Progressing on our heater story – did a longer test which clearly demonstrated that we don’t have enough power. Simply running a heater for 220V on 60V is not giving enough umpf.
So Serge stepped in and proposed coming back to the plan A – 220V. However first things first little bit of additional grinding was needed. I took a cool video of Serge handling that.
Next stage was to refurbish our heater by rewiring it to 220V.
Quick test revealed that all is working happily. Actually we’ve hit 160C in under 5 minutes.
Wrapped whole tube in Kapton to protect it a bit before inserting it in the external tube.
We carried on with doing a test by using a simple wrapping with 50% overlap, followed by heating it up to 140C and letting it cool down.
Tube extraction was easy and we ended up with pretty nice prototype.
While weighing ~80g it is looking perfect, however I am not convinced about its stiffness as as per my estimates two of these tubes needs to be able to carry a whole gondola.
Anyway, weekend’s goal achieved and it’s a promising start to finally start getting some good progress again!
Finally huge thanks to Serge for his never-ending support!
Having a major success with our BIG tubes, we decided that we’ll prepare tubes for a whole frame. While Serge inclined to use our current technology for the rest, I already had a plan to repeat our production process and get some light and awesome ~25mm ones.
When planning ahead, in February 2023 I reached to Vilem and he checked for us on Aluminum tubes available through his sources. Following options came up:
.. then situation somehow changed and apparently we ended up with these:
The idea here is that we’ll use an inner tube with a heater rod to expand another (external tube), which will be used as a mould for our CF tape, so we have an option to contract it and extract the tube after curing. Vili sourced tubes in a perfect condition.
They are awesome! Thank you Vildo!!!
Then I asked Serge to help us with cutting the external one.
Excellent job Serge, as always. A tiny test shown how cool it is.
Well, that inner tube sit in there too well! Testing this with Serge, he mentioned that once we’ll wrap it with CF, friction will be so high that we won’t be able to pull it out. That would be a not good at all. Checking what’s going on I reached to the Engineering ToolBox – (Resources, Tools and Basic Information for Engineering and Design of Technical Applications) and Serge was right!
The value 1 here is pretty bad (e.g. teflon on teflon is 0.04) – it actually is one of the worst values in that table! Apparently this is because Aluminum surface oxidises very rapidly under the atmospheric conditions, and Al2O3 has quite different properties from elemental Aluminum.
Anyway, there are thoughts how to solve this, but that’s for another day. Let’s move to our new … heater! Serge came with an awesome idea to use a Stove Cooktop Burner Element – straighten it and use it as substitute for our heating coil.
Serge did an excellent job and we ended up with this (first picture next to our Alu tubes):
Running ideas on how to actually use it through Richard, while he raised more then few exclamation marks on connecting this straight into 240V mains.
Crunching this for a while I picked a safe way to use our welder again to power this contraption. Testing it clearly shown that Risa’s worries were well in place.
One last question remained – how to keep our heating rod straight in a middle of our inner tube. Brainstorming it with Serge he suggested some high-temperature silicon. Google then came with JB Weld Muffler Seal, 340g from Super Cheap Auto, which apparently withstand temperatures up to 850F (450C) which we assumed to be enough to do the job.
So we ended up applying this muffler cement in rings on the rod, hoping this will do the job.
Finally we couldn’t resist and connected our welder to see what happens and ended up reaching nice 94C while running it on a lowest settings for about 5 minutes.
We’ve run out of time to wait for cement to cure properly, so a proper test will have to wait for another day. Anyway whole this exercise actually worked out well so I am positive this will do the job and we’ll see some tube prototypes in next few days. Stay tuned!
So we are now trying to build envelope coming with shape around something like this:
As you may see it is quite simple concept of joining two ellipsoids with interlaced cylinder reaching maximum diameter of 2m. So the front part is traditional ellipsoid with w=2.5 (A), followed by a central cylinder w=1 (B), closed by another ellipsoid of w=3 (C). The plan is to buckle in the ellipsoid A so it will all end up being ~6m long.
The idea is to do a 5:1 scaled model and send it to Windreiter guys for review and a quote. To be able to do so, we actually need to draw parts which we can glue together next. Here we’ll be using classical pie/rugby-ball seems method, hoping that it will all work out when inflated.
