pathfinder top and bottom spar

[Horby]

Hi all,
I have started to build my wing for my Pathfinder and was wondering how the top and bottom spars go to gether.
Do I just splice the two pieces and cut off the excess?

Warren

[Dan McEntee]

   I have never built one of those, but if the spar stock is of equal length, then yes. make a scarf shaped or angled cut for the splice. Try to offset the splices, that is try not to have them one on top of the other. Put an overlapping brace on the splice. If the spar stock is long enough, make the splice as far out the outboard wing as you can, then cut to length. This gives you solid wood at the wing center where most of the stress is. If you have similar size balsa stock on hand, I think it's worth it to replace the spar stock and make the splices as far out on the wing as you can. When I scratch build Ringmasters, I always use leading edge stock full length and splice it out towards the outboard tip. Ringmasters that are built from original Sterling kits are notorious for being fragile at the wing center joint in even the lightest crash, and that is because they were trying to produce the kit is an short a box as possible, (for cost cutting reasons) and that meant short balsa stock splicing wing leading edges, spars and trailing edges.
   The Pathfinder is one of the kits in my stash and is a fine flying airplane. There is volumes written about modifying and improving many, many airplanes out there, but I can't remember much be written on improving the Pathfinder. Gordan Delaney did a great job designing it Just build it straight and as light as practical, bolt on a reliable power plant and it will do the job for you.
   Good luck and have fun,
   Dan McEntee

[Horby]

I figured as much, Thanks.
I am going electric all the way. I will be selling most of my IC stuff shortly.

Warren

[Dan McEntee]

I figured as much, Thanks.
I am going electric all the way. I will be selling most of my IC stuff shortly.

Warren

    Yeah, if you noticed, I said "reliable power plant". In this day and age, that can cover a wide variety of choices! I'm waiting for someone to come up with a steam powered engine! The electric stuff is just one of those choices. It's just a matter of what you can wrap your mind around, understand, and be comfortable and confident with. I'm just a gear head who like engines!
    Good luck and have fun,
     Dan McEntee

[Leester]

Is this a Kit ?? If it is a Brodak kit most spars are butt joints at the root. Is the wing tapered?? If so your spars won't be flat from tip to tip.

[john e. holliday]

I guess it is just me, but most kits I have that the spars are only long enough to splice in the center get replaced with pieces I can put splices out toward the out board tip.   But as stated, stagger the splices.  A side benefit is it cuts down on wing tip weight that needs to be added.

[Geoff Goodworth]

Warren, normally, I would fully endorse Dan's comments about offsetting the scarf joints.

However, the Pathfinder drawing that I have shows 1/8" ply bellcrank support plates glued to the spars in the first bay inboard of the fuselage. These plates show only as a dotted line on the wing plan drawing. All the detail is in the fuselage elevation drawing.

I would locate the splice joints in that bay, reinforced by the ply support plates. As suggested, I would also use scarf joints for the splices.

[Horby]

Yah it is the Brodak Pathfinder.  I forgot about the plywood bellcrank mount. I am also wondering about the 3" bellcrank.
What does the ARF use? Does any one know?

Warren

[Gerald Arana]

Warren,

I use 4" on everything. 

Just works out best.

Good luck, Jerry

[Geoff Goodworth]

Warren, my drawings suggest that the 4" bellcrank will not fit using the ply mounting plates in the kit. Replace the 3/4" wide ply in the kit with pieces 1" wide and move the pivot back 1/4" and you will be fine with a 4" bellcrank. Obviously, your call, but like Jerry, I would use the 4" bellcrank.

It's worth noting that the lever arms for the pushrods are the same on the 3" and 4" Brodak bellcranks so you need more wrist movement for a given pushrod movement with the 4" bellcrank but the loads that you feel are greatly reduced. Some have likened it to driving cars with and without power steering.

[Gordan Delaney]

The best way is to put the scarf joint as far out as they can go and put the scarf over a rib. So one splice will be on the outboard side and the other will be on the inboard side. Also if the 3 center ribs are not under cut from the spars forward then under cut 1/16 and plank those ribs before the rest of the leading edge sheeting go on. I used the 4 inch on my lastest Pathfinder. I`d have to look at my plans. There might be four ribs that the center sheeting on.
Hope this helps.

Designer of the Pathfinder

Gordan Delaney

[Allan Perret]

A good scarf joint done at a 1:6 ratio or better is not a weak point.  A simple sanding jig setup to sand both scarfs at the same time is easy to make and gives a fast and easy precise fit between the parts with minimal glue weight.  When done like this I have no concern about where I locate the joints.

[Gordan Delaney]

Allen,
I have nno problem with scarf joints either. I was just telling him how I do it. Plus if you don`t know how good of a builder the person is it could be a problem. Not every one is a great builder.

Gordan

[Horby]

Thanks Gord and the others helping,  I will also replace the 3" bellcrank with the 4".

I love this forum. Where else do you get to interact with people in your sport who helped move it forward and shape it.
Can't do that in the NHL or NASCAR.


Warren.

[Balsa Butcher]

...or the person who designed the plane in the first place.