Absolutely crazy Bo fuel tanks

M

MountainDude

Cleared for Takeoff
PoA Supporter
Joined
Jul 29, 2011
Messages
1,018
Display Name
Display name:
MountainDude
It's very frustrating that engineers built such a complicated fuel system that can kill a very experienced pilot. Why not have a "both" setting?
www.flyingmag.com

It’s Up to Pilot to Ensure Quirk Doesn’t Turn Into Pitfall

On the return flight, the pilot burned fuel from the right tank for the first 49 minutes. He then made a fateful decision: He selected the aux tanks.
www.flyingmag.com www.flyingmag.com

"In order to understand how a man described by his old friend as a “really good” pilot who was “knowledgeable” and “particular” about how he operated an airplane, one must first understand the fuel system of the M35.

The airplane had two main fuel tanks of 25 gallons each and two optional auxiliary tanks of 10 gallons each for a total capacity of 70 gallons. Its 260 hp engine burned around 14 gph in cruise. The fuel injection system of the IO-470, like all Continental fuel injection systems, pumped more fuel than the engine needed and sent the unused portion back to a tank. According to the airplane handbook, the vapor return amounted to 10 gph. If a main tank was selected, the vapor return went to it. If the aux tanks were selected, which fed simultaneously, the vapor fuel went to the left main.

This arrangement had several implications. One was that even though the engine was burning only 13 or 14 gph, the 20 gallons of auxiliary fuel would be gone in less than 50 minutes. Another was that if the aux tanks were selected before there was space for the return fuel in the left main, the return fuel would be vented overboard. The POH discouraged switching to the auxiliary tanks before the left main was half empty."
 
That seems ridiculous today, but was there a sane reason why it was designed that way and also why FAA approved it back in the day? One would think, but then again…
 
MountainDude said:
It's very frustrating that engineers built such a complicated fuel system that can kill a very experienced pilot. Why not have a "both" setting?
Click to expand...
That’s not an exceptionally complicated fuel system, you just have to understand it.

While the pilot may be “very experienced,” it sounds like he had limited experience with this airplane and its fuel modifications. Low time in type shows up pretty heavily in accident reports.
 
Last edited:
Beech made it easier by the time the M35 came out. I wouldn't consider that fuel system complicated at all.

I ran tanks dry on my F35 on occasion. Engine power was always restored almost right away after the fuel selector was moved to a tank with fuel in it. I'm guessing that this guy wasn't paying any attention until it was way too late to do something about it. That's hardly a fuel system shortcoming in my book.
 
MountainDude said:
It's very frustrating that engineers built such a complicated fuel system that can kill a very experienced pilot. Why not have a "both" setting?
www.flyingmag.com

It’s Up to Pilot to Ensure Quirk Doesn’t Turn Into Pitfall

On the return flight, the pilot burned fuel from the right tank for the first 49 minutes. He then made a fateful decision: He selected the aux tanks.
www.flyingmag.com www.flyingmag.com

"In order to understand how a man described by his old friend as a “really good” pilot who was “knowledgeable” and “particular” about how he operated an airplane, one must first understand the fuel system of the M35.

The airplane had two main fuel tanks of 25 gallons each and two optional auxiliary tanks of 10 gallons each for a total capacity of 70 gallons. Its 260 hp engine burned around 14 gph in cruise. The fuel injection system of the IO-470, like all Continental fuel injection systems, pumped more fuel than the engine needed and sent the unused portion back to a tank. According to the airplane handbook, the vapor return amounted to 10 gph. If a main tank was selected, the vapor return went to it. If the aux tanks were selected, which fed simultaneously, the vapor fuel went to the left main.

This arrangement had several implications. One was that even though the engine was burning only 13 or 14 gph, the 20 gallons of auxiliary fuel would be gone in less than 50 minutes. Another was that if the aux tanks were selected before there was space for the return fuel in the left main, the return fuel would be vented overboard. The POH discouraged switching to the auxiliary tanks before the left main was half empty."
Click to expand...
Call me old fashioned but on the glorious O-470 my preference is for a carburator. The Bendix fuel injection is simpler. That might not have changed the outcome of this incident though
 
I've owned and flown Bo's for many years. I have a lot to add to this position but the article is baselessly incorrect. EVERY Bonanza pilot is drilled into his/her skull that one always, always, always takes off on the left tank(unless it is empty for some reason). And - concomitantly should in almost all cases LAND on the left tank. There are very few, and very rare exceptions to these rules.

I teach new Bo owners that the plane has ONE and only one main tank and that is the left. All other fuel supplies are aux tanks. I don't care where it is on the plane, the only main tank is the left. This works from the first 35 in 1947 right up to the last one off the line as a V35B/TC. Although the later models have a revised return system, it's still safe to use the the left tank for take off and landing(unless for some reason it's empty).

