need help with correct winch zoom technique

[neonbutterfly]

hi.....well i've got a lot of stick time on my bubble dancer...really love this plane.....scratch built too.....i have been trying to perfect my winch zoom launches......i am using a "real balls" winch which ben owns......so far, here is what i do......

i have good tension at the beginning and throw the plane and step on the gas.....about 1/3 of the way up the line i am pulsing the winch and gaining altitude...when i think i have reached the sweet spot (ie...good launch height...mental picture that this is the spot to start the zoom!!!).....i step on the gas and point the nose down (full down)....do this for about 2 seconds and pull up!!!......

i have pulled to much up and looped off the line and gone inverted (done that more than once).....that wasn't good......i zoomed again....and instead of pulling full up i pulled say 2/3 up and that seemed to work better.....i then have to give it down at the top of the zoom ....so i don't major stall!!!

ion the other hand......i've watched my flying buddy, ben, zoom his icon....and it is amazing.....i know he chages the flaps to run mode when he zooms, but he gets way more altitude and gets farther out then me......better to find those thermals!!!

i would like to hear some of your techniques...especially how you manage the sticks, on the dive and pull-out.....how much up elev you give....how much time are you stepping on the gas before you zoom.....etc.....

being the bubble dancer has no flaps.....it seems that the zoom is like a rocket shot.....ie it goes straight up, looses velocity and when it is at the apex...... feed in some down elev to kill the stall.....is there any way to zoom like the icon???

more of a gradual climb out?...or is this impossible with an res plane.....

need some help here!!..thanks in advance

bob :confused:

[R. Carver]

The plane should never be in a "dive", especially for 2 seconds. Even 1 second is way too long. Should be a quick blip of down followed by a quick pull of up to get the nose pointed towards the sky. At least that's how I do it. My plane never points down more than 30 degrees during a good zoom.
I'll usually stand on the pedal about 3/4 of the way up to start building line tension. I like to think that a good zoom comes from the tension in the line more than the speed of the winch.
YMMV and all that good stuff :)

[seeker]

I am afraid your Bubble dancer will never see the energy retention of the Icon. You can try to ballast her up to get more energy retention on the zoom, but it will come with a weight penalty. The Icon is a molded plane with a near perfect airfoil( .001 accuracy?) that helps the overall flight characteristics as well.
I see it more as a apples and oranges thing. You can't compare the two side by side. How well does your buddies Icon fly in ultra light lift conditions compared to your Bubble Dancer?
Hope that adds some perspective.
Jon

[markdrela]

when i think i have reached the sweet spot (ie...good launch height...mental picture that this is the spot to start the zoom!!!).....i step on the gas and point the nose down (full down)....do this for about 2 seconds and pull up!!!......
You may be diving for too long -- a 2 second dive is way too long, especially for a BD. Modeling the zoom-diving glider as a mass on the end of a long spring, we conclude that the optimum dive time "t" is roughly proportional to

t ~ sqrt( mass / line_spring_constant )

independent of the line tension.

So assuming your BD has 0.4x the mass of the Icon, your dive duration on the same winch should be only sqrt(0.4) = 0.6 times as long. My launch sims for a heavy braided line indicate an optimum dive time of about 0.5s for the Icon, and 0.3s for the BD, which is pretty quick. If you dive longer than this, the glider will still be diving with the line slack, which chews up a lot of energy very quickly. It's also dangerous, because you can overrun the chute and snag the tail.

[neonbutterfly]

thanks mark...that makes a lot of sense.....and really put the zoom technique into perspective......now off to the field to practice......

bob :D

[BMatthews]

The best zooms I've seen do not use much of a dive angle at all. You need to put the nose down a touch but the idea, as I understand it, is to use the " very strong artificial gravity" of the line pull to accelerate the gliding speed of the model. That implies that you keep the model more at right angles to the line so the "extra ballast" of the line pull can accelerate the flying speed. Sort of like pinching a slippery pumpkin seed between two fingers. Or the same way a sailing boat can go much faster than the true windspeed.

If you can find the MINIMUM dive angle that results in the highest speed gain then you have it. Using a lesser dive angle also means that you're sucking in less line and loosing that much less of what you're trying to get. Not only can the guys that keep their dives shallow build up more speed but the ones that strongly dive often don't zoom back up much, if any, higher than the height they had when they started the zoom.

[averen]

There were some altimeter charts (which I can't find anymore) that pretty much show that you get the most altitude off of a zoom with little or no dive at all.

