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How to Install Fuel Tanks in Wood Wings

Posted By:
Jon Banks
1
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0
#1 Posted: 12/16/2010 12:03:48

I am working with an A&P/IA to build a homebuilt aircraft with wood wings.  We are going to add wing fuel tanks in place of the fuel tank between the engine and cockpit for both safety and weight and balance purposes.

 In researching this, we have come across numerous ways that fuel tanks have been installed in wood wings of other aircraft and have even come up with a few ideas of our own.  What we would like to know is if there is one method of installation that is better than the others or one that the FAA recommends over another?

 Thanks,

 Jon



Craig Cantwell
43
Posts
8
#2 Posted: 12/19/2010 09:44:49

Jon: It's really going to depend on the wing design. For two data points, here is how my two a/c were done.

Stinson L-5B: The tank is a drop in unit. The front and rear sides have lips that rest on the spars. The wing has numerous ribs that are cut so that the bottom of the tanks rests on felt cushions. The tanks are secured by straps over the top of the tank, secured to the front and rear spars, pulling them tight against the bottom of the wing. All exposed edges of the tanks are then taped and doped as the wing is covered.

 

Fairchild AT-21: the tanks are bottom loaded into the wing with straps under the tanks drawing them tight against the upper structure. The stiffeners above the tanks have profiles cut into them corresponding the the upper tank form and are covered with felt or rubber strips to prevent fretting. The lower skin in the area of the tank access is a stress panel and is screwed to the front and rear spars. There are a number of formed ribs on the stress panel that have rubber strips on them and contact the bottom of the tanks to help keep them tight to the structure and minimize movement.

 

Whatever route you take, remember that unless your tank is going to be a structural element, you will need to account for the absence of full strength ribs in the tank area. You could place multiple tanks between ribs, but that not only complicates fuel flow, returns, venting and filling of the tanks, but also adds considerable weight for the installation.

 

Food for thought...



Doug Dwyer
Young Eagles Pilot or Volunteer
2
Posts
0
#3 Posted: 12/24/2010 15:07:01

Jon: You should  look at the way Mooney designed the metal fuel tank installation on the M-20 and M20A wood wing models. The tank sits between the D section stub spar and the Main spar and is installed from below. Felt is used to hold the tank in position and prevent scuffing. Its very simple and with the metal cover holding the tank in place it looks good and is efficient aerodynamically and structurally.



Files Attachment(s):
Left Wing Fuel Bay.jpg (221208 bytes)
Jonathan Tibbets
Young Eagles Pilot or VolunteerHomebuilder or Craftsman
7
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#4 Posted: 2/2/2011 09:02:20

Jon: Sometimes a picture is worth a thousand words. I am restoring a Corben Baby Ace which included a complete rebuild of the wooden wings. I removed the old ribs and started with just the original spruce spars. I decided to add wing tanks to increase the fuel capacity and free up space in the fuselage ahead of the instrument panel. I would be happy to send you photos showing how I did it, if you like.

Jonathan