Mini-IMP Aircraft Company

Performance and Load Factors

The performance of the Mini IMP compares favorably with other aircraft in its size and weight class.  It is similar is size and weight to several Formula One race planes and has performance capabilities that approach that level while maintaining “pussy cat” handling qualities, many “creature comforts”, and slow takeoff and landing speeds.

Many inquiries are received regarding the “gliding characteristics” of the Mini-IMP.  We have found that the Mini-IMP (at zero thrust – idle power) will glide approximately 20 to 1.  This amounts to a rate of descent of approximately 400 feet per minute, at 90 miles per hour.

The Mini-IMP has been designed to an ultimate load factor of 6 g (4 g limit).  This safety margin does permit one to overload the aircraft for normal operations.  Design gross weight is 1000 pounds (500 Empty plus 500 Usable).  The structure is adequate for this weight (at the 6 g ultimate) thus for normal operations the aircraft can be loaded over 800 pounds gross and still be adequate for “Normal Category” operations. (such as additional fuel or baggage).  In these instances the FAA requirement of a rate of climb ten times the stall speed (500 FPM for a 50 MPH stall speed) set the gross weight limits.  With the baggage space virtually on the Center of Gravity and with the fuel tanks on the Center of Gravity, the Mini-IMP is not too sensitive to various weight loadings.  The trim provision is adequate for a great range in pilot weights although it is not adequate for the modifications required for two passengers.  The GA(PC)-1 wing section used on the Mini-IMP has a very considerable trim change effect as the airfoil is varied for the possible flight configuration that the pilot might desire, and a trimmable horizontal tail is incorporated in the design to accommodate these effects.  Baggage up to 100 pounds can be easily accommodated without prohibitive trim effects.  With heavier pilots, such baggage loads do result in longer takeoff runs before the aircraft can be rotated, particularly with heavy fuel loads since there is no propeller slipstream blowing over the tail surfaces to assist in “rotation” for takeoff.

We get many inquiries regarding the suitability of the Mini-IMP for operations from rough fields and unprepared runways.  Due to the requirement for retracting the wheels into the wings we were unable to include larger diameter tires on the Mini-IMP since then they could not be retracted completely so as to give the performance we desired from low-powered engines.  These small tires do limit the “roughness” of the runways from which the Mini-IMP can be suitably operated.  The “spring-leg” landing gear has proven to be suitable for rough area taxi operations, but take off and landing in rough areas should be avoided.  The low taxi speed thrust available from the low-powered engines used in the Mini-IMP do not permit taxiing over very large clumps of grass, runway joints, etc., or getting started on uneven ground.  In order to get the desired high speed cruise capability, the compromises in propeller selection makes the low speed thrust available for takeoff and acceleration very limited.  A large clump of grass can effectively slow the acceleration of the Mini-IMP on takeoff from an unprepared surface.  Although, the takeoff speed for the Mini-IMP is not nearly as high as some of the other “mini” designs now available, we do NOT recommend the Mini-IMP for operation from short unprepared runways.

The propeller blades are virtually stalled during initial takeoff acceleration due to the high pitch and low RPM when using a propeller of sufficiently high pitch to give the desired high cruise speed possible with the design.  We now have drawings for a more costly, light-weight, controllable, all-metal propeller suitable for the Mini-IMP which greatly assists with this problem.  This propeller also enables us to take advantage of various “turbo” installations, which are now available for use with some of the VW conversions etc.  Thus we are able to control these propellers to provide low pitch for taxi, takeoff, and climb, and then control them for higher pitch for cruise, and for higher altitude operation where the turbo let us still pull full rated sea level power from the engines.  These turbo engines are NOT to be rated at any higher power than they are designed for (for sea level operation), but the turbo lets you maintain these power levels at high altitude where the unassisted engine rapidly loses power as altitude is gained.  Such engines are not “blown” but are merely “maintained”.  Do not be confused by claims that the turbocharging will increase the power of non-turbocharged engines.  While this might be possible, it is NOT desirable to try to pull more than normal rated power from most modified engines and thus develop more power than these engines are rated for.  Various gearing systems are necessary to let some engines turn at higher speeds than are suitable for propellers.  Such engine conversions must be properly designed so as to avoid exceeding the designed engine speed limitations of the engine.  While excessively high RPM will result in more power, it also results in a quick loss of engine life and durability.  Further, most converted engines do not have sufficient heat rejection.

The Mini-IMP design takes advantage of the very latest state of the art.  The GA(PC)-1 airfoil is one of the most recent (and best) to come from NASA.  It was especially designed for use on aircraft of the “homebuilt” type where the builders are relatively inexperienced, and the people who fly the machine are usually not professionals.  Thus, things like surface smoothness are not as critical as with some other available wing sections.  Also, the flight characteristics of an aircraft with such an airfoil section are not as demanding as they can be with some of the so-called laminar airfoils.  The stall is exceedingly gentle, and the wing has excellent high lift capability without the use of complicated flaps, etc.

The fuel economy and thus operational expense of the Mini-IMP is outstanding.  These features and capabilities have been obtained through the use of new materials, the latest airfoil, and unique design.  However, these capabilities can not be retained if the design and configuration are modified to any great extent.  Any extension of capabilities (such as a two-place arrangement) could only be realized by making the design bigger and using more power.  This would mean an entirely new aircraft if these capabilities are to be retained in a two passenger configuration.  This also means more weight, more structure, more complication, and more cost.

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