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Old Jan 29, 2005, 07:04 PM
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Darwin Australia
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C47 with two AC World CD-ROM motors and one CC Phx 10 controller.

This morning I maidened my C47. It was fitted with two Aircraft World CD-ROM motors connected in parallel to one CC Phx 10 ESC. As well there were several modifications to the control surfaces to reduce their size.

Flight report.

Aeroplane: - GWS C47
Motors: - Aircraft World CD-ROM
Input Power: -static 41.6 Watts. Top speed 36.5Watts
Motor Efficiency: - 57.1-57.4 %
Propellers: - GWS 5 x 4.3
Battery: - Prolux 1600 mAh Lithium Polymer
Rx: - Fieago
Aileron Servo: - GWS Naro Pro
Elevator Servo: - GWS Naro+
Rudder Servo: - Park Flier 09
AUW 15.2 oz Unpainted
CG 78 mm from LE at the wing center

The first flight had one problem, in that the aeroplane wanted to pitch up under full power and dive when power was cut. This is a symptom of a nose heavy aeroplane so I will be slowly taking the CG further rearward. My calculations give a CG further back than the current 78 mm from the LE at the center of the wing.

My reduced to scale size elevator was smooth and effective. The aeroplane has enough power to loop from level flight and flies nicely at about 80% power but needs up trim to keep the nose up on this power setting. A well as the CG change I will probably mix throttle to elevator to help alleviate the pitch changes.

Aileron response was good and smooth even with my smaller ailerons. I did not try to roll the aeroplane but I see no reason that it would not but, like my similar sized Catalina, it would probably loose a lot of height.

I tried a stall turn but more rudder throw is needed to make them look good. I did not try a spin.

Three airborne restarts, from stopped motors, were made during this flight. All were instantaneous and clean starts.

Ken
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Old Jan 29, 2005, 07:13 PM
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Darwin Australia
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Photos No 2 and 3 are the modifications I made to the control surfaces to reduce their size.

The motor instalation for the two motors is shown in photo No 1 and No 4 is my planned colour scheme.

Ken
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Last edited by kensp; Jan 29, 2005 at 07:18 PM. Reason: Wrong Photo
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Old Jan 29, 2005, 09:08 PM
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Ken,

Congrats on your successful maiden. What a great flight report!

My C47 also needs some speed to keep her in air specially during turns, will drop a wing if you are not careful, her turns will look more graceful with the rudder/aileron mixing. There's so many discussions about the CG setting of the GWS C47, the manual's suggested setting is 50-55mm. I like to fly mine between 75-78mm.

Lini
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Old Jan 29, 2005, 09:20 PM
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Darwin Australia
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Here are two photos of the motor instalation. The only change to the C47 is that the motor mount sticks must be cut shorter.

This is the AC World CD-ROM web page with a link to the data sheet for this motor.

Total cost of the twin motor instalation, including the CC Phx 10, was US$ 96 with freight. It took me about 1/2 hour to assemble the two motors

Ken
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Old Jan 29, 2005, 09:26 PM
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Darwin Australia
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Quote:
Originally Posted by lini
Ken,

Congrats on your successful maiden. What a great flight report!

My C47 also needs some speed to keep her in air specially during turns, will drop a wing if you are not careful, her turns will look more graceful with the rudder/aileron mixing. There's so many discussions about the CG setting of the GWS C47, the manual's suggested setting is 50-55mm. I like to fly mine between 75-78mm.

Lini
I wanted to try turns with the ailerons only before mixing in CAR. I forgot to mention, in the fligth report, that it turned well on rudder/elevator but there was a little delay befor it started turning.

Ken
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Old Jan 30, 2005, 04:20 PM
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Darwin Australia
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I have moved the CG back to 83 mm from the LE. Iwanted to test fly this morning before the wind, but unfortunately there was a storm just after dawn this morning. This storm has stired up the wind so its not suitable for test flying now.

Ken
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Old Jan 31, 2005, 05:04 PM
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Today, 01 FEB, it was a perfect morming for test flying. Flew the first flight with the CG at 83 mm from the LE at the center of the wing. The C47 seemed smoother and had less of a tendency to zoom into a shallow climb and slow down. The aeroplane seemed to be flying smoother. When the throttle was cut there was less pitch down. Landed after six minutes flying.

Moved the battery further back so that the CG was at 88mm from the LE. The flying was still smooth with no indication that the CG was too far back and it seemed to be a bit slower. Loops were much smoother and about 30 ft in diameter.

Tried a stall turn but pilot error and flying too low meant that the aeroplane struck the ground at the bottom of the pull out. I realy thought that I would miss the ground by a couple of feet. The only damage was that the front wing mount came off the fuselage foam. One of the propellers broke in spite of the prop saver.

The 1600mAh LiPoly battery cannot be moved back any further so I will have to get a 1200 mAh battery to be able to move the CG further back.

Ken
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Old Jan 31, 2005, 05:08 PM
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I used exactly equal wire lengths to connect the motors. On a symmetrical twin why fit wires that are not equal lengths? As well I used Air Craft World CD-ROM motors that have a machine wound stators so that both motors were identical.

The only brushless ESC that I know has a proven history of working with two motors, in parrallel, is the CC Phoenix so a Phx 10 was used.

Occasionally the first start of the day will be a bit iffy but consequent starts are OK.

The motors are running at exactly equal rpm. This is shown by the fact that there is no beat frequency.

Ken
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Old Jan 31, 2005, 05:25 PM
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nice work, interesting to hear your real world results with twin CD-ROM motors paralleled with one CC PHX controller... Sounds good so far.
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Old Jan 31, 2005, 06:08 PM
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Found more crash damage when I went to change the propeller. As well the grass has made scratch marks in the underside of the port wing. It looks like the GWS C47 is a strong aeroplane.

Ken
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Old Jan 31, 2005, 08:57 PM
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Ken,

Sorry to hear your mishap, I almost lost mine twice during the stall turns, lucky both time was at 3-4 mistake high and she recovered nicely, those moment really make you hand sweat. You got to watch for the turns, it's very scale like but will drop a wing if you don't keep up with the speed.

Lini
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Old Jan 31, 2005, 09:42 PM
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lini

With the CG at 88 mm behind the LE at the wing center the Dak is turning like my Spitfire and Zero. A full 180 degrees, in a diameter of about four wing spans and a bank angle of about 60 degrees, with no sign of the wing dropping. Thats why I got overconfidant. I thought I was flying one of my Warbirds.

Ken
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Old Feb 01, 2005, 04:40 AM
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Today after fitting new props to both Motors I was testing and noticed that if the throttle was opened slowly that the starts were not always clean. If the throttle stick was moved rapidly to full throttle the every start was clean.

Ken
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Old Feb 01, 2005, 05:11 PM
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Now that the battery is in the most rearward position in the battery compartment I will use this 10 gram weight to slowly move the CG rearwards. I will attach the weight with masking tape. When the weight is under the tailplane the CG is at 98 mm from the LE at the center of the wing. The first position I will try will be at the TE of the wing in the position shown.

Ken
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Old Feb 04, 2005, 01:45 AM
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Darwin Australia
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I have been so impressed with the C47's motor set up that I have just ordered a Slope Glider A10 and plan to fit the same motor and controller set up except that I will run 3 cells.

As well I have ordered an Align 10 Amp Brusless controller and plan to test it on the C47.

Ken
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