Cessna C340A Fuel System and procedures

[flycaptjon 2]

I have seen a number of posts and queries about the C340A and its fuel system, fuel burn. In time I may post some diagrams of the fuel system from the aircraft POH, and Maintenance Manual.

 

For now I contribute the following to help the forum users.

 

 

I'm a real world commercially rated multi-engine pilot with over 750 hours in C340A's specifically and other Cessna twins including C310s (got my multi-engine rating in a C-310Q model), C340As, C401s, C414, C421B, and C441 Conquest II.

 

To clarify the Carenado C340 is according to their tech support, is a 1974 C340A II (with the I, II, and III designation of different levels of Cessna factory avionics packages: Nav-O-Matic series 400, 800 and 1000 respectively), with the factory Continental TSIO-520-NB 285hp per side; turbo charged, injected, horizontally opposed 520 cubic inches, or 8.15 Liter engines.

 

The C340A I have flown most often is a 1979 C340A II with the 325hp RAM Series IV engine upgrade.

 

The fuel system in it is identical to the one on the Carenado C340A.

 

• The main tanks are the wing tanks 102 gal/ 100 gal usable
• The auxiliary tanks are in the wings outboard of the engine nacelles. 43 gal usable
• Total fuel 166 gal.

 

Please note the following point for fuel management:

 

• All take offs and landings are to be done on the main tanks (tip tanks).
• It is recommended for longer fuel bladder (rubber bladders)  life that the Aux tanks be kept full regardless if you typically fly short flights as the fuel lubricates the bladders and keeps them from drying out and cracking and leaking.
• In flight you take off on the main tanks noting take off time.
• You burn the mains for one hour, then regardless of altitude full mixture RICH
• Switch tanks to Aux and note the Aux fuel light turns on at the panel.
• With both tanks now on Aux and both lights lit, re-lean the mixtures to the previous EGT settings usually about 1450 to 1650 on the Carenado, we use 1450 with the RAM IV at 82% cruise power.
• If your flight plan is long enough burn the Aux tanks down to no less than 2 to 5 gal per side (you do not want to run the tanks dry, but it you forget and the engine starts to stumble:  the rapid response is mixtures FULL RICH, left tank, left main, right tank, right main and see that it smoothes out then re-lean the mixtures.
• When the Aux have burned down to ~2 to 5 gal per side, mixtures full  RICH, switch to MAINS, and re-lean mixtures.
• You will find that after burning on the Aux tanks for any appreciable time, that the main tanks will INCREASE in fuel. This is because the fuel system (fuel pumps) send more fuel to the engines than is required by the fuel metering unit which supplies fuel to the fuel manifold (kind of looks like a round disk with spider legs) and then to each of the six cylinders. The unused fuel is then send via a pressurized return line back to the main tank (on the side from where it came from) regardless if it was fed from the main or Aux tanks.
• So the return fuel will always increases the fuel levels in the main tanks. It is for this reason that you burn the MAINS for at least 1 hour before switching to the Aux tanks.
• Otherwise, if you took off and immediately switch to the Aux tanks, the return fuel to the Mains, would soon overfill the Mains causing valuable fuel to be pushed overboard via the fuel vent lines and out into the atmosphere... talk about burning $$$ and effective range!

 

So that's all for now, in my first post to this forum. I hope at least some may find this interesting.

 

Clear skys!

 

Captjon

 

[Robk182 0]

Thanks for your post, it help a lot to know that a real pilot of 340 bring to the world of Sim a opinion, a question.. you can certify that de Carenado C340 Flight Dynamics its correct? i mean that the carenado fly on the numbers and like her contrapart in the real life ? (on stock and with the conversion to RAM IV engines).

I always been with the crush betwen the Milviz 310 and this 340, 

 

Robert Bernard

[flycaptjon 2]

Thanks for your question Robert. I have flown the FSX version, so I cannot comment about it because I no longer use the MS FS products since they no longer meet my needs (and I started with FS2.0 on an Intel 8088PC in 1986).

 

I understand the FSX and XP version perform the same based on similar platforms and hardware.

