Premature Release

[Steve Houghton 1]

I have a 2m GF glider (X models Whisper) which I fly from the slope, but this model also comes with a tow hook, so I thought I'd get a bungee as I have recently had a go on a mates Xperience Pro 3m F3J.

The Xperience went up on an 8m length of bungee but I don't know how long the line was so, I bought the F3B Bungee kit from EMC-Vega which consisted of 8m of bungee and 10m of line. From what I read, 4 x the amount of line to bungee is the norm so I now have 35m of line.

I pulled the bungee and after 20 paces it was really tight and I was struggling to hold it. I chucked her up and up she went, however, the line came off the hook before the plane had leveled out. This happened time after time.

The more launches I made I found I coud stretch the bungee further until I was at about 30 paces. Now I had a couple of launches that were better but it is still releasing the glider prematurely.

So my questions are:

1) How do I stop premature release, without resorting to using elevator to level out?

2) Does a bungee stretch further the more you use it? In other words does it have a "breaking in" period. When my mate launched his Xperience it seemed he had nowhere near as much tension on as I had.

See the video HERE.

Steve

A470Soaring.blogspot.com

[Mark Stringer]

Sounds like the bungee is stretching - i have not noticed that myself with my bungees i have to say but maybe it is just that type.

As for the launching I have always teased a little elevator in to keep the tension on the line and the hook attached - the skill is getting the tension right .. too little and it drops the line .. too much and the wings clap hands over the top of the fuselage!

Another trick is you have a bit of breeze is to gently apply a little rudder on the way up .. gently! .. to zig zag on the way up. Combined with the gentle use of elevator you can actually re-stretch the bungee on the way up to keep going - the aim being to be vertically over your bungee stake when the line drops and maybe even needing a little dip to get it to release.

One other possibility is that your tow hook may need to be in a different position .. if I remember right (and dont hold me to this) if you draw a line at about 30 degrees from the chord of the wing down through the nose you tow hook should be about where this line goes through the bottom of the fuselage.

I can't actually remember the length of my bungee but yours sounds a little short overall to me - will have to see if i can find a measurement on it.

Hope some of this helps

[Steve Houghton 1]

Thanks Mark

When I tried mine last week there was no breeze at all, which may have contributed to premature release. I didn't have any launch trim switched on either so maybe I need to try that and just tweak the elevator on the way up.

I think the bungee length is a bit short but I can always add to that later, maybe 30m of bungee to 90m of line, if my field is big enough.

As for the tow hook position? Its in a fixed position with a screw thread already fitted. By my reckoning it's placed roughly ¾" - 1" forward of the CofG.

[Bob Cotsford]

I also seem to remember using a lot more than 8M of surgical rubber and 30M of line. As Mark said, most models would need some up to be held in, you are kiteing the model up the line rather than flying it. If the wings aren't bending you don't have enough 'up' in!

The hook too far forward would lead to a flat climb and an early release, or too soft a bungy would also give a low release. I think cotton-covered stranded rubber bungees do give a bit in the first few stretches and were never as good as surgical rubber tube

[Mark Stringer]

Just looked it up and the consensus seems to be to have the tow hook 2/3 or the way back from the nose to the CofG.

So in your case if it is 1" forward of the CofG then if your glider has a distance of 3" from CofG to Nose then it is OK ... but I doubt that is the case looking at it .. may be worth trying to move it forwards but as you proably dont want to spoil its looks with extra holes then try the other things first.

I have even seen one comment saying that the factory location of th etowhook is too far forward - so what to believe?

[Steve Houghton 1]

Well I have balanced the model so it is a little on the tail heavy side, which gives a much reduced sink rate, but not so far back that you really have to concentrate hard to fly it, after all, I'm fun flying and not competion flying.

Yes I do remember now reading somewhere that the hook position is too far forward, I guess there isn't anything I can do about that. Next time I'll get my thumb on the elevator stick quicker and put the nose down a bit as it is going up very steeply.

So does anyone think adding more line only would be of benefit? I think I will buy another 2 lengths of 10m surgical tubing now that HK have it in stock again. That will mean I can connect various lengths of bungee and line depending on the flying venue.

