and filled the left tank - the right tank would already have less than the left when you take off.
Joe
51 C170A
Grand Prairie, TX
51 C170A
Grand Prairie, TX
There are two fuel selector valves in the later airplanes. One, PN 0413020-3 was intalled in SN's 20267 thru 20285 is a simple Weatherhead valve that allows fuel transfer from wing tanks to the opposite tank even when the selector is in the off position.
The later valve PN 0513020-5 is a more complex valve with an internal cam that upsets check-ball valves from their seats in order for fuel to flow. If properly assembled they will not transfer fuel from one side to the other (or so I'm told.) Mine is the later PN and I've left it in the hangar overnight with one full and one empty and that's the way they remained overnight with the valve in the Off position.
When refueling, some owners place the selector in one tank position or the other until refueling is complete. (Just remember to place it back in BOTH for takeoff.)
The later valve PN 0513020-5 is a more complex valve with an internal cam that upsets check-ball valves from their seats in order for fuel to flow. If properly assembled they will not transfer fuel from one side to the other (or so I'm told.) Mine is the later PN and I've left it in the hangar overnight with one full and one empty and that's the way they remained overnight with the valve in the Off position.
When refueling, some owners place the selector in one tank position or the other until refueling is complete. (Just remember to place it back in BOTH for takeoff.)
I always turn mine off when the airplane is unattended for long periods. I never want to find a hangar full of fuel because the carb float failed. That's what burned down an entire hangar of warbirds in Conroe several years back. $2.2 million in aircraft, plus the hangar and the loss of the FBO's business for the year. My insurance limit is only $1 mil. and I can't afford the difference.
(Arriving at the airport in the early '80's and finding my airplane had dumped it's entire load of fuel onto the ramp and finding the firetrucks there applying EPA approved absorbent all under my neighbor's airplanes really got my attention. I'm glad the fire dept. didn't subrogate the expenses to me and that they didn't report it to EPA. I was uninsured at the time.)
How do you know if your fuel selector really turns the fuel off if you don't try to sample the gascolator with it in the OFF position? What if you had an engine fire? How would you stop it? Just a thought.
(Arriving at the airport in the early '80's and finding my airplane had dumped it's entire load of fuel onto the ramp and finding the firetrucks there applying EPA approved absorbent all under my neighbor's airplanes really got my attention. I'm glad the fire dept. didn't subrogate the expenses to me and that they didn't report it to EPA. I was uninsured at the time.)
How do you know if your fuel selector really turns the fuel off if you don't try to sample the gascolator with it in the OFF position? What if you had an engine fire? How would you stop it? Just a thought.
The simple solution to uneven refueling is to turn the fuel selector to any position except "both" before refueling. This closes the prevents the fuel from cross-feeding through the valve when one tank is fuller than the other one. I only do this when full tanks are absolutely required (long legs) or if I am using auto fuel from cans (time). As a point of safety, if I select "OFF" I always remove the ignition key and place it on the fuel selector as a reminder to turn the fuel selector back to “on both†when finished.
All of the theories on the whys and hows of the uneven burn rates is puzzling and certainly food for thought. George, I agree with you that “stabbing†the rudder on t/o roll would induce some transfer of fuel via the vent but I wouldn’t think it would be more than a cup or two max. Once in flight, assuming (big one here) that the rigging is true and coordination is maintained (on average), there would be equal transfer from left to right as from right to left through the vent tube. As for the vented fuel caps, they don’t do squat unless/when the primary “vent snorkel†or the crossfeed gets plugged. That being said, the vent system should pose no appreciable cause for uneven (perceived) burn rates as noted by the fuel gauges. I just can’t buy the theory.
I am more inclined to think about the fuel selector valve itself as the culprit of the subject. It’s the most significant common component in the fuel system since it is directly attached to each tank, constantly fed by gravity and is always in contact with fuel pressure/s albeit small. In a static environment the valve will equalize the amounts in each tank within minutes if left alone. In a dynamic condition, when the engine is operating, fuel is demanded from the third port of the valve (from the carb) bringing in the hydrodynamic characteristics of the valve. Which raises some questions: Is the demand from the engine equally distributed to the valves internally plumbed right tank input to the left? Where the two fuel supplies merge inside the valve do they meet at equal angles to enter a common plenum? Is there more hydrodynamic friction in the internal valve plumbing from the left input than the right? I suspect that its not and the reason for the perceived unbalanced depletion rates. I guess the easiest way to confirm the theory is to go fly an hour on the left tank, land. Switch tanks, fly for an hour on the right tank and land. Fill up and record the amounts. In order allow for cross-feeding quantitiesfrom the vent, I would do it again in the reverse order and again record the amounts.
