Rib Plotting by Computer

[Jeffrey Cottrell 2]

Hi Guys

In the first stages of building a Chilli Wind, but with a built up wing rather than foam. For the first time in many years I tried the sandwich method to produce the ribs, but so far, results are not encouraging and I doubt they'll get any better.

So, looking for a better way.

Keep hearing about various rib plotting programmes, such as Compufoil etc. but I have no experience with these, and my computer skills remain firmly in the stone age.

So, can anyone suggest a simple to use programme I can download, and a quick 'how-to' on using it?

Hoping for some help

Cheers

Jeff

[adrian garnham]

I find this site very useful:

http://airfoiltools.com/plotter/index

 

[Jeffrey Cottrell 2]

Hi Adrian, thanks for the quick reply.

Did have a look at the site you linked to, but it seems only to be a way of plotting an individual aerofoil according to your needs.

Might be missing something, but I couldn't see it being used to plot intermediate rib profiles, from root and tip templates.

Am I getting this wrong?

Jeff

[kc]

You could try     profili2.com    for a rib plotting program with some free use (and some which require small payment.)    Very easy to use and print out basic ribs if you measure the length on your wing plan.   You just lay out the basic wing shape full size on a bit of paper then mark ribs and measure exactly length of each rib in millimetres.   

Or you could just 'pinch' the rib shapes from some other plan - look on Outerzone for a similar design perhaps a Kaos or another Joe Bridi design

Edited September 22, 2021 by kc

[kevin b]

Hi Jeffrey.

There are quite a few of us on here who already use rib plotting programs.

If it is not something you are going to do often, I would suggest asking if anyone can help you.

The trouble with software is that if you don't use it regularly you forget how to !

(a bit like other "skills" we have acquired over the years )

If you are building from any of the magazine plans Sarik should be able to provide you with laser cut parts. Cutting out wing ribs is boring !

Chilli Wind is a fully symmetrical profile with the deepest point at 33.33% of chord. Shouldn't be difficult to do.

What spar arrangement have you in mind ?

Also how many ribs (including root and tip) and do you want them evenly spaced ?

Edited September 22, 2021 by kevin b

[kc]

If you like my idea of pinching the ribs from another plan then the DirtyBirdy 40 has a supplement with the wing ribs drawn out ready to print.

[Jeffrey Cottrell 2]

Hi Guys, thanks

kc

Had a look at Profili2 website. Couldn't really understand much, so I signed up to their forum  and asked if someone could guide me through the process.

That question never even got on to the forum. I think I saw a notice that all posts have to be approved by the moderators, so still might make it, but I'm not holding my breath.

Nice idea about pinching rib outlines from another plan, but not sure if that will work. Actually got as far as downloading the rib drawings from the Dirty Birdy 40. Looked very close in section to the CB ones, but the trailing edge area is much thinner.

To use them, each rib would have to be individually modified to suit the TE section I have already bought. Rather spoils the object.

Kevin

I am a complete novice at this sort of thing, so if someone on here could help me out I would be most grateful.

Agreed that if you don't use software regularly, you forget how to. Bearing in mind I don't know how to use it in the first place, I'm doubly lost.

Spars are going to be 1/4"sq spruce, one top and bottom at the widest part of the rib. All conventional stuff.

Plan does say the tip rib is slanted forward, but even that can be done with a block tip, so all the construction is entirely conventional.

Just need rib profiles, everything else I can invent.

Anybody help?

Jeff

 

[kc]

you  could of course open the Chilli Wind plan in Adobe Acrobat, select the wing section ,print at 100percent,  and then alter the print size percentage( Custom ) to whatever percent each rib along needs ( as measured off a full size wing plan when you have drawn in the rib spacing )   That should get you a set of basic rib shapes.

But Profili is fairly easy to use - just select a suitable profile from the hundreds available  ( yellow rib shape second from left ) - consider NACA 0013, 0014 or 0015 , 2412 etc etc.   Modify if you want and select spar size, TE & LE size, sheeting thickness.  Then print out each rib at length required as measured from full size wing plan.

Edited September 23, 2021 by kc

[Jeffrey Cottrell 2]

Hi kc, thanks for your help

Trying your idea with Adobe, but still lost.

I have the plan up on the screen in Acrobat reader, and I can highlight the section with the profiles, but I can find no way to either print just that section of the plan or print to custom sizes.

I'm assuming these are in the 'edit' option, but that means I have to open an account, which it won't let me do because it says my chosen password is invalid.

Seem beaten at every turn.

Jeff

[Nigel R]

I would avoid messing with acrobat. Better off investing time in learning to drive Profili or DevWing or Compufoil.

