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Magnum w/West .50 V1 to prop question


Old 11-30-2005, 09:20 PM
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Default Magnum w/West .50 V1 to prop question

Not trying to beat a dead horse here. But I've got a quick question. I've got a Magnum with a brand new West .50 V1, header and genesis pipe. If I use an APC 8x8 prop, should I cut 1" off the header or 1/2" from header and 1/2" from pipe. It looks like if I would cut 1" off the stock header, it will make the header too short. Also, should I run that prop on a new motor. Does it matter. Also, is 120-130mm a good CG for the standard magnum.
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Old 12-01-2005, 11:30 AM
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Default RE: Magnum w/West .50 V1 to prop question

I'd recommend running the 9-6 for first runs and flights, though in truth the load is not far off. But it is also a good prop to trim out the aircraft on as it limits speeds to only 120-125mph and has gobs of static thrust which makes launches easy (though the 8-8 isn't much of a problem, 8-9 okay and 8-10 needs a good heave and no tailwind!).

As to header or pipe, you should be able to trim an inch off the header and have room left to couple the two together happily, but taking 1/2" off each is effectively the same deal. I guess by going 1/2" each you then have a couple of handy spacers should you decide to run 8-9 or 8-10 props, which typically call for 1/2" off and stock length respectively.

I only have the Magnum R so can only comment on its CG, but AFAIK the planform is the same so NP/CG relationships would be the same - 130mm is not "rearward" as far as CG's go for the R, some people run way farther back than that. The recommended CG range is quite forward for groovy flight and reduced twitchiness, but the forward locations don't favor landings very well. I did a NP/CG analysis on the Magnum R by tracing the wing and tail surfaces and measuring up the relationships, and came up with CG's pushing 190mm with fairly conservative static margins. I wouldn't set up there, at least not until I get more daring - however, Weston advised that some European fliers are indeed running that far back! Weston likes it way forward.

So personally I would lean towards the rear of the recommend range to start and not feel worried about sensitivity.

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