RCU Review: Bohemia Models Monocoupe


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    Contributed by: Greg Covey | Published: June 2003 | Views: 32292 | email icon Email this Article | PDFpdf icon



    Monocoupe
    Bohemia Models
    Electric Conversion

    by
    Greg Covey
    gcovey@microwavedata.com



    MODEL SPECIFICATIONS

    USED IN THIS REVIEW

    Wingspan:
    Length:
    Wing Area:

    Weight:
    Airfoil:
    Wing Loading:
    Retail Price:
    Manufacturer:
    Distributor:

    82" (2080 mm)
    50" (1380 mm)
    1054 sq. in. (68 dm2)
    160 oz. (4536g)
    Unknown
    21.9 oz. sq/ft.
    $379.00
    Bohemia Models
    Hobby Lobby

    Motor:
    Receiver:
    No. of Channels:
    Servos:

    Radio:
    Battery:
    ESC:

    AXI 4120/14 Rotating can motor.
    Hitec Supreme 7-Ch. Receiver
    5 (ailerons, flaps, rudder, elevator, .throttle)
    Hitec HS-85BB Servos (ailerons-2,
    Elevator, Rudder)
    Futaba Super-8
    14-Cell HR-SC2600mAh NiMH
    Jeti Advance 70-3P Opto

    I N T R O D U C T I O N

    HISTORY OF 1928 "Monocoupe"

    The Monocoupe 22, the prototype of the 70, was the first light cabin monoplane to be certificated under the Department of Commerce regulations established in 1927. In 1928, nearly 90 percent of all the light airplanes produced and sold in the United States were Monocoupes. The popularity of this light cabin plane lay in the side-by-side seating and the pleasant, though spirited, characteristics of the aircraft that made it fun to fly.

    In the mid-1920s a young advertising man named Don Luscombe flew his open cockpit JN-4D "Jenny" in and out of a small airstrip in Davenport, Iowa, he thought about how much nicer it would be if he could fly in a relatively small enclosed-cabin airplane. Then he could dress in a business suit rather than the usual helmet, goggles, and flight coveralls of the day, and arrive at his destination ready for business or pleasure. He decided to build his own aircraft, a two-place, side-by-side cabin monoplane with a simple but strong structure and a powerful engine. Luscombe was somewhat influenced by the design of the rather rakish-looking Belgian Delmonty-Poncelet Limousine, a high-wing monoplane with a side-by-side enclosed cabin and the reverse curve rear fuselage lines that were to become one of the signature identifier features of the Monocoupes. Luscombe's mock-ups impressed his companions in the Davenport Flying Club so well that, in October 1926, they raised $5,000 to help him start the Central States Aero Company. To build his dream, Luscombe hired a young self-taught designer by the name of Clayton Folkerts who was to later design championship racing airplanes of the 1930s.

    Folkerts built the first prototype, Mono #1, almost single handedly, in about 4 ½ months and E.K. "Rusty" Campbell made the first test flight on April 6, 1927. The airplane configuration was a two-place, side by side, strut-braced high wing monoplane with a conventional tailskid and main wheel landing gear. The fuselage and tail structure was of welded steel tubing. The one-piece wing was constructed with routed solid spruce spars and the ribs were constructed of spruce and basswood. The entire airplane was covered with Grade A cotton.

    Mono #1 received a lot of interest, but just as Luscombe began to think about customers, a fundamental change in aircraft production occurred. The U.S. Department of Commerce Aeronautics branch instituted the Approved Type Certificate (ATC) program requiring all potential commercial aircraft designs to undergo analysis and test for a type certificate. Because Folkerts did not have formal training in engineering, Central States hired university graduate Jerome Lederer, a consulting aeronautical engineer, to verify the performance predictions and the structural integrity of the airplane. Lederer hired two graduate aeronautical engineers, Fred Knack and Bud Whelan, to help in the certification process. Luscombe's and Folkerts' basic design proved to be sound and ATC #22 was awarded to the Monocoupe in January 1928.

    The name Monocoupe referred to the marriage of a monoplane and the coupe, the two-passenger enclosed car. The first model was known as the Monocoupe Model 22 (after its ATC number) and a total of 20 Mono 22s were built. The engine, a Detroit Air Cat air-cooled radial proved to be problematic and several others, including the expensive Anzani, were tried. The solution appeared in the form of the Velie M-5 five-cylinder radial, a similar but more reliable engine than the Air Cat. The engine was nominally rated at 55 hp with maximum of 62 hp available for take-off. The Velie engine came from the highly successful Velie Motors Corporation in Moline, Illinois, and the compatibility of this engine and aircraft encouraged the Velie family to support Luscombe and go into full-time aircraft production. Central States Aero moved just across the Mississippi River to Moline and became Mono-Aircraft Inc., a subsidiary of Velie Motors.