[Mark Stringer]

Looking around bungee sets seem to use up to 30m of bungee (and 107m of nylon)

That is way more than yours and could explian some of your issues - pretty sure this is what i use as it seems a standard ready done bungee set.

A High Start one here for sizes: **LINK**

 

Edited By Mark Stringer on 05/06/2013 13:14:48

[Steve Houghton 1]

This was what I bought HERE and I got that after seeing the height my mate got with his, which was the same length, as seen on the video. When I flew his I easily caught a thermal and could have specked it out. As I say, I can easily add to it. It's the premature release I need to sort out because I'm losing height because of it.

[Erfolg]

I agree the bungee described is not of the proportions we all used to fly off. We used 30m rubber, 120m of mono filament line. The rubber was about 5/16 sq, the line +100lb breaking strain.

The tow hook for tame launching would be 30 degrees forward of the CG, for a true high start, right under the CG.

As per not touching the elevator, it was essential to control the model on the line, maintaining the tension, to reach maximum height. To get off, a dived ping was often seen as desirable.

The how many paces question, in the good old days, it was as many as you could get without the rubber breaking.

[Steve Houghton 1]

Well I've extended my surgical tubing to 30m. I also had 100m of line but when I got to the field and began stretching it out, I realised I didn't have enough field . Fortunately I had the line in about 30m lengths so I unclipped one length and gave it a whirl.

She went up no problem! All I did on this occassion was to use rudder on the way up and no elevator and she released the line all by herself.

Towards the end of the session I was using launch trim to give me some extra tension and height but I'll play around with pinging her off as I gain more confidence.

I have to say I found this a most enjoyable method of launching. Much better than having an electric motor up front.

Steve

A470Soaring.blogspot.com

[Frank Skilbeck]

I think I'm running about 15m of tubing and 50m of line, using my Easy Glider at the top of a launch without much wind I'm getting about 60m, with a light wing I can ping off the line at 70-80m and it a reasonable breeze I managed to kite up to 100m and had to dive to get it to come off the hook.

But as you say it's much purer than having an electric motor up front and great fun. My best from a 70m launch is 317m it was still going up but I chickened out.

[Erfolg]

There are a number of reasons why bungees have fallen into disfavour.

Possibly the most significant is flight time. I would guess from memory, that most pilots could get about 2 minutes without lift. This placed a lot of emphasis on contacting low level lift and efficiency. That is the reason why most competitions models were big.

The other, is that short flight time meant some walking, on a frequent basis.

Yet another limitation you have found, is that a large field is required, preferably in all wind directions, with some additional 50 paces to stretch the rubber/silicon tube.

Then there is the space in the boot for the bungee and the effort of putting it out and retrieving it.

OMG, I am feeling tired at the thought.

On the other hand electric gliders can operate from small fields, need no effort to launch, provide very long flight times, essentially all that is needed is the model and Tx, maybe an extra Lipo for an afternoons flying.

It was some what of a paradox with me that towline and winch launches, were all about getting much higher than was apparently possible by the line length. Achieved by achieving line tension which challenged the footing of all concerned, maintaining the tension as much as possible, whilst the wings dealt with tremendous bending moments, and the model cable of high speed in the ping/dive and then up elevator. Which the competition rule makers never intended.

With the advent of electric competition gliders and the tremendous abilities of modern gliders and motor propeller combinations. Launches are limited to 200m, just about the same that a bungee can achieve.

Perhaps one of these limiters could suite you?

[Frank Skilbeck]

Yes, but the model is more complicated and heavier and having a motor means you are likely to use it therefore losing some of the challenge. Maybe it's time for the bungy (or Histart for non UK readers) to make a come back.

I mus admit I've only rediscovered the bungy this year after 23 years and it is very enjoyable.

[Erfolg]

I am not sure that electric model gliders are are automatically heavier than they were, or necessarily they need to be.

Dealing with the historic issue, most models out of necessity used heavier servos, plus nose weight was often necessary. As an aside most would now have overweight wings, compared with duty that electric gliders typically see.

