Hybrid Paul Janssens Spitfire Mk24/14

[MattyB]

PS - More threads on vac bagging that cover the use of laminating film as a mylar substitute...

• https://www.rcgroups.com/forums/showthread.php?1001599-Vacuum-Bagging-Mylar-substitute
• https://www.rcgroups.com/forums/showthread.php?980893-Vacuum-Bagging-Made-Easier-Aqua-Vac-Foodsaver-Gast-Pump-Tire-Pump

 

This one is also interesting; it details how to convert an aquarium pump for the vac bagging of wood onto foam cores (not really a strong enough vacuum for composites, though):

• https://www.rcgroups.com/forums/showthread.php?966524-Telos-building-thread-with-10-VACUUM-BAGGING-SYSTEM-Tutorial!!!

 

Edited August 2, 2023 by MattyB

[Mike Chantler]

Great 🙂 thanks!  threads look very valuable. Nice to see that other folk use 12v speed 600 sized vac pumps - I had wondered about their longevity.

 

I've tried the thick PVC stuff, and 75 micron laminating film - both which left dimples with me. But laminating thicker laminating film sounds a great idea 👍 - I'm definitely going to give this a go - and so think I now might replace the sheet balsa tail feathers with aerofoil section XPS   🙂

 

[Mike Chantler]

Last night I managed to ignore my own instructions (who reads instructions anyway?)

missed out the tape the beds with protective tape step, noticed as assembling, and pushed in some A3 laminating pouches quickly but they did not protect all of the wing:

 

 

Will sand off easily, but just as well I noticed 😮. I'm going to try and be much more patient in future ...

[Mike Chantler]

Added and shaped this morning 

 

So am now pretty happy with the LE and bagging - will slowly add TE shaping, ailerons, finishing etc (may try laminating film on test first to see what I would do with the LEs).

 

While I'm doing bits of physical stuff to keep me sane - I'll tackle a bit more of the Fusion 360 stuff and think about how to do the rear fuselage (ideas vary from carving foam, doing foam vertical bread and butter, to using 3D prints as moulds - yup no clear ideas yet except probably not lost foam).

[Mike Chantler]

And will think about cannons 🙄

[MattyB]

17 hours ago, Mike Chantler said:

Added and shaped this morning 

 

So am now pretty happy with the LE and bagging - will slowly add TE shaping, ailerons, finishing etc (may try laminating film on test first to see what I would do with the LEs).

 

While I'm doing bits of physical stuff to keep me sane - I'll tackle a bit more of the Fusion 360 stuff and think about how to do the rear fuselage (ideas vary from carving foam, doing foam vertical bread and butter, to using 3D prints as moulds - yup no clear ideas yet except probably not lost foam).

 

Very nice - once your build is finished I might get you to knock me up a set of wings for my fuse on your cutter based on those results! 😉

 

[MattyB]

18 hours ago, Mike Chantler said:

...I've tried the thick PVC stuff, and 75 micron laminating film - both which left dimples with me. But laminating thicker laminating film sounds a great idea 👍 - I'm definitely going to give this a go - and so think I now might replace the sheet balsa tail feathers with aerofoil section XPS   🙂

 

TBH on a model this size (and if it's your first attempt at compositees on the outside layer) I would be included to stick with flat plate balsa - it's less complex and there is no risk of crushing the naked xps cores. Certainly if you are going that route I would recommend you make sure your bagging setup is fully specced out iwth a pressure sensor that triggers the pump to keep it at exactly the right pressure, as you'll need to do that to ensure good adherence without crushing the cores. Doing it over veneer or balsa sheet is a lot easier for starters!

[Mike Chantler]

Thanks Matt, will see how enthusiastic I am at that stage of the build - i've certainly crushed quite a bit of XPS before 🙂

It looked like you were using balsa cores in that thread, do you know if anyone bagged XPS in the same way on that mass build? I'd be worried about warping the XPS?

 

PS I do have a vacuum regulator in the loop.

 

back to work today so build will go a bit slow from here.

[MattyB]

13 hours ago, Mike Chantler said:

Thanks Matt, will see how enthusiastic I am at that stage of the build - I've certainly crushed quite a bit of XPS before 🙂

It looked like you were using balsa cores in that thread, do you know if anyone bagged XPS in the same way on that mass build? I'd be worried about warping the XPS?

 

From memory I was the only one who bagged their Limit - most of the ISA members participating just applied veneer using contact adhesive, or else built up a wing as per the Limit plan. However, I don't think warping should really be a problem when bagging composites straight onto foam - remember the vacuum is acting evenly in all directions, it's the weight on top that keeps everything straight. The bigger challenges are getting the amount of epoxy right (the amount absorbed by the foam will vary depending on the density used), and avoiding crushing the foam whilst still pulling enough vacuum to ensure good adherence.

 

 I've never done bagging directly onto XPS, but I'm sure there are lots of (predominantly US based) experts on RCGroups who could advise you.

 

Edited August 4, 2023 by MattyB

[Mike Chantler]

Experimented with finishing some test 3d prints.

