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F3-RES League Bungees


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StraightEdge
On 03/08/2020 at 16:57, Pete in Northiam said:

Here are my results on bungee materials testing for the BARCS 2m Hi Start Challenge. 

The challenge uses shorter bungees than F3-RES with rules calling for bungees with up to 10m of 6/4mm [OD/ID] surgical tubing and 50m of static line (min 30lb breaking strain).   Our previous supply of tubing from HK went bad so I set out to find substitutes.  I found two suppliers of natural latex tube on Amazon and two UK manufacturers of industrial silicone rubber tubing.  The hoped-for advantage of silicone over latex is durability - latex doesn't last many flying sessions in sunlight over grass - but the elastic qualities of the latex are good.  

These results are from load testing of four samples.  The chart show extension (the ratio of the length under load to the length under no load) against stress (the mass in kg used as load).  The tests run from 0 kg to the lesser of the elastic limit or 4kg (F3RES limit is 4.5kg at 400% extension).  Energy stored is proportional to the area under the curves.  

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The latex samples (blue and red lines) were fairly similar, reaching about 5.5 times unstretched length before hitting a limit.  The Tan 6x4 (blue) proved of inconsistent manufacture and weak in practice with many tears after just two flying sessions.  The Tansoole 6x4 has proven more consistent in manufacture and strength but is not expected to be UV-durable in the long term.  The latex costs about £5 per 10m length if purchased in 50m length.  

The Mocap 5.8mm x 3.8mm silicone sample (pink) are too stiff and stored less than half the mean latex energy.  However, the Hilltop 6mm x 4mm sample (green) shows better maximum extension than the latex and stores 107% of the mean latex energy.  

So, I have just ordered 50m of the Hilltop SP40-1.0-0-CLS Black silicone tubing.  I will make up a full bungee as soon as the order arrives and report back on flight tests.  

The delivered cost is £21 per 10m length and I am happy share this batch at cost plus postage - let me know if you're interested.  If many ask, I'll see about ordering more.  It also comes in white (cheaper) or red (more expensive) supposedly in the same material but I have not tested those.

Below is a pic showing how my bungee terminations for 6mmOD x 4mmID tube: 35mm screw eye, 6mm wall plug and shrink wrap tubing.  If you make them, insert plug and shrink-wrap before screwing in the eye.  This is much the same as the terminations on the Hyperflight F3-RES bungee.  Aside from the odd duff plastic plug (thin walls) the attachments have not let go under full load in test or on the field.  The other pic shows my Heath-Robinson test bed with a bag which I filled bottles of water - it worked!

That's all good for the 2m postal comp.  For full F3-RES the limit is 4.5kg load at 400% extension which the Hyperflight bungee meets with an 8mmOD/4mmID tube.  The Hilltop tubing passes 400% extension easily and stores energy as well as latex but also comes in other cross-sectional areas that might be more optimal for F3-RES.  I've not done the sums yet to estimate which size would be most likely. 

Let me know any questions or comments or if you want a share of the tubing order.  

Cheers --Pete

Pete Newman
BMFA 197508
BARCS 3869

 

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Pete

I've now got my electronic fish scales, and I've got 10m each of (i) my existing original stock of HK red 6/4mm, and (ii) the cheap natural/tan  6/4mm I recently got from China (in my link on Page 1).

To align with your own test data as closely as possible, how much length exactly do I need to cut off each as test pieces?  (Assuming they are short as in your photos, I don't mind losing a tiny percentage of the overall 10 meters of each.)

Also, I had thought to do a simpler 'horizontal' test than your vertical one:   i.e. secure one end of the test piece to the end of a bench with a tape-measure laid out, then note the pull in kgs as I extend the test pieces in steps of say 25%.  It is the opposite of how you went about it (I assume you added weight, then measured extension), but the figures should be accurate enough to then overlay on your own scale.

Jon

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Pete in Northiam
On 16/08/2020 at 10:41, StraightEdge said:

how much length exactly do I need to cut off each as test pieces? 

Also, I had thought to do a simpler 'horizontal' test than your vertical one:   i.e. secure one end of the test piece to the end of a bench with a tape-measure laid out, then note the pull in kgs as I extend the test pieces in steps of say 25%.  It is the opposite of how you went about it (I assume you added weight, then measured extension), but the figures should be accurate enough to then overlay on your own scale.

Jon

Hi Jon-- 

Great to see more tests - I've had to set it aside for a few days.

Any length will do and you don't really need to cut it just extend a section. It's the extension relative to the relaxed length you measure. Mine were about 10cm with Tippex marks or just measured between the terminations (which I was also testing). 

Horizontal should be fine.  I tried sone electronic luggage scales but the elastic confused them! Hence weights. I worked it measuring extension at fixed loads but loads at fixed extensions is just as good 

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  • 3 weeks later...
Pete in Northiam

I finally got to test fly the Hilltop SP40-1.0-0-CLS Black silicone tubing in a 10m+50m bungee for the 2m Hi-Start Challenge League Table (2020) this week (2 Sep 2020).  The weather was about 20C, 0-9mph at the surface and low bubbly cumulus (which I didn't have time to really take advantage of).  I made three launches with a bungee of 10m of Tansoole 6x4 latex tubing with 50m braided 35lb line then three with the Hilltop silicone replacing the latex.  (And the rest of my time sorting out a birdsnest of line and later a line break - I could not tie a bloodknot!)

