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Author Topic: Geodetic wings  (Read 2702 times)

Offline Alexey Gorbunov

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Geodetic wings
« on: May 09, 2018, 02:19:38 PM »
Guys, interesting ribs spacing and ribs angle.
Measurement of angles and distances between ribs in well-known designs give more questions than answers. Is there a rule, or is everything done to someone like it?


Online Ken Culbertson

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Re: Geodetic wings
« Reply #1 on: May 09, 2018, 02:44:07 PM »
Guys, interesting ribs spacing and ribs angle.
Measurement of angles and distances between ribs in well-known designs give more questions than answers. Is there a rule, or is everything done to someone like it?

I do not profess to be an expert on stress but I have never liked the angled ribs unless the wing is sheeted.  They distort the airfoil in a strange manner.  I use stiff 1/16 x 1/4 cross braces under the cap strips before it ever gets off of the jig.  Makes the wing stiff as a board and totally resistant fixing any warps!

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Online Howard Rush

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Re: Geodetic wings
« Reply #2 on: May 09, 2018, 08:32:07 PM »
I think Ken has a good idea. 
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Offline Motorman

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Re: Geodetic wings
« Reply #3 on: May 10, 2018, 07:32:27 AM »
Just copy ThunderGazer.
There will be a sunny day and we will fly our airplanes.

Offline Bob Hunt

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Re: Geodetic wings
« Reply #4 on: May 10, 2018, 11:33:18 AM »
The ThunderGazer (which is actually a Bill Werwage P-47 wing design...) is a Warren Truss wing rib scheme, not geodetic. My understanding is that geodetic wings have the ribs intersecting at an angle, while a Warren Truss arrangement has ribs that are angled but do not intersect.


Offline Matt Spencer

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Re: Geodetic wings
« Reply #5 on: May 10, 2018, 10:57:40 PM »
THIS is GEODISIC / geodetic . Barnes Wallace , the bouncey bomb man .



Like wot some use for tailplanes & Bearer Stiffeners .

Apparently , looking at the DOMES its TRIANGULATION , like wot good frame makers  used on the F 750 Tri / BSAs .( TZ Copied it )

Strongest strength / weight - ridgidity .

Offline Alexey Gorbunov

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Re: Geodetic wings
« Reply #6 on: May 11, 2018, 12:45:14 AM »
THIS is GEODISIC / geodetic . Barnes Wallace , the bouncey bomb man .



Yes, my question was wrong. I want to know about the Warren truss.

P.S.
Google has already helped me. And also my friend-architect and I saw a railway bridge.

Offline proparc

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Re: Geodetic wings
« Reply #7 on: May 11, 2018, 07:41:09 PM »
I like Kens idea. H^^
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Online Ken Culbertson

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Re: Geodetic wings
« Reply #8 on: May 11, 2018, 08:14:06 PM »
I like Kens idea. H^^

Old Free Flight trick.
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Offline Bob Hunt

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Re: Geodetic wings
« Reply #9 on: May 12, 2018, 09:04:48 AM »
Motorman mentioned the ThunderGazer. Here are a few shots of one that was built just like the one David is using in his ThunderGazer, and it depicts the actual Warren Truss scheme that is in David's ship.

Later - Bob Hunt


Offline Ted Fancher

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Re: Geodetic wings
« Reply #10 on: May 14, 2018, 05:45:22 PM »
I think Ken has a good idea.

OMG!!! I agree with Howard!  Was that bump I just felt the Earth shifting on its axis?

Ted

Online Dave Hull

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Re: Geodetic wings
« Reply #11 on: July 27, 2018, 01:22:42 AM »
And note from Bob's photos that the wingtip provides a shear panel linking the TE to the LE at the tip. This should be very effective at stiffening the structure with minimal weight.

