Header tank or not

Installing a UL350is in a Cruzer and am pondering a header tank. There seems to be a lot of good reasons to have one a only a few not to. The possibility of voiding a fuel line during uncoordinated flight is not a worry with a header tank. A duplex fuel valve is not required. A header tank adds a bit to the expense and has a couple of gallons of fuel in the fuselage.

I would appreciate hearing from anybody with some experience and advice with this method.

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Permalink Reply by Jan Eggenfellner on January 11, 2018 at 8:17pm

Yes, the unusable fuel is too much if fuel is returned to the tanks

Permalink Reply by Jan Eggenfellner on January 11, 2018 at 7:48pm

Perfect idea.  The header tank system is by far the simplest and safest way to plumb a fuel injected engine.

Safety of the fuel injected light sport aircraft engine fuel system

A SOLID FUEL SYSTEM IS IMPORTANT FOR ANY AIRCRAFT ENGINE.  THESE ARE THE SYSTEMS USED BY THE THREE MOST POPULAR LIGHT AIRCRAFT ENGINES IN USE

TYPE OF FUEL SYSTEMS USED

ROTAX

  • Dual external fuel pumps
  • External single fuel regulator
  • Fuel return commonly back to primary fuel tanks
  • 6 port duplex fuel selector valve

VIKING

  • Dual in-tank pumps
  • In-tank dual fuel regulators
  • Header tank based system
  • No fuel valve needed

UL

  • Dual external fuel pumps
  • External single fuel regulator
  • Fuel return commonly back to primary fuel tanks
  • 6 port duplex fuel selector valve

 

EXTERNAL FUEL PUMPS

  • UL and Rotax use external fuel pumps for their injected engines.  They are a copy of what was used in cars prior to 1998.
  • When 2 pumps are used together, for takeoff and landing, the amperage draw can be 10-14.   This is a lot since these engines are not equipped with good alternator systems.   Even with a single pump running, the draw is scary high if either the generator or external voltage regulator were to fail.  The dual fuel injectors and sparkplugs cannot work without electricity.  
  • External pumps produce close to 2 x the required fuel pressure for the injectors.  The excess pressure is regulated back down, using an engine mounted fuel regulator.  Excess fuel is returned to the fuel tank.  
  • All this additional fuel, when returned, brings heated fuel to the tank.  The total fuel circulating between the main fuel tank and the engine, then returned, is about 30-35 GPH.  
  • Due to the excessive fuel circulating, the amount of fuel gravity fed to the firewall mounted pumps is also 30-35 GPH.  Hence the large hoses specified.
  • Rotax and UL each use a single fuel regulator at the end of the fuel rail, mounted to the hot, air cooled cylinders.  The Rotax brand is likely to be Bosh but the UL is a no-name copy.  Each is filled with rubber parts and will fail, sooner or later.
  • This is now an antiquated way to feed fuel to a fuel injected engine.  

 

EXTERNAL FUEL REGULATOR

What is the big deal about a fuel regulator?  Well, what is the big deal about a wing attachment bolt?

  • The external fuel regulator is the single point of failure in a UL or Rotax injection system. 
  • An external regulator require external fuel return hoses
  • The regulators used are automotive quality and have a definite life span.
  • The engine ECU (control computer) knows nothing about fuel pressure.  If the pressure is wrong, the engine will not operate correctly, no matter how many sparkplugs it has.
  • A single fuel pressure regulator is not consistent with any other dual capability.  The engine cannot run without it.
  • ASTM was never informed of this. 

 

 

INTERNAL FUEL PUMPS AND FUEL REGULATORS

  • The Viking fuel system does not use a 35 gph gravity drain system, a single fuel regulator or a complex 6 port fuel selector valve.  
  • The Viking system is based on dual, in- tank pumps, each equipped with its own fuel regulator.
  • Each pump draw less than 1.6A and have no external fuel return hoses.
  • Only the amount of fuel used by the engine is gravity fed from the main fuel tanks to the header tank
  • A fuel level gauge measure the exact fuel level of the header tank, providing accurate fuel gauging. 

