The following article by Norman Graf first appeared on Hyperscale in December 2000... I have added additional comments regarding some of the more interesting details of the Avia towards the end of the article.

During the Second World War, Messerschmitt Bf 109 aircraft were produced in factories in occupied Czechoslovakia. After the end of the war, production continued under the designation Avia S-99. When the stocks of Daimler-Benz 605 engines were exhausted, the remaining airframes were modified to use the Junkers 211 engines, which were still in good supply. 

The combination of the airframe and the much heavier and more powerful powerplant was not ideal, resulting in a nose-heavy aircraft with poor handling characteristics. The Czech nickname for this airplane was "Mezek", the word for mule, due to its stubbornness. This became the Avia S-199, which was used by the Czechoslovak Air Force until 1955, numbers of which were also sold to the nascent Israeli Air Force.

The Avia S-199 at the Kbely Aviation Museum outside Prague, Czech Republic, call sign UF-25 (works number S-199.178), is housed in a dimly-lit hangar crowded in with many other exhibits. Clear overview photographs are difficult to obtain. The following photographs concentrate, therefore, on close-ups of the aircraft's unique features, mainly the bulges in the nose of the aircraft necessitated by the introduction of the Jumo 211 and the new cockpit canopy. The aircraft is painted in overall RLM 02 with national markings on the tail and upper and lower wing surfaces. There is rather extensive stenciling and all air inlets seem to be highlighted in blue.

The Nose 

The distinctive nose of the S-199 sports the large bulge covering the cowl-mounted 13mm machine gun breech and spent link ejection chute inherited from the Bf109-G6 and the horizontal bulge covering the engine bearer arm of the larger Jumo 211 engine.  The black circle in front of the starboard windscreen is the flare port, through which the pilot could fire colored communication flares. Note the subtleness of the overwing bulges which accommodated the larger tires of later models of the Bf109.

Note mass balance on aileron and the bulged canopy in the last starboard view.

The Cockpit 

Here are various views of the new cockpit canopy. Note the larger, bulged, all Plexiglas sliding rear section and the head armor with support struts.  The black shape behind the canopy is the retractable cover of the handhold used by the pilot when boarding the aircraft.  The black half-moon shape with the arrow pointing at it is the toe-hold. The blue square is a cockpit cooling vent which could be opened and closed by the pilot.  

The blue and white striped circle is the cover for the oxygen filling point.  Note again the bulge in the wing to accommodate the larger tires of late model Bf109's.

The Fuselage

Port and starboard views of the rear fuselage showing marking and stencil locations.

The Underbelly

Two views of the S-199 undercarriage show the wide stance characteristic of late-model Bf109's. The mounting point for the centerline drop tank is also shown to advantage here. Notice the asymmetric bulge in the lower engine cowling and the prominent bulge in the center protecting a filter for the Jumo 211 engine.  The four pylons are the supports and anti-sway braces for the central fuel drop tank.

Wing Cannon

Two views of the outboard 20mm cannon in its underwing gondola. Note also the FuG16ZY antenna.

Among the most interesting points of this feature is the exceptional clarity of the offset fuel tank mounting which was common to all 109F models and later... note that while the fairing and four anti-sway braces are offset from the center line, the actual retaining mechanism for the tank is mounted along the centerline axis.  This is to allow clearance for the fuel and pressurized air piping to run down into the tank.

This is also one of the very few 109 variants extant with the MG151/20 "Kanonenboote" mounted under the wings; I do not know if these are original 151s or if they are Czech replacements.  The configuration is largely the same, however.