stunthanger.com

Design => Stunt design => Topic started by: Ken Culbertson on June 09, 2021, 02:47:04 PM

Title: Making Rib Sets
Post by: Ken Culbertson on June 09, 2021, 02:47:04 PM
I have time on my hands so I know that either of the options I am asking about are not the most efficient approach but, I need to make a rib set for my own airfoil.  It is basically the Thundergazer with an additional 1/8" thicker TE to house recessed flaps.  I have two options.

1. Draw and cut out each rib individually which I can do but I would really like to find a cheap CAD program to draw them so that I can find someone to laser cut a set.

2. The old sandwich method which usually ends up with some tilted cap strips.  Should I select this option, and it is looking like I will, I would like an opinion on something I have done once n the past.  When I stacked the blanks, I did both sides at the same time then alternated the ribs inboard/outboard.  This resulted in the inboard wing being approximately 1/32" thicker.  To compensate I did not offset the centerline. I didn't notice anything different about how that plane flew compared to others with unequal spans but the same thickness.

Ken
Title: Re: Making Rib Sets
Post by: Ken Culbertson on June 09, 2021, 03:41:16 PM
If you're making a true Thundergazer wing with the Warren truss ribs, stacking won't work. Also, it is very critical to line up the leading edge perfectly straight which is hard to do without the lost foam system.

Motorman 8)
No, it will be a classical "C" tube build with a molded LE.  The Airfoil I have used since the 60's, with minor tweaking, is very close to the Thundergazer.   

Ken
Title: Re: Making Rib Sets
Post by: pmackenzie on June 09, 2021, 05:12:42 PM
Have a look at Compufoil.
It is not that expensive, and simplifies a lot of the tasks involved in doing a set of ribs.

http://www.compufoil.com/product_cf.shtml


You can get the free version and play around with it to see if you like it.
Title: Re: Making Rib Sets
Post by: Ken Culbertson on June 09, 2021, 06:57:17 PM
Have a look at Compufoil.
It is not that expensive, and simplifies a lot of the tasks involved in doing a set of ribs.

http://www.compufoil.com/product_cf.shtml


You can get the free version and play around with it to see if you like it.
Thanks, this looks like exactly what I want.

Ken
Title: Re: Making Rib Sets
Post by: John Miller on June 09, 2021, 08:38:14 PM
I've used Compufoil" for over 20 years now, and believe it's one of the best. There may be a bit of learning required but there are popups available, built intro the program. Over the years the program has gotten stronger, and more capable. The program comes packed with a huge airfoil selection. It also has a NACA generator that will allow you to generate nearly any NACA based airfoil.

With the help of the program you can modify any airfoil, almost any way you desire.  I tend to use one of 4 airfoils for stunt use. a NACA  4 digit,  a NACA 6 digit that I've modified, a Pathfinder "Ice Cream cone" Combat style, and an Eppler 169 symmetrical foil that seems very good. I can change almost every possible feature and can usually come within a pencils line width of matching most any airfoil. It is possible to enter in your own airfoil.

There are several very good options  when it comes to lofting the wing. My most favorite lately has been the ability to create wings with the Warren Truss style ribs. I've lofted several true elliptical warren truss wings for a design I've been working on.

Getting the free version for learning on may be a good idea. If  you begin to understand how it works, you'll want the fully loaded version I use. It is always update-able for free.

John Miller

Title: Re: Making Rib Sets
Post by: pmackenzie on June 10, 2021, 06:54:42 PM
Like anything else, there is a bit of a learning curve :)

A video might help:

https://www.youtube.com/watch?v=3sUmOwucLYM

Once you get it to do something, you will get a better idea how to do other things.
Title: Re: Making Rib Sets
Post by: Dennis Toth on June 11, 2021, 06:01:22 AM
Ken,
Other option is to find a ship that is close enough for the wing style you want and order a set of laser cut ribs (Brodak has them for all their kits), then design around it for the ship you like. I have ordered several rib sets and it is well worth the money and time saved. Also could look at Bob Hunts lost foam approach as I think he could offer the core cut for the warren truss to give you rib templates.

Best,    DennisT
Title: Re: Making Rib Sets
Post by: Ken Culbertson on June 11, 2021, 06:20:39 AM
Ken,
Other option is to find a ship that is close enough for the wing style you want and order a set of laser cut ribs (Brodak has them for all their kits), then design around it for the ship you like. I have ordered several rib sets and it is well worth the money and time saved. Also could look at Bob Hunts lost foam approach as I think he could offer the core cut for the warren truss to give you rib templates.

