|Nov 16, 2013, 01:52 PM|
Siai Marchetti SF260 depron
I started a build log of this indoor model in my blog:
|Nov 23, 2013, 01:14 PM|
Continuing my build log in this thread, blog is too isolated :-)
Been wrexking my brain over how i can stiffen the fuselage without adding too much weight.
So I started coloring the tail :-)
Made a precise cutout for motor and mount in the nose. Added extra layers of depron to stiifen it:
Next up are the wings. Decided to keep the sandwich wings, but then I needed something to tackle the slight torsion in one of them.
So I drew the incidence line, made a notch cutout in the extra depron layer if the nose for the leading edge, and inserted a piece of carbon across the fuse, to fix the trailing edge in place:
First trial fit shows success:
Holding everything against the light shows the construction: below is the main spar, held in the plywood box that will be glued to the fuselage. Still missing in this picture are the depron formers that will go in the still open slots next to the ply box.
In the top part of the image, the carbon poece to hold the trailing edge in place:
It feels very strong and solid, I'm happy with this result.
It even starts to look like a Marchetti:
Only problem remaining to be tackled, is the stiffening of the fuselage between horizontal stab and wing, and where to put the elevator servo.
|Nov 24, 2013, 03:55 AM|
Fuse + wings + motor comes to 86 grams now.
ESC and standard receiver come to 27 grams, i have a micro 4 channel receiver ordered, but I could get rid of the casing of the standard receiver too.
Still to be added to that weight: elevator servo: 8g, prop saver and prop : 10 gram.
I have a 3S 850 mAh Lipo, but it weighs 65 gram. I have to calculate with which 2S I could work here.
Still learning, this is my very first indoor model and scratch build....
|Nov 24, 2013, 01:01 PM|
A bit of progress today.
I chose to add horizontal fuselage parts between the wing trailing edge and the horizontal stab.
I also glued in the formers that will hold the wing and the ply wing box:
When the glue set, it was time to focus on the horizontal stab, and cut out the elevators:
I chose to use the same solution as on my F-22 for hinging the elevators: scrap pieces of blister packaging material. Just cut a couple of rectangular pieces, cut slots in the elevator, and glue the 'hinges' in:
Cut out slots in the stab, and insert the elevator, and we have a clean and light hinge:
I still have to find a good and light solution to connect both elevators to the single servo, to get them to move rigidly together.
Next up are the horizontal fuselage parts on top and forward of the wing, and then we can start placing the electronics.
|Nov 25, 2013, 01:58 AM|
Forgot to mention, did a first estimate on wing loading yesterday evening.
The total weight will be slightly over 200 gram, giving me a wing loading of 23 g/dm2. I think it should be feasible to fly that indoor....
Test ran the engine with a 7x4 prop, and it has plenty power on 3S, should be still good on 2S (but I have none available for the time being). On 3S it has plenty thrust at half throttle.
|Nov 25, 2013, 04:21 PM|
Glued all stiffeners to fuselage, so now it's time for the final stretch.
Been straining the brain again over the elevators.
I first considered a double pushrod, but that would cost me more weight.
I just experimented with connecting both elevators with a short piece of wire:
Don't know yet if this will be firm enough....
Weight and balance are looking quite good, I still have margin enough for a rudder servo, which I might need considering the relatively small ailerons.
|Nov 26, 2013, 02:44 PM|
The wing area is 8,8 dm2.
An experienced indoor rc pilot gave me some great info today, but for my model it's bad news. If I want to follow his good advice, i need to almost halve the weight!
So i've been looking for area's of improvement without too much rebuilding.
1. Instead of my 65g 3S850 battery, I can use a 2S 200 battery, saving me over 40g.
2. If i remove the case of the receiver, I save 8,5g
3. Instead of 2 aileron servo's, I could do with just one. Saving me a 6g servo and a couple of gram in wire. It would also allow me to make the ailerons full span, dramatically shortening the control rods in the process.
4. An alternative motor could save me almost 20g. I need to investigate if it is powerful enough for this model.
With all of these changes I should be able to make this a real indoor model.
|Nov 27, 2013, 03:37 PM|
Took the plunge today and changed the ailerons.
If you look at how they were, it seems really that they are too small:
I drew the outline of the new ailerons, and took a deep breath
Then I cut out a place for the single aileron servo:
I made the new ailerons out of two layers of depron, separated by the small strip I cut from the underside part:
I didn't have more time today, so one last pic to take a new look of the x-th version of my model:
Only 2 servo's left now...
The rest is for tomorrow.
|Nov 30, 2013, 01:10 PM|
Continuous health problems prevented me from making a lot of progress lately, but nevertheless I found a solution for the ailerons.
I tried several setups, but I finally ended up with a single servo, dual pushrod solution that provided my with satisfactory symmetrical aileron deflections:
I bended the pushrods slightly to prevent constant servo binding:
The dual elevator is another thing that has been causing me headaches. How to control two control surfaces without adding too much weight.
Again, I tried different setups, but I settled for connecting both elevator halves via a carbon rod:
This rod passes right through the control horn:
I then glued the rod into a trench I cut in the elevator surface, and a couple of clamps ensure alignment of bothe halves while the glue sets:
The position of the servo will be determined by the cg (or rather, the other way around)
I don't think I will be able to fly tomorrow, even though this model is nearing completion.
|Dec 01, 2013, 11:01 AM|
Finished building today, but I'm not happy.
Total weight is 170g, giving me a final wing loading of 18 g/dm2, which is still way too high for indoor flying.
The motor is just too heavy, and the model is overpowered. If I want to fly it high alpha, this should be great, but I'd rather fly it a bit more scale, so I need to go back to the drawing board.
So I ordered a 1811 motor today, which should give me 140g of thrust, and when combined with a 6A esc and a 2s 200 battery should get me to about a little less than 130g, and 6 minutes of flying time.
It was either that, or make the first Marchetti biplane ever... :-)
But as I already experienced, final weight will have to be determined when I get all the parts together.
Meanwhile I couldn't resist enjoying the view of the finished model:
|Dec 03, 2013, 02:20 PM|
Received the new parts today, and couldn't wait to install them.
1811 motor, 7x4 prop, 10A ESC, 2S200 battery, charging as I write this, but a first motor test felt like it had enough thrust to finally get this bird in the air.
On to the next project!
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