Monster sized Fock-Wulf FW-42

[rockyboy]

Wow rockyboy nice plane! Lots of carving and sanding to come.

Thanks! The dust mask is coming out soon

@wilmracer and @PsyBorg I think some blending of those ideas could work - the holes are a too large for a tic-tac box but I might be able to fashion a similar style pop lid that folds in like a cereal box top...

While that noodles around a bit more, I started on the big spackle job. Finished the rear turtle deck, both sides of the rudder, the tops of both outer wing panels, and about half of the center wing panel when my tub of spackle ran out. I wanted to switch from the DAP stuff and try out the 3M brand next (@willsonman said he was having less sandpaper clogging with it), so another trip to the hardware store tonight.

I also started on the attachment plan for the top of the nose. I cut off the piece at a nice angle at the rear, and glued part of it to the fuselage (blue clamps on the right). Then I glued on a wood scrap to the removable piece to act as a latch (yellow clamp on the left). Next I'll setup for two nylon screws to install near the front. This sets up for an easy battery replacement if that's where they need to go to balance out right.

 

[Grifflyer]

Man I've been of the forum waaaaaay too long. I just got myself caught up on your AMAZING progress!

 

[PsyBorg]

Hey Jonathan.... You haz 3d printer right?

Try making twist lock mechanisms for hatches and wings instead of nylon bolts n nuts.

Look at a set of nail clippers for that J hook pin and cut the lever short. Then All ya need is a slot for the lever to go thru and its a twist to lock things in place. Just add a pen spring and washer on the underside to keep tension.

 

[rockyboy]

Hey Jonathan.... You haz 3d printer right?

Try making twist lock mechanisms for hatches and wings instead of nylon bolts n nuts.

Look at a set of nail clippers for that J hook pin and cut the lever short. Then All ya need is a slot for the lever to go thru and its a twist to lock things in place. Just add a pen spring and washer on the underside to keep tension.

Doh!

Yeah, that would be perfect!

Why the heck didn't I think of that? Jeeze....

Anyway, now that I've got screws and nuts installed everywhere I'll keep them - but making twist lock caps on the 3d printer is now on the task list!

Thanks!

 

[rockyboy]

So today I started a little sanding of the two different spackling compounds I used for some side by side testing.

Well, not on the bottom of this wing. This was spackled only with the 3M Patch plus primer - and as you can see it is very opaque even with a thin coat. Sanding produced lots of very fine dust that was easy to blow or vacuum off.

The top of that same panel is where I had the side by side comparison of the 3M and DAP products. As you can see the DAP doesn't provide the same visual coverage, but the are really almost the same thickness and amount of material. The DAP spread on easier but required a little extra water to be added to the bucket to get it spreading right. The 3M felt draggier applying, and even adding a little water didn't really change that feeling much.
Where they are really different feeling is the sanding. The DAP dries to a weird consistence that seems like it has some rubber cement in it's heritage when it's in thick spots - it just stays a bit flexible. This could be great on drywall, but it clogs up sand paper quickly and is not fun to deal with when trying to make small fillets. The 3M sands great though - doesn't clog the paper up and comes away very quickly with a little 100 grit.

Next up is either testing out my fiberglass procedures on the bottom of the middle wing, or a whole lot more sanding on the rest of the pieces. We'll see which strikes my fancy

 

[PsyBorg]

 

[rockyboy]

Starting the fiberglass layup with one of the more difficult but more out of the way panels first. Using the Famowood Glaze Coat epoxy and 1.5 oz fiberglass. Mixed 30cc of each part and was able to get half of the panel done.

Couple hours later I got back to the house and mixed up another 30cc of each part and finished up the other half of the layup. Tomorrow it'll be time for trimming and then the top of the panel.

I also dropped the order for the motors and ESC's and props. Based on conversation with several builders and flyers at my last club meeting who have experience with both large scale builds like this, as well as big twins, which has helped me come to a few decisions. I'm going for about 75 to 80 watts per pound to get solid scale like performance, and three bladed props to get plenty of thrust at the expense of top end speed that I'm not really looking for anyway.

So I'm starting from the front of the power train with 10x6 3 blade props (plenty of ground clearance and thrust) with PowerUp 42 650kv motors. This combo should draw between 40-45 amps with 6s batteries, so I'm pairing them with 60amp ESC's. I will be running a separate receiver battery pack and not using the BEC's from the ESC's.

I've also had a lot of conversations and done a lot of reading on the issues of long battery lead wires heading to the ESCs. Bottom line - once you extend the ESC battery wires by more than a few inches over the stock length a condition is setup where current ripples.

