Hi. I would like to make ribs for a tapered wing for a self-designed airplane, but I don't know how to do this accurately (I've only made constant chord ribs before). Is there such a thing as a computer program that does this sort of thing? How do you guys make accurtae ribs for tapered wings? Thank you.

not sure what your asking.....by tapered? my guess is thick chord to thin chord? your root rib......you have one? your wingtip rib,you have one? put the root on then the tip on....you now have a line to follow. you can draw them up on autocad if you have the program.

AutoCad? No, I don't, but if this is the one that will help with designing proper ribs for a tepered wings, then I might have to get it. Thank you.

Make a root rib and a tip rib. Mark and drill holes to exactly center ribs properly.

Cut rectangular rib blanks and drill matching holes, 1 blank per rib. Fasten ribs together, usually with a long bolt. Carve and sand until the outline flows smoothly from root to tip.

Separate and voila, tapered ribs.

Tom

You can also draw the biggest rib and scale it down in a copy machine to the percent that corresponds with the location of the rib in the semi-span.

This is the process Jim Whitley describes in his Daddy Rabbit article. It works...

Brian

Thanks for the help guys.

All readers,

Each of us may have a differnt way of doing things.
Perhaps the following method may be useful to someone wanting an easy and accurate method of having all the ribs as should be in a tapered wing either with or without leading edge sweptback.

Fist make a root rib using 1/16" or 1/8" thick ply or pine with its outer face accurate to the airfoil in use.
Then do the wing tip rib similarly.
These two ribs may remain in the wing structure but do not have to be. I usualy leave them in as the two end ribs.

Cut rectangular ribs about 1/16" larger than necessary. Their longer length will go into slots in the leading and trailing edges.

Pile the rectangular raw ribs together (one against the others, no space between them) taking into account any leading edge swetback.

Drill two holes of appropriate size to squeeze them together with two screws, washers and nuts.
Use hand plane or wood chisel (make sure it is sharp) to bring the in between ribs about 1/16" larger than the end ribs, No more than 1/16" to reduce later sanding.

Cut accurately any notches for the wing spars. Use the wing spar material to guage; do not rely on the size the spar pieces are supposed to be (it varies). Example: a 1/4 x 3/8 spar piece is not necessarily accurate. Take into account if the spars have a sweptback. You want the notches to match any sweptback angle of the spars if any.

Yes those angles will change when the ribs are spaced apart in the assembled wing(s) but the difference is not a problem between the ribs and the spars.

Make sure the spars are dead on straight before assembling the wing(s).

Assemble the wing keeping the ribs parallel to the fuselage center line.
Check for flatness or washin or washout if any.
Use a long strip of balsa near the trailing edge to raise the rear ends of the ribs if convenient.
A single tiny drop of CA glue for tacking all future gluing.

Now make (if you do not have already) an absolutely straight piece of pine (or spruce) having a cross section of at least 1" x 2" and about 4 inches longer than the distance between the root and tip ribs.

Glue on the 2" face some 180 or 240 grit sand papercentering it lengthwise and having a length about 2" shorter than the distance from root to end rib.

Glue on some of the same sandpaper the reverse way (grit on the wood) so there is a smooth surface to ride on the end ribs (which already had been made to final dimesions of the airfoil). We do no want those end ribs to be sanded now.The reversed sandpaper willtake into account the thickness of the sandpaper that will bring all the ribs for final dimensions with a traight line root to tip everywehere.
Touch up the root and end rib to the same angle.

Now you know that your covering will touch all the ribs with a proper angle on their contours.
It will also provide a good contact surface if you glue on capstrips on the ribs.

The same long sanding bar can be used to touch up the outer surfaces of capstrips after the end ribs capstrips have been glued on.

I usually do the gluing of the ribs to the spars before installing any capstrips or leading edge or trailing edge sheeting if used (so called D sections of the leading edge to the front spar).

