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Wt and Balance help needed

9 posts in this topic

Posted

My friend has a Skyraider single place similar to what I have been working at. We have not been able to locate any info on how to correctly balance these planes. He will fly way before I get to. So this is ALL the info we have. Not much good for us. Any help will be greatly appreciated. We have 17" tires so the negative moment is -8.5" from LE datum. We tend to think this is loaded ready for flight measurements for correct CG.

post-341-0-02487000-1433080214_thumb.jpg

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Posted

here is a good start I think this is 1 of 7 videos that will teach you how to do a proper W&B

http://eaavideo.org/video.aspx?v=2874081572001

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Posted (edited)

It doesn't matter what size tire you have on - the weight line is from the center of the axle - only the weight of the tire changes with size.  The only time you are concerned with tires is when you change sizes and the weight changes.

EDMO

Drop a line from the leading edge of the wing and measure to the center of the axle to get this measurement -

probably, It will be the same as your drawing if this drawing is for the same kind of plane.

Each model of plane has the CG range figured for that particular plane - they are not all the same.

Edited by Ed In Missouri

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Posted

I sent you a PM with a spreadsheet attached that I wrote that will make it easy to do the WB.  And yes the only WB that are of a concern are the loaded numbers because the plane does not fly without pilot and at least some fuel to get airborn.

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Posted

Paul,

     Does that spreadsheet work for any plane?  Do you have any info on how the fore and aft CG limits are calculated - It seems that each designer has his own dimensions/parameters and similar planes have different ranges, like Kitfox and Avid for the undercambered wing are different, I think?

EDMO

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Posted (edited)

Thanks for all the help....We will go back out to the hangar and set his plane up again and get every station documented, marked with plumb-barbara...his plumb has breasts. I have the spreadsheet and will follow EAA suggested method and compare the outcomes. This should be interesting compared to what we had to work with...not much.

Ed...we both have undercamber wings....ribs are nearly identical to a point .

Edited by Tree top pilot

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Posted (edited)

TTP,

     Just using that as an example:  One designer might use 20% chord for forward CG and 30% chord for aft CG limit (Kitfox?), while another designer with the same rib might use 17% forward and 33% aft (Avid?).....calculation may have something to do with distance to tail feathers, how large the horizontal stabilizer and elevators are, amount of travel, etc. - or just what the designer guesstimated? 

I need to read my design book again to see what it said.  Seems like nothing is "carved in stone"!

      Akflyer said that his plane flies better at a "very aft" (I forget what inches) CG, and I think he confirmed his findings with Dean Wilson.

EDMO

Note:  The figures I stated above are probably not perfect - If anyone wants to calculate them from the factory W/B sheets of each Brand with undercamber wings, I would be happy to see them.

Edited by Ed In Missouri

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Posted

Paul,

     Does that spreadsheet work for any plane?  Do you have any info on how the fore and aft CG limits are calculated - It seems that each designer has his own dimensions/parameters and similar planes have different ranges, like Kitfox and Avid for the undercambered wing are different, I think?

EDMO

Yes, it will work for any plane.  The range for any given plane is set by the designer and this spreadsheet will not help with that but is great for calculating the W/B.  All that is required is that you plug in your own weights and measurements.  I built this spreadsheet when I was changing engines in my Q-2 and was figuring out where to place the engine to achieve proper W/B so it also contains a section called "move something" that allows the user to see the results of moving anything from a battery to an engine from one location to another.  I will be happy to send a copy to anyone that would like one.  Just drop me a PM and I will get it out.  There are a lot of good CG spreadsheets out there that will do the basics. This is the only one I know that has the Move Something capabilities. And yes it will work with new fangled airplanes with nose wheels.  Just plug in your numbers for the training wheel where it says "tailwheeeel. 

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Posted (edited)

Paul,

     I really like that "move something" feature.

Now, for an old fart who don't know a bit from a divot - is this on a CD?  or do I have to write something in my puter?  If so, then I have already crashed!

How much to ship one?  I know CDs cost and so does shipping.  I would be glad to pay you.

Thanks,

EDMO

Edited by Ed In Missouri

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