Why no reserve tanks?

jasc15

jasc15

Pre-takeoff checklist
Joined
Apr 21, 2009
Messages
443
Location
New Jersey
Display Name
Display name:
Joe
Maybe a dumb question, but I know boats and motorcycles use them, for example, and a no-fuel situation in these are less critical than on airplanes. So why not on airplanes? Is the performance hit too much? I think not since you are required to carry a reserve amount anyway, the extra weight carried makes no difference. Wouldn't it be a good idea to have reserve tanks that hold 1 hour of fuel?
 
jasc15 said:
Wouldn't it be a good idea to have reserve tanks that hold 1 hour of fuel?
Click to expand...

To what end? Pilots are supposed to be smart enough to not run out of gas.

Would you include that in ADDITION to the reserves we are supposed to carry? It all detracts from useful load.
 
And what happens when you forget to switch to the reserve tank before the main tanks run dry?

What GA aircraft need is accurate fuel gauges and low fuel annunciators.
-harry
 
Greg Bockelman said:
It all detracts from useful load.
Click to expand...
Carrying the required 1 hour of fuel detracts from useful load, which is why i said the extra weight carried makes no difference. So it wouldn't be in addition to the reserves we are supposed to carry.
 
It's probably a good idea and would have saved lives but we are too stubborn. And maybe too macho.

Just like the TFR issue, we continue to pretend human have no foibles.
 
Last edited:
Reserve tanks for a motorcycle? I have not heard of a specific tank for them. Possibly, but it has been my experience that for motorcycle the most common arrangement was a reserve position on the fuel selector. This really was not a reserve tank but just a valve that would allow one to take fuel from the lowest part of the tank. The idea was that if you were running in the main position and the engine stopped due to fuel starvation then selecting reserve would let you use that last few ounces to pints or gallon to get to the next fuel stop. But the tank itself had no partitions in it.

Of course if you forget to put the selector back to main after refilling and ran out again. You were would have to push your bike to the next stop.

As for airplanes it is an interesting idea. But like the motorcycle idea if one were to become dependent upon it, what would happen when they forgot to set it right at take off? If the pilot is already so lazy as to not be calculating their fuel consumption I cannot help but wonder how well they would be following their check lists.

If there was such a fuel system how much needs to be in reserve? On my Piper Warrior 8 gals would easily give me an hour an a 100NM range, but what if the nearest airport was 150 NM because I was flying in the wilderness? That reserve bought me nothing but the ability to plan my crash. The point is that the reserve amount varies for each flight. Because of that fact having a dedicated tank is not very useful. Instead when planning the flight part of the total fuel load becomes the designated reserve and the pilot monitors fuel consumptions such that if they touch their reserve they take the appropriate and preplanned actions.
 
Last edited:
Because when you are grappling for the little standpipe switch (AKA 1954 VW beetle) you will lose control of the aircraft. Loss of power is a pretty complex moment!
 
bbchien said:
Because when you are grappling for the little standpipe switch (AKA 1954 VW beetle) you will lose control of the aircraft. Loss of power is a pretty complex moment!
Click to expand...
The John Denver effect.

But in a loss of power situation one of the typical checklist items is to switch tanks.
 
ScottM said:
The John Denver effect.

But in a loss of power situation one of the typical checklist items is to switch tanks.
Click to expand...

On my private pilot checkride, I got "yelled" at for not immediately switching tanks AS I was going to best glide airspeed. The reason being, the fuel is a most common reason for engine failures and you might not need to go any further than just switching tanks.
 
ajstoner21 said:
On my private pilot checkride, I got "yelled" at for not immediately switching tanks AS I was going to best glide airspeed. The reason being, the fuel is a most common reason for engine failures and you might not need to go any further than just switching tanks.
Click to expand...

By many estimates, carb ice is a more common cause, by a significant margin, of reciprocating engine failure than is fuel starvation. Carb heat should be the first thing, before the source of heat (exhaust system) cools off. Of course, if the ice is bad enough to stop the engine, the pilot was unaware of either decreasing RPM (fixed pitch) or decreasing MP and cruise speed (constant speed). Gotta be asleep or something.