 

For the XPlane version both in XP9 and 10, I had to modify the aircraft file to meet real life airspeed, climb, cruise and altitude performance. The limitation was primarily in the parameters controlling the effect of critical altitude.

 

Once I raised it to 30,000' I got similar performance. I cannot remember how to affect that in FS since I have not down that in years, but focus on the engine output and turbocharger compensation for critical altitude. At the upper altitudes you should be able to maintain at least FL250/260. Everything will be pushed to the firewall, but you will be within limits. You may be cruising at 130kts indicated with maybe 21/22" manifold and 2200 RPM with the engines leaned out to about 1550-1600C EGT with the RAM IV (the VI is about the same).

 

With 2 pilots and full fuel (166gal.) we can maintain FL260, but with the factory settings I had serious performance issues starting around 11,000' and could not hold altitude and airspeed at 16,000' in my initial tests.

 

In the actual 340 we customarily cruise FL210 to 240 if the winds are favorable. I have picked up anywhere from 100 to 150kts. additional groundspeed in the Jetstream in the winter months and based on flight paths. Conversely, if the winds are working against you we normally fly down FL120 to FL160 for best fuel burn if the upper winds are not working with us.

 

Once tweaked the fuel burn, handling, and other dynamics are very realistic. So other then tweaking the performance there were a few other minor bugs, which I have reported via bug reports to Carenado.

 

Mostly, the analog OAT gauge issues, and the annoying flap gate which should be optional, and the coding of only two stages of flaps.

 

Real C340s have flaps 0, 15, 30, and 45 degrees, so three stages.

 

Hope this helps.

 

Cheers,

 

Jon

[Robk182 0]

Thanks for your reply, and the great info that you give!! Then the C340 need to be tweak to can be fly realistic. Your analisis its fantastic, that its we need.

I never flight in the C340 but in many others yeap so i dont know how its the plane in the real life.

If dont have any problems you can send me or post the aircraft.cfg or the tweaking/modifications that you have done? Sorry for my request but i want fly a C340 like in the real life.

 

Robert Bernard

[jawolfe 0]

Thanks for the help Jon. 

 

My father had a 1977 Cessna 340A on a 135 certificate back in the 90's, which being an A&P and working on it was my job.  I wanted to change the Carenado 340A to the this one with the 310hp engines, so is the critical altitude around 20,000?  We did have the vortex generators for the gross weight increase....but no RAM STC unfortunately.

 

I'm not sure, but I've heard 20,000 might be close. 

 

Also, have you ever had problems with flying in heavy snow and moderate ice and engines loosing power like in the sim.   I can get the engines to nearly quit in heavy snow and moderate icing.

 

Thanks John Wolfe

[flycaptjon 2]

John, I have the POH, service manual and parts manual for the C340/ C340A as well as the Simcom flight training manual for the initial training I took. The 'book' value for the critical altitude with the TSIO-520NB engines is 25,000 ft.

 

That said, when I used that value I did not get actual performance as the 1979 340A with the 325hp RAM IV. I found that neither FSX or XP9/10 do a good job of simulating turbo chargers with automatic waste gates.

 

I changed the value to the absolute ceiling of 30,000 ft. and I was able to get the appropriate speeds with the RAM power settings.

 

75% power

Continuing:

 

25,000'

 

75% Power  33.5" MP / 2450 RPM / 1550F EGT

65% Power  30.5" MP / 2400 RPM / 1550F EGT

 

Maximum Range Cruise

55% Power 27"     MP / 2300 RPM / 1550F EGT

 

Cruise Climb is at

82% Power   32.5" MP / 2450 RPM / 1450F EGT

 

 

Now you only want to climb high based upon winds aloft and tail winds. Depending on your direct of flight and the prevailing winds -- especially at the upper altitudes were the jet stream has an impact -- you may face a 50 to 100+ kt. headwind...

 

In that case, you may want to cruise lower even down to ~FL120 or so to reduce the headwinds.

