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Brett82

Fuss ballast effect on COG check

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satinet

Depends on the model.

My avatars have 5 ballast tubes in each wing root. Actually 2 tubes each side with 5 pieces each. and 3 bars in each side of the wing joner.

As such it's very difficult to remember what the ballast setup is and the permutations are endless. The only situation where i have to change the cg is fully ballasted where it goes forward slightly.

Actually i use the ballast to change the cg as i fly with the cg more forward in duration (unballasted flight).

Ah progress....

My stinger i have to renove  weights depending on the cg which is a bit annoying.

 

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Phil.Taylor
3 hours ago, Scram said:

Brett, seems to me your original question has, by and large gone unanswered - or only partly.

Seems to me that if you have a CoG position in mind, this will apply to both loaded and unloaded (or the other way around  :whistle:  )

If you check your assembled model CoG is where you want it and then take the wings off and set the fus alone on the CoG checker, you may find the balance point has moved.  That's OK.  All you need do now is load your ballast and adjust its position till you get the same balance point.  Put the wings back on and you should have your preferred model CoG.

No need for calculations or marking or measuring your tube length.  You can do the same with 50% ballast, distribute the slugs how you like as long as the pattern is even about the GoG yo want.

Sorry Gerry - if you take the wings off, then rebalance the fus to its own "balance point" (which will almost certainly be different to the whole plane CofG) - then add say 1kg ballast so the fus balances at that same fus "balance point" - then...

when you put the wings back on, the plane CofG will have moved - because you've added 1kg of weight at a distance from the plane CofG to the fus balance point ! (remember "moments" in school maths/physics?)

Brett - just make sure the centre of the ballast sits at the CofG of the plane - for all ballast conditions. Measure the ballast tube with a stick or wire to work out the ballast centre relative to the plane CofG - should be spot on?

Phil.

 

 

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isoaritfirst

You can get many variants using this type of tool rather than fiddling on the floor, So its worth deleting those that add nothing to your day, and keep just enough variants to cover your needs.

Also in many of my model I have added ballast to start with, sometimes this can make the variations easier to handle without having to change nose weights.

My shinto will run through nearly all weight options without changing the nose weight. The one exception is to fly it completely empty at the same CG requires some nose weigh to be removed.

This is a much easier solution than balancing at my desired CG when empty., which led to more variances in the CG position. I also fly empty very rarely and usually only when sports flying when having a more forward CG can often help.

I have a removable piece for the odd occasions that I race empty and wish to retain the sharper handling of the more rearward cg.

I also shift the weight slightly to change the CG if I feel the need to quieten or sharpen the handling

 

 

 

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Brett82
29 minutes ago, Phil.Taylor said:

Brett - just make sure the centre of the ballast sits at the CofG of the plane - for all ballast conditions. Measure the ballast tube with a stick or wire to work out the ballast centre relative to the plane CofG - should be spot on?

 

Phil you will be glad to know I'm sitting with the glider in front of me right now doing exactly that. I decided everything everyone has said is absolutely relevant so if I'm going to do it properly then I need to try it all, no short cuts. 

Once I've finished measuring and know where the centre of the tube is relative to the COG I will check it with Toms formula then I will put the wings and double check it ballasted and empty (normal and inverted so I know for the future).

Mike, looking at your FS4 ballast sheet I have come to one realisation and one conclusion. I just realised how glad I am I only have fuss ballast and I have concluded to keep it as simple as possible. Empty or 100% and maybe 50%. :D

Brett 

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Brett82
40 minutes ago, satinet said:

My avatars have 5 ballast tubes in each wing root. Actually 2 tubes each side with 5 pieces each. and 3 bars in each side of the wing joner.

I really like the Avatar but I think you just put me off.... Only kidding but it would take a bit of getting used to having that many bays...

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Brett82

Right bit of bad news but with a light at the end of the tunnel. 

When I purchased the glider (and Pete will back me up here) a considerable time ago I measured the ballast it came with and made sure it fitted in the tube. The other day while at work, numpty here ordered some more without double checking the measurements. What I remember as 19x32 turns out should have been 20x37...

Anyway, by pure chance it fits perfectly in the tube with no spacers at either end required. The centre of the tube is 106, my COG is 105 so if I use 3x original bigger slugs which are a little heavier and put 1 at the back and 2 at the front with the new lighter ballast in the middle I get a COG with wings on of 105 on my balancer. Its like it was planned. :P

Ballast weighs in at 970g, plenty for me.

I tried using Tony's formula but my digital scale only goes to 500g and my wife's analogue baking scale is not accurate enough. I need a bigger digital scale. She recently took up baking cakes and home made bread so next time we go shopping I think she deserves a new digital scale that can measure up to 5kg, don't you think? :D

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Brett82

I promise when I get a bit more clued up I will stop with the silly question, until then please bear with me. 

You can see the ballast fits perfectly and is held with walls on either side and at the end of the tube. Ignore the gap, to take the pics I only put 1 slug in and it slipped back slightly. 

