Engine Pod - how much support?
 

I am working on a design for a flying boat with its single engine mounted on struts above the fuselage. I plan to use a 0.46 2-stroke in this, because I have one lying around not doing any useful work.

Question: how much strut is enough to keep the engine mounted to the fuselage? I figure it will have to be a metal strut with wooden fairings, or perhaps an airfoiled hollow metal pre-formed strut. Any ideas?

BTW, the plane looks like this (it's the fictional flying boat from Miyazaki's movie "Porco Rosso" incidentally, not a real "Golden Age" plane but quite a believable interpretation of the concept).

Thanks for any suggestions.

RE: Engine Pod - how much support?
 

PORCO ROSSO RULZ! ! ! ! ! :D I loved that movie! Every modeler needs to see it at least once.

I'd suggest you make the struts from solid 3/16 aircraft alloy that is filed/sanded/polished to a fat'ish airfoil shape in the exposed areas. I'm guessing that this will put them at about 1/2 to 5/8 inch wide. With 4 of them this should be a decently solid mounting that can withstand at least some rough landings and the odd wing float bounce. It'll also mean that the buried areas are beefy enough to take the mounting holes and hardware. The smaller diagonal braces could be from 1/8 treated similarly. These really should be a T4 to T6 alloy as even at this size milder alloys would bend like a wet noodle. But the T6 stuff has a far higher yield point so it should be able to flex without taking a setting. IF the model is any larger than 600 sq inches then I'd suggest doing the same things but with 1/4 and 3/16.

Using thinner metal with wood fairings is just asking for bent struts IMHO. If you want to go that route then I'd suggest 1/8 or even 5/32 music wire with wood fairings. It needs to be this heavy to take the flex out and avoid a lot of engine vibes shaking things up.

Best of luck with your Rosso Racer.

RE: Engine Pod - how much support?
 

Hey, thanks BMatthews. Indeed, Porco Rosso should be required viewing for all aviation fans IMHO.

I hadn't considered the availability of solid alloy pieces that I could machine down - just shows my general lack of knowledge about metals vs. wood.

Generally the Porco Rosso plane looks like it is structurally do-able but there are a few obvious weaknesses - the stabilizer/fin connection is one such area and clearly the support struts under the stab will have to play a very active role. The 3-view I included in my first post shows that the elevators have HUGE tip-balancers, and I don't think this is really workable. I don't know for sure, but I don't think the tip balancer should grossly exceed the chord of the elevator.

One note if anyone wants to use the 3-view I posted: look closely and you'll see that the profile view is drawn to a different scale than the top/bottom views. You can't just trace it without correcting the scaling.

Nice thing about doing plans for a fictional plane is that you can be a little bit freer in interpreting the pictures than in a real "scale" project. After all, in the movie, I notice that the hull step shifts back and forth with respect to the cockpit depending on the view. If they can move things around a bit so can I.

RE: Engine Pod - how much support?
 

Those weren't real airplanes?...!!! :(
The step.. put it where steps have to be... maybe a 1/2 inch aft of the c.g. but no further.
I'd do the motor pylon from 1/4" plywood... in the center of the pod.. and forget the tubing.
That would be merely cosmetic.

RE: Engine Pod - how much support?
 

The balance tabs on the tail surfaces look fine to me. It's as much about the area forward to area behind as it is the chords.

However looking at the engine pod and nose side area I'd suggest some additional poetic license be taken in increasing the vertical tail area by about 20% over what it currently is. As it sits I think you're in for trouble in terms of spiral instability and possible unwanted snap rolling.

Using the "scale" struts would definetly make things more complex. Just because of the fact that I'm stubborn I'd go with it but I'd make the wing center fixed to the model along with the engine pod and make the wing panels fit onto the center section.

And while the drawing doesn't show it you'll want to add about 3 to 4 degrees of upthrust to the engine to compensate for the very high thrust line. Study some other high thrust line flying boats to see what I mean.

The bit under the tail could be fattened up and lengthened without hurting the looks. That would help stabilize the tail nicely. I'd still use functional bracing struts though.

And there's no water rudder. You'll likely want one of those.

Many (most?) of the planes in the movie were scale. THat's a big part of what impressed me so much. Just Porco's racer was a work of fiction but even then it's firmly rooted in Savoia Marchetti design school.