Dan
 
Last edited:
It would have negligible effect on fuel starvation or fuel exhaustion statistics because:
If we plan to get down to the reserve (Which most of us do), the same pilots would still fall into the trap of going into the reserve and not stopping for fuel immediately. As in; I've made this trip many times without refueling, I can make it this time.

It would add to the weight because:
There would now be an unuseable amount in the reserve tank as well as the unuseable amounts in the mains.
 
ScottM said:
The John Denver effect.

But in a loss of power situation one of the typical checklist items is to switch tanks.
Click to expand...

Well, taking the John Denver case as example, and all the other tank mismanagement and valve failure accidents of which there have been a few, wouldn't safety predicate the minimum number of tanks? Why do you think Cessna went to the wet wing in the 421C/414A and such? Enough people had screwed up and pumped fuel overboard that they finally changed it to one integral tank per wing.

There is no way of adding "extra reserve" fuel without it eating into your payload. Many times the airliner you are on has left with considerably less than a full load of fuel. You take what you need, and we already have a working system of figuring reserve fuel that we don't need "extra reserve". In all of aviation, gravity is your chief opponent. You want the minimum amount of mass up there as you can get away with to reduce gravities grip every little bit you can.
 
Crikey, Henning. Your mention of mass and gravitational force...:rolleyes:

The simplest reason is lack of complexity. Ain't no way to design a system better than the human brain. As pilots we are taught to use what we have, yes?
 
Richard said:
Crikey, Henning. Your mention of mass and gravitational force...:rolleyes:

The simplest reason is lack of complexity. Ain't no way to design a system better than the human brain. As pilots we are taught to use what we have, yes?
Click to expand...


You have far more faith in the human brain than I do. I had already addressed the complexity issue, with that I was addressing quantity.
 
ScottM said:
The point is that the reserve amount varies for each flight. Because of that fact having a dedicated tank is not very useful. Instead when planning the flight part of the total fuel load becomes the designated reserve and the pilot monitors fuel consumptions such that if they touch their reserve they take the appropriate and preplanned actions.
Click to expand...
Of course, there is that percentage of flights where actual fuel consumed varies from estimated fuel consumed due to improper leaning and leaks/mechanical factors that may not be obvious to the pilot.

But that is splitting hairs, as I believe that is a minority of fuel exhaustion/starvation incidents.
 
Ken Ibold said:
Of course, there is that percentage of flights where actual fuel consumed varies from estimated fuel consumed due to improper leaning and leaks/mechanical factors that may not be obvious to the pilot.

But that is splitting hairs, as I believe that is a minority of fuel exhaustion/starvation incidents.
Click to expand...

Here's a relatively unknown way to lose a bunch of fuel: Leave the primer unlocked. There's a spring-loaded needle on the end of the primer plunger that shuts off the outlet so that manifold vacuum can't suck fuel through the primer. At lower power settings the MP is low (high vacuum) and lots of fuel could either run the tanks dry before calculated estimates, or it could flood the engine on approach so it doesn't respond when you want it.

May fuel injection take over GA.

Dan
 
ScottM said:
Reserve tanks for a motorcycle? I have not heard of a specific tank for them....
Click to expand...
Right, there's no "reserve tank", just two lines into the fuel tank, one which can tap the entire fuel capacity, one which "runs dry" when fuel drops below some level. The purpose is to give you a "reminder" that you're about to run out of fuel. How does it deliver this reminder? By you running out of fuel.

On a motorcycle, you notice the engine start to sputter, and you think "henh? oh ... okay" and you reach down and fiddle around until you find the fuel switch. If you're good, you get it going again before the engine dies completely. If you're not good, you end up on the side of the road, looking down into the fuel tank, seeing fuel sloshing around in there, wondering why the damn thing quit on you.

And thus the problem with using such a mechanism on a plane...