Having a radius of 1m, maximum circumference comes to 6.28.
C=2πr=2·π·1≈6.28319
Divided by 6 to get height of each part we are getting h=1m. Scaling down 5:1 this is 20cm + 2cm for seem we have the first parameter 22cm.
With the W – part A this is going to be half-ellipse of -> 52cm (scaled 2.5m/5 + 2cm for seems), part B is a simple cylinder of 20cm and part C is -> 62cm (scaled 3m/5 + 2cm for seems).
To get this transformed this onto a paper, I prepared myself a tiny Excell helper (with another help from here). Where X is calculated with =B$2*COS(RADIANS($A5)) and Y =B$1*SIN(RADIANS($A5)).
Ellipse A:
H
22.00
W
52.00
a
x
y
0
52.00
0.00
10
51.21
3.82
20
48.86
7.52
30
45.03
11.00
40
39.83
14.14
50
33.42
16.85
60
26.00
19.05
70
17.79
20.67
80
9.03
21.67
90
0.00
22.00
100
-9.03
21.67
110
-17.79
20.67
120
-26.00
19.05
130
-33.42
16.85
140
-39.83
14.14
150
-45.03
11.00
160
-48.86
7.52
170
-51.21
3.82
180
-52.00
0.00
190
-51.21
-3.82
200
-48.86
-7.52
210
-45.03
-11.00
220
-39.83
-14.14
230
-33.42
-16.85
240
-26.00
-19.05
250
-17.79
-20.67
260
-9.03
-21.67
270
0.00
-22.00
280
9.03
-21.67
290
17.79
-20.67
300
26.00
-19.05
310
33.42
-16.85
320
39.83
-14.14
330
45.03
-11.00
340
48.86
-7.52
350
51.21
-3.82
360
52.00
0.00
Ellipse B:
H
22.00
W
62.00
a
x
y
0
62.00
0.00
10
61.06
3.82
20
58.26
7.52
30
53.69
11.00
40
47.49
14.14
50
39.85
16.85
60
31.00
19.05
70
21.21
20.67
80
10.77
21.67
90
0.00
22.00
100
-10.77
21.67
110
-21.21
20.67
120
-31.00
19.05
130
-39.85
16.85
140
-47.49
14.14
150
-53.69
11.00
160
-58.26
7.52
170
-61.06
3.82
180
-62.00
0.00
190
-61.06
-3.82
200
-58.26
-7.52
210
-53.69
-11.00
220
-47.49
-14.14
230
-39.85
-16.85
240
-31.00
-19.05
250
-21.21
-20.67
260
-10.77
-21.67
270
0.00
-22.00
280
10.77
-21.67
290
21.21
-20.67
300
31.00
-19.05
310
39.85
-16.85
320
47.49
-14.14
330
53.69
-11.00
340
58.26
-7.52
350
61.06
-3.82
360
62.00
0.00
Of course we’ll use just a part of those ellipses getting:
As per our last post we ended up with some kind of mysterious power gain. Having few ideas we’ve been able to rule out all at the point when Richard clearly stated that it is the Venturi effect!
So what’s the Venturi effect again?
The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section (or choke) of a pipe. The Venturi effect is named after its discoverer, the 18th-century Italian physicist Giovanni Battista Venturi.
As you can see, it pretty much correlates with what we are experiencing. Input velocity is same, but output one is higher. Well, now how to test this. Richard stated that there is no way to gain whatever energy out of nowhere so with higher velocities we should be also seen higher power demand. And the easiest way to do so is to monitor the input Wattage.
Then we rebuilt our testing setup, plugging our new power meter in front of our 2kW PSU. Running on idle power meter clearly indicated constant consumption ~8W.
Oli and Sam helped with testing where they were checking on highest measured value. I prepared everything to repeat our tests on EDF only, 1m PU tube and our new 6m CF tube. Also received new set of propellers from Chris and I was hoping to duplicate same test on those, but hit some problems there so I don’t have video of guys measuring and following form is just half-filled, waiting for another opportunity.
Measurements above clearly shows that with higher speeds power consumption was clearly growing. Where we were getting very much 20% gain on the wind speed (17.26m/s -> 20.65m/2), our power requirements were also growing – making it 14% higher power input.
