unusable fuel 14-13-2
- Thread starter Alain1
- Start date
Jonathan Baron
New member
Alain:
18 I believe.
18 I believe.
Larry Lowenkron
New member
I just love these planes! Just to show that no two are alike, I calibrated a fuel tank dip stick, by running the tanks dry (No, I didn't do that on the same flight, even though I have a glider rating). Turns out that I could put 20 gals in each tank!!! I couldn't really see much in the way of unusable fuel when I looked, but must admit that I didn't look too hard. I was more concerned about calibrating the tube. Hmmm!??
Jonathan Baron
New member
The 18 comes with a ambigious caveat: for all flight conditions or somesuch. The aux tank is all useable; it's V shaped whereas the wing tanks are square corner affairs.
As Larry, I too have burned nearly 20 gallons from a wing tank. This was in straight and level flight. I watch the fuel pressure needle and when it starts getting twitchy I switch. I've yet to run a tank completely dry, as I do in my Luscombe, probably I believe in gravity more than I believe in fuel delivery systems that defy it
In short, what I believe they mean is that up to two gallons may be unavailable in a climb, descent, or in unusual attitudes. Many aircraft have such limitations. I'm sure you've all seen fuel gauges that have a mark for minimum fuel for take-off. This is based on the attitude for climb and the possibility of fuel sloshing to the rear, exposing the intake port. It's also a reminder, apart from technical reasons, to put some damned fuel in the airplane
As we should neither take-off nor land on the aux tank, on those aircraft equiped with an aux tank, I'd count on close to 20 for cruise, and 18 on the tank you'll be using for either taking-off or landing.
Cruisairs are decent gliders, as Larry notes, Cruisemasters....not so much, but this theoretical four gallon loss should be moot IMO, because I always land with more fuel than that. I may be a Massachusetts Liberal but, when it comes to fuel, I'm a Goldwater conservative :wink:
Jonathan
As Larry, I too have burned nearly 20 gallons from a wing tank. This was in straight and level flight. I watch the fuel pressure needle and when it starts getting twitchy I switch. I've yet to run a tank completely dry, as I do in my Luscombe, probably I believe in gravity more than I believe in fuel delivery systems that defy it
In short, what I believe they mean is that up to two gallons may be unavailable in a climb, descent, or in unusual attitudes. Many aircraft have such limitations. I'm sure you've all seen fuel gauges that have a mark for minimum fuel for take-off. This is based on the attitude for climb and the possibility of fuel sloshing to the rear, exposing the intake port. It's also a reminder, apart from technical reasons, to put some damned fuel in the airplane
As we should neither take-off nor land on the aux tank, on those aircraft equiped with an aux tank, I'd count on close to 20 for cruise, and 18 on the tank you'll be using for either taking-off or landing.
Cruisairs are decent gliders, as Larry notes, Cruisemasters....not so much, but this theoretical four gallon loss should be moot IMO, because I always land with more fuel than that. I may be a Massachusetts Liberal but, when it comes to fuel, I'm a Goldwater conservative :wink:
Jonathan
Alain1
New member
Hey! thanks guys for this. On top of having a decent information, it was very entertaining. The question was for Weight and balance matter. Not for taking risk of how much I can burn before planning a walk...Just did not felt like draining the tanks and since it's a pretty slow season for flying, would have taken a while before having the chance to run dry a tank. But wanted to get this weight and balance issue out of the way, and you guys came to the rescue. Thanks a bunch.
Alain.
Alain.
cruiseair74372
New member
I do run one tank dry almost all the time.I run one hour on left one hour on right back to left until engine gets quite back to right tank and now it is time to pee so I find an airport, pee and fuel in that order. when dry mine will hold 20.3 gals. each. I have done this over 600 hrs and it comes up the same almost every time.
alabamaflyboy
New member
I'm curious how the FAA defines "usable fuel in all attitudes." I wonder what attitudes they are considering.
It seems obvious that if you hold your plane in an extreme slip or skid, it is possible that the fuel in the tank may be pushed (skid) or pulled (by gravity - slip) away from the fuselage fuel port and may not reach the fuel ports at the fuselage, even if nearly half full.
I don't see planes with 50% unusable fuel listed, so the Feds must use a more reasonable definition such as "coordinated flight." Since the fuel thinks the wings are level in turns, it doesn't matter if you are actually level in roll attitude or not, as long as you are coordinated.
So I wonder how they define the limit for slip/skid conditions.
On climbs or descents, there must be a limit to the pitch up or down conditions. On my Cruisemaster and the Vikings that I have seen, there are two ports on the tank, one at the front and one at the back. The fuel lines come together midway between the two ports at a "T" connector and go to the fuel selector valve from there.
If the pitch attitude is such that the fuel doesn't rise to the "T" connector, then the engine will suck air even with fuel in the tanks.
So I wonder what the pitch conditions are for determining usable fuel, as well.