 

ISSUES RELATED TO SYSTEMS DRAWING / RETURNING FUEL FROM / TO A MAIN FUEL TANK

  • A fuel injected engine MUST have a solid fuel pressure at all times, or the engine will stop
  • Having reliable gravity feed, all the way from the wing tanks to the firewall mounted pumps, of 30-35 gallons / hour is much harder than the 2-12 GPH that the engine is actually using.  When this system was used by cars, the pump was mounted right below the fuel tank.
  • There is an illusion that these systems work because fuel usually come out of the pump when turned on.  What is not so obvious is how small the margin is for the system to stop working. 
  • It is likely that even though the pump was never designed to pull fuel on the suction side, that in the airplane application it actually does this to keep up with demand.  Since there is suction, any air leak prior to the pump has the potential for pump cavitation.   An O-ring leak in a fuel drain, gascolator or selector valve would not be good. 
  • Since the fuel is at low pressure (suction) as it enters the hot engine compartment, any exposed metal fuel pump body or fuel system component could cause the fuel to boil and cavitate the pump, dropping the pressure from 43.5 psi to less than 10 psi.  Once the pressure has been dropped, the pump will not be able to re-gain pressure due to the 43 psi fuel regulator at the other end of the engine fuel rail.  (Here is where a small bleed bypass around the pressure regulator would be handy but this is not implemented by either Rotax or UL.  The bleed would allow some fuel to flow, re-priming the pump with fresh fuel and again be able to make pressure) 
  • A larger amount of unusable fuel.  Because more fuel is being returned to the tank, than is used by the engine, fuel is on the move in the tank and not always available at the pickup location.  To guard against this, more fuel must be kept in the tank, shortening the available range.  Also, as the fuel level decrease in the tank, the warm return fuel becomes more and more pronounced and pump cavitation is even more likely.
  • Serious concern of un-porting the fuel pickup location.  As mentioned above, one second without fuel pressure is one second the engine will not operate.  Carbureted engines have a fuel bowl from which the engine can draw fuel.   Not so with an injected engine.  There has to be fuel available to the pump at all times.  With low fuel, and in an extended descent, this is usually not the case.  Some installations add more complexity to the system by the installations of door-post mounted “sumps” in order to have some protection from this.  However, keep in mind that these fuel pockets only last for a few seconds when the system wants to pump 35 GPH in a circle.  The pump will draw the fuel from the pocket in no time flat, bringing back the un-porting issue.

 

THE FUEL SELECTOR VALVE

  • The UL and Rotax systems usually use a duplex / 6 port fuel selector valve.  These are complex, costly and have 6 fuel line connections right inside the cabin.  Another style is from a pickup truck with dual fuel tanks.  These are of terrible quality and are electrically operated.  Cut one open and inspect the construction if considering using one.  Again, there is no backup so be sure it works. 
  • Viking does not use a fuel selector valve.  Fuel simply drains from the two wing tanks into a single header tank.  From there, no selection is required.  The popular C-150 also has no fuel selector. 

 

SO, WHY IS THE VIKING SYSTEM BETTER AND HOW DOES IT WORK

  • The Viking system consists of a header tank and two fuel pumps.  That’s it.  Fuel fills the header tank by gravity.  If the engine uses 6 GPH, the system only has to flow 3 gallons from each wing tank.  (only about 1 qt every 5 minutes)
  • The pumps are inside the tank and submerged in fuel, just like every modern fuel injected car.  The fuel regulators are right on the pump bodies, pre-filer screens are part of the system, etc. 
  • A precise fuel sender unit and gauge are available, allowing the main tanks to be used to a lower level with complete confidence.  The 30 min VFR daytime reserve is in the header. 

