Switch Tanks Before Takeoff

[Shadrach]

34 minutes ago, PeteMc said:

Well...  Sort of think you're over thinking what I'm saying.   By no means am I on the edge of my seat thinking "oh no, this could go wrong or that could go wrong!"  Far from it.  

On the throttle linkage, not one in my wheel house cuz that would really be one of those "sh*t happens."  As for the fuel selector numbers...  I never really cared, but a quick search shows that since 2008 there have been 104 accidents and nothing showed up for throttle linkage (which I'm sure there were some, but too small for my search).  That tracks with hangar flying where I've heard of issues with the fuel selector more than I have about throttle linkage.

 

There have been a $hitload more than 104 accidents involving Mooneys in the last 15 years. They just don't all get recorded.  We've had a few throttle linkage issues here on the forum.  It seems like they get stuck open as often as they do closed.

[Shadrach]

On 12/20/2023 at 12:35 PM, N201MKTurbo said:

It’s not the bearings, it is the vanes. They are running on the housing. The old pumps had metal vanes. About 30 years ago they changed to plastic vanes. They look like carbon filled nylon, but who knows. You are right, it probably won’t hurt, but priming by gravity works better and only takes a minute.

I don't know remember what materiel Ole is using for the vanes but it's hard not to see extended dry run testing that yielded no damage as a confirmation that the design is not susceptible to its previous shortcomings.

[cliffy]

1 hour ago, PeteMc said:

But for years my job was to think of what could go wrong and have a plan.  Even when the odds were miniscule, you still had to go through the thought process.  (And the WORST JINX EVER is when one of the crew would say "this is going to be an easy show."  Something ALWAYS happened! )

I know there is a story here somewhere  :-)

[Pinecone]

On 12/15/2023 at 8:58 AM, Fly Boomer said:

Have you had or heard of issues running a tank dry?  I know guys with carbureted engines that do it, but I also know guys with fuel injection who say that the engine has a tendency to just crap out.  With turbocharging, it could be a long glide down to an altitude with enough air for a relight.

I have not heard or had any issues, but don't want to be the first.

I have run a tank dry to calibrate some fuel dipsticks and the wing gauges. It stumbles a bit, but switching tanks it fired right up.

My concern is, if you are landing, you are not straight and level, so the "useable" fuel may be different.

[Pinecone]

FYI, in most cars these days, it is a good idea to refuel at 1/4 tank remaining and not run them down to the low fuel light.

The fuel pump is in the tank and is cooled by the fuel.  So less than 1/4 tank, the pump runs hot.

A straw poll on one of the major BMW forums found a near 100% correlation for running the tank to the low fuel light and having to replace the fuel pump

[Shadrach]

32 minutes ago, Pinecone said:

FYI, in most cars these days, it is a good idea to refuel at 1/4 tank remaining and not run them down to the low fuel light.

The fuel pump is in the tank and is cooled by the fuel.  So less than 1/4 tank, the pump runs hot.

A straw poll on one of the major BMW forums found a near 100% correlation for running the tank to the low fuel light and having to replace the fuel pump

I must be an outlier. I’ve run several BMWs both gas and diesel past 200,000 miles without a care of letting the tanks run down to reserve. Also two Cooper S’ that were run the same way. If there is fuel running through the pump, they shouldn’t overheat…especially given the tank pump is just a low pressure supply pump. The high pressure pump is up in the hot engine bay.

[Pinecone]

What years?   This straw poll was about 2005.

[Hank]

44 minutes ago, Pinecone said:

FYI, in most cars these days, it is a good idea to refuel at 1/4 tank remaining and not run them down to the low fuel light.

The fuel pump is in the tank and is cooled by the fuel.  So less than 1/4 tank, the pump runs hot.

A straw poll on one of the major BMW forums found a near 100% correlation for running the tank to the low fuel light and having to replace the fuel pump

Thankfully I don't drive a BMW. Neither my Nissan nor Honda has a problem with this; I've been running the Nissan down to 20-25 miles to Empty for 110,000 miles the last four years . . . . .

[Shadrach]

57 minutes ago, Pinecone said:

What years?   This straw poll was about 2005.

