Mini-IMP Aircraft Company


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Mini-IMP Frequently Asked Questions (FAQ)

Q: I am thinking about building a plane and I would be interested in receiving more information about the Mini Imp. In particular I would like to read about the experiences of other builders.

The best way to stay in the loop is to sign up for the free email chat group (see the link on the home page) and then contact the other builders that you find interesting.  You will find them helpful and friendly.

Q: Not withstanding the available components, is this essentially a plans built only aircraft?

We are now offering the Mini-IMP kit as a series of packages so that the builder can spread out the cost of building the aircraft and only purchase the packages that they desire.  Of course, you can still build it "plans only" if you want to.

Q: Can you tell me more about the construction process, as well as, let me know how to purchase plans.

The Mini-IMP is constructed primarily from sheet aluminum, with non-structural, fiberglass fairings. The construction process is similar to other "plans" built metal airplanes. The individual components are manufactured from sheet metal and other materials, assembled into subassemblies and then joined to make the major assemblies. All of the fastening operations are done with Monel blind rivets and/ or bolts. The fiberglass fairings then attach to the metal understructure with screws, rivets and bolts.  Most of the more difficult to manufacture parts are currently available in the packages.

The plans are currently available from Mini-IMP Aircraft Company, P.O. Box 2011, Weatherford, TX. 76086. The cost is $205, postage paid in the US. The additional shipping charge for international destinations is simply the additional postage amount.

Q: How difficult is the airplane to build and fly?

Building an airplane and flying one have little or no relationship to each other.  Please remember this. You must ask yourself, "What do I REALLY want to do".  Are you a builder or a flyer or both? Many people are drawn to the Mini-IMP because the sleek appearance appeals to their fantasy of being a fighter pilot. This is all well and good, but is not the best motivation to be able keep to the long-term task of building an airplane. Building an airplane is not the "instant gratification" that many of them seek. Frequently those persons will stick with it for a month or two, then drift off to some other fantasy. If this sounds like you, they it would not be a good idea to consider building an airplane. It is almost always cheaper and easier to buy an airplane than to build one. It might be a good idea for a new pilot such as yourself to join the local EAA chapter. Sometimes they have a "flying club" airplane that you can use to build time while you build airplanes.... Alternately you might look into going into a partnership with some friends on a simple airplane that you can use to enjoy the thrill of flight while you build the airplane of your dreams.

The Mini-IMP is more or less straightforward to build.  If you are "handy" with tools, etc., you should be able to build it without too much trouble. If you are not, it may be a tedious undertaking.  Get with your local EAA chapter,  they are a wealth of free help and assistance.

The airplane is much "quicker" than a Cessna 150/152 or whatever you are probably learning in, and although it is easy and docile to fly, if the pilot doesn't have some time in an airplane that responds quickly, he could be mentally way behind the airplane and kill himself due to his own lack of skill rather than any deficiency in the design. It is advisable to get a little "dual" in something that goes 180 mph or so before flying the Mini-IMP for the first time.

Q: Can a Mini-IMP use a Corvair engine?

Probably, but nobody has used one yet. There is one aspiring builder who is supposedly looking into it. I recommend the Continental O-200. You can get a mid-time engine for not a lot of money. Also the Rotax 912 and Jabiru 2200/3300 should work well. Personally, I recommend using a certified engine in an experimental airplane.

Q: I would also like to read the newsletter. I imagine it would be very informative and answer several questions I have. Incidentally, are previous issues available?

The newsletter has been replaced by the free email chat group.  Back issues (11) can be made on a  request basis.  See the home page of this site to sign up for the free chat group.

Q: Can you please tell me what a complete kit costs (minus engine)

There are no "complete" kits available. The Mini-IMP is available as a series of packages.  Most kit components (fiberglass, canopy, landing gear, etc.) are also available for individual purchase for the builder who needs to spread out the cost.  The package options and component pieces that are currently available and their prices are listed on the website and the free informational flyer.