Sadly, a few years ago I had to go recover a 1959 J35 that had a forced landing in a field with a collapsed nose gear. The engine suffered a stoppage in flight, when being flown by the A&P who worked on the plane, and was ferrying it at night to its home base. The left tank was empty, the two aux tanks, and the right tank were nearly full of fuel. He came down with almost 50 gal of gas! I repaired the nose gear, removed the gear doors and flew it out of the field to the home base where the damage was repaired.

The Bo tank system is not the most complex, and it's not the least complex, but the one rule is left tank on takeoff and left tank on landing unless the tank is empty(it should almost never be empty).
 
I flew a bonanza with that fuel return system for many years. It’s really not that hard. And you get used to running the tank empty. Granted, that first time in the soup when the motor surges and the tank went empty was not a comfortable feeling
 
The Bonanza(and I think all low wing?) are required to restart the engine in flight with a tank run dry to pass type certification. The immediate thing to do as a memory item if the engine dies is switch to the left tank. If the left tank is in use, switch to the right tank.

My process which will work with any Bo: Start engine and take off on the left tank, unless it is dry(it should never be dry). Burn until it is 1/2 tank. Switch to right tank, burn until it is 1/2. Switch to left, burn back down to 1/2 indicated. Switch to aux and repeat for all aux tanks, switching back to left after each tank runs dry. Run the aux's completely dry, pilot is never going back to the aux tanks, they should be run completely dry. Some tip tanks transfer to the main, and they will need to transfer to the main until the tips are completely empty. Now run right main empty, but do not overfill left tank. Monitor left tank periodically and don't allow it to go over 3/4. Aux tanks empty, right main low or empty, remaining flight is on the left tank to landing.
 
I hope the OP never sees a truly complex fuel system! The BO is a simple system. It would be much more complex if plumbed to return fuel to the tank in use requiring additional lines and a selector.
 
Add in the tip tanks and it becomes something you have to think about and plan prior to flight. It should not be a big deal, but the results show it to be a hazard for some reason.
 
I won't go as far as saying it is unmanageable, but it does seem unnecessarily complicated. As we often do, compare to cars. The last vehicle I ever drove with multiple tanks and selectors was a 90s Ford pickup with front and rear tanks.
 
Know your airplane. Study the manual. Chair fly. It’s not a car and its systems are more complicated. Many airplanes with both standard and aux fuel (factory or added later) have rules about which tank to use when, how much head space needs to be present before changing to a different tank, etc.

For example, on Cessna twins the tips are the mains. And the aux can’t be used until sufficient headroom is provided in the mains. And if you move the cross feed selectors so both point to one another both engines will stop!

Pilots should read the POH cover to cover several times. Yes RTFM.
 
The Bonanza was a revolutionary 1940's design and it evolved over the years. With a low wing aircraft, fuel needs to be pumped to the engine as gravity feed doesn't work. The original design was simple, with two 20 gallon main tanks (left or right) and an optional aux tank of 10 or 20 gallons in the baggage compartment. With a low wing aircraft, since gravity feed does not work, a both position will cause a fuel interruption if one of the tanks either has air in the line or the tank is dry. The fuel selector was simple as well as it only had an off/left/right tank selector. The carburetor returned excess fuel to the left tank via a single vapor return line at about 3 GPH. There was originally a hand pump called the wobble pump, that could be used for starting the engine, in an emergency and to pump fuel from a tank if there was air in the fuel line the engine driven pump was able to sustain the fuel pressure. Over time, the main tanks were increased in size and aux tanks were added in the wings and the wobble pump was replaced by an electric pump. A more sophisticated return system was added by routing excess vapor/return fuel through the fuel selector, so the main tank that was selected also received the return fuel. Even then, the Aux tank fuel returned to the left main tank. So takeoffs required using the left main tank and burning off sufficient fuel to allow for aux tank usage. With the J35, the engine used fuel injection and returned more excess fuel back to the main tanks. With the N model, the main fuel tanks were increased to 40 gallons each, and the system was simplified, that is all the excess return fuel went back to the selected main tank, so takeoff on the fullest tank is now the norm. Tip tanks became a popular STC to add another 30 to 40 gallons, increasing the 5-6 hour endurance to pushing 8 hours. Before anyone pilot's a Bonanza, it is imperative to understand the fuel system and its limitations specific to that aircraft model and to not make assumptions.
 
midwestpa24 said:
I won't go as far as saying it is unmanageable, but it does seem unnecessarily complicated. As we often do, compare to cars. The last vehicle I ever drove with multiple tanks and selectors was a 90s Ford pickup with front and rear tanks.
Click to expand...
Why “unnecessarily”? Many x35 Bonanzas have 6 tanks and one engine. How would you make it less complicated?
 
