Stearman PT-17 Kaydet Conversion from Rubber band Power

[CJRacer19]

Years ago my Grandfather and I built this rubber band powered plane and I want to build a larger glow version. This is the first plane I'm scratch building myself and have some rookie questions. I no longer have the plane we built to refer to, but it looks like the plans show the wing as flat on the bottom. Is this correct? I've only put together a few wings (no biplanes) and they were not flat.

Second rookie question...I believe the dotted line is for the ailerons. Is it okay to put them all the way to the end of the wing like that? This model shows conversion from rubber band to control line, but I want to make sure this is okay for RC before I start.

Thanks

 

[Joker 53150]

First, that's a very cool subject to build, I love the classics like the PT-17! Next, don't take this as trying to talk you out of the project, but I've got to ask how much balsa & scratch-building experience you've got, as this looks like a fairly involved project. If I'm reading correctly, you want to:
1. Enlarge an existing plan
2. Convert a rubber powered plan to glow
3. Do this with limited (?) kit bashing background

How big are you planning to enlarge the plan? Also note that the plan was drawn to handle the stresses created by a rubber band motor, if you go with a glow engine you'll need to beef up the structure to handle the vibration, weight, etc. When going larger (or smaller) than drawn you normally can't simply build to the plans with larger or smaller pieces, but often have to add/remove structure, ribs, fuselage formers, etc., plus change wood sizes as needed. The plan shows this is for a 20" wingspan plane, depending on the size you want to build you may find plans for RC closer to that size. Have you checked Outerzone?

You mention the wing is flat, but the plan page shown indicates some dihedral, which would make sense for a free-flight wing with no ailerons. Or do you mean each wing section has a flat-bottom airfoil? That is pretty common, and it's easier to build than other options.

To answer the aileron question, yes, you can go all the way to the wing tip, but not matter how you do the aileron it's going to require additional fabrication not shown on the plans to create the aileron "pocket", the structure to support the hinges, servos, etc.

 

[CJRacer19]

Thanks for the reply. I have a pretty good woodworking background and will be scaling using a cad program and laser cutter for the parts. In reference to the flat wing, it was the airfoil, not the dihedral. I know toward the front of the fuselage I would need to beef up/modify the firewall and surrounding for the engine. As far as scaling you're saying I can't take a part that was 1/16" and make it 3/16" and expect it to be enough? So I may need to sheet the fuselage with balsa? I was thinking I could just multiply every dimension by 2 or 3 and start there... My main concern in scaling is having the engine fit correctly.

 

[Joker 53150]

How big are you planning to go and with what size engine? If you're going 3x the size and the original plans call for 1/16" ribs, you normally wouldn't just go with 3/16", but instead may go smaller with 1/8", but with more ribs to support the covering. There isn't really a hard & fast rule about how to do it and what to substitute. I wouldn't necessarily sheet this fuselage either, as part of the charm of the design is all the open structure with covering stretched over it. Besides making the engine fit, there is a concern with the overall structure being strong enough to handle the abuse of a glow engine.

One thought is to go online and look at various biplane plans in the size you want to build, and see what they used for balsa thicknesses, rib spacing, etc. Use that as a rough guideline for what you need to do. You may find plans in the size you want already drawn, which will save a lot of work on your end.

 

[CJRacer19]

I've looked at the dimensions on a couple of other biplanes and if I go with a 40" wingspan I may be able to use a 40 size engine. Once I draw the pieces I can make them whatever size I need so I'll just have to start with the firewall and see how things fit. I'll see If I can find some plans and adapt the material dimensions to this one.

 

[roversgonemad]

Rather than enlarging maybe start with a large plan. https://outerzone.co.uk/plan_details.asp?ID=3704 Give outerzone a look, there were multiple PT-17 plans.

 

[CJRacer19]

Yep, I found that last night after Joker suggested it. I had no idea that site existed.

 

[DarkFire]

Outerzone is an endless rabbit hole, ready to suck you in. I already have 20-something plans downloaded, and I'm only just starting on my second balsa build ever!

 

[roversgonemad]

That site is like crack for people who like to build from plans!!