Hey guys, I don’t have any scientific answers here, just hunches. I do know (not from personal experience) that if you keep your fuel selector “on both†and you run out of gas, there won’t be a fuel fire at the wreckage site. Hmmm, did I read somewhere that coating the inside of the fuel selector valve with urethane powdercoat reduces the coefficient of friction….
When the prop is turning, my fuel selector valve stays “on bothâ€.
By the way, what is the burn rate of a 0300/C145 at 2450@(20â€?) vs 2450@(15â€)?
Are you guys telling me that you can actually “feel†the difference in flight with asymmetrically loaded fuel tanks???
JJH55
All of the theories on the whys and hows of the uneven burn rates is puzzling and certainly food for thought. George, I agree with you that “stabbing†the rudder on t/o roll would induce some transfer of fuel via the vent but I wouldn’t think it would be more than a cup or two max. Once in flight, assuming (big one here) that the rigging is true and coordination is maintained (on average), there would be equal transfer from left to right as from right to left through the vent tube. As for the vented fuel caps, they don’t do squat unless/when the primary “vent snorkel†or the crossfeed gets plugged. That being said, the vent system should pose no appreciable cause for uneven (perceived) burn rates as noted by the fuel gauges. I just can’t buy the theory.
I am more inclined to think about the fuel selector valve itself as the culprit of the subject. It’s the most significant common component in the fuel system since it is directly attached to each tank, constantly fed by gravity and is always in contact with fuel pressure/s albeit small. In a static environment the valve will equalize the amounts in each tank within minutes if left alone. In a dynamic condition, when the engine is operating, fuel is demanded from the third port of the valve (from the carb) bringing in the hydrodynamic characteristics of the valve. Which raises some questions: Is the demand from the engine equally distributed to the valves internally plumbed right tank input to the left? Where the two fuel supplies merge inside the valve do they meet at equal angles to enter a common plenum? Is there more hydrodynamic friction in the internal valve plumbing from the left input than the right? I suspect that its not and the reason for the perceived unbalanced depletion rates. I guess the easiest way to confirm the theory is to go fly an hour on the left tank, land. Switch tanks, fly for an hour on the right tank and land. Fill up and record the amounts. In order allow for cross-feeding quantitiesfrom the vent, I would do it again in the reverse order and again record the amounts.
Hey guys, I don’t have any scientific answers here, just hunches. I do know (not from personal experience) that if you keep your fuel selector “on both†and you run out of gas, there won’t be a fuel fire at the wreckage site. Hmmm, did I read somewhere that coating the inside of the fuel selector valve with urethane powdercoat reduces the coefficient of friction….
When the prop is turning, my fuel selector valve stays “on bothâ€.
By the way, what is the burn rate of a 0300/C145 at 2450@(20â€?) vs 2450@(15â€)?
Are you guys telling me that you can actually “feel†the difference in flight with asymmetrically loaded fuel tanks???
JJH55
JJH55< I didn't just make this stuff up. I based my previous suggested explanation/comments upon extensive research and documentation performed by the Cessna Pilot's Assoc, who published their findings in their Tech Note series. It is a multi-page document and is copyrighted, therefore I only printed out below a short summary statement from the Tech Note.
(Note:a this quote addresses the C-172 which has the identical fuel system as the 170A/B models except that the fuel vent is located behind the left wing strut in lieu of the goosneck. Therefore the left tank of those 172's are better vented than the right,...exactly the opposite of our 170's. So,...wherever the quote says "left"...you should replace the word with "right" for a 170 and vice-versa.)\
From Cessna Pilots Assoc. Tech Note #3, "Uneven Fuel Feeding in Single Engine Cessnas": Re: Differences in tank vent pressures (due to vent design and vented cap)
",... however the problem
has been reported on just about every Cessna single engine
model that has a “BOTH†position on the fuel selector. It is
certainly very disconcerting to be flying along and watch
your left fuel gauge going down while the right fuel gauge
continues to indicate full. The funny thing about this situation
is that while only the left gauge is showing fuel usage,
the engine may very well be using fuel from the right tank!
To understand what causes uneven fuel feeding we have
to go through some of the basics of the fuel system. First we
need to know that in most of the single engine Cessnas with
carburetted engines two forces cause the fuel to move from
the fuel tank to the engine. One of these forces is one that
everyone is aware of; Gravity. In fact the fuel systems used in
these high wing aircraft are often referred to as ‘Gravity Feed
Fuel Systemsâ€. Alsovery important is the relationship of the head pressure to ambient air pressure. In regards to even fuel feeding, the
head pressure in both tanks must be equal for the tanks to
flow at the same rate. If the tanks do not have the same
head pressure then the tank with the lower head pressure
will flow the slowest."
And, re: the vent crossover line:
"... This means that when the tanks are full the vent interconnect line is below the fuel level and is full of fuel. When air enters the left tank from the vent line to replace fuel being used, the pressure pushes fuel from the left tank through the vent interconnect into the right tank, replacing any
fuel that has been used from the right tank. " (Of course, in a 170 it is usually the right tank which is better vented due to the vented cap.)