Q: What is the builder reported cost of construction (basic plane, no engine).

Approximately, $10-15K. less engine and avionics.

Q: Will you accept credit card payments?

We can accept credit card payments through PayPal.  The email address for PayPal payment is:  Contact the webmaster before sending any funds

Q: To whom should the check or U.S. Money Order be made payable to?

Make it payable to "Mini-IMP Aircraft Co." at PO Box 2011, Weatherford, TX. 76086.

Q: Do you keep regular business hours?

No, this is a one-man, part-time business. I'm there about 1/3rd of the time. I make my "real" living as an airline pilot for a major US airline. Call or write before you plan to come, and see if I will be in town.

Q: Do you have a copy of the plans that I can look at?

Yes, I normally keep a copy at the hangar.

Q: Do you have a completed or partially completed aircraft on site?

Yes, I have one of each, a complete and flying aircraft and one under construction.

Q: When would be the most convenient time for me to come and visit?

I have an "open house" on an occasional basis. I announce the date via the email newsgroup. That would be the best time to drop by. This is a part-time operation and I don’t spend all day, every day at the hangar.  But, I always try to accommodate interested persons, so if you are passing through the area, call me in advance, and if I'm home, I'll make special arrangements for you to visit.

Q: What I am specifically looking for is something like the Mini-IMP but with a two place side by side configuration. Is that what is in the long nose version? Or do you have, or know of someone who has done a two seat modification?

No, however, there was one aircraft built, the original IMP, but it proved to be too difficult. There are no plans to make another, since it has serious c.g. problems. I do not own the rights to the original IMP. The manufacturing rights and the original 2-place IMP aircraft are owned by Mike Djada of North Richland Hills, TX. His phone number is unlisted. Also, Professor Ed Lesher (deceased) designed and built the "Nomad" several decades ago. It is a configuration like the one you are after. Look in some old issues of Sport Aviation or hire the EAA library staff to retrieve information on the Lesher "Nomad" for you. You may be able to design your own from that.

Q: What can you tell me about the 2-place IMP?

Many people have wondered what ever happened to the 2-place IMP.  I can't vouch for the absolute accuracy of this story but from what I have heard, Molt gave the unfinished project to one of his best "Coot" builders, Mr. Warren Edding of St. Louis. Mr. Edding worked on the aircraft for some time. The unfinished project was purchased from Molt by Mike Brown, of Dayton, OH. who modified it into a 2+2 configuration, finished and licensed the aircraft. Mike Brown intended to produce it as the Ascent I "Tribute". Unfortunately, Mike Brown lost ownership of the aircraft and it ended up in a "barn". Enter Mike Djada…

Mike Djada found the aircraft and recognizing what it was, purchased it from the owner. He has restored the aircraft to flyable condition and has flown it and displayed it at airshows in and around Texas. The aircraft is currently located in North Richland Hills, TX, a northern suburb of Ft. Worth. Mike also owns all rights to the un-built 4-place IMP design and it's derivatives.

Q: Is the Mini-IMP suitable for a two seat side by side modification? (ie.- expanded cockpit width and perhaps up to 120HP engine with a higher gross weight limit?)

No, it would not balance. You will need to design a completely new airplane to accomplish this mission.

Q: Is it possible to turn the Mini-IMP into a 2 place with the addition of slightly more power, and more wing area?

No. It would be necessary to design a totally new airplane since the existing airplane would not balance or stay within loading limits.  It may be possible to make a two place version balance by making it a 3-surfaced airplane like the Piaggio Avanti 180  but we haven't "run the numbers" yet.

Q: What are the ultimate load factors? (or is that what you mean by the design load factors +6/-4g in the performance data?)

According to the literature that Molt wrote, the +6/-4 numbers are ULTIMATE load factors based on a gross weight of 1000 lbs. These are engineering numbers as far as I know, no one has ever tested a wing to failure. Molt intended for the airplane to meet FAA "Normal" Category limits.

Q: There is reference to a short nose and long nose version. What is the benefit of one over the other?

