UltraCruiser Modifications

Hummel Bird Plans Corrections, Improvements & Clarifications

NOTE: THESE CHANGES ARE APPLICABLE TO PLANS ORIGINALLY PURCHASED FROM HUMMEL AVIATION (BILL SPRING'S D-SIZE, HAND DRAWN PLANS). These changes have been incorporated into plans shipped after February 12, 2004 (Bill Spring's D-size CAD dwgs).

(1) There are no ¾ x ¾ vertical angles on the front of center panel as shown in the plans. The nose rib has flange for attachment.

(2) The front stabilizer bolt is in center vertically between skins, and not in center of aluminum angle as shown. Also, be sure to locate front stabilizer hole in side of fuselage ¼” below center line.

(3) Be sure to have the wheels you want to use before welding wheel axle, as some wheels have ¾” and some ⁵/₈” diameter axle.

(4) The nose wheel fork will accept a 10½” OD tire. The fork dimensions may need to be altered to fit your wheel.

(5) Morry’s wheel fairing sketch (available from Hummel Aviation) is based on using 10½” tires (not 11”).

(6) Stringers are cut and butted against bulkhead, not lapped as shown in plans. Rather than try to make them from .040” aluminum, purchase ¹/₁₆” x ¾” x ¾” extruded 6061-T6 aluminum, or use some Cessna stringer stock with holes already drilled.

(7) Replace the springs and chain linkage from the rudder to tail wheel with a solid rod connection for direct steering.

(8) For builders who purchase prefab motor mounts or nose-gear from Hummel Aviation, be sure not to drill bolt holes in bulkhead “A” before receiving prefab parts. This will ensure proper alignment.

(9) On sheet # 9, the horizontal stabilizer on centerline of bulkhead “E” is not the bottom of the stabilizer on centerline of bulkhead “E” as shown. The lower stabilizer mounting should be ¾” below the center line of “E”.

(10) Align the horizontal stabilizer so its top surface is in line with top of wing.

(11) Engine mount—we use 4 engine mounting places on engine, rather than 3 as shown on the plans. Use ½” x .058” wall 4130 steel tube instead of ¾ x .035” tubing, as shown in plans. Note: there are discrepancies as to the mounting dimensions for the nose gear, motor mount to the firewall. These discrepancies are included on page 3, 13 & 15. We suggest using the nose gear dimensions as shown on the attached motor mount sketch. If purchasing prefab parts from Hummel Aviation, the firewall holes can be located after receipt of those parts.

(12) Stiffening beads in ribs are optional. The 45 degree flange on lightening holes should be 25º to prevent warping and cracking.

(13) The alignment beam can be made from ¾” x 4” door casing from lumber yard. Use two pieces with spacers in between to form a square beam.

(14) For larger pilots bulkheads may be extended 2” higher at reference line and wider at centerline.

(15) The fuel tank should be 16” wide (front), 7½” high (rear), 19½” wide, and 8¼” high. The fabricated tank that we sell is made from aluminum.

(15) The correct spar web rivet spacing is 2 rows of rivets on 1" spacing. The two rows are then offset ½".

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