Hi-start question

[billdennis747]

I'm hoping to find some advice. Here in the UK we have a contest class for Classic A1 gliders. As an alternative to a towline we can use a bungee; it says up to 20m rubber plus line to make it up to 30m. It gives no suggestions as to rubber size, or indeed if 20m is appropriate. Does anyone have experience?
Bill

[Jez Wilkins]

Hi Bill

I have experience - but very limited.

I looked on here, before the site went down, for some pointers about what to use for such a bungee, and some of the (Peterborough?) flyers were using 1/8" rubber for their club glider (36" wingspan?) bungee events.

I made up a bungee using 20m of 1/8" rubber, plus 30m of nylon fishing line (I forget what breaking strain - maybe 10 ~15lb)

I tried it at Buckminster, late on one evening, back in the autumn of 2023.  One launch - which I had thought was directly into what little wind there was.  The model was a 'La Mouette', fitted with a Leo Bodnar RDT system.

The model started off O.K. on the line, then veered sharply right - at which point I activated the RDT.  The model came in, with the RDT operated and still on the line.   Some slight damage to the leading edge of the wing, now repaired and the model has not been flown since.

Others experience my vary - just my two'pennorth.

Cheers,

Jez Wilkins

[billdennis747]

Thanks Jez. I assume the veering was a trim issue so my question is, was the bungee powerful enough? I have tried my Aiglet on my existing bungee which I think is Peterborough size (7.5m rubber) and it went up pretty well, if sedately. I would have assumed that for a much longer piece of rubber, 1/8" may not be enough and I was considering 1/4" or 3/16"
Bill
 

[Squirrelnet]

Hi Bill

I guess that means the exact spec is fairly open then ?



 I recently made up a Peterborugh Rules Bungee -  7.5m of 1/8” rubber + 22.5m of line. Like you we found it could cope well with an A1 Hatchetman and some other A1 designs we were flying in very light winds so I would have thought something a bit more than that would work well as an A1 comp bungee  . I would try the same ratio but 3/16" ?

[Ratz (Bruce)]

I use 1/4 inch tan.

Bruce

Hi Bill

I guess that means the exact spec is fairly open then ?



 I recently made up a Peterborugh Rules Bungee -  7.5m of 1/8” rubber + 22.5m of line. Like you we found it could cope well with an A1 Hatchetman and some other A1 designs we were flying in very light winds so I would have thought something a bit more than that would work well as an A1 comp bungee  . I would try the same ratio but 3/16" ?

[Slowmatch]

How much does your A1 weigh Bill?

Light 36" models are sometimes overpowered on the Pboro spec bungee and ping off early - heavier ones (up to 150g) can do better especially in a bit of wind. Wind makes a big difference to the total energy (less wind needs more rubber.)

The 20m of rubber with 10m line seems odd to me - I would expect the other way round. The amount you stretch makes a big difference. 20m of 1/8" will have more total energy than 10m but only if you really stretch it. If there is a maximum stretch permitted then you may well need thicker rubber. Stuart Darmon's postal rule was 2kg max pull at 50m stretch (according to AM April 2021.) I've never measure the Pboro spec for max pull but if I was flying bigger models I would be looking to stretch further, rather than up the spec. My radio gliders of 200-400g fly on about 3-4kg max pull with 6mm surgical rubber but Tan rubber should stretch quite a lot more.

All of the above presumes you want a kiting launch not a zoom catapult. In which case a long and soft constant pull is much better for max height.

[gman]

A reply really to Bill's initial post on this subject. Stu Darmon's postal Classic A1 comp did indeed allow the use of bungee launch. Classic A1 at the forthcoming Birmingham Classic is for towline launch only.
Just for the "avoidance of doubt" as they say, now over to you good guys to continue your discussion about bungees for A1s

Gavin

[billdennis747]

A reply really to Bill's initial post on this subject. Stu Darmon's postal Classic A1 comp did indeed allow the use of bungee launch. Classic A1 at the forthcoming Birmingham Classic is for towline launch only.
Just for the "avoidance of doubt" as they say, now over to you good guys to continue your discussion about bungees for A1s

Gavin

In that case, ignore all I said, although thanks for the  input. I assumed Stu's "Classic A1" was the same as this "Classic A1". I can't tow easily any more (never could) so I'll probably leave it alone.