And, "One good thing to note, and it is an important one, is that
this is not really a problem of uneven fuel quantities being
fed to the engine. Actually the engine is receiving approximately
the same amount of fuel from each tank at any given
time with the fuel selector in the ‘BOTH’ position."
The article goes on to discuss the points I made earlier regarding venting, vent lines, and vented fuel caps, as well as the importance of rigging as it affects fuel flow (which prompted my thoughts on p-factor/rudder useage during initial takeoff and climb, which may take considerably more time than a few minutes, and therefore affect considerably more fuel than a cup or two.) Members of CPA have direct access to the full document.
(Note:a this quote addresses the C-172 which has the identical fuel system as the 170A/B models except that the fuel vent is located behind the left wing strut in lieu of the goosneck. Therefore the left tank of those 172's are better vented than the right,...exactly the opposite of our 170's. So,...wherever the quote says "left"...you should replace the word with "right" for a 170 and vice-versa.)\
From Cessna Pilots Assoc. Tech Note #3, "Uneven Fuel Feeding in Single Engine Cessnas": Re: Differences in tank vent pressures (due to vent design and vented cap)
",... however the problem
has been reported on just about every Cessna single engine
model that has a “BOTH†position on the fuel selector. It is
certainly very disconcerting to be flying along and watch
your left fuel gauge going down while the right fuel gauge
continues to indicate full. The funny thing about this situation
is that while only the left gauge is showing fuel usage,
the engine may very well be using fuel from the right tank!
To understand what causes uneven fuel feeding we have
to go through some of the basics of the fuel system. First we
need to know that in most of the single engine Cessnas with
carburetted engines two forces cause the fuel to move from
the fuel tank to the engine. One of these forces is one that
everyone is aware of; Gravity. In fact the fuel systems used in
these high wing aircraft are often referred to as ‘Gravity Feed
Fuel Systemsâ€. Alsovery important is the relationship of the head pressure to ambient air pressure. In regards to even fuel feeding, the
head pressure in both tanks must be equal for the tanks to
flow at the same rate. If the tanks do not have the same
head pressure then the tank with the lower head pressure
will flow the slowest."
And, re: the vent crossover line:
"... This means that when the tanks are full the vent interconnect line is below the fuel level and is full of fuel. When air enters the left tank from the vent line to replace fuel being used, the pressure pushes fuel from the left tank through the vent interconnect into the right tank, replacing any
fuel that has been used from the right tank. " (Of course, in a 170 it is usually the right tank which is better vented due to the vented cap.)
And, "One good thing to note, and it is an important one, is that
this is not really a problem of uneven fuel quantities being
fed to the engine. Actually the engine is receiving approximately
the same amount of fuel from each tank at any given
time with the fuel selector in the ‘BOTH’ position."
The article goes on to discuss the points I made earlier regarding venting, vent lines, and vented fuel caps, as well as the importance of rigging as it affects fuel flow (which prompted my thoughts on p-factor/rudder useage during initial takeoff and climb, which may take considerably more time than a few minutes, and therefore affect considerably more fuel than a cup or two.) Members of CPA have direct access to the full document.
-
Bruce Fenstermacher
- Posts: 10318
- Joined: Tue Apr 23, 2002 11:24 am
JJH55: Yes I can feel the difference when the fuel gets out of balance buy about half a tank and I use this to my advantage cause of my previously mentioned heavy wing.
George: You and you source may be right about Pfactor and cross feeding between tanks. But at least in my case the rate and amount is as much as a quarter tank indicated between left and right tanks with the left having more when the selector is run on both after topping both tanks in a long cross country at cruise attitude. Yes both of my vented caps and fuel selector are working and recently rebuilt with new flappers and or o-rings.
Again this doesn't bother me I just fill the right tank more and/or fly off the right tank or both to keep the levels where I want it to balance the plane laterally.
George: You and you source may be right about Pfactor and cross feeding between tanks. But at least in my case the rate and amount is as much as a quarter tank indicated between left and right tanks with the left having more when the selector is run on both after topping both tanks in a long cross country at cruise attitude. Yes both of my vented caps and fuel selector are working and recently rebuilt with new flappers and or o-rings.
Again this doesn't bother me I just fill the right tank more and/or fly off the right tank or both to keep the levels where I want it to balance the plane laterally.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
George, I apologize if I implied that you were "making this stuff up". Not my intent. I appreciate all of the research that Cessna has done and unfortunately I am not a member of CPA to view the Tech Notes. The doubt I have regarding the vent system revolves around the fact that using vented caps on both tanks (as on my aircraft) does not solve this problem. Doesn't that render their theory invalid?
JJH55
JJH55