Ultimately, it's just a really inexpensive but dubious "low fuel annunciator". If you want to achieve the same effect without the plane threatening to quit at an inopportune moment, you use an annunciator that lights a little light bulb instead of starving the engine of fuel. Probably a better way to deliver that message.
-harry
 
mantakos said:
Right, there's no "reserve tank", just two lines into the fuel tank, one which can tap the entire fuel capacity, one which "runs dry" when fuel drops below some level. The purpose is to give you a "reminder" that you're about to run out of fuel. How does it deliver this reminder? By you running out of fuel.

On a motorcycle, you notice the engine start to sputter, and you think "henh? oh ... okay" and you reach down and fiddle around until you find the fuel switch. If you're good, you get it going again before the engine dies completely. If you're not good, you end up on the side of the road, looking down into the fuel tank, seeing fuel sloshing around in there, wondering why the damn thing quit on you.

And thus the problem with using such a mechanism on a plane...

Ultimately, it's just a really inexpensive but dubious "low fuel annunciator". If you want to achieve the same effect without the plane threatening to quit at an inopportune moment, you use an annunciator that lights a little light bulb instead of starving the engine of fuel. Probably a better way to deliver that message.
-harry
Click to expand...
BTW on newer FI bikes you really do not see that fuel selector anymore and instead get an annunciator on your instrument cluster telling you that the fuel level is low.
 
/7500

Funny story....

On my first familiarization flight for flying pax over Lake Powell, the pilot left the the GPS (sans current data card) on. It was flashing in big red letters, LOW FUEL for all the pax to see. I thought is weird that not one of them asked about it.

END/
 
1947 V-tail had an auxiliary tank behind the baggage compartment.

Some Chiefs and Champs have a 6 or 12 gal aux tank in the wing root (main tank was in front of the firewall).

These tanks are Aux since you have to refill the main from the aux -- no direct connection between the aux and the engine.
 
Good thing aviation fuel is stable over time. Imagine switching to reserve fuel six years after it was put there, because nobody else put themselves in a situation where they needed to use it.
 
ScottM said:
Reserve tanks for a motorcycle? I have not heard of a specific tank for them.
Click to expand...

BSA Gold Star had a physically separate volume in the single gas tank. The tank wrapped over the top bar. Suction was on the low point on one side. When you ran out of gas, you laid the bike down on its side to pour the segregated fuel over the bar into the side with the suction and then headed for the gas station. Not that it would work on an airplane.
 
TangoWhiskey said:
Good thing aviation fuel is stable over time. Imagine switching to reserve fuel six years after it was put there, because nobody else put themselves in a situation where they needed to use it.
Click to expand...

One day I had the temerity to sump the aux tank in the '47 V...

:yikes:

Yeah ... no need for whatever brown stuff was in that tank....
 
My plane has 3.5 hour endurance on the mains and 2.5 in the "reserve" tanks, and it sucks!!!! I hate having 4 tanks, I'd rather have 2 with the same total capacity. I can end up with 1 hour of fuel spread across 4 tanks. That does not make for a comfortable final approach.

As long as the plane can fly longer than my bladder, then I don't have an issue. Actually, my bird holds enough fuel that I can fill a gatorade bottle, and still land with reserve fuel.
 
COFlyBoy said:
My plane has 3.5 hour endurance on the mains and 2.5 in the "reserve" tanks, and it sucks!!!! I hate having 4 tanks, I'd rather have 2 with the same total capacity. I can end up with 1 hour of fuel spread across 4 tanks. That does not make for a comfortable final approach.

As long as the plane can fly longer than my bladder, then I don't have an issue. Actually, my bird holds enough fuel that I can fill a gatorade bottle, and still land with reserve fuel.
Click to expand...


Why not run the auxes dry?
 
Graueradler said:
BSA Gold Star had a physically separate volume in the single gas tank. The tank wrapped over the top bar. Suction was on the low point on one side. When you ran out of gas, you laid the bike down on its side to pour the segregated fuel over the bar into the side with the suction and then headed for the gas station. Not that it would work on an airplane.
Click to expand...

