F3RES-DEVA A design process

[mikef]

I don't understand '1/64" supporting rib', surely you don't mean you have 1/64" balsa ribs.

I would use a wide light balsa TE if you must have a sharp TE - it will make the rib/TE joint deeper and be stiffer in bending than 1/32 ply.   Do a weight comparison.  A blunt TE would be my choice - maybe 1.5 mm thick at the back  -  that would give the same rib joint depth with a narrower TE.

Can you use a carbon TE and carbon rib caps in RES?

[Tony]

All ribs are 1/16" the 1/64" ply ribs are just for support. The trailing edge has been slightly modified to take the 1/32" it does have a 1.02mm blunt edge. I'll do some weight comparisons. Unfortunately you can't use carbon and caps otherwise that would have been the route to take. 

[martynk]

This is interesting   Following..

Right or wrong, I use a fairly thin section solid (full depth) TE but with a spruce cap at the rear, usually sanded down from 2mm thick spruce or thereabouts to help keep it stiff and help prevent bowing. I have also used a c/f strip (0.006") glued to the front edge of the TE. That also adds a significant anti-bow property - or at least it has remained straight on the model that I have used it..

[Tony]

This is either a labour of love or sheer madness! There are 203 components to the wing and each component is being weighed. The carbon inner and mid panel spars have arrived, not cheap but superb quality. The tip spars are tapered from carbon F1G booms which are very expensive but I have quite a few of them from when I used to compete. I've still 11 paragraphs of work to be completed on the wing until I'm satisfied. The V tail has been through three designs and I'm still not there yet. The fuselage is in it's infancy so far I've only worked out the co- ordinates (It's airfoil shaped) and am trying to learn  basic CAD at the same time. Re the TE I'm still not happy so there's more head scratching to be done, on top of all this I need to work out a jig for the wing. Only a few more hours work then lol 

[satinet]

Let's hope it flies well then....!

[Tony]

So do I! 

[martynk]

On 20/01/2018 at 19:00, mikef said:

 

Can you use a carbon TE and carbon rib caps in RES?

Good question Mike. The official (although there aren't really any) rules say that the flying surfaces should be predominantly wood (the real object of the rule is to prevent glass covered foam or moulded aircraft). The stated exception is that carbon spars are allowed. However, whether a carbon TE could be defined as a spar is an interesting question. I used the TE described above on my F3-RES using the "predominantly wood" escape clause. These thin wing profiles make it very tricky to build a light TE which wont twist or bow. Whether Carbon Caps are allowed - I don't know, personally, I think they (as well as CF TE section) should be allowed as these are (or could be) home construction techniques.

A carbon boom is allowed but not allowed forward of 25%MAC to prevent moulded fuselage pods. That rule I understand and is unambiguous.

[Tony]

Carbon caps and TE I think is getting away from the "Spirit" of the German rules as I can imagine going down this road the next step would be carbon D boxes. Personally I haven't a problem as a lot of my F/F models are built this way so I'm "Tooled up" for making D boxes etc plus you can buy the AG series D boxes from the Eastern European countries quite cheap. When you look at the kits coming out of Germany/Austria and my OD there's a hell of a lot of work goes into the design and cutting files so the "Affordable" aspect is rising. That doesn't mean that a home brew simple model can't be competitive, far from it as I well know in my F/F days.

As I'm on here and I was working on some more detail has anyone had any problems running the latest version of XFLR5 as I've updated mine and the thing keeps crashing on me. I'm running Windows 7.

[martynk]

Yes i agree although i think carbon d boxes are excluded under the skinning rule anyway. 

Sorry, can't  help with xflr5. Never really got on with it at low Re anyway

[Tony]

Ta for the answer on XFLR5 I'm trying to compare the Re at 60, 80, 100, 150 and 200,000 that the germans did in their wind tunnel tests to see how much it varies, including my modified AG ones. At present it won't even let me input panels without crashing including batch analysis I think I've got to install visual studio community and probably go back to an earlier version of xflr and try again. 

[Whitmore]

Hi Tony.

Carbon capped ribs are not allowed I'm afraid. The only carbon permitted in the flying surfaces is in the wing joiners, the spars and the LE's.   'Moulded' wood construction of the wings is also prohibited so your laminated TE may have fallen foul of that anyway?

One of the main structural challenges of F3-RES design is to get thin but stiff trailing edges with wood construction. It's not just the sharpness of the TE but the stiffness of rear part of the section generally - especially as the better RES airfoils are thin in the aftermost 25%. The Slite has the best of these IMO which uses the ply TE ( with lightening holes) and thin rib doublers as per your design. The lightening holes are worth it in this case because the rib doublers form a T-beam structure with the 'end grain' full width part.