Notice that the CA glue is used only for tacking and is not considered proper gluing. All gluing is done with proper glue of your choice and filleted to increase the contact areas of the joints.

Enjoy your build.

Zor

Rib # 8 in the DR is sure off by a lot though!! I can show a file from a Gordon Whitehead book on how to draw out tapered wing ribs but it's easier to draw out the root rib and end rib then use spray mount glue to glue up sheets of balsa between these two ribs then tilt the band/scroll saw table so the blade can touch the first and last rib then just cut and finish sand.

The inker probably???

I'm pretty sure of that. My question to the inker {you should see the plans of the Sukhoi I'm building now} would be how or from what do they used to ink the plans?? Was he drinking/drugging while he was drawing these plans?? Is a true 1/4 inch notch too hard to draw?? Should not a symmetrical rib not be the same shape if you flip them over?? Just little questions.

"AutoCad? No, I don't, but if this is the one that will help with designing proper ribs for a tepered wings, then I might have to get it. Thank you. "

From a LOOOOONG time AutoCAD user. Do not waste your time. AutoCAD was originally designed as an architect tool, and is/was not easily adaptable to airplane drawing. There are too many purpose designed programs, that are less expensive, and much more user friendly out there.

I seem to remember something like Profili, or something like that, had a free version, that would do enough.

Les

Someone above stated using a copier and finding the middle rib via a percent. Can you not make each rib via the copier by reducing the percent by say 8 or whatever percent works each time from the root working your way to the tip and thus have a template of each individual rib?

thanks for the help guys. The method offered by Zor is easy enough. I'll give it a try. Thanks.

when doing the stacked tapered ribs you need to put a blank on the outside of the tip rib when you sand and this will be the tip rib comes out short otherwise

Compufoil is the way to go. Makes all types of ribs as big as you want. Go to Compufoil.com
Frank

aerowoof,

I am trying to visualize what you are telling us.

If the tip rib made of ply or harder wood than balsa is becoming part of the structure I cannot see the need for an added blank.

If the tip rib is to be balsa and same for the root rib then both should be inside (in between) the guiding ribs. ,They should be inside with the stack so it can be sanded with the other ribs to final airfoil.

I am not sure I understand "the tip rib comes out short otherwise".
Short in which dimension(s) ?

<u>Comments added here to my post #8 .

</u>The only time the method of stacking rib blanks one against the other would not work would be if the camber of the airfoil is changing along the root to tip or if the wing thickness does not change proportionally. Like if the airfoil height versus chord would have a different ratio as the wngs arebecoming proportionally thinner toward the wing tips.

This would likely be seen in a delta wing construction.
Then each rib would have to be drawn and cut individually.

Zor.

This technique works fine for ribs of equal spacing. The main advantage is that you can shape better percentage thickness root to tip, that is if you want the root to be a different % thickness than the tip. BUT IF you want unequal spacing root to tip, some trial and error affair will probably be necessary.

CAD drawn rib stack gives all kinds of options to you, such as accurate ribs of any spacing desired. If you want to build a precise thickness percentage, your ribs can be designed with skin undercut in mind. Spar notches and lightening holes in the ribs? NP.....The best of the options is handing the file over to an NC lazer cutter.

More work for sure, but when you say "you designed it" it actually means something

Thanks for the information. My intention is to design and build a simple tapered wing set, where the LE is straight, the taper being at the TE. Ribs spaced evenly.
My intended wing would have a flat bottom trainer type airfoil, have a 10 inch root chord, and 8.5 inch tip chord, about 2.5 feet long per half (5 foot wingspan), for a .28 size nitro engine.
i think I can build one using the methods described above.

Ditto the Compufoil recommendation. It is designed to do exactly what you want to achieve.

Stan

zor,
when you are stacking the blanks all the ribs are stacked on the outside of the root rib.the tip rib needs to be on the outide of its pattern.

aerowoof,

You can put the tip rib on the outside if you wish. It will make no difference since all the ribs are not finished to the final airfoil until the wing is all assembled.

Zor