Interplane Strut Details

The details of the way the rear upper wing spar attaches to the I-strut were changed after serial number 21. On serial number 21 and earlier, there was only one steel strut fitting on the front of the upper rear spar. The eye-bolt that attaches the upper wing to the I-strut is split. After serial number 21 an additional steel strut fitting was added to the front of the upper rear spar. An additional part was added to make the connection, a "universal", Beech part number B17226. This attachment method was also used on the C models.

After the C model, this attachment was changed again. The universal and eye-bolt was replaced by a new "T" shaped eye-bolt with larger thread size. The bushing on the I-strut was replaced by a heavy tab. This photo is of E17B serial number 231 at the Beechcraft Heritage Museum.

My project came with one of the original I-struts and one after serial number 21. These two I-struts design differ in the position of the bushing for the eye-bolt the attaches the wing to the I-strut. In the pre serial number 22 the bushing is positioned under the front surface of the spar and in the later design it is centered at the fore and after center of the spar. On the later design, the bushing is at a lower position to accommodate the additional vertical space needed for the "universal".

Since I didn't disassemble the aircraft, I am not sure how the post serial number 21 I-strut was attached to the serial number 12 wing. Since both of the upper wings only had the steel strut fitting on front of the spar, the newer I-strut must have had a "design-as-you-go" fitting. Since the post serial number 21 design provides a stronger connection between the rear spar and the I-strut, I am going to update the original serial number 12 I-strut to comply with the last version of Beech drawing B17225.

After serial number 21 the round bushing for the eye-bolt was replaced with an oval bushing to accommodate some fore and aft adjustment of the eye-bolt. This oval bushing is made by deforming at short piece of 5/8 X 0.095 tube. I found a 3/8" Allen wrench made a perfect mandril to form this part.

New eye-bolts (Beech part number B17216) and "universal", (Beech part number B17226), were made.