RCU Review: Greg Covey's Amp'd Issue 12: Scale Electric Conversions!

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    Contributed by: Greg Covey | Published: July 2009 | Views: 43968 | email icon Email this Article | PDFpdf icon




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    Issue 12
    Article By Greg Covey

    Print Issue 12 "Scale Electric Conversions"

    Our R/C hobby has so many facets that sometimes it can become overwhelming to take it all in. Recent advances in technology have allowed many of us to enjoy the hobby without being skilled in all aspects of it. I would not likely have become such a model aircraft enthusiast if it were not for the ARF (Almost Ready to Fly) design. Although I learned to repair before I could fly, I am still only moderately skilled in most areas of building, finishing, and detailing a model.

    Today, we can learn almost anything about R/C from the Web. We have on-line communities, clubs, cliques, forums, marketing, and sales. With the click of a mouse button, we can easily spend our entire R/C budget for the season!

    In the past, R/C information was transferred through club members or at trade shows and flying events. Many of the early hobbyists were engineers, machinists, experimenters, and tinkerers that had a real passion for model aviation. Some focused on the engineering problems of the era like radio, servo, and engine design while others were drawn to the replication of full scale aircraft into smaller free-flight and R/C models. These so-called modelers were highly skilled at making exact duplicates of full size aircraft and could create a model from a set of plans on paper or just a few photos. My friend, Paul Weigand (AMA 76011), has been a modeler for over 50 years and has taught me many things about aviation in the last decade. Paul is a retired Automation Mechanic from Kodak and originally learned many of his modeling skills from Don Steeb (AMA 2163). Don was the founder of Don Steeb Inc. Precision Model Equipment which manufactured Atlas Servos in the 1950's & 60's era of R/C. He has been a mentor for many modelers in this hobby. Even Don still comes to the local R/C shows after 52 years and loves the advances he sees in the hobby.

    In this months issue of AMP'D, we'll see how electric flight has improved the performance and appearance of several scale aircraft. Although once originally flown using glow engines, these beautifully detailed planes are now scale electric conversions.

    Messerschmitt Me. 163 Komet

    Back in 1995, Paul decided he would replicate the Messerschmitt Me. 163 "Komet". The Internet back then was not what it is today so you had to use specifications from books or drawings to create your model. Photos were often hard to find. Since the Komet had a small prop in the nose that was actually used to power a generator, he decided that a slightly larger prop for the glow engine would not detract from its scale appearance.

    Paul is shown on the right posing with his model in 1995 that was originally built from Dennis Bryant plans. The plans came from Bob Holman with a fiberglass fuselage.


    In the forefront of aeronautical production throughout the world, the Messerschmitt Me. 163 Komet marked the beginning of a new phase in air warfare. In fact, this revolutionary interceptor was the first aircraft in the world to be powered by a rocket engine, and, had it arrived in the WWII conflict a year earlier, it would certainly have altered the balance between the adversaries. This small and fast combat plane's first mission took place on May 13th, 1944, Piloted by Wolfgang Spate, Commander of test unit 16.

    Early Me 163 A V4 prototype, 1941

    The Komet was the result of two great aeronautical technicians. The first was Alexander Lippisch, who started to work on developing all-wing gliders in 1926. Many of these concepts were used by Jack Northrop in his series of flying wings. The second was Helmuth Walter, who designed the first rocket engine fed by combustible liquids. The Me. 163 was simply a glider which used the revolutionary form of propulsion for only a few minutes which included the time for take-off, ascent, attack, and escape maneuvers. The aircraft was made of steel and aluminum with fabric-covered control surfaces. The pilot, fuel, and engine were all housed in the fuselage while the armament was in the wing root.

    Me 163 replica, 1994

    The Komet took off on a releasable undercarriage and landed on an hydraulically cushioned, extendible, steel skid. With it's 16,000 ft./min. climb, it could intercept bomber formations from above within two minutes. By comparison of the day, it took an Me. 109 almost twenty minutes (or 10 times) to reach the same altitude.

    There were several shortcomings to the design. The liquid fuel was very dangerous and caused many accidents. Engine runtime was only 5 minutes which gave it 2 minutes to seek out an enemy after first reaching altitude. This made it very vulnerable during its retreat as it made a long glide back to base.

    The volatile fuel could dissolve flesh in just seconds so the pilot's flight suit, boots, underwear, and gloves were made of a non-organic, nylon-like material.

    Another shortcoming of the Komet was that its speed became a disadvantage during attack due to the short range cannon that could only be fired from 500 yards away from the target. At 450mph, the pilot had only 2 to 3 seconds to aim and score a hit before breaking off to avoid a collision.

    Chief test pilot, Heini Dettmar, recorded a level flight speed of 623mph (Mach .85) in 1941, which was 155mph above the world speed record at the time. It was kept secret until the end of the war.

    The flight characteristics of the Komet are still seen today with each flight of the Space Shuttle. It is also a delta-shaped flying wing that gets rocket-powered to altitude, and then glides back to earth when its mission is completed.

