Mini-IMP Aircraft Company

Engine Compatability

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Engine Compartment

The engine space behind the main bulkhead is large enough to permit installation of a great variety of available engines. Access to the engine from the sides is provided by removing the left and right engine doors which are retained by means of Camlocä fasteners.  These “doors” also provide the air scoops for directing cooling air over the engine.  The engine MUST be fitted out with a cooling fan.  The fan is positioned in the bulkhead aft of the engine compartment and draws the hot air from below the engine out into the tail cone where it is exhausted out through a suitably screened vent at the top of the tail cone, well forward so as to avoid any turbulence on the flight control surfaces.  Although the prototype is not equipped with an oil radiator, this can be installed if operation in extremely hot climates is anticipated.  The prototype has proven to extremely cool running, and continuous operation at up to 1500 RPM on the ground without forward velocity does not result in exceeding operating temperature limits for either the cylinder heads or the oil in mild climates.

It is not necessary to stop the engine of the Mini-IMP with an idle cutoff provision.  This is possible due to the use of the Flexidyneä which isolates the engine from propeller inertia, which causes most engines to require this shut-down procedure.  Just turn the ignition switch OFF and the engine stops just as it does in an automobile.

Although the engine of the Mini-IMP is directly behind the pilot, the engine mount and structure of the aircraft has been designed in such a way that the engine could only be thrown into the pilot under circumstances of a head-on crash which would not be survivable even if the engine were ahead of the pilot.  The structure and engine mount are further designed to absorb any crash impact that would otherwise be survivable.  The side rails of the basic metal structure have been designed to provide adequate protection to the pilot in the event of a wheels-up landing, although such a landing probably should be made on a grass surface if at all possible.

Engine Compatibility

The Mini-IMP was originally designed to accommodate the two cylinder Franklin 60 HP engine.  It is anticipated that some builders will want to install these engines which are extremely smooth running and are fully certificated.  These engines are equipped with full electric starting, as well as other modern features.  Although these engines were not available for many years after the production rights were sold into the former Soviet bloc, they are once again available and are quite satisfactory.

Since the original concept of the aircraft was to obtain maximum cruise speed and efficiency, smaller engines in the 50-75 HP range are preferred for the short nosed aircraft.  However, the aircraft has been designed so as to permit the installation of aircraft engines up to and including the Lycoming O-235.  The preferred engines include the Continental O-200/IO-240, Lycoming O-235, the various Volkswagen conversions, the Jabiru 2200/3300 and the Rotax 911/912.  The Mini-IMP engine installation is excellent for use of various modified engine conversions since there are no propeller loads introduced into the engine crankshaft by the shaft installation.  The shaft arrangement provides a flexible coupling as well as a slip spline so that engine motions on their rubber mounts as well as thermal expansion of the structure do not impair the engine operation or installation.  Only “torque” is taken from the engine.  Further, the shaft system embodies a cooling fan (part of the kit along with the shaft system) which assures proper and adequate cooling of any of the various buried engine installations.  With such provisions, the various “converted” engines are much more likely to give satisfactory life and operation.

Engines must be equipped with electric starters since hand cranking through the propeller is not easily accomplished although it can be done in an emergency.  The airplane will sit level on the ground (without dropping on its tail) without the pilot being aboard or without special parking provision or ballast.  It can be equipped with turbocharged engines such as the Revmaster 2100D.  This permits high altitude flight and exceedingly attractive cruise speeds on relatively low power and low fuel consumption.  There is adequate space in the baggage compartment behind the seat for a portable oxygen system if high altitude flight is to be accomplished.

Numerous builders have indicated their interest in possible installation of various models of the Continental engine.  Since the Mini-IMP must have an electric starter, this means that engines from the C-75 up to the O-200 would be usable.   New TCM O-200 engines are available as well as factory rebuilt engines.  Cores are plentiful and parts are available too. (cylinders, crankshafts, etc). Another option would be the Teledyne Mattituck Services TMX-200 experimental engine.  They are assembled from new TCM components and run on the test cell prior to shipping.  Essentially the TMX engine is a new "uncertified" O-200 engine. Needless to say the cost is significantly less than a new certified engine.  More information is available at Since the Lycoming O-235 engine is quite similar to the O-200, the designer began constructing a prototype Mini-IMP with the O-200 engine in order to develop drawings which are applicable to both the Continental and the Lycoming engines.  The drawings set includes coverage of these installations as well as the Limbach (and similar Revmaster VW converted engines).  These versions of the Mini-IMP require modifications to the basic structure as well as mechanical arrangement of the airplane.  The O-200/O-235 installation is applicable to any of the other Continental/Lycoming engine installations from the C-65 up.  These new prototypes also permit us to develop full electrical installations for the airplane and all of this information is included in the drawing file.

The O-200 prototype is about 150 pounds heavier and requires additional fuel tankage which is provided for in the drawings.  These prototypes provide even greater performance than the conservative performance being obtained from the Limbach-powered prototype.

Builders contemplating the construction of copies of the Mini-IMP should make necessary decisions concerning what engine they intend to use early in their program so that necessary structural differences can be accommodated in their project to start with.  Due to increased engine weight, the Model “C” requires the use of a longer nosecone, heavier landing gear, and other changes which must be provided at the outset.  When ordering drawings be sure to indicate your anticipated engine type so that we can ship you the appropriate parts.  We do not recommend that you attempt to install the O-200 in the shorter Model “L” fuselage or that you attempt to use the lighter Model “L” landing gear with the heavier Model “C” engine and tankage.  However, to obtain the best possible performance you should not use the heavier parts with the smaller engines either.

We have many inquiries regarding the use of engines like the Mazda rotary engine.  There have been some successful conversion/installations in the Coot amphibian and in the RV-4.  If this is your area of interest, we recommend that you contact the engine vendor directly and purchase a turn-key, well-proven package from them. We do NOT recommend that the individual builder attempt to develop his own unproven engine installation.  This is a time consuming and costly process, which usually results in frustration and “no airplane”.


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