Matty's Marvelous Modular Monstrosity

[Jay Kempf]

I like using a semi rigid film to cut a lot of sanding out of the epoxy slurry stage. Nice idea.

 

[pictsidhe]

Are you stealing my 4am math that makes the impossible possible?

Well, it's better than the 5am math that makes the possible impossible. You are less inclined look to double check that...

 

[Foundationer]

Try a chlorinated polyolefin adhesion promoter.

I'll remember this for the next go! Fuselage rear / vertical tail moulds.

Actually, if you use .016" aluminum instead of plastic, it will be stronger, hold the airfoil better, and probably cheaper.

Aluminium would be better because it doesn't conform to any little imperfections so well, but by the same token getting it right into the tight curve at the nose is a problem. Of course the nose is going to be smothered in micro and sanded anyway but lets not let that sort of logic derail my cunning plan! A serious issue with aluminium is that it's actually quite hard getting a big sheet delivered without at least one ding in it.

Anyway... top mould surface is in so I might lay up a tip tonight. Done 9 hours flying in the past two days too! BUSY BUSY BUSY!

 

[Foundationer]

I've found a pretty huge hole in my knowledge that I'm having trouble filling. Is there a book that details standard control linkages / bellcranks / push-pull tubes / etc. I know roughly what they look like, and I can draw pictures of them, but I don't really know the details.

Any info much appreciated.

 

[Victor Bravo]

The FAA AC 43.13 book is a very good thing to look at, as are the "Standard Aircraft Handbook" and any of the 1940's to 1960's aircraft worker handbooks printed by the aircraft manufacturers.

But the Tony Bingelis books, Sportplane Builder and Firewall Forward are PURE GOLD for specific examples and rules of thumb related to homebuilt airplanes.

Fritz may be able to verify that the Bud Evans designer's handbook could have a section on control systems. I can't remember.

I am certain that there are several industry standard textbooks on aircraft control systems, but a lot of that stuff is probably aimed at transport category and military aircraft. May be overkill for what you are building.

So IMHO start with the EAA Bingelis books immediately, and then research and seek out any other books available on light aircraft design.

 

[Foundationer]

So IMHO start with the EAA Bingelis books immediately, and then research and seek out any other books available on light aircraft design.

Sportplane builder bought and should arrive next week - thank you for the recommendation.

Last night's advanced composites masterclass had to be cancelled because I'd run out of... duck tape. I could only add half a flange thickness to the leading edge.

 

[Foundationer]

The delayed tip is now curing. Tomorrow morning the 'oven' will get put over it and it'll get baked for six hours before demoulding. The oven is a bunch of 50mm insulation foam foamed together to make a sort of lid and a fan heater plugged into a thermostat controlled socket. It gets a *fairly* even heating up to 60 - 70 centigrade from that.

Once that's out I get to sit it on top of one of the bottom skins and make sure the cutouts in the foam core for the spars match up. They should, but it's definitely the sort of thing I would screw up somehow and if I have then best to find out on a tip!

The duck tape and the whole mould process owes a lot to Billski's Fiberglass Bird. Even the way I had worked out to match up the top & bottom skins accurately turns out to be roughly the way he did it! Actually going over his build log again I think the whole thing owes quite a lot to that. That's here if you've not seen it:
https://www.homebuiltairplanes.com/forums/threads/billskis-fiberglass-bird.8344

Also the Europa build manuals are quite interesting:
http://www.europa-aircraft.co.uk/assistance/manuals.php

Attached is a picture of the mould faced with PP & ready to go. No wax or demould agent needed!

 

[pictsidhe]

Thanks to VB, I just had a look for the Bingelis books and found a set of 4 on ebay at a price that I failed to browse on past.
I really do need to get another shelf up now...
I have a rather large collection of reference books now, but few on practical construction methods. Knowing how big something needs to be is 90% of the problem. How to actually build it is the other 90%.

 

[Foundationer]

Wingtip top skin out and looks alright - the gaps in the foam for the spar line up and everything!