I suppose that this concludes it for now, mystery solved a now to back to building our airship again! 🙂
Of of the main concerns with our new tubes is how they will perform as a duct. Having just our original duct the only way to get any clue was to compare those against each other. How ridiculous it may sound, while different lengths (1m and ~6m) – both tubes still share one essential parameter the inner diameter 60mm.
There is also EDF from our jet-cart project, which can be transferred around and we can use it for comparison together with our old friends – 2kW PSU and high-speed Anemometer.
Test #1
Asking Seb to assist we did a test with original tube first.
As you can see, we removed the vector thruster for now and measured peak at 16.84 m/s.
Test #2
Setting up our new [6m] tube took little bit longer, some cutting and some taping was needed.
Being little bit worried about all that contraption not flying away we did a tiny test run.
All good, now ready to roll.
Well and that is where became quite surprised. As you can see, peak came up to 20.32 m/s! That’s quite a different value to our original measurement of 16.84 m/s. Having same tube diameter, EDF, and power levels – I am more then happy to see 20% power increase, but it also horrifies me that goes completely against our assumptions (expected was 20 – 40% decrease).
I assume that using the Watt-meter might tell us if the higher output observed correlates with higher power consumption, or if we’ve been really somehow able to increase a tube performance. No idea what sort of physics might be behind it, unless tube getting seriously heated by Queensland’s sun.
Craiyon’s vision of “power of the sun heating a carbon fibre tube”
Thinking about mechanics of our airship’s keel it is actually one of the most trivial tasks to solve. We’ll be looking to calculate reactions, shear force and bending moment here and then to test it.
Our use-case takes in account our 6-meter-long beam, having two supports in its thirds, where traversing beams will be joined to hold our gondola. Gondola weight is assumed to be ~10kg (100N) and we’ll multiply it by safety factor of 3 getting 300N. Let’s divide this value by four – number of joints – getting 75N per support. To be able to solve this in some easy way, we need to double this value getting nice 150N force in a middle.
So let’s go with bit of theoretical calculations on this first. The easiest way to do this these days is to use e.g. Free Online Beam Calculator, which I like a lot as it is making this task trivial.
Reactions
Support at
X
Y
Mx
2
0 kN
0.075 kN
0 kN-m
4
0 kN
0.075 kN
0 kN-m
Force Extremes
Result
Max
Min
Bending Moment
0.075 kN-m
0 kN-m
Shear
0.075 kN
-0.075 kN
Displacement
0.037 mm
-0.013 mm
Nothing too much to see yet, so let’s have a look at bending moment and sheer forces
The last one is the deflection, which (if we would provide actual tube properties) would finally provide us with a some actual values to test for. Graph below uses Young’s Modulus (E) 200000 MPa, which is clearly too high for our use-case, but as we don’t have any good value here we’ll be using it for demonstration.
Location (m)
Total Deflection (mm)
Span
0
0.037 mm
L/53333
2
0 mm
–
3
0.013 mm
–
4
0 mm
–
6
0.037 mm
L/53333
Now to our actual testing – two chairs serve as a support there, supporting our tube in its thirds. Pillows and cloth in the middle serves to distribute forces bit around so those are not “too pointy”. Below you can see a set of weights totaling 15kg provided by Andrew.
Tube #1 (950g)
Long story short all holding! A minor tube bending’s been noticed, but overall whole tube seemed to be very firm and stable.
Tube #2 (850g)
Again – all holding! 15kg load and tube seems to be stable. Even on the final picture you can’t see any bending whatsoever there.
As you can see Jan being happy – whole this exercise ended up with a huge success, making whole team confident that our tubes will perform well with a 3-fold safety margin.
As always, ping us back with whatever comments and congratulations to the whole team for excellent work!
Just a quick post to announce that our new baby (CF tube to serve as a main duct for our drone) comes out being 6.10m long and weighing just 956 grams only!
Working on our “tubes” project at some stage someone (I think it was Byron) mentioned the “Fail fast, fail often” mantra. Well, the last weekend ended up following this slogan to the last bit! Still, preparing for this post it came to me checking on what it actually means and ended up reading few articles on this.
