Pitbull 2

[oipigface]

Ballast again! 

I’ve been getting my new PB2 ready for its maiden, and succeeded in getting the CG to the recommended 97mm without use of joiner ballast. In order to get my green PB2 to that point I always relied on 540g of ballast in the front joiner. With the new one, noting that the moment of the front joiner is about 1/10th of the moment of the nose, I reckoned that if I could squeeze 54g of lead in the front, I would have a plane that would fly in light winds. I already have the nose in front of the battery full of lead, but there was a space which looked possible on top of the battery, just in front of the aperture in the inner nose. 

I used dental alginate (see BMFA News about a year ago) to make a plaster-of-Paris mould. Alginate is easy to trim with a sharp knife, so where the liquid had flowed in down the sides of the battery, I flattened the bottom of the casting off before I made the mould. I also trimmed off a little lip on the top so that the finished lead casting would slip easily into the nose. This produced a 56g casting, which was a little big. (Not sure why, but it is partly to do with the shape of the lip around the aperture.) I worked at it, removing about 2mm material from each side, and a small amount from the top.  I was left with 46g which fits neatly on top of the battery, and butts up to the bigger nose weight. (See photo.)

This left adequate room for a couple of 5g wheel balance weights on top of the battery, which is where most of the wires go as well. The weights are under the tape in the photo. Measured CG is now 97.1mm, which will do as a starting point.

Remaining jobs: tape up the servo covers, and fling it off!

P.S. If you’ve got one of my PB2 noseweights, and you are thinking you would like one of these additional ones, then you are going to have to make it yourself. This piece is a complicated shape, and I had to destroy the mould to free the lead casting. If you’ld like a couple of spoonfuls of alginate, I can probably help you. 

 

 

[Stefan Bertschi]

I struggled with setting the cg on one of my freestylers too. I solved the issue, not with refined craftsmanship like John, but with throwing money on the issue. The solution for me was 'Tungsten Putty' which is a kind of plasticine mixed with tungsten. Normally used for fishing but also very handy for balancing a plane.

[oipigface]

I did think of mixing tungsten swarf with molten lead to cast a new noseweight, but since I couldn’t find my stock of tungsten swarf, I made the extra little piece to fit over the battery.

[satinet]

Isn't the density similar to lead? (Edit: Of putty)

I found molten lead poured in to the nose to be the most space efficient method down the years. 

Nose in a tub of water. Only works for sealed noses obviously.

[isoaritfirst]

i used the nose weight that John gave me. Together with a 2100 life battery. The battery is a very snug fit and needed reworking and it’s Mylar cover removing as well as around 1mm removing from the fuselage reveals. 

There is plenty of room left in the nose for more lead. Originally balanced at 97 without problem. 

 

[oipigface]

11 minutes ago, satinet said:

Isn't the density similar to lead?

I found molten lead poured in to the nose to be the most space efficient method down the years. 

Nose in a tub of water. Only works for sealed noses obviously.

I’ve never done this for safety reasons. The PB2 has a hole about 5mm diameter in the nose, but this could be effectively sealed with tape. Lead is about 11.3g/cm3, tungsten about 19.3. So a mixture could reduce the volume of a casting of a given weight substantially.

[f3fisa]

2 hours ago, oipigface said:

 Lead is about 11.3g/cm3, tungsten about 19.3. So a mixture could reduce the volume of a casting of a given weight substantially.

Tungsten putty has a density of 10g/cm3.

David.

[mikef]

The Tunsten putty I got was much less at 2.75 gm/cm3.  Have you checked yours yourself?

https://www.barcs.co.uk/forums/topic/7198-not-enough-room-for-nose-weight-try-this/?tab=comments#comment-147156

 

[oipigface]

I don’t know if any of you have looked carefully at the pushrods in your Pitbull 2. They are square!!

So now that I’ve broken one, I need to know where I can source 1.5mm square CF rod. I’ve tried Google. Robotbirds have some but only in 750mm lengths. I need about 1100mm. The other usual suspects only have larger sections.
I can probably get it from Baudis, but that would be pricey. Another alternative would be to sleeve the breaks, but the rods run very close to the inside surface of the fus, and I’m not sure that could be done without causing binding.

[Andy_B]

and you cant use the conventional round ones because John ?

[oipigface]

11 hours ago, Andy_B said:

and you cant use the conventional round ones because John ?

I don’t know what shape the outers are. 

[Andy_B]

ahhhh so there snakes 

should have realized when you said 1.5mm

[wookman]

If you can fit 1.5mm square snakes in the tubes then can you not fit dia 1.5mm in the same tubes? They would be equally well supported and have less friction. Not to mention being much easier to source.

[oipigface]

OK, chaps, time for a new thread. I had an email from Pavel at Baudis today, which included this:

 “Finally we would like to inform you that we are working on a new model Pitbull 3. 
We estimate it should be available around March or maybe even in February, but it is hard to estimate any precise timing in the current situation.”

 

[Les]

30 minutes ago, oipigface said:

OK, chaps, time for a new thread. I had an email from Pavel at Baudis today, which included this:

 “Finally we would like to inform you that we are working on a new model Pitbull 3. 
We estimate it should be available around March or maybe even in February, but it is hard to estimate any precise timing in the current situation.”

 

I wonder if this will be the lift version? 

[oipigface]

More news in a new thread soon.

[knewt]

On 03/04/2019 at 17:02, isoaritfirst said:

i used the nose weight that John gave me. Together with a 2100 life battery. The battery is a very snug fit and needed reworking and it’s Mylar cover removing as well as around 1mm removing from the fuselage reveals. 

There is plenty of room left in the nose for more lead. Originally balanced at 97 without problem. 

 

Mike, did you manage to get a Jeti Rex 7 in there?

[MikeE]

Yes, model was built with a Life 2100 pack and a rex 7. And Pico switch. 

Dave DeMott now owns it, I don't know it's current configuration. 

[knewt]

Thanks Mike, it was the height of the Rx I was worried about, so that’s great news. 

Cheers

K