In the case of both my 2m and +3m model, I used heavier than necessary lipos to avoid the need for additional nose weight.

Although my electrified 3m Alegbra, did need a lump of lead on the tail. There was the option of shortening the nose to avoid this, as there is so much space available doing nothing..

I have noted that those who are competition minded, typically use a very small Lipo of a high "C" rating, as it is needed for one launch per round only. The other trend seems to be that very high powered motors are not being used, just high powered. The reason being the 200m cut out. Now it is about getting to both 200m and where they want to be in 30s. I have been told, that my suggested, very high speed dive from below 200m, with a coarse prop, to continue with a zoom beyond 200m is not permitted.

I am not convinced that there is any material difference with or without electric drive, as going much below 8oz ft^2 will not realise any benefit most of the time. I do not know if electric competition models ballast these days to deal with windy conditions, but think being able to penetrate will continue to be a requirement.

By all means bungee launch if that floats your boat, I just cannot see it catching on with the majority. I can se that your landing skills will improve, also you will become more experienced at scratching at lw level for lift.

I guess something else I have observed, that all glass models, designed specifically for electric flight, are better in every way than my old towline models in all respects. Gliders such as AVA/Bubble Dancers are incredible, in the right weather conditions, almost still air, seem to stay up all day. It is a paradox that moulded wings are probably much stronger and very much lighter than my old built up wings, exceeding their performance in every way. That is other than cost.

There is a certain something about bungees, as there was with slope flying, it was simplicity. Many just find that electric gliders are easier still.

[Vecchio Austriaco]

I agree to Erfolg why bungees are no longer popular. But I have to say when I used it I had less than 11 stones (for the precise guys 68kg) - and I am sure the exercise was good for me

Now I fight to stay below 16 stones and fly electric...

Found my bungee stuff in the loft - is not too old an in good condition. (Graupner, approx 6 years old) Round rubber with textile protection, 150m nylon, parachute, all on a plastic bobbin.

Anybody interested in exercising? - 25£ - less than a month of gym membership

VA

[Erfolg]

Hi Gerhard

Yes, my own bungee is lying in my model room.

I even had an used skean of bungee rubber, in a plastic bag, until recently.

Perhaps more sadly, I still have my power winch in my garden shed, taking up valuable space. It should either be donated to a user, or more probably consigned to the rubbish dump.

In our club we do have one person who occasionally tries to use a bungee. Surprisingly, this causes real logistical problems. As he is on one of the boundaries, and we are in the middle.

I am even less enthusiastic with respect to modern winches, as when I was pressed into service to launch a F3b, for one of our members, I was not sure that I was not about to be launched also. We had one person complain of a damaged shoulder trying to hold on. I felt all the time I was engaged in an unequal tug of war competition and I was loosing badly.

Just like you Gerhard, I could sprint at one time for a hundred or so yards, pulling a model up, that was trying to hold me back. Alas no more, as you could see. I even had hair then!

I do admire the purists though, seeking Nirvana.

[Erfolg]

Thought a picture of my Bungee and winch may be of interest.

The electric winch is to much of a faf to get out.

[Panther1]

Seems to me your Bungee is made for a heavier glider and does not have a nice elastic stretch for a lighter one. I use to have 50 meters of bungee and 50 of line and could get to amazing heights. 8 meters I wouldn't contemplate as that just becomes a catapult, not a bungee.

[Erfolg]

Panther you are spot on, both my devices shown were used for competition type models, as that is what I did all the years back.

Of course light model could be used, with care with the bungee.

But the set up was designed for well over 100 lb of tension. That is a tension where a man could barely move forward against at its max, and provide a good ping.

With respect to the bungee, I feel "doggy stakes" are a must. Screwdrivers totally unacceptable as they can and do come out of the ground, which can result in injury.

[Steve Houghton 1]

Well I have extended my bungee to 30m plus, I can't remember how much line, but it goes up a treat now, the way it should.

I just need to find a bigger field to fly off now. I guess thats the beauty of electric power!

Steve

A470Soaring.blogspot.com