Wet Wing Update

[SpruceForest]

Carlo closed out his wings in July, and we are jigging up for fuselage work on both aircraft as he completes all his wing set's detail work (TE stuff; retract landing lights; flush mount on wingtips, etc.). I had a chance this past Tuesday for a brief visit after the local chapter meeting where Carlo's wife briefed her participation and past management involvement with the ARC Air Races. Good stuff that should show up on the chapter YouTube channel.

The fuel cells are close to bring buttoned up and pressure checked, and once that is done, set aside for fuselage work.

IMG_0886.jpg

In terms of a summary for others contemplating the job:

- Don't even think about it without good engineering support and a wealth of wet wing build and repair experience. Also - the PITA/skill factor to get that riveting done with change in access to the LE box and tank area ups the bar... one of the reasons why I went with the plans-built tank design on mine, despite access to the engineering expertise and SME support

- Based on elimination of the separate fuel tank and addition of structure to handle the higher inertial loads on the lower skin and internal ribs, Carlo expected a very moderate reduction in weight - something like a 5 lb reduction in weight - and increase in fuel capacity to 31 gallons per side, with final capacity and delta weight TBD.

- The major structural changes were:

- - Retaining the wing ribs through the tank area as load-carrying structure and anti-slosh baffles, with an additional rib to create four bays and keep loads reasonable

- - Skin joints moved outboard of the end rib of the fuel bays and a triple rivet line inboard to spread the skin loads

- - Extension of the 032 upper surface aft-spar-to-lower-surface-main-spar skinning out to the ends of the fuel bays

- - Lower skin aft of the main spar to 040 through the entire fuel bay

- - Elimination of separate fuel tank mounting hardware (and elimination of the concentrated loads from that hardware on the main and stub spar)

- - Elimination of the main spar lightening holes within the fuel tank footprint (with associated added complexity of bucking the LE skin rivets and wet riveting the cell!!!)

- - Addition of the 063 milled upper surface inspection ports

- - Addition of weight from all that ProSeal on all rivet lines internal to tanks

Again - not something to be contemplated lightly, but the weight reduction, elimination of some complexity on the structural side (those concentrated loads from separate tanks), and additional tank volume made it something Carlo saw as desirable.

The pic shows the access panels off and vent system install being wrapped.

Re: feedback: Bob found the project interesting, but was not going to endorse or review for obvious reasons. Mark wisely repeated the mantra of 'build to plans.' Without Carlo's background (adult life as as working A&P-IA; multiple scratch-built show plane wins at Oshkosh, etc.) and his available engineering support, not something to consider.

[rodsmith]

I'm wondering why the inspection ports are on the top of the wing instead of the bottom. Looks like the tank takes up the same area as the plans fuel bay. I would have thought that it would have a larger capacity than 31 gallons, also thought there would be more weight savings over separate aux tanks, pump, plumbing etc. Something I would have loved to do but no way I had the skill to accomplish. Is this an A or B wing?

[SpruceForest]

Access is needed to seal/reseal and that generally is a job that gets done so seldomly that it coincides with wings being pulled to ease access... so no real advantage to have those ProSealed ports on the underside with those additional leak points. As the panels are flush and milled out of ribbed 063, no aerodynamic penalty.

The wetted area is same footprint as the standard Patrol wing, but the additional space taken up by reinforcing hat sections, etc. on the standard wing is reclaimed for a calculated 5 gallons (231 cu in per gallon) with the same expansion room, etc. Estimate is conservative - could be more, but I suspect we are pretty close to that 31 per side.

A wet wing does save weight over plumbing in aux tanks and additional pumps, but when compared to the stock Patrol design, the vents were run out to behind the struts and with the capacitance sensors used in lieu of sight gauges plus the heavier skinning on top and bottom, so about 5 lbs per side delta as calculated, but could be a bit more. Carlo also combined the innermost ribs by stretch-forming the second flange and going to a bulb-section stiffener, so two center 032 ribs were eliminated there for a delta in structural weight of about 14 ounces (the flanges and heavier bulb-section stiffener cost about 4 ounces).

Weight or another 1.5 worth of fuel at low cruise not a good enough reason to put the extra time and fab tasks into the build. Carlo just likes the efficiency, and having lived with the Mustang Too for a decade or more, he feels that - for him - it is a better solution than separate tanks.