“Fail fast, fail often,” as a mantra has seen some success. SpaceX comes to mind. But “fail fast, fail often” has been around for years. Thomas Edison, by example, “failed” 9,000 times before he was successful with his light bulb invention.
I picked the quote above as it resonated with me well – we failed too many times over the weekend! 😀
Plan B (Friday)
Based on our a new plan (see the end of our previous article) Serge and I tested 150C curing with single CF strip – two wraps, to check if we’ll be able to take it away when mold cools down.
Gloves ready!
We ended up preparing 20g of resin mixture (4g harderner + 16g resin).
All resin work started going much faster now when we know what to do. Demolding spray -> CF bath -> wrap -> white tape -> office tape. 15 minutes later all ready to heat up.
Keeping it for 20 minutes at 150C and wrapped seemed enough for our purpose so we let it cool down and unwrapped it.
Anyway, even cooling it down under water and using ice didn’t help and we needed to cut the tube to remove it from the mold again. There were not even signs that it would go off peacefully. Serge then used leftover resin to glue it in a tube again and we left it overnight to cure as is.
That did actually pretty well and we were able to see some mechanical stability being demonstrated for a first time.
Plan B+ (Saturday)
Before moving to a Plan C (splitting the tube) the idea came in that our demoulding spray might not be the best for our use case, so decided to re-run Plan B with our original TR mold release wax.
Eight layers applied
Eight layers later – tube mold looked like coming straight from Madame Tussauds museum. Serge needed to leave so Seb stepped in as the main assistant.
He seemed to actually have some good fun about it.
.. but it failed again. Even with X layers of mould-release wax – all still the same, it won’t release and we ended up cutting it again.
Plan C (Sunday)
Becoming reasonably desperate, I decided to go with the Plan C – cutting the tube. Not having Serge around to come with some better idea and being pretty upset after all those set-backs, it actually felt pretty relaxing to start manually splitting that two meter-long tube in half (Chris’s idea of split tubes modified by me to be doable in our environment).
It took one hour to chew through that pipe. It was far from being perfect, but also could look worse. Using caliper it was clear that there are probably 2-4 mm missing now on circumference, while those two halves flexed nicely.
I also prepare a jig to keep those halves split away to get additional gap which can be used afterwards to assist another demoulding attempt.
We used Kapton tape to bridge the gap on tube and Seb helped with another wrapping & heating round.
… and after all those failures, we finally had a nice tube. Short one, with imperfections, but it was a tube!
Plan C+ (Sunday night)
Finally seeing a way forward we instantly started preparing to demonstrate how to manufacture longer tube and took this opportunity to show how tube joining will work as well. Seeing how our mold flexes on longer distance, I decided to prepare new spacer which will fit between those halves.
We have that tube preparation already pretty much mastered and stopping in a middle and joining afterwards didn’t seem to be a big deal.
Seb then removed spacer-rods and after bit of wrestling – it worked out!
Final tube came out being roughly 65cm long and weighing 74 grams, which still fits into our plan.
I tried to demonstrate its stiffness on following video.
As you can see, that worked out very well! As always there are few things to improve, but there is a good potential that we’ll be really able to produce some decent tubes here!
Thanks for reading and don’t forget to leave us your comments & ideas as always!
We couldn’t resist with Serge and did another session to release the tube of the mandrel. Following the plan we started with filling the tube with ice to check if it’s going to do the job.
It is not that obvious on those pictures above, but it seems to be cracking, it did nothing.
We’ve resented to the plan B – using a brute force and cut it off.
It didn’t go well and took us probably 10 minutes to do so and while we made it, our Aluminium tube suffered some serious scratches.
On the other hand, holding our first tube attempt was pretty satisfying and it clearly has some parameters we are looking for. We agreed that if we’ll be able to take it off the mold properly, it is likely that it’s going to do the job.
Anyway, it was time to check at least some parameters.
As you can see on pictures above, we ended up very close to producing one meter tube weighing 135g. When we take weight of CF tape used ~ 94g it comes with 70:30 CF to resin ratio – which is apparently very good. Next stage would be vacuum bagging where it is possible to reach 75:25, still very close!
In preparation for our next stage we made another trip to ACME Composites and finally got our Resin and HTG Hardener.
