Micro Sinbad

[Konrad]

Yikes, per Solarfilm the nominal weight of Litespan is 30g/m^2 and SoLite is 22g/m^2 so for about one sheet of covering I'm suffering a weight penalty of about 3.7 grams! I knew that but really like the look and ease of use of the Litespan.

With my 150 mAh 45C battery my weight looks to be coming in at 49g. With the pushrods and stuff I'll be lucky if I'm coming in under 50g!

Well with the lessons learned with this kit I might have to get a modern one cut by Aloft and try again. I'll finish this one with the knowledge that this isn't the bee's knees I was hoping for!

 

[Hank GB Z]

I think you should call it the bees knees.

Looking forward to test flights.

Hank

 

[Konrad]

Because of the orange pollen sacs!

 

[Konrad]

I hate being greeted by a process failure!
Here the paint has migrated under the covering. I should have sealed the edges with more balsaloc prior to painting. Now I need to look for some orange paint. But it will never look correct!

On the subject of processes, tooling is very important.
Elsewhere on the Net, we can see crushed balsa wood from the attempts at applying the iron on covering. You see this particularly in the thin areas like the trailing edge and center line spines.

On the micro Sinbad the spine to vertical fin radius is fraught with danger. Any discontinuity in that curve will propagate through out most of the turtle deck.

The key to avoid this is not to fall into the trap of using more pressure to attach the covering. But along with that, is to not use tools with a well defined edge.

My fillet radius was done using a large 21st Century iron. The key to this iron is that it has a lot of radii along the shoe. A narrow nose and the edge is away from the main surface of the shoe. This means that I'm not likely to crush the balsa fibers with that edge when manipulating the covering for that difficult fin to fuselage junction!

Now I do own and at times use trim irons. But I try to avoid then as they (the shoe) lack thermal mass. They tend to cool down as soon as the shoe hits the covering. If I compensate for this with higher heat I tend to burn many of the lower heat covering before getting them to bond to the balsa.

All the covering work on this micro Sinbad was done with a full size iron.

 

[Konrad]

Just messing around. How does aero tow sound?

 

[Hank GB Z]

Hey Konrad. The bleed under the covering doesn’t look to bad. Maybe just blend it into an anti glare Matt black patch like on a WWII fighter.

I like the aero tow idea.

Hank

 

[Konrad]

Hum, I like that! I'll keep that anti glare panel as a back up plan.

 

[Hawaii Sloper]

I hate being greeted by a process failure!
Here the paint has migrated under the covering. I should have sealed the edges with more balsaloc prior to painting. Now I need to look for some orange paint. But it will never look correct!

Ahh Konrad, you have that monkey on your back whose name is perfectionism! Most people will just enjoy this model when they see it. Nice job. I share that same burden but am learning to avoid it when it doesn't matter. It's a Beast!! LoL

 

[Konrad]

LOL
My models are far from perfect or even extraordinary builds.

My build threads might appear to be striving for perfection, and I am. But I'm showing details of problem areas I have with the product. Not to just complain, but to show these to aid future builders with what I hope are workable solutions.

This build was focused more on building process in an attempt to elevate these micro builds just a bit. Mainly to show how will the structure perform when covering.

I like to put some emphasis on my mistakes. I do this so that beginners know that even guys with 50 year experience make mistakes. And to show that most mistakes don't spell doom for the project. I recall one of my students having a light bulb moment when he said; It wasn't that I don't make mistakes. It is that I know how to fix most of them.

Please believe me when I say I'm enjoying the build. A lot of this is because of the added features/effort I'm adding to this model. Such as the on off covering ramps for the spar. I also point to the fact that the wife thinks I'm nuts with me running around the house making swooshing noises. (I claim I'm training the parts to fly in close formation)

Now with that having been said, I'm a bit concerned with my build. The fact that I've lost around 3 grams in the tail and lightened the canopy blocks I'm still going to have problems meeting the weight call out of 56 grams! I'm actually a bit shocked when I read that folks have had these come in at 44g and 48g with the sheeted tails and in flying trim. My choice of covering might add 3 to 6 grams. I can't see my modification to the wing hold down is adding 10grams!

Happy New Year!,

 

[Konrad]

Who knew that glue has a shelf life? This tube of RC-56 is over 10 years old. I was surprised that it was even semi liquid. It actually looked like cottage cheese. Now a sane person would have thrown it out. But as I don't have a real local hobby shop and I didn't want to spend all day in the fabric stores looking for this glue under another name. I talked myself into thinking it will work. Well, it bonded fine, but it did not flow. Or to put it mildly it looked gross!

So to hide the glue line I wrapped some covering to act as coaming. Not my best work but it is a lot better than it looked earlier in the morning. Also I was able to use this coaming to hide the paint repair for the black paint that had gotten under the covering. I'll need to paint the vertical glue lines with some black paint, but that's for another day.

 

[Konrad]

As you might know I don't subscribe to the notion that if it looks right it will fly right. That might fly for an artistic designer but as a design engineer that's a no go!
My creed is form FOLLOWS function not the other way around. To that end system integration is key to a good flying model.

With this micro Sinbad I've deviated from the designer's intended radio system. This design was drawn to use a "brick" with 2 linear servo. I've chosen to use 2 rotary 2.2 gram servos and a discreet RX. As a result I've had to make major changes to the servo mounting and push rod routing. While these are my changes, I think much of this can be applied to the as designed configuration. Key to all this is servo resolution. If you need to cut down on the servo motion in the radio to less than 80% it is time to reassess the linkage geometry.