    For more historical information on the Me. 163 Komet, read Schiffer Military History Volumes 20 and 57

    Proof of Scale

    Paul's 1/6th scale Me. 163B Komet won the best sport scale at the CNYMAA Symposium in 1996, when this show was big enough to use a NY State Fair Grounds building.

    When entering a scale competition, a "Proof of Scale" booklet is often used by the competitor to validate the specifications of the model.

    Here are comparisons of specs between the real prototype Komet and the 1/6th scale model:

    Me. 163B Specifications:

    30.5 feet---------------------
    18.8 feet---------------------
    4 feet------------------------
    210 sq. feet------------------
    18.8 feet---------------------
    8.2 feet----------------------
    8566 lbs----------------------
    42 lb/sq feet------------------

    Wing span
    Wing root cord
    Wing tip cord
    Wing area
    Wing loading
    1/6th Model
    ----------------------61 inches
    ----------------------16 inches
    -----------------------8 inches
    ------------------20 sq. inches
    --------------------37.5 inches
    --------------------16.4 inches
    ---------------------------8 lbs
    -------------------25.6 oz/sq ft

    Scale Master Conversion

    The original model used a Super Tigre .61 ABC glow engine with a MAC's tuned pipe and an 11x8 APC glow prop. The engine used 16oz of fuel. The cowl side was mostly removed for the cylinder head to protrude. This non-scale appearance was greatly improved from the conversion to electric power.

    Much of the detail work was left unchanged, including the releasable undercarriage that is ejected just after take-off.

    The new electric power system used the following components:

    Scorpion 4025-10 motor
    Jeti Opto 77 ESC
    8s 3850 Thunderpower eXtreme V2 batteries
    APC 12x12 e-prop.

    The power level measured 1650 Watts at 68.7 amps which provided 12,300 RPMs and 203 w/lb.

    Take off weight is 9 pounds with the 14oz gear so the flying weight with an 8s 3850mAh pack is 8lbs 2oz. This was about 10 ounces less than with the glow power system!

    Test Flying the Komet

    The new electric-powered Komet was Ready-To-Fly at 8.25 lbs without the dolly.

    Almost two decades after he first built the Komet, Paul does a final inspection on the new electric-powered model. Not only does the cowl look more scale but the Komet can now glide quietly while the "generator" prop free spins in the air.

    Komet Flying Video (23meg)

    Grumman F7F Tigercat

    Although conceived in 1941, by the time the twin-engine Grumman F7F Tigercat hit the streets, it never saw action in WWII. The XF7F prototypes first flew in December 1943, and the first production models were delivered to the Marines in April 1944. Some F7F-3N and -3Ps did deploy to Okinawa during the very end of the war but never tangled with the Japanese. It was fast and powerful and would have been a formidable foe to enemy aircraft. Although the F7F was too late for the "Big One", it did see serious action some five years later in Korea. (Ted Carlson/Flight Journal Magazine)

    The Kondor Model Products (or KMP) Tigercat was a beautiful fiberglass ARF model of the Grumman F7F Tigercat. Although the kit came with retracts, they were typically discarded due to their weakness. Often the best part about these fiberglass KMP ARFs was the shell itself. By combining this beautiful shell fuselage and sheeted wings with some skilled craftsmanship and new electric technology, the result can be a very special electric scale conversion.

    Built by Paul Weigand and funded and flown by Ron McGrath, this KMP F7F Tigercat is a beautiful scale replica of the Grumman twin-engine piston fighter.

    The weak (for a 30lb model) stock KMP landing gear was replaced with much stronger retracts from the giant scale specialist, Sierra Giant. Owner, Darrel Tenny custom CNC's these retracts for this specific model. They are a very strong, beautiful looking, scale landing gear.

    The nose gear retract was modified to include a steering servo.

    The Tigercat conversion used two E-flight Power 160 Outrunner Motor's, two Castle Creations HV-85 ESC's, and two sets of ThunderPower eXtreme V2 5AH Lipo packs.

    One combined 10AH pack feeds both ESC's in parallel. On the advice of Castle Creations Tech Support, Paul added 6 capacitors for the long battery leads.

    The full throttle current draw was 140-amps for the whole system. This provided 2465 watts from each motor when using 19x10 APC e-props.

    JR's 10-amp, 6-volt VR6010 High-Current Voltage Regulator installs between a model aircraft's battery and receiver to deliver a constant 6V to the receiver and servos. The regulator has a fail-safe On/Off switch and is also sold under the Spektrum brand name. Ron used two of these regulators for redundancy.

    The stock wing tube sockets were replaced with new fiberglass tube sockets to use carbon fiber wing tubes. The stabilizer halves were also made removable with servos mounted inside. The Tigercat used two JR R922 9-channel receivers, one in the wing, and one in the fuse. Each receiver had 3 satellites, for a total of 8 receivers, and is fed by two separate 10-amp regulators. Talk about redundancy!