Thinking about how to get ready for another go, we formed a new plan:
1/ Test 150C curing with single CF strip – two wraps and check if we’ll be able to take it away when mold cools down
2/ If it won’t we’ll use ice
3/ If it’s going to work out we’ll continue and will try to do 30 cm strip keeping enough tape to potentially continue
4/ Assuming that 3/ worked out – we’ll try to continue and do another 30 cm and so on
5/ In case we won’t be able to continue, or that joint won’t work we’ll cut it of and do another – separate 30cm tube and try to join them together with overlap
6/ If everything fails we have a plan B – Chris came with a plan to split our tube in half to create a gap or space which could be used to release the tube when curing finished
Going through our latest obstacle – releasing our CF tube off the Aluminium mandrel – it made me to do some thinking and recap some calculations on what should we actually expect in this field.
So let’s start with Wikipedia again – Aluminium’s Thermal expansion coefficient (CTE) (α) comes as 23.1 ×10-6/°C
All credits to Wikipedia!
Now, our Al tube comes with 60mm in diameter, which makes our initial circumference of 3.14 * 60 -> 188.4 mm.
Case #1: ΔT – 40C
Our initial test was reaching max 70 C for 90 minutes. While starting on beautiful Queensland summer’s 30 C, that makes our total temperature change (ΔT) of 40C. Using our tube’s diameter, AL CTE and delta we get the circumference change.
188.4×0.0000231×40 -> additional 0.1740816 mm (174 μm) to our original circumference value
Going back to our diameter
188.5740816÷3.14 -> 60.0554 mm
Just for reference, Hair’s breadth comes ranging anywhere from 17 μm to 181 μm [millionths of a meter] – yep, it would be very thin hair gap there!
Case #2: ΔT – 70C
While case #1 temperature change (ΔT) was 40 C, because of Queensland, we’ll now improve our chances by reducing the base line to 0 C. That ramps up our total temperature change (ΔT) of 70 C. In this case we’ll get following change.
188.4×0.0000231×70 -> additional 0.3046428 mm (304 μm) to our original circumference value
Going back to our diameter
188.7046428÷3.14 -> 60.09702 mm
Coming back to our hair’s breadth comparison, we are still within a limit of a single hair (17 μm to 181 μm) here.
Crayion’s response when asking to draw me two strands of thin hair
Case #3: ΔT – 150C
Let’s go wild and aim for our final ΔT of 150 C. This is going to be achieved by heating our mold to 150 C, while cooling it to 0 C afterwards with a common ice.
188.4×0.0000231×150 -> additional 0.652806 mm (652 μm) to our original circumference value
Going back to our original diameter again
189.052906÷3.14 -> 60.2079 mm
Doing our final hair’s breadth comparison – we finally made it over the single hair (17 μm to 181 μm) limit here – let’s be humble and say we’ll have “two hairs” space there. Would it be enough? No idea.
As per our Day 1 Seb wasn’t available (Sunday rock-climbing training) so I asked Greg to assist us and we started with planning first.
While probably even more cryptic then the one from previous day, decoded it comes like this:
Apply the demolding spray
Weigh all CF so we can calculate amount of resin mixture needed
Check if anyone has any urgent needs now (restroom visit)!
Check all tapes are ready
Calculate resin needs
Prepare resin mixture (wet-job timer starts here)
Apply 1st layer – this is probably one major change to our original plan. Serge came with idea that having a first layer wet will do well as excess resin will be soaked by the second one.
Apply 2nd layer – this one comes as a dry one
White tape with 50% overlap
Office 80%-90% overlap to squeeze the job even more (wet part of our job finishes)
Job started with the demolding spray application. Serge places several markers there so we won’t miss a spot.
The next in the line was the CF weighing which worked out being roughly 47g per layer.
Based on this value we decided to prepare 150g of resin mixture in a 1:3 ratio (1 part of hardener on 3 parts of resin). Then we hit quite an interesting & unexpected obstacle just before getting it mixed – I’ve been recommended to use Nitrile gloves – but how the heck do you put them on in ~30C heat-wave?
Mixing resin was easy with scales – 37g of hardener + top up to 150g with resin. Our wet-job timer started here!!
The next stage was to make sure that all CF is getting wet properly.
On to laying the first (wet) layer + Serge using squeegee to spread resin evenly on top.