[USch]

Years ago, in my club we used to fly small RC gliders of about 150g weight, launching with a bungee. As a rule to make-up the length of rubber vs. filament we used a relation of 1m rubber, 3m nylon filament, the same as the Pboro spec bungee.  Experience was that more rubber just added weight not supported by the model, which in turn leads to lower max. height. Believe it !!!

Urs

[Viperkite]

One thing I have learnt (the hard way) about bungee is to always launch directly into the wind. A side wind can power dive the model into the ground. On A1s I use one third 1/8 th rubber strip to two thirds kiteline. For A2s I use 3/16 strip.

[Jez Wilkins]

In that case, ignore all I said, although thanks for the  input. I assumed Stu's "Classic A1" was the same as this "Classic A1". I can't tow easily any more (never could) so I'll probably leave it alone.

Seems as though Bill has decided that it is not for him.  Thanks for starting the topic though, Bill.

I hadn't realised until Slowmatch's/Jon's post that Bill's initial post had mentioned a total bungee length of 30m (up to 20m of rubber, plus line to make up to 30m).  The length for traditional towline for 'Classic A1' is 50m, I'm sure.  Wasn't the total length of the bungee also 50m?  I cannot remember the edition of the Aeromodeller in which it was mentioned - and my Aeromodeller magazines are not easily to hand at present, either.  I've looked online - but not managed to find the article in question - it was about the postal competition, wasn't it?

I think that the problem with my veering launch, was not a trim issue, as Bill suggested - but was actually that I did not launch directly into wind - although I thought that I had done so.  In other words, what Viperkite has stated.

If you are towing, you can at least adjust which way you are running/walking, depending upon what the model is doing.  Not so with a bungee launch - once it's gone, it's gone!!    

Cheers,

Jez Wilkins       

[Slowmatch]

April 2019 and April 2021 Jez. But looking at it I think I've misread with regard to the 2kg at 50m, which was referring to the towline.

[billdennis747]

Again, thanks for all the input on my wild goose chase. I think the Classic A1 rules, Stuart's that is, may be found at the bottom of New Clarion March 2023

[PeeTee]

Just a thought for Gavin, couldn't Stu allow bungees for next year's A1 competition? We are all getting older and I suggest that you may get a few more entries. I know that in my club about two people still fly gliders whereas more would probably have a go! I'll have to dig out my Aiglet and French glider I have around somewhere 

Peter

[stupid]

Hey Bill,

   Over here across the pond we call bungee launch (Hi Start launch). Must be something to do with the metric system, or whatever. Bungee's are about 1/2" in diameter and the kids use long lengths of it jumping off high suspension bridges for a thrill. Anyway.

   I won't tell you what I do with Hi Start because I don't know how my experiences will relate to what you're trying to do,  knowing the wing area & the weight of your model is necessary. I've uploaded some information In the Builders Plan Gallery here on the Hip Pocket Aeronautics website. You'll find a link for Builders Plan Gallery at the top left corner of this page. Eventually, as I have just uploaded it in the Miscellaneous Articles section, 9 pages from a Frank Zaic Model Aeronautics Publication.

   Don't get discouraged, I have the same problem in this hobby trying to find information. It seems as though what were looking for is scattered everywhere across the Internet. And the new algorithms only give you search results for something that someone wants to sell you. Or from some ass h__e Wanker trying to make a dime farthing off of YouTube.

       Bob         username stupid, although I'm considering changing it to brain fart

https://www.flyingacesclub.com/PFFT/HiStartRevisited.pdf

[Jez Wilkins]

April 2019 and April 2021 Jez. But looking at it I think I've misread with regard to the 2kg at 50m, which was referring to the towline.

