Member postings for Chris Barlow

Hi Rob.

Yes the rudder actuation is a tough one if you want to keep the hinge lines and don't want external snakes or pulls. You could always "adjust" the hinge line 1/4" forward and/or offset the elevator bell crank to one side as I've seen on a couple of blogs.

Depends who notices!

Andy is already scouring the blogs looking for sinners and heathens!

Thanks Chris. I managed to stop myself from unwrapping it earlier by chopping down the neighbors conifer trees which have started to rub against the shed roof. He's in for such a surprise when he comes home!

I also had a bit of an epiphany regarding mixing ratios. I usually use Zpoxy which is a 1:1 mix ratio but have now changed to Easy Composites laminating resin which is 100:30 resin to hardener. The voices in my head were arguing how to calculate the required amounts to mix 20g of resin when a quiet, rational voice from somewhere behind my forehead explained for 20g resin divide by the sum of the ratio, multiplied by the resin amount. The balance up to 20g is hardner!

so, 20g mix / (100 resin + 30 hardener) = 0.1538

0.1538 *100 resin = 15.38g resin

balance to 20g = 4.62g hardener

To be certain I tracked down an epoxy resin calculator online and checked the amounts for a 100:30 ratio.

I don't know why this has confused me before as it seems so simple now!

Edited By Chris Barlow on 01/02/2020 19:36:22

The Sabre fuselage is quite sleek Chris so I wouldn't worry about it getting a little "fat"

Maybe it's called a Dog because it has a wet nose?

Keep going, we're nearly half way there!

Getting close to paint and details now. This is where the time goes though!

Impatience got the better of me and I couldn't wait a full 24 hours for the resin to cure so after approximately 20 hours cure time I have removed the peel ply.

It came off relatively easily, pulling the ply at 180 degrees to the surface with a consistent, moderate force. Fortunately it didn't peel the wing skins off at the same time!

The finish is very flat and has filled in the cloth weave nicely. There is a slight texture left by the peel ply which does give it a slightly rough feel but I expect this will sand off very easily.

Overall I'm very impressed with the finish and will definately be using peel ply again on the JP, U-2 and Meteor wings.

The way I understand it, which may not be completely correct, is the peel ply is polyester to which the epoxy resin does not stick to very well, at least not as well as the glass cloth. when the glass cloth is wetted out with resin the peel ply is laid over it and squeegeed down. Any excess resin is wicked into the peel ply weave leaving the bare minimum which is trapped like the inside of a mold to fill the weave of the glass cloth.

When cured the peel ply is "peeled" off the glass cloth, which is possible due to the epoxy not sticking to polyester very well, leaving the glass cloth adequately "filled" requiring only primer and sanding before paint.

There are a few good videos on youtube showing the process including some by Danny Fenton. The goal is to achieve a better and lighter finish than a 2 coat resin technique with less effort. Win/Win (if it works)

That's a very clever and neat solution to the problem of flaps and ailerons with central servos! I might have to try that on something.

Well, what a disappointment!

I've been very busy at work this week and as it usually happens when you're busy time flies. In fact somehow I have lost a day thinking today was Thursday. I had planned to get in the shed by 6pm and get the top half of the Sabre wing glassed having spent most of the week glassing everything else, including a Jet Provost.

Unfortunately today isn't Thursday. It's Friday, and at 9pm I realised this. Friday night is indoor flying night from 8pm till 10pm, something I look forward to even more now my club field is muddy and inaccessable and the weather is pants! Flying with a different breed of loonies and comedians from the PSSA guys on Fridays is always a good laugh.

And now I've missed it!

Still, I have made a little more progress on the Sabre over the last week with parts being glass clothed. The last part of the airframe was the top of the wing and since it is quite a clear area I had decided to try using peel ply over the glass cloth for the first time. I usually blot and scrape all the resin off the cloth, let it cure then spread another resin coat over it with a card and finish with sanding and primer...and more sanding, and more primer...

I have wanted to try peel ply for a while as it is supposed to eliminate the second resin coat and the sanding required so with a refresher course of youtube videos when I got home I rushed out to the shed to give it a go, and missed the flying!

So I now have a stripey wing and will have to wait to see if I have messed it up or not!

And a couple of fuselages basking in a warm shed curing!

Yes, there is a "smudge" of filler on the JP's back where my 1/8" balsa went flat instead of curved!

If it's any help I drilled the holes for the forward (pivoting) wire oversize to allow the pre bent wire and bush to pass through over the bend. The wire and bend fits through the hole in the bell crank without the bush, and out through the other side, as the bush is pushed into the bell crank. The oversized hole also helps in getting the wire accurately perpendicular to the fuselage.

