KickAce

What hi-start do you have...? There are differences between them such as small up-starts, 2-meter standard, 2-meter havey duty, etc... How long is the rubber/line on the one that you are using...? Ussually walk back streching the rubber 3-times it's length will give you a good launch... Does the plane rock back and shoot up like a kite or does it have more of a forward motion, could be that the tow hook is too far forward... Just a few things to check...

pimmnz

I know of at least on club member who, when came his time to launch, made sure we were all under cover, his model was vicious and would eventually ping off somewhere up the launch, usually pointing straight down until one day when it launched perfectly straight and floated off into the breeze like a lady. Congratulating the pilot revealed that the RX was switched off... Less controlling is best, until you can manage the sideways swing to build up stretch and energy for a proper ping at the top.
Evan.

aeajr

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First, let me welcome you to the privledged few who will learn to fly on unseen forces. ;

1) What hi-start did you get? Iwant specs and/or a link. How much rubber, what size and how much line?

2) what strength of pull are you getting in pounds or Kilos? Use a fish scale to measure it. Should only cost a few dollars at a fishing store.

3) Where do you have the CG set compared to the MFG recommendations?

4) where is the tow hook relative to the CG

5) Are you launching into the wind?

Go back and read the thread to see if you can identify opportunities to improve your launch.

jeffEE

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Thanks for a great posting. I have just started my un-powered flying. I think the idea of watching my plane gets its wings snapped in half by a hi-start has been put aside. Here are my co-pilots, 1997 and now.

aeajr

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Either those boys are getting bigger or the planes are getting smaller.

From my experience, you have to seriously miss match the hi-start and the plane to risk wing damage from a hi-start. But Ithink we all had that moment or two of anxiety when we did that first launch.

I think it has been mentioned several times, but as you gain experience with your plane, start to move the CG back from the stock position. The lighter nose will allow the plane to be more responsive so it can read the lift better. Do this slowly over many flights.A little move, even 1/4 of an inch, can make adifference on a 2 meter plane. But only you can judge what works best for you.

ARUP

A scale is a great idea. I am like you and 'do it' by feel. When my plane launches to my liking I just drop some kind of marker (the box the hi-start comes in) onto the ground. I can then just walk back to the said marker for subsequent launches. (The only other discipline harder to master in its entirity than sailplaning is rubber powered FF).

aeajr

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Working by feel is great when you are an experienced pilot. But when you are new, having a reference point, provided by a scale, can be an excellent training tool.Knowing how it should feel when it is right will help the new pilot, orthe newhi-start pilot,gain confidence.

vh2q

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I made a hi start from small diameter black bungee, about 60', and then 120' of light line. I have tried to launch it 4 times and crashed 4 times. If I crash again I don't think my Aspire will be salvageable. It climbs at about 30 degrees, then immediately rotates in an arc to the left and noses straight into the ground. This all happens so fast you can't control it. I have moved my attachment point as far forward as it will go. This glider flies fine with a Cox Black Widow on a pylon over the wing, the balance and trim are fine. But I don't like the additional drag and would like to fly "naked". Is this bungee too severe? Or am I not throwing hard enough? When you have crashed it 2 or 3 times, it's hard to get up the courage to hurl the glider full force.

aeajr

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Bungee cord, the fabric covered cord, is terrible or launching gliders. I don't recommend it at all.

Also you say "small diamater" which means it probably is too weak.

You need Latex tubing, typically surgical tubing, which is not fabric covered. This allows the rubber to stretch up to 3X its rested length. Go back and read the first post and you will understand.

Silicone rubber can be used too as long as it is not fabric covered..

Note that in some parts of Europe, uncovered latex tubing is also called Bungee, but in the US, this refers to a fabric covered elastic which is not well suited for launching thermal duration gliders like the Aspire.

lbarnes

Our club has a Hi start that has a 12V starter hooked up direct drive to a spool.

It is ON/OFF and if not careful you will fold the wings on the glider when trying to launch it.