Both coopers were first gen S models I dated one and married the next, an 04 and an 05. BMWs we’re 2001 323ci, 2009 328i touring, 2014  535d and 2015 535d. There were a smattering of e30s in my teens and twenties. I owned some and dated others. Not a fuel pump failure in the lot.

[Pinecone]

Great.

Thinking about it, it may have been that every fuel pump failure was in a car run to near empty, and no car filled at 1/4 had a failure.

NOT that all cars run low had failures. 

[EricJ]

3 hours ago, Shadrach said:

Both coopers were first gen S models I dated one and married the next, an 04 and an 05. BMWs we’re 2001 323ci, 2009 328i touring, 2014  535d and 2015 535d. There were a smattering of e30s in my teens and twenties. I owned some and dated others. Not a fuel pump failure in the lot.

Many of the fuel pump "failures" I've had to deal with were due to a car sitting for a long time, and autofuel additives will ruin a pump in a year or so by varnishing the commutator surface if it isn't ever run.    Either that or on cars that get used the pump doesn't actually fail, but there's a small leak in the hanger somewhere that keeps it from making full pressure.   Gotta get in the tank, regardless, however that's best done on that particular vehicle.    I had to fiddle around with all of that stuff on my E36 BMW because there was an emissions leak that I had to track down.   It was all reasonably easy to get at, and I think over time I did both ways.    I had to drop the tank when we welded in all the rear suspension reinforcements for the track, so I did some stuff then, and I think I also had to get at it in place once or twice, since it's tough to drop with the suspension and driveline in place.   Never for the pump, though.

I'm never sure whether working on cars or airplanes is worse. 

 

[Shadrach]

On 12/20/2023 at 5:12 PM, Pinecone said:

Great.

Thinking about it, it may have been that every fuel pump failure was in a car run to near empty, and no car filled at 1/4 had a failure.

NOT that all cars run low had failures. 

When I was in high school (~1990) a friend of mine was gifted a green 1976 Ford LTD (aka Kermit) with a 351ci V8. As a consequence of its incredible thirst for fuel (6-8mpg around town) and his shallow teenage pockets, it was frequently left wherever it ran out of fuel, which Happened every few weeks or more. Of the many things that failed on that car, the fuel pump was rock solid.. 
It’s unbelievable to me how dated a 15 year old car looked prior to Y2K…and also what incredible POS’s Detroit was making in the mid to late 70s just as Mooney was turning out it’s most revolutionary airframe.

[Fly Boomer]

10 hours ago, Shadrach said:

When I was in high school (~1990) a friend of mine was gifted a green 1976 Ford LTD (aka Kermit) with a 351ci V8. As a consequence of its incredible thirst for fuel (6-8mpg around town) and his shallow teenage pockets, it was frequently left wherever it ran out of fuel, which Happened every few weeks or more. Of the many things that failed on that car, the fuel pump was rock solid.. 
It’s unbeleavable to me know how dated a 15 year old car looked prior to Y2K…and also what incredible POS’s Detroit was making in the mid to late 70s just as Mooney was turning out it’s most revolutionary airframe.

Kermit may not have been new enough to have an electric pump in the tank.  For sure, my first cars (1950s) didn’t.

[Shadrach]

23 minutes ago, Fly Boomer said:

Kermit may not have been new enough to have an electric pump in the tank.  For sure, my first cars (1950s) didn’t.

I’m admitted unfamiliar with the particulars of that era. Kermit definitely had a pump in the tank as did most of the cars I’m familiar with from the 60s and 70s. I know my old man’s 54 XK120 had one as he talked about whacking it with the wheel mallet to unstick it.

How were your cars supplied with fuel?

[cliffy]

Most cars just had an engine driven fuel pump just like airplanes do to this day

Most of them looked just like the diaphragm pumps we have on Lycomings today 

IN fact the early airplane ones were adapted from automotive engine driven pumps 

[GeeBee]

While there are exceptions, submerged in tank fuel pumps became "de rigueur" as a result of the requirements of electronic fuel injection. 

[Pinecone]

1 hour ago, Shadrach said:

I’m admitted unfamiliar with the particulars of that era. Kermit definitely had a pump in the tank as did most of the cars I’m familiar with from the 60s and 70s. I know my old man’s 54 XK120 had one as he talked about whacking it with the wheel mallet to unstick it.