My IO-550 which is a bear to start when heat soaked on the ground, will retire just fine after you run a tank is run dry.

The problem with the design when you put in these aftermarket tanks is how involved the fuel selector ends up being. Even the Navion which only has a "BOTH" position for the mains has the tips returning fuel to the main. Oddly, and nobody has been able to explain this to me, the return isn't constant. At very low power settings (like close to idle), you can suck a 20 gallon tank dry in 20 minutes (it goes back to the main). I managed to suck the tank dry in the middle of a procedure turn in my IFR training much to the consernation of the instructor.

So you either just return the fuel to one tank and warn the pilot you're doing that or you make a more complex fuel selector that puts things back in the tanks it came out of. Or you just suck out of one tank and xfeed into it. There's upsides and downsides to all of these.
 
Like any complex, high performance plane, good type specific training is a great idea. The bonanzas have some other nuances beyond the fuel system that might not be obvious from just reading the POH.

Link to the ABS training site. The online course is really good. There are many qualified instructors out there to add flying to the mix too. A few are on this site.

Training

TRAINING PROGRAMS AND INFORMATION.
www.bonanza.org www.bonanza.org
 
I have a 6 tank bonanza (1955 F35) with 2 mains, 2 wing auxes, and 2 tip tanks. Fuel management is certainly more involved than a 172, but it’s not terrible. I spent some time on the ground planning my fuel management for my first long cross country. What makes it more difficult is that for the 4 wing tanks, I only have 1 fuel gauge. I can toggle between left and right with a switch, and there is another switch to toggle between mains and Auxes. I have to be extra careful to make sure I am monitoring the correct tank
 
"It hasn't killed me yet, so it can't be that bad."
Its a complicated system. Simplicity reduces workload, increases safety. Looking at the interior pictures of a lot of 35s, many that have their panels redone have also removed the piano keys. Sure, the piano keys work, but they aren't safe. Finding the right one quickly in the dark or during an emergency must be interesting.
 
Wrench978 said:
I have a 6 tank bonanza (1955 F35) with 2 mains, 2 wing auxes, and 2 tip tanks. Fuel management is certainly more involved than a 172, but it’s not terrible. I spent some time on the ground planning my fuel management for my first long cross country. What makes it more difficult is that for the 4 wing tanks, I only have 1 fuel gauge. I can toggle between left and right with a switch, and there is another switch to toggle between mains and Auxes. I have to be extra careful to make sure I am monitoring the correct tank
Click to expand...
Making it even more funner, all the switches are polished alum, and they run in sequence right across the lower panel. Plus, the gear and flap switches look - identical! :biggrin:

I was feeding from aux, and monitoring right one time, and man I thought I was getting great fuel econ! The gauge wasn't moving fast at all. Zoiks.
 
This would probably be why the FAA has fuel systems and fuel management in every ACS.
 
Making it simpler for the pilot usually means complicating the plumbing. The Bellanca Viking's system looks like this:

1730070059222.png

The selector valve returns fuel to the tank it came from. Note that there is only one return from the engine; in the diagram above we see return lines from either Lycoming or Continental engines, from the Lyc's injector servo or the Continental's fuel pump.

So that diagram looks simple. But get into a Viking and pull the floor out to get a look at the plumbing, and it's a serious snarl of aluminum tubing around the selector valve. I can't find an online service manual to show it, but it would be no fun to take that selector out for rebuilding.
 
Last edited:
Barrett50 said:
Making it even more funner, all the switches are polished alum, and they run in sequence right across the lower panel. Plus, the gear and flap switches look - identical! :biggrin:

I was feeding from aux, and monitoring right one time, and man I thought I was getting great fuel econ! The gauge wasn't moving fast at all. Zoiks.
Click to expand...
Maybe in the earlier models. My flap switch has a shape of a flap on it and my gear switch has a wheel. You can see the 2 part fuel gauge switches on the left, but everything else is lights.
 

Attachments

  • IMG_2247.jpeg
    IMG_2247.jpeg
    1.6 MB · Views: 20
I bet there isn't a correlation between fuel system complexity and instances of running out of fuel. Just a guess. But working on the theory that you either know how it works, or you don't, and either develop good procedures, or don't...and somewhat biased because I read a lot of PA-28 crash reports years ago, and even with a perfectly functional selector it's apparently easy to screw up the options of "left/right/off".
 
Even with a simple system, pilots will run out of fuel to the engine with fuel in the tanks.