I want to avoid drilling to glue in a nut and drilling a slug for a screw. Looking at the pics do you think I can hold the last slug with tape? It is a tight fit anyway even without the tape. 

DSC_0001.JPG.487f4d68cd2408876a0b4484e6fd5ba0.JPG

DSC_0002.JPG.bb1945c26ffab3bfb6d4cf8bced0549e.JPG

I would make sure the tape overlaps, plus the nose cone will stop it coming un-done.

Any thoughts? 

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isoaritfirst

In my skorpion I had a small epp spacer at the end. 

Its worth having it there as a bump stop. 

I wrapped the epp in insulation tape to increase its strength. 

The piece also had a piece of epoxy board inserted into it. This served two purposes. One as a handle to help lift out the packing piece and second it was tall enough to almost reach the inside of the nose cone. As the nose cone was taped in place the wedge became wedged inplace. 

Worked very well easy to change ballast without turning the model upside down. And everything was secured once the nose cone was pushed back. 

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pete beadle

Hi Brett

I do believe you have just exposed a perfect case of model flyer's synchronicity....

When all the planets move into perfect alignment (just like your ballasting) it is futile to hold back and deny the omens......

Can I make one suggestion though?.....DON'T explain the happy coincidence that this new digital scale is effectively a present to you as well at the time of purchase.......wait until the good lady is using the new scales on a fairly regular basis (for whatever culinary purposes she needs them) and then make sure you draw no connection to her "present" happily also being useful to you.......to the ladies, timing is everything mate:whistle::yes::D

Congratulations and good luck for the success of this neat and VERY cunning plan......Baldrick would be proud.......

Regards

Pete

BARCS1702

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Brett82
4 hours ago, isoaritfirst said:

In my skorpion I had a small epp spacer at the end. 

Its worth having it there as a bump stop. 

I wrapped the epp in insulation tape to increase its strength. 

The piece also had a piece of epoxy board inserted into it. This served two purposes. One as a handle to help lift out the packing piece and second it was tall enough to almost reach the inside of the nose cone. As the nose cone was taped in place the wedge became wedged inplace. 

Worked very well easy to change ballast without turning the model upside down. And everything was secured once the nose cone was pushed back. 

Hi Mike

Thanks for the advice. I wanted to avoid an end stop as it is so tight it would mean removing the front slug and to keep it balanced it would also need to remove the back slug and replace it with a spacer. That would take me down well below 800g.

I do have some very soft foam that I can put on the front wall which will be soft enough to still fit the slug but still give some protection. 

You have given me another idea though. I have plenty of Carbon cloth and some really cool foam board from Jeff that is very stiff but simple to cut with a Stanley knife. I can take the board and make sort of a handle type fin shape to sit on top of the last slug that can also go into the hole above the slug (can be seen in the pics) to help prevent it rotating onto one of the pushrods. I can then take one of the more narrow 19mm slugs, wrap it in a layer carbon (including the board above it) to make one of the slugs into kind of a plug with a handle that secures it down when the nose cone is in place. I have spare slugs so that's no problem and a way to vacuum bag it so it may work. 

The carbon can either go all the way around the slug or I can cut it so it only goes down deep enough on either side so it cannot move at all once the nose cone is in place, kind of like a cap to sit on top of the slug. 

Its just a lot of work to go through if a simple strip of tape will hold it down. Would look really nice though if I got it right....

Brett

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Brett82
3 hours ago, pete beadle said:

Hi Brett

I do believe you have just exposed a perfect case of model flyer's synchronicity....

When all the planets move into perfect alignment (just like your ballasting) it is futile to hold back and deny the omens......

Can I make one suggestion though?.....DON'T explain the happy coincidence that this new digital scale is effectively a present to you as well at the time of purchase.......wait until the good lady is using the new scales on a fairly regular basis (for whatever culinary purposes she needs them) and then make sure you draw no connection to her "present" happily also being useful to you.......to the ladies, timing is everything mate:whistle::yes::D

Congratulations and good luck for the success of this neat and VERY cunning plan......Baldrick would be proud.......

Regards

Pete

BARCS1702

Hi Pete

I have it all worked out and trust me, there will be no mention of it being a joint gift....

Generally when I work on my planes its at night after the boys have gone to bed. My wife gets bored so she goes upstairs and reads leaving me free to use the scale to weigh my gliders without her ever finding out. Just got to make sure I put it all back exactly as I find it...

Take care mate.

Brett

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Scram

Glad you sorted it despite my wonky advice.

As for scales, just use 'em and remember for couples, "what's yours is mine and what's mine is me own!!  "  :bye:

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Brett82
28 minutes ago, Scram said:

Glad you sorted it despite my wonky advice.

As for scales, just use 'em and remember for couples, "what's yours is mine and what's mine is me own!!  "  :bye:

Hi Jerry 

Your advice was actually one of the ways I did check it. I decided to try each step and see if I got the same result. 

I measured the tube and marked the centre on the fuss. I then marked the COG on the fuss then checked to see where the fuss COG was (further back than the other two).

Once fully loaded the fuss only COG actually moved forward, closer to the full COG and the centre of the tube. Once the wings were on though and placing the ballast in a certain order it balanced bang on the COG. 

