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Author Topic: Fuel and Twin Commanders (Part 1) - an important read...  (Read 960 times)

Russell Legg

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Fuel and Twin Commanders (Part 1) - an important read...
« on: October 10, 2015, 12:30:35 am »
Hello Folk,

The following is a series of raw conversations regarding TCFG members' thoughts/experience with fuelling Aero Commanders and operating associated fuel systems.
These conversations are sourced from the TCFG Chatlist in the early 2000's and are strictly the opinions of members at the time.
While I am sure the experiences discussed are still as relevant in 2015, it should be noted that some key members featured have since passed out of Commander ownership.

Wing Commander Gordon will undoubtedly recall the times...

Enjoy!

Cheers

Russell
VH-CAU
560E s/n 726




In a message dated 03/05/01 19:43:25 Pacific Standard Time, N700PF writes:

Anybody know if there is an 8 to 10 gal cell in the system?? 

I tell ya, if there is any one thing I find a mystery in the Commanders, it's
the EXACT volume of each bladder.

In all my years of asking, looking, calculating, I never got a straight-up
answer on what each bladder's capacity is.

I asked TCAC. I asked two fuel cell overhaulers.  Nothing ever came of it.

What I do know is that there is a "range" of fuel load on a Commander and to
be up to 10 gallons light is not out of that range.  (I think it is, but I'm
just a pilot, so my opinion does not count.)

I do not think there is a 10 gallon bladder in the standard 156 gallon
configuration.   A 685 or 690 has lots of little bladders (22, if memory
serves me) but not your 680-E.

OK, here's my set of bad answers to your good question, in order of
probability:

The size of the bladders does vary, especially if overhauled or
reconditioned.  This will account for some loss of volume.

Placement of the bladder can effect volume -- meaning if a wing bladder is
put in and all its corners are not "square" you'll lose some capacity.

Also remember that the temperature of the fuel does affect volume and if your
fuel is other than standard (59 F)  your volume will be off from book value. 
There are charts available (but don't ask me where -- Tylor Hall may have
these) that correct for this and it usually has an impact on BIG fuel loads;
not 156 gallons, but it's worth mentioning.

Also, this phenomena is important when you place warm fuel in your tanks, go
to altitude and cold-soak the fuel system.  Your fuel volume will shrink. 
Most piston aircraft don't get high enough to get that cold, but this, and a
clogged vent system evidently led to a fuel starvation incident in a
Commander a few years ago. 

Remember, I'm NOT a mechanic (I don't have the patients nor the intelligence
to be one) but have been around two or three Commanders and have seen these
situations.

I hope some of the A&Ps and "hands-on" type of members speak up on this.
You are correct for the standard temp of 59F. One cubic foot = 7.48 Gallons.

If you had all of the dimensions of the different bladders one could figure the

Volume.  The tank charts that I have are on much larger tanks like 12,000 gallons.



I would hate to think that I had 156 gallons on board and was making a long flight.

Only to find out I was 10 to 14 gallons short and about two miles short of the runway.

The silence could be defining.



I watched as a wing bladder was being put into the wing of a 182 once.

It was a real fight to get it in the hole and straight.  I can see where one fold in the fabric

Could leave one a little short on fuel.



There is a 1959 Commander 680E, N8468C for sale. Does any one know its history???

Being a new addict on the block I know that there will be a number of
> > things
> > > I will learn, which are common knowledge to the rest of the planet.
> From
> > > now on I will not do a pre-flight without my Leatherman Tool and my
cell
> > > phone in my pocket.
> > >
> > > Yesterday with family in tow(Wife, 9yr old, 11yr.old) I commenced to
> > > pre-flighting on our 500A.  At the point where I intentionally "dump"
> > $1.50
> > > worth of Av Gas on the weeds, there was a problem.  After $1.50 it
> wasn't
> > > slowing down much.  Somewhere around $3.00 to $4.00 panic made its
> > > appearance.  At about $5.50 the "Keystone Cops" performance started.
I
> > > stuck my finger in the hole, yes Little Dutch Boy, me.  Next a
> spectacular
> > > hand-off to my wife, Little Dutch Girl now.  I ran, hurried(49 yr.old
> fat
> > > man moving fast) into the mechanics and begged for supplies.  I found
a
> #5
> > > tubing cap fit the end of the drain tube.  Wife is now relieved as cap
> is
> > > installed, only $.75 loss.  As usual when in doubt, call Yoda(Kernick,
> > sorry
> > > Harry I was in a panic).  Yoda advises the technical fix is "the
Whack".
> > > Leatherman tool fit in the door well a couple of whacks and $2.00 more
> in
> > > fuel and the emergency was over, blood pressure returned to normal.
> > >
> > > I'll probably carry that #5 cap with me on pre-flight for a while too.
> > >
> > > Sorry to be long-winded
> > >
> > > bilbo
> > >
> > >

I don;t know about other models, but my AC560 with GO-480's has an often overlooked recurring AD to tighten the screws on the engine mounted fuel pumps every 25 hours.  I have this done at the same time I have my oil changed.  I have never had fuel pressure problems, in over 250 hours of flying mine.

