proper zoom technique for the bubble dancer

[neonbutterfly]

hi....i have been doing some zoom launches with my BD.....so let's hear your winch/zoom technique......

bob :confused:

[rdwoebke]

I'm a guy with lack of knowledge on zooming too. I folded the spar on my now gone Bubble Dancer attempting a zoom on it's 7th winch launch. I'm slowly working my way up to stronger winch launches on the Allegro and might feel gutsty to try zooming again some day. I have I think 11 winch launches on it. I'd be interested in hearing some techniques on knowing when/what/how on an RES model like this and also if there is some way to reasonably practice the zoom without a winch.

Ryan

[Bernd Brunner]

I´m practicing zoom lauches on a strong highstart with small 15oz HLG´s, F3J-Pikes or 2m planes. The dynamic of the launch depends mostly on the relation between the weight of the plane and the force of the highstart. Second point is the relation between rubber and line. We are using 45´ rubber and 140´ line. A longer line will decrease the dynamic ot the launch. A relation greater 1:7 (weight/tension force) is good. 1:10 is fun! An example: The planes weight is 2lb and the tension force is about 20lb. :-)
After practicing highstarts with zoom, my first two-man tow F3J power-launches where without surprise and without too much stress (for me..). With the highstart, you can practice the whole procedure including switching between flightmodes a.s.o.

Try it, you will like it!

Bernd

[rdwoebke]

Bernd,

Thanks for the info. Hmmm.. I thought a shorter line in relation to the rubber would be better for practicing the zooms. I have a pretty strong high start in relation to my 20 ounce Allegro. I'll have to practice some more next time I have the opertunity to lay a high start out. I'll also have to work on lengthening my line.

Ryan

[2motheus]

Bernd,

Thanks for the info. Hmmm.. I thought a shorter line in relation to the rubber would be better for practicing the zooms. I have a pretty strong high start in relation to my 20 ounce Allegro. I'll have to practice some more next time I have the opertunity to lay a high start out. I'll also have to work on lengthening my line.

Ryan

I think you misunderstood Bernd's statement.

[Bernd Brunner]

Hi Ryan,

with this setup of the highstart the launch-height is about 350 - 400ft. The rubber we are using (OD 9.6mm 1/3"/ ID 4.8mm 2/10") can be stretcht up 600%. During the lauches we do, i think the rubber is stretched by 350%. Before i start diving for the zoom the rubber is still stretched, so a lot of the energie in the stretched rubber can be tranformed into speed.
A stronger rubber, with a higher spring constant, where we reach a force of 20lb with 250% stretching of the rubber, is also possible, but you will have less time for the whole procedure.
With my planes the lauches are nearly vertikal, an in a light breeze it seems, that the rubber will be additional stretched.

BTW how long is your rubber and the line? What kind of rubber are you using?
Strong rubber with a short line sound more like bungee..

Bernd

[rdwoebke]

BTW how long is your rubber and the line? What kind of rubber are you using?
Strong rubber with a short line sound more like bungee..



I'm not sure on the diameter of my rubber. It is a NSP Pinnicle high start, I want to say either the standard or the large. Anyhow, it moves the Allegro pretty quickly. I guess I could get a fish scale to measure how much tension I am generally using. Mine is kind of old but the rubber is good. The line is way shorter than original due to a line break and loosing the top of the high start. I'll have to go measure the rubber length and try to get close to your ~ 1 foot rubber to 3 foot line ratio. Then I'll see if I am launching with between 9 and 12 pounds of tension. That is near your 7:1 and 10:1 pull ratios.

Thanks for all the help!

Ryan

[rdwoebke]

I think you misunderstood Bernd's statement.

I think you are right.

[tonyestep]

You can practice zooming from a hi-start but the altitude gain is minimal. The incremental altitude you get from zooming off a towline comes from speed gained in the dive beyond the speed you would gain in a normal dive due to the acceleration of gravity. To gain much, the plane has to be going pretty darn fast, at least 50 mph.
(For a full explanation see http://www.mvsaclub.com/docs/zoom.htm)
The best contest launchers get their planes up to 70+ mph, and an F3J or F3B launch is much faster than that.

Needless to say, the wing has to be strong to stand this. The BD has a design redline speed of 90 mph, which is enough for a heck of a winch zoom. I do not believe that mine is any stronger than any properly constructed built-up wing, and it will take a very aggressive launch. Our club has Real Balls winches; when I get to the top I just stomp the winch pedal, hold it down, dive straight toward the turnaround for half a second, and pull full up. I stay on the pedal until the plane is off the hook. The plane has tolerated 4 years of this, no problem so far. I do the same thing with the little Allegro, which gets going so fast it scares the hell out of everybody watching. Even an Ava will take a pretty hard launch, although not as hard as the BD.