    The installation of the Velie engine into the Monocoupe airplane, along with a few minor improvements, resulted in the Monocoupe 70 that was issued its Approved Type Certificate (ATC 70) in September 1928. In June 1928, Phoebie Omlie, a racing pilot, announced her intent to fly her Velie-powered Monocoupe Chiggers in the National Air Tour and with it she also won the lightweight division of the Women's Air Derby in August 1928. The Monocoupe 70 flew at air races around the country with Omlie, Johnny Livingston, and Vern Roberts. Luscombe established dealers and distributors around the country and even wrote a book entitled Simplified Flying for advertising purposes. More than 350 of the Model 70 and its incrementally improved companion Model 113 (ATC 113 issued Feb. 1929) were produced. The flashy good looks did not come cheaply though, as it cost between $2,500 and $3,000 to buy. While the standard Models 70, 110, 113 and 125 were more docile to fly than the 110 and 113 Specials, it really was not an airplane for the novice pilot.

    George Law purchased Monocoupe Model 70, NC6730, serial number 133, in July 1928 and it went through a succession of sixteen owners before it was severely damaged in a crash in 1940. Robert and Glen Jordan sold the aircraft when it was declared not airworthy and three additional owners passed it along until it was given to famous racing and test pilot Tony LeVier in 1975. He acquired title in March 1978 and had the aircraft restored with its striking black fuselage and vertical tail with orange wings and horizontal tail. Some people suggest that the only original parts of the airplane are the nameplate and the paperwork, nonetheless, it is one of only a few of the famous type still in existence. LeVier donated it to NASM on December 12, 1983, and it was stored in California until it was lent to the California Museum of Science and Industry in Los Angeles in 1984.

    Copyright © 1998-2000 National Air and Space Museum, Smithsonian Institution

    Full Scale Specs

    Wingspan 9.7 m (32 ft)
    Length 6 m (19 ft 9 in)
    Height 1.9 m (6 ft 3 in)
    Weight Empty 360 kg (795 lb)

    INTRODUCTION

    When I first saw the Bohemia Model's Monocoupe, I couldn't help but think of the history behind the plane. The short "snub" nose wasn't pretty, but, it was needed to balance the plane with the heavy rotary engine.

    I also had the opportunity to test a new larger size outrunner motor from AXI. It installed easily behind the firewall and could spin a 13" prop without the need for a gearbox.

    The quality of the ARF construction, and, overall size of the plane with its 81.5" wingspan, provided for an enjoyable conversion to electric power! All the parts were carefully wrapped in either foam or bubble-wrap. Only my wing halves needed a touch-up with the heat gun on a few small areas.

    Kit Contents after they are unwrapped

    C O N S T R U C T I O N

    TAIL ASSEMBLY

    I started my tail assembly by first mounting the servos in the fuselage. I built the elevator and rudder servo assembly outside the plane and then installed it into position before gluing with 5-minute epoxy.

    The servos were first mounted on the posts outside

    The entire assembly was then glued into place

    I placed the horizontal stabilizer on the fuselage tail and traced an outline onto the stabilizer with a black marker pen. This included the leading edge notch that will align with the vertical stabilizer leading edge post and also with the slot in the fuselage tail.

    The elevator halves are joined together by gluing the pre-bent joiner rod into the pre-drilled holes and channel slots. I used 5-minute epoxy. Before attaching the elevator and rudder to the stabilizers, I cut the ends off of each side of the supplied nylon hinges. I cut through the outer set of holes to shorten the length of the hinge. This allowed it to fit into the slots easier. I then glued the hinges onto the stabilizers using a small amount of 5-minute epoxy. Finally, the control surfaces (elevator and rudder) were attached.

    The clevis was CA'ed onto the tail ends of each control rod

    Both stabilizers were glued at the same time using 5-minute epoxy

    Once test fitted, both stabilizers were glued onto the fuselage tail at the same time using 5-minute epoxy. I then mounted the control horns per the diagram and attached the clevis to insure good alignment. Be sure that the 4 adjustment holes on the control horn are in-line with the gap between the stabilizer and the control surface. Since the control surfaces are rather large, it is important for the servo to have the best mechanical advantage (or leverage) to move them. Having the control horn swivel directly over the hinge line also provides for equal throw in either direction.