Primarily the addition of some baggage space behind the seat.

Q: It is not clear what the difference is between your short nose and long nose versions (for a length increase of 1 foot there seems to be a 260 increase in empty weight, so there must be something I missed)

These numbers reflect the actual weight numbers for Molt's original short nosed prototype which had mechanical landing gear, a Limbach VW engine (63 hp) and minimal avionics and Pat Hart's long nosed airplane which has hydraulic landing gear, a Continental O-200 engine (100 hp) and full avionics. Like the ads sometimes say "your actual weight may vary... "

Q: I would like to know the cockpit dimensions.

The cockpit is 26 inches wide. The seat is highly reclined so that the actual height is somewhat misleading. A pilot 6'4" can fit in reasonable comfort, however because the pilot is significantly forward of the c.g., once the pilot weight gets much above 240 lbs or so the aircraft begins to become too nose heavy and will not rotate for takeoff.  This is more of a concern with the long-nosed airplane, the short-nosed airplane should work just fine for heavier pilots.

Q: What is the useful weight with full fuel?

Approximately 220-250 lbs., depending on the empty weight of the particular airplane and the limit g loads that you expect to be able to pull.

Q: …and I assume the Mini-IMP flies like a dream?)

Yes. Everyone who has ever flown one loves it. But it is NOT a trivial airplane to build. None of the tasks are difficult, but it is more complex than many of the other designs available to the amateur builder today. If you are a low time pilot or one with a limited level of experience, I would recommend that you BUY a good RV-4 or 6 and go out and have some fun. It is ALWAYS more expensive to build any airplane than to buy the same thing from someone who is tired of theirs.

Q: Are there any Mini IMP construction websites?

I believe that this, the official Mini-IMP website, and our free chat group, on Yahoogroups are the only ones that exists. If there are any others, I'd like to know about them too.

Q: Essentially I am trying to find a design that I can be sure I will be able to complete once I have started, so the more detail the better (I don't want to end up abandoning a half finished project!)

In that case, I would in all honesty recommend an RV-7 or RV-8. They are wonderful airplanes and have outstanding support. Alternately, one of the better "ultralights" like the Kolb Firestar, Titan, etc. make wonderful airplanes and don't cost much.

Q: I have heard about TPG. What is it?

See the TPG page on this website

Q: Also, are these kits still using the TPG concept?

This is a common misconception. The Mini-IMP never used the TPG concept. The TPG concept was used on the Micro-IMP, Perigee, and Bullet 2100. The Mini-IMP is sheet metal with fiberglass, non-structural fairings.

Q: What is the purpose of the Flexidyne™ coupling?

The purpose of the Flexidyne™ in the Mini-IMP drive train is to act as a torque limiting, "slip-clutch" device which slips ONLY during initial engine start and most importantly when the engine is accelerating or decelerating through various narrow RPM ranges at which a highly destructive, torsional resonant feedback occurs. At all other engine speeds, the Flexidyne™ is "locked up" and operates with no slippage and thus no power loss or heat. You can think of the Flexidyne™ as the mechanical analog of an electrical diode. It is a device which permits the transmission of power in one direction but not in the other.

Q: How many Mini-IMP's have been completed and how many are flying?

Molt apparently did not keep historical records. It has not been determined how many "kits" were sold by Molt. It is believed that approximately 25 kits were sold and at least 6-10 have been completed and flown.

Q: Who has a flyable Mini-IMP?

The known flyable Mini-IMPs in the U.S. belong to Gary James, Dr. Joe Biancarelli, Al Hilligass and Pat Hart. Several others are very near completion. Several others have been flown but have been damaged or destroyed and are no longer flyable. There are at least 2 flyable Mini-IMP's in countries outside the U.S.

Q: How long does it take to build a Mini-IMP?

