Cessna 180 Group Build

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[SteveM]

The plan shows this being done via a butt joint, which is an exceptionally weak way of producing the joint and will result in a lack of stiffness, and likely banana-ing when we cover. This is because; in general glue does not like to be in tension. If you imagine butting two pieces up and gluing them, them bending them upwards, the bottom of the joint where the glue is gets stretched and is in tension, and will simply pull away. However glue likes to be in shear i.e. is strong when we want to make it slide.

To use the glue more in shear and less in tension we will join these with a scarf joint, this also has the advantage that it increases the glue area - also increasing the strength of the joint.

Oh hogwash. Yes, the scarf is stronger than a butt joint, but your reasoning is all wrong.

The main reason butt joints are weak is that you are gluing end grain to end grain (or possibly end grain to long grain) which causes glue to wick away from the joint and on a microscopic scale has a very small bonding area. It would be like trying to glue the end of two bundles of drinking straws together. A scarf joint exposes more long grain, increasing the bonding area and reducing the wicking effect (and yes, more surface area of the wood that you can apply glue to). I think they wrote this book for you.

PVA and CA are both well known to be weak in shear and strong in tension. What an astonishing amount of misinformation in one post!

[BassettsAllSorts]

Hi Guys,

Without a doubt these kits have a few problems, but you can't blame the kits for all of the problems that are being experienced. For instance you cannot blame the difference in the two fuselage sides for the banana fuselage per se, the two sides come from identical die cut sheets, cut with the same die on the same machine. They are - to all intents and purposes the same. You could blame the stiffness of the balsa, but the sheets look to be a similar density (thus stiffness) to me but I wouldn't know exactly without being there so you might be able to comment on that.

Don't be fooled with the laser cut stuff, sure it looks good BUT they are comparatively costly, and you still need to be able to think on your feet and make corrections/ adaptions/ interpretaions. The other thing is that try not to be seduced by the warbirds! They are very difficult to trim, at the end of the day the originals were designed to fly fast and be unstable to make them manouverable, we want stable and slow for FF rubber flight so the two things are not made easily compatible. I think that the 300 series will be laser cut next, these are a lot more ideal for first time rubber FF so I would recommend those if you want to stick with Guillows, even I gave up with the 300 kits, if you think this one is bad, then please do not buy one of those they are awful!

This is a £10 - $15 kit, the prop and nosebush is a couple of bucks the wheels maybe 50 Cents each, so what you are getting is pretty good for the money. If you make some small accomadations for that you can make these things fly OK. As I said I make all of the corrections needed to the wing parts in 20 minutes or so, not a massive problem. This is why I'm trying to do some notes on these kits to point out the obvious flaws that any experienced builder would pick up on without any hesitation.....

Tom, did you crack the wing spars? If not your wing may not end being straight. Also did either of you build in any dihedral into your root ribs?

Andrew

Hi Andrew

I was blaming myself in my post. I got complacent as it went along didn't check the notches correctly, I filled some of the gaps before fitting at the bottom of the ribs but I just wasn't thorough enough. I think for the money these kits are great fun. I was really disappointed in myself for not checking. It still amazes me how much you need to know to build these little beauties!!

Also I quite enjoy trying to make things good so they fit but I just have a habit of missing them and cracking on without taking a step back and thinking about it. Still that will come with each build.

Your posts with the pictures really show my inexperience so I'm really pleased that I bought this plane and got on this forum!

From reading other posts I knew about dihedral and I looked at the plans and I didn't see any reference to it on the instructions so I just built it flat to the plans

I am a bit of a sucker for instructions and even though my brain was saying crack the wing spars on the bend the plans had no indication of that as far as I can see unless I am being stupid (Which does happen quite often!). It just said a "slight bend in the strips" here although I could have missed the reference.

Oh well I might still manage to get her airborne!

And that tip on the dihedral is great thank you I'll certainly use that in the future.

I pulled the wing off of the plans and it seems nice and straight so hopefully I'll be OK.

Also I have read that the warbirds are hard to get going (Scigs seems to be the expert on getting them up in the air). I thought I might build them and try to fly them. I only paid £10 per kit so its no great shame if they explode on impact! I'll still have my super cub and ,hopefully, my cessna to go out and enjoy in the air!

Tom

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[BassettsAllSorts]

I agree on the end grain point, thus the requirement to "double glue" and I was remiss not to mention that point. But I stick with my original theory, the joint is in a large amount of tension due to bending which makes it even weaker as it is being prised apart. By using a joint at least in partial shear you get a stronger joint.

The same rationale would apply if I used metal, no end grain there, it would still be stronger for both of the reasons I mentioned irrespective of the adhesive used. We are talking comparatives here, some glues are better in tension shear etc, but all glues are best used in shear if at all possible.

Steve, may I say thanks for your contribution and critisism, it is always welcome, but I beg you please back off a little..... your tone is both aggresive and rude. I would like to think that if you and I do not agree on a single point that would be fine and we argue technical all day, but I'd like to think that we could be civil to one another in doing so.

Tom, no worries, The instructions are far from ideal, this would be an ideal kit if it was made better and the instructions were complete!

Andrew

Hi Andrew

Agree with your post, it seemed a little on the harsh side!

I still think its a good kit and I am having a great time with each build. I'm enjoying seeing other people build and its a relief to hear people are having problems like me.

Keep up the good work with the tutorials!

Thanks for all your help.

I'll finish this model flat to the plans to keep it even and move on with the next build.

I'm having trouble getting some blue tissue for the covering so it may well be a yellow "banana" Cessna!!

Tom