Heh. Fuel exhaustion procedure checklist: Initiate steep turn to the left. ;)
 
The Pitts I fly has a 5 gallon aux tank in the top wing that I only fill when traveling (can't acro with fuel in it). It's a separate tank that has a feed line into the main tank. But here's the rub, the fuel drains down slower than the airplane burns it. So, when I get down to about 10 gal. or so in the main, I rotate a switch to start feeding the 4 to 4.5 gallons of gas that didn't vent out in flight down into the main. If I were to forget to switch it on early and run the main out then I'm just carrying that extra gas to the crash site.

I agree with Harry, we need accurate gauges with low fuel indications when there's still an hour or more of gas in there. Come to think of it, I have that already with the fuel totalizer computer in my Pitts. Now if I could just remember to accurately set the amount of fuel I take off with...
 
That's really interesting about the Pitts. I had no idea.

It floors me that the most brilliant minds on the planet still can't build an affordable, accurate, fuel gauge for light aircraft that can also make it's way through the Certification process.

The best we've come up with (and mind you, it's good and cheap) is an impeller in the fuel flow and a human to push the fill-up button on the totalizer?

What would you pay for an accurate fuel gauge in your aircraft? Is it an economic problem? Are we all too cheap?
 
denverpilot said:
That's really interesting about the Pitts. I had no idea.

It floors me that the most brilliant minds on the planet still can't build an affordable, accurate, fuel gauge for light aircraft that can also make it's way through the Certification process.

The best we've come up with (and mind you, it's good and cheap) is an impeller in the fuel flow and a human to push the fill-up button on the totalizer?

What would you pay for an accurate fuel gauge in your aircraft? Is it an economic problem? Are we all too cheap?
Click to expand...

My experience is that fuel gauges are accurate. But I don't rely on them exclusively. I cross reference against elapsed time, known fuel burn rate, and the starting fuel level, which I verify during pre-flight.

I don't think gauge problems are the root cause for most fuel starvation incidents. I think it is get-there-itis: "I've flown it with this low a fuel reading before. I'll just run it a little lower. I'm sure I'll make the intended destination without wasting 30 minutes on a fuel stop."

Sputter.
 
Interestingly, the only time I evey ran out of gas, in probably about a million miles of driving, was on a motorcycle. A BMW 1200RT to be exact.

I am anal about going off my trip odometer when I ride a bike, as most bikes don't have a gauge. The Beemer did. The one time when the gauge decided to fail was the one time when I failed to display the trip odometer (Beemers have a bad habit of not displaying the last set display on the console.)

So I ran out of gas on the highway, with the gauge showing a quarter tank left. I pulled off to the side of the freeway. Sure enough, I travelled 318 miles, out of range of the tank, after I punched up the trip odo.

I don't trust reserves, gauges, or any of that crap. Elapsed miles or time. Or a totalizer if I so have one.
 
The four fuel gauges in our Pathfinder are quite accurate. Between that, and the fuel flow gauge, and the clock, it's pretty hard to imagine running out of fuel.

And yet, I personally know two pilots -- GOOD pilots -- who have crashed because of insufficient fuel to make the flight. I knew a third who died because of it.

This, to me, is the ultimate mystery of aviation and aviators.
 
There are plenty of safety features already designed into aircraft that don't relieve the pilot of the responsibility of good planning, so it seems to me that there is really no negative impact of having some reserve system designed into the aircraft in addition to the planning of the pilot. A simple one would be the standpipe feature mentioned above used in some motorcycles (I originally thought it was a separate tank for reserve fuel, but the different pipe lengths is a more elegant solution). At least if you've neglected to plan sufficiently for the flight and run out of fuel, the engine sputtering and stopping can allow you to restart and focus on getting safely to an airport rather than panicking and causing unnecessary harm.
 
On my plane I have a clear plastic sight tube that indicates the level. My sons plane has a translucent window in each wing root and you can visualy see the fuel level while flying. The old floating cork on a wire that protrudes through the gas cap is just about fool proof as well.
 