How were your cars supplied with fuel?

Most cars in the 60s and 70s with carbs did not have fuel pumps in the tanks.  They had a mechanical diaphragm pump on the engine.

Jags and some other Euro cars had an electric fuel pump near the tank, but not IN the tank. It would be very difficult to whack a pump inside the tank with a mallet.

In tank fuel pumps came around with fuel injection.

My 55 Chevy, 71 Fiat 850, 76 Toyota Corolla, all had engine driven mechanical fuel pumps.

My BMWs and Fiat 500 all have in tank fuel pumps.  E36 M3 LTW, E46 M3, Z3M

[Fly Boomer]

2 hours ago, Shadrach said:

I’m admitted unfamiliar with the particulars of that era. Kermit definitely had a pump in the tank as did most of the cars I’m familiar with from the 60s and 70s. I know my old man’s 54 XK120 had one as he talked about whacking it with the wheel mallet to unstick it.

How were your cars supplied with fuel?

Mechanical pump bolted to the engine.

[EricJ]

2 hours ago, Shadrach said:

I’m admitted unfamiliar with the particulars of that era. Kermit definitely had a pump in the tank as did most of the cars I’m familiar with from the 60s and 70s. I know my old man’s 54 XK120 had one as he talked about whacking it with the wheel mallet to unstick it.

How were your cars supplied with fuel?

Engine driven diaphragm pump, very similar to the mechanical pump on airplane engines.    The introduction of electronic fuel injection meant much higher fuel pressures were needed at startup and during operation, so in-tank electric pumps that were always primed became the solution for that.
 

[Fly Boomer]

38 minutes ago, Pinecone said:

My 55 Chevy, 71 Fiat 850, 76 Toyota Corolla, all had engine driven mechanical fuel pumps

That’s funny.  I had a ‘55, ‘56, and ‘58, plus the Fiat 850, and currently drive a Toyota.

[GMBrown]

My 67 Camero has a diaphragm driven by a rod that ran off a cam on the crankshaft.  (327 CI V8)

[Pinecone]

22 hours ago, Fly Boomer said:

That’s funny.  I had a ‘55, ‘56, and ‘58, plus the Fiat 850, and currently drive a Toyota.

Why funny?  Great minds think alike.

 

[William Munney]

Start on the fullest tank, then taxi and takeoff.  Once you have a clear and demonstrated functioning pathway from the tank to the engine, why would you change it for takeoff?  Stick with what is working until cruise.

[Pinecone]

Because the other way prevents a BIG surprise when you switch tanks at cruise.

I KNOW both tanks are feeding before take off.

[wombat]

4 hours ago, Pinecone said:

Because the other way prevents a BIG surprise when you switch tanks at cruise.

I KNOW both tanks are feeding before take off.

Please don't take any of this too seriously, but....       I already know both tanks worked before taking off, because they worked last flight.   What happened while the plane was on the ground that would have caused it to work the previous time but not this time?   If the answer is 'nothing' then you gain nothing.    If the answer is 'something',  then... What the heck are you doing to your plane?

The thing is, there will be a first time that it fails.   If we assume that there is a 0.0001% chance of failure any given time you use it, it's just as likely to fail in flight regardless of if you tested it before.   If testing it before is good, why not test it twice?  (Left, Right, then back to left)... You only tested it one direction if you just swap the one time!  If testing it once is good, I should probably test it twice.  If twice is good, more is better.   To be extra safe, I should sit on the taxiway and swap fuel tanks until I run out of gas.

If the selector valves have an average lifespan of 10,000 movements, and an average flight has 2 changes in flight, then by doing a fuel tank swap before each flight reduces the life span of your valve by 33%.   

If I landed and dropped off a passenger, should I test again before taking off again?  What if I just did a stop-n-go?    What if I stopped for lunch?   What if I stopped, took a nap in the hangar and then took off again?  What if I went home in the meantime to nap?  How does the selector valve know if I went home or not?

 

Seriously, I don't think there is single perfect answer here.   Follow the regulations, evaluate the risks, and mitigate them until your mitigation costs and risk acceptance level are good for you.