 

Yes, with the heavy and freezing precip, you will encounter induction icing. When that occurs pull the 'Alternate Air' on. It is located on the pedestal below the auto pilot head and the cowl flaps.

 

When that occurs, I pull alt air 'ON' and cowl flaps 'closed' and monitor the CHT keeping it > 300F and < 450F (usually not a problem in freeze levels).

 

Hope that is useful,

 

Cheers,

 

Captjon

[jawolfe 0]

Thanks so much for the help Jon.    I really appreciate the performance numbers you've provided.

 

I completely forgot about the alternate air cable.......too many Annual Inspections ago, but now I remember the cable going to the induction system.

 

 I'll adjust the file to 25,000ft for the correct critical altitude. 

 

We looked at getting the American Aviation Inc., STC for bigger intercoolers for even better performance for the 340, but got a King Air C90 shortly thereafter, so things changed.

 

I still I have a sweet spot for the 340 and what it can do.

 

John Wolfe

[paula 0]

after reading this post I have a few small questions if you dont mind.

I noticed during flying that the left and the right gauge for fuel shows that the one sometimes gets faster empty than the other one.

is that normal in case the engines are sync.

 

another question is if one main tank is empty then I switch to the aux tanks.

question is: is there a way to switch fuel from the main tank left to the right one?

because if the left maintank is still filled with 5 gallon and the other one is empty then I cannot use the left one anymore.

[flycaptjon 2]

Hi Paul,

 

No the unbalanced fuel burn is not normal in the real C340 or in the Carenado 340. There is an anomaly in in FS as I understand it in the fuel selection.

 

In the C340 you should start with full tanks both mains (tip tanks) and Aux tanks.

 

Before starting verify:

 

Left engine, left main

Right engine right main

 

starting #1 first then fuel pump on low

start #2 then fuel pump on low

 

idle at 1000 rpm to warm the engines

 

Fly for one hour on the mains then increase mixtures full rich

switch left engine left Aux

Right engine on right Aux

ensure you get the lights and fuel flow with no power loss then re-lean for cruise altitude.

 

If you find you are still burning uneven try the following.

 

switch to the C172 and start the engine verifying the fuel selector is on the 'both' position.

 

Then switch to the C340  and it should properly feed from the proper tanks. I have heard this is a bug in the simulator if you shut down with an airplane such as a Bonanza or Mooney with either a right or left tank feed only, and then go to the Carenado airplane either C340 or King Airs.

 

Hope that help you out.

 

Good questions. Always glad to help.

 

captjon

BTW, in Cessna Twins NEVER run the mains dry and then switch to the Aux tanks. There is a risk of engine loss and no restart.

 

Instead use, the Cessna procedure I have described. Also, never a good idea to run the Aux tanks dry. Burn down to 5 or 6 gallons per side, then mixture full rich again and switch:

 

Left engine left main

Right engine right main

 

monitor as before and then re-lean the mixtures.

 

The engine driven fuel pumps deliver MORE fuel to the injector manifold and then injectors than the engines require. The metering unit sends the unused fuel back via the return lines to the MAIN tanks only on the respective side.

 

So when using the Aux tanks the Main tanks will actually become fuller. That is the reason you must burn the mains for an hour before switching to the Aux tanks. Once the mains are full any extra fuel is vented overboad via the fuel vent lines...

 

Not only are you throwing away precious fuel and BIG $$$ these days, but you are reducing your range and what you may have flight planned...

 

captjon

[Robk182 0]

Hi capjon

 

This procedure works on the 310 too? 

 

Redgards

Robert Bernard

[flycaptjon 2]

Hi Robert,

 

Yes, with the exception of the Aux tank capacity options... the C310 is virtually the same. I have flow C310J, L, N and Q models and you use the same fuel management procedures as with the C340. The fuel selector positions and labeling is the same as the C340 (and for that fact the C400 series piston twins as well).

 

I believe the Milviz C310 is an R model. The R model 310 made the optional three bladed props from the Q model standard equipment and had a lengthen nose, so more baggage area up front like the C340.

 

Happy Flying,

 

captjon