The key to constructing the spar is to make SURE that the carbon is stuck to the shear webs EVERYWHERE with slow-setting epoxy. If it is, the wing will take a very satisfactory zoom.

Tony

[rdwoebke]

The key to constructing the spar is to make SURE that the carbon is stuck to the shear webs EVERYWHERE with slow-setting epoxy. If it is, the wing will take a very satisfactory zoom.


Tony,

I like to think I know where I went wrong on the construction of my BD wing that resulted in a spar failure and corrected it in my Allegro Lite build. That said, I am still pretty gun shy and absolutely suck at launching.

Thanks for the link. It is an interesting read and some food for thought.

Ryan

[Bernd Brunner]

I have made some logs with zlog last weekend, when i´ve practiced zoom launches with my his-start.

Model was a pike superior. wind 2bft.
As you can see, i start diving at 81m for 0.8sec to 71m (or 64m) and then zooming to 126m. The climb rate during the dive is about -35 to -50m/s.

http://static.rcgroups.com/forums/attachments/3/2/2/4/9/t996874-97-thumb-pike_highstart_zoom.jpg

I´ve used the hi-start described before: 15m rubber / 50m line. Stretched 500%

Bernd

[aeajr]

Interesting discussion.

At our club meeting last night we had a discussion about winch launching which is not the same as hi-start launching. The topic of zooming came up. Our speaker, John Hauff, is a very experienced contest pilot of 20 years with many wins and high placements in soaring contests.

He drew a very clear distinction between "zooming" and "pinging" which may be relevent to this thread.

He described a zoom as a high speed exit from the winch line at about a 45-60 degree angle where the speed comes from stepping on the pedal, then a brief dip and an exit from the line with a lot of speed at that middle angle. He says he prefers this approach as it allows him to cover a lot of ground up wind so he can explore the air beyond the winch area more effectively as he gains some reasonable additional height.

He described a ping as a similar process but with a radical upward climb of perhaps 90 degrees looking for the greatest altitude but not covering a lot of ground. There is very little downwind travel in this method. Your are essentially trying for straight up.

Both methods are used. The Ping puts a greater strain on the wing and is more likely to cause a wing break.

So, how does this translate to a hi-start?

I have a Pinnacle XL hi-start that I have used to launch Gentle Ladies at 26 ounces and Legends at 80 ounces. I have successfully zoomed all of these planes off this hi-start.

For me the key is that this hi-start is both powerful and heavy. The rubber is 3/32 thick and will yield over 30 pounds of pull at 300% pull. It is really much stronger and heavier than you would use for the lighter planes. We launch them at 150% pull at 12 to 14 pounds pull. And, when launching these planes, I use the 100 feet of rubber with 500 feet of line. If there is 5 mph or more in breeze we will get all that line up and a large % of the rubber even with a Spirit.

Back to the zoom.

At the top of the launch, perhaps 3/4 way to the spike, we either have energy left in the hi-start or we have the weight of the hi-start that we have lifted. A brief down tick of about 1 second provides some significant acceleration, then we zoom off the end, even with a Spirit. I would say we are gaining 50-75 feet using this higher speed 45 degree angle exita and covering significant down wind ground without over stressing the wings.

Even when winch launching my Thermal Dancer, I more typically go for the zoom rather than the ping. I go for speed off the line and about a 45 degree angle more than the straight up ping. Then I will take the climb angle steeper if I have the speed till I am near stall, then flip to a horozontal float at the last second. I picked up this last second turn from learning to side arm launch my Boomer and watching the DLG guys launch.

I don't know if this is a helpful addition to the tread but I thought the ping vs zoom distinction might be helpful. Ask yourself, which you are trying to do, a zoom or a ping.

Clear skies and safe flying.

[tonyestep]

Here are a couple of data points. At our club contest last Sat I put my WSTech vario in my Bubble Dancer. We launched off 150 meter lines with winches. I didn't get a reading on my first launch, but my second was 509 feet and my third was 490 feet.

In order to get the best launch with a BD, you need to get everything set up right so it will rotate fast. Throw it with a lot of line tension, get it going as steeply as possible, and pressure it so the wings bend as much as your nerves can stand. As soon as you can see the bottom of the wings (i.e. sooner than you think), a slight dip, ping off, climb vertically. The dip should last no more than 0.4 second.

The BD is, I think, the highest-launching RES plane, but the Unlimited planes can launch higher. I was getting launches of around 600 feet with my PP. The RES wing can't develop as high a CL, since you don't have launch flaps, and you don't have reflex either, so there's a bit more drag in the vertical climb.

[rdwoebke]

Tony,

That is very interesting information. Thanks very much for sharing that. You are kind of my "go to guy" for things zoom/winch related. Your info that you share, Mark's sims, JoJo's logs, even Gordy's writings have been useful to me as I try to get a better handle on this winch/zoom/ping thing.

Ryan