How to convert the Combat Models A-10 Warthog to Electric Ducted Fan.

Introduction:

The Combat Models A-10 Warthog was designed for a single pusher prop .32 to .45 two cycle glow engine. I will describe how you can make a successful electric jet model complete with turbo fan scale sound and flight performance similar to it's big brother. 

As an added bonus to this project when we traveled to the large electric event *KRC 1998 I was awarded 2nd place for 'Best Technical Effort' and was very proud since this is a large show and had many models present. They were impressed with the small amount of wire used. When I realized Keith Shaw came in 3rd place I was even more happy that I had achieved a nice accomplishment for this area.

History:

First let me start with a little history. After many years of flying different glow powered prop and ducted fan jets I became very interested in scale jets however the two cycle sound of that glow motor was a big detractor for me to expand my jet fleet beyond the sport jets and the type of flying I was doing at the time although I desired a more realistic approach it didn't appear I would reach it unless at that time make a heavy investment in a Turbine powered system.

In the early 1990's I began to move towards larger electric prop planes and found great enjoyment in being able to locate an open area and fun fly without going to the regular flying field and multi-motor prop designs showed me I could create a much larger airframe. As time marched on by 1993 I began to notice an increased popularity to the developments of a couple noted pioneers like Bob Boucher and Keith Shaw along with many others in the electric field and it was clear electric flight was hear to stay and growing fast. 

As several countries had major political changes and the worldwide barriers begin to drop it was clear we had areas all around the world contributing to electric flight in a large way. Many areas in Europe had been forced to rapid development because so many of the glow fields were being shutdown without recourse because of noise in proximity to nearby population. Not only did the traditional prop planes but the jets as well and so came the scale jet modeler's creating a strong movement in using electric motors with fans to create some very nice models. Once I saw this I was hooked for sure. 

With that knowledge I felt a starting point could be achieved to not only help solve the scale sound issue but also an added benefit of eliminating all the glow fuel requirements and everything else that goes with it and the cleanup routine. I then pursued the market for an appropriate model to start with and quickly found that most of  the jet market was designed for the larger glow motors and I would probably need to scratch build something around a fan. I desired a full featured jet that would have Aileron, Elevator, Rudder, Throttle and Retracts. Traditional Taxi out, Takeoff, Fly around, Land and Taxi back was my basic scenario. Not much to ask. :)

Component selection:

When hauling batteries ROG is a tall order, however it was still going to be my objective. After researching the current fan technology it was quite clear to me that a company called WeMoTec who had also recently acquired another company making EDF units called Electro Jet Technologies began producing electric ducted fan units aimed at high RPM. Since these fans were purpose built for high performance electric motors I knew this was an important step towards a successful project and I would not need to construct a fan from scratch.

At that time being in Arizona, I was reminded almost daily of a particular interesting jet called the A-10 and have always admired it's unique flying abilities along with that Turbo fan sound so it was a easy decision to make it my first adventure in EDF. After researching for kits I found a interesting company called Combat Models in San Diego whom made just what I needed. It's base construction was injected foam and it was very scale and lightweight so the project was on.

Before I purchased the CBM A-10 kit I received the assembly video tape and after watching it I felt that the suggested lightweight fiberglass process over the foam components would be very beneficial to the models durability and longevity without adding much weight. After inquiring about the process CBM mentioned a third party called Modernaire Aviation that could do that process for me along with the assembly and painting scale details. Once I contacted them and discussed my project I was sold on their detail package and provided to them the changes in adding strength for the battery compartment  and motor/fan nacelle areas along with eliminating the normal modifications for pusher operation and all fuel proof requirements. They did a wonderful job assembling and detailing the model for me nicely so I could continue with the radio and power package design and installation.

During this project I contacted as many people as I could around the world who had successful experience with EDF jets to study there accomplishments and note the components in use to determine performance guidelines. At that time the  WeMoTec *Eco Fan Pro showed data with the Ultra 930/10 that had the numbers I was coming up with in order to power the A-10 properly. I was then lead to *Unbeaten Path Imports who had the fans and motors so I wouldn't need to import anything.

Construction:

I started to design the internal layout and placement of the various components by weighing each assembly. Since the instructions call for a good amount of lead ballast in the nose I was able to take advantage of this by positioning the servos and batteries such that no additional weight was required for the proper balance point at the C.G. given in the documentation.