    The control horn holes are mounted over the hinge for best leverage

    The fixed position tailwheel mounts easily with supplied hardware

    The fixed position tail wheel mounted easily with 2 screws and a custom plywood cover. The undercarriage and wheels also installed easily with the supplied plastic fixtures, screws, and self-locking nuts. I choose not to install the balsa planks on the undercarriage to reduce drag in-flight.

    The undercarriage and painted wheels also installed easily

    All the plastics were cut and sanded smooth before test fitting into position

    At this point, I cut all the plastics using scissors and sanded the edges smooth with a fine grit sandpaper. I later choose not to use the wing servo covers.

    WING ASSEMBLY

    I skipped over the black laminate cover for now and did a test fit of the wings after first installing the two metal rods in the center section. When I was satisfied with the fit, I decided at this point that I would not be using the flaps. I felt that the plane would take-off, fly, and land relatively slow without flaps due to the aggressive airfoil design and rather large wing area. I taped the flaps up using clear cellophane tape.

    The wings were test fitted and measured to be 81.5" long

    Plenty of table space is needed to assemble a model this size


    The servo bays were very nicely set up to accommodate various sizes. My Hitec HS-85BB "Mighty Micro" ball bearing servos are smaller than standard size servos but they fit perfectly without modification. I mounted the servo onto the supplied posts first and then routed the extended servo lead through the wing with the help of a spare metal control rod.

    The white control lever was epoxied into the aileron and the two black suspension levers were glued into the wing at the same time. Be sure to align these levers in the proper direction. While the epoxy was drying, I soldered the brass caps onto the control rods. The remainder of the linkage was assembled per the manual diagram on page 9. You may need to cut the metal control rod length before soldering.

    My Hitec HS-85BB "Mighty Micro" servos fit without modification

    The "Y" adapter input lead was extended to reach the receiver

    To finish the wing assembly, I installed the eye hooks into the fuselage end of each wing half after first opening them up half way. This allowed them to extend inside the wing center section and provided an easier connection for the rubber band support. A longer eye hook would have worked better here.

    The wing halves were then fitted onto the center section. To test the ailerons, I connected the servo leads to a "Y" adapter in the center section that extended down into the fuselage to the receiver. The single input of the "Y" adapter was lengthened with a 12" piece of ribbon cable. Alternatively, you could also purchase another 12" extension cable.

    The eyelet hooks were opened up to provide easier access

    The wooden dowels and Velcro allowed for easy wing assembly

    My ailerons tested out fine and needed only a minor adjustment for proper alignment. The black plastic wing center cover was mounted using several small wooden dowels in the front and Velcro on the back. This provided easy access for wing assembly in the field

    POWER SYSTEM:

    Since I was using an AXI 4120/14 outrunner motor, I decided to try to balance the plane with the motor mounted behind the firewall. This made it easy to mount the motor with four M4 screws, and, as it turned out, the plane balanced fine using my 14-cells of HR-SC2600mAh NiMH. When mounting the motor directly against the firewall, I needed to slightly counter-bore a larger diameter hole in the rear of the firewall. This allowed room for the motor shaft holding clip to rotate. Alternatively, you could add some thin washers on the M4 screws in-between the motor and the firewall.

    I decided to install my battery packs, one 8-cell pack and one 6-cell pack, from the front of the model just below the firewall. I routed the connection from the combined packs to the ESC outside the bottom of the fuselage. This would allow me to screw on the front cover and easily re-charge the packs in the field without removing them.

    AXI 4120/16 Power setup

    Since I was using an Opto-coupled Jeti ESC, it had no Battery Eliminator Circuit (BEC). Instead of using a separate receiver battery, I used an Ultimate BEC (or UBEC) from Kool Flight Systems. The Ultimate BEC is an external circuit that taps power from your battery pack and regulates the voltage to the necessary 5 volts to power your receiver and servos. It does not replace the speed control. However, it provides the BEC function in a speed control with much more capabilities.

    Power Setup

    AXI 4120/14
    SETUP
    Power Supply
    14-cells
    Current
    43 Amps
    Prop APC 13x8 e-prop
    Gear Ratio
    none
    RPM
    8200
    Battery
    HR-SC2600mAh
    Battery Type
    NiMH

    FINAL ASSEMBLY:

    The kit provides an addendum sheet to the manual along with the pins to allow easier assembly and disassembly of the wing support struts in the field. The support struts are stored with the wing halves and connected to the fuselage using the new pins.