Straight to the second (dry) one.
White tape! (~10 minutes in). Here you can see that we ended up with few “white” patches where tape seems not to be having enough resin. This will be visible even more later, but raising it here as it became apparent for the first time (pretty early in process). It is likely that we still had a good chance to add some resin to fix this at this stage.
… and yes, final layer with the office tape!
Done! All in roughly 15 minutes!
Well done Greg and Serge! 🙂
At this stage we found ourselves in an interesting situation – what should we do next? As we couldn’t get the actual resin I’ve been looking for we ended up with a more traditional one which sort of even doesn’t require any heat-assisted curing. It can cure on its own though several days. Another question here was when should we expect that curing process to start as being almost an hour in the “wet” job, while mixture’s viscosity was still – honey-ish.
We left an excess resin in a jar so we can oversee that actual curing process and it actually all happened in a matter of minutes … right just when team (Serge & Greg) left. Resin temperature suddenly spiked to 90C+ and I couldn’t pinch its surface anymore.
Seb then had a quite a fun testing it – and we were quite amazed that he needed to use a hammer to actually smash it.
Discussing it further with Serge we decided to test the high-temperature (70C) curing on it as well. And so we did!
Heater needed to be injected in the wider tube again and we wrapped whole contraption in a thermal insulation to reduce the heat dissipation. Strangely contact of our temperature probe with that aluminium foil seemed to confuse readings again so I decided to cutout a bit to avoid any. That also opened way how to cross-measure temperature with our IR thermometer.
Richard’s heater & Seb’s monitoring system did the job and together with a bit of manual overload we’ve been able to keep pretty stable 70C for 90 minutes.
Giving it another hour to cool down – we started removing the white-tape wrap. It was strangely satisfying experience seeing how it is coming out.
At the end I took few pictures of that texture – it looked perfect!
Well and here we are! We apparently have an awesome CF tube ready, but I don’t seem to know any way to get it from the mold! Not like it would be glued to the Al tube, but it is so tight that it is clear that stripping it away will be difficult to the point where I am already quite negative that it will work out.
Anyway, there is still a chance that our Al tube expansion wasn’t big enough as we were using different resin than intended for our final go (150C). We should also consider using even more of that de-moulding spray, probably in multiple layers (4+) – one by one when they get dry.
Finally, there is that problem with CF not being properly wet on few places. That needs to be something we need to watch after next time.
Otherwise, I think this was an amazing job for our first go! When around and having some ideas, please leave us those in comments, as always more brains comes handy.
What a weekend! Huge thanks to whole team first (Serge, Greg, Seb, Richard & Chris … and more) – because we made it! There were so many things happening both days that I decided to split it in two (still pretty chunky) posts.
We started with Serge about 2pm Saturday with forming a plan!
While not readable well, it sort of goes like this:
Clear the tube
Build a resin applicator
Apply release film
1st carbon fiber (CF) wrap & seal ends
2nd carbon fiber (CF) wrap & seal ends
3rd layer resin protection tape
Weigh CF tape + measure time for the wet-works (just a note)
While Serge started working on the resin dispenser, work progressed in parallel on clearing the tube. That’s important so resin has limited grip on it and releases the mold with ease. For this I ended up using Septone Ali Brite Aluminium Cleaner 1 Litre from Good Guys, what ended up being a wrong decision.
While this product seems being recommended all over the shop, it didn’t deliver – our aluminium tube still being scratched and dirty even after 5 minutes of polishing. Serge came straight with a better solution – bringing in a green sponge for washing dishes & dishwashing paste – and it came with an instant results. Still doing this properly took us probably 30 minutes.
Meanwhile Serge built the resin dispenser by reusing old squeegee and Loaf Pan from K-Mart.
Final picture TBA.
The next step was to apply the release film – ULTRALEASE EPX PARFILM MOULD RELEASE from Barnes, however we decided not to do it and leave this step for the wet run.
Apply the 1st CF layer next – Serge realized that ends of our CF tape needs to be taped so they keep together, also found that picking up a right angle how to apply the tape might be bit tricky.
Apply 2nd CF layer – that already went much easier together. That also came with some of our first measurements, it looks like we need ~2 meters of tape per layer.
