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How Many Wing Ribs

For Own Design Sport Model

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Andrew McKelvey 104/07/2020 16:58:01
15 forum posts
4 photos

I am designing a sport model which will initially be about 52" wingspan and I have decided to use a built up wing rather than a foam core one, cutting foam cores is hard work on your own! I haven't any foam and I'm not going out, got loads of balsa.

So the question arises for a wing that will be about 620mm each panel and about 300mm constant chord with full length ailerons give or take the bit in the centre and about 15% depth, how many wing ribs would you build into the wing. Had selected a NACA 0015 or 0018 section.

I was thinking something like a Wot4 built up wing but as I don't have one I cant count them.

Is there a rule of thumb I don't know about it looks to me the spacing can be as small as 50mm and as large as 80mm for this size wing, my Panic Bi Plane has them closer at the root and further apart at the wing tips.

Any thoughts?

J D 804/07/2020 17:15:35
1774 forum posts
88 photos

How many may depend some on what covering or partial covering you use. EG, all film , all sheet, or perhaps sheeted leading edge.

Measuring on mine shows 40mm on a little Veron Cardinal to 80mm on DB Major Mannock.

Richard Clark 204/07/2020 17:21:33
424 forum posts

Regardless of size I suggest no more than 50mm apart. Make the ribs our of 1/16 balsa and use 1/16 x 3/16 cap strips.

Don't fit the leading edge 'diamond' (or diagonal) fashion. It may reduce the time shaping the LE but it makes a first class rib splitter in a hard landing or if the plane, or even just a wingtip, hits something.

Nigel R04/07/2020 18:03:47
4453 forum posts
717 photos

Put one rib every 2.6" I would say

Peter Miller04/07/2020 18:15:56
11784 forum posts
1416 photos
10 articles

I would agree with 2.5"roughly to get even spacing.

I favour my leading edge design which uses a 1/8" leading edge with the sheet glued onto that and then a 1/8" cap strip over the front to round it off.

I also prefer 3/32" ribs,especially over a 12" chord with capstrips of course

Martin McIntosh04/07/2020 19:04:24
3719 forum posts
1296 photos

Years ago I scaled up a design by a well known scale modeller and used 1/16th for the ribs. He advised me that in the future to use light 1/8th instead. These are no heavier than using harder 1/16th, do not split when cutting and give twice the gluing area. Done it ever since where appropriate. As above, sheeted wing up to 75mm, open structure 50mm with 1/4" cap strips. I always fit a 1/8th false LE, sheet the wing then a very soft LE afterwards.

Don`t forget to fit light 1/16th shear webbing between the mainspars before removing from the building board if you want a straight wing.

Dad_flyer04/07/2020 20:02:33
357 forum posts
320 photos

Have you got this month's magazine? Copy Peter's basic structure from Miss Sizzle, or if you have older copies then Miss Deeds has a 300mm chord.

Simon Chaddock04/07/2020 22:59:40
5861 forum posts
3109 photos

The spacing of the wing ribs largely depends of how accurate you want the wing section to be. The ribs may be a nice NACA section but the area between the ribs will not. The closer the ribs the nearer the section will be between the ribs.

Now whether the change in the wing section between the ribs makes any significant difference to the performance or handling is another matter. wink 2

Gary Murphy 104/07/2020 23:27:46
491 forum posts
12 photos

With this sort of question I am surprised you have not got more "ribbing" : )

perttime05/07/2020 06:13:07
228 forum posts
18 photos
Posted by Martin McIntosh on 04/07/2020 19:04:24:

... He advised me that in the future to use light 1/8th instead....

Some have cut ribs out of Depron sheet, or similar. I recall even 6mm sheet is not far from the weight of "regular" 1.5mm balsa.

Nigel R05/07/2020 07:50:57
4453 forum posts
717 photos

I would not go to the 18% section. Personally I think 12% is nice, with 15% being max. The stall behaviour is largely determined by the LE shape. More thickness just adds drag to reduce top speed. 

Light 3/32 sounds good for this size.

Are you making it a d box type structure? That will keep the first third a nice shape which is the second most important bit of the airfoil. LE being the first. 

Pete m's structure is perfect. I like soft 3/16 for the LE strips, is the only change I would make to it. Gives a bit more meat to form the LE from.

Edited By Nigel R on 05/07/2020 07:53:45

Andrew McKelvey 106/07/2020 17:13:04
15 forum posts
4 photos


Basically I have gone for this as a design looks like most other wings I've ever seen.

I have gone for 11 wing ribs with 45mm gap at the root (3 off) one actually sit over the fuselage, the gap is 65mm otherwise, they are all 3mm ribs with 6mm cap strips. It is D section sheeted leading edge with 1.5mm shear webs, spars are 6mm balsa. I haven't decided on aileron construction because it isn't stock size 48mm. Also I haven't made my mind up to make it two piece with a joining tube or one piece, its about 620mm each panel.

I have also redrawn the section and gone for a 14% depth S8035 section, the idea was to go thick because I didn't want a ballistic missile just something that potters about, but would pull the shapes but nice and slowly. A sort of cross between a Wot4 and a Ripmax Jive if there can be such a thing, however I haven't got the resources to test every little change, spose I could make a thick one and a thinner one!

I am surprised there isn't more science to this design malarky just seems to be preference and what has gone before and it's if it looks good it should be ok

Any thoughts

Edited By Andrew McKelvey 1 on 06/07/2020 17:16:02

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