 

CAN I USE A VIKING HEADER TANK WITH A UL OR ROTAX ENGINE

  • The short answer is – yes you can.  Viking has such a system and it is being tested on a UL engine.  The long answer is much more complex and you need to understand it if you are contemplating such a conversion.  Here are the details.
  • First it is important to understand how the original system works and the reason for why things are the way they are. 
  • Fuel pumps:  The fuel pumps are big, heavy and draw a lot of current for a reason.  In order to reliably produce 43 psi of pressure, additional capacity is used, and then regulated down.  Because the pumps are external to the fuel, they are only cooled by the fuel running through them and by convection.  If the pump slowly got hotter and hotter during operation, a vapor situation would surely occur.   
  • In order to use fuel for pump cooling, excess fuel needs to flow through the pump.  Most systems run 3-5 times more fuel through the pump than what is used by the engine.  The main reason the fuel is returned back to the fuel tank is to cool it.  The fuel also cool the fuel rail and purges air from the rail when first primed for starting.  
  • If we eliminate the large pumps, we also eliminate some of the heat put into the fuel.  Some fuel must still be returned to the header tank since these fuel rails are not designed to purge air without a return at the last injector.  A small amount of return also helps cooling the fuel injectors. 

 

 

THE VIKING HEADER TANK SYSTEM USED ON THE UL OR ROTAX ENGINES

  • The system operates exactly as if used on a Viking engine, with one exception.  There is a small amount of calculated fuel return from the fuel rail back to the header tank.  The existing fuel regulator is replaced with a bleed large enough to purge air from the system but small enough for the in-tank pumps / regulators to easily maintain 43 psi of rail pressure.  

Test setup with pump and fuel return

UL pressure regulator replaced with machined part to provide steady return along with pressure control from in tank dual fuel regulator.

Measuring return fuel amount.

keeping an eye on fuel pressure

Related VIDEO

Viking Fuel System 1

Views: 329

Comment

Comment by Jan Eggenfellner on November 28, 2017 at 6:04am
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Actually, the fuel pumps are the shutoff valves and are in the header tank.  So no valves at all, anywhere.  The fuel can run in a continuous aluminum line, inside a thin PVC conduit, all the way from the aft service bay through the firewall.  I suggest finding a place for such a conduit in order to run other essential stuff as well. One on each side of the fuselage is even better.  In any case, no high fuel pressure connections anywhere inside the airplane.  Gascolater is not used.  The header tank itself has provisions for the installation of a fuel drain.  Also, because the pumps regulate / circulate fuel internal to the tank, no fuel is ever stationary for water to collect into a pocket, during operation. 

Be careful about your definition of a Rotax "Engine Failure"   A fuel system failure is not an engine failure.  It can however cause the engine to shut down :)

Comment by Geoff Klestadt on November 27, 2017 at 10:01pm
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The only downside I can see with Jans design is that you have high pressure fuel lines in the cockpit (at least on a Ch750) and where to put the gascolater and fuel shutoff which will both be I think, working under pressure. Jans design also i think, fixes an issue with the rotax pumps getting vapour locked in some installations on hot days - instant engine failure.
Comment by Jan Eggenfellner on November 20, 2017 at 2:47pm
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Yes, the latest fuel system has only been available for one year

Comment by Mark Charles Kuba on November 20, 2017 at 2:24pm
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I have a 110 Viking it is different it returns fuel to the tanks.

Permalink Reply by Jan Eggenfellner on January 11, 2018 at 7:51pm
Comment by Jan Eggenfellner on November 13, 2017 at 8:49pm
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Hi, Dave
Each in-fuel pump has it’s own regulator. So no issue there.
Your engine has the same style regulator out on the engine. The difference is that there is just one of them. Dual everything but not the regulator. Your question also touch on a more complex issue regarding the vacuum compensation of the fuel regulator. Not sure if that is your real comment but to touch on that issue, keep in mind that the manifold vacuum is close to atmospheric since the throttle is usually open. Also, the fuel regulator has a very minimal control of the mixture above 75% power.
Comment by David J. Beaulieu on November 13, 2017 at 1:53pm
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Jan, thanks for bringing up the discussion.  Interesting, informative and will help most of us with our considerations regarding fuel systems and fuel injected engines.  I'm running a UL350iS and can see the merit of a machined part to maintain pressure through the rail (eliminate a moving part with a limited useful life), but how do you compensate for altitude change and maintaining a three bar differential to atmospheric?  In your system, is that done via the pump's regulator?  Dave (happy user of the Viking Steel Bungee)

Permalink Reply by Oliver Reik on January 12, 2018 at 6:46pm

Jan,

I don't know why the moderators let you do this, but I consider all your posts in this thread as aggressive marketing of your header tanks and a sales pitch for your engines.

