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High Start Beginner


TJ Alexander
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I used the motor out of my Multiplex Easy Glider Pro, which was a HIMAX C2816-1220 It had a 9by6 folding prop and used a 3S2200 mah battery. This motor is really too powerful but as it was available I used it and it gives quite a spectacular rate of climb

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  • 10 months later...

Hello, for years I have launched my Bird of Time,( 3 meter) with my high start out here in the flat lands of Kansas. 100 feet of 1/2 inch OD surgical tubing and 400 feet of kite string to great effect. What I was wondering is just how big/heavy a sailplane I could get away with using this set up? Or just get into elec launch from the start? I was looking for something more scale. Anyone using this kind of High Start for something that had more weight?----Bob C

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  • 2 years later...

The German company EMC-Vega supply a range of five different strength (diameter) rubber tubes for bungee/high start, I have three.

 

Their strongest rubber is 'scale' which they say is for models in the 8 to 20 kilogramme range. They also provide information on using their rubber doubled.

 

I believe the 20 kg models are being catapulted off a slope with a very short bungee, same as full-size practise.

 

Most of the Multiplex range of large gliders kitted in the 1980s and 90s were provided with belly mounted hooks intended for winch launching, my ASW 22 is 4 metre span and weighs 4 kg. The worry for me would be a wing tip catching the ground and cartwheeling (supposed to be launched from the ground).

 

The headwind makes a big difference, I have launched an F3J glider (3.5 metre span, 2 kg) on 150 metres of monofilament line staked at one end, no rubber.

 

My personal limit is if the glider is too big or heavy to test glide from a flat field then I won't winch/bungee launch it (slope only). The largest gliders I will bungee launch are 'Open' class RES models which are around 12 ft span, the most common size of model I bungee launch is 100" (100S class). Without the test glide there is no way of knowing if the trim (pitch and roll mainly) is good, if it's wildly out then a bungee launch can be exciting. If a model's trim is out on its first slope launch it's not such a problem as the airspeed/energy is usually much lower and the distance between the model and ground (height) is much more than with a hand launch on a flat field (the hill falls away).

 

The Multiplex ASW 22.

 

DSC_0103.thumb.jpg.57b7f3da5947c045d648d2a9488f4a75.jpg

 

Chris Foss Multi-Phase about to be bungee launched, 142" span, rudder, elevator, spoiler.

 

1125610246_PictureorVideo232.thumb.JPG.53d3572349e669656aa1283ff3259ce4.JPG

 

Chris Foss Centi-Phase 100" span RES. This size is my comfort zone for bungee launching.

 

P9179008.thumb.JPG.dc80079df87854072eeb6b45b797ded7.JPG

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flat field launch.  My high start is 100 feet of 7/16 OD surgical tubing and 400 ft of kite string. I have not ever had any problems launching my  sailplanes but I am usuallly just staying with what has worked in the past.  Is there any guidlines for the proper pull in pounds I should being shooting for?

  Any suggestions on the max size I should go for on my next build?-------------Bob C

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I've translated an old EMC-Vega page:

 

The high start with tubular rubber is a practical launching technique, which has little set-up time compared to winch launching. Also as a launching aid on slopes and for heavier electric models, a bungee start is ideal for faster ducted fan models.

 

These super tubular rubbers are made from protein-free, UV-stabilized natural rubber manufactured for EMC-Vega with unrivalled precision (0.07mm tolerance) using the dip drawing process. (Therefore only available in lengths of 25 and 50 feet, which we connect to the length for you with plug-in connections). The material is coloured anthracite to increase UV protection and reduce temperature stress differentials. It has a usable maximum stretch of up to 700% (breaks at 850%)! The optimum range of use is 2-5.5 times the stretch with a long-lasting, even pull. Launch your glider initially with a pull of 3-5 times the model weight. For jets/ducted fan and bungee launches use 5-10 times the model weight. Please note, however, that a strong man can hardly hold more than 18 kg of starting tension at shoulder height due to the laws of mass and leverage.

 

With higher starting forces only the ground launch is possible. From 30 kg you should pre-tension in pairs.

 

A good high start launch kit consists of: 22 - 30 m of rubber plus approx. 100 m of rope plus a parachute. 7.35 m is sufficient for slope soaring and with ducted fan or starting aids for e-gliders. It may be useful to lay out up to three strands in parallel in order to be able to cover larger weight ranges. e.g. 3 x F3B for 3-4 kg / 5-8 kg / 9-12 kg gliders. For F3B gliders, the three strands can also be linked in series to form a 22 m strand. A 22 m rubber stretched 4 times (88m) has more energy than a 29.4m rubber stretched 3 times (89.2m)!!! The relation rubber length (stretched)/rope length is about 1:1 to 1:1.5, i.e. with 22 m rubber 70 -130 m cord makes sense. Accordingly, 22 + 3x22 +70 = 158 m or up to 22 + 4x22 + 130 = 240 m space length are required.

