Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Magnum CG

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Old 01-07-2009, 11:42 AM
  #1  
MJD
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Default Magnum CG

I've babbled incoherently before about how surprised I was at the difference between the Magnum's recommended CG and what comes up on a basic workup. I am aware there are additional factors to consider, like sharp LE, sweep, color, smell, the desire for a groovy feel at speed, whatnot. But the difference is so large I cannot imagine it can all be accounted for by other factors. Even with a 10% static margin, which normally is on the nose heavy side but very safe and flyable, it is way back in comparison.

Does anyone see anything obvious I botched or missed here? It is entirely possible I am staring at it and not seeing something I know better about being the AD bonehead I can be at times. I may cross post this to the aero forum, but there are some people here who have recently started walking upright and using basic tools, and even some who have Magnums, so I thought I'd post it here first.

As I am getting bored with mine (not complacent, just the limits of the aircraft are now bugging me), I may start moving the CG for fun next season to find out where it gets nervewracking. Someone's gotta do it and report back. I understand some folks fly them back at 190-195mm or so (I think I also heard 210 from one guy), but even those are ahead of the numbers here.


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Old 01-07-2009, 12:18 PM
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vicman
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Default RE: Magnum CG

Here is mine on the jig. It launches with the greatest of ease and lands very nice too. Glide path, motor off, is about a third of what a quickie 500 has. I'm very pleased with it at this location. The spread on the jig is 8.62"
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Old 01-07-2009, 01:00 PM
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Default RE: Magnum CG


ORIGINAL: vicman

Here is mine on the jig. It launches with the greatest of ease and lands very nice too. Glide path, motor off, is about a third of what a quickie 500 has. I'm very pleased with it at this location. The spread on the jig is 8.62"
Maybe I can't see right or something - is your CG 8.62 back from the LE, or..?

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Old 01-07-2009, 02:49 PM
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Default RE: Magnum CG

The rollers on the jig are 8.62" apart. The cg is 2.75 or so from LE.
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Old 01-07-2009, 06:13 PM
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Default RE: Magnum CG


ORIGINAL: vicman

The rollers on the jig are 8.62" apart. The cg is 2.75 or so from LE.
Holy mackerel that is forward.
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Old 01-07-2009, 07:01 PM
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Default RE: Magnum CG


ORIGINAL: MJD


ORIGINAL: vicman

The rollers on the jig are 8.62" apart. The cg is 2.75 or so from LE.
Holy mackerel that is forward.

What Vic is saying is that the cg is 2.75 back from LE at 4.31 out from CL of airframe.

Bob E.

Me thinbks I used about 200-205 8" +/- 1/8" MM back from wing root.
I know that my first Magnum ran out of elevator on the landing flare, sank like a stone, it's CG was at book settings.
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Old 01-07-2009, 09:58 PM
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Default RE: Magnum CG


ORIGINAL: Crazy4Flight


ORIGINAL: MJD


ORIGINAL: vicman

The rollers on the jig are 8.62" apart. The cg is 2.75 or so from LE.
Holy mackerel that is forward.

What Vic is saying is that the cg is 2.75 back from LE at 4.31 out from CL of airframe.

Bob E.

Me thinbks I used about 200-205 8" +/- 1/8" MM back from wing root.
I know that my first Magnum ran out of elevator on the landing flare, sank like a stone, it's CG was at book settings.

Ah okay - I couldn't quite decipher the gizmo, I see whassup. Thanks. That seems to be about 5.15" from the root LE, or 131mm.


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Old 01-07-2009, 10:33 PM
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Default RE: Magnum CG

C4F understands how it works. That was why I took a pic of the jig from the top so you could see what I had.

My plane does not handle like a pylon racer at all but is a smooth bird on TO, in the air, and when landing. The battery is as far back as I could fit a square pack as well as .5 oz on the tail of the fuse.
The SJ .50 on the nose is a little more than what a .46 would be hence the weight.
I'm happy with mine and look forward to flying it for a long time.
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Old 01-07-2009, 11:13 PM
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Default RE: Magnum CG

Vic,

I too put my Rx battery aft of the elevator servo and lead on the tail too.

Bob aka C4F

Magnum #3 has been started, 1 lightly used Magnum, it had an OS.46 FX & std servos
Servos installed Hitec HS-5645MG for elevator and aileron, 425BB throttle,
Rx Hitec 555 with base load mini whip antenna.
Tomorrow I install the SJ.50 from my last Magnum, set CG and control throws.
Then wait till spring.
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Old 01-08-2009, 01:00 AM
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Default RE: Magnum CG

I had my magnum set up at 140mm to start, and it ran out of elevator on landing. This made it stable in flight, but it was not fun to land. I came to the forum and found out that it needed to be further back than the recommended setting. I took a gamble and moved it back to 185mm. What a huge difference. It make the plane much easier to fly and you could literaly pull the nose to a 45 degree angle on landing. It would just float in.
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Old 01-08-2009, 09:01 AM
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Default RE: Magnum CG

Bob, I copied your battery install when I did mine.
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Old 01-08-2009, 09:06 AM
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Default RE: Magnum CG


ORIGINAL: vicman

Bob, I copied your battery install when I did mine.

Did you tape it to the fuselage or cut a hatch and put it inside? [sm=spinnyeyes.gif]
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Old 01-08-2009, 09:16 AM
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Default RE: Magnum CG

The tape method created waaay too much drag so I cut a hatch and put it inside the fuse.[sm=bananahead.gif][sm=wink_smile.gif]
My weight is glued to the very tail end and wrapped with a pc of fg tape.
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Old 01-08-2009, 09:21 AM
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Default RE: Magnum CG

my tail weight used the sticky back tape and two screws.
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Old 01-08-2009, 09:26 AM
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Default RE: Magnum CG

I started with the sticky tape but the sick speed this thing goes caused failure.
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Old 01-08-2009, 09:37 AM
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Default RE: Magnum CG

Sticky back tape will fail due to prolonged fuel/oil exposure. [&:]
Sticky back was to hold in place for pilot drill and fastereners.

New Magnum will have Hitec HS-5645 MG on control surfaces. Got a great deal on a bunch of them.
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Old 01-08-2009, 10:26 AM
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Default RE: Magnum CG

I just got a Magnum, have not begun the build yet.

If I read correctly, the CG needs to be further aft than what is recommended by Weston?
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Old 01-08-2009, 10:56 AM
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Default RE: Magnum CG

YEP, the Weston manual locatioon is nose heavy, it will fly but sink like a birck with the power off. There is more information here in other threads. Do a little digging. it is out there. also try the ARF section.

bob
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Old 01-08-2009, 11:07 AM
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Default RE: Magnum CG

What he said...[8D]
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Old 01-08-2009, 03:47 PM
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Default RE: Magnum CG

Well Magnum #3 is nearly done. Just need to set CG and dial in my rates. I got #3 from a buddy used. Dropped in a Jett .50 from Magnum #2, 2 used digitals + 1 standard, recycled battery, switch, extentions, rx, antenna, ect..... The gap from spinner to nose ring needs to be addressed, I will make a filler ring. First flight at least 3 months from now.

Bob

This is NOT an R version. My buddy put checkers on the bottom after the "graphite trim blew off.
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Old 01-08-2009, 05:50 PM
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Default RE: Magnum CG


ORIGINAL: Julian537
I took a gamble and moved it back to 185mm. What a huge difference. It make the plane much easier to fly and you could literaly pull the nose to a 45 degree angle on landing. It would just float in.
That's a good data point to have!
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