Air Magically appeared in Header Tank

11-25-2013, 11:38 AM

Russ Kotlarek | Air Magically appeared in Header Tank

This past weekend I was down at Planemakers trying to help David transition into his new Seawind. The biggest stumbling block was several inches of air was appearing in the Header tank and yes it is a plugged but purgable tank.

After a couple days of searching for the source it ended up to be the boost pumps vented the bypass pressure into the header tank instead of one step further from the header tank back into the input of the pumps themselves. Cavitation of the fuel in the pumps created the bubbles and feeding it back into the header tank simply held it there.

Certainly the Airflow design works best in this arrangement having these return lines go back into the input of the pumps not all the way back to the header tank. I realize and argument could be made that a vented tank does not have this issue and correctly so as long as the vent line never becomes plugged nor pressurized a problem all of us know can exist. I still believe a Turbo Props fuel design is the most reliable but it does require power and most importantly a very difficult addition to an already built seawind.

Bottom line is the boost pumps create a fair amount of bubbles while cavitating so insuring those very real bubbles do not get trapped in the fuel system is worth checking into.


11-25-2013, 07:18 PM

Fred Lohr


thanks for you input on this topic. I have to say that after our discussions on the great "to vent or not to vent" contoversy, i now agree that there is no downside to having the optical moniter in your header tank. But here is my next question on the mystery of how air gets in to the header.. Are we talking about air or vaporized fuel? They are two different things. So you propose that the pumps cavitate and then deliver those bubbles to the header as you suggest in some setups., are those gases vaporized fuel, or dissloved air or some mixture of both? Vaporized fule would "unvaporize" pretty quickly if its not hot, right? Why are the pumps cavitating in the first place? And maybe it is just a pinhole leak that allows air in on the suctionside of the pump, or a bad regualator that allows air in. If it is a diaphragm style regulator, it will go bad sooner or later.. The original kit regulators supplied with the mallory pumps went bad for sure. the airflow one has not been a problem..

As you can see, I have more questions than answers, but your input is very thought provoking... For me, I will always vent the has worked for 8 years now.

11-25-2013, 08:37 PM

Russ Kotlarek

I'm the last person to fully understand cavitation but from what I have read on the web it is a real process that under huge pressures differences can create bubbles that can even go as far as to lean out an engine. My guess is we do not have pressures near that level in the Airflow pumps that will lean an engine as those bubbles continue to flow through but if gathered in a Header tank could result in a bad day some day.

However, vent or not you are correct an optical sensor in the header tank would be the best warning system of such oddities happening under any circumstances.

Plane Makers is actually installing these sensors without removing the tank by drilling and tapping the holes they have found good success in sealing up the sensor without a Weld Bung.

11-26-2013, 08:16 AM


Interresting thoughts....

I would have assumed that any "return fuel" would go directly back to the main tanks where they can vent properly.

I have had unvented and vented. I have proved to myself that vented headers, any way you do it, is the best way to go.

12-06-2013, 07:43 PM

keithw | Header Tank/ Fuel System/Vent Non Vent

I have 540 Hours on N80CC, 12 AirVenture Cup race"s (Two of which were the 1000 mile contests from the east coast (wright bros. first flight to Oshkosh Wi.) and many hours pushing 22/23 gal per hour/ hour after hour and never , I reiterate Never! Never!Never! have I had a single fuel glitch hicup Nothing Nothing Nada!!!!!!!!!!!! THE HEADER TANK MUST BE VENTED TO THE LOW PRESSURE SIDE OF THE EPENAGE. THIS IS BY THE BOOK, BOOK BOOK!!!!!!!!! Get all the details from the SNA Build Manual. I doubt that anyone has even looked at it for ???????? ever. I built N80CC by the book. John at Planemakers was my Guidenace and Direction. Read my testimony where I wrote "i firmly beleive that I am flying the finist airplane made" Keith Joseph Walljasper Builder/Pilot Seawind N80CC

12-08-2013, 10:16 AM



I would still install fuel level sensors in the header tanks......

12-08-2013, 10:42 AM

Russ Kotlarek

Agreed Mike... I have heard never so many times and with all do respect to those who have flown for such a long time does it really hurt to know for sure if your header tank is being drawn down even a couple inches by putting in some type of sensor.

One never knows when a leak or condition could develop and knowing is indeed the key to possibly making a very bad possibly fatal day nothing more than a blink on the dash. Please put the sensors in owners it is so minor and so effective.


