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Sbach 300 - an attempt at a lightweight build out of heavy 5mm european foam board

#21
've build several of the FT3D's, the wing on the plans is far too small. I have better results with a larger wing. To me your wing looks small, a larger wing will reduce the wing loading. Might want to consider a wider wing cord.
Just something else I wanted to ask, have you flown the FT 3D with *and* without the VGs? And if so what is your opinion on them?

They seem like something they just kinda slapped on without much calculation, and if it's true that they improve the handling so much then it means the concept in general is quite useful ;).

The shark teeth on the Balrog seem to work quite well too, but then again, I haven't flown it without them, so maybe it's just a great plane in and of itself :p. I'll probably want to put either one of them on the Sbach, and the VG's would be a couple of grams lighter, so...
 

Merv

Well-known member
#22
have you flown the FT 3D with *and* without the VGs? And if so what is your opinion on them?
No, I've never used the vortex generators. I've seen other planes with VG's and they seem to work. I have had problems getting the wing incidence correct. My current version is off. I had do give the motor a lot of up thrust (6-7 degrees) to compensate. I'll be more carful with my next one.
 
#23
Update #2 - Fuselage (part 1)

Things are moving ahead, albeit pretty slowly. I am ok though not quite ecstatic ;) with the way the fuselage is turning out. I made a couple decisions at the start which perhaps make it a bit more complex than it needed to be.

The good news is I am still quite on target in terms of weight; the completed part of the fuselage weighs 70 grams, leaving some 100+ grams for the rest of the air frame - i.e. the tail, the gear and fuselage fairings / hatches.

For a long while I was undecided whether to glue in the power pod or use FT style removable BBQ stick mounting, in the end i decided to glue it in. With one paper layer removed and an opening for the hatch on top, the latter would make the fuselage somewhat flimsy, especially for an aerobatic plane.

One final lesson learned is: build first, draw the parts later. The opposite has its advantages, but is far more time consuming as some issues only become apparent when building, and may require redesign and redrawing of the parts.

Photos:

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#24
Update #2a

Ok so the FB wing spar joiner was definitely not sturdy enough... it was either: reinforce it with plywood, or make a new one. I opted for the latter, using 10 mm balsa and some 0.6 plywood. The FB + plywood option is equally viable though (popsicle stick reinforcement should work as well, just need to cut/sand it to fit inside the spar opening).

The wings and fuselage have now been glued together; the plane is starting to take shape :).


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Merv

Well-known member
#25
I use bamboo BQS as spars in my FT3D, 2 on top & 2 on bottom, foam webbings between them. The idea is to from an I beam. Carbon fiber arrow shaft would also work.
 
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#26
I use bamboo BQS as spars in my FT3D, 2 on top & 2 on bottom, foam webbings between them. The idea is to from an I beam. Carbon fiber arrow shaft would also work.
yeah all good and workable ideas. I am actually thinking of a project (actually probably second in line after I finish this one) where I intend to use a carbon fiber tube for spar.

My intention is to make removable wings with a square cross-section FB spar, that would fit snugly onto a carbon tube acting both as a wing joiner and major spar reinforcement for wing mid-section. Similar to how it's done in many commercial models (obviously).

My worry with this is that the foam in FB spar will compress and perhaps wear out over time (especially with frequent wing removal/attachment). Thinking of maybe pre-compressing it during build time, I think reinforcing it with either plastic tape or some other type of plastic film on the inside would also be in order.

But I am getting way ahead of myself here ;).

incidentally, I am guessing that CF arrow shafts have standardised dimensions, any idea what is the typical cross-section diameter?
 

Merv

Well-known member
#27
My intention is to make removable wings ,
any idea what is the typical cross-section diameter?
Ed form Experimental Airlines uses a lot of arrow shafts in his wings. Many are "removable", that is the wing can be folded for transport.

I'm guessing 6-7 mm, they are just a bit thicker than FB.

I have build several of his planes, I've not had any trouble with wear. My planes don't last long enough for wear to be a problem. I go through 2-3 planes a year.
 
#28
Update #2b

A little dilemma...

So I have built the fuselage sides/engine fairings (not sure what to call them, TBH). It took me 5- 6 hours to design and build these, and they turned out quite all right. It was a bit challenging, but also quite fun in all.

I actually intended for them to be optional, as they add weight (16 grams each) but also take away a little bit of wing area. So not only will they harm the plane's performance a little, but it's likely that if I use them they will actually tip the flying weight over the intended 600 gram limit.

Still with several hours invested (and being a sucker for scale looks) I am really pretty sure that I will glue them on in the end ;). So the solution I am contemplating is to finish the plane and weigh it before that (optional is optional, after all :p) then put on them as the finale of the build.

And I am thinking I am going to redesign the fuselage for the second ('production") build, so that they become an integral part and not just add-ons.

One interesting thing i discovered is that the same glue/label remover I use to peel off the paper, when applied directly to the foam, softens it making it a bit mushy to the touch but also easier to curve and bend without creasing or cracking.

I expect the rest of the build to be quite straightforward from now on, the last remaining thing to figure out is how I want to lock the front and canopy hatches, other than that - the finish line is in sight.


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