The *Eco Fan Pro was mounted in the nacelle so that the distance from the edge of the fan housing to the edge of the intake is 1-3/4", The mounting flanges were recessed and secured. The motor wires were brought into the access area and connectors applied. I had planned a removable top nacelle cover however once everything was in place I decided to secure it since the additional construction to make a proper hatch could compromise the strength and only in a major motor or fan failure would a hatch be required if neither the front or back access had enough room.

The rear underside fuselage hatch gains access to the Motor wiring, Speed control and Charge/Arm switch embedded into the hatch for ease of use and does not need to be opened under regular use. You can also see in the lower right corner a 1/4" area is left open which is the exit air as it comes through the front and passes by the batteries and controller. The Charge connectors and Charge/Arm switch is operational from the outside. The hookup is designed so the switch the Red/Positive connection between the speed controller Red/Positive input or the Charge connector Red/Positive using both sides of the DPDT switch for additional contact size to make the lowest possible resistance connection. The Black/Negative battery lead is common for both the Charging connector and Speed control Black/Negative input. The speed controller output connections attach directly to the motor connections and are also doubled since each motor wire has a connector, this method proved very convenient when profiling the power package using the Astroflight Whatt meter so all areas can be probed for data however not required.

The battery compartment is located just in front of the leading edge of the wing area in the fuselage 2-1/4" and forward with both packs stacked together with a air gap between them for cooling. A balsa locking frame was put in place to secure them since I was not going to make these field removable. Another possibility would be to design the top canopy as a hatch for field changing however at the time keeping the structure sound and in one piece was my goal.

The nose gear area also provides good airflow that moves through the center of the fuselage and back towards the tail. This of course is key to keeping the system as cool as possible under the high continuos load the system is in.
 

2  - *Graupner Ultra 930/10 brushed motor.
2  - WeMoTec *Eco Fan Pro
1  - Astroflight 204D 50 amp brushed speed controller.
2  - 10 x *RC-2000 Zapped cell packs.
14 - Red/Black Sermos connectors.
1  - 1.5' of Red 13AWG and 1.5' of Black 13AWG Silicone multi-strand.
1  - 40 amp DPDT arming/charge switch.
1  - Robart 605 and 607 pneumatic retracts.

Wing Span: 52" or 132 cm.

Length: 47" or 119 cm.

Wing Area: 423 sq. inches or 2730 cm squared.

Weight: 7.6 lbs. or 3447.23 grams. flight ready.

Motors: 2 - WeMoTec *Eco Fan Pro with 2 - *Ultra 930/10 motors in (parallel hookup).

Power: Performance enhanced / Zapped - two *10 x RC-2000 cell packs in series hookup.

Controller: Astroflight 204D, rated at 60 amps

Surfaces: Throt., Rud., Elev., Aile., Robart pneumatic retracts, Flaps.

Radio: Hitec Prism 7x, 1200mah flight battery with Micro 535 rec. and HS225bb servos.

38.5 amps full throttle.

7 degrees nose high for proper thrust angle and short rotate takeoff.

*Note: 

KRC has since been retired and the NEAT fair is the new event.

WeMoTec replaced the Eco Fan Pro with the Midi Fan in 1999

I now use RC-2400 performance enhanced cells along with other motor options. Astroflight and Aveox.

Modernaire Aviation. Jerry McGhee and Alex Whyte. Are both in the Air Force and have since been relocated.

Unbeaten Path Imports who is now closed due to the untimely death of the owner Andy Fok in early 1999
 

Large kit box.

Pre Molded kit parts.

This is all the power package items needed for EDF use.

Standard wing attachment so your able to transport easily.

Two standard servos used for the Flaps and Ailerons. Notice the robart quick release connectors, the tubing is two different colors so it's easy to transport without remembering hookups.
 

The fans are recessed in the nacelles.

The charging connectors and Arm/Charge switch are external for ease of use. Notice the notch in the lower right area of the hatch. This is for the exit air flowing through the fuselage.

You can see the speed control is used to not only make the connection but positioned inline so no additional wire is required from the battery compartment/

Here you can see some of the carbon fiber used throughout the model to help the structure. This is included with the kit.

The elevator and rudder servos are place all the way forward to keep them clear of the battery compartment.

Here you can see the forward access hatch and see the air fill connector and the flight pack charge receptacle with the on/off switch. You can also see how the air travels from the nose gear area.

The retract tank sits just about the wing. Again you can see the carbon fiber used to strengthen areas.

With the forward hatch removed notice the battery compartment and the two stacked packs. The retract servo and valve along with the receiver are all above. The airflow moves through this area and back.