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Foka 4 (I/4 scale)

Let us all watch your new project progress.
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Martynk
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Re: Foka 4 (I/4 scale)

Post by Martynk »

Thanks Brian

I am going to use a ball link on the Elevator (and Rudder) horns with proper dowelling pushrods back to the servos. This should give a nice slop free linkage.

The tailplane isn't huge by any stretch of the imagination, my biggest challenge is to make it as ding proof as possible.

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Peter Balcombe
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Re: Foka 4 (I/4 scale)

Post by Peter Balcombe »

Martin,
Make sure that the pushrods are either stiff enough not to bow due to flying loads trying to push back on the pushrod, or else provide one or more supports along the length of the pushrod to keep it straight.

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Martynk
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Re: Foka 4 (I/4 scale)

Post by Martynk »

Will do...

Thanks

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Andrew Ray
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Joined: 19 Mar 2015, 19:15
Location: Staffordshire

Re: Foka 4 (I/4 scale)

Post by Andrew Ray »

Hi Martyn, nice job.

CF tube makes for a nice stiff pushrod, particularly over longer lengths and needs less support. I quite like using bowden cable running in PTFE tube making sure the tube is secured at regular intervals to prevent flexing under compression, many manufacturers use piano wire (or similar) in a tube preinstalled in a glass fibre fuselage (or even a 2mm carbon rod with the adaptors glued on).

Looking forward to seeing more.

Andrew

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Martynk
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Re: Foka 4 (I/4 scale)

Post by Martynk »

Thanks Andrew

Yes - I think carbon tube would work well and is lighter than pine dowel which I was planning on using. I need to nip down to the LMS this weekend, I'll see what they have available

Fus parts didn't arrive yesterday :(

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Martynk
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Re: Foka 4 (I/4 scale)

Post by Martynk »

The parts have arrived.. :) That's the good news :)
parts1.jpg
and
Parts2.jpg
The bad news is that the deck is too wide. I have just found a bug in DevFus. It's not horrendous. Basically, there are two 1/4 spruce longerons that run down the centre of the Fus, The Fus is built in two halves using the deck as as a building board. What the program has done when it calculated the width of the deck was to ignore the pre-configured longerons. This means that I can either cut it back to size or laminate the longerons top and bottom (using 1/4 x 1/8 spruce). I have chosen the latter, this will give an effective size of 1/4 x 3/8 for the side longerons. Edit - this will mean a few tweaks to each former to increase the slot depth by 1.5mm top and bottom but that's no real problem

So, this morning, I added the two sides and let them dry, flipped the deck this lunchtime and added the 2 on the other side.
Fus2.jpg
and
Fus3.jpg
At least a start has been made, I need to make the wing centre section as this will be used for placement of the wing securing parts in the upper fus and I want to make sure it all lines up before I commit too much glue to wood.

More to come, but slowly, I am thinking this through carefully as I am working through the challenges

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Martynk
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Re: Foka 4 (I/4 scale)

Post by Martynk »

Its going together fairly quickly and easily..

Its like a 3D jigsaw - almost 6 feet long..
Fus4.jpg
Lower fuselage in cradle
Fus5.jpg
Rolled over. Still have got some work to do around the canopy front but still thinking about it
Fus6.jpg
The undercarriage in place. Quite fiddly to get it in and aligned correctly but seems OK now. Maybe a bit too springy but the skid will absorb any excess impact (I hope).

This morning I did a test fit of the fin and started work on the tail piece.

Can anyone advise what sort of decalage I should be looking at for this? I think its set at +4 as per the full size but that seems way too much and I believe that about +2 would be about right for a 25%MAC CG

Thanks

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RobbieB
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Re: Foka 4 (I/4 scale)

Post by RobbieB »

Martyn,

1.5 to 2 degrees will be just fine - 4 degrees will give you a model that will not be very nice to fly.

Also, you will almost certainly be able to move that 25%MAC back incrementally to a position that suits you and your flying.

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Martynk
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Re: Foka 4 (I/4 scale)

Post by Martynk »

Thanks Robbie

Thats great.. I'll go for 1.5 degrees - it will keep the model more neutral..

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Martynk
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Re: Foka 4 (I/4 scale)

Post by Martynk »

I have had a comment about the wheel mounting from a Scale Soaring builder in the USA suggesting that I may be better rigidly mounting the wheel in a box rather than making it sprung as I have done. The tyre is quite soft however there is nowhere obvious where I can make a box and make it strong enough without adding a lot more wood. I am planning on boxing in the wheel - but purely to prevent crud from getting into the fuselage, i.e., it will not be a structural load bearing component.

Any thoughts on this? If I have to make changes I need to do this now before I start sheeting/planking the fuselage.

Thanks

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