Dave

Online Lauri Malila

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Re: Geodetic wings
« Reply #12 on: July 27, 2018, 09:25:30 AM »
For sure, the tip block makes wing stiffer.
But doing so, it also indicates that ribs/capstrips don't do their job properly. L

Online Ken Culbertson

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Re: Geodetic wings
« Reply #13 on: July 27, 2018, 12:03:04 PM »
For sure, the tip block makes wing stiffer.
But doing so, it also indicates that ribs/capstrips don't do their job properly. L
Having never built or flown a Thunder Gazer I am curious if having the tip weight box so far forward is by design or because the tip design really didn't allow for it?

Ken
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Online Lauri Malila

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Re: Geodetic wings
« Reply #14 on: July 27, 2018, 02:36:25 PM »
Shouldn’t it be in cg, or on line drawn from l.o. guide through c.g..?

Offline Chris Wilson

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Re: Geodetic wings
« Reply #15 on: August 01, 2018, 05:04:25 AM »
Guys, interesting ribs spacing and ribs angle.
Measurement of angles and distances between ribs in well-known designs give more questions than answers. Is there a rule, or is everything done to someone like it?
45 degrees seems like a good angle to remember as that is the angle that forces in shear webs have to contend with etc.
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Offline Trostle

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Re: Geodetic wings
« Reply #16 on: August 01, 2018, 10:20:35 AM »
45 degrees seems like a good angle to remember as that is the angle that forces in shear webs have to contend with etc.

A structural engineer that knows a lot more than I do about this stuff explained that the ribs should be set at 45o to the quarter chord line for maximum torsional strength.  But I think this envisions the use of egg-crate intersecting ribs for increasing the strength and to minimize the voids between ribs which adds a lot of wood.  (In other words, the ribs would all be 90o to each other.)  One of the reasons I think we see the "geodetic" structures on these stunt designs is to obtain some improved torsional stiffness while at the same time reducing the number of ribs need to accomplish that.  The angles used on these designs may not be optimum for maximum stiffness, but they are effective at improving stiffness while reducing the amount of wood to do so.

Keith

Online Brett Buck

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Re: Geodetic wings
« Reply #17 on: August 07, 2018, 10:27:50 PM »
Having never built or flown a Thunder Gazer I am curious if having the tip weight box so far forward is by design or because the tip design really didn't allow for it?

Ken

  I think it's pretty close to the nominal CG, but it doesn't make a huge difference. You can (accidentally) skew the principal axes by having it way off the nominal Y axis of the airplane but it's pretty hard to get it too far off without adding weight to both tips to do it on purpose. It was not a huge effect when I tried it, compared to the normal variation of mass properties.

    Brett

Offline jim gilmore

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Re: Geodetic wings
« Reply #18 on: August 08, 2018, 08:10:24 AM »
How does one figure out the shape of the angled ribs ?

Online Howard Rush

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Re: Geodetic wings
« Reply #19 on: August 08, 2018, 12:05:43 PM »
How does one figure out the shape of the angled ribs ?

People use CAD to draw a solid wing, then take slices of it.  Bob Hunt does his CAD with a slab of foam.  I use a spreadsheet. 

It's pretty easy to match most any reasonable airfoil (maybe not including flaps) with the modified NACA 4-digit formula given in the Abbott and Costello book.  That gives you a sorta-polynomial formula for the airfoil.  I did this using the Impact root and tip airfoils.  For each point on a slanty rib, you know the local chord, the fraction of that chord that point is behind the LE, and the fraction of span that point is between the root and the tip.  Interpolate between the root and tip airfoils to get the airfoil formula for that place on the span.  Then calculate the airfoil ordinate for the fraction of the local chord that the point is behind the LE of the local chord.  Use that method to calculate the shape of all the ribs.  Then there's removing 1/16" or whatever for the sheeting and capstrips.  I take pairs of points on the airfoil a hundredth of an inch or so apart, then calculate a perpendicular to the line between them halfway along the line.  I go out 1/16" - laser kerf along that perpendicular and locate a point for the final rib.  Then take the coordinates of the final rib to a CAD program as a polyline and have the laser cut it. 