Aerostars had a simple fuel system. One tank in each wing (wet wing) one fuselage tank. Fuel selectors to ON. Fly.

With full fuel in all tanks, engine draw from fuselage tank for part of it, then draw from the wings until they are empty, then the remainder of the fuselage tank. All via gravity. One fuel gauge showing total fuel on board. EASY.

So pilots decided to fly around with both engines in Cross Feed, feeding from the wing tanks only and ran out of gas with a fuel fuselage tank.

So they had to change to 3 gauges, one for each tank. Of course, now you have add them up in your head to determine total fuel.
 
Pinecone said:
Even with a simple system, pilots will run out of fuel to the engine with fuel in the tanks.
Click to expand...
Navions by default have an ON-OFF fuel selector. Pretty uncommon for low-wing singles. This is because the wing tanks drain into a small header tank in the fuselage and then to the engine. The sump drain is sticking out of that tank (along with a safety wired plug that I guess you can use to drain the tanks quickly, but I just unscrew the quick drain).

Then there are a gazillion factory and STC aux schemes. Originally, they put a tank under the rear seat (just inaccessible space in a stock Navion). The fuel valve then got a OFF-MAIN-AUX setup. The engines were still carbed back then. If you upgraded to an injected engine, your return most likely always went to main. The second factory aux (which I have) is a tank that stands upright on the right side of the baggage compartment. This just has a manual valve which drains it into the right main tank (via a hole that on the left side has the fuel quantity sender).

Then they started putting tip tanks on them. There's probably six or more ways to hook those up. One design, from the so-called "factory" (the type certificate was bought by an established Navion mod shop) is just outright loopy and dangerous. Of course, the factory thought they could make money by cramming through an AD that declared all fuel valves suspect. They're solution was an ill-fitting ANDAIR valve with banjo fittings that dangerously sat above the recess in the floor the original valves did. The FAA really can't say know when a manufacturer comes around saying they need an AD (an idea which was unheard of until people like Hartzell decided either they couldn't deal with the liability or they needed additional profit). At least the Chicago ADO responsible for this decided to approve just about any AMOC someone wanted to submit. The Type Society PMAd a better designed Andair installation with A/N fittings and it sat fully in the recess. It also added the button that you have to press before you can turn the fuel off (my wife has turned the fuel off on downwind trying to go from TIP to MAIN).

My plane had tip tanks from Brittain (now Osborne). The fuel valve was just a four position one similar to the tractor valve that originally came with the plane. When I ordered the AD-compliant one from JLO, the new one looks identical to the old one other than it has a part number stamped on it and comes with an ICA sheet.
 
The 'one tank' solution in the older Bo would be fuel critical after an hour in the air. It was only 20gal, with 17.6 useable. I've drained each tank so when I refill I know exactly how much I have avail until dry. The right wing tank holds 20.6, the left wing tank holds 20.7(I drained it by the sump), and the 10gal aux actually holds 11.2 up to the filler.

I've flown a few Navions, and love them but those fuel tanks need printed instructions to get right. The AD for the valve was a nightmare for a while.

Probably the best fuel system on a GA plane is the light single Grummans. A big dial knob with arrow, with the two gauges directly above. The knob can go to OFF, far left, LEFT, aims the knob right at the gauge for left, and RIGHT, aims the knob for the right tank. There is no both, or aux, or tip, or transfer, or anything. If one runs out of gas in a small Grumman, there is just no excuse.
 
Dan Thomas said:
Making it simpler for the pilot usually means complicating the plumbing. The Bellanca Viking's system looks like this:

View attachment 134650

The selector valve returns fuel to the tank it came from. Note that there is only one return from the engine; in the diagram above we see return lines from either Lycoming or Continental engines, from the Lyc's injector servo or the Continental's fuel pump.

So that diagram looks simple. But get into a Viking and lull the floor out to get a look at the plumbing, and it's a serious snarl of aluminum tubing around the selector valve. I can't find an online service manual to show it, but it would be no fun to take that selector out for rebuilding.
Click to expand...
Exactly, it can be designed as a simple user system, or a simple mechanical system both have their issues. Simple users system equal complex mechnical system which increases Cost, Weight, and adds more failure points to the system. (think all those extra fittings that could leak). Of course a simple mechanical system means the user has to understand it and operate it properly. Of course when they built them the sales department really pushed for more useful load (less weight) and more fuel (more tanks) oh and keep the cost low. The people buying them just cared that it worked not really how complex it was to operate, they could learn or pay someone to learn that.


Brian
 
Not complex at all. Pretty simple actually. Read and understand the POH and you’re good. Like flying any other airplane.
 
You must log in or register to reply here.
Back
Top