wing dihedral

[Robin125]

Hi team members, I am gaining experience building balsa models, but want to know how important is it to get an exact wing dihedral set up as per instructions on plans. Also setting ribs to spars, should each rib be set in contact with both leading and trailing edges AND flush with the modelling board? So hard to get it right!

 

[John Rixon]

Very! As for the ribs leading and trailing, this depends upon the 'foil section, some will require the leading edge to be raised from the surface, some will be flush. Best plan is to pin the lower spar to your board (and, seriously, this board does need to be flat!) then lay the ribs on the spar, using a square to ensure they are at 90 degrees. You'll soon know what the score is, many aerosol sections will have the trailing edge on the board, but if its a stunt plane, or scale, you will need to act accordingly It's pretty straightforward to make a jig, upon which to pin your trailing edge to if it is raised, Leading edge a bit trickier, but if you have the trailing edge firmly glued in, and the ribs accurately seated, then its a breeze fitting the leading edge with cyano, which sets instantly!


I cannot, however, stress enough how important accuracy is here, and the smaller the model, the more critical it is for flying true! What is it you are building?

 

[Robin125]

Hi j

Very! As for the ribs leading and trailing, this depends upon the 'foil section, some will require the leading edge to be raised from the surface, some will be flush. Best plan is to pin the lower spar to your board (and, seriously, this board does need to be flat!) then lay the ribs on the spar, using a square to ensure they are at 90 degrees. You'll soon know what the score is, many aerosol sections will have the trailing edge on the board, but if its a stunt plane, or scale, you will need to act accordingly It's pretty straightforward to make a jig, upon which to pin your trailing edge to if it is raised, Leading edge a bit trickier, but if you have the trailing edge firmly glued in, and the ribs accurately seated, then its a breeze fitting the leading edge with cyano, which sets instantly!
I cannot, however, stress enough how important accuracy is here, and the smaller the model, the more critical it is for flying true! What is it you are building?

hi john, sorry for the slow reply. I am building a Westwings 'merlin' at the moment. It is a glider. After this I will go on to scale models, maybe Spitfire.

 

[John Rixon]

Ah, ok, well at 35" span, you really want to be as pernickety as you can, as any errors will mean unstable flight. It's very easy though, just keep checking everything is as it should be - for wing ribs, I'd use a steel ruler upright, as a square , if you see what I mean? It'll get in between the ribs easily! As for dihedral, again, make two simple but identical supports to rest the tips on for the correct angle, pin them to the board, then pin the wing tips to them while the glue dries. Keep checking for twists etc until you are happy all is square and true.

 

[Robin125]

Ah, ok, well at 35" span, you really want to be as pernickety as you can, as any errors will mean unstable flight. It's very easy though, just keep checking everything is as it should be - for wing ribs, I'd use a steel ruler upright, as a square , if you see what I mean? It'll get in between the ribs easily! As for dihedral, again, make two simple but identical supports to rest the tips on for the correct angle, pin them to the board, then pin the wing tips to them while the glue dries. Keep checking for twists etc until you are happy all is square and true.

Hi john, thanks for the help. The Merlin glider is ready for 'skinning' now. The wings seem to be 'warp free', however the wing and tailplane angles are slightly out. Should I sand down the fuselage or use packing to bring them into alignment?. This will be the 1st model that I hope to see fly. The others are hanging from ceiling!

 

[John Rixon]

Hard to say without seeing it, but certainly, the angles should all be true - tail fin vertical, and tail plane with correct dihedral. If you set it up on a table, propped up, then stand back and very carefully eye up all the angles from front and rear, if there are any discrepancies as you have mentioned, then packing will be needed! Of course you will need to run all these checks again after skinning and doping! I kind of miss the old Balsa days, but in the end, I got fed up with crashing planes that had 6 months hard graft in them, not to mention a load of expensive electronics and engines! I think gliders are great, but here in East Anglia, we don't have the best geography for them!