To start the radio installation I set my servo arm to be as short as I think practical. I have to clear the servo output shaft. Here I've drilled a 0.026" hole in my servo arm at 5.5mm. (The OEM servo arm holes are 0.04" which are way too large for a micro)

Next is to choose a control horn that is long enough to allow the anticipated motion. Here I'm using a 6.5mm rudder horn and an 11.5mm elevator horn. These horn lengths will dictate where the push rod exits will be.

I use the push rod cross over method to try to get as straight a push rod run as practical. Since this means the push rods will cross they need to be on different planes (geometric term) so as to not rub. (Rubbing causes cross talk and centering problems) Make sure the push rods run free. This is why my rudder pushrod is above the servo arm as it exits the fuselage above the elevator push rod. (This is a function of the control horn length).

I think the plans call out 0.020 music wire as the push rods. I find these too flexible for my liking without the use of a Bowden tube. So I'm using 1mm carbon push rods for the added stiffness, control response. I use 0.025 music wire to make my "Z" bent ends. To attach these Z ends to the carbon push rod I use small heat shrink tubing. This affords me the needed adjustment if needed as I can slide the ends along the push rod. Once the plane is in trim I can lock the Z bend onto the push rod with a small drop of thin CA glue.

Now making this type of push rod is dangerous in that the heat to shrink the tubing can damage the iron on covering. I find that some aluminum foil makes a great heat shield. Just make sure there aren't any large holes to allow heat to burn the covering when applying the heat gun.

 

[Hank GB Z]

Hey Konrad,

What FrSky Rx is that you’re using? And what protocol does it run?

Thanks,

Hank

 

[Konrad]

It is the dated VD5M. I think it runs on V8 and D mode. It is an indoor RX. Not sure I want to use it with the micro Sinbad as I like to make long runs along the ridge top. Also I need to find the Male to Male jumper plug to set the bind protocol.

 

[Wayne]

Shame for not cleaning up those servo arms.. LOL Every time I trim a servo arm I sand a radius onto the end and I always ask myself why in the world am I doing this?

 

[Konrad]

I see I've failed to mention rudder hinging. Because of the way I cover the fuselage and vertical fin I find it isn' practical to use a film/covering hinge. Here I'm using a floppy disk as the hinge material. I strip of the black with some acetone. I cut a narrow strip to become the flexible hinge. Make 4 slots in the hinge line and insert the floppy disk material. A very small drop of CA on each hinge and the rudder should be attached just fine.

This brings the build of the Aloft micro Sinbad to a close. All I have to do is come up with a battery harness. Well, actually I want to come up with a more modern RX. So this project will have to wait until I have a chance to go up north after the rains.

So before I put this in the back of the closest is there anything anyone would like me to go over with the build?

Some spec's are that as is the weight is at 51.5 oz, uh sorry grams. CG is showing to be 45mm aft of the LE. So it looks like I only have 4 grams of weight to play with before my build is considered over weight. I'm still trying to figure out how come I'm 1.25 times heavier than some of the published weights?

 

[Konrad]

Shame for not cleaning up those servo arms.. LOL Every time I trim a servo arm I sand a radius onto the end and I always ask myself why in the world am I doing this?

Actually that is something I save for after the maiden flight. It allows me to change servo arm sides as a function of the odd spline count. I try to set my push rods to be at 90° to the servo arm with the control surface in center trim. Also the extra length might come in handy should I need to drill another hole to make the arm longer.

I wonder if those long servo arms are where those 10 grams are hiding?

 

[Hank GB Z]

Looks great! I am really looking forward to flight reports. Thanks for the info on the Rx. Don’t worry about the weight. You’re still under the 2oz upper limit written on the manual.

Hank

 

[Konrad]

Barely under the 2 oz call out! I took out a lot of mass out of the rear I thinned the canopy blocks and still I'm heavy! CG is way aft. I read that Jensen added 8 grams to balance. The video is using a 500mAh cell to balance. Gravity must be strong in my home! My scale is acurate to 10 mill grams.

I actually like this build (it is one of the more advanced Aloft micros) that I'm thinking of getting a new one from Aloft. The second time around I think I'll stay with the designed radio configuration and use so-lite as the covering.

 

[Red]

Mine flies at 51g. I used a brick, 130mAh cell and Parklite covering. No hinges (used covering) and built exactly as supplied. Wood density plays a big role in final weight, that might have something to do with it. I wouldn't fret though, a few extra grams won't make a large difference, the wing loading is very light regardless. They are best for early mornings when the wind is just starting to ruffle. Yours will probably penetrate a bit better. They can actually be too light.

Red

 

[Konrad]

Thanks!

The wood in your kit (my kit) was actually pretty good, not contest but good. I did use a heavy covering 30g/m^2. But I'd have thought that loosing 3 grams out of the tail would have compensated. Obviously not! (Actually was surprissed that litespan was so heavy).

I think this should be a warning to others to watch the covering weight. Not only can't the structure handle the stress of the usual shrinkage of the heavier coverings. But that the added nose weight will drive the model to being close to 150% or more over weight. I'm at 51.5g with the CG very far aft at 45mm.
My battery is a 150mAh rated at 45c @ 4.51 grams. But with the aft CG, looking at the battery for weight loss is not the right place to look.

It was a fun build that I think it is worth a do over!

All the best,
Konrad

P.S.
Parklite is advertized at 36g/m^2. If true then my mass problem isn't in the covering.