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OSMG1891   .91 VR-DF Small Head 
TECH NOTES
The O.S. Ducted Fan Engines are designed to develop high power at high RPM.
These are used in Jet (ducted fan) Models where the engine drives a turbine-
like impeller (compressor) that draws a large quantity of air through a shroud
to create thrust. These engines are NOT covered under the O.S. 2-year warranty.
Because this is a high-performance engine, reliability is sacrificed.
The Ducted Fan does NOT come with this engine. One must purchase the fan to fit
BOTH the engine size and the specific plane (these fan units are typically
manufactured by the same people who make the plane kit - a company like
Jet Hangar Hobbies (562) 467-0260 )
FEATURES: Rear Exhaust                                                        .
Schnuerle Porting
2-piece Crankcase
2-Crankshaft Ball Bearings
Rear-Mounted Carburetor
Drum Rotor Induction
ABC piston/cylinder (aluminum piston with a chromed brass cylinder)
INCLUDES: One Assembled .91 VR-DF Engine w/small head
One Set of Instructions and Poster
One Exhaust Adaptor w/screws and O-ring (OSMG2709)
Bellcrank for use with the remote needle assembly (OSMG7258-comes
with the engine!)
SPECS:    Construction: Aluminum and Aluminum alloys
Displacement: 0.91 cu in
Bore: 27.7mm (1.09")
Stroke: 24.5mm (.97")
Max Output: 4.8 BHP at 22,000 RPM
Practical RPM Range: 2,500 - 25,000 RPM
Weight: 662g (23.4oz)
Length: 133.5mm (5.26") from carb intake to front of drive washer
Width: 43.5mm (1.71") neglecting the engine mounting flanges
52mm (2.05") distance between mounting hole centers
Height: 103.3mm (4.07")
Crankshaft: 5/16-24
REQUIRES: Glow Plug (O.S. #8 or #9 (OSMG2691 is recommended)
Tuned pipe (we don't carry, contact the manufacturer of the kit).
Fuel with 20% MINIMUM lubricant content and 20%-50% Nitromethane
Wildcat Ducted Fan fuel exceeds these requirements
COMMENTS: This engine is the "small head" version of the .91 VR-DF engines.
This engine is designed to operate where space is at a minimum.
This engine works w/ Dynamax or Turbax fan units. If the purchaser
wants this to work with Byron fan units, order OSMG1890, it has a
larger head for maximizing cooling, or swap cylinder heads -

ADDITIONAL COMMENTS:  It is suggested that the cutomer uses a Ramtec fan unit
as opposed to the Dynamax unit. The Ramtec has a much
higher pitch which "loads" the engine better.
ACCESSORIES
THIS IS A DUCTED FAN ENGINE.  STARTING EQUIPMENT IS IN AIRPLANE KIT ACG.
COMES WITH EXHAUST ADAPTER, BUT REQUIRES TUNED PIPE, COUPLER AND GLOW PLUG.
FOR USE WITH DYNAMAX AND TURBAX FAN UNITS (WE DON'T CARRY).

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