Rib Scale up and Re-Sizing Problem
 

OK--Lets try this one. I know I will not have the technical terms that some use here but will try to convey what I'm trying to do. I i'm taking a fully symmetrical wing, constant cord from 60 in to 120 in. (double) Now If I have a wing cord of 10.5 inches and a rib thickness of 2.312 after I scale it up it would make the rib 4.625 thick for a 120" inche wing WOW. This would be like flying a 2 X 4. One kind gentleman on the forum here said to make adjustments to the thickness on the 12 to 15 percent rule. I can live with that. But will that not change the general symmetrics of the original design? Not that It would matter to me as long as it still flew but I know in increasing the plane overall I must keep the same increased thickness at the trailing edge for strength. Whats the word on this?? Hooker53

RE: Rib Scale up and Re-Sizing Problem
 

Hold on a moment. That means the prototype has a 22% thickness? Unless it's a funfly type I think you'll find that your measurements are off somewhere. But it can't be a fun fly type as the aspect ratio is in the area of 6:1. Did you actually measure these dimensions off the plans?

RE: Rib Scale up and Re-Sizing Problem
 

I'm afraid so bruce. Thats actual measurements. Right down to the 1/64. This bird is Chuck Cunninghams Hooker. Well Now----Lets back up just a Min. The measurement I took was without the stripe Ail. in the measurement. With it in the cord you have 12" but thats still about 19.3, right? So where does that put this thing in the scale up?? I still can't build a wing 120" span with a 4.625 thick rib??? There are some other things to concider also. The present ribs are on 3" centers with .125 balsa. After the scale up they will be 6" apart. So I have to dec. to fill in the gaps and keep them 3" apart and increase the thickness to about 3/16 and cap strip them or keep them 3" apart .125 tk. with cap strips. (1977). Thanks

RE: Rib Scale up and Re-Sizing Problem
 

Oh yeah. A guy in my club had one of those. Nice flyer, you could do a lot worse than to pick one of those as the inspiration.

If you want to keep the charactaristics then you're stuck with the airfoil. Frankly I doubt there would be much problem with changing to another but it will alter the flying a little. If you want one that would be thinner then I can recomend the Eppler 474. That puppy just does NOT want to stall. Of course then it's harder to do the snapping type maneuvers so you'll need lots of throw.

Iin any event an airfoil is an airfoil. If that's how thick it has to be then follow it. For a 120 inch Hooker you're going to need a honkin' big engine.... but I guess you already know that... :D

RE: Rib Scale up and Re-Sizing Problem
 

Bruce, the present 60 in. Hooker is coming in at about 5.3 Lbs with a OS 46 LA. The engine size that Chuck incorporated was .61. This made it a white streak. I admit it's not 3d with the OS 46 la but it surprised me. lets for alittle bit consider what the present day 46 is to a .61 25 years ago. I'm thinking that the one I scale up will come in at about 14 to 17 Lbs but this is unknown now. I hope I can get something like the ZDZ-50 or about 3 ci to pull it. I don't know. Hooker53

RE: Rib Scale up and Re-Sizing Problem
 

I am not sure if I am missing something but surely if you are scaling it up to twice the size then if the original is 10.5" chord with 2.312" thickness the scaled up version would equate to 21"chord with a 4.624" thickness which would be about right?

Like Bruce said, it is a little much (more like 3.5" thickness would be ample) but it would keep the original design characteristics in proportion.

I dont know what way you are going to cut the ribs but to make them from sheet would be rather costly at that thickness. I would prefer building the ribs up from balsa strips and strapping them with 1/64th ply cossets.