What were trying to do is build a variable speed control for the 12V starter.

Anyone have a schematic for such a modification??


Larry

aeajr

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That is not a hi-start it is a winch.  Hi-starts don't have motors.

pnaton

You high start newbies should enjoy this short clip of champion Mike Smith
giving a tutorial on using a bungee.

Paul Naton
http://glidefast.typepad.com/
http://radiocarbonart.com/

[youtube]http://www.youtube.com/watch?v=mTd3PGC8zOs[/youtube]

aeajr

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Thanks for adding that video.

invertedthoughts

Tagged cause I want to make one. (don't want to spend $60 that I've seen them for on Ebay)


Where is the cheapest place to get the surgical tubing. What diameter would you all recommend for 3 meter gliders? (BOT and Robbe ASW 19)

aeajr

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e-bay has been the cheapest place I have found latex tubing.  I have purchased there several times to make hi-starts.

Light 3M planes, say under 65 ounces, can be launched with 5/16 latex tubing.  If you plan to get into larger or heavier planes, you might wish to go to 3/8 tubing.  If I was building a 3M hi-start I would use 3/8 tubing.  That is 3/8 OD, outside diamater. This assumes a 1/16 tube wall but the wall can vary from 1/32 to 3/32.   Naturally the thicker the wall, the stronger the tubing.  So a 5/16 OD with a 3/32 wall might be comparable to a 3/8 OD with a 1/16 wall.

If you are trying to go cheap and buy from e-bay you MUST confirm that the tubing is a solid pice and not a box of short pieces.  Both kinds can be listed and sometimes they don't say, you YOU must confirm this.

Here are some examples:
http://cgi.ebay.com/50ft-BLACK-RUBBE...item3f06aeb46a

http://cgi.ebay.com/UP-START-LATEX-R...item2a0e718f2a

http://cgi.ebay.com/UP-START-LATEX-R...item2a0e719ca6

You can join pieces to make longer rubber.  So, for example you could join two 25 foot lengths to make a 50 foot piece.  The method is discussed in the thread.
http://cgi.ebay.com/50ft-BLACK-RUBBE...item3f06aeb46a

aeajr

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aeajr

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I have often recommended against using hi-starts in freezing temperatures, however so many people have related their positive experience with hi-starts in cold weather that I felt I should relate this to you.  I still do not plan to use my hi-starts in freezing weather but I have alternatives.

I have a ford long shaft winch, which is my main launcher.

I also have a OneWinch, www.onewinch.com which works like a winch but has no batter or motor.  You may want to give it a try.

aeajr

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aeajr

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Getting Latex rubber tubing that is sold for hi-starts is your best approach, but there are others. One option is to buy Theraband or similar exercise tubing. Look at the charts to get an idea of the strength.

Try to find it in full rolls as sometimes they sell it in cut up sections for exercise machine use. I have seen listings for 100' but have learned that it is actually four 25 foot sections You can join the sections but it is better to have a solid roll.

As you know the rule is that the hi-start should have at least 3X the pull as compared to the weight of the glider when you pull it 3X its rested length. Remember you don't have to pull it all the way to 3X length to launch. The chart below shows the pull with a 1X and 2X stretch. We are going to go up to 3X so multiply accordingly. Looks like a 1.5 factor from 200 to 300%.

For under 2M gliders or very light 2M gliders in the 1-2 pounds range, the red should work well.

If you are flying 2M to 2.5 meter gliders, in the 1.5 to 3 pounds, the green should be good.

2M to 3M gliders in the 2 to 4.0 pounds the blue should work.

If you gliders are typically over 3 pounds to about 4.5 pounds the Black is for you.

If your glider has a fairly strong wing you can go up a color for a stronger launch. I have launch my 35 ounce Spirit at 12 pounds of pull and I launched 28 ounce Gentle Ladies at 10 pounds of pull, around 6X the weight of the glider but it is not necessary to go that high.