 

Light sanding of spinner with 180 grit followed by 4 coats high-build primmer:

 

Not bad for a matte finish, but you can still see the 3d layers, especially at the top where it was awkward to sand.

 

Next attempt used polyester resin plus micro-balloons - however, it never set!!! Being a cheap skate I thought I would use some catalyst it got with a tooling kit a while back with cheap can of resin from Halfords, after a little investigation discovered MEPK only has shelf life of 6 months and my hardener was at least 5 years old!! Dunce 🙄 lol

 

So new MEKP on order!  

[Mike Chantler]

Was scratching my head a bit about how to do the aileron hinges - normally I put light kevlar below the top skin and this gives a bullet proof and very tight hinge. However, the ailerons span two of the wing foam sections so you can't do this for the spit, and I've only ever built straight-edged wings before. So remembered some guys on rcGroups cutting out sections from foam veneered wings and putting in wood sub TE and aileron facing before cutting ailerons out, they used some thin ply to create aligned spaces for the hinges. Had a test go on that wing I bodged with too little vacuum:

 

Think this worked well in dry fit:

but it's easy to mess up the skins - so thought I would glass the wings first - and this would also limit warping of ailerons. But to glass the wings I need the tips.

 

Edited August 5, 2023 by Mike Chantler

[Mike Chantler]

So cut TE with newly purchased right-angled Dremel attachment:

This thing is brilliant! 🙂 🙂 🙂 Should of got it ages ago.

 

Then added XPS tip blocks with 3mm lite ply reinforcement:

 

Now have to resist trying to carve the tips before glue completely set 🤔

 

 

 

[MattyB]

On 05/08/2023 at 20:58, Mike Chantler said:

Was scratching my head a bit about how to do the aileron hinges - normally I put light kevlar below the top skin and this gives a bullet proof and very tight hinge. However, the ailerons span two of the wing foam sections so you can't do this for the spit, and I've only ever built straight-edged wings before. So remembered some guys on rcGroups cutting out sections from foam veneered wings and putting in wood sub TE and aileron facing before cutting ailerons out, they used some thin ply to create aligned spaces for the hinges. Had a test go on that wing I bodged with too little vacuum:

 

Think this worked well in dry fit:

but it's easy to mess up the skins - so thought I would glass the wings first - and this would also limit warping of ailerons. But to glass the wings I need the tips.

 

 

TBH at this stage that looks more work to me than just cutting out the ailerons, angling and facing them with balsa (along with the false TE where they will attach), then bagging them separately. You could then install a cyano or std pin type hinges pretty easily, or just go with tape tension hinges which are easy to check and maintain on a glass wing, and nice and free in operation.

[MattyB]

On 05/08/2023 at 21:08, Mike Chantler said:

So cut TE with newly purchased right-angled Dremel attachment:

This thing is brilliant! 🙂 🙂 🙂 Should of got it ages ago.

 

Then added XPS tip blocks with 3mm lite ply reinforcement:

 

Now have to resist trying to carve the tips before glue completely set 🤔

 

 

Will those tips not be susceptible to landing and handling rash, even under glass? On a PSS model tips do tend to take some abuse...

[Mike Chantler]

5 hours ago, MattyB said:

 

TBH at this stage that looks more work to me than just cutting out the ailerons, angling and facing them with balsa (along with the false TE where they will attach), then bagging them separately. You could then install a cyano or std pin type hinges pretty easily, or just go with tape tension hinges which are easy to check and maintain on a glass wing, and nice and free in operation.

 

Yes, good point, and I will likely rethink this. I'm kind of used to using kevlar under the skins which ends up with a pretty neat and indestructible hinge:

 

 

However, on the elliptical wings I can't do this as the top skin does not follow a straight  line at the aileron hinge (it goes across two of the foam panels). So will likely just use balsa facings and std hinges. But first will cover wing in light-weight glass to reduce the chances of the ailerons warping which I have had happen before 😞

[Mike Chantler]

5 hours ago, MattyB said:

 

Will those tips not be susceptible to landing and handling rash, even under glass? On a PSS model tips do tend to take some abuse...

 

It's hanger rash which is the main problem for me - as our slopes are nice and grassy, although there are some isolated small rocks that we manage to find(!)

 

Recently I've taken creating wing and fuselage bags for my planes which has helped enormously.

 

More of a problem is that the foam contact glue, although it sands, it is tougher than the XPS and can leave high points if it gap fills at all. You then need quite a bit of patience that balsa and aliphatic would not. 

 

I may yet cut these tips off and replace with balsa 🙄

[Mike Chantler]

Little progress as weather been good for going up the hill and am back at work. Sadly broke fus of the model I have been flying continuously for the last year so this will need some attention.

 

But got the new MEKP catalyst, mixed up, painted on to half size bit of 3D print, and still sticky after 2 days!

 

Turns out there are two types of polyester  duh!  🙄 . One cures with MEKP and one  cures with BPO paste, ISOPON laminating polyester is the latter  🙄 Now waiting for the other stuff.