Once centralised and in position the bush was glued to the tail plane fairings with epoxy and micro balloons. Mine is slightly different in that I made my own bell crank and I have used a PTFE bush instead of a brass tube but I think the principle is still the same?

Once glassed I was going to glue the wire joiners into the tail plane halves with epoxy but I think I'll use a dab of Uhu instead as this will secure them in place but will allow easier removal in the event of any damage. (similar to the pritt-stick idea)

I too tight for cheques!

Slopeside beer tokens?

Yep I can do that if it's OK with Andy.

I have already sent Martin and Gordon a copy of the DXF files for them modify and produce a PDF plan from so that may be appearing soon?

If anyone would like a copy of the sliced plans please PM me.

I always said you were odd Gordon!

A couple of drop tanks built in balsa from Andy Meads 3D drawing. More details in my build blog.

Thanks Phil/Chris

Yes the drop tests went fine. I also set the win at an upward angle of about 30 degrees to see if the clevis would jam if the tank came off at an angle but that was fine too.

I was thinking of a hemispherical dome on the tank fitting into a concave recess in the pylon for the ant rotation, or maybe just a very short 3mm pin? There is also the tank brace which I intend to fix to the tank and clip to the wing with a single magnet and steel washer. Dont want that too strong and prevent the tank from dropping.

Very neat Phil.

How do you get your photos so clean and dust free? Do you build and photograph in different areas or just clean up and vacuum for each photo?

Or is it OCD?

Lots of learning on YouTube Chris.

Having started messing with the drop tanks I got distracted and whilst they were on the bench I couldn't resist planking them to see how they look.

I installed the threaded rod into the tanks to allow the fitting of an M2 metal clevis for the drop mechanism. The clevis can be adjusted in length to allow a snug fit to the pylon.

After planking the clevis will protrude to fit into the pylon.

The tanks weigh just under 40g before finishing which is comparable to Andys 3D printed tanks at 36g before internal structures to allow "hanging"

Mr Meade also came up with an excellent idea of cutting tapered planks for the tanks using the laser cutter which I just had to try. 20 minutes drawing a plank calculated to match the radius of the tank and 6 minutes to cut 13 planks.

The big advantage is that whilst I was fitting the first batch of planks the laser was cutting another batch. The disadvantage is the smoke and smell of burnt balsa, which followed me into the house to the disapproval of the wife & kids!

The tanks will be held to the pylons in a notch cut into the servo horn

To test the release mechanism I had to wire up the servo leads exiting the wing. These were soldered to two Multiplex plugs each with 6 pins. I used a common positive and negative for the servos and used the remaining 4 pins on each plug to connect the PWM (signal) wire for each servo.

The soldered pins were then potted in hot melt glue using a brass sheet mold clamped with a zip tie. I coated the inside of the brass with silicone grease, clamped it around the plug and filled it with hot melt. The brass does a good job of dissipating the heat from the glue and is helped by dipping into some methelated spirit and allowed to evaporate.

I know you can buy a mold to do the same job, but I'm cheap!

One plug is coloured black with permanent marker to differentiate between left and right. The other end of the plug is soldered to Futaba servo plugs to connect to the RX

It may look a bit clunky but those big blocks of hot melt glue are great for gripping when unplugging wings and protect the soldered joints perfectly.

So with the wing servos wired up and connected to a servo tester I could finally try the pylon release mechanism. The servo arms rotate forward to release so the air flow pushing back on the tanks should force them off the pylons. Just need to add some fins and anti rotation detents now!

Edited By Chris Barlow on 19/01/2020 04:05:39

That's a fine looking sculpture there Pete. It's a shame to melt it down into goo!

How do you deal with the blue foam sanding dust? I have only used it in small amounts and the dust is horrible! Sticks to everything through static and clogs the vacuum filters up very quickly!

Good to see progress on the Sabre builds again Steve. It's a landmark step when you get the joined halves out of the clamps and have a full fuselage to work with.

Only got these 2 of the tail, and the wide angle doesn't really show the slight taper on this one. I did measure it tonight and the taper is from 49mm at the leading edge of the tail plane to 40mm over the exhaust pipe so approximately a 5mm taper on each side over the tailplane distance.

Those airbrakes look very impressive Dirk, can't wait to see them in action.

I was thinking along the same lines for the canopy and will also be fitting it to some formers glued to the fuselage, that is after I've fixed the cockpit hole which I have cut a little bit too low at the back!

Good to see more progress Chris.

What is your plan regarding the cockpit? Are you going for the pilot bust from shoulders up or full depth with seat & instrument panel, and maybe even pilots boots?