 

As to Dirty Birdy 40 or Kaos, from memory, the Bridi designs all use an 18% (thick!) blunt nose section that is not very much like the CW section.

 

"Chilli Wind is a fully symmetrical profile with the deepest point at 33.33% of chord. Shouldn't be difficult to do."

 

Thickness is 12% (or possibly even a bit less! CW is a slippery beast) - it is something very close to a NACA63A012 with an ever-so-slightly sharper LE... A Quabeck HQ0-12 would be a close match too.

 

I would jump at kevin's offer!

 

Edited September 23, 2021 by Nigel R

[Andy Stephenson]

The biggest problem with simply scaling ribs is that the trailing edge remains constant thickness (or close to) so this needs to be adjusted out of proportion to the profile.

[kc]

Nigel is right - persist with Profili etc but find a 13.5 percent airfoil.   Chilli Wind is actually 13.5 percent according to the article ( measures 13.33percent on my Outerzone printed copy )  The Dirty Birdy 40 is actually 15.7percent thick - not the same but not enough to make much difference if one wants an easy life! 

However if you do want to use Acrobat for something else use Adobe Acrobat Reader DC and then select the section to be printed, choose the snapshot icon ( camera) or 'copy' and then choose 'print' and select 'custom size' in the print menu - choose 100 percent or less as required.  I have just done that and printed the Dirty Birdy 40 at both 100 percent and 70 percent.   My copy is just the free Adobe updated automatically.

 

Edited September 23, 2021 by kc

[kc]

Andy is also right of course.   The easy way out is either to use an existing wing design like the DirtyBirdy40 or to persist with the sandwich method using filler pieces to make the taper less severe.

The DB40 didnt look too out of place when I placed the airfoil on the Chilli plan .......

[Jeffrey Cottrell 2]

Hi Guys, thanks

Nigel

Given up on trying with Acrobat. From what I understand, being able to edit images involves downloading the professional version, and I don't want to clog up my computer with software I'll probably never use.

I suppose if I would want to do this regularly, might be worth getting to know Accufoil or Profili, but this one's a once off, and I'd much rather be building.

That NACA foil looks pretty close. Not worried about the different LE. I'll be sanding that to an eyeball profile anyway.

Did notice Kevin asking for more detail on the structure, but I didn't read that as an offer, and didn't want to presume.

So, Kevin, if you're about. Is this a job you could do for me, and I would be happy to pay you for your time?

Andy

Good point about the TE thickness, and this would apply to the LE as well, so that's out.

kc

As I said to Nigel, this will be a one-off. Learning Accufoil or Profili is simply not worth the time for me.

Did print off a copy of the Dirty Birdy ribs, but apart from the thickness the depth at the trailing edge is only about half the Wind. If I wanted to use those, I would have to adjust each rib separately, which rather spoils the idea of having them printed.

Having spent £6 (six) each on a couple of TE sections from SLEC, going to make sure I use them.

Having said that, Joe Bridi certainly designed some pretty models. Might put the 40 on my 'sometime' build schedule, along with the Birdy 10 and Baby Birdy I already have the plans for.

So, I guess it all boils down to whether Kevin was offering to do this for me.

 

Over to you

 

Jeff

 

[Nigel R]

from the original CW plan I have here:

 

335mm root chord

41.5mm root thickness

12.4%

 

outerzone doesn't always scale quite right...

 

DB, yes, looks a bit thinner than kaos... which is very thick:

13-1/4" chord

2-3/8" thickness

18%

 

splitting hairs a bit, though, for which I apologise

 

[Nigel R]

1 hour ago, Andy Stephenson said:

The biggest problem with simply scaling ribs is that the trailing edge remains constant thickness (or close to) so this needs to be adjusted out of proportion to the profile.

 

in practice that is not a problem - most airfoils are near flat at the TE, so the aileron part of the section is consistent across the span, as the angle the top and bottom surface join at does not change

[kc]

My Outerzone printed Chilli Wind plan shows 300mm by 40mm - measured at the fuselage sides.   Maybe the foam cutting templates are longer?   My printer might have distorted a bit but not that much.  An actual foam wing measures 300mm too and thats with the wing glassed but slightly flattened to meet the bulkhead as usual.

A total of 12 pounds real money for TE makes foam wings look more attractive........

[Jeffrey Cottrell 2]

Hi Nigel

From the plan I have here, bought not downloaded, I measure the root chord as 305mm, not 335mm. This is backed up by measuring the wing cut-out on the fuz side, where I get the root at 300mm.

If right, that would make the thickness 13.6%.

That's quite enough hair splitting for one day.

