HUNGARIAN GLIDERS
1933-2000
Type designation: R-25
Name: Mokány
Designer: Ernő RUBIK
Class: Standard class
General arrangement: Cantilever, shoulder wing, single seat, all-metal structure, fixed wheel, V tail unit, bat-like airbrake
Crew: 1
First flight: September 25, 1960
Manufacturer: Esztergom Facility of Pest Area Machine Factory (PGE)(formerly Sportárutermelő V., Esztergom)
Number of built: 1



Short history:
In 1958 the MHSz, the central organization controlling all flying sports in Hungary, placed an order with PGE to design and produce a two-seater glider for basic instruction, a single-seat training and a single-seat standard-class performance glider. The specification called for all-light-metal structures, easy and common maintenance characteristics as well as similar flight characteristics. As regards the schedules of the development works priority was given to the standard-class ship, as it had been planned to participate with this glider at the world championships in 1960.
The concept of the three gliders was based on the - design, production as well as operational - experiences gained with the R-23 Gébics. The design work aimed for as much common assemblies and parts as possible, and for common production technology.
The first design, the standard class glider got he designation of R-25 and the name of "Mokány" (a person, who has plenty of guts).
First flew in September 25, 1960, missing the world championships. Testing this glider nearly 100 flights were flown. Then performance measurement flights followed, which were conducted by the Aircraft Department of the Technical University of Budapest. The most remarkable flights with the glider are the following: 101,8 km/h speed over a 170 km distance flight; 315, 320 and 306 km distance flights, all flown by György Petróczy in 1962. At present the glider is exhibited at the Permanent Aircraft Exhibition of the Hungarian Museum of Transportation. Only one example had been built as the prformance targets were not met.
The glider was certified for cloud flying, spins and basic aerobatics.

Structure:  All-metal
   Wing:
The tapered wings have split ailerons with unusually small area. The wing's airfoil is NACA 643-618 section modified by Rubik's corrugated light-metal skin in front of the main spar. The other parts of the wing are fabric covered. To control the glide-slope on final a bat-like airbrake system is fitted which is similar to that of the R-23 Gébics.
The fuselage and wing attachment is similar that of the R-23 Gébics. The glider can be easily and quickly assembled/disassembled. The control system of the ailerons connect automatically.
When closed the bat-like airbrake fits tightly into the fuselage's side.
   Fuselage:
The lateral view of the fuselage is similar that of the Gébics. The front part has elliptical cross-section and nests a comfortable cabin. The one-pice plexiglas canopy streamlined into the fuselage's outline, and provides good visibility for the pilot. The rear part of the fuselage has a circular cross-section the radius of which is reduced gradually toward the tail. The tail unit has a V-form arrangement. To balance the control surfaces Flettner-type control system as well as mass balancing were used. The deflections of the secondary control surfaces fitted on the trailing edges of the main control surfaces are always forcing the main surfaces to their neutral positions. The result of this system is that the glider can be flown with hand-off controls. The landing gear consists of a wheel positioned in front of the c.g. of the empty glider, a nose skid streamlined into the fuselage's bottom, and a tail skid made of a steel spring-band. The non-retractable wheel has a spring suspension.
The fuselage is an aerodynamically refined version of that of the R-23 Gébics.
   Tail unit:
The V-form tail surfaces have light-metal structures, which consist of main spars made of tubes and specially corrugated sheets in front of the spars without ribs, and behind the spars fabric covered ribs. The surfaces can be folded up for transportation without disconnecting the control mechanisms.



Larger picture


Dimensions:
   Wing:
     Span, m: 14,98
     Area, m2: 11
     Aspect ratio: 20,5
     Chord (root), m: 1,02
     Chord (tip), m: 0,48
     Airfoil (root), m: NACA 643-618 mod.
     Airfoil (mid-span), m: NACA 643-618 mod.
     Airfoil (tip), m: NACA 643-618 mod.
     Dihedral, degree: 3
     Sweep, degree: -1,03
     Washout: None
   Aileron:
     Span, m: 2,2
     Mean chord, m: 0,19
     Total area, m2: 0,84
     Balancing: Aerodynamic(Frise) and 75% mass
   Flap:
     Type: None
   Airbrakes:
     Type: Bat-like
     Position (upside/downside): Under the wings on the sides of the fuselage
     Total area, m2: 0,6
   Horizontal stabilizer:
     Span, m: 2,88 (projection of the V surface)
     Area, m2: 2,46 (projection of the V surface)
   Elevator:
     Span, m: 2,46 (projection of the V surface)
     Area, m2: 2,46 (projection of the V surface)
     Airfoil: NACA 0012-63 mod.
     Balancing: Aerodynamic and mass
     Trim: Flettner tab
   Vertical stabilizer and rudder:
     Total area, m2: 1,72 (projection of the V surface)
     Rudder area, m2: 1,72 (projection of the V surface)
     Balancing: Flettner tab
   Fuselage:
     Length, m: 7,31
     Width, m: 0,61
     Height: 1,14
     Cross section, m2: 0,5
   Landing gear:
     Type: Fixed wheel with spring suspension
     Wheel diameter, m: 0,260
Masses:
   Wing, kg: 90
   Fuselage, kg: 46
   Tail unit, kg: 10
   Empty glider, kg: 160
   Gross, kg: 250
   Ballast, kg: None
   Wing loading, kg/m2: 22,7
Speeds:
   VNE, km/h: 250
   Max. speed with open airbrakes, km/h: 190
   Max. aerotow speed, km/h: 100
   Max. winch speed, km/h: 80
   Max. speed in rough air, km/h: ?
   Stall speed, km/h: 60
Performance:
   Min. sink, m/s (at gliding speed, km/h): 0,7/70
   Best L/D (at gliding speed, km/h): 28/79
Start methods: Winch, Aerotow



Origin of data and 3-view drawing:
Jereb Gábor: Magyar vitorlázó repülőgépek, Műszaki Könyvkiadó, 1988, Budapest
(Gábor JEREB: Hungarian Gliders, Technical Publishing House, 1988, Budapest)

Gábor FEKECS E-mail: fekecs.gabor@t-online.hu