My guess would be that the screws loosen, even with the safety wire, allowing air in the system.  This could cause over-reving, and low fuel pressure.

There is a SB for the Commanders that does say to
use the boost pumps for every takeoff and landing due to the possibility
of vapor forming in the lines however.  This SB reports that the
boost pumps are rated for 1000 continuous hours of operation.

Most of my fuel pressure problems (in flight) on the 680-F Series were due to
clogged screens in the Simmonds fuel injection units.

These fine mesh screens must be ultrasonically cleaned - - and more often
than you would think.  Perhaps that could help, but I have usually seen the
need for boost pumps around the 8000' level in the 680-F series, as well.


In the second issue of the Flight Group News I wrote an admittedly sarcastic
article about checklist use in the single pilot airplane that won me the
coveted "Worst Man in Aviation Award," bestowed upon me by TCAC and
FlightSafety.  (This article also appeared as a reprint in one of the last
issues of the Flight Group News.)

They failed to notice I supplied a checklist along with the article.

I tried to point out that the Commander cockpits are set up for a very
efficient and natural flow pattern ... unlike the factory checklist sequences.

But that's old news.  On the topic of boost pumps, here's some food for
thought:  Continental engines used to have pressure activated boost pump
output rates.  If a lower than normal fuel pressure was sensed, the electric
fuel pump would kick into high.  That also happened when it wasn't needed and
that flooded engines and caused incidents with fatalities.

That's NTSB speak for crash -- and an AD removed that system from most
installations, if memory serves me. (CE300s, CE400s and AC-500A come to mind.)

Lycoming engines don't seem to suffer from this problem and "boost pumps on"
for takeoff is a good thing.

However. (You all knew this was coming, didn't you?)  Of the partial power
losses I've had on approach in Lycoming and Continental powered twins, all
were caused when boost pumps were turned on.

It is true that something was out of adjustment, somewhere, and please don't
come at me with the old bromide of "well, you should have flown a better
maintained airplane."   All airplanes are in a state of semi-partial
perfection (gads, I'm diplomatic), all of the time.

I am happy to NOT use boost pumps on landing, turning them on as a reaction
to power loss instead of inviting power loss due to them being on.

So there you have the classic struggle between textbook theory of what's
right vs. field experience.  I'm not sure which holds the moral high ground,
but I know which method keeps the engines running.

            I just got back from a few minutes riding on the pointy end of
the arrow.  I would rather have flown last eve when the sunset was
spectacular, but when I lit the old gal up, no fuel press. On the R engine
driven.  I pulled the pump (in the dark) and took a look.  It seems that a
couple of tiny pieces of rubber were holding the pressure relief valve open.
       I took the opportunity to install some new "O" rings and I am back in
biz.  Here is the deal.  I never use the boost pumps on take off.  Didn't in
my last Commander or my Duke ether. I know, I know, the book says always use
them, but I always forget to turn the dang things off, and in 1500hr or so of
ME flying I have never had a fuel pump fail, until last night.
       I caught it on the ground run, it wouldn't run without the boost pump
after priming.  I was amazed how small the offending pieces of rubber were
and how completely they had shut the pump (engine) down. (they came from a
new hose I built and obviously didn't clean well enough)
       Anyway, it was a wake up call for me.  Fly by the book.  I will be
using boost pumps from now on.  I just need to figure a way to remember to
turn them on and then off.  Just another day in Commanderland

capt jimbob
Anybody know if there is an 8 to 10 gal cell in the system?? 

I tell ya, if there is any one thing I find a mystery in the Commanders, it's
the EXACT volume of each bladder.

In all my years of asking, looking, calculating, I never got a straight-up
answer on what each bladder's capacity is.

I asked TCAC. I asked two fuel cell overhaulers.  Nothing ever came of it.

What I do know is that there is a "range" of fuel load on a Commander and to
be up to 10 gallons light is not out of that range.  (I think it is, but I'm
just a pilot, so my opinion does not count.)

I do not think there is a 10 gallon bladder in the standard 156 gallon
configuration.   A 685 or 690 has lots of little bladders (22, if memory
serves me) but not your 680-E.