Not really fair dead-air testing, but in my opinion the Hilltop won on energy stored (took more tension to hit the elastic limit), very smooth power delivery, lower vertical speed but better launch height, pinging off two of the three launches at well over 60m.  My telemetry log shows VSpd in red and the spike shows where I topped out.  First three launches are latex (very first duff, my error), second three are silicone.  

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I pre-stretched both tube types before measuring 10m.  Below are pics of how I terminated the tubing except I used fatter-threaded 45mm screw eyes from Amazon to suit the B&Q Diall 6mm x 30mm nylon wall plugs).  Slide heatshrink tube over the end, insert a wetted wall plug, shrink the cover tube tight leaving slight overlaps that will seal against the screw eye, then screw it in.  The winged plug jams very nicely inside the heat-shrink tubing and I have not had a connector fail (yet!).

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The only hiccup in all this was Hilltop: I ordered online 1 x 50m piece (about £110, so £22/bungee) and they delivered 2 x 25m pieces which gives me 4 at £27.50 / bungee.  They would not budge on the difference between the order and the delivery so beware!  If one or two of you would like 10m (say £30 posted + £2 terminated?), let me know.  If the one I made lasts as well as it looks I won't need many!

Happy to discuss 🙂 

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  • 3 weeks later...
Pete in Northiam
On 05/08/2020 at 13:59, cirrusRC said:

thanks for your efforts Pete.    Will wait to hear your report on the Hilltop test flights.

I've been using the Hilltop bungee since the 5th round of the 2m Hi-Start Challenge League Table (2020).  Over 50 full-stretch launches, no failures or apparent degradation or damage to the tubing.  I'm now offering the bungees for sale in limited quantities.  They are 10m of 6mm OD x 4mm ID Hilltop silicone rubber tubing terminated with screw eyes.  £30 + postage at cost (about £3 in UK) plus £3.50 for an optional 50m of 30lb breaking strain braided non-stretch line (same postage, not 35lb in photo).  Bring your own stake and pennant/parachute. I can take payment via PayPal.  Contact me directly (p.r.newman at lineone dot net) if interested!  

Cheers --Pete

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Edited by Pete in Northiam
Correct line specification + add "own stake"
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Pete in Northiam

I have sold out of my first batch of tubing so thanks to those who bought a short-field bungee :) I look forward to reading about their use - once the current gales subside!

If anyone else among you might want one, please email me (p.r.newman at lineone dot net).  No up-front payment, just an indication of interest please.  

The minimum order quantity for the tubing means I need to sell four to break even at those prices.  

Please let me know if you want in on the next batch. 

Cheers --Pete

cc: 2m Challenge thread

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  • 6 months later...
Pete in Northiam

Now we're back to flying, I have ordered the silicone tubing to make more 10m-length bungees for the short-field 2m Challenge postal competitions.  See my earlier posts in this thread for details.   I am happy to offer fully-terminated bungees at the same price as last year: £30 + £3 UK postage with the option of 50m braided 30lb breaking-strain Dacron line for £3.50 extra (no additional postage).  This price just about covers my costs.  These will be white tubing with identical properties to the black tubing (but not a raised price!).  I expect to have them ready in about two weeks and I can take payment via PayPal.  

If interested, please email me directly at p.r.newman at lineone dot net.  

Cheers --Pete

cc: 2m Challenge 2021 thread

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Pete in Northiam

Help!  Looking further ahead to possible full F3-RES competition, I just re-read the Draft 0.1 BARCS F3-RES Rules on the bungee specification limits and I'm confused.  The current draft say:

Quote

The bungee/rubber element shall not exceed 15m in a relaxed state and shall not exceed 45m when tensioned with a 4kg load

Then I looked at Hyperflight's (out of stock) F3-RES High Start Silicone Rubber (I have one, it's good!) which claims to be an "F3-RES legal high-start".  Except, according to the chart (see below) on the product page, at 4kg load it has a 350% extension (i.e. 52.5m). 

So then I found an English translation of the European F3-RES rules.  These say:

Quote

When extended to a length of 45 meters, the rubber tube shall not exceed a pull of 4 kilograms

This is not the same as the draft BARCS rules, it's sort of the inverse: load at a given extension (Europe) versus extension at a given load (BARCS). So the Hyperflight item is legal in the Euro rules (at 45m it pulls 3.8kg) but not the draft BARCS rules (at 4kg it extends to 52.5m).  

Personally, I think the Euro rules would be easier to police on the field (measure pull at a fixed distance on the ground from the stake) than the draft BARCS rules (measure a distance on the ground at a fixed pull).  

Does this perhaps warrant a change to the draft rules, @martynk et al? 