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I have used a spring balance to measure the '3 to 5 times model weight pull' which worked but is over complicated in reality. It doesn't take into account any headwind. The answer on stretch is somewhere between not enough and too much! I have used gentle launches on new models, they fell off the line at 50 ft and landed ahead and one launch where I stretched too much in windy conditions resulted  in the model describing an arc to the left (rolling on the line) instead of launching straight.  With a new model I would always start off gently then add paces/stretch until it achieves a full launch height.

 

I use the number of paces of stretch, 60 to 80 with the EMC rubber which is stronger than the amber surgical tube type. For my surgical tube bungees I stretch to 100 or 120 paces, it never really reaches a stretch limit. In windy conditions the model often stretches the tube more and rises above my head and behind me.

 

Whichever type of rubber I'm using I use the reel it is stored on to mark the best launching spot on the ground so that I don't have to count the paces for subsequent launches.

 

A pennant tied to the line end of the rubber is a good indicator of launch height, when it stops rising the model is at full height, hanging on longer will lower the launch height.

 

I should add that the 12 ft span models I launch are very light, 64 ounces or 2 kg.

 

Must confess that I don't bungee launch often nowadays and I have dismantled my F3J winch to compact it for storage. Electric gliders are very convenient (fit battery, launch) and there are no worries of folding the wings through overstress. I fly with 300 sheep (they are all better than me!) and there is a risk of them getting tangled in the line and/or chewing it. 

 

Some photos:

 

Surgical tubing, 3/8" diameter:

 

20180129_140638698_iOS.thumb.jpg.09d8e783d1e0276560eb5cca3d032dc2.jpg

 

EMC-Vega 'All-round' rubber:

 

IMG_1581.thumb.JPG.b25ba3ed8bc29233e1c8feaa0f89200b.JPG

 

Cotton covered elastic, this type hits a definite stretch limit and delivers its power quickly rather than progressively, useful in calm conditions but not recommended otherwise.

 

IMG_1590.thumb.JPG.24d2306f5ad2d1d2b7d20b391240a420.JPG

  

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Just thought of another high start/bungee launch tip, if you use a transmitter neck strap it can end up swung round to your back (one hand on the fuselage, one hand on the nearest wing to hold it level when it's gusty) which is not good when you need to find the sticks quickly.

 

A transmitter harness or tray stops that happening and is the way forward. Better still is to have a buddy launch for you.

 

The same problem happens in F5J (electric launch thermal gliders up to 4 metres span) when it is gusty, I have to have my left hand on the transmitter to start the motor. If my timer/helper launches then there is a slight delay while they find their stop watches, acceptable if you're not trying to qualify for the British team!

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Hello all, I must have posted this before but can not fine my question--so here goes. My hi start is 100 feet of 7/16  OD surgical tubing and 400  feet of kite string and I have used it to good effect, but the stretch has always been just an estimate based on the fact that I have never pulled the wings off. Can anyone give me something more scientific? " How many  pounds of pull should I be aiming for based on glider weight/wing span/construction ?"  I have heard to take the weight of the glider and multiply by 5 for the line pull. Any thoughts? Thanks in advanced

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  • 2 years later...

From experience I fully agree with the Gentle Lady, and the Sophisticated Lady is fine as well, as is the Multiplex Easy Glider. I started on the Hi-Start with a Robbe Silence foamy, and later a Sig Riser, which was and still is teriffic! When build like the plan the is very strong, I once ripped the Hi-Start with it, the plane was fine. Nowadays I mostly shoot up my Höllein AndREaS RES glider. For the last couple of years I have been using the RES bungee from SETA Modelltechik. It is geared towards the RES competitions but very suitable for the 2M stuff weighing maximum 1KG. It has 15 meters (amost 50ft) of bungee tubing, and 100 meters (328ft) of 0,7mm yelllow nylon. This set is worth it's weight in gold. It is not explosive, but releases the energy nice and gradual. Stay away from the woven stuff. Give HI-Starting a try, when you had your first thermal flight you will be hooked. Look mom, no engine!

The pictures are my Pilot QB2500, a friend captured it beautifully.

This is the stuff I use:

https://zeller-modellbau.com/zubehoer/zubehoer-res-modelle/hochstartschlauch-silikon-8-mm-o-15-m-gelb-seta-modelltechnik/

 

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Edited by High_Start
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It is an old school glider, doesn't like too much wind, but thermals very well. I have since put an electric motor in the nose, I know, heretic at work, and I can easily get 1 hour flights on a 3S2200 in dead air. Very relaxing bird, and Pilot still is a great brand. I have a Lavender I am planning on building this year.

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11 minutes ago, High_Start said:

However, nothing beats sending a glider up the high start, the chute drifting down is a bonus.

I agree,  Just the wind noise of the glider going up the line.  There's something magical about it as the energy it is using is your own, as it was your muscles that stretched the bungee, unless of course you have a 'fetchermite' to do that for you! 😁

The bit I really like, is that in a decent wind, even though you think you've stretched the bungee as far as it will go, often when you release the glider, the wind stretches the bungee even further, so the glider goes back from the launchpoint as the full length of the bungee lifts the ground.

Edited by Robin Colbourne
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