I'll see if I can find them again, but I wasn't able to after searching through the forum. Essentially they tried different dives and the winner (by a large margin) was with almost no dive.

Jared

[jrgospod]

Mark,

If you are still following this thread I have a additional question. Would kitting the BD up on a windy day and then at the last few seconds adding tension/speed/energy make a difference in the launch? It seems like you would have out more line/height when you ping off the ring. Then again maybe all you would do is just pull the plane down to the same height to get the tension and energy.

John

[averen]

Where does Dr. Drela get all these nifty toys to do the simulations! Man, wishing I went to MIT...maybe one day my fiancee will get some cushy job up on the East Coast so I can hang out with these guys :)

When I was flying my Spirit Elite (no where near as nice as a Bubble Dancer) I used to love "kiting" the plane up the line on a windy day. There were times that I would launch and the chute would go 100+ feet behind us...those were the days. Unfortunately I couldn't penetrate once I got up there...but I had a nice launch!

Jared

[Jurgen]

I'm working on my zooms either. Jojoen stated his zooms were much better since he installed more powerfull/faster servo on elevator. Seems good servo speed is mandatory. I still have to change that in my Zenith but one can achieve this by using the largest servo-arm posible but then you make the neutral play bigger, or you just buy a more apropriate servo. Airtronics 94761 (darn i cant get this in europe) and Volz micro max xp come in mind.
Jurgen.

[Jurgen]

So for elevator i replaced the futaba 3150 - short servo arm with a futaba 9650 & longer arm.
The 9650 has same (little more) power than 3150
The 9650 has double the speed of 3150
The 9650 has double the price than 3150. (82 euro instead of 40)
(I would liked the Volz but with post it came about 120 euro, a 50% price increace !)

The 9650 has plastic gear but i dont need torq on my elevator anyway, and it has an even better neutral point than 3150, typical for nylon.

So with the longer arm on this incredible fast servo (actualy a mini digital car servo) i have this elevator whiping like hell. I suppose if i want to stay up i just have to do UP-Down very fast as a kind of dolphin tail motor :D

Result: i am in full control of the zoom now, jojoen was right! Better energy recuperation of the line tension thus higher zoom, much less chance of getting the tail cought by the line/parachtute.

Jurgen.

[tonyestep]

Figuring out the physics of a zoom is not hard. See
http://www.mvsaclub.com/docs/zoom.htm
for a simple explanation. Armed with the info there, you can easily make an excel spreadsheet that will let you play with various inputs.
For a typical plane on a typical winch, the dive should be about 0.4 seconds. The nose should point right at the turnaround to minimize line drag; however, the dive is so short that when you see a good guy do it, the dive looks shallower. The only thing that makes the plane zoom is the incremental speed gaine by pulling in line faster than the acceleration of gravity; altitude gain will be a function of the speed the plane is flying when it leaves the line.
The plane starts out going fast, ends up going slow, and the speed lost is converted into altitude. To simplify, assume that it's climbing vertically in a vacuum; then its velocity will diminish by 32 ft/sec each second it's zooming. If it starts at 128 ft/sec and rounds over to glide when it's traveling 32 ft/sec, it will zoom for 3 seconds. Its average velocity over that time will be halfway between the start velocity of 128 and the end velocity of 32, i.e. it will climb at an average rate of 80 ft/sec for 3 seconds. That's 240 feet gained (no calculus required). Now 128 ft/sec is moving right along (87 mph). Lower terminal speeds will produce lower zooms. Understanding the essential concept of converting speed to altitude will take the mystery out of how to practice your launch technique. P.S. get a strong airplane.

[aeajr]

What a great discussion!

This is just a matter of interest, but anyone have any ideas about the forces created by the zoom techniques discussed here?

If you a carbon/kevlar competition plane on the end of that winch line, I presume you can hit it as hard as you like, but for those lesser craft made of wood and glue, I was wondering what kind of forces we were exerting, especially since they are opposite the force of hte launch. When you hit that up elevator, the flex force on the whole plane, going from the climb, to the dive to the turn for height must be pretty significant.

I just broke a stab mount on my plane. The only place we can figure that it happened was on the zoom, so I was wondering what kind of forces were involved.

