Micro Sinbad

[Konrad]

The wife gave me the best present, TIME!

So I spent it giving the world a fillet!

I hope folks can see why I added the extra dorsal radius. Also notice that there isn't any crushed wood on the spine from the iron.

What I'm showing here is the first shrinkage. I like to let things stabilize over night and see how the structure and film relaxes before going on to higher heat shrinkages.

I do have more photos but I have yet to annotate them.

 

[Hank GB Z]

Merry Christmas Konrad.

The fillet looks awesome.

Hank

 

[Konrad]

Thank you!

Merry Christmas to you & yours.

 

[Konrad]

Ok some process photos of covering a film fillet.

Some key points. This process requires the use of slack, stretch and shrinkage. This is an easy enough process after one understands how to do this with the your film of choice. These micros are NOT the best to learn how to do this. Mainly because of the forces used in the stretching. I use my index finger to support the structure while stretching. This works great but does test your commitment to the hobby!

While not too critical on this fuselage I like to allow some slack when first tacking the covering to the fuselage. With out this slack it is often easy for the tabs to tear into the radius fillet.

Another important point is to bring the waste all the way over the spine and attach it to the spine on a plane ( a geometric term) that isn't likely to see heat when attaching the other side. I like to rub some CA on this waste just to add some more bond strength. Remember that this area will be under a lot of stress as you apply the other side covering!

A big hint is the use of a your feet or a set of helping hands to hold the fuselage while you pull and apply the heat.

On the subject of heat this is critical that you know the temperature at which the adhesive activates and when the film starts to shrink/stretch.

Also don't go to full shrink until the opposite side it applied. You want to be able to balance the forces on the structure.

 

[Haoyang Wang]

Also I saw this the other day. This would make an awesome small RC glider.

Yes, they are fun. For high start launch, they use the same rubber as in the rubber-powered planes. The rubber is weak but very stretchy, suitable for these delicate airframes.

Or make it into RC, and throw it off the slope while waiting for the wind to come. Float forever.

This is my Kirby Prefect, built several years ago from the kit by Easy Built Models. Rudder-elevator RC. The wings and wing struts are removeable.

With a totally unscale-like dihedral angle of 8 degrees, it turns very tight and is fun to fly. I have been thinking about building one with ailerons, so that it can turn with the scale dihedral (i.e., almost none), but haven't got around to do it.

 

[Konrad]

Is that a Guillow Edge 540 I see under the wing?

 

[Haoyang Wang]

Is that a Guillow Edge 540 I see under the wing?

Oh yeah. I built one when it just came out. While I was so proud of my Sharpie drawings, the actual flights were disappointing. Earlier this year, I had some ideas on improving the flight, so I started building the 2nd one. To my shock, while Guillow's included some nice balsa in the initial release, in the current release the woods have been back to Guillow's old quality standard. As my 2nd build progressed and the weight tallies went up, my motivation went down. The fuselage has been in the bare frame for quite a while now.

(Before the color faded, the nose was yellow and the the plane in dark blue. Try using your imagination.)

 

[Konrad]

Earlier I showed how to test with a ruler (preferably with the wife's credit card) for a smooth transition on or off the stringers. Here I'm showing this in action. I'm showing several pictures and light condition so as to minimize folks thinking there is some photography tricks at play.

What you see here is the first shrinkage with Litespan at about 115°C.

Also notice the pull tabs. One of the problems I had as a beginner to iron on film covering, was not wanting to waste any. But to iron on film properly you need a bit more overhang than what you might at first expect. This overhang allows you to pull and stretch wrinkles out of the bonding area and into (on to) the waste tabs.
So when cutting out your covering pieces give yourself enough overhang (waste)!

 

[Konrad]

More of the same. Again with these high stress covering techniques (film sliding over each other) do use another plane/surface to anchor the bottom sheet of film.
One issue I'm seeing with this micro Sinbad is that the kink in the spine is acting a bit like a spring and is moving around when attempting to shrink the covering. This instability is causing some issues with the film tension (wrinkles). To try eliminate this I've hardened the spine at the kink with some thin CA.

While I love Litespan as it has the look of tissue. It unfortunately has the same draw back as one needs to apply the adhesive and let it dry prior to moving on with the covering.

 

[Hank GB Z]

Having covered several planes in litespan I am double impressed with how well that fillet came out. Making those fillets was hard enough with So-lite.

Hank

 

[Konrad]

Thank you - @Hank GB Z

I was a bit surprised to learn that this was actually my first Litespan film fillet. And that has been close to ten years since I covered an airplane in Litespan.

What Hank is getting at is that with Litespan it is real easy to debond the covering while shrinking of stretching the film. When this happens it is often best to start again with a new sheet of covering. (Key is to not allow the hot iron near the bonding zone. But when you do have to do this keep the tension on while the adhesive cools. This is a good idea regardless of the iron on film).

I'm here laughing at myself! After all those posts about using enough overhang I made a rookie mistake on the canopy. The piece I used was only oversized by about 13mm to 25mm. As a result I couldn't pull the wrinkles away into the waste. If you look real close you can see that I pulled so hard as to start to tear the covering. Also at the nose you can see some of the effects of covering fold over. All rookie mistakes!!!

And the real killer was that because of the lack of overhange it took me over an hour to cover the hatch! This is real bad as the kit build (balsa part) should only take about 2 to 3 hours to build!

