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Even Later In The Day

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Mark Elen11/04/2020 20:58:33
527 forum posts
1022 photos

Hi Mark,

Beautiful. That looks spot on!

Cheers

Mark

Mark Ellis 125/05/2020 20:57:04
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19 forum posts
13 photos

Hi all, Just when you thought it was all over lol!

So I finished the build in March this year (2020) but then the lockdown happened and our club field closed, I never got the chance to fly Ballerina.

Then today, following the government and BMFA guidelines and beautiful weather, i grabbed the opportunity to maiden her. I always fly my own aircraft for the maiden.

I worked hard to get the C of G right and I thought I had, nose down tendency when fingers placed on main spar position, model upside down with battery installed.

So I took off.........fairly quick in to the air but straight away I new it it was too pitchy, very hard to control when ever I applied elevator. I gained height and levelled off and found with no pitch inputs she flew very nicely, quite nippy too.

I tried to do a few practice approaches, wanted to get her on the ground as soon as possible but it was clear that my work was cut out to avoid taking home a bag of splinters.

Anyway, did my best, suppose the lack of flying over the last few months didnt help. Ballerina's wheels hit the ground pretty hard and she bounced back up in the air about 6 feet. By this time she had stopped flying, fell to the ground and cartwheeled a few feet.

Happily though, the only casualty seems to be the prop and maybe the undercarriage a bit bent........ good job it wasn't a not so cheap ARTF!

My Ballerina has an AUW of 2.2KG, I think i probably put about 200g of lead in the nose to balance her. I have set all the controll throws to the initial recommended settings.

Does anybody have any views on this? my first thoughts are with the Centre of gravity and I need to invest in a proper jig to ensure I have this right. What else could it be?

I am keen to get this sorted cos I'm sure when it's right she will be a great plane to fly.

Cheers

Mark

Peter Miller25/05/2020 21:05:13
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11086 forum posts
1308 photos
10 articles

Hi Mark

The CG should be at 25% of the chord back from the leading edge.

Mark Ellis 127/05/2020 19:29:40
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19 forum posts
13 photos
Posted by Peter Miller on 25/05/2020 21:05:13:

Hi Mark

The CG should be at 25% of the chord back from the leading edge.

Thanks Peter.

I have balanced it "approximately" on the main spar, I assumed that was where it should be as that seems normal with most models. I say approximately as I just use the fingertip method which I'm guessing isn't all that accurate. Looking at the plans again, 25% of the chord from the L.E, would put it about 1 centimeter forward of where it is now. I have read the dire consequences of an aft CofG today, would that much difference make it so unstable in pitch?

The symptoms certainly suggest an aft CofG

BTW, I checked my elevatorthrows, function, end points and expo but all seem to be OK.

Think its time to invest (or make) a proper CofG jig.

Cheers

Mark

Peter Miller27/05/2020 21:04:51
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11086 forum posts
1308 photos
10 articles

I would suggest sticking to 25%.

I use a 15% tailplane which is a little smaller than manywhich is whythe forard CG is better. One or two people who have balanced one of my models a bit further back didn't like the handling until they moved it forward

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Has home isolation prompted you to start trad' building?
Q: The effects of Coronavirus

 Yes - for the first time
 Yes - but Ive bashed balsa before
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