Thanks Slowmatch/Jon.   If I remember correctly, the 2 kg related to the tension that the rules required you to apply to the towline, when measuring out your 50m.

I think the Classic A1 rules, Stuart's that is, may be found at the bottom of New Clarion March 2023

Thanks Bill.  The article where I remember the bungee option for the Classic A1 postal competition being mentioned was in the Aeromodeller magazine.  The Clarion article does mention 'no more than 20m. of rubber' and 'not exceeding 50m. relaxed length', for the bungee option.

couldn't Stu allow bungees for next year's A1 competition? We are all getting older and I suggest that you may get a few more entries.
Peter

I'm sure that the 'age thing' was mentioned by Stuart, in the Aeromodeller article, as a justification for the 'bungee option', in relation to the postal competition.

Cheers,

Jez Wilkins

[Jez Wilkins]

Hey Bill,

Over here across the pond we call bungee launch (Hi Start launch). Must be something to do with the metric system, or whatever. Bungee's are about 1/2" in diameter and the kids use long lengths of it jumping off high suspension bridges for a thrill.

It seems as though what were looking for is scattered everywhere across the Internet.

Hi Bob/stupid.

Yes, we have 'bungee jumping' over here in the U.K., also.  For Aeromodelling, we seem to use 'hi-start' and 'bungee' interchangeably - Bill used both terms, in his opening post.

Years ago, a work colleague described 'The World Wide Web' (as it was known, 'back in the day') as a place where somebody had taken a library full of books out of their spines and then scattered all the pages randomly across the floor.

Sometimes Aeromodelling information is easy to find - other times not so much.  I tried, but could not find, a web version of the Aeromodeller article where the (updated) Classic A1 postal rules were published.

Cheers,

Jez Wilkins   

[billdennis747]

Just a thought for Gavin, couldn't Stu allow bungees for next year's A1 competition? We are all getting older and I suggest that you may get a few more entries. I know that in my club about two people still fly gliders whereas more would probably have a go! I'll have to dig out my Aiglet and French glider I have around somewhere 

Peter

Hello Peter. Stu is not running the Classic A1 postal again because it only attracted two entries (and one of those was me; the other knew what he was doing).

[gman]

Hi Peetee, Stu and I really did consider allowing Bungee/HiStart for Classic A1 at the Birmingham Classic as Stu had already been approached by a potential flyer. We decided against because of the possibility of bungee lines becoming a trip/entanglement hazard unless we both supplied (what configuration?) and set up the bungee away from other fliers. This we weren't prepared to do for maybe a couple of entries. At the risk of being very contentious, we also reasoned that a "proper" glider event was for towline launch....now I'll duck for cover.
Gavin

[stupid]

I tried, but could not find, a web version of the Aeromodeller article where the (updated) Classic A1 postal rules were published.

   Well, another brain fart! That's what I get for skimming through the previous post's at 2 X the speed of light. Now that I understand that you're trying to find out what the rules are,   Nevermind. You can file my post in the bin with the rest of the rubbish.

           Bob/brain fart

[DavidOWade]

Some of us have been playing with bungee-launch A1 gliders for a couple years at our Perris, California site. My last A1 is about 140g and it goes up well with 1/16" rubber using the 1/3 rubber and 2/3 string guideline. It seems that most of the rubber is on the ground when it releases. In fact if I stretch the rubber too far out the glider gets really high but it doesn't release at the top because there is still too much tension (this also makes it hard to release in lift). Then it overflies the stake and continues down in an arc until either the tension relaxes or the line is behind the hook to pull it off. By that time it has lost a lot of its altitude. I would like to learn of a standard rule that is used in the USA for line and rubber length (or line and rubber weight). We have played around with a couple lengths based on field condition but I think 75'/25' line/rubber is too short for nice flights if you have a decent field to fly at.