Obviously this will vary widely with the experience of the builder and the available tools. An experienced builder with a good shop can build the Mini-IMP in 1500 hours or less. A first time builder may require much more time. The highest number of hours taken that are documented are by Senor Bernardo de Sousa Dantas of Sao Paulo, Brazil. It took him about 5000 hours. It should be noted however that he made numerous changes and that the time listed included building his own VW aircraft conversion from an auto engine. The recent availability of additional pre-fabricated components such as wing ribs, tail parts, etc. have reduced the required man hours from the earlier airplanes.

Q: What parts available and what is the cost?

See the current order form on this site, it lists the parts that are in stock. We add new parts on a regular basis.

Q: Are construction photos available?

Laser reproduced prints of 100 black and white photos that Molt took during the construction of the prototype are included with the Builders Manual / plans. They can be purchased separately for $35 and are made available in .jpg format on a CD-ROM (included in the plans) for viewing on your computer.

Q: Is a Builders Manual available?

Currently, the plans / Builders Manual, is a complete retyping and re-printing of the original text and drawings supplied by Molt. Molt's plans were first made available in 1975, prior to the huge surge in homebuilt activity. The plans were pretty good by 1975 standards but are not up to the standards of today's major kit suppliers. The manual is undergoing a continuous process of upgrade and improvement and the current edition is VASTLY superior to that originally supplied by Molt. The current manual is supplied in a 2" 3-ring binder with laser-printed text and photo collection. Most of the drawings are on 8 ˝" x 11" paper (as originally drawn) with several larger sheets and one large drawing of full sized patterns. As the manual is updated, reprints will be made available to registered plans holders for only the cost of reproduction and mailing.

Q: What is the cost of individual fiber glass parts?

Generally the parts are sold as a package deal. However, it you have a special need (a new design) or have damaged your existing parts, replacements can be obtained on an individual basis. Contact us with your SPECIFIC needs and we will provide a quote.

Q: Are the current fiberglass parts going to be made available in CARBON FIBER at additional cost to fiberglass?

Since the fiberglass parts are non-structural and don't weigh much to begin with, it is unlikely that any additional performance advantage would be gained by making them out of carbon fiber. However if that is what you REALLY want, we can custom make them on an individual basis. Contact us with your SPECIFIC needs.

Q: Has anyone looked at or is supplying foam/fiber glass wings/stabilizers as per Long EZ type structure?

We currently have a molded, composite vertical tail and are in work on stabilizers, etc. Additional parts will be made available as the program progresses.

Q: Has anyone done calculations on the Flexidyne™/shaft system for maximum horsepower (I'm looking at using a rotary engine derivative approx. 130/140hp).

Not to our knowledge. The drive system seems to have been designed empirically rather than theoretically or through detailed calculations. If you intend to put a larger engine in the aircraft than originally intended you MUST do your own design and testing on a ground test stand to ensure that your proposed installation is safe and airworthy.

Q: I take it that the Flexidyne™ works somewhat like a bicycle pedal & wheel?

Actually, I'm not sure exactly how a bicycle hub works.  I assume that a bicycle hub is a type of "sprag clutch" in which case the Flexidyne™ is not the same.

