twopper

Hi

I'm going to build a Curtiss Ascender from a set of CAD plans, I have found a service to laser cut the ribs and formers but I am unsure of which type of ply to use. Birch ply is strong but heavy and Lite ply is light but weaker, any advice from experienced builders would be welcome.

Thanks

Twopper

Al Stein

Interesting choice of airplane -- I hope we get to see pictures of your model!

For materials, size is a big question. Size aside, your wing is far rearward and your engine is mounted at the tail, so the fuselage has a pretty easy job just holding the canard and some equipment.

Maybe we can start with assumptions and then adjust to the real world...

For me, I'd probably build that plane for about a .40 sized 2-stroke (because I really like that size engine, not because it's a superior way to go), so I'd look at the slippery design and guesstimate that something like a 5 foot span would fly really well on that size engine. (You'll have to fill us in with what you were thinking for size here.) I think I'd sheet the fuselage or plank it to keep the sleek look of the original plane. I think I could build that in under 4 pounds -- maybe not very much under considering the weight of a balsawood skin.

So, given those assumptions, balsa is fine for wing ribs... 3/32 balsa is popular for planes that size. They definitely do not need to be anything heavier than that. Use firm wood and quarter-sawn ( "C-Grain" ) is best, but not necessary. For fuselage formers for this plane, 1/8" light ply will be great for the most part. Do use something like the birch ply for your firewall, and use 1/4" there (or else laminate two half-thickness parts if your birch ply is thinner).

OK, so that's ribs and formers for the mid-size plane... What size are you actually going for?

CoosBayLumber

My Feedback: (1)

To vary from the subject, are your plans based upon the free downloads which used to be available from the Fort Worth hobby site? It was a favorite download for awhile. If it is, it used to be noted therein the A/C plans are not for a model, and a model has never been constructed from them, nor flown by using the plan.

Just wanted to mention this, as it has come up quite some time ago too. Is best to work with plans from a model which has been flown and tested.


Wm.

Al Stein

Wm makes an excellent point... and this is your first scratch build isn't it? We want the first one to have a good flying design because we don't want a problem design to build into a problem airplane and possibly leave you thinking that the problem was your building.

So, here's a thought... Bashing the design of something proven may be a safer way to get a flyable Ascender if the plans you have aren't flight proven. So that leaves us with the question, what looks enough like the Cuirtiss Ascender that a face-lift would make it believable? Without any detailed study, a couple of possible candidate designs that do fly are the SIG TriStar

or maybe a proven version of "Burt" Rutan's Vari-eze

rchawaii

That would be my choice -not that it matters of course Aloha Al nice to see ya.

Al Stein

Hey Chuck -- good to see ya buddy.

It hadn't occurred to me before, but suddenly I'm seeing coroplast canard designs in my head... The Tri-Star's an awfully skinny little ship -- which means lots of surface for it's amount of lift... it might be cool as ong as a little speed isn't a problem. Hmmm... So many things to do and so much trouble getting to them these days.