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F3-RES League Bungees


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martynk

To stop clogging up the F3-RES league posts I have created this new post for F3-RES bungee alternatives.

 

I mentioned in my last post that the new batch of Silicon Red 6x4   from HK - which is the 'approved' bungee for the F3-RES league doesn't appear to be made of Silicon - its more of a plastic material. It goes white when you try and stretch it and actually doesn't stretch very far at all. 

I have found this on eBay and ordered it but I suspect it may be a HK product simply being resold in the UK. Its considerably more expensive as well.

https://www.ebay.co.uk/itm/RED-6mm-Silicon-Rubber-Bungee-Hi-Start-for-EDF-GLIDERS-HI-Start-Release-Tubing/232032593480?

I'll let you know how I get on with it. I also have some brown 6x4 silicon tube I can test but I cant remember where it came from.

 

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  • 1 month later...

Hi Marc

Stay away from the Hobbyking bungee. They have updated the description to say it only has a 1x stretch which is useless for our needs. 

I am trying a brown silcone bungee found on eBay. It stretches well but seems to lack ooomph. The search is still on. 

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Too late I bought one, think it might be for the bin totally useless. I have at least ten metres of the "old" bungee that I bought about 25 years ago and it's in perfect condition unused

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SilentPilot

I think maybe I got a freak good batch from Hobby King!

My Radian goes up beautifully. Will be checking it out with my Algebra soon too! :D

I also have a bigger Hi-Start but that is only used for my Ka-8. 

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pete beadle

Hi all

I think there's a few quid waiting to be made by the first flyer to find out where the NHS gets the surgical rubber they used to buy in bulk, and that Dick Edmonds used to get for us all!:thumbsup::)

Regards

Pete

BARCS1702

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  • 10 months later...
Pete in Northiam
On 23/08/2019 at 21:23, pete beadle said:

I think there's a few quid waiting to be made by the first flyer to find out where the NHS gets the surgical rubber they used to buy in bulk, and that Dick Edmonds used to get for us all!:thumbsup::)

Regards

Pete

BARCS1702

I'm on the case! 🙂 

I'm in need of a bungee for the BARCS 2m postal comp and I have twice bought crap latex tube on Amazon.  Classic natural latex "surgical" rubber tube seems to be a Chinese enterprise for the most part nowadays and little of it is UV proof or durable for outdoor use.  Silicone "rubber" tubing is the way to go for durability and performance so I'm now in contact with several UK manufacturers and suppliers of silicone tubing used in the medicine and the food industry. 

I have samples of 6mmOD x 4mmID silicone tubing (for the 2m comp) coming but there's a lot of parameters to play with.  High extension is fairly easy to get (up to 7 or 8-fold before breaking) but none of the manufacturers list elastic modulus (ie extension per unit force) in their data sheets so some experimentation is in order.  Costs for bare tube are around £100 per 50m spool with not a lot of difference between sizes.  

I will report back.  

Cheers

--Pete Newman
BMFA 197508
BARCS 3869

 

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pete beadle

Hi Pete

The great advantage of the (hollow tube) surgical rubber DickE used to sell was that it released its tension slowly.

The majority of solid rubber tube sold today, red black or natural colour is MUCH too vicious for model gliders, especially lightweight ones

The EMP rubber was very susceptible to UV attack, especially if left out, in direct sunlight, for any length of time....such as at the flying field(!)

Our answer to this was to keep a couple of 3/8th round wooden dowels in the bag you stored the bungee in and, if the bungee gave way on launch, you'd insert the dowel(s) into both  ends of the break, and carry on:yes::thumbsup: Simples!

Good luck with sourcing a replacement....I never did:(

Regards

Pete

BARCS1702

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StraightEdge
8 hours ago, Pete in Northiam said:

I'm on the case! 🙂 

...

I will report back.  

Cheers

--Pete Newman
BMFA 197508
BARCS 3869

 

Well done that man!  I did get two 10m lengths of natural-coloured 6mm Latex  via eBay from China (arrived relatively quickly), then gave one to Cirrus.  Neither of us have yet tested it in anger, but a casual pull appears similar to the original (i.e. good) red stuff that HK did until a year ago or so.

https://www.ebay.co.uk/itm/323757660344

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Pete in Northiam
On 16/07/2020 at 15:17, pete beadle said:

Our answer to [breaks] was to keep a couple of 3/8th round wooden dowels in the bag you stored the bungee in and, if the bungee gave way on launch, you'd insert the dowel(s) into both  ends of the break, and carry on:yes::thumbsup: Simples!