Here is a description of how the Flexidyne™-drive shaft works (it is difficult to describe without diagrams). The Flexidyne™ was invented in France and is used in industry as a "torque-limiting, slip clutch" during the start up cycle of high-inertia, electric motor-driven, industrial equipment such as conveyor belts, bark chippers, mixers, etc.  It was originally known as a "PowderMatic" transmission.  The device consists of two semi-hemispherical "bowls" joined at the lips. The "bottom" on one bowl half is attached to the prime mover, in our case the engine. Protruding from the "bottom" end of the other bowl half is a drive shaft that rides on bearings and is NOT physically connected to the bowl. We will refer to the two joined bowls as the "housing". Centered and freely rotating inside of the housing and attached to the end of the protruding shaft is a donut shaped metal plate which has been shaped in such a way as to be "wavy" around its circumference. This is the "wavy plate" or rotor. The rotor is free to spin in the housing and of course the output shaft also spins. At this point, you can see that if the housing is turned, nothing happens to the rotor/shaft except perhaps for bearing friction and no torque is transmitted. The housing is now partially filled with a "flow charge" of thousands of 0.020" diameter steel balls which flow almost as if they were a liquid, in fact, they are referred to as a "dry fluid". Now, when the housing is rotated by the engine, the balls are flung by centrifugal force to the outer circumference of the inside of the housing. This causes them to "lock up" and behave almost as if they were a solid on the wavy plate and cause the wavy plate and its attached output shaft to rotate along with, and at the same speed as the housing. The engine and the drive shaft are now "coupled". There is considerable "slipping" during the initial spin up but virtually no slip at normal rotational speeds. This is the desirable characteristic for the industrial applications. In our case the situation is somewhat different. At speed, with the flow charge behaving like a solid (or VERY viscous fluid) the entire drive shaft behaves as if it were one solid unit and it is possible to turn the output shaft and cause the housing to turn. However, there is a maximum torque limit to this behavior, which is what we desire.

Any intermittent combustion engine produces torque "pulses" which twist the drive shaft. These pulses travel down the drive shaft from the engine output flange toward the propeller hub. At the prop hub, the torque pulse is "reflected" and travels back down the shaft toward the engine. If the reflected pulse arrives at the engine output shaft at the same time as the next engine firing pulse occurs, then the pulses add together in "wave addition" and start back down the shaft at a larger magnitude than before. If this continues, then a "torsional resonance feedback" develops and the forces in the shaft rapidly build up to a level much higher than the structural strength of the shaft. If allowed to continue, it will snap the drive shaft or the engine crankshaft in two. The actual engine rpm at which this torsional resonance occurs is a function of the length of the shaft, the stiffness of the shaft and other design variables but it ALWAYS occurs, no matter how much "damping" is applied. As mentioned earlier, with the Flexidyne™ "locked up", the shaft can transmit torque to the housing and thus the engine, but when the feedback torque becomes too great, the rotor "slips" slightly through the flow charge in the housing and unloads the shaft. This is the key to preventing shaft failure. The Flexidyne™ will "slip off" all feedback torque loads greater than a certain value and allow the engine to accelerate through the torsional resonant rpm. After passing through the resonant rpm's the Flexidyne™ again "locks up" and allows full torque to be transmitted from the engine to the drive shaft. Thus, there is no power loss at the normal operational rpm's and the device only acts to prevent damage at resonant rpm's. This torsional resonant behavior is NOT a function of shaft "balance" or damping. No matter how well balanced your drive shaft is (and it must be balanced), the resonant behavior will occur at certain rpm's. This is why shaft designs with various "vibration dampers" etc, don't work and still fail. The problem is not vibration, it is torsional resonance. The only proven way to combat torsional resonance with some type of device that unloads the shaft at the harmonic frequencies. The simplest and most reliable of these devices is the Flexidyne™.

Q: Where can I read more about the Mini-IMP?

There have been several articles about the Mini-IMP in the various magazines which cater to the homebuilt aircraft movement. Here are a few:

Mini IMP

    Sport Aviation: 5/75, 6/75, 3/76, 7/77, 10/80, 2/81, 8/84

    Sport Aviation Nov 75 p. 18 Airfoil Selection for the Mini-Imp

    Sport Aviation Apr 76 p. 19 Mini Imp Flight Testing Continues

    Private Pilot 4/76

Micro IMP

    Sport Aviation Aug 79 p. 12 The Taylor Micro Imp

    Sport Aviation Sep 80 p. 16 The Micro Imp, A Design with Logic


    Sport Aviation Sep 73 p. 31 The IMP, a new kind of Trailer

Other Reading

    Sport Aviation Mar 80 p.20 Thereby Hangs the Tail (characteristics of inverted V tail)

    Sport Aviation Mar 82 p. 36 A Solution to the Long Shaft Problem (ie Flexidyne™)

    Sport Aviation Dec 88 p.38 The V Tail for Aircraft


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