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Rubin II Pattern Plane

Old 10-18-2008, 11:21 AM
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joetach
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Default Rubin II Pattern Plane

I have just completed a Wolfgang Matt Rubin II. It really is a gorgeous plane. Can anyone out there tell me the proper CG location? I was told that it is right on the wing tube. However, when I use that location the plane is VERY nose heavy. So much so that it needs a full 7ozs. of lead in the tail section to achieve a neutral balance which just doesn`t seem right to me. Also, the wing tube location is slightly aft of wing center which makes the CG location over 50% of the wing chord at the fuselage. Any help would be very much appreciated.

Thanks,
Joe
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Old 10-18-2008, 12:16 PM
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Default RE: Rubin II Pattern Plane

Joe, hello.

See you do not get an answer so a did look for a picture and found one.
This plane (Rubin I I did found) I did see, does have a swept back wing with nearly straight trailing edge?
It can be good the CG location is on that point they say.
Second fact is what you write on the location of the tube, also that is the best point for the tube, in the location of the CG.
I do not know the plane so someone will give the right position I hope.
If not we can calculate, but than I need the planform of the wings
Succes Cees



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Old 10-18-2008, 04:40 PM
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Default RE: Rubin II Pattern Plane

use the vanessa CG machine. you CANNOT go wrong that way. do a search here on rcu.

david
Old 10-18-2008, 06:49 PM
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Default RE: Rubin II Pattern Plane

here's a link to the vanessa cg machine.

http://home.mindspring.com/~the-plum...%20Machine.htm

david
Old 10-18-2008, 06:54 PM
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Default RE: Rubin II Pattern Plane

David,

When you don't know where the CG has to be positioned what is the profit of this tool in that case?
The problem is Joe isn't acquanted with swept back wings I think.

Cees
Old 10-19-2008, 05:48 AM
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Default RE: Rubin II Pattern Plane

it is very simple once you get your plane hanging. if the planes tilts it's out of balance, if it hangs level you are balanced. look at the design again and i'm sure you will understand.

david
Old 10-19-2008, 06:09 AM
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Default RE: Rubin II Pattern Plane

Hello David,

Of course I understand this design, I see it also on websites in in the Netherland.
But, if you doubt about the right position just Joe does, than he doesnot have a problem with locating the CG but with the location far aft.
Mostly this happens when it is a "first" swept back design for a pilot, just I often see on the feild!.
When you haven't the plan you have to calculate the position and not listen to people who do say it hase to be on 25 or 33 % of the wing, because that are the people that did not have yet a plane with swept back wings!!!!!

Joe how is it going?

Cees
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Old 10-19-2008, 07:09 AM
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Default RE: Rubin II Pattern Plane

1st of all he IS asking for help with the cg location. and if you use this device the pendulum will point right at the cg (once you get the plane balanced). what am i missing here?

david
Old 10-19-2008, 07:12 AM
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Default RE: Rubin II Pattern Plane


David,

This is the question:

Can anyone out there tell me the proper CG location?

See the first post.

And not: Can somebody help me to locate the CG position?

Cees
Old 10-19-2008, 07:17 AM
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Default RE: Rubin II Pattern Plane

well i don't know what it is and there's a chance it would take a while for someone to get an answer to him. so i offered an alternative. maybe he wants to fly right away, after all he just finished it. some users of the cg machine won't fly without setting their plane's balance 1st this way.

david
Old 10-19-2008, 08:22 AM
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Default RE: Rubin II Pattern Plane

David

It looks we have a bigger problem than Joe.

and BTW when the CG is on the location of the tube you only need a rope, not a machine.

Cees
Old 10-19-2008, 09:00 AM
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Default RE: Rubin II Pattern Plane

Joe; I use to fly the Saphire I by Matt. Great flying pattern design. Post some pics of your Rubin II.

Well, back to the matter at hand. I believe you mean you need to find the AC (aerodynamic center), and NP (neutral point) of the aircraft. The CG (center of gravity) is where ever you make the plane balance between the AC and NP. Try out this calculator to determine the two, and it will explain how the AC, CG, and NP affect the aircraft. I hope this helps? It helped me, and I use it to set up everyone of my pattern ships. It has not failed to be correct every time. If you have any questions just email me at ([email protected])....

