pitch-wise torque from a high engine

[squeakywaffle]

I'm researching what would be involved in building a rough approximation of this:

http://www47.tok2.com/home/clearblue2/model/00-03/SAVOIA_01.jpg

It's not a real plane... it's from a movie I saw a while ago and I thought it was cool.

Anyway, the thing that concerns me most about this design is the high-mounted engine. I know there's going to be quite a bit of torque produced by an engine mounted that far off the centerline of the plane- is it going to be a problem? I came up with a little lever assembly that could link the throttle to the elevator to provide a small amount of trim based on the power the engine is putting out, but this might cause so much drag as to make the whole thing pointless.

On the other hand, it almost looks like the size of that fictional engine could shift the balance of the plane up enough to put the axis of thrust pretty close to the cg. Obviously I'm not going to be able to come up with an engine that big (and it would be a bad idea!) but putting the fuel tank, radio, battery, etc. up there in the back of that pod could provide the same kind of balance. It is supposed to be a fairly fast plane, though, so I would probably err on the side of power with the engine.

Anyway, what do you guys think about the general validity of that design for a fast-ish sport scale model? I obviously haven't started crunching any numbers yet, but my gut feeling says I could probably make it work with some careful design and construction.

Also, what's generally used to build those flying boat hulls? I was thinking fiberglass, which is something I know very little about...

[raptor22]

It is definitely flyable, but will require trim changes as you change engine power because of the high thrustline.

You can build the boat hull out of whatever, but it (obviously) needs to be sealed. Fiberglass is nice, but you could also do it out of wood if you did the whole varnish sealing thing, made all your joints super tight, etc.

No matter what, don't expect it to be too fast, it seems to be very draggy with that huge boat fuselage, pontoons, engine pod.....

--Alex

[Tom Harper]

Squeaky,

Nice model. The high thrust line should not cause any problems. It looks like the weight of the engine is just forward of the LE. That's fine. You do not want it any farther back. I'd use four degrees of up thrust in the engine mount and a couple of degrees of right thrust.

Are you going to build it?

[Sparky Paul]

I saw that plane last night in a cartoon, along with some other old-timey's.. about 1923 Schneider Cup time.. That one and the Curtiss R3C, and an Italian flying boat..
The high thrust line might be a problem with pushing the nose into the water.
My high thrust planes need some up-elevation and a healthy toss to get them going up.
A foam body covered with EconoKote would be good for the first one.
MOF, I have this one waiting for a reasonable day at the lake..

[squeakywaffle]

Thanks for the replies!

It is definitely flyable, but will require trim changes as you change engine power because of the high thrustline.

You can build the boat hull out of whatever, but it (obviously) needs to be sealed. Fiberglass is nice, but you could also do it out of wood if you did the whole varnish sealing thing, made all your joints super tight, etc.

No matter what, don't expect it to be too fast, it seems to be very draggy with that huge boat fuselage, pontoons, engine pod.....

For the pitch trim changes, I was thinking I could be clever and link the throttle servo to the elevator pushrod. I came up with a straight, horizontal control horn with its center mounted on a rail so it can move freely on a horizontal plane, with a linkage to the elevator servo on one end and the throttle on the other. Then, I could put the actual elevator pushrod just a little closer to the center than the elevator servo linkage, so both the throttle and elevator servos contribute to moving the elevator, using the horn as a lever and its linkage to the other servo as a fulcrum for that lever (assuming my servos are solid enough).

As for drag, I was thinking of compensating for the bulky airframe by using a skinnier airfoil (my thought process being that it produces less drag and requires higher speeds to produce lift). I haven't done much research on airfoils yet, though, and I don't know much about them and/or whether that would help. Maybe a slower flying plane would be a better idea... :rolleyes:


Squeaky,

Nice model. The high thrust line should not cause any problems. It looks like the weight of the engine is just forward of the LE. That's fine. You do not want it any farther back. I'd use four degrees of up thrust in the engine mount and a couple of degrees of right thrust.

Are you going to build it?

I hope I'll end up building it! I'm starting to feel like it might actually happen- I don't have any experience in designing models from scratch (actually I don't have all that much RC plane experience at all, just an old Gentle Lady many years ago and a more recent Kadet) but I think it's all within my grasp if I just slow down and do everything carefully.

I at least have a decent background in physics, so I should be able to get the numbers right.


I saw that plane last night in a cartoon, along with some other old-timey's.. about 1923 Schneider Cup time.. That one and the Curtiss R3C, and an Italian flying boat..
The high thrust line might be a problem with pushing the nose into the water.
My high thrust planes need some up-elevation and a healthy toss to get them going up.
A foam body covered with EconoKote would be good for the first one.
MOF, I have this one waiting for a reasonable day at the lake..

Porco Rosso? :)
I watched that movie a while ago and this idea has been sitting on the back burner ever since. I love those old planes!