Thanks, Pete B!  I won't be spending more dosh to send back the Tansole so that's a good workaround until I get a better replacement sorted. 

First silicone sample has arrived and I've got a test setup sorted.  This one is a bit too stiff still - has a higher limiting load than the Tan but stores about 10% less  about half the energy at the limit.  I'll post the results when I get the other sample or two.  

 

Edited by Pete in Northiam
I added up the energy wrongly!
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Sheepish

Hi All

Has anyone tried Theraband exercise tubing?

I have some red coloured tube to try but due to my faffing about I haven’t got around to it yet.  It feels and looks good and if I believe the spec sheet then it should work well and I wondered if anyone else had tried it.

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Pete in Northiam
On 18/07/2020 at 20:03, Sheepish said:

Has anyone tried Theraband exercise tubing?

No but it looks interesting thanks.  The specs on the Thereband web site don't go very far on the stress-strain curve (just 100% extension).  Have you got more detailed data?  I think we need to know it will go to 500% extension (5 times relaxed length) would be very useful.  

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Sheepish

Hi Pete

This spec shows up to 250% and there was a lot of  discussion on RC Groups at one point but I’m not sure how much of this was informed by actual usage and how much by pure speculation.  The advantage of this stuff, if it works, is that the secifications are tightly controlled and it’s readily available in lengths up to 100m in continuous pieces.  
It can also be bought in short sample lengths which could be used for a little cheap research perhaps.  As soon as I get a chance I will try launching my PureRes with what I have and let you know what I find.  I have 10m of the red tubing.
The prices do vary dramatically for the same item though so be careful if you buy some.😎

 If anyone knows (or is) a friendly physio it might be possible to get a trade price perhaps?

MWPG7Bq-xzCkp9Z037erX9tL2iHsdtvyTnmupAPY
 

 

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Sheepish

Hi Pete

This forum thread below might be an interesting read.  
Most of the detailed information I have seen has come via slingshot enthusiasts Forums.
Not sure about the hunting and killing bits but they do research the rubber for their slingshots in much detail and it should be transferable information for us. 
 

https://slingshotforum.com/topic/39-thera-band-and-tube-resistance-elongation-chart/

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pete beadle

Hi Sheepish

Discussion seems to be centering on availability currently, when I personally think it would be better to consider what you actually want in a GLIDER bungee

For me, the most important consideration is for a good glider bungee is to provide a long, slow, constant pull on the launch

The short, sharp, powerful (solid) ones are completely useless if you want to be able to "kite" your gliders on launch and, for me anyway, that is an important consideration

Oh, and Sheepish, the very last person you should be speaking to is your friendly physio....most of them have no idea where their surgical rubber comes from(!) You need someone in NHS Procurement, which, at present will mean a private company contracted to the NHS

Keep up the search though:thumbsup:

Regards

Pete

BARCS1702 

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Pete in Northiam

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% 4kg at 300% extension - see below).  Energy stored is proportional to the area under the curves.  

249500731_2020-08-01Results.thumb.jpg.41d8e62413f39ea0ac3a734527a0bf49.jpg

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

[Edit 2020-09-23: I had misstated the BARCS F3-RES rules on bungee extension spec.  Although my tests were aimed at the short-field 2m challenge, the Mocap tubing may be suitable for a full F3-RES bungee.  --Pete]

 

20200803_162126.thumb.jpg.1b8f547fcd6a24ada5bb046243c7186e.jpg20200801_151308.thumb.jpg.bd233eb25e068e441df20112b5d900c0.jpg

Edited by Pete in Northiam
Mis-stated F3-RES bungee load-stretch rules
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cirrusRC

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

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paulj

I took my Madres out on Sunday and used my old (2 years?) bungee from hobbyking. I didn’t manage to get to the top of the launch - The glider came off the line between 40 and 60 feet up. Very disappointing. Does the old hobbyking bungee degrade? Any ideas? Nothing has been changed on the model from the last successful flights some months back...
By the way - I am still willing to give lengths of fishing line away if anyone wants to make up a bungee for the hi-start challenge league - send me a pm if you’re interested...

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