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1/2a Pusher - Cox black Widow

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1/2a Pusher - Cox black Widow

Old 04-28-2011, 12:08 PM
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Phantom805
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Default 1/2a Pusher - Cox black Widow



Hi,<o></o>



I have this pusher airframe and I would like to put a cox black widow in it. The problem is that the COG is really far back (50% of the Wing Chord) even with the battery in the nose.

Currently with radio gear and engineit weighs 15.5 Oz.
The wingspan is 35.5" inches
and the chord is 5.5" inches<o></o>



To get the COG to 30% of the Wing Chord I will need to add another 2.5 Oz ballast which brings the total weight up to 1lb 2Oz. My question is will it fly with this amount of weight? If so would I be able to get the groundspeed to takeoff on tarmac? (It has dowelingto addan undercarriage). Finally, am Iright in thinking that the black widow with the brass driveplateis suitable to use as a pusher? I have a Tee Dee 049 if the black widow is not sufficient but would prefer to use that on another project.

Thanks in advance

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Old 04-28-2011, 01:18 PM
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Rusty-Gunn
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Default RE: 1/2a Pusher - Cox black Widow

Perhaps adding tail dragger landing gear might help with more weight up front instead of just plain dead lead weights. At least the amount of lead you might need to add might be less.
Old 04-28-2011, 02:36 PM
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Andrew
 
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Default RE: 1/2a Pusher - Cox black Widow

Your wing loading is already at 11.4 oz/sq.ft. If you add another 2 oz of lead, it will be 13.3 oz/sq.ft - that's a pretty high wing loading for a small plane. If it does get off the ground, it will likely be a handfull. Anything you can do to lighten the tail instead of adding more weight would be preferable.
Old 04-28-2011, 06:23 PM
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windy city
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Default RE: 1/2a Pusher - Cox black Widow

Here is a long shot,,, If the Black Widow has a tank, switch to a sure start type backplate and a remote tank in front of the engine. This will move the CG forward a bit,
You might get by with a little less added weight to balance.... Like I said it's a long shot, I don't know if it is even possible with that airframe.

Best of luck
Fred
Old 04-28-2011, 06:42 PM
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hllywdb
 
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Default RE: 1/2a Pusher - Cox black Widow

Move the servos as far forward as possible
Switch to CF pushrods
See if you can move the firewall as far forward as possible and still have prop clearance

If you still need 2oz in front, mount another black widow in the front It will solve the power issue!

Good luck!
Bill
Old 04-30-2011, 01:24 AM
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Phantom805
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Default RE: 1/2a Pusher - Cox black Widow

Thanks for the suggestions. Even with the servos mounted forward it is still too far back. I don't think that I will be able to take enough weight out of the back either. I think the best bet would be to cut off the nose and mount the engine at the front. That will also reduce the weight by ~3oz as I can replace the nicad receiver battery with a lightweight lipo. What would be a sensible wing loading for an airframe of this size?
Old 04-30-2011, 11:00 PM
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BMatthews
 
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Default RE: 1/2a Pusher - Cox black Widow

Actually as much as I like to keep my 1/2A models down to around 10'ish oz/sq ft I have to admit that I've had some pretty good flying from a few models that are up around 12 to 13 oz/sq ft as well.

The weight of the model is fine. It's the relatively small wing area. The wing in this case would have been better if it were more around 6 to 6.5 inches in chord. That would have given you more wing area to work with.
Old 05-02-2011, 06:36 AM
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R/C Phile
 
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Default RE: 1/2a Pusher - Cox black Widow

It looks like the weight is in the ballpark. The Sig Hummer has similar wing area and weight and is purported to be a fine flyer.

It's just that 2.5 ounces is a huge 16% of the total weight of the plane.. Keeping that weight off the aircraft will improve every performance aspect significantly, so much that I would even consider elongating the nose to minimize how much you have add if any at all..

As for launches it seems the plane is a natural for hand launches / belly landings with the engine mounted on top. Also, the absence of an undercarriage helps keeping the weight down as well.
Old 05-05-2011, 10:07 PM
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rc doc
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Default RE: 1/2a Pusher - Cox black Widow

That plane looks just like one from Royal in Denver back in the 80's. I still have the plans and looked at them the other day. The Royal kit had tricycle gear and flew very well on a cox Black Widow with a Cox pusher prop. If I remember correctly I had full sized servos and a Royal 1/2A receiver. It flew better than the pilot did. I hand launched it all of the time. IT lasted all of one winter. I can get the plans copied if you are anyone wants them.
RC DOC

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