Questions from a Potential 337 Buyer

[Denhamblin]

Originally Posted by Justadude

In my search for a 337, today I looked at a 1975 P337 that was in very good shape, good times on airframe and engines, and well equipped. The plane had the engines reman'd and all upgrades done in 204 by the Rocket Aircraft LLC. To my understanding, many were part of Riley back in the day.

The big question for all of the knowledgeable folks on the board is what to do with the AE wing tanks (plus fuel xfer/fuel dump equipment) that Rocket installed in 2004. I've read all of the treads on this board, plus anywhere I could find information. A lot of emotions to say the least. Is it best to walk away from this plane, insist that the seller go through the removal and final AD inspection, or negotiate in a $ value to accommodate the removal (and what would/could that $ amount be?). As an aside, I saw no skin cracks or smoking rivets when inspecting the top of the wings.

Appreciate the help here. I really like what these planes can represent in usefulness, while appreciating the complexity and financial commitment required.

Thanks in advance,
Bob

One other thing. You can't just simply uninstall the Flint tips. You would need to replace the closeout rib in both wings since they are heavily modified when you add fuel tanks outboard of the closeout rib. I'm not sure what AE does with the closeout rib. Finding those ribs may be both difficult and expensive.

[Justadude]

Thank you for the very quick and detailed response. Very much appreciated.

The 1975 model came with 150G. tanks as standard, and guess by default the "long" wing.

The Max Take Off Weight MTOW was increased from 4700 to 5120 through the AE Wing Exetension STC and AE Fuel Transfer STC. Max Landing Weight is unchanged at 4465. No change to standard 225hp turbo engines. The plane does not have winglets.

Regarding removal of the AE tips/tanks, I don't know how/if the close out ribs are modified. Also would assume that sourcing those may be a challenge, and then adding back on standard wing tips or Horton tips since it has the Horton Stol kit installed.

Understand the suggestion for caution for using the plane above 4700 lbs gross weight and potential concern. I have no way to measure how may of the 510 hours of flight time were above that level, since the AE tips were installed.

Once again, thank you for your comments.

Bob

[JamesC]

For peace of mind you might have to search for over-stress micro-cracks in the spar from carrying the extra weight, with dye penetrant or acoustic emission techniques. All at a cost of course, along with removing the tanks.

[Denhamblin]

Originally Posted by Justadude

Thank you for the very quick and detailed response. Very much appreciated.

The 1975 model came with 150G. tanks as standard, and guess by default the "long" wing.

The Max Take Off Weight MTOW was increased from 4700 to 5120 through the AE Wing Exetension STC and AE Fuel Transfer STC. Max Landing Weight is unchanged at 4465. No change to standard 225hp turbo engines. The plane does not have winglets.

Regarding removal of the AE tips/tanks, I don't know how/if the close out ribs are modified. Also would assume that sourcing those may be a challenge, and then adding back on standard wing tips or Horton tips since it has the Horton Stol kit installed.

Understand the suggestion for caution for using the plane above 4700 lbs gross weight and potential concern. I have no way to measure how may of the 510 hours of flight time were above that level, since the AE tips were installed.

Once again, thank you for your comments.

Bob

Bob,

If the AE extension carried fuel then they likely needed to modify the closeout rib and replacement of those ribs would be necessary if you decided to remove the AE extensions. I don't even know if you can find new ribs for a 337 but with a 210 the cost of buying new (or reused) ribs is about $3,500 (last time I checked).

What is more important is whether you have to remove the AE extensions to comply with the AD (and if you need the additional fuel). If removal isn't necessary and you actually want the additional fuel then you may just want to do an inspection of the wing to ensure there are no issues with it.

I don't know what limitations may have been in effect to fly the aircraft at 5120. If there was a limitation to keep more fuel in the tips when flying at that weight then that would be a mitigating factor. Fuel out at the wing tips will counter the loads created by increasing the wing area. With my tips, you can not completely empty the tip tanks until your GW drops below 4330. With a GW at 5120 you would have to do the math to figure out if you could burn enough fuel in the mains to allow you to transfer the fuel from the aux tanks. But, again, I would look at the limitations of the STCs involved.