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Magnum R C of G setup advice

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Old 09-05-2004, 04:07 AM
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heliraptor
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Default Magnum R C of G setup advice

Hi

I've been reading a few posts lately where guys have been using lead on the tail to help get the Magnum R C of G right.

My C of G is set at 140mm, and it glides perfectly for a reasonably slow landing, in fact if you get it spot on, it almost just flops down.

Flight doesn't sem to be affected and it still flys like its on rails both inverted and upright.

I'll try and snap a picture later if I get the wings off today, as its hard to explain, it's all to do with the positioning of the battery.

My rx is right up front behind the tank, servos in their stock positions.

The battery which is an 1800mah square (rectangle) pack, not flat, and is positioned in quite a weird place.

The flat platform that runs right down the centre has square portions cut into it with a cross shape in it. Take the one right at the back and dremel out the centre of the cross large enough so you can slip the nicad pack vetically (If the magnum is sitting flat) through the platform so it sits on the underneath of the fuselage, held in place evrtcially by the platform. Then using silicon or hot glue, glue it in place.

The picture will explain better.

This way I have no added lead, perfect C of G and flight characteristics.

Lee
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Old 09-05-2004, 04:23 AM
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Dave03B
 
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Default RE: Magnum R C of G setup advice

I've got nearly 150g in the tail of mine but thats my fault for having an Irvine 53 on the front.
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Old 09-05-2004, 04:24 AM
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Default RE: Magnum R C of G setup advice

I had heard about the balance difficulty and put my Rx and Battery as far after as possible.

It was way out of balance.

I had to strip out the radio. My battery now sits in front of the throttle servo and my RX toward the back (not right at the back though). I have no lead and it balances at about 139mm. I am using a JR 1100mAh RX pack.

I have no spinner yet though. I am putting the spinner on this weekend and swapping the pack for a 700 mAh pack. Move the RX to the back and I will still not need any lead. I can't work out how people get them tail heavy either. Maybe it was just the earlier Magnums that had this?
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Old 09-05-2004, 04:28 AM
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Default RE: Magnum R C of G setup advice

I have the old magnum. And with a 420g engine on the front, and the nicad (700mah falt) on the plate infront of the ele servo and the rx infront of that.......I needed 160ish g of weight in the tail to balance it at 140mm.
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Old 09-07-2004, 09:54 AM
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Default RE: Magnum R C of G setup advice

I have been flying the Magnum for 2 years now. Don't add lead. If you are wanting top performance out of this plane, don't make it heavier, make it lighter (still needs balanced).

I don't know how many flights you put on it in a day, but an average day for me is two or three flights at the field. Why would you cram a 1700mah battery in there. You only need enough battery in there two run the servos and reciever 4 or 5 times. I am running a 700mah, 6 volt battery, I check the battery capacity after each flight. 700 mah is a lot lighter than 1700. My magnum ( I have two) balances out slightly nose heavy with NO LEAD, battery sits next to Elevator servo, and reciever sits just infront of battery and elev servo.

You can also save weight with the Spinner backplate. Lighten it up. There are smaller, and lighter servos out there that are strong enough to do what they are supposed to.

If you have no other choice but to add lead then do it, but eliminate all other possibilities for balancing your plane before you go and make it heavier.

If you are running the Webra engine that comes in the combo kit, put a BVM mixture control in line with the carburetor. Open the engine needle three full turns, adjust the mixture with the mixture control and put it on a dial on your radio. I have done this on one of mine and after I go full throttle for take off, my hand goes from the throttle stick to the dial during flight, richening or leaning the engine. Maxx performance!!!
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Old 09-07-2004, 10:39 AM
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Default RE: Magnum R C of G setup advice

You say don't add lead and make it lighter.

Then you say use a BVM mixture valve and a 6V pack. Isn't this a bit of a contradiction?

My understanding that the inflight mixture valve is not to increase power but to increase engine longevity. The ducted fan boys tweak their engines to be as lean as possible for take off because they need all the power they can get. In flight they richen it up to reduce engine wear.

IMHO you don't need a mixture valve on a magnum. It is hardly short on power at take off!
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