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CG Excursion

14 posts in this topic

Posted

Hi All,

my name is Marco Mille and I'm writing from Italy.

I have bought 6 month ago an Avid of second hand. I'm interessed to know what are the excursion limit of C.G. of AvidFlyer or  if is possible have a construction manual. I have operation manual only.

thanks

Marco

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Posted

Is it a speed wing, stol or Heavy Hauler?

I have the manual in PDF and will burn a copy and send it out to you today.  you can email me your address at akflyer_2000@yahoo.com.

The CG range is 11.185" to 16.5" from the leading edge of the wing.  I have been told that the plane has been flown as far back as 19" with no ill effects, but you are a test pilot if you fly outside the 11-16.5" range

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Posted

thanks, but another person have send me a manual already.

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Posted

Hi , I´m looking for the construction manual too ,I would be very gratefull...

Thank you very much.

Kind Regards

David Santiago Garcia

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Posted

Mine is at 18" and flys great with 532 

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Posted

I wonder if that 16.5" aft cg limit isn't set by requirements for the tri- gear version, not pitch stability?

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Posted (edited)

One question I have regarding C of G position is : How to determine / what incidence does the extended leading edge have on C of G position. The original C of G is measured on the spar leading edge....an extended leading edge is going to change that measurement ( also, does it  change the C of L) ? As I see this the aircraft C of G stays where it is for a specific loading (extended LE same as no extension) but the measurement is going to be wrong.......so the pilot could be outside the envelope thinking he is inside !!!!!!!!

Let me know your thoughts..I am a bit unsure about this one. It came up because I compared empty aircraft C of G with another Catalina who has extended LE. and all the measurements are quite off compared to mine.......

P.s Same problem when you do your initial aircraft weighing to find your C of G position

Edited by flywise

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Posted (edited)

C of L has everything to do with C of G - but for instance, the Leading Edge extension of, say 4", does not change C of L that much when you divide the length of chord into equation - maybe 1/2 that much, or maybe it does move it forward that much?  I had this all figured at one time for nosedragger front engine, but Chemo has clouded brain right now - I also added about 6" more to flaps (from 9" flaperons to 15" flaps/ailerons) (Ailerons alone have to be about 10% of wing to work well) to do my figures - Maybe take two readings - one from original leading edge and one from new half of extension and compare them?  Sorry I cant help much now.  Where are the real Aero Engineers?  EDMO

Edited by EDMO

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Posted

Adding a leading-edge extension shouldn't change the CG position much at all, since the moment arm of that weight is so small, but will change the aerodynamic center, shifting it forward.  This reduces static margin, so your aft CG limit will come forward.  (Forward limit too, but no biggie.)  Be careful!  Stay away from the original aft limit until you know where the new aero center is.  With the LEX are you re-referencing all your weight moment arms to the new LE location, or keeping the front edge of the front spar as the reference?  That could account for differences in your values vs. Others.

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Posted

The guys I know of use the new extended leading edge as a reference for all c of g calculations instead of the original L.E... and this is what makes all moment arms quite different to what it should be (even though the L.E. extension is a small error it becomes a big one when you multiply by the arm dimensions to get your moment arm ).  I believe it's safer to use the original L.E. but am unsure of the effect...

 

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Posted (edited)

Here are some numbers for you to work with:  "The AC (Aerodynamic Center of Lift) is approximately at 25% of wing chord." 

The CG range is usually 20% (Forward) to 30% (Rearward) of wing chord, although some makers - (Kitfox?) - use 33% as Rear limits. 

If you are working with the standard early wings with short flat flaperons, then 25% of 51" chord is 12.75" - Adding 4" to leading edge makes it 55" chord and 25% of that is 13.75".  So by moving the leading edge forward 4", you have moved the AC forward about 3". 

 I think you can do all your measurements and calculations, (20% and 30% chord CG range) from the new leading edge as your new data point, and be accurate to 1/2" or less.   If you have figures different than this, please post them.   EDMO

Edited by EDMO

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Posted

I flew my Avid Mk IV at about 17 inches (1/2 inch aft of the limit of 16.5) and I could feel the difference in the flare to land, much less pitch stability. The longitudinal dynamic stability about neutral in the flare, so that if you pick the nose up a bit more than needed, it wants to keep going slowly nose up with neutral longitudinal stick. When I get back in the air I will explore this a bit more.

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Posted

Newbie question.  Do Avids tend to be built nose heavy or tail heavy?  I have not weighed ours yet so I’m just wondering what I can expect.  

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Posted

Newbie question.  Do Avids tend to be built nose heavy or tail heavy?  I have not weighed ours yet so I’m just wondering what I can expect.  

Most tend to be towards the forward edge of the CG range.

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