It should be pointed out (especially since your're again bashing you competitors for allegedly selling outdated technology), that a GDI fuel injection system looks very different than a port fuel injected system and that it depends, in addition to the two electrical low pressure pumps, on a single high pressure pump, which actually adds another potential single point of failure. This high pressure pump increases the fuel pressure to over 200 bar. You now have a fuel line with around 3 bar running through the cabin which ends on a plastic(!!!) connector on the Viking 130 engine, which again increases the pressure to +200 bars.

GDI is more modern than port fuel injection? Maybe. A lot more stuff to go wrong? Absolutely!  Particularly in aviation more 'modern' is certainly not always better. I guess there is a reason why Rotax laid out their iS engine the way they did... 

@everybody

I would strongly recommend for anybody who is potentially interested in installing a header tank, particularly if it also replaced the original fuel pumps and regulators, to consult with the manufacturer of your engine. The fuel pressure regulator in any fuel injected engine depends on a certain pressure at a certain flow. Viking doesn't publish any specifications, the low current draw however suggest that the pump a significantly less powerful that the pumps used by ULPower, AeroMomentum or Rotax.

Also make sure that the pressure of the pump is sufficient and that the pressure drop on the long way from the header tank to the engine is withing acceptable limits.

Another thing to look at is if the fuel remains sufficiently cool under all circumstances. If the return fuel is pumped back into the wing tanks, it has quite a bit of time and a big surface to cool down. If it is only returned to a header tank, it will heat up much faster, increasing the risk of vapor lock.

Finally, think about where you want to have shut valves and if you want to maintain the capability to draw fuel only from one of the wing tanks: The system will very quickly become very complex!

We decided to run steel braided, single piece fuel hoses to this Andair duplex fuel selector: http://www.andair.co.uk/product/duplex-fuel-selector-fs2020-d2/

Two fuel lines from the selector to / from the engine and two lines to / from each tank. Very simple, clean and easy to operate.

As mentioned in my other post I am absolutely not opposing header tanks, but they also come with some significant disadvantages which should also be taken into consideration. Keep in mind, that problems with the fuel system are the #1 reason of engine failures in experimentals! 

Permalink Reply by Jan Eggenfellner on January 12, 2018 at 8:20pm

You should read them as advise from someone that has done this for 30 years.  I know you are not able to do that.  In any case, I will not try to convince you of anything.  You have your mind set.  

I will now just report on the findings made from the testing going on.  Much more enjoyable )

Permalink Reply by Oliver Reik on January 12, 2018 at 11:13pm

Jan,

As mentioned in my response to Loren, my main point is that you should IMHO not disguise your promotional posts as helpful responses to an OP's question as the ultimate truth. Leaving competitors out of the game also wouldn't hurt. Just scroll through the thread, most of it is consumed by your promotional posts and videos, badmouthing other solutions.

Back on topic, I wonder how you can so confidentially say that your fuel pumps would be compatible with the ULPower or other fuel injected engines?
Please share your pump’s flow / pressure diagram here in this forum.
I would also like to know what ULPower’s requirements are, in order for their fuel injection system to function properly?
Are you suggesting that the OP should remove the original pressure regulators and block off the rail? If yes, will there be a downside to it? What about vapor lock?

I don't think you want to seriously brag about your experience!? While I recognize the success of Viking, I rather look at companies, who sold thousands of engines with combined millions of hours on them. As far as I now, none of the current certified aircraft, which are equipped with fuel injected engines, is using a header tank. Also, non of them is direct injected.
Van's, who recently reported the first flight of its 10,000st plane, of which many are fuel injected, also doesn't use header tanks.

