Ballast tubes! How to make a fast, easy and good setup.

[Doc James Hammond]

Hi Guys,
Over the (Many) years I have seen more ways to keep ballast in ballast tubes than I can shake a stick at.

Mostly they involve Nuts screws washers and bolts - and other laundry related systems. All have been ingenious - some more than others I have to say.

Me? I use the good old Kelly Johnson KISS principles for most of my stuff.

To whit - and Guys this is really fast and easy!

First, measure the ballast tube for the slugs you want to use, in this case 8 of them, normally it would be an odd number but this is just to demonstrate, so I'm also using and nasty old glass tube which I made years ago. Now I use all carbon tubes. But they are hard to see in the pictures!

OK, then add 6mm at the back end for the cap and 1 x slug length (I use 35mm) for the opening plus 12mm at the open end for the front end cap.

So here we have (8 slugs) 280mm+6mm+12mm = 298mm PLUS the opening which would be 38mm = 336mm TOTAL.

Now cut the tube to length.

 

[Doc James Hammond]

OK Next: After roughing the inside of the tube ends and cleaning with solvent, glue in the nicely fitting (You did make them like that...right?) end caps with slow setting epoxy. Don't forget to give a nice fillet outside on the back end and inside AND outside on the front end to add a bit of strength.

What I tend to do here, by the way is to cut quite a chamfer on both sides of the 5mm plywood cap "button" to let the epoxy get the best key.

When cured, mark and roughly Dremel out the opening. Use a set of diamond files to get it to the correct size so that the slugs drop in and out easy - but don't make the opening too large. Test the slugs to make sure they slide in and out just by tipping the tube, then take off all the rough edges - I have cut myself by not doing that!

 

[Doc James Hammond]

Then: test the slug total length in the tube and make sure the last one in is just tucked in slightly from the end - maybe 4 or 5mm back from the opening.

Now cut yourself a THINGY from EPP or some other kind of hard flexible foam and bung it in!

Note, to do its job, said THINGY does not need to be tight at all, so make it secure, with a slight pressure - but easy to remove.

Now you know why you need a little recess at the front and back of the opening - its to let the foam go inside just a little so that there is no chance whatsoever of slugs or foam escaping - And...BINGO.

Your slugs are going nowhere, they are pressed into the rear of the tube by the THINGY and contained by the ballast tube walls so you don't have to worry about any aerobatics or stressed flying.

Added to that, Gentlemen, if you land hard, or stop quickly, the slugs will be cushioned, at least a bit, by the foam,so adding another small margin of safety.

Just like all good girls should be, its fast, easy, and cheap!

Enjoy:

Doc.

 

[Doc James Hammond]

Heres a better look maybe - I did this sketch some while back.

Doc.

 

[Konrad]

I learned how to make these tubes from Wayne elsewhere on the web. Much to my surprise I got rather good cylindrical results. Other than the last 10mm or so, the tube will allow a 19mm x 60mm slug to pass through. That last 10mm became a bit distorted as I tried to be fancy and neck down the end to aid in holding ballast in place. Now the kicker is I was aiming for a inside diameter of 17mm and wound up with an inside diameter of 19mm! This really is bad as I often claim that as an aerospace machinist I often had to hold tolerances down to 3 Helium light bands (0.000035")!

I think there is a link in here, as to how to make the tube.
https://forum.alofthobbies.com/index.php?threads/blejzyck-elf-1-5-slope-sailplane.764/

Looks like I’ll need to stop by Aloft Hobbies and upgrade to tungsten!
https://alofthobbies.com/ballast-tubes.html

All the best,
Konrad

P.S.
Found my problem, I need to do a better job counting the revolutions of the indicator (F.I.R.)!

 

[glideher]

ive used large mouth stars for my tubes, but my gliders are 35 to 40" wingspan, they work great,
i would think carbon fiber tubing would work for you guys as well with thin ID!!?

 

[Konrad]

Have a link to the "Large Mouth Stars"?

My tubes are aimed at the 1.5 meter to 2.7 meter class of model. The one above has a wall thickness of 0.6mm nominal, and weighs in at just under 11 grams. As this one will be laying down in contact with the fuselage for its full length I see no reason to go with carbon. But for application where the tube is unsupported spiral wrapping of carbon might be beneficial.

All the best,
Konrad

 

[Wayne]

What is a large mouth star?

 

[Konrad]

Guys when you added the feed slot to the bottom loaders, do you try to fill the space from the diverging diameters? The ballast tube has an OD of 18mm while the fuselage has a diameter of 32mm.