[Tuomo]

0.3-0.5 sec seems reasonable time for the dive. Been playing with my logger again... ...here are some graphs fron yesterdays practice session :)

Plane is Valo Models Snake, line EMC Vega 1.15mm (mono), winch Oberfulgmodellbau EW4 (std. F3B winch), drum diameter 55mm. Steady 2-3m/s wind with very weak thermal activity. 150 meters to turnaround.

These are long full line tows. I can realistically hope that 4-5 sec on the line takes me to 200 meters.

JW has elsewhere stated how important is to throw plane well. I have been working on that and also on the use of camber in the first 2-3 seconds of launch. I have some snap flap mixed to the wing, just to take the flex out from flaps and ailerons. A good launch is a process where built on powerfull acceleration -- when you have the speed and tension built up at 3 seconds, rest is easy.

What do you think?

[Jurgen]

When i see a graph like that i always wonder how comes so little line is reeled in, that winch must be stalling all the time?

PS: i like that magic wizard spell on top: Hinausharjoittelua pernasaaressa !!
Harry Potter would be jealous on that one :)

[Jurgen]

One of the most fancy video i ever saw about winch-launching but this concerns F3B style:
60Mb movie (http://www.lomcovak.cz/FAL1.mpg)
20Mb movie (http://www.lomcovak.cz/FAL2.mpg)
Jurgen.

[Jurgen]

In the F3B movie you can clearly see launchflap is deployed untill just before the zoom, this in contrast to the F3J launches Tuomo describe where launchflap is retracted fast after launch (2 sek). Seems difference in contest rules and planes leads to other tactics.
Jurgen.

[Tuomo]

In the F3B movie you can clearly see launchflap is deployed untill just before the zoom, this in contrast to the F3J launches Tuomo describe where launchflap is retracted fast after launch (2 sek). Seems difference in contest rules and planes leads to other tactics.
Jurgen.

Hmm... You are propably right. Launch time is not crucial in F3B. Other points that come to my mind are related to the fact that F3J planes have more wing area (and lift) available and they are rarely launched with heavy ballast (as is done in F3B speed task).

I would really like to know.

Jurgen: Funny continent we live in - one currency, so many languagaes ;)

[mdennis]

In the F3B movie you can clearly see launchflap is deployed untill just before the zoom, this in contrast to the F3J launches Tuomo describe where launchflap is retracted fast after launch (2 sek). Seems difference in contest rules and planes leads to other tactics.
Jurgen.

I don't fly f3b, (for all that matters, I don't really fly f3j), but I'm learning this thermal duration stuff. If you saw me fly you'd understand. :rolleyes: I have been told to leave the plane in launch mode, (flaps and ailerons cambered down), until right before the zoom at which point they go to speed mode, (reflexed up). Essentially what you describe as a f3b style launch.

The reason the flaps remain down for a f3b launch is that they are typically heavier due to ballast and need the extra lift? Since I am flying a lighter f3j type plane, I should switch to speed mode a couple of seconds after I throw the plane, so it will have maximum speed at the top. As I ballast up for windy days I should leave the wing cambered further up the line?

How about these launch and speed positions? Should the position, (angle), of ailerons and the flaps be the same or should the ailerons have less deflection?

[Jurgen]

I don't fly f3b, (for all that matters, I don't really fly f3j), but I'm learning this thermal duration stuff. If you saw me fly you'd understand. :rolleyes: I have been told to leave the plane in launch mode, (flaps and ailerons cambered down), until right before the zoom at which point they go to speed mode, (reflexed up). Essentially what you describe as a f3b style launch.I called this F3Blaunch only because the movie is taken from a NYX FURIO Vtail.

The reason the flaps remain down for a f3b launch is that they are typically heavier due to ballast and need the extra lift? Since I am flying a lighter f3j type plane, I should switch to speed mode a couple of seconds after I throw the plane, so it will have maximum speed at the top. As I ballast up for windy days I should leave the wing cambered further up the line?Good questions indeed. We need more expert pilots here who flies both F3B&F3J to help us. For sure the contest F3B rules (and i believe TD is alike) allows longer winching times at no cost of points. F3J is different, each sekond on the line cost you soaring points.