Best,    DennisT
I have done that with a Brodak set that was close before and I agree it was well worth it.  I looked through their set and didn't find anything close to the Thunderbolt/gazer.  If what I am building now were not a "classic" I would do the lost foam but it isn't.  I am stretching it as much as I can internally but I think the Warren truss might be a bridge too far.  I do think it might be a good idea though to get a lost foam mold for my PA design before he retires again.

Ken
Title: Re: Making Rib Sets
Post by: pmackenzie on June 13, 2021, 05:46:29 AM
To do geodetic ribs you need the paid program, with the $21 lofting option add on.
Title: Re: Making Rib Sets
Post by: Serge_Krauss on June 13, 2021, 06:51:14 AM
Profili is a good option. It comes with a wide variety of extra functions, but the old basic has been sufficient for me to accomplish what you want to do.
Title: Re: Making Rib Sets
Post by: Paul Smith on July 19, 2023, 11:37:31 AM
Have a look at Compufoil.
It is not that expensive, and simplifies a lot of the tasks involved in doing a set of ribs.

http://www.compufoil.com/product_cf.shtml


You can get the free version and play around with it to see if you like it.

Is the $38 product stand-alone or is it an add-on to something besides a basic Windows 12 operating system?
Title: Re: Making Rib Sets
Post by: Steve Glass on July 20, 2023, 12:29:04 AM
If you use the sandwich method, try adding sacrificial spacers between each rib pairs. You will have much less bevel and less size variation.

For the spacers, I use two pieces of 6mm depron between each rib pair and you can use these for riblets to save waste.

Steve
Title: Re: Making Rib Sets
Post by: Dan McEntee on July 20, 2023, 08:57:02 AM
If you use the sandwich method, try adding sacrificial spacers between each rib pairs. You will have much less bevel and less size variation.

For the spacers, I use two pieces of 6mm depron between each rib pair and you can use these for riblets to save waste.

Steve


   I think it was Charlie Reeves that advocated just making two sets of blanks for two sets of ribs, and store or sell the extra set. That solves the taper issue and if you decide to build another model or need to repair the wing you are one step ahead of the game that way.

    Type at you later,
     Dan McEntee
Title: Re: Making Rib Sets
Post by: Lauri Malila on July 30, 2023, 05:27:22 AM
.
Title: Re: Making Rib Sets
Post by: Tim Wescott on August 02, 2023, 08:07:38 AM
... The old sandwich method which usually ends up with some tilted cap strips. ...

This works if you're using a rod-type jig that makes it easy to flip the assembly before it's all built:

Cut the ribs any old how (sandwich, stack of templates, whatever).  Don't worry about a bits standing a bit proud.  Get the wing framed, then take a long sanding board and sand the tops & bottoms of the ribs flat.

Finish the wing.
Title: Re: Making Rib Sets
Post by: Ken Culbertson on August 02, 2023, 02:09:31 PM
This works if you're using a rod-type jig that makes it easy to flip the assembly before it's all built:

Cut the ribs any old how (sandwich, stack of templates, whatever).  Don't worry about a bits standing a bit proud.  Get the wing framed, then take a long sanding board and sand the tops & bottoms of the ribs flat.

Finish the wing.
I have done that, still got some cap strips tilted.  However, sanding the cap strips with the big bloc works.

Ken
Title: Re: Making Rib Sets
Post by: Air Ministry . on August 22, 2023, 08:45:43 AM
For ribs with to much curve , or a curve at the end , rolling a dowel , round knife handle , or pencil , along the inside of the cap strip , with the palm of your hand , or suchlike , will ' pre curve ' em .
If its to soft it'll crush . So thicker sheet sometimes used , before  the big long sanding sticks applied  . But generally you get away with it .  Test a few before  you settle that dodge , stops em tilting
or droping the edges on real soft wood . Really wants something with grain , for cap strips .

Nuther dodge is ' pin stripeing ' brush - a little thing with say 1 inch bristles , from the art store , for pre doping ( fitted ) cap strips - as it tends to dope the outside & not the edges , wotcher dont want .

A old trick is last step to run sandpaper ( block ) along the cap strip etc EDGES . I think it was Bob Gieske , so as the tissue dosnt ridge / droop along em . Seems to work good .
Your just knocking the ' hard edge ' off . Bearly discernable , not ' radiusing ' the edge .
Title: Re: Making Rib Sets
Post by: Douglas Bykoff on August 25, 2023, 11:24:36 AM
Today a desktop laser machine costs under $300. It will easily cut balsa and thin plywood. It is a worthwhile investment.


https://youtu.be/RWAJ5-E8v7E?si=TbWl3OWLNZny4WdH