Re: XFLR5 - some versions are very buggy. I've stuck to an older one that works well and never upgrade  I seem to remember doing the same comparison - I think I uploaded results on the RCG thread...

Jon 

 

 

EDIT: Yeah - here you go: https://www.rcgroups.com/forums/showpost.php?p=34812029&postcount=73

[Tony]

Cheers Jon, I'm sticking with 1/32" for the TE, did a test piece and it seems strong enough. Would be very interested in your results you've posted of RCG can you remember what thread it was in?

Slowly getting there with the design, 99% happy with the wing some minor corrections to sort out. 4th V tail version is now completed so I'm 100% done on that.  Fuselage is 50% done. If I can get XFLR sorted I'll run an analysis and hopefully that's that. What started as a doodle as taken me around 6 weeks so far working on it every day. FYI the wing area is 36.92 sq, A/R  11.3,  span 1994 mm projected actual 2040 mm, V tail 6.37 sq.

 

EDIT. Didn't see your edit! Actually I had read this before but good reading. If this wing works out, which it should, I'm already thinking of giving myself more headaches in designing a Zone V2 version lol plus about a months reading on G-T's post on RCG

[Whitmore]

Hi Tony,

Do you have a three view of your design at all? 

Re airfoil development: Zone V2 is a flapped DLG airfoil and while probably better than some of the accepted standard airfoils for F3-RES it's not optimised for it. This is my problem with the Mad-RES which uses "Synergy Modified". Presumably they have chosen some set value for the flap. But actually with no flap you can have a better airfoil and more thickness at the hingeline ie a stiffer TE. That said it's considerably thinner than some of the built up wings so in many ways an improvement.

Gerald designed two fixed RE airfoil families for DLG called Polymild and  PolyHot. As DLG foils they have a high speed requirement (ie launch) so are still not optimized for F3-RES but I've had some success in XFLR5 by modifying them a bit. The Baba Competition's BC30-70 series and the Slite AG27 both do well too.

The unknown factor is that these '3rd generation' F3-RES foils were designed for very accurate moulding in composite wings and so built up/film covered wings may under perform. And the problem always seems to return to how to manage the trailing edge structure in wood only. The Slite method is the best I've seen in this area.

 

Jon

[Tony]

I looked at the BC series before choosing the AG. The BC series needs some work on the upper transition to the trailing edges especially the BC50 hence me choosing the AG. My mods to the TE's are very minor to aid construction. I have the madres but there's something I don't like about her I can't put my finger on it, to fly her really well you have to but quite a lot of input on the sticks, by that I mean really subtle inputs and I've flow her a lot with a lot of CG changes until I was happy.

Here's the v tail and wing, wing has a little work left to do but not much. The ruddervators on the tail extend to the tip not at the pic shows. All TE's on both  have lightening holes, the tail has a projected weight of 10 gms covered. Not finalised the wing weight yet

[Tony]

If the LE on the tip panels look a bit "off" it's because it's balsa as I didn't like the thought of using 1.5 mm carbon as I think it would be difficult to cover perfectly. The balsa extends forward of the true carved LE. The inner and mid panels have 2.5 and 2 mm carbon LE's

[StraightEdge]

On 15/01/2018 at 11:31, Tony said:

1. Dihedral. Too much? At present my gut feeling is I have to much. For comparison my MadRES has and EDA of 8.5, I like the way she flies, not too disimilar to my DLG's which I'm used to. Trawling through all the current designs available they're running EDA's between 10.5 and 12 more towards the 12. I have .5 degree washout on the mid panel and .5 degree on the tip panel so from root to tip overal is approximately 1 degree.

Hi Tony

Just an academic question:  what does EDA stand for?

And a tangential question:  how does your MadRES handle brisker wind conditions (any need for ballast), and any other comments on it?  Also, it seems to have a higher aspect ratio relative to most of the other RES kits available - does this relate to your experience of it's DLG-like flying performance, or is there another reason?

Jon

[satinet]

Effective dihedral angle

[StraightEdge]

Presumably this reduces a polyhedral wing to a simpler dihedral equivalent, and there's some method of calculating EDA?

[Whitmore]

Here you go Jon: http://peterboroughmfc.org/technical-articles2012/08Dihedral.htm

(There's a link to a calculator file too.)

Jon

[StraightEdge]

Cheers Jon!

Jon