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Fuel vents on yak fuel tanks

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javiercarrascob

Joined: 06 Sep 2009
Posts: 62
Location: Virginia

Posted: Thu Jul 28, 2011 7:12 pm Post subject: Fuel vents on yak fuel tanks

Hello Team,



I'd been following the "fuel flow from tanks" topic and in the same token I have a question regarding the Fuel Vents.



I have noticed small drops falling from the right wing (when looking at it sitting in flying position in my Yak-55m), the first time I noticed was doing vertical flight but I dismissed as condensation or rain as the plane sat overnight with no covers while there was a storm (and yes as soon as I preflight the plane I saw water coming off the ailerons.)



So I decided to look at again and I can see what I think is fuel drops leaving the plane from the right wing while doing acro (inverted or vertical) but it is only from the right wing and it does not amount to anything on the fuel levels (if I fly heavy on the right wing I have more fuel there if I fly heavy on the left, it cross feed to the left).



While I do cross country, there is no loss of fuel so leveled flight or seating on the tarmac means no fuel loss.



So is this normal? and I never noticed before? I assume that some fuel will get caught in the fuel vents and can drip off. but I rather hear your opinions.



Thanks, Javier

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CD 2.0

Joined: 21 Feb 2011
Posts: 43

Posted: Thu Jul 28, 2011 10:48 pm Post subject: Re: Fuel vents on yak fuel tanks

Javier, a few years a go, a Yak 50 had a fuel leak happening only while practicing aerobatics.  The aircraft was landed for inspection and the A&P's found nothing.  They opened all access doors and panels looking for signs of leaking fuel and found no evidence.  Flying again and everything went normally until a snaproll at the top of a loop was performed at approximately 2300 ft. At this time fuel fumes filled the cockpit and raw fuel was seen in the cockpit... as the aircraft accelerated down to the backside of the loop, pilot's vision was blurry and the fumes were significant.  Landing safely, they now discovered a significant crack in the fuel tank.  



Apparently a static grounding tab welded to the tank had more than likely resulted in excessive stress being applied to it from a bonding strap that did not have enough slack. During repeated high G aerobatic flight, the lack of slack in the bonding strap caused it to pull on the welded tab attached to the fuel tank which then caused the beginning of the crack (and resultant fuel leak) to form. The faint initial fuel fumes that the pilot experienced earlier were when the crack was just beginning to form and under heavy G loading a very small amount of fuel leaked out. The design of the tank and the location of the crack caused it to finally leak badly only when it was nearly full and negative G was applied. 



It could be just a simple loose connection in the fuel system but the fact that it only leaks while pulling G's could indicate that it's something else.  Check if the fuel tank grounding tab weld is damaged or cracked causing the fuel leak. If the tank is shifted from its mountings it could strain the tank ground strap attached to the tank grounding tab and every heavy 'G' loading could apply excessive stress to the tank tab.



Keep us posted with this issue. 

Carl



 	  javiercarrascob wrote: 	
		  Hello Team,



I'd been following the "fuel flow from tanks" topic and in the same token I have a question regarding the Fuel Vents.



I have noticed small drops falling from the right wing (when looking at it sitting in flying position in my Yak-55m), the first time I noticed was doing vertical flight but I dismissed as condensation or rain as the plane sat overnight with no covers while there was a storm (and yes as soon as I preflight the plane I saw water coming off the ailerons.)



So I decided to look at again and I can see what I think is fuel drops leaving the plane from the right wing while doing acro (inverted or vertical) but it is only from the right wing and it does not amount to anything on the fuel levels (if I fly heavy on the right wing I have more fuel there if I fly heavy on the left, it cross feed to the left).



While I do cross country, there is no loss of fuel so leveled flight or seating on the tarmac means no fuel loss.



So is this normal? and I never noticed before? I assume that some fuel will get caught in the fuel vents and can drip off. but I rather hear your opinions.



Thanks, Javier

- The Matronics Yak-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?Yak-List

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