12-08-2013, 11:37 AM

keithw | Never,never

Russ and Mike I hope I "never" have to retract this Message and the previous one but I would like to ask the question, What is the procedure for imeadiate action when the sensor indicates low "LOW HEADER TANK FUEL LEVEL" Land and vent the header tank? Russ, you sure have me thinking about the header tank sensors. I like the Idea and am in no way negative of this precautionary adition to the system. My thought is that once that alarm,light ?--- is indicated in flight, (what to do) As i think about this situation( I want to know more) No. 1 Is the level continuing to drop and at what rate? No. 2 Is the level fluctuating between no light meaning full and 75% light? Russ, Those that have been installed are at what level 75% full? No. 3 I want to know if the level continues to drop to 50% full. No.4 I want to know if the level is cotinuing on to 25% and 0% ???????? As this progression continues the pilot has some very factual information to guide his actions. My thoughts are that I will proceed with plans to modify my header tank with no less than at less than 4 (four) sensors. Will advise as this long winter sets in. Keith Walljasper N 80 CHARLEY CHARLEY God Bless You All and Have A Merry Christmas P S Mike in Canada Tell us about your trip home from Planemakers and the low header tank lights. Please as I cant remember all the details,

12-08-2013, 03:51 PM

Fred Lohr

i agree with everything keith said about vented header tanks and by the book fuel system and venting with minimal modifications. Some reasonable changes to the book include improved airlfow performance dual fuel pumps with regulator and 1/2 inch lines from the tanks with ball valves added at the wing roots.

How about putting in a fuel probe with a digital guage readout on the dash for that header tank...Only one hole, with more information. like how low is it and how fast is it moving under what conditions. you could add an audible or visual alert light or beep next to the guage when it gets to a predetermined level.

Many of the flat screen display manufacturers (such as the GRT) have the capacity to display extra stuff like fuel levels. some even sell the probes. might be a good winter project.

12-08-2013, 04:40 PM


When I flew my plane home from Florida (just after purchase with a capped header tank vent) over Jacksonville at 5500 my low header fuel level light came on. First thing that came to mind... What the hell is this light for? OH CRAP! I pulled back on the throttle just enough to keep me in the air and called Jacksonville to alert them I might be coming in. I circled a few times loosing a slight bit of altitude. About 2 min later the light went off and I went back on course. Slowly increasing power... No problems the rest of the way home. About 3 months later I was at KMSV doing a few touch n go's & full stops. I was taking off when the light came on again. Can't pull back throttle to much or I’ll end up in the woods. Leveled off, light went off. I landed. Nothing looked wrong so I tried it again. In the pattern the light came on again so I throttled back and landed. This time I opened the vent and all I could hear is the air rushing in or out? Before taking off again I reconnected the vent. Now the header is vented. All was great after that, no problems. This got me to thinking about the header tank. What if I had a clog in the vent line and or a clog in the fuel line? I decided to add a second header tank and three sensors in each tank. One is a level sensor which is in the top of the tank, one is a few inches down from the top and the other is where the fuel exits the header. The sensors are on a very very bright red led to get my attention.

So in answer to your 1st question; what do you do if the light comes on? This depends where you are in flight. Either way I will pull the throttle just enough to keep me in the air and land ASAP. The more I think about it circling was the wrong thing to do especially if the problem is due to uncoordinated turns. Straight and level or as close to level would have been better.

1- Why would it be dropping or continuing to drop? Uncoordinated turns, clogged or no vent, vent tube on side of pylon cut wrong sucking the fuel out thru the vent line to mention a few.

2- Depends on where the sensors are.

3 & 4 - Why wait LAND... The header tanks only hold approximately 16 ounces. That will go fast!! Maybe 1-2 Minutes.

One good point about throttling back is that in case of an engine failure the plane will not abruptly nose up since the power setting will be low

One of the best things you can do is increase the fuel lines from the wing root to the engine with minimum ½ “ lines.

Just my 2.5 cents

12-09-2013, 09:48 AM

keithw | keep the ideas comming

Hey Love all the input. Fred love the full blowen fuel level system in the header tank. Keith

12-11-2013, 12:25 AM

mike reibling | Air in my header tank

I'm glad to see people are talking now... I have been up to my eyeballs busy and haven't had the time to contribute.... sorry.

As some of you know I put a sensor in last spring and it has alarmed off and on ever since. I have put on over 100 plus hours since.

I can't seem to find any clues yet but one thing I haven't tried is turning off my fuel pumps yet to see if that has any effect.

Keith ... you make a good point... what do you do if it alarms?

Well I can tell you.... you get pretty dam concerned the first few times.

I think my plane has been doing this all along...700 plus hours now.

I don't like it and I will be happy when I get an answer but I don't think the engine is likely to fail.

All I can say is it is happening......and we all should try to figure it out.