Also, while the ports are very close to the bottom of the tanks, they are not "exactly" at the bottom of the tank, so a little fuel will remain below the bottom of the port. It's about 1/2 to 3/4 of an inch on my tanks, if I remember correctly. The tanks do slope up slightly, due to the dihedral of the wing, so very little would be left.
On the subject of running a tank dry, one of my friends was flying an older plane and ran a tank dry. The fuel selector picked that time to jam - it had worked OK when he switched to that tank. He was fortunate enough to be "almost" close enough to an airport to make it. By putting the plane in a slip attitude with the selected tank high, he was able to get another 5 minutes of fuel out of that tank before it ran "absolutely" dry.
That was enough to make the airport. (These days, he never runs a tank down to less than about 30 minutes flying time before he switches to a fuller tank - just in case.)
Interesting discussion, folks. I'll check my Cruisemaster documentation and see what info I can find.
Dave
It seems obvious that if you hold your plane in an extreme slip or skid, it is possible that the fuel in the tank may be pushed (skid) or pulled (by gravity - slip) away from the fuselage fuel port and may not reach the fuel ports at the fuselage, even if nearly half full.
I don't see planes with 50% unusable fuel listed, so the Feds must use a more reasonable definition such as "coordinated flight." Since the fuel thinks the wings are level in turns, it doesn't matter if you are actually level in roll attitude or not, as long as you are coordinated.
So I wonder how they define the limit for slip/skid conditions.
On climbs or descents, there must be a limit to the pitch up or down conditions. On my Cruisemaster and the Vikings that I have seen, there are two ports on the tank, one at the front and one at the back. The fuel lines come together midway between the two ports at a "T" connector and go to the fuel selector valve from there.
If the pitch attitude is such that the fuel doesn't rise to the "T" connector, then the engine will suck air even with fuel in the tanks.
So I wonder what the pitch conditions are for determining usable fuel, as well.
Also, while the ports are very close to the bottom of the tanks, they are not "exactly" at the bottom of the tank, so a little fuel will remain below the bottom of the port. It's about 1/2 to 3/4 of an inch on my tanks, if I remember correctly. The tanks do slope up slightly, due to the dihedral of the wing, so very little would be left.
On the subject of running a tank dry, one of my friends was flying an older plane and ran a tank dry. The fuel selector picked that time to jam - it had worked OK when he switched to that tank. He was fortunate enough to be "almost" close enough to an airport to make it. By putting the plane in a slip attitude with the selected tank high, he was able to get another 5 minutes of fuel out of that tank before it ran "absolutely" dry.
That was enough to make the airport. (These days, he never runs a tank down to less than about 30 minutes flying time before he switches to a fuller tank - just in case.)
Interesting discussion, folks. I'll check my Cruisemaster documentation and see what info I can find.
Dave
Jonathan Baron
New member
I doubt your P.O.H. will give you info beyond a lube chart, what switch does what on the panel, and how to clean your upholstery, Dave. I have the original manual and the CAA manual for my 14-19 and the only truly useful information in it involves rigging.
Besides, I got the terminology all wrong. It's "under all flight conditions." This is also the wording for the Viking....not that this helps in any way whatsoever
It comes down to this: in cruise in smooth air you probably can count on 20 if you don't mind running a tank dry. Keep in mind that, at the normal burn rate of 12-14 gallons an hour for an O-435, that's four to five minutes per gallon. Thus, IMHO, it's not worth it to go after those two "lost" gallons. You might say that it's really four gallons (both wing tanks) but the aircraft is placarded against using the aux for take offs and landings. Why, exactly, I don't know but I'm not inclined to test the veracity of the rule.
These are the sorts of issues that seem to be more important during the winter months when we're not flying as much :wink:
Jonathan
Besides, I got the terminology all wrong. It's "under all flight conditions." This is also the wording for the Viking....not that this helps in any way whatsoever
It comes down to this: in cruise in smooth air you probably can count on 20 if you don't mind running a tank dry. Keep in mind that, at the normal burn rate of 12-14 gallons an hour for an O-435, that's four to five minutes per gallon. Thus, IMHO, it's not worth it to go after those two "lost" gallons. You might say that it's really four gallons (both wing tanks) but the aircraft is placarded against using the aux for take offs and landings. Why, exactly, I don't know but I'm not inclined to test the veracity of the rule.
These are the sorts of issues that seem to be more important during the winter months when we're not flying as much :wink:
Jonathan
Thanks for the information! My Cruisemaster is labeled 18 gallons usable for the wing tanks and 14 gallons for the aux. And for some of the trips that I have planned I am going to need to burn 18 out of one main and 14 from the aux in order to have a prudent reserve when I get to my destination. Reciently I put in one of the JP Instruments fuel totalizers so that I could have a better idea of what I am using, to this point it is checking within 2 tenths of a gallon (to the plus side). After reading this, my plan is to burn the 18 and 14 while watching the fuel pressure gauge closely. Comments and suggestions are welcome.
Monroe
7676B
Monroe
7676B