Hopefully I can combine careful hull design with the right thrust angle, surface angles, etc. to get this thing to lift off under its own steam. I'm planning to put together a "test rig" with the real wing and stabilizer, but with a bare-bones fuselage and wheels so I can fine-tune it before taking the real thing to the lake.


Here is a three-view:
http://www.plasticmodels.com/pics/FMN-FJ1.jpg

And some more pictures:

http://www.animationinsider.net/gallery/albums/userpics/10002/up%20high2.JPG

http://www.nemoprod.net/anime/dvd/prosso/screen03.jpg

[vintage1]

Don't get clever. Many flying boats used this layout - upthrust on the engine is generally all that is required to counteract the pitch down moment.

IIRC theh fulls size Walrus even had sidethrust built into it as well.

[Tom Harper]

I had the same impression as Sparky. I was sure I'd seen it as a Schneider racer, but not so. It does have the flavor. Somewhere between a Machi-7 and a Savoia S-51.

Thanks for the 3-view. Should make a nice flying model.

[Sparky Paul]

The fuselage below the cabin on mine is a styrofoam block sanded to shape. The cabin is just some balsa sheet to provide support for the wing, tail boom and motor pylon.
It fell together in less than a day, using the pre-built wings and tail from a Yard Stik ARF. (A handy cheap source of parts for the lazy. :) )

[squeakywaffle]

Don't get clever. Many flying boats used this layout - upthrust on the engine is generally all that is required to counteract the pitch down moment.

IIRC theh fulls size Walrus even had sidethrust built into it as well.

Just out of curiosity, what's the purpose of sidethrust? Is it something to do with the propwash?


I had the same impression as Sparky. I was sure I'd seen it as a Schneider racer, but not so. It does have the flavor. Somewhere between a Machi-7 and a Savoia S-51.

Thanks for the 3-view. Should make a nice flying model.

The official name of the plane (according to the movie) is the Savoia s.21, but only one of those was made and it looked nothing like this one. Apparently the most similar plane is the Macchi M.33.

It definitely has that Schneider cup flavor... the movie is set around that time.

[BMatthews]

I've seen Porco Rosso as well. A great cartoon for any airplane lover! The airplanes were obviously drawn by someone well versed with aircraft history and the interwar classic age.

If you look at 3 views of the over the wing flying boats you'll find that they all use from 2 to 5 degrees of upthrust to solve the problem of the high thrust line. This one isn't actually that high above the wing so it will need a minimal amount of upthrust. Maybe 2 degrees.

Hey squeaky'? Do you have a link to where you got the 3 view from? I'd like to get a larger version and play with the idea of an electric or gas powered copy of my own.

And I must pick up a copy of the DVD for my library.

PS: Never mind about the link. I pulled it out of the "quote" of your post and found out it's just the same small one. Oh well, it's not really a scale model anyway... :D

[squeakywaffle]

I've seen Porco Rosso as well. A great cartoon for any airplane lover! The airplanes were obviously drawn by someone well versed with aircraft history and the interwar classic age.

If you look at 3 views of the over the wing flying boats you'll find that they all use from 2 to 5 degrees of upthrust to solve the problem of the high thrust line. This one isn't actually that high above the wing so it will need a minimal amount of upthrust. Maybe 2 degrees.

Hey squeaky'? Do you have a link to where you got the 3 view from? I'd like to get a larger version and play with the idea of an electric or gas powered copy of my own.

And I must pick up a copy of the DVD for my library.

This is the best I can do for you:

http://www.plasticmodels.com/kpitem.asp?ItemCode=FMN-FJ1

I don't actually know whether that page is for buying a "plastic model" or a larger copy of the three-view. I don't think a bigger copy of that image exists on the internet, anyway.

I was just going to go off screencaps from the film (which is great, by the way). I'm not too worried about getting the proportions exactly right because it's not actually a real plane. :D

(edit: I didn't see your edit :rolleyes: )

Anyway, keep us posted if you decide to build it. I'll do the same... I'm planning to build a model with a 70"-80" wingspan and probably a fairly large engine for a plane that size. The plane in the film has a big V12, so I'm going to try to make it as quick as possible.

[Tom Harper]

When Googling I found this link:

http://porco.anime.ru/planes.htm

It has a clean sideview drawing.

[peterangus]

squeaky

My Lohner exhibits the usual effects of a thrust-line well above the CG. Flying was made easier when I mixed some up-elevator with hi-throttle. [at the Tx]

Upthrust is effective only if the tailplane is immersed in the prop slipstream. It works by influencing the download on the tail. It should be benificial.

I suggest a surreptitious increase in wing area. This is the only effective way to improve the L/D ratio. Thinning the wing section below 10% will produce no benefit.

"Fastish"? A full-size version would do about 200mph max, and alight at about 70.

[vintage1]

Upthrust is effective only if the tailplane is immersed in the prop slipstream. It works by influencing the download on the tail. It should be benificial.
.

Not totally true...unless the prop is actually over the CG...but the point is true ENOUGH to be well founded.