There's a little extra fussiness.  For calculating straight ribs, I use the side of the rib closer to the wing root.  For calculating slanty ribs, I take a line from the root side of the rib at the TE to the tip side of the rib at the LE.  This gives the right shape after you knock off the protruding edge with a sanding block.  You gotta do something similar to get the angled spar slots to come out right. 
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Offline jim gilmore

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Re: Geodetic wings
« Reply #20 on: August 09, 2018, 09:06:47 AM »
So most use cad to do this? with the exception of cutting a foam wing and cutting it up.

Offline Bob Hunt

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Re: Geodetic wings
« Reply #21 on: August 09, 2018, 04:13:33 PM »
Yeah, but the beauty of the Lost-Foam system is that you get a form-fitting fixture in which to build the wing! Mu, ah, hah, hah!  H^^

And, the ribs will have the absolute correct shape in profile, and the correct angles when viewed from the top and from the front. Not easily done with CAD and laser cutting... It's automatic with the Lost-Foam system. The ribs will make full contact to the sheeting and the molded leading edge shells; even on a tapered wing.

Bob Hunt

Online Howard Rush

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Re: Geodetic wings
« Reply #22 on: August 09, 2018, 10:25:46 PM »
Not easily done with CAD and laser cutting...

True, if you don't have electricity.  But then you couldn't hotwire foam, either.
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Offline Bob Hunt

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Re: Geodetic wings
« Reply #23 on: August 10, 2018, 09:51:35 AM »
I heat my Nichrome wire over a camp fire...

Bob

Online Howard Rush

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Re: Geodetic wings
« Reply #24 on: August 10, 2018, 02:02:22 PM »
Explains the marshmallow fragments in my wing.
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Offline Bob Hunt

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Re: Geodetic wings
« Reply #25 on: August 12, 2018, 06:36:09 AM »
Kumbaya...  ;D

Offline Target

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Re: Geodetic wings
« Reply #26 on: August 12, 2018, 11:05:27 AM »
I think you can get templates of angled ribs in Profili 2
Regards,
Chris
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Offline JHildreth

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Re: Geodetic wings
« Reply #27 on: February 12, 2019, 06:14:15 PM »
CompuFoil is another piece of software to consider for wing design.  It will handle just about any combination of airfoil and wing layout you can imagine.

Joe

Offline EddyR

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Re: Geodetic wings
« Reply #28 on: February 12, 2019, 09:35:51 PM »
  Most of our stunt model wings with ribs at a angle are not geodetic construction.  They are closer to a Warren Truss design. The best angle is around 33 degrees not 45.  I guess the guy who has built the most of a design would be the expert. I have posted at least 10 different models over the years about this type of construction,all I beam. I am no expert but I have tried many methods of crossing and angling  ribs. I have seen pictures of wings where the ribs crossed six times. The most I did was two times. Bob Hunts method builds light and strong and that is what one wants.  With out the sheeting it would be very weak so a lot of extra ribs would be needed. I did it more for looks than any perceived advantage. FF guys have been building them since the early 1930's using the I Beam method. Geodetic is used more in domes and has many pieces all getting smaller as it gets to the top,
  Warren Truss strength is in the vertical or length of the bridge or wing. It is not great at resisting a twisting motion.  On our wings we must resist twisting and a D-tube works better than a I Beam.   But I beams are pretty and simple to build.
EddyR
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Offline phil c

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Re: Geodetic wings
« Reply #29 on: February 17, 2019, 08:17:57 PM »
CompuFoil is another piece of software to consider for wing design.  It will handle just about any combination of airfoil and wing layout you can imagine.

Joe

Compufoil does work for typical wings.  Not flying much anything typical, I found it often made screwy decisions on how to layout the spars and ancillary stuff.  I ended up using it for the rib shapes, which are good.  Then adding the structure in with CAD.  It's difficult to add landing gear parts, retracts, etc.
phil Cartier

Offline Motorman

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Re: Geodetic wings
« Reply #30 on: March 16, 2019, 12:12:33 PM »
Yes, my question was wrong. I want to know about the Warren truss.

I knew that, hence my Tundergazer suggestion.


Motorman 8)
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