Avid Wing Tanks

10 posts in this topic

Posted

All,

I wanted to get some opinions on the new tank design for the Mark IV. I have some thick skin but I want to try and keep this conversation as civil as possible :) Keep in mind I will still be able to provide the original fiberglass tanks Avid used to make.

 From the research on this site and other forums, firsthand opinions from customers, and reviewing the competition, I have developed a new design that aims to accomplish the following:

-Maintain the same fluid volume as old tanks

-Allows for use of fuel with up to 10% ethanol without causing premature damage or failure

-Does not cause significant weight increase

-Does not cause significant price increase

-Sits inside ribs so that tank profile cannot be seen after covering

 

Having said all of this, I decided to go with an aluminum tank that slides inside the first 6 ribs closest to the fuselage.I have attached a picture below that shows the concept - the tank in the picture was a fiberglass mock-up. This is by no means a final design and I would appreciate your thoughts and input as we continue to make improvements to the design.

 

Tailwinds,

Mark

Picture2.png

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Posted (edited)

Would that be 6 individual tanks? If so thats alot of extra fittings inside the wings to slowly drip.  I do like the idea of it being completely hidden under the fabric. I would also think about making it fit in either the under camber wing and  the riblett airfoil because eventually your gonna have to switch these planes to the more desirable airfoil. :)

Edited by TJay

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Posted

My own opinion, for what it's worth.  There was a good reason why Avid and Kitfox went away from aluminum tanks, and both tried them.  The wings do flex in flight, and the flexing causes cracks in the tanks that of course then leak.  If the tanks that were only 18" long cracked, what chance does a 6' long tank have?  Also, do you increase the odds of the tank's outlet unporting with the long tank?  If you were flying uncoordinated, will the fuel all end up at the outboard end of the tank?  What kind of baffeling do you plan?  Not trying to bash you, but these are some of the negative thoughts I had when I pondered your tank idea.  Glad you are advancing the Avid aircraft progress, would be nice to see you make a complete success out of all of this.  JImChuk

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Posted

I have never seen the original aluminum tanks (that cracked...). The traditional fiberglass tanks are a structural part of the wing. I the aluminum tanks were conceived the same way the flex of the wing could/would crack them.

But if the tanks are "free floating" within the wing there would be no stress an they would remain intact - but we would loose the structural function of the tank. With no tank installed in the wing there is a diagonal tube in place.

The only real issue with the original fiberglass tanks is if they are not compatible with ethanol. So if a ethanol resistant resin is used I don't really see the issue with the traditional tanks. 

The issue with having multiple connected tanks in the same wing isn't so much the fuel flow out as fuel in... unless the connection can manage the flow correctly. 

Fred

 

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Posted

Fred is spot on re: free floating alum tank. Here are pics of my Aerotrek wing tanks, notice 'thru-tank' provision for drag tube to maintain structural integrity of wing. Not one reported tank failure in thousands of individual installs and many years of trouble free fleet operations.

image.jpeg

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image.jpeg

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Posted

Just like a Piper wing tank.  They have tubes through them for the drag cables to pass.  This allows the tank to "float" in the bay.

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Posted

I have never seen the original aluminum tanks (that cracked...). The traditional fiberglass tanks are a structural part of the wing. I the aluminum tanks were conceived the same way the flex of the wing could/would crack them.

But if the tanks are "free floating" within the wing there would be no stress an they would remain intact - but we would loose the structural function of the tank. With no tank installed in the wing there is a diagonal tube in place.

The only real issue with the original fiberglass tanks is if they are not compatible with ethanol. So if a ethanol resistant resin is used I don't really see the issue with the traditional tanks. 

The issue with having multiple connected tanks in the same wing isn't so much the fuel flow out as fuel in... unless the connection can manage the flow correctly. 

Fred

 

Free floating would be good, unfortunately with the original fiberglass tanks cracks can develop from the stresses even without ethanol. :o(  I like the idea of rotomolded, not sure how much weight gain there would be though.

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Posted

The problem is roto-molded polyurethane is not strong enough for the structural needs.  

This is why fiberglass is still being used, with an updated resin which is better resistant to modern gasoline additives including ethanol contamination.

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Posted (edited)

Doug,  How many gallons do each of your tanks hold?  I can see a huge twisting stress difference in your short tanks and the long tanks that Avid showed.  The long tanks don't look like a good idea.  I second the motion for short plastic tanks - weight difference should not be a problem - just cost of tooling up to make them.  Somehow, other kit makers have managed to do that. 

Kitfox and Avid used to buy their tanks from the same maker - Ron's Fiberglass.   EDMO

Edited by EDMO

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Posted

@Ed - 22.5 gals, 22.0 gals usable total on the wings

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