B.135
General Data
Wingspan: 10.85m
Length: 8.50m
Height: 2.60m
Wing Area: 17.00m2
Engine: H.S 12Ycrs
775CV at Sea Level (880mmHg)
850CV at Sea Level (960mmHg)
860CV at 3300m (880mmHg)
Empty Weight - 1906kg
Fuel - 234kg
Pilot - 80kg
Parachute- 10kg
2x 7.92mm Vz.30 - 24kg
2x 450 rounds - 30.6kg
Aimer - 0.35kg
1x 20mm MG/FF - 43kg
60 rounds - 25.7kg
Radio Equiptment - 24.5kg
With addition of other accessories the loaded Weight of the plane was 2421kg give or take
Surface of Ailerons: 1.15m2
Wing Chord Max: 2.117m
Landing Flap Angle: 55 degrees
Horizontal Tailplane Surface: 2.234m2
Horizontal Stabilizer Surface: 1.152m2
Elevator Surface: 1.082m2
Vertical Tail Surface: 1.462m2
Fin Surface: 0.480m2
Rudder Surface: 0.982m2
Aileron Deflection
Up: 16 degrees
Down: 11 degrees
Elevator Deflection
Up: 27 degrees
Down: 24 degrees
Trip Tab Deflection
Up: 19 degrees
Down: 20 degrees
Rudder Deflection
Left: 28 degrees
Right: 28 degrees
Source: KuÄŤera, P.; BĂlĂ˝, M.; Bernád, D. (2003). Avia B-35/B-135 (in Czech/English). Praha, Czech Republic: MBI. ISBN 80-86524-03-5
History
Originally designed by Czechoslovakia for their Airforce. However after Czechoslovakia capitulated in March 1939, the germans halted the future of the aircraft. They however allowed the ones that Bulgaria ordered to be built and sent to the Bulgarian Airforce. 13 Aircraft (not including the B.35 prototypes) were built and ended up being exclusively operated by the Bulgarian Airforce.
Fun Facts
The Mock up of the plane featured a HS.12Y-1000C engine which was still in developement. However since the 1000 horsepower engine wasnt ready yet, they retained the 860 Horsepower engine from the B.534-IV to get the project started. If Czechoslovakia wasnt forced to capitulate their B.135’s would of been powered by the 1000hp engine as intended. Instead the B.135 was ever only powered by the HS.12Ycrs engine with 860hp which is what the Bulgarians recieved. The Armament for the Czechoslovak Airforce was to consist of:
1x 20mm Vz.36 (Oerlikon FFS) - 60 rounds total [Motor-Cannon]
2x 7.92mm Aerial Vz.30 - 900 rounds total [Cowling]
However after the capitulation of Czechoslovak and now under German sphere of influence…
1x 20mm MG/FF with 60 rounds [Motor-Cannon] was chosen instead.
The B.135 can also carry 1x 100kg bombs or 2x 50kg bombs
[The mock up example]
1000hp engine with 3 prop blades
Bulgarian Performance Test Results of the B.135
Max Speed, Bulgarian Tests
462km/h at Sea Level
478km/h at 1000m
495km/h at 2000m
511km/h at 3000m
527km/h at 4000m
529km/h at 4150m
519km/h at 5000m
507km/h at 6000m
The Czechoslovak test with the best achieved max speed for the B.135
470km/h at Sea Level
535km/h at 4000m
Climb Rate from one of the Czechoslovak Tests
Time to 1000m: 1:26 , [Bulgarian test is 1:36 at higher weight of 2447kg]
Time to 2000m: 2:47
Time to 4000m: 5:35
Source: KuÄŤera, P.; BĂlĂ˝, M.; Bernád, D. (2003). Avia B-35/B-135 (in Czech/English). Praha, Czech Republic: MBI. ISBN 80-86524-03-5
I also calculated the Stall Speed (Without Flaps at Sea Level)
V = Stall Speed in m/s
L = Lift Force needed to lift the plane in Newtons (Weight of aircraft in kg x gravity)
Cl = Lift Coefficient
P = 1.225kg/m3 Air density at Sea Level
A = Wing Area in m2
Loaded at 2421kg , ~1.40 CL_Max Wing Lift Coefficient [Normal Wing Flow]
~145km/h IAS
Source Claims 140-150km/h Stall Speed
Source: KuÄŤera, P.; BĂlĂ˝, M.; Bernád, D. (2003). Avia B-35/B-135 (in Czech/English). Praha, Czech Republic: MBI. ISBN 80-86524-03-5
According to the test flight on 3rd July 1941 the plane dove to 715km/h, even at this speed the controls were easily handled and the pilot didn’t notice any vibrations. According to Airwar.ru the maximum safe dive limit is 804km/h IAS
Now whilst the Czechoslovaks did built the B.135’s for Bulgaria…
The aircrafts had to be assembled together in Bulgaria
Internal Schematic