OK, here's my set of bad answers to your good question, in order of
probability:

The size of the bladders does vary, especially if overhauled or
reconditioned.  This will account for some loss of volume.

Placement of the bladder can effect volume -- meaning if a wing bladder is
put in and all its corners are not "square" you'll lose some capacity.

Also remember that the temperature of the fuel does affect volume and if your
fuel is other than standard (59 F)  your volume will be off from book value. 
There are charts available (but don't ask me where -- Tylor Hall may have
these) that correct for this and it usually has an impact on BIG fuel loads;
not 156 gallons, but it's worth mentioning.

Also, this phenomena is important when you place warm fuel in your tanks, go
to altitude and cold-soak the fuel system.  Your fuel volume will shrink. 
Most piston aircraft don't get high enough to get that cold, but this, and a
clogged vent system evidently led to a fuel starvation incident in a
Commander a few years ago. 

Remember, I'm NOT a mechanic (I don't have the patients nor the intelligence
to be one) but have been around two or three Commanders and have seen these
situations.

I hope some of the A&Ps and "hands-on" type of members speak up on this.
Remember, when you fuel a Commander, you're filling 5 interconnected bladders
from one single point on the right wing. 

If the right wing is low, either due to a steeply sloped ramp or a low strut,
you cannot fill the bladders in the left (high) wing all the way.

Further, he instructs, when topping off, politely ask the line service
professional (nozzle jockey, ramp rat) to clean the windows or check the oil
after the first "top off."    If you do this, the fuel level will settle down
and you'll get as much as 12 more gallons in.
The Commander manual gives a range allowing for as little as 155 gal
so it is pretty close Now that I know what it really holds I will plan
accordingly.  At 40 gph we are really only talking about 10 minutes or so.  I
suppose the antique pump at the little FBO I live at could also be in error??
       Thanks for all the advice.  Jb

>The size of the bladders does vary, especially if overhauled or
>reconditioned.  This will account for some loss of volume.
I wouldn't think this would effect over 10-20 gallons though.
(That's a large change in bladder size)
Unless you noticed a large discrepancy between the bladder and the wing
close-out area
when you installed the new fuel cell, this would be unlikely.

If you have had the plane for awhile, you will instinctively know what
your fuel loads should be with various temperature ranges.

>Placement of the bladder can effect volume -- meaning if a wing bladder is
>put in and all its corners are not "square" you'll lose some capacity.
This would be more likely.

I recently replaced 3 fuel cell bladders in my 500B (after the AD
inspection)
and it took me longer to position the bladders than it did to tie them
off.
The positioning of the laces and proper security of the tie downs
can decrease the amount of fuel that is distributed within the set.
(You can refer to the maintenance manual and it will show you the proper
fuel
lacing pattern to use on the fuel cells)

The interconnect tubes allow fuel to evenly disperse between the bladders.
If one bladder is not properly tied up into the upper attach points then
a decrease
in volume can occur. (Gravity can work against fuel distribution,
especially
if the top or corner of the bladder is pushing down or in on the incoming
fuel)

I've seen were a fuel bladder was incorrectly tied in, causing one corner
to displace
a large portion of the fuel cell bladder inward, this resulted in a
folded in bladder.
This could easily displace a good portion of your fuel capacity.
(volumetric displacement)

But after some time, the bladder may find it's natural position and
hopefully
allow more fuel to enter, thus reducing your fuel discrepancy.
(This could also cause leaks in the interconnect tube connections later
on)

>I did manage to squeak another 7.5 (148.5 total) gal after it sat over night,
>but that is still a bit short??
>Harry Merritt, they guy who sold it to me, suggested it was missing a blatter.
Looking at my illustrated parts catalog, I only show the typical 5 cell
system
exactly like my 500B. The catalog refers to 500 series, 560, 680F and FP.
Is there any difference between your 680E and the 680F?
Chris's chart says 223 gallons for the 680E, if this is true then you
might have
a completely different fuel system than the diagram that I'm looking at.

My maintenance manual says the fuel system is comprised of 5 cells which
hold a
total of 150-159 gallons. If you're on the lower end then your close.
When I refueled after the fuel cell installation, I was on the higher end
of 157 gallons.
(I made sure the laces were tight and properly positioned).

I'm sure Morris can fill in the details.
Hope this helps.
Randy

The fuel systems on the 500B and the 680E are the same.   
Interesting that your book gives a rang of 150-159.   Mine, for the 680E,
says 155-159??

The 680E does have two additional "outboard" tanks with a capacity of about
33.5 gallons each, right?

The "Main" fuel system is identical to a 500 series; 5 bladders holding
around 156 gallons.

Just wanted to clarify that point for everyone watching this thread.

KG