    By using a separate receiver system in the wing, it greatly reduces the connections to the fuselage. All you really need is a power connection.

    All the power and air connections can be made after the wing is bolted down. Custom made motor mounts and Top Flite dummy engines were used. The E-flite Power 160 outrunners were made to look like the F7F prototype's gear boxes.

    Owner Ron McGrath and builder Paul Weigand carry the 30lb F7F Tigercat to the flying field for testing.


    Test Flying the F7F Tigercat

    The All Up Weight (AUW) of the F7F Tigercat was 30lbs, 5ozs, which gave a wing loading of 72 ounces/sq. ft. Although they were not installed for the initial test flights, the idea was to change to Mejzlik 18x10 3-bladed props for better scale appearance.

    The video shows just how much power the F7F Tigercat had on take-off. Ron never went above half-throttle except when performing a loop. The rock solid retracts from Sierra Giant proved their worth when landing the 30lb model.


    F7F Tigercat Flying Video (23meg)



    Today, we can learn almost anything about R/C from the Web. We have on-line communities, clubs, cliques, forums, marketing, and sales. Recent advances in technology have allowed many of us to enjoy the hobby without being skilled in all aspects of it. These advances in Lithium batteries, spread spectrum radios, and brushless motors, when combined with ARF (Almost Ready to Fly) designs, have created exciting new opportunities in model aviation by once again expanding the scope of R/C through electric flight.

    In this months issue of AMP'D, we saw how electric flight has improved the performance and appearance of several scale aircraft. By using both on-line and local community resources, we can learn a great deal about our hobby. When combining the building skills of the past with the latest technology, older existing designs and new ARF models alike can all become beautifully scaled electric conversions.

    When you fly electric, fly clean, fly quiet, and fly safe!


    Special thanks for contributions by:
    "Papa Jeff" Ring, Paul Weigand, Ron McGrath


    This section of AMP'D cover some of the questions that our readers have sent in and I thought would be interesting for others.

    Michael M. asks:

    Hello Greg,
    I'm writing you in regards to your Part III article on the Hangar 9 33% Edge 540 E-Conversion. I am currently working on a program which will be characterizing several carbon epoxy props as they relate to a particular aero body in a wind tunnel. The best way to accurately control/characterize the props are to mount them on an electric motor (don't want fuel fumes in a wind tunnel). We have decided to use the AXI Gold 5330/20 Double and 2 Jeti Advanced Plus 90 Opto Speed controllers (same as in your article) for reasons relating to required speed and power. I'm particularly interested in the AXI 5330/20 Brushless Motor connections as they relate to the electronic speed controllers and the receiver.

    Since I'm in a wind tunnel I will not be using batteries, just a single rack mounted power supply. I will not be driving/controlling any servos for ailerons, rudder and elevators...only the throttle. Your schematic shows a Discharge Protection Module (DPM) in between the Battery Packs and each ESC. Is the DPM there to protect the batteries or the ESC? Since I'm running the motors from a power supply and not from batteries do you think I need the DPMs? The second question...did you use a simple "Y" connection between the receiver and the two ESCs or is there more to it than that.

    Thanks in advance for your help.

    Greg: Hi Michael,

    The DPMs are there to protect the batteries so you won't need them. The concept of DPMs was not very popular in the market even though it protected your expensive batteries. The cost, weight, and complexity was too much for non-engineering type hobbyists.

    A simple Y-harness between the two ESC control lines and the receiver throttle channel is all you need. Remember to extend the three motor wires, if needed, and keep the wires from the ESC to your power supply 18" or less. This will allow most any ESC to compensate for motor inductance changes and prevent a blowout. The wire length between the motor and ESC can be very long (like up to 10'). If you need to run power supply wires longer than 18" then add some 220uF-330uF capacitors (or similar) with a proper voltage rating using the technique shown on the Schulze Tips Page.

    Good luck on your project!

    Ask questions by e-mailing me at greg@rcuniverse.com


    Enerland 20C, 25C, 30C, and 40C LiPo Packs available at Hobby Lobby Int.

    E-flite PT-19 450 ARF
    Switches from Radio Control to Control Line and back again in just a few minutes!


    ParkZone P-51D Mustang BL BNF
    The Bind-N-Fly? Revolution continues with a fully aerobatic tribute to the most successful fighter of WWII!


    Super Tigre Brushless Electric Power Systems

    Super Tigre has been well known and liked for their glow engines for many years. They have now released a brand new line of electric power systems designed to provide modelers with that same dependable quality at a very attractive price!

    Not only is this new line of electric power products an excellent value, they come with a 100% quality guarantee that is backed by the full support and service that modelers have come to expect from Great Planes.

    All the items are matched to work together and there is NO SOLDERING REQUIRED! The 3-cell Lithium Polymers packs come with a Great Planes ElectriFly compatible charge connector and a separate discharge connector that mate to the Electronic Speed Controllers (ESCs).

    Print Issue 12 "Scale Electric Conversions"

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