I thought if I check it all then that's the best way to learn so I know for the future. Thanks for the help mate, we need to go flying some time. 

Brett 

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John T

Hi Brett,

Sounds like my solution may be a bit late yet you could make a ballast tube from rolled up card exactly the same length and tape it in exaclty the same position above the one in the fuz to experiment with slug quantity/position etc.with the wings attached, as per picture below.

I also use tape to hold the first slug in position, yet i insert a piece of thin ply the width of the fuz under the tape just to stop any bowing in the tape, as per picture below.

Also worth noting with the Skorpions are the tail joiners that have an habit of snapping if they are the smaller diameter ones. I tried many solutions and ended up fitting solid stainless bar, which had very little affect on the cg.

 

Skorpion ballast tube.jpg

Skorpion ballast tape.jpg

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isoaritfirst

Using John's picture this is what i tried to explain earlier. It is far less fiddly than using tape.

Tape works fine, but if you are at a comp and want to switch ballast quickly it is a right faff with cold wet fingers.

The wedge piece does need to be made of epp or similar so that when it is inserted it is squeezed slightly then the pressure keeps it in place when the nose cone is removed.

58b5fa8ad7195_Skorpionballasttape.thumb.jpg.aea94a8bd10f2264ecbf4d605cc3c7fd.jpg

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pete beadle

Hi JohnT

Could I ask you what model this is, in your pics?

It's obviously an RCRCM plane, but it looks a lot like the RCRCM Sigma 3.7 I sold recently(?)

If it is being used simply as an example of what you do to check ballast positioning, I'd understand but, if it is the Sigma 3.7, I'd seriously doubt that fitting any ballast at all to that model would improve its flying qualities or performance at all.....fitting a ballast tube would strengthen it, yes, as the one it's fitted with does, but using ballast(?).....I really would doubt it

For me, the Sigma was one of the two models that RCRCM got right....the other being the Typhoon.....but, whereas ballast improved the Typhoon I'd seriously doubt that making it any heavier would improve what the Sigma does best.....light wind soaring.....scratching, if you will.....and, if you doubt that, see Mike's very impressive vids when he's enjoying the plane, almost certainly without added weight....... 

So JohnT, will you tell me what model is it please?...and my apologies for interrupting.....

Regards

Pete

BARCS1702

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satinet

Mike raced the short wing sigma in f3f races - I'm certain he would have used ballast. 

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John T

Hi Pete

The model is a Skorpion DSL, still own it, fly it, love it fully ballasted.

Just never got it sorted for the light wind days.

John

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Brett82
14 hours ago, John T said:

I also use tape to hold the first slug in position, yet i insert a piece of thin ply the width of the fuz under the tape just to stop any bowing in the tape, as per picture below.

Thanks for the photos and help John, Maybe a little late on this occasion but using the tube on top is a good idea for future reference, I will give it a try. I laid up some carbon a few months ago, just a flat piece from some scrap carbon mat I had been using for something else that I would have otherwise just chucked away. I could cut  it to use like your ply board under the tape. Sounds like I love carbon  but I simply don't have any ply at the moment. Just need to sand the edge so they are not sharp so it doesn't cut the tape. Just need to see if I can be bothered to go to all the effort of my drawing below.

4 hours ago, isoaritfirst said:

The wedge piece does need to be made of epp or similar so that when it is inserted it is squeezed slightly then the pressure keeps it in place when the nose cone is removed.

Mike that is very similar to what I was thinking but i was trying to work out what to do at the bottom of the EPP wedge (where it joins the tape in your pic). If I use that foam I have it is very firm (but not EPP) but it will compress if I cut it to just the right height. I want to form a sort of up-side-down "skateboarders half pipe" out of carbon to sit on top of the slug with the foam wedge sticking up, like what you have drawn. Maybe if I lay carbon going halfway up the wedge and not cover the foam completely it will still allow it to compress with the nosecone on, yet still ensure the bond between carbon and foam is not going to come undone. Here is what I mean, not to scale and top and bottom layers will line up on the sides, I just drew it like that so its easier to see the layers.

58b6c5c964645_Ballastcap.png.94b848c4eccddeb242a7ab23c12675b9.png

3 hours ago, pete beadle said:

Could I ask you what model this is, in your pics?

Pete I am more than 100% convinced that's a Skorpion in Johns pics. Looking at how the wing saddle merges with the fuselage at the trailing edge and how the loading slot for the ballast has been designed with the curve going up by the pushrods. That is exactly like my Skorpion, I spent hours  trying to set my flap center point with no clear wing saddle at the trailing edge to help as a guide. Only worked it out after I set the ailerons and lined the flaps up with them which seemed correct after I got the template from you a few weeks later. 

Brett

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Brett82
Just now, John T said:

Hi Pete

The model is a Skorpion DSL, still own it, fly it, love it fully ballasted.

Just never got it sorted for the light wind days.

John

You beet me too it as I was about to hit submit...

For once I am correct but to be fair the wing saddle is a dead giveaway...

Thanks for the help John

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