Max Endurance Question

bdon661

bdon661

New member
Do any of you with Franklin powered Cruisair time have experience with running a tank dry in cruise? I've logged many many hours of time flying long distances in a Super Cub with 18 gallon wing tanks and the standard drill on a long flight was to burn 45 minutes out of one wing tank, switch to the other tank and run it dry, then switch back to the other tank and be on the ground within 30 minutes. This practice consistently provided a conservative reserve but maximum endurance within the constraints of conservative operations. When the tank ran dry, the engine coughed a couple times, but ran normally the moment I switched tanks. I never tried that practice with a low wing light airplane and was curious how many seconds of "is it going to catch?" I'd have to endure with a Franklin powered Cruisair.
 
That was my standard drill as well with 3 tanks on long hops. In freezing temps, I checked all the tanks for feed after about an hour at altitude, too.
Looking at the fuel pressure gauge and switching when the tank starts to slurp is practical if you know the fuel gauges well. Even though the Franklin should catch in a few seconds if run dry, it is disruptive if you have the airplane trimmed perfect and the altitude nailed. If you have passengers, there is a scare factor as well - having the engine go quiet.

Yeah, I don't know of any prob with the Franklin re-lighting quickly - with just the engine driven pump and no need to wobble(no electric boost pump). But, I don't have the number of seconds, maybe 2 or 3? Anyone?
ron
 
Both the 14-13-2 and 14-19-2 that I have experience with have always lit after a few seconds of quiet, but it does upset the passengers so I try to leave a gallon or so in the tank. There are a few NTSB reports on the 14-19 series that did not end well after running a tank dry. There is a warning about running the AUX tank dry in the Cruisemaster Flightbook.
 
The previous posts are correct. With pax it is very disturbing to flame out and they'll remind you long after the flight. In the two tank Cruisair, I take off, climb to altitude and cruise for a total of one hour. Cruise for two hours on the second tank and what is left in tank #1 is reserve. If you have done a good job leaning
as you went up, as well as cruise, you should have about 1 hour to fuel exhaustion. You should have about 8 gallons in tank 1 and 3-4 gallons in tank 2.
In the Cruisemaster, you won't get nearly the time from the tanks.....but you have the aux tank.
In the two valve Cruisemaster, you MUST turn off the aux fuel after selecting a main tank or you risk
sucking air all the way to the ground.
Dan
 
Thank you to everyone for the insight. I only do max endurance / run it until it coughs fuel management when I'm alone. If anyone has a 12 gallon Cruisair aux tank and the appropriate fuel valve they'd like to sell, please let me know. I enjoy long flights and the extra hour and change of endurance would be most welcome.
 
My butt hurts at 2hrs and I want OUT at 3. It is nice to have extra fuel on-board when the FBO is closed.
 
Just as a side note" The very first piece of advice I got when I bought a Cruisair, was that when changing tanks, to always reach all of the way down and feel both valves, so that you dont turn the wrong one off. I have never forgotten that little tidbit, and maybe it will save someone else from having the silent treatment from their airplane. _____Grant.
 
Like others have said...for long cross countrys I fly for 1 hr on the left tank, run the right dry. I figure the amount I have remaining is however long it took to run the right empty, minus 50 minutes. I seem to burn about 8.3 gph on a 400 mile x country at 6-8000 ft. running 2550 rpm, leaned ~100 F ROP.
Larry Lowenkron
 
I run my Viking tanks dry on long trips. Switch to good tank THEN elec boost pump. Not the other way around. I'd say 2 to 4 seconds for a relight, quicker if you hear it start to stumble.

I do have to say even at 10,000 agl it's the longest 2 to 4 seconds of your life.
 
grant is right.. hopefully you will only mistake the shut-off lever for the tank selector once !

doubly hopeful you never do it after you've run that tank dry !

I did it once.. at about 1000 ft agl when the airplane was brand new to me.

but not the double no-no. :oops:
 
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