Does anyone have a 350 is set up with a header tank?  During my early testing of 515ZC I had a forced landing secondary to fuel starvation from one tank.  I have not been able to calibrate any less than 4 gallons until the float comes off the bottom of the tank.  I’m totally unreliable under that measurement.  I was going off of fuel burn and the Skyview said 13 gal left.  The other side still read a reliable 7 gal.  I was heading back to the airport when I lost power.  I initially thought it was an ECU failure and tried to change ECU power to backup and tried the manual setting on the pumps.  By the time I switched over the tank I was too close to the ground and had to land rather than continue to try to restart.  On the ground, I had 1/2 gal left in the left tank and 7 in the right.  The data from the Dynon showed irriatic fuel pressure then zero.  Compatible with fuel starvation.  I have since changed my k factor to more closely approximate hourly fuel burn of about 6.5/hour. At 2600 rpm.  It was at 4.7 gal per hour or about 30% low.  Hence my mental miscalculation.  

No damage was done to the airplane, and I filled the tanks and flew it out of there after further testing to make sure no clogs, fuel flow etc.  (and a visit from the FAA.). 

Currently,  I have a duplex valve and the return line goes to each corresponding tank.  I think the only solution is a header tank feeding from both sides and a red cube fuel flow to the Dynon.  Intake and output side.

As as I read between the lines of some of the posts, I am not the only one who has difficulty with the current placement of the fuel floats.  I see some very elegant solutions of placing the float in a vertical manner, but still somewhere near the main spar end. I dont see how that will pick up the lower couple gallons either.  Putting in  a different brand of sender will not change the fact of no gas to make the float work.  The factory Cruzer will supposedly read down to almost empty.  I’ve tried recalibrating the senders in level flight attitude.  (Wing is close to 0 deg.  Window sill at about -3 deg.). 

I cant find anyone who thinks capacitance type senders are a great idea.  I’d love to dip stick the tank but I can’t see fuel from the filler cap until about 4 gallons are added.  

Id like to know if anyone has installed the Viking header tank with the 350 is.  Viking  just posted a video with the header tank and showing their setup.  As I think I understand their setup, they don’t have a return line from the engine.  Will that work on the UL engine?  They vent the pressure with a small relief valve near the header tank.  They have a separate fuel gauge on the header tank of 2.5 gal.  Basically the 1/2 hour reserve.  I can scrap the return lines and T the tanks together without having to open up the wings. 

Please dont flame me too bad for running out of gas.  I think there are some things that can be learned.  

1. They say fly the airplane all the way to the scene of the crash.  I had to verbally, out loud tell myself to push the stick forward to keep from stalling.  All your brain wants to do is pull back on the stick to keep the plane in the air.  

2.  I was fortunately in a familiar place when it quit and knew right where I was going to land.  

3.  Think about what you will do if the prop stops on you.  

4.  I think there has got to be a better and safer way to set up the fuel system.  

5.  There is a 6% mortality rate to running out of gas.  

6.   Practice early on in your first 40 hrs learning how this aircraft performs as a glider.   

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Thanks for sharing your experience with this community Fred. This is how we learn.  

Fred, appreciate you opening up this discussion - no reason to flame.  You executed well under the circumstances and that you should certainly feel good about!  This discussion should also behoove the rest of us pilots to mentally rehearse how we might react in a similar scenario.  To address the fuel starvation issue, I will ask - have you seen the SkyTec video regarding the testing and development of a header tank install associated with a fuel injected Rotax engine? Here is a link to the header tank, , a bit of searching on the site or on YouTube will bring up the videos.  In my opinion it is definitely a valid solution to the problem.  I run a 350iS on my 750 STOL, with a simple on/off valve, this header tank, 1/2" lines and their sump along with a optical sensor in the header tank to a low fuel warning light and audio system.  If the header tank is ever less than full, I get a warning and I've got at least 10 minutes to get it on the ground with power.  Like you, when calibrating the fuel tank quantity gauges, I was not able to have fuel quantity indications until 2 gallons of fuel was in a fuel tank (same for each tank.)  Practically, that means when my gauges are near zero or zero I still have 4 gallons of fuel onboard in addition to the 1 gallon in the header tank.  Regardless, at that point I'm planning on being on the ground.  If not, I  am in a situation where the clock is running to find an airfield or off airport landing site before I get the low fuel warning.  I also have two FT-60 Red Cubes, and my fuel burn is averaging a bit over 4 gal/hr inclusive of pattern work and cruise.  I've verified this against fuel added and flight time over the past 70 hrs of using the engine.  When calibrating the tanks, I also calibrated a dipstick which I use before first flight of the day.  In the end, this means I am fairly confident in my onboard fuel, the fuel burn rate, and my approx 1 hr of reserve fuel which is essentially along for the ride.   Accordingly, I operate and plan my flights with these known factors.  Ideally, I wish the header tank was a bit bigger and had a visual type sight gauge on the side in addition to the optical sensor.  Another builder (Joe Harrington) has a 4 tank system installed along with this header tank.  He may be a good point of contact for some questions as well.  I haven't seen a lot of documentation/info regarding testing of the Viking header tank system as it relates to operating the UL350iS.  IMO, the retrofit for mounting on a completed airframe may be a bit of a challenge, but certainly doable.  Anyway, FWIW, add this info to your decision making matrix.

