Hey guys,

I have a small pylon style plane with a simple plank balsa wing that needs strengthening. I considered adding a spar, but it's a bit tricky to cut one in and the servos are in the way where it really needs to be. I want to glass the wing, but don't want to add too much weight with any resin soaking in to the light balsa.

Can anyone link up with a how-to? I have fibreglass and laminating resin, but probably need some sort of primer to prevent too much of the thin resin soaking in.

Michael.

hi Mike, how big is the wing take a pic.and what is the engine as a weight consideration might be warranted.
By the sound of it without looking a ply spar may be best, but show a pic.
Dave.

Thanks for the response dave. The model is a tiny 23" wingspan speed thing called an Adrenaline Rush. It's just a 5mm shaped balsa plank for a wing. Normally you would buy the kit, but I scratch built mine. As it happens I think I used too light balsa and the wing snapped in flight.

As for an "engine" it's a 3000kv electric running on a 3S 850mah lipo. It makes only 270W, but as it only weighs 180g, every bit of weight needs to be there for a reason!

Anyway, in my deliberations, I've found a solution. I have a mate with some vacuum gear so we're going to bag the wing in glass either side. you wet out the glass first before applying it to the wing, so there should be minimun resin soaked into the balsa. Should be pretty much bullet proof when we're done.

Cheers,
Michael.

Hi Mike nice model and looks good fun, even with the wing soaked in resin and bagged it will still need a cross spar, the resin is brittle and has no flex so it will snap suddenly and adding fiber glass as well will make it heavy, I would myself put a 3/16 ply cross spar with GRAIN LENGTHWAYS on the C.of G. put the ply cross spar at least half way along each wing and going continuously across the center of the wing this will add very little weight but will be able to flex in the turns.
I would not resin coat it.
The method i use to add cross spars to existing wings is and i have just done this on a much larger wing then yours a 90 inch Ziroli P40 which is about 4 inches deep. I bought the aircraft for $300 second hand with a super tiger 45cc glow engine in. I will be refurbishing the whole aircraft and adding retracts and putting in a decent Gas engine and selling the Super tiger glow
This was a finished foam wing covered in Balsa but with no cross bracing just fiber glass 4 inches each side of the center line it would not have held for long.
I have cross bracing 3/4 of the way across the wing i put 2 sections in mine one on the C.G and a shorter one further to the rear but as yours is so small just one along the C.G.will do.
First i drill holes through the wing at each end of where the cross brace will go i then attach steel rules on top and below from the 2 drilled holes, this will be a cutting guide so you can cut against the rulers and get a good strait cut, i then carefully cut through with a knife the first inch completely through making sure i have the blade up against both steel rules.
I then get 2 or maybe 3 hacksaw blades stuck together at each end with sellotape the amount of blades depends on the thickness of the ply you are pushing in. i then cut with the hacksaw blades against the steel rules the complete length of where the ply bracing will go, i then cut a rough size of ply with grain lengthways i put white glue in the cut and on the ply and tap the ply through the wing and hay-presto i know have cross bracing.
Yours will be much simpler just drill each end of where you want the bracing to go and you will only need a ruler on the top as its a thin wing but if needed put a steel rule on the bottom as well or you may end up with a wobbly cut.
Cut through trying to get a vertical cut.
Cut through and use one maybe two blades depends on the thickness of your ply cut the length you want and tap in a ply brace covered in glue next day when its dry trim of the access wood and sand smooth, you can then finish in any manner you like but i would leave out the resin as its to heavy.
Dave.