How about these launch and speed positions? Should the position, (angle), of ailerons and the flaps be the same or should the ailerons have less deflection?I have been advised both systems by different people, thats confusing. The less-aileron angle is advocated by people who swear this is kindof having a wash-out on tow and therefore more stable, others say this is not true and advocate the equal angle method. I do equal angle on mine. Calling for Radio-carbon-art: when is that launching video coming out covering all those specific insights?:)

[Jurgen]

This is somewhat the best i can perform with the Zenith (Corado2) so far.
Line: mono speedline 1,25mm
Winch - turnaround : 200m (650ft)
Gentle headon breeze.
Bucket : 500 ft
Top : 725 ft
Zoomhight : 230 ft. (usualy 200ft)
Competitors do better but i'm proud on this so far :)

I do a vertical up zoom, should i go little shallower instead?
Jurgen.

[oakman7004]

What a great discussion!

This is just a matter of interest, but anyone have any ideas about the forces created by the zoom techniques discussed here?

If you a carbon/kevlar competition plane on the end of that winch line, I presume you can hit it as hard as you like, but for those lesser craft made of wood and glue, I was wondering what kind of forces we were exerting, especially since they are opposite the force of hte launch. When you hit that up elevator, the flex force on the whole plane, going from the climb, to the dive to the turn for height must be pretty significant.

I just broke a stab mount on my plane. The only place we can figure that it happened was on the zoom, so I was wondering what kind of forces were involved.

Well, if I recall correct!

Some years ago I read an article in Aufwind (GER soaring magazine) that a full F3B launch gtives up to 25G in the pull up phase (after the dive). They had tested this and showed nice graphs. Proof is essential for our german friends. ;)

I also think they tested F3J starts with some smaller G forces as result. This probably comes from that in a F3J start you have a different dive and pull up due to the time issue (you'll get other angels, so to speak).

Cheers Jonas Ekman

[Tuomo]

I do a vertical up zoom, should i go little shallower instead?


Basically, when zooming you are transforming kinetic energy to altitude. Kinetic energy of the plane is greatly increased when streched line is released, a sort of rubber band effect. Aerodynamic drag reduces efficiency of this process. If you do a very shallow zoom, climb takes longer time and plane is slowing down every second...

I do not know what is the right way to do release, but I do the initial zoom almost vertical and then gradually push to glide when plane slows down. The elevator movement in release is very shap full up! A 100 meters (300ft) F3J zoom seems to take about 3 seconds and average climb rate is 30m/s (look at the graph in post #14).

In F3B with the energy stored in 200m line, you should be able to zoom higher.

BTW Jurgen, do you have proper wing bend before release? Most F3J planes also flap their wings violently to andhedral after release :p

[Jurgen]

My full carbon wings seem to be very stif, no flappings in any phase.
I can do higher zooms, till 80meter, but have do dive longer for it, resulting in no alt gain at the end.
In moderate wind i never see a bending, only in higher windspeeds i can see the wing bending. Should i be albe to bend my wings in a moderate windspeed also? In the flight of the showed graph the winchdrum (55mm) is turning very slow, almost stalling before i make the dive.
At the moment i'm adding preset up-elevator trim (more and more, very progresively) for launching, i seem to get more linetension this way troughout the whole tow, and need less launchchamber for it. Halfway tow (4-5 sek) the extra chamber is out and climbing on its neutral-manufactured 3% chamber further on, see picts what is "neutral" 3% for the Zenith.
Jurgen.

[Tuomo]

Corado seems to have a rather thick wing with high camber. The Snake I have flown this summer is different. It comes with HQ/W 8/2 airfoil. Wing is also quite narrow which makes it even thinner. Even with UHM spars, it flexes in wind.

Pre set elevator is related with tow hook place. Ideally you can fly tow with neutral elevator and have magnificient tension on line. If you need up elevator, you might have place the hook too far forward?

(EDIT On the other hand, you report winch almost stalling. Perhaps you could have more speed with neutral elevator and the current hook place. Speed is lift = tension to the line. With speed you can also reduce camber faster = more speed = more tension. etc.)

Generally the hook is a few milliters in front of CG.

Launch camper is another thing, also slightly related to elevator trim. With 3% camber you should be able to fly most of the launch with neutral setting. What happens if you go to 1.2mm reflex 1-2mm before release?

Thirdly, are you sure that you throw your plane with line at high enough tension? The higher the tension, the faster you get to the high-speed mode with high tension on line.

You should also try a thinner line. 1.15mm sems to quite good allround line and in calmer conditions also 1.05mm is quite safe. Keeping the line submerged in water makes it more flexible.

[Jurgen]

Thx Tuomo for the insights, gonna work on that.
I would never install the futaba 9650 again, see: http://www.rcgroups.com/forums/showthread.php?t=570586
Jurgen.