Link to AC,NP Calculator

http://adamone.rchomepage.com/cg_calc.htm

Old 10-19-2008, 09:22 AM
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Default RE: Rubin II Pattern Plane

Thanks so much all! Though I DO understand how to find the EXISTING CG on the plane, what I DO NOT know is if it IS THE CORRECT location for the plane? Case in point: The existing CG is 1" forward of the wing tube. Now,...if I move my balancer to the wing tube location, the plane needs a full 7 ounces of weight added to the tail to achieve a neutral ballance. Hence my delema: which is the proper location? Where the plane naturally ballances...OR on the wing tube which "appears" to be very nose heavey...OR somewhere in between! Again, the builder of the plane who is a very familiar with it says just to fly it where the CG is now and tweak it from there. You know the story, as 2 people a question and get 4 different answers (or more!). I have e-mailed The designer of the plane (Wolfgang Matt) three times in the last week and have yet to get a reply.

Thanks ALL,
Joe
Old 10-19-2008, 09:31 AM
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Default RE: Rubin II Pattern Plane

you should always shoot for a 1/4 of the mean aerodynamic chord as a starting point.

david
Old 10-19-2008, 09:32 AM
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Default RE: Rubin II Pattern Plane

try this link for your swept wing plane mean aerodynamic chord.

http://www.airfieldmodels.com/inform...amic_chord.htm

david
Old 10-19-2008, 10:56 AM
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Default RE: Rubin II Pattern Plane

Thanks SOOOOOO much Kevin. The link you provided me is exaxtly what I need. The term CG is definately NOT a correct one in terms of the dynamics of an aircraft in flight, but it does keep it simple for most flyers/builders. THanks to ALL who have given me their suggestions. I`ll post the pics as soon as I can. I also owned a Saphir . It was a super smooth flyer until I "dumb thumbed" it into the ground at full bore (Don`t even ask!).... THanks again guys...

Regards,
Joe
Old 10-19-2008, 11:18 AM
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Default RE: Rubin II Pattern Plane

kevin, that is a nice link to have on hand. thx.

david
Old 10-19-2008, 11:20 AM
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Default RE: Rubin II Pattern Plane

Your welcome Joe. Anytime I can help a fellow pattern flier....[8D]

Old 12-23-2008, 05:07 PM
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Default RE: Rubin II Pattern Plane

Hi Guys,

Does anyone out there have any plans for the old Wolfgang Matt Rubin 11? Though I asked this question once before, and received several helpful replies regarding CG placement, I was wondering what the CG placement was per plans? Or, if anyone had the Rubin series of pattern planes, perhaps they might remember the CG placement. Happy holidays to all you and yours, and may the "God`s of RC" smile upon you always!

Joe
Old 12-23-2008, 06:00 PM
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Default RE: Rubin II Pattern Plane

Hi Joe,

I saw that you finished a RUBIN II two months ago,did you flew it allready?,can you post some pictures?,i remember seeing the ad of Pica/Robbe inside RCM about 12 years ago and telling myself what an awesome,elegant and cool looking plane the RUBIN is.The sleek lines of the fuse and misile like apearance made me crazy about Pattern flying.

Do you know where i could get one of these?,or if someone here has one please let me know,as i have my old YS120FZ laying around and she`s begging me to bring here to life again lol,but i`am not that skilfull to build a kit yet so ARF would be ideal.
Sorry i can`t help you with the proper c.g location.

Good luck with your cuest to find the plans for this bird.

Greg.
Old 12-23-2008, 06:24 PM
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Default RE: Rubin II Pattern Plane

Thanks for the link Kevin.

I input the UFO's measurements off the plans I built from and the online calculator gave a CG range of 6.71" to 7.8" back from the root LE using Static Margins of 5% and 15%. A Static Margin of 10% gives the CG at 7.26" back at the root.

The plans show the CG in two different places. That is, the wing plan view has it at 6.55" back, and the fuselage side view shows it at 6.675" back. Both of these are slightly nose heavy according to the online calculator. The CG's on the plan calculate to an average Static Margin of about 16%. I guess he wanted it to be extra safe for your first flights.

David

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