For a horribly mangled lay person's explanation, this is how I understand and am approaching this. On the end of an ESC where the battery wires go there are a couple round can shaped electrical components known as capacitors (or surface mount capacitors on the small ones). These are there to temporarily hold extra current that's being drawn and then "sloshes forward" when the draw suddenly stops, and especially when going from high to low throttle settings. For good examples of this concept, refer to videos of "water hammer" explanations related to washing machines. The sudden opening and closing of the valves cause back pressure jumps into your water lines and unless a pressure relief valve / water hammer compensator is installed near your washing machine it will eventually do damage to your built in water lines (as well as bang really loud).

So the best thing to do is extend the wires that go from the ESC to the motor instead of the battery to ESC wires. The alternative is to add more capacitors in parallel to the battery leads and as close to the ESC as possible. There a few commercial options for this - Castle Creation's has one that's good for about an 8 inch battery extension that works by adding in 880 uF of capacitance to the circuit. I'm looking at maybe 12 - 16 inches of extra wire, so I'm going to make my own capacitor pack - and I want to have some extra head room on this.

I'll be adding (3) 1000uF of capacitors at each ESC. This will let me keep the ESC's in the nacelles where they will get plenty of cooling, and keep the batteries in the fuselage where they can be moved forward for CG without adding dead weight. So by theory, this should work just fine and keep the motors and ESC's running strong even with the longer feed wires. There are some naysayers of this approach on other forums of course, but they tend to be people speaking without having actually tried this method.

 

[foamtest]

Awesome work, I’m glad I was able to meet you finally! I’m a little disappointed that this wasn’t ready to fly however,😉 but that’s okay. Keep up he good work and hopefully we’ll meet again... at Flite Fest.

 

[rockyboy]

Awesome work, I’m glad I was able to meet you finally! I’m a little disappointed that this wasn’t ready to fly however,😉 but that’s okay. Keep up he good work and hopefully we’ll meet again... at Flite Fest.

Hey now - can't rush genius... or dementia... or whatever the heck this is

Look forward to seeing you at Flite Fest - unless Airforce Academy schedules conflict in which case we expect stories and pictures

 

[wilmracer]

I'll be interested to see your capacitor setup. I've been using the CC ones on big builds for a while but I just don't know enough about the electronic stuff to be comfortable doing a DIY setup. Good luck!

 

[rockyboy]

The power train arrived today - including the capacitors ordered from Amazon. I'm still thinking on how I want to physically arrange/hold/secure the capacitors. Perhaps a little strip of perfboard like Castle uses on their fancy ones.

Once I measured and drilled the firewalls they got glued into place - weights going on to let them cure over night, and then I'll put a little fiberglass strip around the front to really hold them in place.

So while the center section is standing up in the background with the firewalls drying, I did the figerglass layup on the bottom of the left wing panel. It went on so nicely... especially compared to working around the nacelles on the center section.

Also on the to-do list is making the cowlings. I've been re-reading some good threads on both fiberglass molding and plug pulling methods as it's new ground for me. I've got some thick balsa blocks I can use as the raw stock, so I'll be carving away on that soon.

 

[rockyboy]

When I checked on this panel I found a couple spots where the epoxy cured with a ripple because I didn't spread it thin enough. So on the top side of the wing I spent more time looking from every angle and squeezing carefully with the old gift card to get all the extra epoxy out.

So I ended up with plenty of extra epoxy in the cup to add a strip of fiberglass over the firewalls and down the sides of the nacelles

And across the tops of the servo access plates. This way the paint will have a common surface and hopefully the plates won't stick out so much.

 

[rockyboy]

Center panel top fiberglass done. This is pretty much the half way point. Just the fuselage, right wing panel, and vertical stabilizer to go.

 

[willsonman]

All great stuff. I'm glad you found success with the 3M spackle.

I messed with the in-line capacitors years ago. I recall that it was critical that the capacitors be rated as "low ESR" or low electrostatic resistance. This is to aid in the voltage being dumped as efficiently as possible without resistance... which can cause inductance and mess with the pulsing nature of the 3-phase current our brushless motors use. My Idea at the time was possibly being able to use a lower C rating on a battery pack to help cut hobby costs with higher-rated batteries. In the end it did not amount to much BUT I found that the battery I tested with did come down cooler, so it WAS doing something. I used home copper wires in parallel and soldered the caps to them. Wrapped the whole thing in electrical tape with XT60 connectors on each end. The electrical theory makes sense to me and I can see the logic behind it. I'm just not smart enough in this field to take a measurable approach and weigh the advantages and disadvantages to make a clear cut call on the matter. Worth mentioning is that I have seen the Castle solution applied a few times and those who have used it seem to like it.

 

[rockyboy]

Thanks Josh! I did make sure to source low ESR capacitors - should have mentioned that earlier. Package of 6 of these is the same cost as 50 of the regular ones

I do like the idea of using 12ga home copper wire as the primary conductor to tie the capacitors into the ESC power leads - should remove any resistance of significance from that segment of the circuit. At this point I've reached as far as my electrical theory extends with this and feel pretty confident about moving to field testing.