So far I have tried adjusting speed, yaw and plugged my vent all of these had no effect. It didn't feel very good when it alarmed and I new my vent was plugged.

I can say it has always taken about 20 to 30 minutes minimum after take-off before it alarmed.

In response to Fred.... yes more sensors the better... one is just enough to cause extra stress.

Mike Reibling

12-11-2013, 05:09 PM

Tom Saccio | Air in header tanks

A while back, I installed one sensor in each of my two header tanks. Since then, I've had two flights of about 3.5 hours each. I have no vents in the wings, the header tanks have no vents either. All the tanks are piped into tees inside the plane and off the tees the lines go up to and under the engine inside the cowling. I have never had an issue with low fuel in the header tanks. I also have lines connected to the tops of my header tanks that connect to a saf-air valve that is outside the plane in the wheel well. Before each flight I push the saf-air valve to see if any air escapes. None has as of this posting. Let's keeping hoping all stays well.

12-12-2013, 12:00 AM

mike reibling | air in header tank

Tom ... how big are your header tanks and what fuel pumps are you using?

Have you got the plane maker sensors in your tanks?

Mike Reibling

12-12-2013, 08:54 AM

Tom Saccio | Air in header tanks

My header tanks only hold about 2 qts of fuel. They are the original tanks that came with the kit. The sensors are from Plane Makers and the fuel pumps are the duel pumps from Air FLow. MY pumps are only used to prime the engine for starting. I've never used them in flight. There never seemed to be a need for them.

12-15-2013, 11:14 AM

mike reibling | air in the header tank

Has anyone else put sensors in and experienced the air in the header tank issue?

Mike R

12-15-2013, 05:12 PM



12-21-2013, 09:11 AM

Fred Lohr

so i am kind of bored cause i cant fly my seawind, and have been thinking about this header fuel guage thing. Here is the quandry... i have close to 900 hrs on my seawind and have never had a hiccup from the engine. Vented Header. So if I add sensors or sender and it lights up from time to time i have created what? Anxiety! Turmoil! Distrust!... To Those Seawind Pilots with incredibly hot, sexy, insatiable, playboy model wives or girlfriends (approximately 90% of us i would guess) this is analagous to spying on them to see if they might be cheating.

Do you really want to know and ruin everything?

That being said, if i did want to spy on my header tank, i might add this sender

Westach model 395-5s-1b-5 (aircraft spruce 10-01262) and a digital guage

like Belite digital (aircraft spruce 10-05312).

As to the mystery of how air gets in...Does anybody know how the fuel pressure regulators behave when subjected to suction? They are designed to shunt pressurized fuel back to the header at a certain pressure, but what happens when you apply a vacuum to them, such as with an engine driven pump sucking fuel up from an unvented header. At what negative pressure will the regualtor allow air into the system? Can the diaphragm or spring loaded washer or whateverit is wear over time and leak a little under suction?

Food for thought. I have to attend to my wife now.

12-22-2013, 12:28 PM

mike reibling | Air in the header tank

Fred.... If I thought like that I would have to remove the phone & email bugs and GPS tracker off of my wife. I feel trust is very important.

You must have been a comedian in your previous life?

Keep it up.

Fred.... I am taking your approach but I still think there is something to be learned and I wish I have more than one sensor. It's 10:00am Sunday it's sunny and - 30 but my baby is in a heated hanger now so I'm going flying today.

Marry Christmas to all and hopefully you all get high during the holidays.

Mike & Kris Reibling

12-22-2013, 02:07 PM


This is going to be a tough act to follow...

12-22-2013, 02:42 PM

Tom Saccio | Air in the header tank

I just let my wife run rampant. I stuck a sensor in her once and she didn't like it.

01-21-2014, 10:35 AM

Larry Brunzlick

I still do not understand why Seawind went with such a complicated fuel system- header tanks with separate vents and all.

I copied the fuel system used on Pipers and probably many other certificated planes. It is tried and true with probably over a million hours on the entire fleet(s).

½ inch fuel lines from the wing tanks to the fuel selector switch, then to the electric boost pump (I have an Air Flow performance dual system), then to the engine driven pump and engine. There is a fuel filter between the electric and engine driven pumps which is not nearly as efficient as the filter on the injector induction servo but that’s a different story. I will be checking that filter every 20 hrs. until I no longer find a significant amount of grit.

The wing tanks of course have to be vented. Some certified aircraft have venting fuel tank caps. But since we have sealed caps, I have wing tip vents tied to both wing tanks and tied to an additional vent that goes up to the engine compartment and has a large bug proof screen on it. I used 5/16 inch lines rather than the standard ¼ inch.