Forced landing

17 posts in this topic

Posted

I had a little excitement last night. It was a beautiful evening. I wanted to check the deer and hunters out. Filled my tanks completely full. That gives me about a hour and half range. 45 minutes into my flight and around 18 miles from the airport I glanced at my fuel level and I only had about a inch of fuel showing in the sight window. I'm thinking what the hell. I was assuming the gas line from my outboard tank to the in board tank was kinked again. I headed straight back to the airport. Bucking a little headwind and flying straight into a setting sun at 200 agl I figured is not going to be a good thing. Finally hit the freeway that goes by the airport. Still 5 miles out. Tried crabbing the airplane wing high. While doing that I reached back and opened the bleed valve.  No more fuel draining into the header tank. In the back of my mind I did not want to land on the freeway. The sun was  right on the horizon so I would have been looking straight into it. I headed away from the highway still at 200 agl and 1 1/2 miles from the airport. Most of the crops have been harvested some fields plowed some not. With a standing corn field and a small river coming up I went through my emergency procedure in my head. Fan stops turning, nose down, look for a spot to land, fuel off, ignition off. I no more than crossed the river and it quit. Nose down, find a spot, fuel off, ignition off. Thank the Lord I was within gliding distance of a harvested bean field. I came close to the trees but made it over them into the field. This was about the only time I look at my airspeed on landing. I set it up at 60 ias. 30' off the ground I pulled full flaps. It was one of my better landings. After calming down a little I got out and checked things over. What I found is my gas cap vent on my outboard tank turned 180 degrees pointing to the rear. It drained some fuel on the wing. I checked the tank, it was full. After a couple of minutes I could hear fuel draining into my header tank. After a few minutes I had enough fuel to fly back to the airport  a  mile and a half away. Lesson learned, make sure your tanks are vented into the wind and I should have not tried to get back to the airport. If it would have quit 30 seconds earlier or later things would have turned out different. 

 

 

 

 

 

 

 

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Posted

Mark, it's time to rethink those wing-tanks.

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Posted (edited)

Jolly good thinking and flying - Glad you and the bird are OK - more experiences make better pilots  :BC: .  EDMO

Edited by EDMO

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Posted

Ha I love the ( thank the lord I'm with in gliding distance) So what would you say to the big guy if you weren't with in gliding distance LOL.

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Posted

I think the tanks are fine. I just need to fix the vent tube.

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Posted

Glad you're back at home safely with the bird. Those vent tubes will get you if they aren't correct for sure! I've heard many other stories of them causing planes to come down with full tanks. 

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Posted

Ohh, I love happy endings! :)

So was the cap not tightened or did the vent tube become loosened from the cap allowing it to swivel?

I assume you modified the cap to add the vent tube, what method or adhesive did you use to secure the tube?

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Posted

Glad it worked  out good for you.  Nice having lots of fields around.  (wish I had more)  JImChuk

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Posted

My new one has the vent tube in the inboard tank and nothing in the cap. Hope it doesn't try and push the fuel back to the outboard tank.

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Posted (edited)

I put vent-pressure tubes on all 4 of my tanks - If you only pressurize one tank it could make the gas siphon out of the other tank if they are connected.   Mine are only connected when I want them to be by opening both valves.   EDMO

Edited by EDMO

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Posted (edited)

Bandit, glad you had a happy end on your "adventure". My mantra when flying is "Always know where to land". Sometimes it prevent me from going where I want. "Height is safety" is another one... 

C5Engineer, you worry me... I can easily see 3 (bad) scenarios, there might be a 4th good one but 3 against 1 is not the odds you want.

A)  If your caps are relatively airtight the fuel flow will work only a short time (just enough not to return safely to the airfield...). As fuel lines are narrow very little, or no, air will go backwards through the line and replace the used fuel. A vacuum created when using the fuel would easily stop the flow. Even with some air coming through the caps it would reduce the flow as the flow of fuel will have to compete with the less effort flow of air from the inboard tank vent. See also (C).
Your vented inboard tank will be all you have to fly on.

If your caps are not even slightly airtight 2 things could happen...

B) A vacuum is created by the airflow and you can ask C5Engineer how fun that is...

C) A vacuum is not, or only partially, created by the airflow and the outboard tank remain, more or less, vented. If the ventilation of the inboard tank is good (vent turned into the wind and therefore creating a slight pressure in the inboard tank) this pressure can prevent the flow from the outboard tank. The result will be similar to (A), but maybe a few miles later...

D) Sure, you could always be lucky and have just the right amount of air getting through the caps and not to high pressure by the inboard tank vent... That is, however, walking on very thin ice...

And the really stupid scenario is when we have a vacuum on the inboard tank vent and it siphons fuel into the air directly from the correctly vented outboard tank... I think you would feel the smell easily so this probably would not go too far... 

So...
The outboard tank is feeding the inboard tank and any pressure in the inboard tank would be of harm as it could counter the flow into the inboard tank... 
We want a positive pressure in the outboard tank that will help the fuel flow but we actually don't need the additional pressure in the outboard tank.
Any vacuum created by the outboard caps (or bad vent line) will reduce the fuel flow and could even drain the outboard tank if the air but only if the fuel drained is replaced by other fuel or air. The fuel, or air, in the outboard tank could only be drained if replaced through the fuel line. The fuel line goes to the inboard tank or eventually to another outboard tank.