 

[bdog1]

Hi All :
A different question but still ballast tube related -
I will be building a NCFM M-60 plank and would like to use a ballast tube with it .
I have not found any pictures of a tube installed in a plank,have been reading that the M-60 is very critical on its CG for best performance ,I am thinking that the ballast tube must be installed in the fuse as you will not know the exact location until flying and trimming,with the tube in the fuse you could fit a spacer for the exact CG once it is determined.
NCFM recommends balancing on the tips of xacto blades to find your starting CG, pretty finite .
Am I on the right path ?
Mike

 

[Konrad]

Got a link to the ship?

All planks are more sensitive to CofG than conventional lay outs. I NEVER subscribe to the need for knife edge balancing of model CofG. The CofG for a model is done to set the margin of stability. The key word here is margin.

Now I do use knife edge balancing when dealing with rotating mass but that is a different type of balancing (static and dynamic {dual plane, an geometric term}).

With planks I find that the faster they fly the more one wants to shift the CofG aft. the Kingberg 100 wing had a servo moveable mass to trim for this at speed.
https://www.worthpoint.com/worthopedia/klingberg-flying-wing-100-large-rc-497995682

For a plank wing can you add mass (penetration ballast) inside a wing spar? I assume there isn't much chord to place the ballast tube.

 

[bdog1]

This is the M-60
https://www.rcgroups.com/forums/showthread.php?1360509-M60





I just found my answer, its in the wing

Build it with the tube. If you install it as designed (on the CG) it will fly the same, with or without ballast. But with ballast it is way more fun!


Quote:
Originally Posted by Buenperro
That's how I've been flying up till now. It'll be nice to have a ship with the ballast option and from everything I've read, the M60 is a great choice.

On more than one occasion, I've brought the planes out I thought would fly in the conditions at hand only to have them change making me wish I had dragged the either a heavier or lighter one with me. The M60 will most likely pay for itself in the long run as I will no longer have hire a Sherpa!
I have the ballast kit in mine and it is great. There are 11 lead slugs that are about 3 OZ each to fully load the tube up. You can put in any combination of lead or wood dowels to equal 11 to fill the tube, matching the weight to the situation. I have flown in 40 MPH wind with all 11 lead slugs and it was fast! When it is blowing about 20 MPH I have 5 lead slugs and 3 wood dowels on each side of the slugs to load the tube up. The added weight makes it penetrate better, handle better, and more importantly go faster.

 

[Doc James Hammond]

Guys when you added the feed slot to the bottom loaders, do you try to fill the space from the diverging diameters? The ballast tube has an OD of 18mm while the fuselage has a diameter of 32mm. View attachment 1478

YES Konrad. If not you will have a banana shaped, or missing front end very quickly.

I do it the other way round. I glue in the ballast tube with a nice lot of goop around the entrance.

Then after cure I Dremel out the opening. Since you have already made the ballast opening, I'd seal it from the inside with tape then goop it in.

Cheers,

J.

 

[Doc James Hammond]

Hi All :
A different question but still ballast tube related -
I will be building a NCFM M-60 plank and would like to use a ballast tube with it .
I have not found any pictures of a tube installed in a plank,have been reading that the M-60 is very critical on its CG for best performance ,I am thinking that the ballast tube must be installed in the fuse as you will not know the exact location until flying and trimming,with the tube in the fuse you could fit a spacer for the exact CG once it is determined.
NCFM recommends balancing on the tips of xacto blades to find your starting CG, pretty finite .
Am I on the right path ?
Mike

Unless there is a big difference between the CG and the MAC position on the model, ie, forward sweep or rearward sweep, then ballasting would be very unwise until the CG is firmly established.

After that extreme care would be the order of the day.

Cheers,

James

 

[bdog1]

Thank You Konrad !
I found this thread while looking for a good link to post for you.

 

[bdog1]

That's what I had been thinking James,was why I wondered about installing it in the fuse.
The thread consensus seemed to indicate that the factory recommended CG was close enough...

I know many subscribe to building to a weight by adding strength rather than ballast but I am a east coast flyer and our conditions change rapidly as weather fronts move through,it would be nice to adapt with the ballast .

* I am hoping there will be a Stormbird in my future
Mike

 

[Doc James Hammond]

That's what I had been thinking James,was why I wondered about installing it in the fuse.
The thread consensus seemed to indicate that the factory recommended CG was close enough...

I know many subscribe to building to a weight by adding strength rather than ballast but I am a east coast flyer and our conditions change rapidly as weather fronts move through,it would be nice to adapt with the ballast .

* I am hoping there will be a Stormbird in my future
Mike

Hi Mike - what model is it that you are talking about? - any links?

Good to hear you are thinking about feeding a 'Bird!

James.

 

[RalfH]

I'm slowly getting my Blejzyk Hammer together and was just wondering about the ballast tube installation as well. Are you guys glueing the tube along the whole length to the fuselage? And what is the preferred glue, epoxy with microballons?