    The strut modification allows for easy wing assembly in the field

    For a better scale appearance, I created some mock cylinder heads from wine bottle corks. By cutting the cork both lengthwise and widthwise, I created 4 heads. A second cork was needed for the 5th head to simulate the original Velie M-5 five-cylinder radial engine look. I painted the heads silver and CA'ed them to the painted firewall. A black 2" HLHS200 spinner completed the look.

    The cylinder heads were made from cork

    The finished Monocoupe looks very scale.

    READY TO FLY

    The kit comes with decals already applied to complete the authentic look of the aircraft. I tested my power system with the 14-cell, 2600mAh NiMH pack and APC 13x8 e-prop. I measured 8200 RPMs at 43amps. The pull felt very strong and made me confident that it would be sufficient power for this plane. I was Ready-To-Fly (RTF) at about 160oz (or 10lbs).




    F L I G H T R E P O R T

    TAKEOFF:
    The model had plenty of power for a grass takeoff into a 10mph breeze. The huge wing area lifted the plane easily and gently. The tailwheel lifted first and then the whole plane. The Monocoupe took-off with authority into clear, blue sky!


    FLIGHT PERFORMANCE:

    I expected the model to fly well but I was surprised at just how much power the AXI rotating can motor provided. I could easily cruise around at 1/2 throttle in a 10mph breeze. The plane wanted to continue climbing so I added a few clicks of down trim to the elevator to obtain level flight.

    Our maiden flight was with a 10 mph breeze that shifted directions. Although it handled well, this is probably the most wind that I would fly the model in. You will get a more relaxed flight with 0-5mph winds.

    There were no bad stall characteristics exhibited and the model turned very well with just the rudder control. Aileron turning was fun, and, as expected, I didn't miss having flaps. My smoothest turns were made with a combination of rudder and ailerons. My Futaba Super-8 transmitter can easily program the needed mix of rudder and aileron but I used both sticks for turning on the initial flights. We had fun taking turns on the sticks and talking about increasing the scale looks even further.

    LANDING:

    Landings were simple but can be fast if you don't properly reduce speed. The model has plenty of lift so it can require a large area to land comfortably. Although flaps would help in slowing the plane down for landings, I feel that using a proper approach is best for this design, although, this is likely just my personal preference. We had plenty of power for a few "touch-n-gos" before landing.


    The plane is large and easy to see in the air. When landing, the front wheels touch down first and then the tail wheel.

    CONCLUSION:

    The Monocoupe turned out to be an easy electric conversion project. Using the direct drive AXI rotating can brushless motor eliminated the need for a gearbox and made for a simple installation behind the firewall. The power system proved to be an excellent choice for this rather large historic model. There are no brushes or gears to wear out. The ease of maintenance on a direct drive solution is very attractive. Since it will fly in some wind, and, take-off from grass with authority, I plan to fly my Monocoupe often in the upcoming Summer months.


    S U M M A R Y

    1-POOR 2-NEEDS IMPROVEMENT 3-AVERAGE 4-VERY GOOD 5-EXCELLENT

    Take-Off:

    Packaging:

    Landing:

    Construction:

    Basic Aerobatics

    Hardware:

    Low Speed Flight:

    Instruction Manual:

    High Speed Flight:

    Ease of Assembly:

    Stall Characteristics:

    Kit Completeness:

    Scale Flight:

    Finish Quality:

    HITS

    MISSES

    bullet

    Very Scale looking

    bullet

    High quality, solid construction

    bullet

    Short assembly time

    bullet

    Excellent scale performance

    bullet

    Good Parts Fit

    bullet

    Easy conversion to electric

    bullet

    Easy field wing assembly

    bullet

    Wing Eye Hooks too short

    1928 Monocoupe E-Conversion

    The 1928 Monocoupe from Bohemia Models is a great electric conversion. Check out Hobby Lobby for more information on this great model.


    May 2003

    P R O D U C T I N F O R M A T I O N

    Hobby Lobby International
    5614 Franklin Pike Circle
    Brentwood, N.J. 37027 USA
    Tel: 615-373-1444
    Email: sales@hobby-lobby.com
    Web Site: www.hobby-lobby.com

    Hitec RCD USA, Inc.
    12115 Paine St.
    Poway CA, 92064
    Phone: 858.748.6948
    Fax: 858.748.1767
    Web Site:
    www.hitec.com
    Kool Flight Systems
    Ultimate BEC (UBEC)
    Available at Hobby Lobby Int.



    Comments on RCU Review: Bohemia Models Monocoupe

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    The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply generally to similar products by the manufacturer. We cannot be responsible for any manufacturer defects in workmanship or other deficiencies in products like the one featured in the review.

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