SZD Ogar (oz3915)

About this Plan

SZD Ogar. Radio control sport-scale powered glider.

Quote: "Unique in concept, the Polish SZD Ogar powered soarer is a natural for modeling. Stand off scale by Howie Applegate.

I suppose all of us want to build a model that's a little bit different from the rest. While going through a soaring magazine, I saw some three view drawings of several sailplanes. Ogar caught my eye as 'the' different airplane. A powered sailplane without a power pod seemed quite novel. Before starting construction, let's take a minute for some background on the full-sized machine.

Ogar is a Polish design, built by SZD. It has a 17.5 meter span (approximately 56.5 ft), two place seating configuration, with the student in the front seat and the instructor in the rear. The seats are staggered so the occupants' shoulders overlap (the student's right with the instructor's left). Power is a 68 HP (a VW engine modified for aircraft). The ship has a partially retractable wheel in the belly and is equipped with wing tip casters to help prevent ground looping.

I took a few liberties with this ship to ease construction and still insure good structural qualities. I decreased the aspect ratio of the wing from 16 to 1 down to 14 to 1. This permitted me to place the spar near the maximum curvature of the wing and still keep the leading edge planking from becoming too wide. Naturally the tail area was increased and the wheel is a dummy glued to the belly. The wing tip casters were omitted, and a set of optional tow hooks were added. The fuselage was slimmed down also. Now let's get down to building.

Fuselage and Boom: The fuselage is definitely the most difficult part to build. The construction is 1/8 sheet profile reinforced with 1/64 plywood on both sides. This profile can be pinned directly onto the plans. Use some scrap strips of 1/64 thick plywood as shims to to support the areas where the doublers are not used. The vertical fin substructure should be added while the profile is still pinned down. The elevator cable sheath may now be installed as the boom bulk-heads must be notched to clear this and also the Gold N' Rod sheath. The. Gold N' Rod sheath should be running slightly up hill going toward the front of the fuselage and also climbing toward the top of the fuselage. It should exit the boom about 1/4 in above the profile piece and about 1/4 in higher than the horizontal centerline of the boom.

Now, glue all the left side bulkheads into position. The boom bulkheads should al-ready be notched to clear the elevator sheaths. Also, fuselage bulkheads #5 and 6 should be drilled and/or notched to hold the sheath. Add a 1/16 balsa shear web to the boom (grain lengthwise); this will help hold the boom straight during the planking operation. Next, add the left side longeron and the canopy longeron. Note: Make sure these two longerons do not get accidentally glued together. Complete the left side of the fin with its LE and spar. Add the 1/16 x 3/16 ribs (notch for cable sheath). The left side is now complete. Glue on all the right side bulkheads and add the 1/16 balsa shear web. The rudder Gold N' Rod rests along the outer contour of the boom bulkheads, either above or below the shear web. Notch the boom bulkheads and notch and/or drill fuselage bulkheads #5 and 6 and install sheath.

I did not want my antenna wire to be external of the boom for fear of the prop eating it, so I installed another tube under the planking of the boom. I used the left-over sheath from the flex cable and installed it on the left top side of the boom along the outer contour of the bulkheads. The antenna tube also runs uphill toward the wing inside the fuselage, so it is accessible from bulkhead #5 for ready insertion of the antenna wire.

The right side of the fin can now be installed after which both sides of it can be covered with 1/32 sheet balsa (grain span-wise).

The boom is now ready for planking. If you wish to install tow hooks, cut out the fuselage profile piece where shown on plans. The planking can be cut away later to suit the tow hook mount. All planking should be 3/32 medium balsa. My method of planking is as follows: Cut the first plank (about 1/8 wide and glue it anywhere along the length of boom. Now bevel the edge of the 3/32 sheet to suit the mounted plank; cut it off the sheet about 1/8 wide and glue it in place. Narrow strips work best on highly curved surfaces such as the boom; wider strips may be used on less curved surfaces, as on the fuselage sides. Planking is not difficult, but it does require some care in keeping the seams tight. I suggest you use Ambroid glue, not white glue for planking, as white glue is very difficult to sand and may tend to give flat spots on the sanded planks..."

Here is Howie Applegate's SZD Ogar from Flying Models magazine issue 08-77. Wingspan 72 in, for Cox Baby Bee .049 power.

Direct submission to Outerzone.

Update 29/11/2016: added article, thanks to RFJ.

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