Still trying to wrap my head around getting the nose and tube in the right place at the same time, it seems cutting the opening into the tube after its installed may simplify getting everything in the right place and orientation.

Ralf

 

[Konrad]

RalfH, don't over think it. Just take a bit of time to think the placement of the radio and tube. As I think the Hammer is a wide body glider it should really not be an issue. On my Mefisto things are a bit tight. I wanted to fit the 5 cell 1300 mAh battery, 2 servos, and shoot gun style ballast tube. This meant that the servos needed to be mounted askew/side by side. This compresses the length needed to mount the servos, giving me space to put the ballast loading window. Something to be aware of, is that the nose cone will need a 4 to 5 mm full circumference pilot to key upon.

To size the ballast tube figure out how long the tube needs to be to house your ballast. Divide this length by 2. Add 5mm to this length. Now find where the slugs stop (see doc's stops) and from there mark this (length +5mm) from that stop.Now find the OEMs recommended (or what guys like on the web) balance point. Mark this on the wing mount. Cut a hole in the wing mount to see into the fuselage. (Remembering where the wires and wing mounts go might help). Line up the two marks (the balance point and the center mass + 5mm marks). from here see how far forward you need to go to add the second half of the ballast mass. As in my case you might have to add length to the ballast tube to get the tube far enough forward into the nose section to allow for loading of the ballast weights. Cut the ballast tube to this desired length. Plug the front of this tube real well with a thick plywood plug.

I glue in the ballast tube for its full length with a thick slurry of slow epoxy and cabosil. Make sure there is a mound to support the rear stop. Line up the the marks (the balance point and the center mass + 5mm marks) .I use slow epoxy to glue the nose on. I like to have the servo that will be the closest to the ballast tube installed just to make sure there are no problems. Wax the inside of nose cone, Slip it on the nose cone. From the cut out you made in the wing saddle make sure the inner nose is all the way forward in the nose cone. Align the nose cone to the fuselage and tape in place. Make sure the ballast tube is all the way down in the epoxy cabosil mix (Micro Balloons is ok). You might want to add a lot of this mixture to the back inside of the nose just before slipping it on, to help surround the area that will make up the loading slot. Set aside until full cured.

The reason you added that 5mm of ballast tube aft of the recommended CofG is that you will eventually want to move the center of gravity further aft than what the manual says. When this happens you will have some length to move the ballast aft keeping it over the new aft CofG. In the mean time you can add a 5mm spacer before adding your weights.

I find that it is best to cut the loading slot after the nose and tube are installed as there is no way to get to the back side of the area from the top. So add enough glue and fiber around the area where you will be cutting out the window. You really don't want the void I show between the ballast tube and fuselage.

All the best,
Konrad.

P.S.
I think this is going into a bit too much specific detail for Blejzyk kits. I will try to cover this in a bit more detail in my Mefisto thread.
https://forum.alofthobbies.com/index.php?threads/mefisto-build-blejzyk.284/

P.P.S.
Thanks for the 15mm copper couplers that will be used as lead carriers

 

[Doc James Hammond]

I'm slowly getting my Blejzyk Hammer together and was just wondering about the ballast tube installation as well. Are you guys glueing the tube along the whole length to the fuselage? And what is the preferred glue, epoxy with microballons?

Still trying to wrap my head around getting the nose and tube in the right place at the same time, it seems cutting the opening into the tube after its installed may simplify getting everything in the right place and orientation.

Ralf

Ralf - first thing is get your ballast tube and your slugs and cut the ballast tube to length - leaving enough extra tube for the two stoppers and the ballast insert hole. I use 35mm slugs, and 6mm thick plywood stoppers so my ballast tubes are always 50mm longer than the ballast I want to use.

ie; ballast insert hole = 36mm, then add 2 x stoppers = 48mm mm then add 2mm clearance = 50mm Total extra length.

It's best to use an odd number of slugs so that you can divide them if you need to with one always in the middle at the CG. I use 9 slugs mostly.

So If I use 9 x 35mm slugs I get 315mm plus the extra 50mm length = 365mm total.

Then find the centre of the BALLAST in the tube - this will mean that the tube is to equal length because you have the ballast insert opening so the front end will be longer. So then mark the centre of the BALLAST - not the tube.

Make sure to place the centre of the ballast mark exactly on the CG mid range. Then glue the tube in all along its length using as much epoxy and filler as needed - don't use microballoons because they are useless - filling can be silica, cabosil, etc or simple wood dust.

Note: Microballoons add no strength and have no place on any glider construction.

Gluing along the length of the tube adds a lot of strength, so the ballast tube can be then regarded as a structural member of the fuselage assembly.

Cheers,

Jams.
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