4

R/C Soaring Digest

The

Foka 4

was the final production development of the SZD-24 series manufactured by SZD Bielsko in Poland. Approximately 200 of the SZD-24 series were manufactured starting in 1961.

Developed as a Standard Class sailplane, the

Foka 4

is of mixed construction with a fiberglass composite forward fuselage section and the remainder of the airframe being made of wood. The ailerons, elevator and rudder are fabric covered and the wings were fabricated with plywood skins, being built up in concrete molds which resulted in excellent surface accuracy and finish.

The SZD-24-4A

Foka 4

featured in this walk around is owned by Gary Busk of the Dallas-Ft. Worth area and is flown from Caddo Mills airport just east of Dallas.

Gary flies his Foka 4 regularly and we were lucky enough to be at the airport when he returned to the field from a successful cross country flight.

Gary’s

Foka 4

is the only one flying in the U.S. to his knowledge though he knows of one presently being restored in California.

Gary was kind enough to loan me the sailplane’s service manual from which the accompanying drawings were copied.

A few points of interest when looking over the photos and drawings of this classic sailplane are the canopy and the way it rolls forward when opened and how the wing is attached to the fuselage. Note too the fixed main wheel located behind the CG which is a nice feature for scale aerotow and simplifies the overall layout for a scale model.

It’s pretty amazing to realize this is a 40+ year old sailplane design and it’s to Gary’s credit that the

Foka 4

can still be seen thermalling over Texas.

Thanks to Gary Busk for the time taken to allow us to photograph his sailplane and loaning the service manual to me.

Thanks also go to Dale King for taking me out to Caddo Mills, Texas, to see the sailplanes of the Southwest Soaring Association.

SSSSZZZZDDDD----22224444----4444AAAA FFFFooookkkkaaaa 4444SSSSttttaaaannnnddddaaaarrrrdddd CCCCllllaaaassssssss SSSSaaaaiiiillllppppllllaaaannnneeee

SSSSppppeeeecccciiiiffffiiiiccccaaaattttiiiioooonnnnssss::::

Wingspan - 14.98 mLength - 7.0 m Height - 1.7 m

Dihedral - 2 degrees Wing Area - 12.16 sq m

Aspect Ratio - 18.5 Wing root - c = 1.218 m, NACA 63-618

Wing tip - c = 0.39 m, NACA 4415Weight - 245 kg, 385 kg max., loaded

Max speed - 260 km/hrStall speed - 70 km/hr

Min. sink - 0.7m/s @ 79km/hr Max. L/D - 34:1 @ 94km/hr.

SZD-24-4A

Foka 4

Standard Class Sailplane

Text and Photos by Mark Nankivil, <nankivil@covad.net>

December 2005 5

6

R/C Soaring Digest

December 2005 7

8

R/C Soaring Digest

December 2005 9

10

R/C Soaring Digest

December 2005 11

12

R/C Soaring Digest

December 2005 13

14

R/C Soaring Digest

December 2005 15

16

R/C Soaring Digest

December 2005 17

18

R/C Soaring Digest

December 2005 19

20

R/C Soaring Digest

December 2005 21