 

In meantime printed off a full size section of nose:

 

 

You can see the 3d print layers:

 

But light sanding and two layers of polyester should do it 🙂

 

And yes my 3D design skills are primitive! But will do for up the hill.

 

I plan to use 3D print for top half of front fus. 

 

Still needs modified for battery box, ballast tubes and some longitudinal carbon rod re-inforcement (otherwise   I suspect it will be vulnerable to breaking  along the print laminations). Will post models for anyone who is interested later after i'm happier with design.

 

 

 

[MattyB]

3 hours ago, Mike Chantler said:

You can see the 3d print layers:

 

But light sanding and two layers of polyester should do it 🙂

 

And yes my 3D design skills are primitive! But will do for up the hill.

 

I plan to use 3D print for top half of front fus. 

Doeant look crude to me! It’s a long tie since I looked at that fuselage, but from memory Paul’s original mould had no exhaust stack detail, so you are well ahead on that front. 
 

3 hours ago, Mike Chantler said:

Still needs modified for battery box, ballast tubes and some longitudinal carbon rod re-inforcement (otherwise   I suspect it will be vulnerable to breaking  along the print laminations).

What are you printing in, LW-PLA? I have precisely zero experience on n 3D printing, but understand from watching videos there are several tried and trusted methods for improving the strength when using that - see this video at around 6m40s on.

 

 

[Mike Chantler]

The double skin is a neat approach - I like that 🙂

 

For a slope model I suspect you still need longitudinal carbon or similar, I've been flying two incarnations of a 60" plank with a 3D printed fuselage pretty continuously over the last year and a half. The foam/carbon wing of the first version collapsed in a brutal straight-in crash (totally my fault) because I had used surface carbon spars without a webbing spar as an experiment. The fuselage was in perfect shape afterwards and could of been reused except I fancied a different colour and a couple of mods to the battery arrangement. It does have a double layer skin, but not the spacing and bracing between the two skin layers.

 

V2 ended up going into the hill in 50-60mph wind when I was curious about just how big a loop I could do with full ballast 🙄

It went in at an angle breaking the nose off along a print layer line - some other crashes have all had the fuselage break in the same plane but different places as the print is weak for tension forces applied normal to print layers.  I don't think the double skin will really help you for this failure mode, especially for a slope model flown in windy conditions.

 

Adding holes for longitudinal carbon tube in the design is pretty easy and within my Fusion 360 skills 🙂 so will likely go for this simple solution. The double and spaced skin will likely challenge my brain power, not so much in terms of creating it, but rather the knock-on effect it will have with the rest of the 3D model, so will likely leave this for now 🙂

 

PS there is a nice  video here on how to use kevlar thread to put 3D prints into tension, this I suspect would be lighter than carbon rod but a bit more awkward to organise in a model.  

 

 

 

[Mike Chantler]

While humming and hawing about the rear fus design and tail feathers, I did a little more to the wing. Sanded and filled tips. Could not remember filler mixture from last plane so wrote it down this time 🙂 

 

 

 

20g glass is just to help hide wood grain as wings are very stiff and veneer is pretty ding resistant. And, yes, am being lazy just using WBP. Did think about using mylars/epoxy/vac bag,  but got scared and used tried and tested (I would not like to build these elliptical wings again 😮 )  Putting glass on now as I warped the ailerons when i did them separately on another build with WBP.

Edited August 19, 2023 by Mike Chantler

[Mike Chantler]

Was going to use 5mm balsa for tail feathers but then discovered I'd use up quite a bit of the unwarped/nice 5mm stuff I had left.

 

So had a look at MattyB's links and some youtube vids and decided to have a go with the mylars. Cut some cores:

 

 

 

Just as well I cut 3 cores as I kind of jumped when pouring in the epoxy hardener  (went from 30% to 60%)

Thought I'd get away with it as this was just to see if 2x 125 laminating film would work for mylars.

 

Used some food saver vac bag tube which worked a treat:

 

But the extra hardener made the glass stick REALLY well to the laminating film despite being covered in release agent!!

 

 

Quite a mess!!! lol 🙄

 

Tried again with correct ratio and worked well enough for first propper attempt 🙂

 

 

Some dimpling - but would be fixed using thicker mylars or less pressure (than .5 bar) I think. But would be good enough for light sanded deep fill primer and top coat as is I think.  🙂

 

 

 

 

[MattyB]

Cool that you are trying the lam film mylars, great stuff.

 

in breaking news, I was up in the loft on Friday and look what I found…

 

 

 

Purchased in 2009!

 

 

 

 

 

[Paul De Tourtoulon]

8 hours ago, MattyB said:

in breaking news, I was up in the loft on Friday and look what I found…

I looked up in my loft and sadly there wasn't one up there.🤢

[Mike Chantler]

14 hours ago, MattyB said:

 

 

 

Purchased in 2009!

 

14 hours ago, MattyB said:

What a bargain!! When does the build start 🙂 ?

 

 

 

 

 

 

 

 

[Mike Chantler]

Polyester I guess? the T33 I have has a bit of flexibility in the fuselage which helps its robustness I think 😁