Hi guys

I read somewhere of some dlg contests in the states and the UK offering the option of launching using some type of catapult. I know to many of you this amounts to blasphemy, but to guys like me, who've had a history of shoulder problems its a welcomed option.

As far as I can understand, this is not a kiting type launch like we get out of a histart, but follows the trajectory of a typical discus launch (thus minimising bending stresses). Does anyone have any details of this method? I'd appreciate any information on towhook placement or construction, bungee material, photos, anything at all...

Thanks

Dan

I believe just about all contests will allow you to have a 'designated launcher' who will launch for you. Caveat it you have to be standing with them at launch (able to tag them).

Hi Dan,

You are correct that at UK F3K competion we do allow models to be launched by bungee/hi-start if the pilot chooses.

The reason for this rule is to encourage those who are not able to discuss launch, to take part. (we have several of the regular competitors who are in their 70's)

Although I agree that the F3K rules do allow for a "proxy launcher", this does not get rid of the fact that the competitors also need to be able to practice by themselves. However we do encourage the use of proxy launchers too.

The specifications of the bungee/histart are strictly regulated, along with the amount of stretch the pilot is able to apply. Through some development the guys using bungies have found that a launch seems to work better if they use the bungee to add speed to the model before release, rather than to kite up the line.

If we did not allow for bungees we would probably loose some competitiors, so the attitude is to make the sport accessable to all.

The stopwatch is only started when the model is off the bungee, and also the competitors are at a disadvantage when it comes to turnaround times.

The history of "hlg" in the uk is slightly different to the states. We used to have a "mini-glider" catagory which used bungees rather than javelin launch, so again there are many people out there who still have models that can only be used by bungee.... and we want to get them flying in F3K comps.

Hi Richard

I think you've hit the nail on the head. If I was competing I would probably get a friend to throw for me, but for practice I think this is the way to go.

Do you have any specific details on some of the launch systems used? I would be trying to avoid any bending forces at all. Are they just a scaled down histart with a forward positioned hook or do they use a catapult like the electric ducted fan guys use?

Thanks

Dan

Richard, I sent you a PM with a few questions...

I'd betcha they could make a good one on Mythbusters.

I would wonder if tha ATL ATL type of thrower would allow for similar launches. These devices were used by the primitive peoples around the world to throw spears faster than an arrow out of a bow. Requires much less physical effort than a spinning discus launch but may be usefull for keeping the hand launch process for folks who have difficult with the physical effort of a spinning launch. I will post some pictures of the method and will try it next chance i get with my dlg.

Hi Dan,

For discussion on the tow-hook placement take a look here :- http://www.flyquiet.co.uk/smf/index.php?topic=728.0

If you need more information, on setting up a bungee model, the father/son team Arthur&Jeff Ott are the ones who have the bungee launch perfected. Arthur uses a Blaster converted to V-tail. If you send them a PM on the flyquiet forum (their handles are "oldott" and "jefo") you will definately get a reply.

A copy of the rules we use for bungee's : -

7.6.1.2 Launching

(a) *As a UK interpretation of the international F3K rules, launching may be by hand or by “mini bungee”. Hand launching may take place anywhere within the designated launching and landing area (see 7.6.3 below) giving consideration to any competitors using a mini bungee.

(b) If a mini bungee is used, it must be supplied by the competitor and have the following characteristics:

(c) A maximum un-stretched length of 20 metres of which a minimum of 15 metres must be of non stretching line.

(d) A clearly visible pennant must be attached to the model end of the line

(e) The bungee must be staked securely enough to withstand sustained tension. The stake should be positioned 5 metres upwind of the windward edge of the launching and landing area.

(f) The maximum stretched length of the bungee at the point of launch shall not exceed 27 metres. Any competitor using a bungee shall also provide a 27 metre non elastic tape where one end is anchored by the bungee stake; the other end shows the maximum permissible stretch at launch. The maximum pull at a 27 metre stretch of the bungee shall not exceed 6 kg.

(g) The bungee and 27 metre tape shall be reeled in by the competitor at the end of his/her slot unless the competitor, or someone else using this competitor’s bungee, are flying in the next slot*

Originally Posted by joe schnur

I would wonder if tha ATL ATL type of thrower would allow for similar launches. These devices were used by the primitive peoples around the world to throw spears faster than an arrow out of a bow.

Joe,
This has been discussed here many times in the past. The Atlatl gets it's launch velocity from the flexibility of the dart. The dart is about 8 feet long and during the initial part of the launch it flexes like a bow and then unflexes as the dart leaves the throwing stick. This unflexing is what gives the propulsive strength of the launch. The dart is actually acting like a bow.
So unless you build a handlaunch with an extremely long and flexible fuselage, the Atlatl method will give very little launch velocity.

The way I see it, a great launch can keep you in the running for a top spot.

So...for all those who would prefer to read air better, let's allow smoke flares to be deployed 15 seconds before a round starts.

Why? Because the way I see it, being good at reading air can keep you in the running for a top spot.

Hi Richard

Thankyou very much for the reply and link - exactly what I've been looking for. I know one of the attractions of dlg is the physical side of it, but I'm really interested in the flying that happens after the launch. My hope is that low level thermal hunting will help me improve my air reading ability for 2m and larger thermal flying.

Dan

Hi Richard

I know a Blaster is a moulded model, is something like a Supergee or Apogee going to be able to survive this type of launch?

molded and bagged models seem to have similar strength when it comes to in-flight loads... so yes, I think a supergee would handle this kind of launch with no problems at all. We have another competitor who regularly flies a Longshot using the same method.

The "catapult" style launch will put much less stress on the model than a "kite" launch, as there not so much bending force on the wing with the "catapult".
To be honest I think a model has to cope with much more stress from a standard discus launch.

Backlog. Someday I'm gonna finish my rotary launcher before I die. It uses a center post that driven by an electric motor . This has the glider attached to it by a tether.

The post height is determined by the W/S. On start up the centrifugal force brings the glider to level flight. The tether is then released and up she goes.

The devil is in the details but the prototype looked good. I'm to old to launch by hand and I just have to get back to this project. Can you imagine the speed and height this thing will reach?