Here's a screen-snip of Hyperflight's product chart:

1516029852_Hyperflightbungeeextensionchart.jpg.6e7e4aa041e0be8ebc93afc0b84d8756.jpg

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martynk

Hi Pete

 

For simplicity, we selected a 10m 6/4 silicon tube for the Postal events - originally from HK until they changed the spec.

 

You are correct,  the full F3-RES is a different spec, and is 15m long, the bungee size can be anything but is dependent on meeting a pull test - but this has a higher pull than the postal version (as you would expect with a longer tow line). My own experiments suggest that a 7/5 silicon tube is nearly there. Hyperflight actually sell the correct bungee.

 

Does that make sense?

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Pete in Northiam
24 minutes ago, martynk said:

You are correct,  the full F3-RES is a different spec, and is 15m long, the bungee size can be anything but is dependent on meeting a pull test - but this has a higher pull than the postal version (as you would expect with a longer tow line). My own experiments suggest that a 7/5 silicon tube is nearly there. Hyperflight actually sell the correct bungee.

Does that make sense?

Thanks for the quick answer and yes, I did mean the full BARCS F3-RES rules - I'm very happy with the postal rules 🙂  And I've assumed you are in on drafting the full version - sorry if I'm wrong about that!

But the Hyperflight bungee does not meet the BARCS full F3-RES rules as they are drafted.  As the chart shows, at 4kg pull, it extends by 350%.  So 15m relaxed becomes 52.5m extended (15 x 3.5), greater than the 45m allowed by BARCS rules. 

That's my point: the Euro rules say what the max pull at 45m should be (Hyperflight is ok at 3.8kg) but BARCS rules say what the length at 4kg pull should be (Hyperflight is not ok at 52.5m extension). 

I feel the way the Euro rules put it makes more sense.

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martynk

Good point, I hadn't realised that...

 

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John Minchell

Easy to fix Martyn - just add in the wording to say that the bungee can have a max pull of 4kg OR a max extension of 45m as tested on the field. 

This will allow for variences of the rubber from different sources (and some line stretch).

Similar to the F5j or F5RES situation of max a motor power run of 'x' seconds OR a height attained of 'y' meters, when the Altis/RC electronics height limiter switches off.

John M

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Pete in Northiam

SOLD OUT! The latest batch of the 10m bungees for the 2m Challenge is now all sold and will be dispatched this week. Thanks to everyone who bought one. However, do let me know if you are interested (no money in advance). At the current (non-profit!) price, I need to know I have at least four firm orders for a batch to be economic due to the supplier's tubing prices and minimum order quantities on other parts.

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StraightEdge

Pete, I'm up for a bungee if you do another batch.

Jon

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Pete in Northiam
10 hours ago, StraightEdge said:

Pete, I'm up for a bungee if you do another batch.

Jon

Ok noted. I've had a couple of other enquiries so will probably hit minimum order on tubing soon. Will you also need the 50m braided line? I try to get all the materials in together. Could you email me too please p.r.newman at lineone dot net so I can contact everyone in one go. Cheers --Pete 

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StraightEdge

Hi Pete, I've emailed you, and yes please to the braided line as well.

Cheers, Jon

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Pete in Northiam

I will be making up another batch of  short-field 10m+50m bungees as I am confident to hit the minimum order quantity for tubing. 

Who else wants one?  Please email me directly: p.r.newman at lineone dot net.  I want to place the tubing order early next week so please let me know ASAP.  I will also be ordering braided line so please say if you need that as well.  Details as above in this thread, prices should be the same as before.  

At least I seem to have the fabrication process sorted as I have also had time to fly again!  🙂

Happy days! --Pete

 

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Simon H

Hi Pete, e-mailed you with a request for the 10M + 50M bungee. Thanks

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  • 2 weeks later...
Pete in Northiam

A note to anyone who bought one of my most recent batch of bungees with the blue heatshrink ends

One user reported the ring-eye and plug pulled out on first use.  Subsequently, my batch test piece (same materials) also failed a re-test.  Other users, however, have reported flying with them without issue so far. 

The failure seems to stem from the blue heatshrink used in the batch re-softening and hence reducing the compression of the silicone tubing onto the plastic plug. 

I have emailed everyone who owns a bungee from that batch with a proposed fix at no cost.  Please check your junk mail folder or contact me directly if you haven't seen it.  Either return the bungee to me for upgrade and a refund of postage or let me know and I will post you the upgraded heatshrink (a heavier gauge and adhesive lined) along with detailed instructions if you want to repair it yourself.  You will need a hot-air gun at 140C to conduct the repair.  

This only applies to the batch with blue ends (serial numbers NDB#5 to NDB#14).  I have no reports of failures in the original batches using a dark orange heatshrink.  Repeated testing of batch samples for that batch, and the forthcoming batch using the upgraded heatshrink, show them to be good.  Please do let me know if you hit any problems so I can help solve it and help others avoid it.  

Sorry for any hassle!  

--Pete

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  • 2 weeks later...
Stevevw

Pete

Did you send me any heatshrink? Not seen any yet.

Steve Wheeler

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