Not sure I follow your point about the trailing edge. If I use a scaling system rather than plotting, surely that would reduce all dimensions, including the te depth by the same factor. Since the tip length is about 2/3 of the root length, would that not reduce the te depth from 14mm at the root to 9.25 at the tip.

kc

Good point, but I'm not sure your conclusion is correct. Looking at the plan, a foam wing would be cut to the size of the wing panel alone, so even if I got panels cut I would still have to buy te section to suit. So cost of foam panels + £12 for te.

Only way round this would be to get the panels made to the complete dimension including the ailerons, then cut those free for hinging.

Might be a better way to get a consistent section, but introduces more issues than it solves.

I do have a problem with two te section pieces of standard stock size costing £6 each, but ho hum. Just hope when they arrive that they'll be straight. That sort of cost for bent pieces would be cause for concern.

SLEC order due to arrive any minute, so I'll soon find out.

Fingers crossed

Jeff

 

[Jeffrey Cottrell 2]

Hi all

Just a follow on from my last post.

SLEC order just arrived, and the te sections are straight enough for me.

Woo, and occasional Hoo!

Jeff

[RottenRow]

There are different versions of the Chilli Wind plan out there, which has been mentioned previously on another thread on this forum.

I have the Outerzone version, printed onto A4 in poster mode and taped together (keeping an eye on straight edges with a long rule). It is also titled 'RCM&E Plans Service' but has no plan number.

The wing's root and tip profiles are shown and measure 8" and 4" respectively. Not only that but the plan actually states these measurements. Note that the fuselage side cutout is slightly less (by about 3/8") as the taper has to be allowed for. Using foam wings the pointed front of the joined wing panels is cut off.

If (when) I build one of these I shall basically use the method as described by KC above and reduce the wing section outline by x% for each successive rib. Note that you can't just set a photocopier (or scanner/printer) to the same percentage and reduce each already reduced rib (unless you want an elliptical wing). Rather keep your 'master' (12") rib outline in the copier and set the reduction to multiples of x% for each successive rib. For my Chilli Wind plan, x% works out at 2.4%. So first reduction will be 97.6%, next one 95.2% etc. I may have to juggle a bit if the copier won't accept decimal points in the reduction percentage. Some do some don't.

I've built several models this way over the years. The method is similar to what is known as 'lofting' but without drawing everything out by hand.

Brian.

[Jeffrey Cottrell 2]

Hi Brian

Not sure what Chilli you have, but those numbers look strange.

My Chilli Wind plan has the lengths printed, but these are 12" at the root down to 8"at the tip.

Thought it might be the Breeze you were measuring, but even that measures at 10 11/16" at the root out to 7" at the tip. Have you discovered an unknown smaller version of the Breeze, perhaps a Chilli Draught?

Considered using the %'s on an enlarger, but would this not reduce all dimensions by the same amount? I'm concerned about the trailing edge depth.

At the root it is some 14mm, but since the tip is only 2/3 of the root, I think you would find the trailing edge depth at the tip only some 9.25mm.

Would need some shaping of the te section to acommodate this.

Just my thoughts

Jeff

[RottenRow]

Sorry Jeff,

 

My typing error... should have read 12" and 8" (ie 4" difference between root and tip). My plan is the one on Outerzone.

 

Yes using the % settings on a copier will reduce all dimensions by the same amount, but as long as it's the overall wing section outline that you are reducing that is exactly what you want. Draw just the section outline, and the centre line, on the 'master copy'. Forget about the L/E and T/E until after you have reduced them, then add them onto each of the reduced copies at the correct size for the wood you are using. So your 14mm will be 14mm on all ribs, etc. You wouldn't have to reshape the T/E section at all (as long as its angle is the same as the original section).

 

Sorry about the confusion with the wrong dimensions.

 

Brian.

[Nigel R]

apologies for numerical cockup

 

305mm indeed, giving 13.6%

 

"measure twice"

 

(or not, in my case!)

Edited September 23, 2021 by Nigel R

[kc]

Balsa trailing edge certainly is dear!   Of course it's handy to get it ready made but it is easily possible to make from sheet by either planing away the waste or cutting a sheet on a bandsaw when just over 2 inches width will produce two 1.75 by .5 inch ailerons.    I suppose we shall have to get used to saving at least the ailerons for recycling after a crash!

[Jeffrey Cottrell 2]

Hi kc

Agreed, that is expensive, but so are the alternatives.

Had a look on SLEC, and came up with this.

The ailerons on the CW are 19" or so, so couldn't be cut from one sheet.

So, it's either two sheets of 3" wide at £6 each, or one 4" wide at £8.47. Ok, the 4" is cheaper, but I do not posses a bandsaw, so most of it would end up a shavings on the floor.

Much as I resent spending that much on a couple of pieces of balsa, guess we'll just have to get used to our hobby getting more expensive.

I blame the chinese, and their wind turbine blades.

Jeff