From a testing perspective, I'm thinking of multiple start/stop taxi runs and checking temps of the components to see if I can get it to fail on the ground first. If that looks good, I'll try slow and lazy flight for a short bit and be gentle with throttle up and throttle down. Actually I think I'll always try to be gentle on the throttle up and throttle down with this model after the initial ground testing just because I don't have a more scientific or rigorous way to tell if an ESC is stressed and ready to fail than temperature checks and looking for smoke signals. Maybe I should get some temperature telemetry sensors for this too...

 

[willsonman]

I think the only telemetry sensor that could possibly tell you anything would be a current sensor. You could test this on the bench with and without the caps in-line. You could then export the CSV file in your transmitter and create some graphs to see if there are any abnormalities in the current draw.

 

[rockyboy]

I think the only telemetry sensor that could possibly tell you anything would be a current sensor. You could test this on the bench with and without the caps in-line. You could then export the CSV file in your transmitter and create some graphs to see if there are any abnormalities in the current draw.

Do you think impending ESC failure would show up as fluctuations in current draw before the final smoke letting event (where current draw spikes because of the short)? Or are you thinking of looking for reduction of voltage and/or current spikes to show the caps are working as intended?

It sounds like a fun test to do anyway - just curious which angle might yield the clue. I think I'll want to do this test with 100uf, 200uf, and 300uf of capacitance to see what level is really needed for the length of wire I'm going to be using too...

 

[willsonman]

My hypothesis would be that you would see instability in voltage or current or spikes of some sort when throttle is applied abruptly. I would not expect any observation when applied at a slow rate. Again, the point of the caps is to take the load off the battery to account for the power surge in the extended length of the wire. Your peak voltage or current, I would expect, would be exactly the same. It's those variances that I would expect would take a hit on the battery, and possibly also on the ESC. Remember, that the incurred inductance of the wires will return back primarily to the battery so your cathode and anode are taking the brunt of trying to stabilize the current flow... not a good thing to do chemically. I do not think ANY of this will tell you much of a failure point. If you are drawing 30A... it's still 30A and your ESC should be able to handle 30A. Same with the battery. This is more about measuring a possible stress point in the electrical system that, over time (probably extended), could erode reliability. You can also expect a SLIGHT increase in efficiency since some of that stress is translated to HEAT, which is lost energy from the system. So if you eliminate the stress, it eliminates heat, and increases efficiency.

Again, this is MY hypothesis. Feel free to disagree and test. These are by no means statements of fact.

I should also note that ultimately I gave up on integration of this in any of my setups because I also thought that any increase in efficiency in the vast majority of my setups would rarely be worth anything, and the additional weight of the caps and copper would probably negate any increase in efficiency.

THAT SAID: I do think that in your particular application, some value will be far more noticeable and it may well prove worth the investigation.

 

[rockyboy]

Thank you for your thoughts on this - seriously appreciated - and I'm very likely to do some bench testing on this cause my curiosity is up

The primary reason I'm going down this path is due to the repeated horror stories of ESC's failing when the battery leads have been extended. And I don't want to put the ESC's deep in the fuselage and deal with the heat build up. And I at this point I really want to experiment and get some data and real world application of this to counter all the FUD (Fear / Uncertainty / Doubt) surrounding this subject on the other forum's threads.

 

[FoamyDM]

Rockyboy great thread and project. This talk of caps Is intersting and I am curious for a test of the discussions followed by a weight/benefit analysis. (Not sure how that would be done.) In power systems capactors are used to do two things. Stabilize spikes, and correct for voltage drop in the system.
So if nominal output is 115V at the home, it may come out the substation at 116V but hit your house at 113.5V due to system line losses. At 112V, let's say, the motors in your house and business don't operate right. So at a calculated point along the branch you put a capacitor as a rectifier and bring the voltage back up. This allows the overall substation output to be lowered. And it means as a supplier we need less energy. This is especially helpful during peak times to mitigate the high demand overage costs associated with summer and winter peak demands. In here it means less/no brown outs from voltage sags due to higher line losses during peak current as you gun it. Higher flow equals higher losses/distance. In short runs this loss is relatively negligable, bit as you lengthen that distance it shows.

I want to ad this disclaimer: while I work in the electrical engineering Dept. Of a utility, I am not an electrical engineer. And I may have it understood wrongly.

In water terms I DO understand, the caps are like water towers. They help mitigate resource shortages (pressure and flow) during peak demands.

Reading on what I wrote... I'm afraid this helps nothing but my own brain. Except serves as encouragment for @rockyboy to keep on!