Hi,

In the Guillow's instructions they stipulate coating the outer surfaces of the balsa with dope, then sand lightly. Once I tried doping all the balsa surfaces and it seemed to really strengthen the frame but made the plane too heavy for rubber powered flight.

My question is... When converting a Guillow's kit to free flight (.049 engine) wouldn't the extra weight of doping more surfaces be fairly insignificant compared to the benefits of the added strength?

Does doping even really add stength (or am I imagining it)?

Has anyone done this with a Guillow's kit before?

Unforgiven:

The doping might add some strength to the wood, but that's not why we do it.

Any wooden airplane, engine powered, will need protection from oil and fuel residue.

So if you want the airplane to last any length of time, you have to accept the added weight of whatever finish you use to protect the wood.


Bill.

Not sure about balsa, but in full scale the first coat of dope on the airframe improves adhesion of the fabric, a glue of sorts, and yes each coat of dope adds weight. on an airframe the size of a gillows kit weight could would be small. perhaps shaving or sanding a little wood from the under sides of stringers and the face of aft bulkheads or lightening holes in the bulkheads during building could make up the difference. What do you think bill?

bearmech:

I think if he really uses an 049 on a Guillow's kit conversion he's going to have so much excess power he wont notice the weight of a few extra coats of dope.

But you are most definitely correct. A little extra sanding will remove weight, but there's a fine line between removing weight and airframe strength when using an 049 on a plane an 020 would fly nicely.

Bill.

True, most of our planes mine any way are overpower relative to what's required for flight!

Thanks guys! I appreciate the input. I hadn't considered the need for protecting the wood from fuel spills outside of what I was planning to do for the engine area.

1) Dope should be thinned, at least 50/50
2) Use Nitrate dope to glue fabric to the frame
3) Use Butyrate dope to shrink fabric and for fuel-proofing.

HTH. Jim.

I doped my Spirit of St. Louis frame. I haven't covered it yet though. I noticed doped wood seems stronger than undoped wood. I believe the dope dries within the pourous network of balsa cellulouse.

Kraus