We are getting close now but let me tell you a story first.
I have, like the most of us, a Mikuni fuel pump. It is small and doesn't look very impressive.... I have a rather big (6 liter) inboard tank made of some fancy, very sturdy, plastic. The inboard tank has metal fitting molded into it. This inboard tank was full and both the inboard vent and the feed from the outboard tank were turned off... This was obviously not intentional...  
I taxied to the end of the field when the engine started coughing slightly. I increased the throttle and it stopped coughing, back on idle it coughed again so I taxied back. Better safe than sorry. That little piece of Japanese fuel pump had just done its job, sucking the fuel out of a closed container. The inboard tank was now deformed, imposed, to a degree I could never have done even by jumping on it. The metal fittings were no longer airtight so I had to get a new inboard tank.
This to say that we don't only count on gravity flow, we are getting the fuel sucked through the lines with more (negative) pressure than we might expect...

Yes to fuel, no to air...
The easy solution is to have an inboard tank without permanent ventilation. The only time you need to vent the inboard tank is when filling it up, i.e. when the outboard tank is empty and the inboard tank is being used as the last fuel supply and you fill up the outboard tank. With fuel in the outboard tank you can now vent the inboard tank until it is full (i.e. filled from the outboard tank). The inboard tank vent can therefore come out under the belly rather on top where you don't want it.
The outboard tank should always be vented. Creating a positive pressure (venting into the wind) is better as it will in best case create a positive pressure and in worst case at least not a vacuum. However, as explained above, a neutral vent will work just fine and even a vacuum will largely be compensated by the fuel pump suction (in the speeds we fly) under the condition that there is not another open vent in the system (like an always open vent on the inboard tank...).

Having a vented inboard tank is normally not a problem as long as the the outboard tank is correctly vented into the wind with a positive pressure created. But if the pressure is too great the inboard vent can bleed (we have seen many damaged lean roofs due to that). 

However, the only added value of having the inboard tank always open is when you cannot see, or measure, the fuel level in the inboard tank. The original Avid Flyer inboard tanks were all metal and no probe and therefore had to be always vented. 
Once air is in the inboard tank it will only be replacing the fuel going out with the same amount going in. I.e. is you empty the inboard tank to say 50% after having emptied the outboard tank, it will remain on ~50% even when you top of the outboard tank. (Sure there will be a slight compression of the air in the tank and maybe you will have it 55% filled...). Just temporarily open the inboard tank valve until new fuel chases the air... 

As controlling the fuel and air flows is critical I would suggest avoiding having outboard tanks communicate as an empty tank is a tank filled with air - feeding into what is supposed to be a fuel line! By manually switching from one wing tank to the other we keep a better control of the flows and the fuel remaining.

Placing a probe alerting when the fuel level goes down in the inboard tank and a led on the dashboard has made me fly more relaxed. Once the led start flashing I switch to the other wing tank, purge the air in the inboard tank through the inboard vent valve until the led stops flashing.   

 

Sorry about a long, soap box, post...

Regards

Fred

 

 
 

 

 



 

 

    

 

Edited by FredStork

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Posted

Glad you made it back safe.  I love the gas caps I installed on my AVID.  They are level with wing.  I simply drilled a hole in them and aluminum sodered (sorry for spelling) the tube in.  They will never spin in flight.

post-526-0-12959200-1369847016.jpg

 

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Posted

I know that feeling!  

10yrs ago in my KF2.  Took off with 4 gall in the "lap" tank behind the instrument panel, flipped the gravity drain valve open for the (full) aux wing tank.

Fly along a bit and I only have 2 gall in lower tank!?? (Later found xfer line was airlocked).

Made it to the airport... but eyeing roads and fields even more than normal.

But I really found it interesting how much I was talking myself out of a precautionary landing on a quiet country road....  Not good ADM!

Besides, it was my perfect excuse to exercise emergency authority and land on a road (something I have always wanted to do!)

Since that day, I have a new way of looking at the precautionary landing decision.

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Posted (edited)

We got a lot of "airlock" experience with the J3 - the STC for adding wing tanks said that they had shut-off valves on each and were to be used to fill the nose tank by gravity when it got low.  We found out that if the line to a wing tank had air in it the gas would not flow into the bottom of the nose tank if there was enough gas still in the nose tank.  What made the problem worse was that the lines had to be aluminum so you couldn't see the air or fuel in them.  EDMO

Edited by EDMO

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Posted (edited)

Ohh, I love happy endings! :)

So was the cap not tightened or did the vent tube become loosened from the cap allowing it to swivel?

I assume you modified the cap to add the vent tube, what method or adhesive did you use to secure the tube?

The problem with the polymer tanks is that the filler neck is threaded. When you turn the cap to tighten it the cap does not tighten to the same position. This is why I drilled the hole in the cap and pressed the vent in. This way I can turn the vent into the wind each time I fill it with fuel.

Edited by Bandit

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Posted

Bandit, if you always start turning from the same position (like from a mark on the cap facing forward) would you not always end up in approximately the same end position? My filler neck is threaded but the threads so big the there is only 2 or 3 entry positions allowing a fixed vent...

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Posted

Thanks Fred, good idea.  I will check that out.

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