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Using a bungee

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Mel Jones04/12/2017 08:39:12
46 forum posts

I have a Sonata glider which I have flown from the slope, but I have a problem when flying from our flat field site using a bungee.

I cannot get a successful launch, the model is "pinging" off the line very early.

I have tried adding a little down elevator during the launch and this helps a little.

The c of g is set correctly, and the tow hook is 10mm in front of this point.

Can anyone suggest what it is I am doing wrong?

Denis Watkins04/12/2017 08:42:35
2124 forum posts
108 photos

The hook has different positions for "tow" and "bungee" and is usually marked on the plan

It sounds like yours is set to tow

Check the instructions on this one

From the internet reads

I have located the c of g for my Sonata, I did this by trial and error the plan shows a c of g point but in glide tests is was found to be to far back so another 10gms of lead added to the nose and the second test proved to be just about right.
Once the c of g was found I then fitted the tow hook a few millimetres in front of it, the glider was flown from my bungee with no problems at all.
I had forgotten what it was like flying this way, the model is quite sluggish on the controls because of the slow flight speed, need a thermal or three now.

Edited By Denis Watkins on 04/12/2017 08:54:03

Steve Houghton 104/12/2017 10:00:56
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1847 forum posts
136 photos

If the model keeps pinging off the hook early, I think I'm correct in saying that the hook could be a little too far back from the COG point.

It's been quite some time since I used a hi start to launch a glider, and I always had a little up elevator dialed in to increase the angle of climb, and also it helps to keep the line attached to the hook.

This video was taken a few years ago of me launching my X Models Whisper on a hi start.

Tom Sharp 204/12/2017 17:14:12
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2512 forum posts
12 photos

Your not pulling the bungee tight enough. I always used to walk 100 yds or more back to get sufficient tension

Mike Etheridge 105/12/2017 08:36:12
1296 forum posts
335 photos

When my nephew Nigel and I used to launch my old 8 ft span Micro Mold Sprite from a bungee, as has been suggested above, we stretched the bungee to it's fullest extent before attaching it to the plane. Once the plane was in the air we discovered that no movement on the elevator was necessary until the point of detachment of the bungee. However rudder movements were necessary to keep the plane on course. When we last flew the plane at the Common Broughton Gifford, we forgot about the elevator issue and an up-elevator input fractured the ABS fuselage and the tail assembly ripped off and had to be mended with duct tape. The plane I bought in the 1970's still exists.

2016-01-13 21.06.47.jpg

Basa05/12/2017 10:36:06
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36 forum posts

Hi Mel , it could a few things not quite right as some have already suggested or could simply be that you may not be putting enough pull on the bungee , one has to be ' brave ' on how much tension is required to keep it on the hook . When released it should not need elevator but needs to climb at a very steep rate using rudder to keep straight on line and into wind . The steep angle of climb should maintain tension to keep it on line until the glider is over the bungee anchor point , when it should come off the hook . Please ensure that the anchor cannot pull out when under tension . Hope this helps.

Steve Houghton 105/12/2017 11:09:27
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1847 forum posts
136 photos

Yep, that bungee needs to be really tight, and you need 3 - 4 times the amount of line to bungee, so 30m of bungee tubing to 90m of line.

The hook needs to be ¼" - ½" forward of the CoG. If you have it right on the CoG the launch can be quite vertical and difficult to control, a ¼" will still give a very steep climb so I would recommend ½", which should make for a very controllable launch.

I prefer to attach the hook when it is slack then pull it tight, although if you have a partner, they can pull it tight and then attach the model. With so much tension on the line, you need to hold that model out behind you with a straight arm, as if it were a javelin, then bring your arm up over your head and release it. I remember seeing a video or two of people who had little tension on the line, launched with a bent arm, as if throwing a ball, and the model hitting them on the back of the head laugh. Use the rudder to control direction on the way up. Sometimes you may find that the line doesn't want to come off the hook. If this happens, push the nose down briefly, then sharply up and the line should ping off.

I found this video for you, about mostly what not to do.

Mel Jones05/12/2017 14:06:22
46 forum posts

Thank you all for your input.

I think my problem is with the tow hook not being far enough forward of the c of g, I have dug out the plan and measured where it should be, and found that my model was a little nose heavy. I will correct this and try again.

Steve, you have a great blog site, I must make the effort and come visit your neck of the woods for some sloping.

Thanks again.

Steve Houghton 105/12/2017 14:10:51
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1847 forum posts
136 photos

Anytime Mel, we have some awesome, huge slopes to fly off, in all wind directions.

Steve

Rich too05/12/2017 19:03:39
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2475 forum posts
940 photos

I taught myself to fly on a bungee - the old surgical tubing type - do they still make them? Ours was stolen whilst we were flying one day! It was stretched out across the field and someone nabbed it!

You do not want down elevator. If anything up elevator will keep the line taught and it should go up like a kite. yes

john stones 106/12/2017 13:29:36
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8858 forum posts
1379 photos

My bungee days, Xmas day if I remember right.js11.jpg

Fatscoleymo06/12/2017 14:01:16
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221 forum posts
86 photos

Gor Blimey John!.....should have issued a warning before posting that photo!!!wink

Fats

Steve Houghton 106/12/2017 14:09:18
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1847 forum posts
136 photos
Posted by Rich too on 05/12/2017 19:03:39:

I taught myself to fly on a bungee - the old surgical tubing type - do they still make them? Ours was stolen whilst we were flying one day! It was stretched out across the field and someone nabbed it!

You do not want down elevator. If anything up elevator will keep the line taught and it should go up like a kite. yes

Rich - Yes you can easily get the surgical tubing from HobbyKing I joined 2 10m lengths together I think on mine.

Then I used 70m of 80lb test fishing line and a corkscrew type dog lead peg thingy to secure it into the ground.

Frank Skilbeck06/12/2017 16:02:40
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3807 forum posts
91 photos

Don't forget to add the parachute to bring it back when it unhitches from the glider.

john stones 106/12/2017 16:19:31
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8858 forum posts
1379 photos
Posted by Fatscoleymo on 06/12/2017 14:01:16:

Gor Blimey John!.....should have issued a warning before posting that photo!!!wink

Fats

Cheeky, thought my name was warning enough. face 1

Mike Etheridge 107/12/2017 10:23:06
1296 forum posts
335 photos

To anchor the bungee we used a fishing rod rest. Unfortunately Bungees are not allowed at Epsom Downs and Bartons Point clubs where I fly my planes, so my redundant bungee has been in the loft for years. However I gather that this could be relaxed at Bartons Point provided there is a limited number of flyers? In the past I have flown with a bungee at Croydon Airport, South Norwood sewage works site and as I mentioned before at Broughton Gifford Common. I am not really sure what the objection is to bungees although there is a defined area / segregation for kite flyers at Epsom Downs where obviously long trailing lengths of line could be hazardous?

Edited By Mike Etheridge 1 on 07/12/2017 10:23:37

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