Savoia Marchetti S55X 1933 Twin Hull Flying Boat

[Papa]

In  my life one out of three ain't bad.

Jack.

[bweaver]

I have had some distractions to deal with, so now I am back at the project. 

After covering the sides of each hull, I have now built a dry dock cradle to support the hulls where required and I can construct the rest of the plane on them. 

I will now proceed to construct the wing and get it mounted before adding the blocks to the hulls and shaping them into the wing.  I also have to plan for a couple of access hatches and arrange for the servo installations.

The photos depict the cradle and the covered hulls.  The beer was placed in the picture so that it is possible to relate to the size of the model.  The contents of the beer are now gone.  (Another distraction)

Thanks for the construction suggestions.  There is likely room in each hull for a pretty good size battery or a larger one could be placed within the  centre of the wing section between the hulls.  I'll cross that bridge as construction progresses.  This is where I would appreciate some further consultation.

[Wingnutz]

The beer was placed in the picture so that it is possible to relate to the size of the model.  The contents of the beer are now gone.  (Another distraction)

Thanks for the construction suggestions.  There is likely room in each hull for a pretty good size battery or a larger one could be placed within the  centre of the wing section between the hulls.  I'll cross that bridge as construction progresses.  This is where I would appreciate some further consultation.

Glad you're enjoying the beer along with the build! Helps wash down the balsa dust.
For what it's worth, I think Jack's two battery, one in each hull suggestion is likely to be the only way to balance this model without ballast. Perhaps you could make the final decision after the airframe's done and you can estimate better where the battery(ies) will have to go to avoid ballast. I'm betting Jack is right.

[sihinch]

Jack is always right!! :-)

[Papa]

Thanks Simon, It's nice to have a fan, your money's in the mail!

For the sake of correctness, Bruce can you edit the title and spell Marchetti with an "i". Alessandro would be most pleased.

Jack.

[bweaver]

I never could spell.  I have corrected the segments of the thread that I was permitted to modify.   

Thanks for the advice for balancing the plane.  I feel there will be allot of room for the varying placement of the esc(s) radio, battery(s) etc as the construction continues.

[Papa]

Sorry to be such a PIA.

Have you decided on one or two motors?

Here's a picture of Laddie Mikulasko's Dornier DoX.

These are all can motors, one in front and one behind in each nacelle.
It can be done. This model flies well but very scale like.

Jack.

[bweaver]

Jack, I was initially thinking of only one electric motor because I have one that would be suitable. 

I need to have some further advice on the use of two.  For example, I really don't know how I would determine the motor sizes, battery(s), esc's, etc., because I have had no experience in this area.  I really need that multi-motor session coming up in the March meeting to get a grasp on this end of things. 

I see no problem mounting two motors on the pod, but for determining the power requirements; I wouldn't know the weight of the model until I get it pretty well constructed, covered with balsa, servos installed, etc.  Then because I want to make it water tight, I don't know if the finish applied will add allot of weight too?

I'm definitely not counting out two motors.   But the decision will have be made at a later date.

[Papa]

I'll start the discussion.

http://www.hobbyking.com/hobbyking/store/__17345__NTM_Prop_Drive_Series_28_26A_1200kv_286w.html

This would be a small diameter but two would put out about 450 to 500 watts. Two props 8x4 would look about correct. Two 20 A SEC's and two 4S batteries. It's a 40" span and probably come out around 3.5 to 4.0 Lbs. Two motors are more efficient than one large one of the same combined size.

Jack.

Jack.

[piker]

Yikes!  3.5 to 4 lbs for 40" span?  I hope not.  I'd start with the wing area and a desired wing loading to determine weight goal.  Then choose motors based on that. 

Looking at the cord to span ratio I estimate about a 300sq/in wing area (you can correct that estimate with the real wing area).  That's 2.08 square feet.  With an aircraft of that size and type I would aim for 18 oz/sqft wing loading MAX.  At that, the final flying weight will be around 36 oz., or 2-1/4 lbs.  I would go for a power loading of 100w/lb for a power requirement of 250watts.  I think that would be plenty.  That's two 125w motors.  It would be nice if these could be run off of 1x 3 cell battery mounted in the center section of the wing, but, as Jack pointed out, you may have CG problems.  However, looking at the aircraft layout, those pontoons don't extend out ahead of the wing very much, so I don't know how much help two, say 1000mah, 3 cell batteries are going to help.

[bweaver]

I'm back at the construction of the Savoia Marchetti S55X. 


I have cut out the ailerons and will be installing the servos.  Which side of the wing should the control rods exit?  Top or Bottom? and how do waterproof the servos and control rod areas?  Any help would be appreciated.


Bruce

[piker]

Cool!  I'm glad you're back at it, Bruce!

I'd put the control rod exits on the bottom.  First, because it looks better, but also because then any water that does get in, simply drains out.  If you put the holes on top, water will go in and never come out.

I just leave a hole for my servo arms to exit and hook up a direct pushrod (on my M-33).  It hasn't cause me any issues.  You could create a fairing that would help to keep the water out.  I would also suggest that the area where the servo sits be closed off from the rest of the wing.  That way, if the plane does go under, the water will stay in that one area and can easily drain out through the hole.

[Papa]

My preference would be to come out through the top. But if I remember correctly this is a high wing model so the servos are far from the water. It may not matter that much. You can silicone the seams and use shrink film to reduce the possibility of casual water getting in. Otherwise you would have to use the new water repellents such as http://www.hydrobead.com/#!consumer/component_41229
http://www.rustoleum.com/product-catalog/consumer-brands/neverwet/neverwet-kit


Jack.

[Papa]

Correction now I agree with Piker. Bottom for drainage.


Jack.

[bweaver]

Thanks guys. 


Getting on it.  I will be posting photos as the construction progresses.
Bruce