Congratulations on a sucessful engine out landing and recovery.  You did good!



Thanks for the reply.   Couple questions and comments.  Are the feed lines and the vent lines from the individual tanks open with no valves?   I saw in the video that they were concerned with fill rates.   Shouldn't the tank be full at all times until the last 3 liters?   I saw that they had some data regarding the fuel line diameter.  Obviously,  1/2 inch line will flow several orders faster than 3/8.  I have aluminum 3/8 lines from the tank to the wing root.  Just with gravity drainage I think my measured number was about 24 gal/hour thru the 3/ line. 

My questions about the viking installation are secondary to the volume of the tank and the ability to place it behind the back wall in the hell hole.  My other question was the ability to change the pumps on the firewall to internal tank pumps.   I'll check with viking before I get any further along. 


Where in the system do you have the red cubes?  I am installing the intake line between my fine filter and the intake and the out put after the one way check valve..  They also restrict the diameter to 1/4 inch thru the cube. 

Fred, will try to answer what I think you are asking me.

(1)  My 1/2" feed lines from the tanks each incorporate a service shutoff valve in the wing root area.  My vent lines run free and clear from the header back to the tank.  I did reduce the 1/2" vent lines to each tank down to 3/8" via a AN reducer.  Like you, I had already plumbed (with 3/8" aluminum) and closed the wing portion containing the vent return plumbing to the outboard side of the tank.  The right side tank fuel runs to the header through an additional crossover shutoff valve.  I believe the plumbing difference (longer path and additional valve) creates a fuel flow difference contributing to unbalanced fuel tanks, which is not significant in my mind.

(2) One way I can envision the header tank being less than full is when unporting the fuel tank outlet during sustained steep banks or steep descents with low fuel levels in the main tanks.  If leveling wings and pitch doesn't put out my fuel low warning lights/audio, then I may indeed only have what remains in the header.  Clock starts running for a landing area at the point.

(3)  I have the old style (Black) ECUs which requires two Red Cubes to give the Dynon the flow in and flow out data to calculate fuel flow rate via software.  Mine are located just after the fine filter prior to the injectors and just after the fuel pressure regulator outlet but before the one way check valve located by the header tank return tube.  If you have the new style ECUs, it use to be only one Red Cub was required to get fuel flow. But for some reason, I think that is also no longer the case and you may not even need a cube.  I am not certain but am curious, so I need to do some research.

Cheers!  Dave

David, I am building  a 750 stol with the UL350is and Skytek header tank and hardline kit. From viewing your posts and photos, it looks like you are running the same combination. I have searched your build photos ( very good source of info I might add) and cannot find a photo of a fuel valve between header and pumps. Did you install one? I am considering putting one on pilot side cabin wall between front seat support and firewall within easy reach and visibility. Also where did you route your supply and return hoses from engine to header tank? Any info would be appreciated. Thanks, Dean

Hi Dean, I did install a simple off/on ball valve just forward of the front seat support, halfway up from the doorsill and floor.  From there the fuel lines run a straight line to bulkhead fittings on the firewall and to the filter/pumps,etc.  So exactly the way you are considering it sounds like.  If I can grab a pic this week I will do so and post.  The downside is that I cannot reach the valve from the right seat if flying fron that side.  Supply and return lines (engine to header) are routed under the pilot seat, along the left cabin side to the firewall bulkhead fitting.  Following the forward fuselage stiffeners/longeron also keeps an adequate slope in the lines for drainage back to the low point of the fuel sysem where the sump is below the header tank.

Hope this helps, if not, keep asking!


Thanks Dave. 


Link to header tank design by Skytek and Rotax

Well done Fred!   

Impressive to to say the least and thanx for sharing.

I also went through mental gymnastics when building the plane regarding the fuel system including aerobatic type flexible intake lines in the tanks.   In the end went with stock system albeit aluminum fuel lines, dual gascolators and a nice fuel selector valve on console.

one thing that has been beat into my thick head over the years from some outstanding instructors and pilots is to never ever ever use aircraft fuel gauges and especially fuel flow meters to determine fuel quantity.   Manually dipping the tanks before each flight, especially during a break during cross country flights, and using rpm for fuel consumption is the only data which is real and then I still apply a big fudge factor.    The other lesson was to always fly with full tanks, one quarter tanks are considered empty.

After all kinds of fancy improvements to the fuel system lots of time and money have finally gone back to what they tried to teach me,  dip tanks rpm fuel consumption and fly with full tanks.     The nice glass cockpit displays and numbers are only to impress ground pounders.  Actually newest plane is all steam gauges,   yes I’ve become a Luddite!

I read with interest the previous discussions on the failed faucet fuel pump and have since removed same.   Fuel flow increased by two times during tests lol.

Just my experiences and thank you again for sharing yours.  

Cheers Vic

Fred, thank you for the Viking fuel system order.  Viking or UL, they all need a reliable low of fuel.  

Here is a writeup we did a while back:



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