And if you have some heavier glides or want a STRONG pull for a STRONG launch on a strong glider then get the silver or even the gold!

My hi-start would be between black and silver. I have launched 2M through 4M planes from 30 ounces to 85 ounces from that hi-start. On the 2M I may only pull it back 2X. On the 4M or heavier planes planes I pull it all the way.

How much pull can you handle?

That is a personal decision. I can handle the full 24 pound pull on my hi-start by myself but it is a bit tricky pulling, holding and releasing the plane with one hand while holding the radio in the other. For many people anything over about 16 pounds of pull starts to become hard to manage alone. By my standards 16 pounds of pull should be good for a 64 ounce glider in calm air and up to about a 75 ounce glider with a 5 mph breeze.

Amazon has all the colors in 100' lengths but they are actually made up of 4 25 foot sectons that you would need to join. Joining is not hard but a solid piece would be better.

here is a RED listing
http://www.amazon.com/Thera-Band-Res...eraband+100%27

AMA-69405

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Here's some additional info in the form of a chart showing most of the major players in the high start market (including TheraBand). It's pretty self explanatory, but be sure to read the notes at the top of the page for more insight.

aeajr

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Gary, it comes up too small to read on my screen. Can you post it as a .PDF?

AMA-69405

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On my machine, you have to click on it a total of 3 times to get actual size... click on the thumbnail to open, then click on the super thumb to get web page format, then click once in the imaged text area to enlarge.

Yes... I'm too cheap to buy the Adobe converter. :-) I've heard there are some free converters out there, just haven't gone looking... any suggestions?

aeajr

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That worked. Thanks.

I have seen these theoretical tables before. No problem with them as I have not tested everything he has listed. However I have tested and used the Aerofoam 3M, the Pinnacle L and the Dynaflite HD. On those three his theoretical numbers come up 2-3 pounds below the actual measured pull that I got during tests at the field using a spring scale. For example the chart predicts 17 punds for the Aerofoam 3M. We have 3 at the field and they all test at 19 pounds using two different scales. That 2 pounds is about an 11% variation from the predicted. Not bad and it is probably better to err on the low side and that is how I see these tables, about 10 to 15% low.

Maximum glider size is another point of departure. He uses a 5:1 ratio of pull to glider weight but he does not qualify the basis of that ratio in the table. I have found that 3:1 is adequate with a 5 mph breeze for most gliders. I have found that 4:1 is good in calm air and very good with a breeze. 5:1 or higher is what I call a strong launch which is fine but not required. I have launched as high as 7:1.

However, again, these are opinions so mine is no better than his. There is no objective standard so there is no right or wrong. I will tell you that an 82 ounce Legend has been launched with an Aerofoam 3M into a 5 mph breeze with no problem.

But all information is useful. The reader has to judge and these tables at least give relative numbers to look at. The absolute numbers may not be exactly right but they are close enough and the strength ratio of one to the other is probably pretty accurate.

AMA-69405

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In every case where the manufacturer/retailer provides tension numbers, the chart agrees within about 10%. Sometimes high, sometimes low, but always somewhere between spot-on and plus or minus 10%. Keep in mind that temperature and rubber age can affect readings, so I would say your 11% delta is certainly within the range of expected testing deviation.

Precisely... that's why I put the chart together. Otherwise it's difficult for a novice to understand, for instance, why the Dynaflite Heavy Duty, Hobby Lobby 2 meter, Hobby King 8 mm, TheraBand Red, and the NSP Medium are all the same device, practically speaking.

aeajr

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A few more examples of hi-start launches:

https://www.youtube.com/watch?v=JghL7LRFQoo

https://www.youtube.com/watch?v=tUHykiGOOyU

Hi-starts are not just for little woodies. The Nan Shadow is a high end composite competition glider

https://www.youtube.com/watch?v=RGHcya0WPEQ


Mike Smith is a world class competition pilot.
https://www.youtube.com/watch?v=mTd3PGC8zOs