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|The pusher powered model in flight (click small images to enlarge).||The motors and pusher props of the original Vulcan (click small images to enlarge).|
I decided to use the previous prop powered Vulcan plan as the basis for my new design. This model used two outrunner motors rated at 540 Watts, supplied by two 3-cell LiPo batteries. The motors turned 8x6 props. The current was not measured so I don't know their power consumption. Being new to electric ducted fan power, at first I thought that I could use a pair of 70mm EDF units, but I was advised that this would not be enough for such a large model.
Various fan possibilities for the power system were considered such as a single 110mm fan with bifurcated ducting, or two 90mm fans, or even four 70 mm fans. After considering these options, it was decided the electric power system for this model would use four 70mm fans, to be supplied by four 3S LiPo batteries.
|This large model uses 4 x 70 mm EDF units to provide thrust.||The availability of a laser cut parts set saved time and effort.|
I soon realised that the necessary modifications to the previous design would be quite extensive, so I would have to draw up a new set of plans for this model. I made the new plan over the original one.
The main design changes from the pusher prop powered model were:
1. Installation of four 70mm fans in
the wing roots, directly between the intake and exhaust
2. A large opening bomb bay to accommodate the batteries and make access easy
3. Moving the landing gear – this would now be situated in the scale position, whereas previously it had occupied a space which was now needed for the fan units.
The new model shared much of the design of the prop powered version. I had a laser cut wood parts set for the prop powered Vulcan. I used many of these laser cut parts for the new model although of course some of the parts had to be modified. This was still a lot easer and quicker than building from scratch so I was off to a good head start.
Construction of the model started with the fuselage. The basis of the fuselage is circular balsa formers and stringers. When finished, the fuselage was covered in 2.3mm balsa sheet. The canopy was shaped from pink foam.
|The fuselage is constructed using formers and longerons.||The wing root area at an early stage of construction.|
|The completed fin is held in position.||The wings start to take shape.|
The tail fin is the same as for the pusher powered model and only has a few parts. These were glued together and the structure was then sheeted with 2.3mm balsa. Although the model has nose wheel steering, it does not have a rudder. This would be an easy modification and one which I feel the model would benefit greatly from.
The Vulcan’s wing is straightforward to build. The lower surface is flat, allowing the wing to be built in one piece on a flat building board. The elevons were made up as normal using the part set for the pusher model. The entire wing was sheeted in 2.3mm balsa.
The full size Vulcan’s wing has a slightly drooped leading edge near the wing root, allowing the aircraft to make extremely tight turns at high altitude, in many cases even being able to out turn many fighters of the day.
|More progress on the wings.||The underside of the completed airframe.|
I used the mechanical retracts from the previous Vulcan for this new model. My old pusher used to bounce a few times like a nodding dog before leaping skyward, so for this model I added some packing under the nose gear unit to make sure the model would sit in a slightly nose up attitude for easier take offs. The full size Vulcan needed a nose leg extension to maintain the wing at 3.5 degree angle on the ground for easier take offs. The bomb bay doors were narrowed at their front end so that the nose leg could retract.
Another possibility for the landing gear
would be a set of the new electrically operated retracts.
These seem to work very well and would be the best course
to take with this build as they do look the part slowly
opening and closing giving a sense of scale to the proceedings.
I believe that this type of retracts will become the norm
as they avoid the hassle of air bottles and pumps or extra
servos and leads.
|Starboard main landing gear installed.||The completed but unpainted airframe. It's a big model!|
For this model a new AR7000 receiver was purchased and placed with in the bomb bay area. The model uses two digital servos for the elevons. The method of providing RC system power is by using a UBEC and an 800mAh LiPo battery.
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