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Non parallel wing ribs - Terminology?

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Martin_K12/11/2019 10:42:01
169 forum posts

What is the name for the style of wing construction where the ribs do not run straight from leading to trailing edge?

I have seen two variations;
V ribs, which do not cross
X ribs, which do cross

see photos below.

Bob Cotsford12/11/2019 10:51:54
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IIRC geodetic, though your picture show a hybrid in that they use straight front rib sections with geodetic rears.

Edited By Bob Cotsford on 12/11/2019 10:53:15

Martin_K12/11/2019 10:59:10
169 forum posts

Thanks Bob,

I just tried 'geodetic' in a search term and produced many hits.

The web is great, if you already know the name of what you are looking for!

Martin Harris12/11/2019 11:36:40
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Best known example was the Wellington bomber designed by Sir Barnes Wallis of bouncing bomb fame. It results in a very high strength to weight ratio. Many years ago, I owned a share of an SHK glider which used a form of geodetic construction for the 17 metre wings - the main spar in each wing only extended to about 8 feet...

Alan Gorham_12/11/2019 11:51:46
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I think it's a common misconception that Barnes Wallis designed the Wellington. I think that it was designed by Vickers chief designer Rex Pierson using the geodetic construction that Wallis had developed when designing the R101 airship.

Martyn K12/11/2019 12:05:52
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Warren Girder for V Ribs

Geodetic for X with straight ribs intersecting the cross and also a straight rib where the X ends.

However, it appears that the term geodetic is also widely used for any diagonal load bearing wing rib now.

Martyn

Edited By Martyn K on 12/11/2019 12:06:37

Martin Harris12/11/2019 12:25:47
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Posted by Alan Gorham_ on 12/11/2019 11:51:46:

I think it's a common misconception that Barnes Wallis designed the Wellington. I think that it was designed by Vickers chief designer Rex Pierson using the geodetic construction that Wallis had developed when designing the R101 airship.

I stand corrected - I always assumed Barnes Wallis lead the design team.

Didn't Wallis design the R100? However, I don't believe the R100 used geodetic construction although the gas bag lifting loads were supported by wires arranged in a geodesic configuration.

Edited By Martin Harris on 12/11/2019 12:28:14

kc12/11/2019 12:33:53
6511 forum posts
173 photos

Wikipedia says the R100 used geodetic construction ( R100 was Barnes Wallace and successful while R101 was not )

kc12/11/2019 12:44:11
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There must be various ways of plotting the airfoil for diagonal use but whats the best? Or is it easiest to just use 90 degree ribs with plain diagonal pieces ( or sand the oversize plain bits to match the ribs )

Martin Harris12/11/2019 12:46:58
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Wikepedia also states [in a different article]:

"A further consequence of the new rules for airframe stress design was that a new way of harnessing the lifting force of the gasbags had to be found. Wallis's solution to this problem later led to his innovative geodesic airframe fuselage and wing design for the Wellesley, Wellington and Windsor bombers."

My interpretation is that the gas bags were slung using wires arranged in a criss-cross arrangement using geodesic principles - i.e. following the shortest distance between 2 points on the surface of the object - and Wallis developed this thinking to the lattice structure formed from aluminium channels [forming the shape rather than following it] which he named Geodetic Construction.

We're probably departing into semantics and in fact, Alan only stated that Wallis developed geodetic construction while designing the airship. Whatever, the principle certainly worked and many Wellingtons returned with structures still providing sufficient integrity after being hit by enemy fire that would have downed many other types.

Edited By Martin Harris on 12/11/2019 13:03:12

Martyn K12/11/2019 13:20:59
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Posted by kc on 12/11/2019 12:44:11:

There must be various ways of plotting the airfoil for diagonal use but whats the best? Or is it easiest to just use 90 degree ribs with plain diagonal pieces ( or sand the oversize plain bits to match the ribs )

That's what we often used to do when I flew free flight. A better was is to triangulate the diagonal on paper and then plot the extended rib using standard x and y airfoil coordinates but on the stretched rib. Its easier to do than explain. Basically plot the x co-ordinates on the extended baseline but keep the y cordinates the same as the straight rib.

Martyn

Martin_K12/11/2019 16:05:08
169 forum posts
Posted by Martyn K on 12/11/2019 12:05:52:

Warren Girder for V Ribs

Geodetic for X with straight ribs intersecting the cross and also a straight rib where the X ends.

However, it appears that the term geodetic is also widely used for any diagonal load bearing wing rib now.

Martyn

Conventions of how models are described may not have kept up with the introduction of composite materials. A carbon fibre tube as the main spar with a hybrid mix of balsa rib styles attached.

I have previously done all wood construction, assembled with PVA / Aliphatic glue. A first attempt at carbon / wood glued together with cyano looks to be an interesting next step.

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