Ah, the old dual feed points from the tank trick. My old Honda 90 had 1 gallon on the main setting and another 0.45 gallons on reserve. 100 miles on main and 45 miles to find a gas station. Never had a problem. Then I got a 1969 Honda CL-175 and found out that when you hit reserve you had about 8 miles worth of gas, about 100 yards less than I needed. :rolleyes2: Oh well, it was an easy bike to push.

I'll stick with the "BOTH" position on the C-172 and C-182. So simple even a caveman can do it.
 
I agree with those who've said that good gauges are important. What I've found is that most aircraft actually have pretty good gauges in them if they're working properly, the problem is that they rarely work properly after however many years in service, and people don't bother fixing them.

Also, since most aircraft have multiple tanks, you don't necessarily need to have a special "reserve" tank, you can time your tanks such that you have reserve fuel. That's what I do typically to give myself a little backup, the sort of "I screwed up, time to find an airport." Never had to use it and never intend to. Most motorcycles these days don't have the "reserve" anymore, they just have a fuel light. The reserve was a function of no fuel gauge or other low fuel indicator. You'd hit the reserve, and that would tell you that you needed to find a gas station soon. In a plane, I'd hope that one plans better.
 
Last edited:
Henning said:
Why not run the auxes dry?
Click to expand...

Per the POH, I'd have to tun the mains dry first.

I just can't bring myself to make that standard operating procedure. The POH even warns that if you run the line between the fuel selector and the engine dry it can take up to 10 seconds to fill it back up. Seems like a bad plan.

Really, I have an airplane with 6 hour tanks and I can only stand to be in it for about 3 hours at a go anyway. So its kinda moot.

My point was that a "reserve" tank doesn't make things better. I think it makes it worse, by dividing your fuel up. And then to know exactly how much fuel you have, you have to resort to running tanks dry. I've done it before, I'm not doing it again.
 
COFlyBoy said:
Per the POH, I'd have to tun the mains dry first.
I just can't bring myself to make that standard operating procedure. The POH even warns that if you run the line between the fuel selector and the engine dry it can take up to 10 seconds to fill it back up. Seems like a bad plan.

Really, I have an airplane with 6 hour tanks and I can only stand to be in it for about 3 hours at a go anyway. So its kinda moot.

My point was that a "reserve" tank doesn't make things better. I think it makes it worse, by dividing your fuel up. And then to know exactly how much fuel you have, you have to resort to running tanks dry. I've done it before, I'm not doing it again.
Click to expand...


What are you flying?
 
denverpilot said:
It floors me that the most brilliant minds on the planet still can't build an affordable, accurate, fuel gauge for light aircraft that can also make it's way through the Certification process.

The best we've come up with (and mind you, it's good and cheap) is an impeller in the fuel flow and a human to push the fill-up button on the totalizer?

What would you pay for an accurate fuel gauge in your aircraft? Is it an economic problem? Are we all too cheap?
Click to expand...

How would you measure the fuel in a tank that is sloshing around? What about in a nose high attitude or nose low attitude?

For a simple aircraft like the cherokee 140, visually confirming the fuel in the tank and watching the clock is almost fool-proof. In other words, more technology isn't needed to reduce the risk of running out of fuel to an acceptable level. Adding some magic fuel gauge would just mean more dollars not spent on fuel to, ya know, fly the airplane.
 
AEROBAT said:
The old floating cork on a wire that protrudes through the gas cap is just about fool proof as well.
Click to expand...

No, it's not foolproof. Had one of those. The wire sticks up in the slipstream when the tank is full, and the drag on it can make it stick in its guide. Everything looks good until you get a bit of turbulence and the float drops down to the surface of the fuel. Startling.

One must be aware of fuel burn rate and time; there are few trustworthy gauges out there. Even the best float-type gauges fail when the floats break off or fill with fuel and sink; that will indicate zero fuel and maybe precipitate a precautionary landing in an unfavorable and risky spot when there was no need to do so.

Dan
 
You must log in or register to reply here.
Back
Top