Rotax, who sold in 2014 their 50,000st carbureted 912, who put thousands of hours of testing on their fuel injected iS variant and who already accumulated many, many, thousands of hours with this engine in the field, also consciously decided to go with port fuel injection and is using external fuel pumps as well as an external pressure regulator for their installations.
Interestingly, they decided to make everything, including sensors, redundant. What do you say about that?
They actually published a video in which they discuss in detail their choices regarding the installation of a 912iS in a CH750. They decided to go with a header tank as they were concerned about unporting the of the tanks, but purposely wanted to have external high flow fuel pumps, to get possible air bubbles out of the system: http://www.rotax-owner.com/en/videos-topmenu/builder/415-bs-750-2
This is an interesting choice, which I respect. I however made a different decision, as under normal circumstances air in the system is not really a problem, even in an uncoordinated turn: While the fuel pick up in the lower tank might indeed become unported in an uncoordinated turn, the fuel would actually cross feed from the higher tanks into the unported lower tank if the fuel selector is set to 'both', rather than that air would be sucked in.

I like your clean header tank solution, but particularly in aviation there is almost never a simple answer to questions like the one raised by the OP.

Permalink Reply by Loren Warner on January 12, 2018 at 8:57pm

John Bell asked "I would appreciate hearing from anybody with some experience and advice with this method."  

Many builders share their experience and knowledge, but I doubt you will find anyone with as much research and experience as Jan has on this topic.  Unless I'm mistaken, no one is preventing representatives from UL, AeroMomentum, Rotax, etc from answering John Bell's question, so why don't they?   

Permalink Reply by Oliver Reik on January 12, 2018 at 11:12pm

I actually also think that it would certainly be beneficial for any company who wants to sell anything to Zenith owners and builders (actually including Zenith themselves) if they would frequent forums like this, answer questions, give advice and maybe even inform about their products.

In my opinion, GRT, Garmin and Dynon are for example doing outstanding jobs in this regards in the Vansairforce forum. None of them ever badmouthes any of their competitors, their posts are always carefully crafted and strike a factual tone.  

Jan however often suggests, like in this thread, that any solution, other than the one he coincidentally happens to sell, is outdated and inferior.

This is a tone I don't like in his marketing e-mails and which I find simply wrong and misleading when the are disguised as 'helpful' responses to an OPs honest question about the pros and cons of a header tank.

Permalink Reply by Loren Warner on January 13, 2018 at 12:02am

I'm sure that most members are able to take the information offered by Jan, and others, and come to their own conclusion.  I happen to find Jan's research and suggestions to be very well thought out, and I do not take offense if he, or anyone else, happens to profit as a result of the information they share.

Permalink Reply by John Austin on January 13, 2018 at 7:24am

Unless I'm mistaken, no one is preventing representatives from UL, AeroMomentum, Rotax, etc from answering John Bell's question, so why don't they? 

Loren,

The Zenith.aero Forums does not allow commercial or business use of the Forums, i.e., doesn't want vendors advertising or conducting business on the Forums.  Members tell me that they want these forums to be unbiased discussions between builders and flyers that aren't trying to sell them anything.

I think you don't hear from the other engine vendors because (a) one must be a member of Zenith.aero to participate and therefore actually build and fly Zenith aircraft, (b) they respect our member rules, and (c) know that in the EAB community, word of mouth advertising from actual customers is the most effective marketing for their engines.

Quite frankly, if all the engine vendors jumped in here with pages and pages of photos and videos, biased comments (how can you sell something and not be unbiased?), or slammed their competitors, the non-vendor members would have difficulty keeping a coherent, unbiased conversation going among themselves ... which is what the Forums are all about!  Most vendors have readily accessible websites and I would encourage members to visit them, gather information, and freely discuss here on the forums the pros, cons, and ownership experiences.

John

Zenith.aero Forum Moderator

Permalink Reply by Loren Warner on January 13, 2018 at 9:14am

John,

Oops, I forgot they had to be members to chime-in.  

Permalink Reply by Darryl Legg on January 14, 2018 at 3:06am

I too find that the posts by Mr Eggenfellner extremely biased and nothing short of pushing his products through this forum, and his rude scathing criticisms of other products as very derogatory. I am not sure anymore if this is the Zenith builders and flyers forum or the Viking advertising forum. Other business owners do not push there products as they have more class and not as blatently crass as this man. He should be removed from pushing his products all the time. Look at this thread, it has become the viking fuel system forum.

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