pretty much.
An axial flow jet engine uses air inline with the engine and thus can’t use a separator.
Earlier centrifugal jet engines pulled air in from the side and could use such a system.
the Russians have used a “FOD” door on some of their fighter jets that pull air in from above while they taxi around to avoid picking up the parts left over from the last jet that taxied by. But it can’t be used in flight.
OG Snake on a Plane
Some people might not know you’re joking. The FOD doors are actually because Soviet fighters could/would operate from primitive fields.
That was true for Soviet civil airliners as well. IIRC that’s why the YAK-40 had three engines and a straight wing.
And the IL-86 had passengers board through the cargo hold where they would stow their baggage themselves, and then ascend a stairway to the cabin.
Why do planes have separate fuel tanks that the engine has to take turns drinking from (and thus another thing for pilots to monitor)? Why not have a common tank at the lowest point that all the other fuel tanks feed into then have the engine pull from that one tank? I can see how turning and maneuvers can make things slosh around but a one-way valve is easy enough so fuel doesn’t run out.
Maybe a fighter plane which can be expected to do crazy maneuvers needs something different but most planes fly straight and level 99% of the time and maneuvers are docile and short.
Doubtless there is a good reason for it. Curious what that is.
Because the wings represent empty space that isn’t useful for baggage. And most planes are capable of feeding multiple tanks at the same time.
In simpler planes it’s cheaper to have a primary tank which doesn’t port air during normal maneuvers such as landing. In such a case a pilot will run the secondary tank dry at altitude so all the remaining fuel is in the primary tank for landing.
I get why fuel is in the wings but I see on some planes there is an automated switch which changes ffrom right tank to left tank and back again on some schedule. The pilot can also manually control this if things get too uneven.
Why not hook right and left tanks to a common tank at the lowest point in the plane and then have the engine run from that? No need to switch tanks.
Tanks leak, and with isolation valves, some of the fuel supply could be preserved? It’s my guess, anyway.
Not something limited to aviation. Anyone else remember pickup trucks with fuel tank switches between, IIRC, left and right? I don’t know why that existed for trucks either, beyond the reason I guessed at above.
Tanks are already connected to switching valves that allow either tank or both tanks. In a low wing plane the space underneath is taken up by the wing root and using that for fuel means adding complexity to the plane with access panels. Not a big deal but it adds to the cost. In a high wing plane the undercarriage is set up structurally for the landing gear.
There are planes with a tank behind the engine bulkhead but do you really want want to be third in line in a crash behind a tank that’s pierced by engine mounts? Most small planes have the structural integrity of a badly rusted 1940’s VW bug.
Many good answers so far.
In general, the tanks plural are tucked where they fit. There isn’t one single unobstructed space that’s big enough to carry a useful fuel load. And that collection of tanks is eventually connected to the engine(s). What you’re mostly seeing is the difference between how much of the interconnection is passive and gravity driven versus actively pumped. And how much of it is automatic versus subject to pilot control.
A Cessna 150 has one engine and 2 tanks. The two tanks outlet lines come together, then pass through a single on/off valve, the flow to the engine. The pilot’s fuel management tasks are limited to
In low-wing GA singles it’s common to have a 3-way valve: Off, feed from left tank and feed from right tank. The difference is needed because otherwise slight imbalances in trim or fuel load would, due to a cousin of the free-surface effect, lead to one tank emptying into the other and overflowing it. So the pilot’s task gain a new one: switch back end forth every so often so things dont’ get too far out of balance.
I hit send too soon while writing this post by accident so I have to quit now before my edit times out.
The F-16 had IIRC 6 fuel tanks wedged into nooks and crannies in the fuselage. The wings were too thin to fit any fuel tanks. Plus optionally 3 external tanks on the wings and centerline. The two seat version carried a bunch less internal fuel because the space for the second cockpit was gained entirely by greatly shrinking the forward-most fuselage tank.
Fuel management was mostly automated. All the various tanks were plumbed together in a specific way, had both air & electric driven pumps, and was controlled by a mechanism that kept the CG under control and kept the downstream-most tank as full as possible at all times.
It was possible for that to go haywire, and when carrying external fuel there were sometimes reasons to prefer one over the other. So we had a knob with 6 settings IIRC: Normal, Fwd, Aft, Centerline external, Wing external, or Both external . But unless something was unusual, the knob stayed in “Normal”.
I’ll quit now; big airplanes are a different matter and not relevant to this thread. I only mention fighters because @Whack-a-Mole did.
I don’t know about the 150/152 since I’ve never piloted one; but the Cessna 172 has a four-position selector: OFF, RIGHT, LEFT, and BOTH. Dad’s Skyhawk had a reminder to switch to a single tank above 5,000 feet.
I use to fly a Piper short wing that had a 4 position switch. OFF, LEFT, RIGHT, OFF. I’m guessing they were real keen on pilots selecting the left tank for landing because the right tank would port air on banking maneuvers. I watched someone kill the engine turning base by having it on the wrong tank. Things you learn not to repeat.
The 150 I flew also had a belly tank with a fuel sample port, but yes just an off/on switch. The 172 has left/right/both/off. We set it to right after shutting down the engine as it reduces fuel dripping from the tanks.
Brian
I’ve never heard of a belly tank in a 150. I would expect a belly sample port to be a low point in the system for the purpose of directing water to the lowest point. It’s more a place to drain off water than to sample fuel.
I had one on my Piper short wing which brought the total to 4 drain ports. One on each wing tank, one in the engine compartment and one in the belly.
I misremembered it being a tank, but it definitely had the same fuel sample port that was on each wing.
Known as teh “belly drain”
This in addition to the lever in the engine compartment.
Brian
Or don’t, with extreme prejudice.
Not GA, but here’s something you don’t see every day. (The fall looked painful.)
“Impairment or mental illness is suspected,” Nogle told reporters.
Ya think?
I dunno. People do way crazier things than that for attention.
I was thinking they had come up with a new economy class to attract more flyers.
It could also be symbolic. He lost everything gambling down to his shoes. Top of the world Ma.