Savoia Marchetti S55X 1933 Twin Hull Flying Boat

[bweaver]

I have started building a twin hull flying boat called Savoia Marchette S55X  first built in 1933.  It is a small plane with a 40 inch wing span.  I am building it from Carsten plans which I had purchased over 30 years ago while I was still flying control line.  The plane is originally supposed to be control line with a 15 to a 19 nitro engine. I am converting it to a 4 channel electric. 

The wings and hulls are built up balsa with balsa sheeting.  You can refer to the drawings I have attempted to attach for a look at the plane.

I will try to capture the construction as it progresses along.

[piker]

A very cool subject, Bruce!  I hope this means you'll be joining us for some float flying next year.

BTW, what, if any, changes need to be made to a control line design to concert to RC?  I know some control surfaces need to be added, and perhaps the fins straightened, but are there other considerations like wing section, tail surface areas, AOA of wings and motors?

Oh, Hey!  Now that you're making it electric, you can make it the twin it was always meant to be 

[Wingnutz]

Hooray!
You've started your build thread! I'm really looking forward to reading about such a neat subject! Congratulations on being invited to join the Robert Pike and friends Float Flys!...they're fun!

[bweaver]

Robert, I plan on replicating the scale control surfaces for RC purposes. So this means the ailerons, rudders and elevator will be similar to those proportions shown on the drawing.  Would you suggest changing any of these?  You may have a point about making it a twin engine, but I think for now I will just put a dummy free wheeling prop on the rear.  I also plan on adding some dihedral to the wing. (Because as a control line model the wing on the drawing is straight.)

Does anybody have any suggestions on how I can make the plane water tight? What type of finish should be applied?  Suggestions and comments would be helpful.

Thanks, Bruce

[Papa]

Congratulations Bruce, nice choice.

I would suggest you consider increasing it to around 52" wingspan. easier to build with bigger parts.
You can water proof with Polyurethane or epoxy inside or you can fiberglass outside.

I agree with Robert regarding two motors.
Being pull and push and counter rotating you can use smaller motors and offset torque effects.

Looking forward to the blog.

Jack.

[bweaver]

Thanks for the information on waterproofing Jack.  I wish I had discussed this build before I started, because your suggestion to make the plane bigger makes sense.  Unfortunately I have already cut the parts and kitted the plane at the original plan size.

Now that two of you have suggested using two motors, I will definitely give it some thought.  Perhaps someone with multi-motor experience could share their knowledge with other members at a future meeting on what is needed to accomplish such an installation.  I would find such a presentation helpful.

As you can see from the photo I have started construction of the twin hulls. FYI - I call those things attached to the keel 'formers' and 'bulkheads'. What do I know?

[Papa]

Bruce a "bulkhead" is solid and a "former" is open. In my Northstar both are used.

I will make that a subject for our next pilot's Meeting. All about multi engines.

Setting up twin motors is nor very difficult. I have one that will be maidened in Spring.

You just have two ESc's and two Motors, you can use one or two batteries.

Mine have counter rotating propellers so torque issues are largely eliminated.

Jack.

[bweaver]

Jack, Thanks for the clarification on the bulkhead/former matter.  My bulkheads will be modified to become formers in as the plane construction progresses for the purpose of putting batteries and related equipment into each of the hulls as deemed necessary. 

Respecting the proposal for the next pilots meeting, would it be possible to have the multi-engine presentation at the March Pilots Meeting instead of the February meeting?  Unfortunately I have other commitments and will not be able to attend the February Meeting.  I really wouldn't want to miss it. 
Thanks,
Bruce

[Wingnutz]

Bruce,
What an interesting aircraft you've chosen! Googled it and found many S55s made S. Atlantic crossings back in the 20's when this was still a risky business for most airplanes. It's history lays to rest any concerns about the unusual design having questionable airworthiness.  I've attached a photo of the only surviving S55 which is in a museum in S. America. It has a particularly distinguished history and the coolest paint scheme! Finding out about unusual airplanes is always fun!
The unusual twin hull design has me wondering what you'll do about the battery(ies)...

[Papa]

Bruce can use two smaller batteries, one in each hull.

That is a really neat colour scheme.

March it is.

Jack.

[piker]

Or a single battery in the center section of the wing... if there's room.

[Papa]

While deferring to the master I see some negatives to Robert's suggestion.

The centre of balance will be high.

You may have to beef up the wing structure.

You may not have sufficient room to move the battery forward for balancing.

Jack.

[sihinch]

Just want to say Bruce that this looks awesome.  Cant wait to see it.

[Papa]

I was in my "Think Tank" this morning and I though two inrunners would work great for this model???

Jack.

[piker]

While deferring to the master I see some negatives to Robert's suggestion.

The centre of balance will be high.

You may have to beef up the wing structure.

You may not have sufficient room to move the battery forward for balancing.

Jack.

Yah, yah....  Keep shovelling...   

Centre balance?  Nah.
Beefing up the wing?  Nah
CG range?  Well, you're probably right