Which Latex Surgical Tubing ???.

[Gunnergolly]

Hello

I've been flying electric gliders for about eight months now, however i have always fancied having a go at a bungee launch but couldn't due to field size restrictions.

I now have access to an airfield so have a lot more space available, i recently bought a Dynaflite Bird of time as i also wanted to have a go at flying an RE machine.

I did my first bungee launch today, followed by two more launches that also went very well with the BOT climbing nicely, unfortunately the bungee that i'm using soon runs out of "pull" even when stretched to it's limit.

I'm currently using 10 meters of 8mm "blue" hobby king latex tubing along with 30 meters of nylon string with a "chute" attached, I wanted to start small and build up gradually.

The above "short" setup was cheap, intended only to give me my first experience of bungee launching and probably achieves about 120 feet in height.

To achieve a full height launch I'm really not sure what type/size/length of bungee/string i should be using for my BOT glider.

Also my "google" searches are only bringing up short lengths of tubing, i'm maybe wanting a continuous 30 meter length of latex tubing.... are there any suppliers of long lengths of latex tubing in the UK ??.

My BOT glider is only intended as a bungee trainer glider and for a bit of "back to basics" simple fun on those calmer days. I'd prefer the replacement  bungee to be slightly overpowered for the BOT, so that it can be used on a slightly heavier glider at a later date.

Any recommendations for suppliers/suitable latex sizes and ratios of bungee to tow line would be much appreciated.

Thanks

Chris.

 

 

 

[Jef Ott]

Although "everyone" back in the day swore by silicon tubing, I had a great deal of fun (and absolutely no breakages) using 30m (25m was just too fierce. 30m was perfect) of 10mm cotton covered bungee and 120m of 35lb breaking strain nylon monofilament fishing line. Silicon tube bungees always seemed to be fracturing when the thistles come into season.

I think I may have some of the bungee elastic in the shed, PM me your address if you have problems sourcing the bungee material of your choice, you can have it on a pay me if you're happy, return it if not, basis.

I found the B&Q heavy duty ground stakes (for anchoring horses tethers) to be of excellent quality and never pulled out of the ground. 

 

 

[thermaldoctor]

I would look at EMC Vega in Germany. Better product, more choice and postage is surprisingly cheap. Also a good range of chutes, lines etc. You only need a sort length of bungee.

Hope that helps.

[simon_t]

Another vote for emc vega from me.  My 'f3b' latex bungee is perfect and lasted quite a few years now

Simon

[Austin]

EMC is probably the best stuff but Thera-Band works well.

Beware Thera-Band 30m box normally comes cut into 3 pieces of about 10m. 

http://www.thera-bands.co.uk/index.php?id_product=102&controller=product

[Gunnergolly]

Thanks for your replies, especially to Jef for your kind offer..... much appreciated. 

I'm really looking after getting my hands on some decent quality bungee, pay the price and taking good care of it so that hopefully it lasts a long time.

The Vega EMC MR-F3B 29.4 M (https://www.emc-vega.de/en/high-start/megarubber/f3b1/mr-f3b-29-4-m) looks like the kind of stuff that i'm after.

It's rated for a 4m, 4kg glider so it should easily handle my 3m BOT, however i'm not sure what my BOT's AUW is so i will weigh it tomorrow. The BOT's future replacement will probably be a heavier glider and the F3B tube's rating will also cater for this.

One concern that i have is that the Vega EMC stuff is expensive and i will be using it on a tarmac runway, how will the tubing cope with this, how durable is it ?.

The Thera-band (heavy duty) looks like a possible viable option (https://www.athleteshop.co.uk/thera-band-reg-tubing-30-5-meter-very-light?gclid=CLC7kr_UyMsCFUa4Gwod-G8Lfg). 

Just as a matter of interest what bungee/line lengths are you guys using and what kind of heights are you obtaining.. what AUW are your gliders, just gives me an idea of what i can expect and what can possibly be achieved. 

Thanks.

 

 

[Austin]

18 minutes ago, Gunnergolly said:

One concern that i have is that the Vega EMC stuff is expensive and i will be using it on a tarmac runway, how will the tubing cope with this, how durable is it ?.

It's durable but I don't think it will last long with constant use on a tarmac runway. You only need a small cut in it and it's likely to get worse quickly.

 

[Gunnergolly]

 

42 minutes ago, Austin said:

It's durable but I don't think it will last long with constant use on a tarmac runway. You only need a small cut in it and it's likely to get worse quickly.

hmmm... this leaves me with a bit of a problem as the runway intersection that our club uses is bordered by crop on all sides (The runway is shared with a full size gliding club and we have been assigned a portion of the runway that were able to use). 

Laying out the bungee in the crop fields is not an option and so i would "doggie" stake the end of my bungee in the small grass verge that borders the runway. There is absolutely no avoiding that my bungee will come into contact with the tarmac, it makes Jef's original offer of his cotton lined bungee seem the best way to go now. I'm guessing that the trade off is that the cotton outer inhibits the bungee operation adversely ?.

Jef.... is your cotton lined bungee a 30m length ?, if so i will PM you tomorrow.

Thanks.

[Jef Ott]

I'm on nights, so can't measure the bungee cord left on my drum currently, but I am pretty sure I can do you a 30m length - PM me if you're still interested midday tomorrow.

 

[Jef Ott]

Is there a cure for losing marbles? I remembered what I had as 10mm shock cord... It was actually sold as 8mm, and measures 7- 8mm diameter.