Question: the top skin is a lot more curved than the bottom skin and trying to whet out the carbon while stuck to the top of a bit of PVC foam that's not 'laying down' in the mould is annoying and is likely to cause all sorts of problems. So which of these should I do, or something else?

a. heat form the PVC core to the mould shape somehow then wetlay both sides and bag.
b. outer skin, add PVC, bag then do the inner skin in a separate operation.
c. Something else.

I'd like to keep it in one operation but not sure I can while keeping it reliable...

 

[Foundationer]

Question again: the top skin is a lot more curved than the bottom skin and trying to whet out the carbon while stuck to the top of a bit of PVC foam that's not 'laying down' in the mould is annoying and is likely to cause all sorts of problems. So which of these should I do, or something else?

a. heat form the PVC core to the mould shape somehow then wetlay both sides and bag.
b. outer skin, add PVC, bag then do the inner skin in a separate operation.
c. Something else.

And while looking for hardware info I came across a PDF of a Sydney Camm (designer of the Hawker Hurricane) book on aircraft construction from 1919!
http://www.survivorlibrary.com/library/aeroplane_construction-a_handbook_on_the_various_methods_1919.pdf

 

[Bank angle]

Question again: the top skin is a lot more curved than the bottom skin and trying to whet out the carbon while stuck to the top of a bit of PVC foam that's not 'laying down' in the mould is annoying and is likely to cause all sorts of problems. So which of these should I do, or something else?

a. heat form the PVC core to the mould shape somehow then wetlay both sides and bag.
b. outer skin, add PVC, bag then do the inner skin in a separate operation.
c. Something else.

And while looking for hardware info I came across a PDF of a Sydney Camm (designer of the Hawker Hurricane) book on aircraft construction from 1919!
http://www.survivorlibrary.com/library/aeroplane_construction-a_handbook_on_the_various_methods_1919.pdf

 

[Bank angle]

Hi Foundationer,

Sir Sydney Camm a great designer.
Have you seen this book, The Glider by Stelio Frati?
I think you would find it very interesting and maybe relevant to your project. I couldn't attach it, please Google it.

 

[Foundationer]

Hi Foundationer,

Sir Sydney Camm a great designer.
Have you seen this book, The Glider by Stelio Frati?
I think you would find it very interesting and maybe relevant to your project. I couldn't attach it, please Google it.

I had heard of 'The Glider' but not actually got hold of a copy. Thank you for reminding me / pointing me in the right direction - I found a PDF & I'm going to see if I can add that to my Kindle for some holiday reading!

 

[Bank angle]

Lots of shear force and bending moment diagrams! Enjoy.

 

[Bank angle]

Sorry to load up your kindle but this is an interesting project with lots of detail on its main spar which uses protrusions.
MITE wing design and construction.pdf

 

[Foundationer]

Sorry to load up your kindle but this is an interesting project with lots of detail on its main spar which uses protrusions.
MITE wing design and construction.pdf

That's interesting - thanks! First thing I noticed is that the 'allowed' strength he's quoted (from VLA ACJ 572(b)) for carbon appears to be 20% of the strength that's actually quoted by Marske etc. for Graphlite.

Specifically is states "The use of the following stress levels may be taken as sufficient evidence, in conjunction with good design practices to eliminate stress concentrations, that structural items have adequate safe lives: Carbon Fibre Rovings in Epoxy Resin - 40daN/mm^2 (58,000psi odd).

 

[Bank angle]

I agree this figure looks low compared to machine made protrusions but I guess he wanted a "certified" stress he could work to. There's not much out there data wise.
I'm sure Marske's figures are accurate but for a sailplane type wing you may have to design for deflection rather than max. strength.

 

[Foundationer]

Designing for deflection is really interesting because what deflection is acceptable? My tips do 28cm deflection on 8.2m span at n=6 with a FOS of 2 (I think, off the top of my head) which seemed fine when I worked it out. Tiny deflections under normal loading. Good old carbon fiber.

 

[Bank angle]

Apologies, for protrusions read pultrusions.

 

[Bank angle]

Yes a good question! I guess being able to get full aileron control movement upto rough air and or manoeuvring speed and one third control deflection above that?