 

[Konrad]

Since I've decided to use the 2 supplied magnets as the rear hold down for the wing I need a system to hold the canopy captive. Here I'm using a dual pin 90° method. I place the canopy vertically onto the fuselage then install the wing. As the wing moves forward to seat up against the former the wing front hold down pin holds the canopy captive. This is a very convenient system when using magnetic wing hold downs. It might be a bit too fussy if using rubber bands of screws.

Now to work on the sliding block puzzle that is the installation of the stabilizer and elevator into that closed end slot.

 

[Hank GB Z]

I like the canopy hold down system. Do you have to rake the wing all the way off or just slide it back?

Hank

 

[Konrad]

Technically just slide the wing aft to clear the pin. In practical terms that is removing the wing.

 

[Haoyang Wang]

Covering polyspan / litespan over compound curves is no easy matter. So impressed on how well this has turned out. Congrats!

This is how I cover with polyspan / litespan:

1. Glue the covering to the airframe using Uhu glue stick.
2. Iron shrink it.
3. Spray on Krylon clear paint to seal the covering. These materials can be quite porous (especially polyspan) and it may take many coats of sprays (> 4?) to seal it.

 

[Konrad]

Thank you!
But I fear the camera hides a multiple of sins! Right now I have shrunk the structure at about 140°C. So I only have about 15°C before I start to damage the film. Right now on a scale of 1 to 10 I'd give myself a 7 maybe an 8 if I'm charitable. When I'm finished I'll try to show the problem spots and offer some fixes for next time.

I'll have to try the Uhu glue stick. Are there more than one formulation of Uhu glue stick? Is it a heat activated adhesive? Or do I need to apply the covering right after I've applied the glue, then allow it to dry?

Polyspan and Airspan I think were the same product, needing to be sealed. I liked sealing it, as the dope would bond to the rest of the structure and add a lot of rigidity. But like silkspan one had to be careful of gaining too much weight with the paint.

Litespan is a non-porous film that does not need to be sealed and is fuel proof. With the way I use paint it actually ends up being a lighter covering on my models. But it is not as stiff as a tissue or sealed Airspan.

 

[Konrad]

I'm sorry to say it looks like I forgot to take enough in-process photos. But I think I give enough details in this thread.

The trick to installing the stabilizer in that small a slot is to not have the elevator hinged or covered.

First I cover the fixed part of the stab top and bottom, with a large flap to be used as the elevator covering a bit later.
I then wrap one side of this covering around the stab. Install the elevator and move it aft into the pass through window. I then slide the wrapped side of the stab into the fuselage slot. Unwrap the covering and position the upper and lower flaps to go over the elevator. Position the elevator against the fixed stab and iron the top flap to the elevator keeping tension to hold the stab and elevator together. Make a good seal at the hinge line. Do this for bot left and right sides. Finish covering the top of the elevator. trim the waste.

Now the second trick. Make sure you have a large enough pass through window to allow you to flip the elevator on top of the fixed stab. With the stab and elevator laying on top of each other bring the bottom flip up and over the elevator. Iron down the exposed hinge faces. flip the elevator back into its normal position and finish covering the elevators as normal.

There you have covered, installed and hinged the stab into the fuselage.

I think this is worth the added work as the full depth rear fin post adds so much strength the the vertical fin. Without this full depth post, far too many of my vertical fins fold over as a result of my landings and general hanger rash!

 

[Konrad]

Well, I have to say that the designer looks to have captured the essence of the larger Sinbads. When I first got this kit I was a bit concerned about the loss of the tear drop wing mounting platform and how it would effect the look of the turttle deck. I also thought the longer nose would make the model look odd. But seeing the micro Sinbad all fleshed out I'm impressed at how good the micro SInbad looks.

Now for the hard part of the build, any build, that is system intigration (radio installation)!

Well, I'm now in a state of depression! As shown my micro SInbad is coming in at 44 grams, and that is without the battery or push rods!

Earlier @Red said these came in at 2oz. In modern units of measure I take that to mean about 56 grams. But watching some of the earlier linked to videos I heard the builder say that his "airframe" came in at 44 grams. He said that while showing an aircraft ready to fly.

I hope his AUW wasn't 44g ready to fly. But rather that his weight of 44 grams was for the airframe minuse the radio and balancing weight. If the weight of 44grams was of just the balsa and covering then I'm still in the running as my "airframe" is coming in at 38 grams without the radio and stuff.

 

[Haoyang Wang]

So each side (up side and down side) of the stabilizer and elevators is covered in one piece as a whole? Wow.

Single color is the most unforgiving, as you cannot hide seams under another piece of covering. It looks like this litespan blends well at the seams.

When you cover the top side, do you have to leave a small gap at the hinge, to make sure the elevator can freely go down? Maybe do the down side (folded) first, followed by the top side (flat)?

Uhu glue sticks can be clear or color-tinted, but I think they are all the same. Just glue it and wait till dry.

 

[Konrad]

I bevel both the elevator and fixed stab 8° to 10° to allow for surface movement. When covering I pull the stab and elevator as tight as possible. When done with the covering of the stab assembly the elevator will pop up in the free state. I then come back and with the elevator pulled down I re-heat the hinge line. I keep the elevator down until it cools. This seems to take off much of the strain on the hinge. (Note it is because of hinge forces that I like the larger servos).

Yes as to the single piece, but with a split to allow for the rudder.

You are too kind about the seam hiding. You can see I was a bit sloppy with the wing top pieces at the center line. (Way too large an over lap and off center).

Note: with a smaller elevator I'd use more of an angle. But with this large an oversized stab and elevator and that some set ups are stating to cut way down on the elevator movement. I kept the bevels shallow to keep as much material as I could in the elevator coupler.