Most cotton covered bungees in use for launching models were 5 or 6mm, so this is heavier than was standard, but my mind had exaggerated it!

[Jef Ott]

It transpires that a well known auction site has a seller with plenty of 30m lengths of 8mm shock cord, delivered for less than £14 inc p&p.

The term "Everlasto" is used in the sub-description.

Should be good for 2.5 - 3.8m gliders weighing 1.2 - 2.5kg.

 

[Gunnergolly]

Thanks for your help Jef, I've ordered up 30m lengths of both the 8mm and 10mm cord. I'll report back on how i get on with it. 

Thanks...

[martynk]

I use 50m of 8mm cotton covered bungee plus 100m of monofilament. It involves a lot of walking to stretch it. My bungee chord is at least 30 years old. I usually get 90m launch heights in calm conditions with that mix

 

 

[Gunnergolly]

Managed to try out my new cotton bungee today in less than ideal windy conditions with my Bird of Time ..... my test and maiden flights always seem to happen in less than ideal conditions !!!.

I'm using 30m of 8mm cotton covered bungee along with 125m of 1.2 mm nylon line and the initial two launches achieved about 200 feet of height.

I then moved the tow hook back one hole so that it's now roughly on the COG, had a couple of scary launches where the glider practically looped back on itself whilst going up but managed to recover and only achieved about 120 feet .

As expected it certainly feels slightly less stable on the line with the tow hook in a more rearward position but the climb angle looks better.

Next two launches achieved 330 feet and even in the windy conditions the potential of the BOT became apparent, although it feels a bit weird flying an RE only machine. 

I'm new to this bungee launching so my technique will need a lot of working on as i'm pretty much learning on the job !!.

So my next question is how do i counter this "potential" of my glider wanting to veer off to one side and loop back on itself after the initial release ?.

Is it better to launch the glider parallel to the ground in order to get some airflow over the rudder for stability and then let her pull naturally into a climb ?. Once it has settled into the climb it's stable and flies itself off the hook nicely. One of the bad launches was slightly cross winded so that was obviously a contributing factor to the veering off.

I'm a beginner so what's the safest way of launching ?.

Here's a shot of my BOT after today's outing, due to the recent bad weather i haven't done any flying so i've installed some HK "scissor" brakes. Once the elevator compensation has been optimized i think they'll work out nicely... 

So far happy with the results which i hope can be improved upon with more practice.

Regards

Chris.

 

 

 

[Jef Ott]

To stop veering, a quick momentary dab of down elevator. Once the model is tracking straight up, apply up elevator to stretch the line, until you reach good height, then let the elevator stick go, to build forward speed, so that when you pull up again, the model leaves the line going almost vertical.

I am surprised that you are only getting, at most 330 ft, 400ft should be well within reach without any breeze, and 470ft + with a breeze.

How much stretch are you giving the elastic?
I would think that 70 paces should be about right until the elastic is run in and then 80 paces should be possible.

The rule of thumb for tow hook pos on a rudder elevator bungee model, is 30 degrees forward of the CG drawn down the side of the fus from the bottom of the wing.

Hope you can visualise what I am saying, if not I will draw a sketch.  

[Gunnergolly]

Thanks Jef

My lack of height at the moment is probably due to my lack of technique , thinking back on a couple of launches i was almost certainly initially putting in to much down elevator and unloading the bungee tension to much to soon. My highest launches were achieved when i didn't touch the elevator and allowed the model to go straight into a climb, however this is when the veering was also more likely to occur, i'll keep your quick "dab" of down elevator in mind.  

I was initially able to stretch the cotton bungee to just over double it's length, after the fourth launch i was definitely able to stretch it that little bit further as it loosened off. I'm basically stretching it until i can just feel the bungee rubber going taught and will give no more.

Regarding my hook position i have now moved the hook from the third hole back and relocated it to the most forward hole. Initially for my very first (10m of HK bungee and 30m of nylon) bungee attempts two weeks ago i initially started off with the hook in the second hole and i never had a problem with the glider veering on launch. I'm guessing that my new forward hook position will provide even more stable launches at the expense of height as the glider will want to naturally climb at a shallower angle ?.

This is what i have now:-

The 30 Deg rule of thumb would place the tow hook here, but obviously the depth of the fuselage of the model is also a contributing factor.

I will not be able to test this new hook position until probably this Wednesday when i can use the airfield.

Apparently our club has an electric winch somewhere that hasn't been used in years and so i will be looking at becoming it's new custodian and possibly giving it a refurbishment if it's still in half decent working order. 

Thanks for your help.

Chris. 

  

 

[Jef Ott]

I think the point of using the 30degree method is that the angle of climb should be stable no matter what the depth of the fuselage is. If your model is stable at 15degrees, then there is no point in going further forward. The plane may benefit from a more rearward CG in the glide though, which will not alter the rate or angle of climb, although you may want to apply a touch of up elevator for the launch, compared with the resultant glide trim.

Have fun!

[evad]

Hi Guys ,

Im wondering how your joining the bungee and the line together is there a preferred method ?

last year I built a small bungee with some hk rubber tubing and builders line , but had problems with using wooden dowels as joiners with screw in eyes as they kept pulling out every few launches 

with this bungee being solid rubber are you just knotting them to form a loop and tying the line to the loop ? 

cheers dave    

[Jef Ott]

43 minutes ago, evad said:

with this bungee being solid rubber are you just knotting them to form a loop and tying the line to the loop ? 

Yes

[evad]

thanks jef 

 

dave